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Magnesium-lime process for decolourization of kraft mill effluents Rush, Richard John 1976

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MAGNESIUM-LIME PROCESS FOR DECOLOUR!ZA7TON OF KRAFT MILL EFFLUENTS  by  RICHARD JOHN RUSH B.A.Sc. U n i v e r s i t y o f W a t e r l o o , 1974  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  i n t h e Department of CIVIL  ENGINEERING  We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e required standard  THE UNIVERSITY OF'BRITISH COLUMBIA A p r i l 1976  In  presenting  an  advanced  the I  Library further  for  degree shall  agree  scholarly  by  his  of  this  written  this  thesis  in  at  University  the  make  that  it  purposes  for  freely  permission may  representatives. thesis  partial  be  It  financial  for  is  gain  of  British  Columbia  2075 W e s b r o o k P l a c e V a n c o u v e r , Canada V6T 1W5  Date  iA^w'tP  SO  )  /QlQ>  by  for  the  understood  of  University  British  extensive  granted  C i v i l Engineering The  of  available  permission.  Department  fulfilment of  shall  reference  Head  be  requirements  Columbia,  copying  that  not  the  of  copying  agree  and  of my  I  this  that  study. thesis  Department or  for  or  publication  allowed without  my  i ABSTRACT A m a g n e s i u m - p l u s - l i m e c o a g u l a t i o n p r o c e s s , i n c o r p o r a t i n g magnesium r e c o v e r y by s l u d g e c a r b o n a t i o n , r e c e n t l y d e v e l o p e d f o r w a t e r treatment  has been t e s t e d f o r i t s a p p l i c a t i o n t o t h e d e c o l o u r i z a t i p n o f  kraft mill effluents. b i o l o g i c a l treatment of a conventional  T o t a l b l e a c h e d k r a f t m i l l e f f l u e n t (BKME), a f t e r and e f f l u e n t from the f i r s t c a u s t i c e x t r a c t i o n  stage  b l e a c h e r y (E-j o r T-20 e f f l u e n t ) were examined i n t h e  laboratory. I t was shown t h a t a combination  o f low magnesium and low l i m e  dosages can a c h i e v e b e t t e r d e c o l o u r i z a t i o n o f k r a f t m i l l e f f l u e n t s than 3-5 t i m e s as much lime a l o n e , lime ( a s CaO) a t pH  (i.e.:  30-60 mg/1 M g  + +  p l u s 375-475 mg/1  -11.1 f o r BKME; and 150-300 mg/1 M i g  3750 mg/1 l i m e (as CaO) a t pH  -12.1 f o r T-20 e f f l u e n t . )  ++  p l u s 1.875C o l o u r removals  o f 90-95% were a c h i e v e d u s i n g e i t h e r f r e s h o r r e c y c l e d magnesium. R e s u l t s o f t h e s t u d y showed t h a t g r e a t e r than 90% magnesium r e c o v e r y can be a t t a i n e d by o p e r a t i n g t h e s l u d g e c a r b o n a t o r t o a f i n a l pH  - 7 . 5 , w i t h complete m i x i n g and a good C 0 d i f f u s e r s y s t e m p r o v i d e d . 2  (Key words: magnesium, l i m e , k r a f t m i l l e f f l u e n t , d e c o l o u r i z a t i o n , c o l o u r r e m o v a l , Magnesiurn C a r b o n a t e  Process.)  ii TABLE OF CONTENTS Page ABSTRACT  i  TABLE OF CONTENTS  i i  LIST OF TABLES  iv  LIST OF FIGURES  v  ACKNOWLEDGEMENT  vi  CHAPTER 1  INTRODUCTION  1  2  SUMMARY  6  3  BACKGROUND ON THE COLOUR PROBLEM  9  3.1  Nature o f C o l o u r i n Pulp M i l l E f f l u e n t s  9  3.2  E f f e c t s o f C o l o u r on R e c e i v i n g Waters  17  3.3  Summary o f C o l o u r Removal T e c h n o l o g y  20  REVIEW OF MAGNESIUM COAGULATION PROCESSES  25  4.1  H i s t o r i c a l Development  25  4.2  Theoretical Considerations  33  4.3  Practical Considerations  45  EXPERIMENTAL MATERIALS AND METHODS  48  5.1  Selection of Effluent  48  5.2  Sample S t o r a g e  51  5.3  Chemical  Preparations  51  5.4  A n a l y t i c a l Techniques  52  RESULTS AND DISCUSSION  57  R e s u l t s o f T e s t i n g w i t h F r e s h Chemicals  57  4  5  6 6.1  6.1.1 J J a r T e s t R e s u l t s  57  Ill  Page 6.1.2  6.2 6.2.1 6.2.2 7  Batch D e c o l o u r i z a t i o n and Magnesium  Recovery  Results  55  R e s u l t s o f T e s t i n g w i t h R e c y c l e d Magnesium  98  J a r Test Results Batch D e c o l o u r i z a t i o n and Magnesium Recovery Results  gg T08  CONCLUSIONS AND RECOMMENDATIONS  1 2 3  7.1  Conclusions  123  7.2  Recommendations f o r F u t u r e Research  123  7.2.1  Bench S c a l e  123  7.2.2  P i l o t Scale  124  7.2.3  Concept f o r F u l l S c a l e Implementation  126  BIBLIOGRAPHY  128  APPENDICES  135  A  Development o f T e s t P r o c e d u r e s  135  B  S e t t l e a b i l i t y o f T - 2 0 , _ E f f l u e n t and Polymer Selection '  149  C  Example C a l c u l a t i o n t o D e r i v e t h e Sludge and S u p e r n a t a n t Volume R e s u l t i n g from Sludge Dewatering to 5% a n d 60% S o l i d s 153  D  S l u d g e C a r b o n a t i o n M o n i t o r i n g Data  155  iv LIST OF TABLES TABLE  DESCRIPTION  PAGE  1  C o l o u r L e v e l s o f V a r i o u s P r o c e s s Sewers and Comb i n e d O u t f a l l s f o r Nine B.C. B l e a c h e d K r a f t M i l l s  10  2  S o l u b i l i t y o f M g ( 0 H ) a t 25°C  34  3  T y p i c a l C h a r a c t e r i s t i c s o f C r e s t b r o o k P u l p and Paper Ltd. Total M i l l E f f l u e n t  49  4  Average R e s u l t s o f S e v e r a l I n - P l a n t C o l o u r B a l a n c e s  2  a t C r e s t b r o o k P u l p and P a p e r L t d .  50  5  J a r T e s t s w i t h F r e s h C h e m i c a l s - BKME  59  6  J a r T e s t s w i t h F r e s h Chemicals - BKME  59  7  J a r T e s t s w i t h F r e s h Chemicals - BKME  60  8  J a r T e s t s w i t h F r e s h Chemicals - BKME  60  9  J a r T e s t s w i t h F r e s h Chemicals - T-20 E f f l u e n t  63  10  J a r T e s t s w i t h F r e s h C h e m i c a l s - T-20 E f f l u e n t  64  11  J a r T e s t s w i t h F r e s h C h e m i c a l s - T-20 E f f l u e n t  65  12  B a t c h D e c o l o u r i z a t i o n I n i t i a l C o n d i t i o n s and R e s u l t s  67  13  Summary o f D e c o l o u r i z a t i o n Loop Mass B a l a n c e R e s u l t s  72  14  Summary o f C a r b o n a t i o n Loop Mass B a l a n c e R e s u l t s  79  15  Carbonation Supernatant C h a r a c t e r i s t i c s  81  16  Summary o f B a t c h T e s t Volume B a l a n c e R e s u l t s  82  17  C 0 S o l u b i l i t y o f Various Temperatures  87  18  J a r T e s t s o f T-20 E f f l u e n t w i t h Lime a l o n e  19  J a r T e s t s o f T-20 E f f l u e n t w i t h F r e s h MgS0  20  J a r Tests with Recycled Mg  + +  - T-20 E f f l u e n t  102  21  J a r Tests with Recycled Mg  + +  - T-20 E f f l u e n t  103  22  Jar Tests with Recycled Mg  + +  - BKME  104  2  100 4  101  V  LIST OF FIGURES FIGURE  DESCRIPTION  PAGE  1  Magnesium C a r b o n a t e P r o c e s s Diagram  3  2  T y p i c a l M o l e c u l a r Weight D i s t r i b u t i o n o f A l k a l i L i g n i n o f S i m u l a t e d K r a f t P u l p M i l l Wastewater  14  3  C o l o u r vs. pH f o r T o t a l M i l l E f f l u e n t  15  4  S o l u b i l i t y Diagram f o r Magnesium i n W a t e r ^ a t Atmosp h e r i c C o n d i t i o n s ! T o t a l Carbonate = 10 M  35  5  Temperature  36  6  Comparison o f T h e o r e t i c a l S o l u b i l i t y o f M g ( 0 H ) With Observed J a r T e s t and P i l o t P l a n t V a l u e s  7  S o l u b i l i t y o f MgCO^'XrlpO as a F u n c t i o n o f Time For The I n d i c a t e d H y d r a t e Forms  39  8  Lime R e q u i r e d t o R a i s e t h e pH t o 11 as a F u n c t i o n o f t h e Raw Wastewater A l k a l i n i t y  39  9  Lime v s . P e r c e n t C o l o u r Removal a t Three Magnesium Levels  61  10  S c h e m a t i c o f M a t e r i a l S o u r c e s and S i n k s  70  11  pH v s . C o l o u r , M g and C a i n t h e S u p e r n a t a n t From a T y p i c a l BKME S l u d g e C a r b o n a t i o n U s i n g F r e s h Chemicals  91  pH v s . C o l o u r , M g and C a i n t h e S u p e r n a t a n t From a T y p i c a l T-20 S l u d g e C a r b o n a t i o n Run U s i n g Fresh Chemicals  92  pH v s . C o l o u r , - M g and. C a i n the 'Supernatant From a BKME S l u d g e Carbon a t-ioifr Runuusing R e c y c l e d Magnesi urn  120  14  pH v s . Colour^';Mg and C a i n t h e S u p e r n a t a n t From a T-20 S l u d g e C a r b o n a t i o n Run U s i n g R e c y c l e d Magnesium  121  15  S c h e m a t i c o f t h e EPS Magnesium C o a g u l a t i o n P i l o t P l a n t  125  12  13  I n f l u e n c e on Magnesium S o l u b i l i t y  + +  + +  ++  ++  ?  38  + +  + +  + +  + +  vi ACKNOWLEDGEMENT I wish t o thank Dr. W. K. Oldham and Dr. R. M. R. B r a n i o n f o r t h e i r s u p p o r t and g u i d a n c e t h r o u g h o u t the c o u r s e o f t h i s s t u d y . I would a l s o l i k e to e x p r e s s my thanks t o Mrs. E l i z a b e t h MacDonald f o r h e r v a l u a b l e a s s i s t a n c e and p a t i e n c e w i t h me i n the C i v i l E n g i n e e r i n g Water P o l l u t i o n C o n t r o l L a b o r a t o r y . A l s o acknowledged  a r e the p e r s o n n e l a t the Skookumchuck M i l l  o f C r e s t b r o o k P u l p and Paper L t d . f o r a s s i s t a n c e i n o b t a i n i n g m i l l e f f l u e n t samples and the E n v i r o n m e n t a l P r o t e c t i o n S e r v i c e a t B u r l i n g t o n , Ontario f o r partial funding. Thanks a r e a l s o due to my w i f e , L i n d a , f o r p r o v i d i n g e n c o u r a g e ment when I needed i t , t o my f e l l o w g r a d u a t e s t u d e n t s f o r b e a r i n g w i t h and to Mrs. I r e n e Green f o r d o i n g most o f the t y p i n g .  me,  1 CHAPTER 1 INTRODUCTION The p u l p and p a p e r i n d u s t r y i s n o t o r i o u s f o r i t s h i g h w a t e r consumption.  T h i s h i g h w a t e r use i n e v i t a b l y l e a d s to the d i s c h a r g e o f  l a r g e volumes o f w a s t e w a t e r s t h a t g e n e r a l l y c o n t a i n s i g n i f i c a n t l e v e l s o f BOD,  COD,  suspended s o l i d s , t o x i c i t y and c o l o u r . T r a d i t i o n a l l y ,  w a s t e w a t e r t r e a t m e n t has been aimed a t r e d u c i n g BOD,  suspended s o l i d s ,  and i n Canada, t o x i c i t y , w i t h l i t t l e o r no emphasis on c o l o u r  removal.  The l a c k o f emphasis on c o l o u r removal a p p e a r s t o have been f o r two reasons.  F i r s t , c o l o u r i s e x t r e m e l y d i f f i c u l t and e x p e n s i v e  t o remove  and, s e c o n d l y , no u r g e n t reasons t o remove c o l o u r have been i d e n t i f i e d . However, i n r e c e n t y e a r s a c o n s i d e r a b l e amount o f e f f o r t has gone i n t o development o f c o l o u r removal t e c h n i q u e s , prompted by a t r e n d i n the i n d u s t r y toward w a t e r c o n s e r v a t i o n through reuse and r e c y c l i n g o f p r o c e s s waters.  In a d d i t i o n , t h e r e has been an i n c r e a s i n g p u b l i c demand f o r  s u r f a c e w a t e r s t h a t n o t o n l y a r e f r e e o f harmful s u b s t a n c e s , but a l s o look clean. W h i l e many t e c h n i c a l l y f e a s i b l e c o l o u r removal p r o c e s s e s been d e v e l o p e d  have  and some ( n o t e a b l y l i m e t r e a t m e n t i n the U.S.A.) have been  d e m o n s t r a t e d on a f u l l - s c a l e b a s i s , no p a r t i c u l a r method o f c o l o u r r e d u c t i o n has emerged ajg the ' p r a c t i c a b l e t e c h n o l o g y ' . t o happen.  T h i s i s not l i k e l y  Because o f the wide range o f e f f l u e n t s and v a r i e t y o f c i r c u m -  s t a n c e s w i t h i n the i n d u s t r y , no one method i s l i k e l y t o be a p p l i c a b l e i n all situations. A l t h o u g h Canada has no f u l l - s c a l e c o l o u r removal f a c i l i t i e s a t t h i s t i m e , r e s e a r c h and development work i s b e i n g conducted mental , i n d u s t r i a l and u n i v e r s i t y s e c t o r s .  by  govern-  D u r i n g the p a s t y e a r the  author  2 r e v i e w e d o n g o i n g r e s e a r c h and a l s o the l i t e r a t u r e p e r t a i n i n g t o c o l o u r removal t e c h n o l o g y .  The f i n a l r e p o r t on t h i s s t u d y by Rush and Shannon  (1975) i d e n t i f i e d s e v e r a l s p e c i f i c a r e a s s u i t a b l e f o r f u t u r e r e s e a r c h e f f o r t s by t h e E n v i r o n m e n t a l P r o t e c t i o n S e r v i c e (EPS) and  Wastewater  T e c h n o l o g y C e n t r e (WTC) a t the Canada C e n t r e f o r I n l a n d Waters (CCIW) in Burlington, Ontario. One p r o m i s i n g method o f c o l o u r r e d u c t i o n i d e n t i f i e d , was a magnesium c o a g u l a t i o n p r o c e s s d e v e l o p e d and t e s t e d by Thompson e t a l (1972) f o r the t r e a t m e n t o f w a t e r s u p p l i e s . The s y s t e m has proven t o be f u l l y as e f f e c t i v e as alum f o r t h e removal o f o r g a n i c c o l o u r and t u r b i d i t y from n a t u r a l w a t e r s .  A t the same t i m e , i t e l i m i n a t e s s l u d g e d i s p o s a l  problems common t o a l l o t h e r c h e m i c a l t r e a t m e n t p r o c e s s e s .  The b a s i c  o p e r a t i o n a l sequence f o r such a system, termed a Magnesium C a r b o n a t e (MgCOg) P r o c e s s i s shown i n F i g u r e 1.  By c a r b o n a t i n g t h e s l u d g e g e n e r a t e d f r o m  the magnesium and l i m e c o a g u l a t i o n , s o l u b l e magnesium b i c a r b o n a t e (MgfHCOg)^) i s r e c o v e r e d i n the f i l t r a t e f o r r e c y c l e and l i m e i s r e c a l c i n e d f o r reuse.  CO^ from t h e l i m e k i l n can be used f o r both s l u d g e  and e f f l u e n t c a r b o n a t i o n . So, t h e o r e t i c a l l y a l l t h e components o f t h i s s y s t e m can be r e c o v e r e d and r e u s e d . Very p r e l i m i n a r y s t u d i e s by Thompson and h i s c o l l e a g u e s and by V i n c e n t (1974) a t Domtar R e s e a r c h i n Quebec, i n d i c a t e t h a t magnesium hydroxide, precipitated 'in s i t u  1  by l i m e a d d i t i o n , t o a c h i e v e a pH o f  11.0 o r g r e a t e r , would have s e v e r a l advantages o v e r the l i m e a l o n e systems c u r r e n t l y i n use f o r c o l o u r removal.  Most i m p o r t a n t o f t h e s e i s a l o w e r  l i m e r e q u i r e m e n t , meaning a l o w e r pH i n t h e t r e a t e d waste and l i k e l y l o w e r o v e r a l l t r e a t m e n t c o s t s , due t o the a p p a r e n t r e c o v e r a b i l i t y o f a l l the chemical  components.  MgC0 -3H 0 MAKE-UP 3  2  LIME (TO pH>1l) UNTREATED WATER OR  f  TREATED EFFLUENT  WASTEWATER A PRIMARY CLARIFIER  RECARBONATION  CO SLUDGE ( C a C 0 + Mg(OH) + IMPURITIES) 3  Mg(HC0 ) 3  2  CaC0  3  2  VACUUM FILTER  2  C0  RECYCLE  2  SLUDGE CARBONATION  ROTARY LIME KILN  C a O FOR RECYCLE  FIGURE 1. MAGNESIUM CARBONATE PROCESS DIAGRAM  ( THOMPSON  ETAL.1972) CO  4 The main c o n c e r n i n t h i s p r o c e s s does n o t a p p e a r t o be i n t h e d e c o l o u r i z a t i o n , b u t r a t h e r i n t h e s l u d g e c a r b o n a t i o n f o r magnesium r e covery.  The c r i t i c a l f a c t o r s have been i d e n t i f i e d as (1) s e p a r a t i o n o f  magnesium from t h e p r i m a r y ' c o l o u r s l u d g e  1  without s i g n i f i c a n t colour  r e l e a s e and (2) good o v e r a l l r e c o v e r y o f magnesium so t h a t i t does n o t a c c u m u l a t e i n t h e lime r e c a l c i n a t i o n s t e p s and s e r i o u s l y a f f e c t t h e r e a c t i v i t y o f the lime. P i l o t p l a n t t e s t i n g o f t h i s MgCO^ P r o c e s s f o r t h e t r e a t m e n t o f h i g h l y c o l o u r e d k r a f t m i l l e f f l u e n t s was p l a n n e d a t t h e Wastewater T e c h n o l o g y C e n t r e , f o r l a t e 1975. In o r d e r t o p r o v i d e t e c h n i c a l i n f o r m a t i o n f o r t h e o p e r a t i o n o f t h i s p i l o t p l a n t , t h e a u t h o r was c o n t r a c t e d i n May 1975 t o conduct a l a b o r a t o r y s t u d y o f k r a f t m i l l e f f l u e n t d e c o l o u r i z a t i o n by t h e Magnesium C a r b o n a t e P r o c e s s ( a l s o r e f e r r e d t o h e r e i n as magnesiump l u s - l i m e t r e a t m e n t and magnesium c o a g u l a t i o n ) . A p o r t i o n o f t h e t o t a l a n t i c i p a t e d r e s e a r c h package was s e p a r a t e d o u t , and i s r e p o r t e d h e r e i n . The s p e c i f i c o b j e c t i v e s o f t h i s r e s e a r c h i n c l u d e d : 1.  p r o v i d i n g b a c k g r o u n d i n f o r m a t i o n on t h e c o l o u r p r o b l e m c r e a t e d by p u l p and p a p e r m i l l s ;  2.  r e v i e w i n g magnesium c o a g u l a t i o n  processes;  3.  d e v e l o p i n g methods and m a t e r i a l s f o r t h e d e c o l o u r i z a t i o n o f s e l e c t e d c o l o u r e d waste streams from a b l e a c h e d k r a f t mi 11;  4.  g i v i n g a b r i e f j a r t e s t e v a l u a t i o n o f t h e a b i l i t y o f magnesium-plus-lime a.  to decolourize;  t o t a l b l e a c h e d k r a f t m i l l e f f l u e n t (BKME) a f t e r b i o l o g i cal  treatment;  b.  e f f l u e n t from t h e f i r s t c a u s t i c e x t r a c t i o n s t a g e o f •k-k  a CE-jDE D b l e a c h e r y (E-| o r T-20 e f f l u e n t ) , and s e l e c t 2  t e n t a t i v e optimum c o n d i t i o n s f o r s u b s e q u e n t b a t c h t e s t i n g o f these e f f l u e n t s ; conducting several batch d e c o l o u r i z a t i o n - s l u d g e carbonat i o n t e s t s o f both BKME and T-20 e f f l u e n t t o d e t e r m i n e t h e e x t e n t o f c o l o u r r e l e a s e and magnesium r e c o v e r y d u r i n g sludge carbonation; e v a l u a t i n g t h e e f f i c i e n c y o f r e c y c l e d supernatant.; as a s o u r c e o f magnesium i o n s ( M g ) and d e t e r m i n i n g w h e t h e r the ++  use o f t h i s m a t e r i a l g i v e s s i g n i f i c a n t l y d i f f e r e n t mass b a l a n c e r e s u l t s than b a t c h t e s t s w i t h f r e s h c h e m i c a l s ; d i s c u s s i n g t h e r e s u l t s and making c o n c l u s i o n s and recommendations f o r future research. These were t h e main o b j e c t i v e s o f t h i s s t u d y . C = Chlorine E ==Sodium h y d r o x i d e D = Chlorine dioxide  6 CHAPTER 2 SUMMARY T h i s r e s e a r c h s t u d y was composed o f e s s e n t i a l l y t h r e e main parts. 1.  Development o f t e s t p r o c e d u r e s .  2.  T e s t i n g w i t h f r e s h magnesium and f r e s h l i m e .  3.  T e s t i n g w i t h r e c y c l e d magnesium and f r e s h l i m e .  Methods and m a t e r i a l s were d e v e l o p e d f o r i n v e s t i g a t i n g d e c o l o u r i z a t i o n o f c a u s t i c e x t r a c t i o n (T-20) e f f l u e n t and t o t a l b l e a c h e d k r a f t m i l l b i o l o g i c a l l y t r e a t e d e f f l u e n t (BKME).  In a d d i t i o n , a d e t a i l e d p r o -  cedure f o r s t u d y i n g magnesium r e c o v e r y f r o m a s l u d g e c a r b o n a t i o n p r o c e s s was d e v e l o p e d . Based on p r e l i m i n a r y j a r t e s t i n g o f t h e t o t a l m i l l e f f l u e n t , a dosage o f 60 mg/1 M g  + +  (added a s a s o l u t i o n o f MgSO^) p r e c i p i t a t e d by  500 mg/1 Ca(0H)2 (375 mg/1 CaO) was s e l e c t e d f o r use i n b a t c h magnesium r e c o v e r y s t u d i e s . A t t h i s dosage o f f r e s h c h e m i c a l s , > 90% o f t h e i n i t i a l c o l o u r was removed a t a c o a g u l a t i o n pH o f 11.1-11.2. Similar j a r testing o f c a u s t i c extraction effluent with fresh c h e m i c a l s l e a d t o t h e s e l e c t i o n o f 300 mg/1 M g , i n c o n j u n c t i o n w i t h 2500 ++  mg/1 C a ( 0 H )  2  (1875 mg/1 CaO) and 2 mg/1 o f an a n i o n i c polymer (Dow A - 2 3 ) ,  as t h e c h e m i c a l dosages f o r use i n b a t c h magnesium r e c o v e r y s t u d i e s . Under t h e s e c o n d i t i o n s , 90-95% o f t h e i n i t i a l c o l o u r was removed a t a f i n a l pH o f 12.1-12.2. C o l o u r r e l e a s e i n b a t c h s l u d g e c a r b o n a t i o n t e s t s o f BKME w i t h f r e s h c h e m i c a l s ranged f r o m 25.0 t o 38.1%.  Mass b a l a n c e r e s u l t s o f t h e s e  t e s t s showed t h a t 75.6-85.9% o f t h e magnesium s e n t t o t h e c a r b o n a t o r was r e c o v e r e d i f t h e f i n a l s l u d g e was 5% s o l i d s o r 90.0-91.5% i f t h e f i n a l s l u d g e was f i r s t dewatered t o 60% s o l i d s .  The magnesium l o s t i n t h e f i n a l  7 s l u d g e made up 2.9-7.1% o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s mass ( a s MgO). Calcium losses i n t o the carbonation supernatant v a r i e d from 2.0 t o 10.0% o f t h e t o t a l C a  + +  mass i n t h e system.  In t h e T-20 e f f l u e n t runs w i t h f r e s h c h e m i c a l s , c o l o u r r e l e a s e was l e s s , r a n g i n g f r o m 17.0 t o 26.9%.  From 68.0 t o 79.1% o f t h e M g  + +  sent  t o c a r b o n a t i o n was r e c o v e r e d , assuming t h e f i n a l s l u d g e was 5% s o l i d s , o r 89.3-90.7% i f 60% s o l i d s was a c h i e v e d .  In t h e s e t e s t s , t h e i n c i n e r a t e d  f i n a l s l u d g e s o l i d s ( r e c a l c i n e d l i m e ) c o n t a i n e d 2.9-8.9% MgO.  Large C a  + +  l o s s e s i n t o t h e s u p e r n a t a n t , r a n g i n g f r o m 11.5 t o 3 5 . 1 % o f t h e t o t a l , were a l s o i n c u r r e d i n t h e s e r u n s , i n d i c a t i n g t h a t l o c a l i z e d a r e a s o f low pH were p r e s e n t i n t h e c a r b o n a t i o n column d u r i n g t h e s e t e s t s . E x p e r i m e n t s , u s i n g r e c y c l e d s u p e r n a t a n t as a s o u r c e o f M g , ++  showed t h a t t h i s m a t e r i a l was an e f f e c t i v e s o u r c e o f magnesium i o n s f o r subsequent p r e c i p i t a t i o n by l i m e .  However, i n o r d e r t o r e a c h a h i g h enough  pH f o r > 9 0 % c o l o u r r e m o v a l , i n c r e a s e d l i m e dosages were r e q u i r e d t o overcome t h e h i g h e r a l k a l i n i t y o f t h e s u p e r n a t a n t p l u s e f f l u e n t m i x t u r e . Dosages s e l e c t e d f r o m p r e l i m i n a r y j a r t e s t i n g o f BKME w i t h r e c y c l e d s u p e r n a t a n t were 60 mg/1 M g  + +  (80% r e c y c l e d + 20% makeup MgSO^)  i n c o n j u n c t i o n w i t h 625 mg/1 C a ( 0 H ) (475 mg/1 CaO). F o r t h e T-20 2  e f f l u e n t , dosages s e l e c t e d were 300 mg/1 M g MgS0 ) i n c o n j u n c t i o n w i t h 5000 mg/1 C a ( 0 H ) 4  + +  2  ( 8 0 % r e c y c l e d + 20% makeup (3750 mg/1 CaO) and 2 mg/1  o f an a n i o n i c p o l y m e r (Dow A-23). In t h e t e s t s w i t h r e c y c l e d M g  + +  t h e more c o n c e n t r a t e d s l u d g e  e x t r a c t e d f r o m t h e b a t c h r e a c t o r appeared t o a f f e c t C 0 t r a n s f e r e f f i c i e n c y 2  i n t h e c a r b o n a t i o n column, and l i k e l y r e s u l t e d i n a n o n u n i f o r m pH d i s t r i bution (apparently pockets o f high pH), t h e r e i n . This r e s u l t e d i n s l i g h t l y  8 less colour release, a reduction in C a  + +  l o s s e s to the r e c y c l e d s u p e r -  n a t a n t , and a l s o somewhat lower magnesium r e c o v e r y i n t h e s e t e s t s than w i t h f r e s h magnesium ( i . e . , 60.0 t o 82.3%). I t i s , t h e r e f o r e , v e r y i m p o r t a n t to i n s u r e t h a t complete and e f f i c i e n t C 0 bonation tests.  2  mixing  d i f f u s i o n systems a r e p r o v i d e d i n f u t u r e s l u d g e c a r However, i t s h o u l d be n o t e d t h a t the MgO c o n t e n t o f the  r e c a l c i n e d l i m e d e c r e a s e d and o v e r a l l q u a l i t y o f t h e l i m e improved c o n s i d e r a b l y o v e r the c o r r e s p o n d i n g runs u s i n g f r e s h c h e m i c a l s , because o f the better C a  + +  r e t e n t i o n i n the s l u d g e .  Hydrogen i o n a c t i v i t y p r o v e d t o be t h e main f a c t o r a f f e c t i n g the outcome o f t h e s l u d g e c a r b o n a t i o n t e s t s , and c o n t i n u o u s measurement o f pH i n the s l u d g e c a r b o n a t o r , t o a f i n a l pH o f a p p r o x i m a t e l y 7.5,  was  j u d g e d to be t h e most e f f e c t i v e method o f c o n t r o l l i n g the b a t c h c a r b o n ation. F i n a l l y , t h e r e s u l t s o f t h i s s t u d y showed t h a t t h e s o - c a l l e d "Magnesium Carbonate P r o c e s s " , i n c o r p o r a t i n g magnesium r e c o v e r y by s l u d g e c a r b o n a t i o n , which was d e v e l o p e d f o r w a t e r t r e a t m e n t , can be a p p l i e d t o the d e c o l o u r i z a t i o n o f h i g h l y c o l o u r e d k r a f t m i l l e f f l u e n t s . search i s warranted.  Further re-  CHAPTER 3 BACKGROUND ON THE COLOUR PROBLEM 3.1  N a t u r e o f C o l o u r i n Pulp M i l l E f f l u e n t s O r g a n i c c o l o u r i s a v e r y complex component o f n a t u r a l  and some w a s t e w a t e r s . in water treatment.  F o r decades, c o l o u r removal B l a c k and C h r i s t m a n  waters  has been a c o n c e r n  ( 1 9 6 3 ) , H a l l (1970) and o t h e r s  have reviewed much o f t h e s i g n i f i c a n t r e s e a r c h i n t h i s a r e a . The c o l o u r i n p u l p and paper m i l l e f f l u e n t s can be e x p e c t e d t o have unique p r o p e r t i e s o f i t s own, r e s u l t i n g from t h e c h e m i c a l r e a c t i o n s d u r i n g p u l p i n g and b l e a c h i n g .  However, many o f t h e o b s e r v a t i o n s  and r e s e a r c h t e c h n i q u e s o f w a t e r c h e m i s t s p r o v i d e e x c e l l e n t b a c k g r o u n d i n f o r m a t i o n f o r i n v e s t i g a t i o n s o f p u l p and p a p e r m i l l c o l o u r c h a r a c t e r istics.  Colour values encountered  i n m i l l wastes a r e g e n e r a l l y s e v e r a l  o r d e r s o f magnitude h i g h e r than s u r f a c e w a t e r v a l u e s . T y p i c a l c o l o u r v a l u e s f o r some p u l p and p a p e r e f f l u e n t s a n d o t h e r s u b s t a n c e s o f g e n e r a l i n t e r e s t have been g i v e n by T y l e r and F i t z g e r a l d (1972) as f o l l o w s : Bleached k r a f t m i l l e f f l u e n t Caustic Extract Unbleached  kraft mill effluent  Magnesium base s u l p h i t e e f f l u e n t Coffee  2,000 APHA U n i t s 20,000 APHA U n i t s 700 APHA U n i t s 5,000 APHA U n i t s 10,000 15,000 APHA U n i t s  Coca-Cola  8,500 APHA U n i t s  D r a f t beer  1 ,000 APHA U n i t s  N o r t h e r n Canadian waters  100-200 APHA U n i t s  10 R e s u l t s o f a study by B.C. R e s e a r c h (1973) o f c o l o u r l e v e l s i n n i n e B.C. k r a f t m i l l s (shown i n T a b l e 1) more o r l e s s c o n f i r m  these  g e n e r a l i z a t i o n s and a l s o show t h e l a r g e f l u c t u a t i o n i n c o l o u r o f t h e same e f f l u e n t s t r e a m . TABLE 1 COLOUR LEVELS* OF VARIOUS PROCESS SEWERS AND COMBINED OUTFALLS FOR NINE B.C. BLEACHED KRAFT MILLS (B.C. RESEARCH, 1973) COLOUR IN EFFLUENT STREAM IN APHA.UNITS Mill  Caustic Bleach  Acid Bleach  Whole M i l l Outfall  A  1248 +  530  11430 + 1747  646 +  148  3664 + 1293  B  3504 + 1565  9472 + 2380  854 +  185  2544 +  708  C  1464 + 601  5484 + 3125  617 +  105  3668 +  886  D  3724 + 1101  4448 + 1197  1121 +  449  2600 +  670  319  7376 + 1857  678 +  249  2308 +  420  1359 + 1119  9254 + 1236  1121 +  449  1992 +  299  868 +  365  E  782 +  F  *  Unbleached White Water  G  966 +  504  9420 + 2692  H  2664 +  943  16964 + 3301  2341 + 1210  2160 +  872  I  1707 + 636  22780 + 5925  1600 +  2222 +  511  Values e x p r e s s e d sampling  693  as means and s t a n d a r d d e v i a t i o n s , r e p r e s e n t i n g 10  dates. S i m i l a r i n v e n t o r i e s o f m i l l p r o c e s s c o l o u r l o a d s and s o u r c e s  s h o u l d be c o n d u c t e d a t o t h e r m i l l s t o g e t a c l e a r e r p i c t u r e o f t h e c o l o u r contribution o f various e f f l u e n t s . It i s g e n e r a l l y accepted that almost a l l the c o l o u r o f these e f f l u e n t s i s due t o l i g n i n a n d / o r l i g n i n d e r i v a t i v e s ( H a r t l e r and N o r r s t r o m , 1969 and Swanson e t a l , 1973).  However, t h e p a r t i c u l a r method o f wood  p u l p i n g and p u l p b l e a c h i n g employed w i l l d e t e r m i n e t h e c h a r a c t e r i s t i c s  11 o f t h e e f f l u e n t and t h e n a t u r e o f t h e chromophores ( c o l o u r p r o d u c i n g structures) present. Fundamental r e s e a r c h has been g o i n g on i n t h e f i e l d o f l i g n i n c h e m i s t r y f o r more than 100 y e a r s b u t o n l y r e c e n t l y has t h e s t r u c t u r e o f the l i g n i n m o l e c u l e been f a i r l y w e l l e l u c i d a t e d .  Although a p r e c i s e def-  i n i t i o n o f l i g n i n i s d i f f i c u l t , i t can be t e n t a t i v e l y d e s c r i b e d as a h i g h l y branched o r c r o s s - l i n k e d , h i g h l y r e a c t i v e p o l y m e r w i t h a s u b u n i t o f m o l e c u l a r weight o f about 840. S e v e r a l reviews o f l i g n i n  chemistry  have been c o m p i l e d , e . g . , Sarkanen and Ludwig (1971) and Marton  (1966),  and p a r t s o f t h e s e two r e f e r e n c e s a r e devoted t o t h e r e a c t i o n s i n v o l v e d i n chemical p u l p i n g and b l e a c h i n g p r o c e s s e s .  In a d d i t i o n , works by G i e r e r  (1970), G i e r e r e t a l (1973), and Bodenheimer and Smith (1966) p r o v i d e d f u r t h e r d e t a i l s on p u l p i n g and b l e a c h i n g r e a c t i o n s . D u r i n g p u l p i n g , n a t u r a l l i g n i n o f wood i s d i s s o l v e d by a p p r o p r i a t e c h e m i c a l s i n p r e p a r a t i o n f o r subsequent during pulp bleaching.  s e p a r a t i o n from t h e wood f i b r e s  Important r e a c t i o n s i n t h e s e p r o c e s s e s i n c l u d e  s u l p h o n a t i o n , s u l p h i d i z a t i o n , and h y d r o l y s i s i n p u l p i n g and h a l o g e n a t i o n and o x i d a t i o n i n b l e a c h i n g .  These r e a c t i o n s r e s u l t i n v a r i o u s s t r u c t u r a l  u n i t s , which give r i s e t o e f f l u e n t c o l o u r .  A l t h o u g h a g r e a t deal o f  e f f o r t has been aimed a t i d e n t i f y i n g t h e s p e c i f i c chromophoric  groups r e s -  p o n s i b l e f o r c o l o u r , t h e m a t t e r has n o t been c o m p l e t e l y r e s o l v e d .  Most  o f t h e r e s e a r c h t o date has d e a l t w i t h k r a f t e f f l u e n t s , s i n c e t h i s i s t h e predominant p u l p i n g process i n use. K r a f t p u l p i n g gives r i s e t o t h i o l i g n i n and a l k a l i l i g n i n whereas s u l p h i t e p u l p i n g r e s u l t s i n 1 i g n o s u l p h p n i c a c i d or p r e c i p i t a t e d lignosulphonate. I t i s r e c o g n i z e d t h a t r e a c t i o n s i n t h e b l e a c h p l a n t f u r t h e r degrade t h e p r o d u c t s o f t h e p u l p i n g o p e r a t i o n , s o t h a t t h e b l e a c h p l a n t e f f l u e n t s c o n t a i n a c o m b i n a t i o n o f p r e - e x i s t i n g chromophores and some  12 a d d i t i o n a l p o s s i b l y d i f f e r e n t , c h r o m o p h o r i c groups c r e a t e d by the b l e a c h i n g process i t s e l f .  F a l k e h a g e t a l (1966) have summarized the major chromo-  p h o r i c systems i n k r a f t l i g n i n as CH = CH double bonds c o n j u g a t e d w i t h the a r o m a t i c r i n g and q u i n o n e m e t h i d e s  and q u i n o n e s which may a l s o s e r v e  as o x i d a t i v e s p e c i e s c r e a t i n g f u r t h e r chromophoric s t r u c t u r e s .  Minor  systems i d e n t i f i e d i n c l u d e d c h a l c o n e s t r u c t u r e s , f r e e r a d i c a l s and metal complexes w i t h c a t e c h o l s t r u c t u r e s . I t i s assumed t h a t a c o m p o s i t e s e r i e s o f chromophore systems a r e p r e s e n t i n t h e s e e f f l u e n t s . Subsequent s t u d i e s by the N a t i o n a l C o u n c i l f o r A i r and Stream Improvement (NCASI) B u l l e t i n #239 and #242, (1970), M e s h i t s u k a and Nakano (1973) and o t h e r s have p r o v i d e d more s p e c i f i c i n f o r m a t i o n which c o n f i r m s t h e s e g e n e r a l i z a t i o n s . In p a r t i c u l a r , o- and p- benzoquinone  are found  to be i m p o r t a n t i n t e r m e d i a t e c o l o u r e d s t r u c t u r e s formed i n b l e a c h i n g and the p r e s e n c e o f m e t a l s , p a r t i c u l a r l y i r o n , has been shown by the l a t t e r a u t h o r s to c o n t r i b u t e t o the c o l o u r o f l i g n i n d e g r a d a t i o n p r o d u c t s . Complexing o f i r o n w i t h o r g a n i c m o l e c u l e s was a l s o r e p o r t e d i n NCASI B u l l e t i n #273 (1974) but i n s u f f i c i e n t work has been done on t h i s t o d e t e r mine the r o l e o f m e t a l s i n c o l o u r f o r m a t i o n . S e v e r a l p r o p e r t i e s o f the v a r i o u s chromophores a r e i m p o r t a n t when c o n s i d e r i n g c o l o u r removal t e c h n i q u e s . include i) polydispersity i i ) solubility  The more noteworthy o f t h e s e i i i ) pH dependence  iv) electrical  charge. One o f the most i m p o r t a n t c h a r a c t e r i s t i c s o f l i g n i n s and t h e i r d e g r a d a t i o n p r o d u c t s i s t h e i r p o l y d i s p e r s e n a t u r e ( e x i s t o v e r a wide range o f m o l e c u l a r w e i g h t s ) .  M o l e c u l a r weight d i s t r i b u t i o n s of organics  i n p u l p m i l l e f f l u e n t s have been s t u d i e d u s i n g gel f i l t r a t i o n t e c h n i q u e s as r e v i e w e d and d e s c r i b e d by Obiaga and G a n c z a r c z y k (1972) and o t h e r s .  An  example o f a m o l e c u l a r w e i g h t d i s t r i b u t i o n , f o r a l k a l i l i g n i n , i s shown i n  13 F i g u r e 2.  V a r y i n g d i s t r i b u t i o n s have been f o u n d f o r d i f f e r e n t e f f l u e n t s ;  however, a l l have d e m o n s t r a t e d p o l y d i s p e r s i t y .  In g e n e r a l ,  molecular  w e i g h t s i n k r a f t p u l p m i l l e f f l u e n t s seem t o be lower than i n s u l p h i t e l i q u o r s , and both p u l p i n g e f f l u e n t s c o n t a i n more h i g h m o l e c u l a r w e i g h t c o l o u r e d compounds than do b l e a c h i n g e f f l u e n t s because o f the f u r t h e r degradation which occurs during bleaching. e f f l u e n t may c o n t a i n m a t e r i a l s o f M.W.  T y p i c a l l y a combined m i l l  5 400 t o £ 1 5 0 , 0 0 0 .  F u r t h e r i n f o r m a t i o n on the p o l y d i s p e r s e n a t u r e i s p r o v i d e d i n p a p e r s by S h o t t o n e t a l (1972), McNaughton e t a l (1967), Pew and Connors (1971) C o l l i n s e t a l (1967) and (1971), and S o u n d a r a r j a n  and Wayman  (1970).  The f a c t t h a t the c o l o u r e d m a t e r i a l s e x i s t over a broad m o l e c u l a r w e i g h t range compounds the p r o b l e m o f c o l o u r removal and c o m p l i c a t e s the s t u d y o f removal mechanisms.  F o r example, t h e r e i s c o n s i d e r a b l e e v i d e n c e  that  v a r i o u s s i z e f r a c t i o n s o f the l i g n i n compounds are r e s p o n s i b l e f o r d i f f e r e n t amounts o f the t o t a l c o l o u r .  Rankin and Benedek (1973) have  shown t h a t i n t e r m e d i a t e m o l e c u l a r w e i g h t m a t e r i a l (average m.w.  5,600)  i s r e s p o n s i b l e f o r the l a r g e s t p o r t i o n o f the c o l o u r o f a l k a l i n e I n d u l i n (a commercial k r a f t l i g n i n ) w h i l e h i g h m o l e c u l a r w e i g h t s p e c i e s ( ^ 1 5 0 , 0 0 0 m.w.)  e x e r t v e r y l i t t l e c o l o u r and s m a l l e r ( 1 4 , 0 0 0 m.w.)  constituents  c o n t r i b u t e some c o l o u r . The e f f e c t o f pH on o r g a n i c c o l o u r e d m a t e r i a l i s w e l l known from e a r l i e r work i n the w a t e r t r e a t m e n t f i e l d .  A s i m i l a r pH - c o l o u r i n t e n -  s i t y r e l a t i o n e x i s t s i n m i l l e f f l u e n t s . That i s , as pH goes up, c o l o u r goes up.  The c o n v e r s e o c c u r s when the pH i s lowered.  The i n t e r a c t i o n i s  r e v e r s i b l e but n o t l i n e a r as d e m o n s t r a t e d by a curve o b t a i n e d by m i l l e r (1972) i n F i g u r e 3.  T h i s r e l a t i o n s h i p i s a t t r i b u t e d to changes i n  the q u i n o i d s t r u c t u r e p r e s e n t i n t h e s e w a s t e s . have been found by o t h e r s .  Hersch-  Somewhat s i m i l a r c u r v e s  SO i  50 i  20 l  5 I  0.5 i  xlO  3  M.W.  ELUTION VOLUME, mi FIGURE 2.TYPICAL MOLECULAR WEIGHT DISTRIBUTION OF ALKALI LIGNIN OF SIMULATED KRAFT PULP MILL WASTEWATER. ( G A N C Z A R C Z Y K a n d O B I A G A . 1 9 7 4 )  4*  2600 CO  § 2200 o  O i Q.  CC  Z)  1800-  O _i O o  1400-  1000  FIGURE3.COLOUR Vs. pH FOR TOTAL MILL EFFLUENT  (HERSCHMILLER 1972)  16 Marton (1971) d i s c u s s e s the pH r e l a t e d b e h a v i o u r o f l i g n i n s .  In  aqueous s o l u t i o n , l i g n i n s behave as h y d r o c o l l o i d s ; they are s o l u b l e a t low concentrations  i n the absence o f d i s s o l v e d s a l t s ; as the pH i s l o w e r e d  n u c l e i s t a r t to form and a t pH 3 p r e c i p i t a t i o n commences.  Other s t u d i e s ,  i n c l u d i n g NCASI B u l l e t i n # 273, ( 1 9 7 3 ) , have n o t e d p r e c i p i t a t e f o r m a t i o n and c o n c u r r e n t c o l o u r decrease when pH i s a d j u s t e d to = 2.5 o r l e s s . Whether o r not l i g n i n d e r i v a t i v e s i n pulp and p a p e r m i l l e f f l u e n t s are s o l u b l e depends on many f a c t o r s , i n c l u d i n g pH and  molecular  w e i g h t d i s t r i b u t i o n . I t i s l i k e l y t h a t , i n most c a s e s , a combined s y s t e m o f s o l u b l e and c o l l o i d a l p a r t i c l e s w i l l be p r e s e n t .  However, t h o s e i n  a l k a l i n e k r a f t m i l l e f f l u e n t are g e n e r a l l y c o n s i d e r e d to be s o l u b l e , w h i l e i n s u l p h i t e l i q u o r , t h e r e a p p e a r s t o be two f r a c t i o n s o f l i g n o s u l p h onates.  These are termed <* and ^ f r a c t i o n s where the <* f r a c t i o n has  high  m o l e c u l a r w e i g h t s g e n e r a l l y c o n s i d e r e d to be c o l l o i d a l and fi has s m a l l molec u l a r w e i g h t m a t e r i a l u s u a l l y t h o u g h t o f as t r u l y s o l u b l e , ( P i l i n s k a y a e t a l , 1973). A n o t h e r f a c t o r which c o u l d have p a r t i c u l a r i n t e r e s t i n c o l o u r removal i s the e l e c t r i c a l charge on the c o l o u r p a r t i c l e s . A c c o r d i n g  to  Swanson e t a l (1973), a l l f r a c t i o n s o f u n b l e a c h e d k r a f t m i l l e f f l u e n t c o l o u r have been f o u n d t o c a r r y a r e l a t i v e l y h i g h n e g a t i v e c h a r g e .  Re-  f e r e n c e s to e l e c t r o p h o r e t i c m o b i l i t y ( o r z e t a p o t e n t i a l ) o f c o l o u r i n o t h e r waste streams are s c a r c e ; however, i t i s g e n e r a l l y a c c e p t e d  that  the m a j o r i t y o f these c o l o u r bodies are n e g a t i v e l y c h a r g e d . In summary, i t can be s a i d t h a t b a s i c knowledge and u n d e r s t a n d i n g o f t h e s e chromophore systems i s not w e l l d e v e l o p e d and more work i s n e c e s s a r y t o a c h i e v e t h i s .  considerably  17 3.2  E f f e c t s o f C o l o u r on R e c e i v i n g Waters A l t h o u g h s e v e r a l r e g u l a t o r y a g e n c i e s now e n f o r c e c o l o u r removal  r e q u i r e m e n t s , and many methods o f d e c o l o u r i z a t i o n have been  developed,  s u r p r i s i n g l y few s t u d i e s have been aimed a t q u a n t i f y i n g the e f f e c t s o f c o l o u r on the r e c e i v i n g e n v i r o n m e n t . The r e a s o n u s u a l l y g i v e n f o r r e q u i r i n g d e c o l o u r i z a t i o n o f p u l p m i l l e f f l u e n t s i s that r e c e i v i n g water c o l o u r a t i o n i s a e s t h e t i c a l l y objectionable.  However, i t i s n o t y e t known what magnitudes o f c o l o u r change  can be d e t e c t e d o r which i n t e n s i t y o r hue p e o p l e c o n s i d e r u n p l e a s a n t o r i d e n t i f y with p o l l u t i o n .  The r e s u l t s o f a s t u d y by NCASI i n t h e U.S.A.,  d i s c u s s e d by Gellman and B e r g e r (1974) s h o u l d p r o v i d e some b a s i s f o r s e t t i n g c o l o u r removal g u i d e l i n e s f o r a e s t h e t i c r e a s o n s .  In t h i s s t u d y ,  c o l o u r e d d i s c h a r g e s from s e v e r a l m i l l s i t e s were c a r e f u l l y v a r i e d o v e r a b r o a d range o f c o l o u r i n t e n s i t i e s .  For each c o l o u r l e v e l , the p e r c e p -  t i o n s o f a s c r e e n e d p a n e l o f s t u d e n t s were studiied a t a number o f v i e w i n g a n g l e s and under v a r y i n g shade c o n d i t i o n s . The f i n a l NASCI r e p o r t s h o u l d be a v a i l a b l e i n t h e n e a r f u t u r e . A n o t h e r much c i t e d e f f e c t o f c o l o u r i s t h a t i t causes  problems  a t downstream water t r e a t m e n t p l a n t s . Bouveng and L u n d s t e d t (1966) and (1968) and Hedburg e t a l (1968) have s t u d i e d the c o a g u l a n t r e q u i r e m e n t s f o r p r o d u c i n g p o t a b l e water from s u r f a c e water a f f e c t e d by k r a f t and sulphite mill effluents.  They found t h a t both e f f l u e n t s caused i n c r e a s e d  c o a g u l a n t (alum and a c t i v a t e d s i l i c a ) r e q u i r e m e n t s , w i t h the s u l p h i t e e f f e c t s b e i n g more pronounced than k r a f t . An e x t e n s i v e s t u d y by P r i h a (1971) o f 1 i g n o s u l p h o n a t e b u i l d u p i n a l a r g e F i n n i s h l a k e c o n f i r m e d t h e s e f i n d i n g s . The r e s u l t s o f t h i s s t u d y show t h a t , when l i g n o s u l p h o n a t e c o n t e n t i s moderate (3-5 mg/1),  18 l a k e w a t e r can be p u r i f i e d i n t o s a t i s f a c t o r y d r i n k i n g w a t e r w i t h t i o n a l methods.  conven-  When t h e c o n c e n t r a t i o n i n c r e a s e s , the n e c e s s a r y amount  o f c h e m i c a l s a l s o i n c r e a s e s , and a p o i n t i s f i n a l l y r e a c h e d when s a t i s f a c t o r y d r i n k i n g w a t e r cannot be o b t a i n e d even w i t h h i g h c h e m i c a l  dosage.  It i s repeated throughout the l i t e r a t u r e t h a t l i g n i n - d e r i v e d c o l o u r b o d i e s a r e b i o l o g i c a l l y s t a b l e and a r e t h e r e f o r e u n a f f e c t e d by c o n v e n t i o n a l b i o l o g i c a l t r e a t m e n t systems.  This generalization requires  c l a r i f i c a t i o n , f o r t h e r e a r e r e s e a r c h e r s who f e e l t h a t m o d i f i e d b i o l o g i c a l systems a r e c a p a b l e o f a c h i e v i n g a s i g n i f i c a n t degree o f c o l o u r removal ( e . g . , Ganczarcyk and Obiaga (1974) and NSRF ( 1 9 7 4 ) ) .  Some work  has been c a r r i e d o u t to determine t h e e x t e n t o f l i g n i n d e g r a d a t i o n and the l o n g - t e r m BOD e x e r t e d on a r e c e i v i n g stream.  Both K r o n e r and Moore (1954)  and Raabe (1968) d i s c u s s e d l i g n i n d e g r a d a t i o n and c o n c l u d e d t h a t (i*:) t h e r e are m i c r o - o r g a n i s m s which a r e c a p a b l e o f d e g r a d i n g l i g n i n and ( i i ) deg r a d a t i o n i s slow and u s u a l l y i n c o m p l e t e .  K r o n e r and Moore (1954) s t u d i e d  the p e r s i s t e n c e o f k r a f t l i g n i n i n water under v a r i o u s c o n d i t i o n s . They found t h a t 41-46% o f the l i g n i n remained a f t e r 20 days o f a e r o b i c , d a y l i g h t d e g r a d a t i o n c o n d i t i o n s . They a l s o d e t e r m i n e d t h a t exposure t o s u n l i g h t and the p r e s e n c e o f a l g a e enhanced  decomposition.  Raabe (1968) p r o v i d e d e v i d e n c e t h a t l i g n i n d e g r a d a t i o n does o c c u r i n r i v e r waters and t h i s d e g r a d a t i o n does e x e r t a l o n g - t e r m oxygen demand. The d e g r a d a t i o n o f l i g n i n o v e r a 100 day p e r i o d was s t u d i e d .  Results  s u g g e s t e d t h a t 5-20 day BOD was r e l a t e d t o c a r b o h y d r a t e c o n t e n t , whereas l o n g term BOD was l a r g e l y due t o l i g n i n d e c o m p o s i t i o n .  More r e c e n t d a t a  from a s t u d y by Bouveng and Solyom (1973) c o n f i r m e d Raabes' (1968) work, ( i . e . , t h a t pulp m i l l e f f l u e n t s contain a r e a d i l y degradable o r g a n i c f r a c t i o n and a s l o w l y d e g r a d a b l e f r a c t i o n ) .  They f o u n d t h a t u n b l e a c h e d  kraft  19 m i l l e f f l u e n t s c o n t a i n a h i g h e r p o r t i o n o f the r e a d i l y  degradable  f r a c t i o n than b l e a c h e d k r a f t e f f l u e n t s . P r i h a (1971) p o i n t s o u t t h a t d e g r a d a t i o n o f l i g n o s u l p h o n a t e s  is  e x t r e m e l y s l o w , and even when c o u p l e d w i t h n a t u r a l f l o w t h r o u g h a w a t e r system, i n p u t o f t e n exceeds o u t p u t .  He o b s e r v e d a b u i l d - u p o f these  p o l l u t a n t s i n a l a k e where they e x h i b i t e d s t r a f i f i c a t i o n and  seasonal  concentration variation. A n o t h e r more o b v i o u s concern i s the p o s s i b i l i t y o f  decreased  l i g h t p e n e t r a t i o n , c a u s i n g a r e d u c t i o n o f p r i m a r y p r o d u c t i v i t y , the b a s i s o f the e n t i r e a q u a t i c f o o d c h a i n .  A number o f p a p e r s i n c l u d i n g t h o s e by  Edmondson (1956) and J o n e s (1966) d e s c r i b e the r e l a t i o n between l i g h t i n t e n s i t y and growth r a t e o f a l g a e .  However, s u r p r i s i n g l y l i t t l e work  has been done t o d e t e r m i n e What e f f e c t , i f any, p u l p m i l l c o l o u r has on photosynthesis  by  phytoplankton.  P a r k e r and S i b e r t (1973) s t u d i e d the impact o f a pulp m i l l e f f l u e n t upon the A l b e r n i I n l e t i n B r i t i s h Columbia.  They c o n c l u d e d  that  i n c r e a s e d a b s o r p t i o n o f the l i g h t by the e f f l u e n t c o l o u r s i g n i f i c a n t l y reduced p h o t o s y n t h e s i s  such t h a t i t was p a r t i a l l y r e s p o n s i b l e f o r the  oxygen d e f i c i e n t c o n d i t o n i n the mixed zone and around the h a l o c l i n e . A more r e c e n t s t u d y o f the e f f e c t s o f p u l p m i l l c o l o u r on p l a n k t o n p r o d u c t i o n i n B. C. c o a s t a l w a t e r s , conducted  phyto-  by S t o c k n e r e t a l  (1975) i n d i c a t e s t h a t c o l o u r may be a more s e r i o u s p r o b l e m than p r e v i o u s l y suspected.  These r e s e a r c h e r s found t h a t c o l o u r i s one o f the c r i t i c a l  f a c t o r s d e p r e s s i n g p r i m a r y p r o d u c t i v i t y around m i l l s and showed a l i n e a r r e l a t i o n s h i p between l i g h t a t t e n u a t i o n and c o l o u r .  They a l s o found t h a t  t h e r e was some t o x i c i t y a s s o c i a t e d w i t h t h e c o l o u r , but t h i s was l i m i t e d to about a 150 meter r a d i u s around the m i l l o u t f a l l .  F u r t h e r s t u d i e s are  20 underway t o show more c o n c l u s i v e l y any t o x i c e f f e c t s o f c o l o u r - c a u s i n g compounds. A n o t h e r s i m i l a r s t u d y c o n d u c t e d by B. C. R e s e a r c h (Walden,  1975),  u s i n g f r e s h w a t e r l a b o r a t o r y c u l t u r e s , has a l s o found p r i m a r y p r o d u c t i o n t o be s i g n i f i c a n t l y r e d u c e d by p u l p m i l l e f f l u e n t c o l o u r . T e s t i n g one s p e c i f i c green a l g a e a t normal daytime l i g h t i n t e n s i t i e s , p r i m a r y p r o d u c t i o n was r e d u c e d by 80% a t a depth o f 1 metre i n a c o l o u r as low as 15 C. II. When a mixed c u l t u r e o f a l g a e from l o c a l B. C. l a k e s was t e s t e d under the same c o n d i t o n s , about 40% r e d u c t i o n i n p r i m a r y p r o d u c t i v i t y resulted.  F u r t h e r s t u d i e s a r e a l s o p l a n n e d by t h i s r e s e a r c h e r .  3.3  Summary o f C o l o u r Removal T e c h n o l o g y  3.3.1  General S e v e r a l comprehensive l i t e r a t u r e r e v i e w s o f c o l o u r removal t e c h -  n o l o g y are a v a i l a b l e .  The more r e c e n t o f t h e s e i n c l u d e r e p o r t s by T y l e r  and F i t z g e r a l d ( 1 9 7 2 ) , V i n c e n t ( 1 9 7 4 ) , Gellman and B e r g e r (1974) and Rush and Shannon (1975).  I t i s n o t p o s s i b l e i n the c o n t e x t o f t h i s r e p o r t t o  p r o v i d e an i n - d e p t h l i t e r a t u r e r e v i e w .  However, a b r i e f summary o f a l t e r -  n a t i v e d e c o l o u r i z a t i o n methods i s p r e s e n t e d h e r e , w i t h more d e t a i l s on the e x i s t i n g f u l l - s c a l e l i m e t r e a t m e n t f a c i l i t i e s i n t h e U.S.A. C o l o u r r e d u c t i o n can be a c h i e v e d by e i t h e r t e c h n i c a l w i t h i n t h e m i l l o r by e f f l u e n t t r e a t m e n t systems.  changes  In-plant modification  can range from s i m p l e i n e x p e n s i v e measures, such as p u l p washing and b e t t e r 'housekeeping  1  p r a c t i c e s , t o complex t e c h n o l o g i c a l changes such as  i n c r e m e n t a t i o n o f oxygen b l e a c h i n g . While i n - p l a n t changes s h o u l d be cons i d e r e d and implemented as a f i r s t p r e f e r e n c e , e x t e r n a l t r e a t m e n t may o f t e n s t i l l be r e q u i r e d . T h e r e a r e a l a r g e number o f e x t e r n a l t r e a t m e n t methods which a r e  21 known to be t e c h n i c a l l y f e a s i b l e f o r c o l o u r removal from p u l p m i l l e f f l u e n t s . Chemical t r e a t m e n t methods, based on p r e c i p i t a t i o n w i t h Ca 3+ 3+ Al  , o r Fe  2+  ,  , have advanced t o the s t a g e o f f u l l s c a l e a p p l i c a t i o n , as  has t h e r e s i n s e p a r a t i o n method o f Uddeholm-Kamyr.  The Rohm and Haas  r e s i n p r o c e s s , membrane p r o c e s s e s ( b o t h u l t r a f i l t r a t i o n and r e v e r s e osmosis) and a c t i v a t e d carbon a d s o r p t i o n have been t e s t e d on a p i l o t s c a l e , w h i l e c e r t a i n foam s e p a r a t i o n t e c h n i q u e s , o z o n a t i o n , magnesium c o a g u l a t i o n and e x t r a c t i o n w i t h amines, have been examined on a s m a l l e r l a b o r a t o r y s c a l e . These are methods known to be t e c h n i c a l l y f e a s i b l e . Economics i s a n o t h e r q u e s t i o n t h a t remains t o be answered by f u r t h e r p i l o t and f u l l s c a l e t e s t i n g . S e v e r a l o t h e r methods have been and a r e b e i n g i n v e s t i g a t e d . These i n c l u d e i r r a d i a t i o n t r e a t m e n t , a d s o r p t i o n on f l y ash and o t h e r waste m a t e r i a l s , a d s o r p t i o n on a c t i v a t e d a l u m i n a , l a n d d i s p o s a l , e l e c t r o l y s i s and b i o l o g i c a l  treatment.  It i s well established that conventional biological  treatment  systems are i n e f f e c t i v e i n t h e removal o f c o l o u r from p u l p m i l l e f f l u e n t s . In f a c t , a c o l o u r i n c r e a s e a c r o s s waste s t a b i l i z a t i o n ponds i s n o t uncommon. Thus, some form o f advanced o r t e r t i a r y t r e a t m e n t i s n e c e s s a r y f o r c o l o u r removal. Chemical c o a g u l a t i o n t e c h n i q u e s have been d e v e l o p e d t o the g r e a t e s t e x t e n t , w i t h t h e use o f aluminum and i r o n s a l t s most p o p u l a r i n Europe, S c a n d i n a v i a and Japan, and l i m e t r e a t m e n t d o m i n a t i n g i n the U.S.A.  Full  s c a l e d e m o n s t r a t i o n o f c h e m i c a l t r e a t m e n t f a c i l i t i e s has shown t h a t 85-90% removal o f t h e t o t a l m i l l c o l o u r can be a c h i e v e d w i t h a l l t h r e e o f t h e s e popular coagulants.  G e n e r a l l y , t h i s has meant t h a t the r e s i d u a l c o l o u r  i n t h e t r e a t e d e f f l u e n t has ranged from 100-200 3.3.2  CU.  C u r r e n t Lime Treatment T e c h n o l o g y i n the U n i t e d S t a t e s Because l i m e use and r e c o v e r y i s a l r e a d y an i n t e g r a l p a r t o f  22 k r a f t p u l p p r o d u c t i o n , lime t r e a t m e n t became t h e e a r l y f a v o u r i t e f o r e f f l u e n t d e c o l o u r i z a t i o n f o r economic r e a s o n s .  In the l a s t few y e a r s  s e v e r a l v a r i a t i o n s o f l i m e t r e a t m e n t methods have been p a t e n t e d and a t l e a s t f i v e o f t h e s e have been d e m o n s t r a t e d  on a f u l l - s c a l e b a s i s .  Re-  s u l t s o f t h e s e a r e d i s c u s s e d v e r y b r i e f l y h e r e , t o g i v e some background  on  the lime dosages and c o l o u r removal e f f i c i e n c i e s a c h i e v e d by c u r r e n t lime practices. 3.3.2.1  M a s s i v e Lime P r o c e s s A t the I n t e r n a t i o n a l Paper Company's b l e a c h e d k r a f t m i l l i n  S p r i n g h i l l , L o u i s i a n a , dosages o f 10,000-30,000 mg/1  l i m e were used to  t r e a t c a u s t i c e x t r a c t i o n s t a g e and u n b l e a c h e d d e c k e r e f f l u e n t . A c c o r d i n g t o Oswalt and Land (1973), t h i s t r e a t m e n t r e s u l t e d i n about 72% r e d u c t i o n i n the t o t a l m i l l e f f l u e n t c o l o u r .  T r e a t e d e f f l u e n t had a pH o f about  and was r e c a r b o n a t e d b e f o r e d i s c h a r g e t o a waste s t a b i l i z a t i o n pond.  12.2 In  t h i s p r o c e s s , the l i m e - o r g a n i c s l u d g e i s i n t e g r a t e d i n t o the k r a f t r e c o v e r y system. 3.3.2.2  M o d i f i e d Lime (Lime Mud)  Process  A l s o t e s t e d a t S p r i n g h i l l was a system t h a t r e p l a c e s a p o r t i o n o f the l i m e dosage w i t h l i m e mud (CaCO^) from t h e r e c a r b o n a t i o n c l a r i f i e r . Oswalt (1974) r e p o r t e d t h a t c o m b i n a t i o n s such as 3000 mg/1 p l u s 8,000 mg/1  o f f r e s h CaO  o f lime mud worked as w e l l as the massive lime p r o c e s s ,  f o r r e d u c i n g t h e c o l o u r o f the f i r s t c a u s t i c e x t r a c t i o n s t a g e e f f l u e n t . Foaming problems were n o t as s e r i o u s as w i t h massive l i m e t r e a t m e n t . 3.3.2.3  Minimum Lime P r o c e s s e s A t l e a s t t h r e e p a t e n t e d v e r s i o n s o f t h e minimum l i m e p r o c e s s  have been, o r are b e i n g t e s t e d .  These are based on a d d i t i o n o f a p p r o x i -  mately s t o i c h i o m e t r i c q u a n t i t i e s ( w i t h r e s p e c t t o t h e average  molecular  w e i g h t o f the c o l o u r b o d i e s ) o f l i m e t o t h e c o l o u r e d e f f l u e n t . I n t e r s t a t e  23 Paper Company's v e r s i o n , a t t h e i r l i n e r b o a r d m i l l i n R i c e b o r o , G e o r g i a , was the f i r s t f u l l - s c a l e l i m e d e c o l o u r i z a t i o n f a c i l i t y i n the U.S.A. The most r e c e n t r e s u l t s , p u b l i s h e d by EPA ( 1 9 7 4 ) , s t a t e t h a t about 50% o f t h e t o t a l m i l l e f f l u e n t ( ~ 1 2 0 0 C U . ) dosage o f a p p r o x i m a t e l y 1000 mg/1  as C a ( 0 H ) . 2  i s combined w i t h a l i m e  A f t e r f l o c c u l a t i o n and  c l a r i f i c a t i o n , the e f f l u e n t has a r e s i d u a l c o l o u r o f about 125 C U . c o n t a i n s 700-750 mg/1  of Ca(0H)  2  a t a pH o f 12.2.  and  The t h i n l i m e s l u d g e ( 2 %  s o l i d s ) from t h e c l a r i f i e r i s t h i c k e n e d to about 6% and d i s p o s e d o f i n a s l u d g e pond.  A t the p r e s e n t t i m e , the h i g h l y - a l k a l i n e , d e c o l o u r i z e d  e f f l u e n t undergoes n a t u r a l r e c a r b o n a t i o n i n a l a r g e s t a b i l i z a t i o n pond. F i n a l pH i s c:10.2 and a l l but 35 ppm o f t h e c a r r y - o v e r l i m e i s p r e c i p i t a t e d i n the pond.  E f f l u e n t recarbonation i s planned f o r the near future  a t t h i s mi 11. The G e o r g i a P a c i f i c Company's p a t e n t e d p r o c e s s was d e v e l o p e d a t the C r o s s e t t , Arkansas m i l l .  Gould (1973) r e p o r t e d 90% c o l o u r removal on  a b l e a c h e r y e f f l u e n t s t r e a m a t the Woodland Maine M i l l . C r o s s e t t , 2000-3000 mg/1,  However, a t  as CaO added t o t h e e f f l u e n t from the f i r s t  c a u s t i c e x t r a c t i o n s t a g e o f the b l e a c h e r y , t y p i c a l l y , reduce c o l o u r v a l u e s o f 12,000 C U .  down to 4000-5000 C U .  Lime s l u d g e i s combined w i t h l i m e  mud b e f o r e d e w a t e r i n g t o 60% s o l i d s and r e c o v e r y i n a k i l n . A t the C o n t i n e n t a l Can Company's m i l l i n Hodge, L o u i s i a n a , dosages o f a p p r o x i m a t e l y 1000 mg/1  o f GaO are added t o t h e e n t i r e e f f l u e n t  o f an u n b l e a c h e d k r a f t - N e u t r a l S u l p h i t e Semi-Chemical r e p o r t e d by S p r u i l l (1973 and 1974). from an average o f 1200 C U .  (NSSC) m i l l , as  The system t y p i c a l l y reduces c o l o u r  to 300 to 400 C.U., w i t h i n d i v i d u a l  removal  e f f i c i e n c i e s b e i n g q u i t e dependent on NSSC p r o d u c t i o n ; t h i s a c c o u n t s f o r 60% o f t h e c o l o u r , a l t h o u g h i t i s l e s s than 25% o f t o t a l p r o d u c t i o n .  Here,  24 e f f l u e n t i s r e c a r b o n a t e d and s l u d g e i s dewatered t o 35% s o l i d s and r e c o v ered i n a k i l n . In g e n e r a l , c u r r e n t l i m e t r e a t m e n t t e c h n o l o g y has proven t o be f a i r l y r e l i a b l e and e f f e c t i v e .  The main drawbacks appear t o be t h e l a r g e  amount o f s l u d g e r e s u l t i n g from t h e h i g h l i m e dosages, and a l s o the need f o r more e f f i c i e n t e f f l u e n t r e c a r b o n a t i o n systems.  25 CHAPTER 4 REVIEW OF-MAGNESIUM COAGULATION PROCESSES 4.1  H i s t o r i c a l Development T r a d i t i o n a l l y , l i m e , f e r r i c c h l o r i d e and alum have been the p r e -  f e r r e d c o a g u l a n t s f o r water and wastewater  clarification.  Until recently,  the huge volumes o f c h e m i c a l s l u d g e s were viewed as more o f a n u i s a n c e than as a s e r i o u s p o l l u t i o n problem.  But w i t h t h e i n c r e a s i n g t r e n d toward  t e r t i a r y ( c h e m i c a l ) t r e a t m e n t o f e f f l u e n t s and the l a c k o f s a t i s f a c t o r y s l u d g e d i s p o s a l o r r e c o v e r y a l t e r n a t i v e s ( e s p e c i a l l y f o r the huge volumes o f alum s l u d g e b e i n g g e n e r a t e d ) , the p r o b l e m has been compounded. D e s p i t e p r o g r e s s b e i n g made i n the a r e a o f s l u d g e d i s p o s a l and r e c o v e r y , the r e p l a c e m e n t o f t h e s e t r a d i t i o n a l c h e m i c a l s , as p r i m a r y coa g u l a n t s , now appears q u i t e p o s s i b l e . A p r o c e s s - r e c e n t l y r e p o r t e d by Thompson, S i n g l e y , and B l a c k (1972) uses magnesium c a r b o n a t e as a c o a g u l a n t . T h i s new t e c h n o l o g y stems d i r e c t l y from B l a c k ' s e a r l i e r work on e l i m i n a t i n g p o l l u t i o n from l i m e - s o d a water s o f t e n i n g s l u d g e s a t Dayton, Ohio.  Here,  B l a c k had been f a c e d w i t h t h e t a s k o f s e p a r a t i n g the h i g h l y h y d r a t e d M g ( 0 H ) from the f i n e , c r y s t a l l i n e C a C 0 o f the s l u d g e . 2  3  T h i s was n e c e s s a r y f o r two r e a s o n s . 1.  The M g ( 0 H ) has g e l a t i n o u s p r o p e r t i e s s i m i l a r to A U O H ) ^ , 2  making the s l u d g e more d i f f i c u l t to dewater t h a n i f CaCO^ were p r e s e n t alone. 2.  In cases where l i m e r e c o v e r y i s t o be p r a c t i s e d , a b u i l d u p  o f i n s o l u b l e magnesium o x i d e w i l l r e s u l t i f t h e magnesium h y d r o x i d e i s n o t removed, b e f o r e c a l c i n a t i o n . Up t o t h a t t i m e , s e v e r a l p h y s i c a l methods o f M g ( 0 H ) s e p a r a t i o n , 2  i n c l u d i n g s e l e c t i v e s o f t e n i n g and the use o f a c e n t r i f u g e t o s e l e c t i v e l y c l a s s i f y M g ( 0 H ) i n t o the c e n t r a t e , had been attempted but were c o n s i d e r e d 2  unsuitable.  26 In 1957, B l a c k and E i d s n e s s demonstrated  t h a t M g ( 0 H ) c o u l d be 2  s e l e c t i v e l y d i s s o l v e d from CaCO^ by u s i n g carbon d i o x i d e gas. a l l o w e d subsequent s i n c e 1958.  T h i s has  c a l c i n a t i o n o f CaCO^ t o h i g h q u a l i t y CaO, a t Dayton,  F o r a t i m e , the s u p e r n a t a n t , c o n t a i n i n g d i s s o l v e d magnesium  b i c a r b o n a t e , was d i s c h a r g e d t o a r e c e i v i n g stream.  However, by  1970  t h e r e was c o n s i d e r a b l e p r e s s u r e f r o m l o c a l a u t h o r i t i e s to remove t h i s d i s s o l v e d m a t e r i a l . T h i s l e d B l a c k and h i s a s s o c i a t e s t o the d i s c o v e r y o f a r e l a t i v e l y s i m p l e and i n e x p e n s i v e system t o r e c o v e r the magnesium as MgC0 -3H 0 from t h i s e f f l u e n t ( d e s c r i b e d by B l a c k , Shuey and 3  (1971)).  2  Fleming  T h i s w i l l be d i s c u s s e d i n d e t a i l i n a l a t e r s e c t i o n on magnesium  recovery. D u r i n g the same p e r i o d , B l a c k d i s c o v e r e d t h a t f r o t h f l o t a t i o n p r o v i d e d a h i g h l y s e l e c t i v e method o f s e p a r a t i n g r e l a t i v e l y pure c a l c i u m c a r b o n a t e from c l a y , s i l t and o t h e r c o n t a m i n a n t s .  T h i s was t r u e o n l y i f  t h e magnesium had been removed p r i o r t o f l o t a t i o n . U n t i l t h i s t i m e , l i t t l e a t t e n t i o n had been g i v e n to magnesium as a c o a g u l a n t , a l t h o u g h magnesium h y d r o x i d e had l o n g been r e c o g n i z e d as an e f f e c t i v e coagulant with p r o p e r t i e s s i m i l a r to the h y d r o l y s i s products o f aluminum and f e r r i c i o n s .  F l e n t j e ' s (1927) work a t the Oklahoma C i t y water  t r e a t m e n t p l a n t i s an e a r l y example o f magnesium enhanced c o a g u l a t i o n .  He  a t t r i b u t e d improved c l a r i f i c a t i o n o f water w i t h i n c r e a s i n g l i m e dosage t o p r e c i p i t a t i o n o f magnesium h y d r o x i d e from t h e h a r d water.  Further studies  p r o v e d magnesium c h l o r i d e to be an e f f e c t i v e c o a g u l a n t as w e l l .  In o r d e r  to use t h e magnesium b i c a r b o n a t e n a t u r a l l y p r e s e n t i n the w a t e r , F l e n t j e o p e r a t e d the p l a n t u s i n g e x c e s s l i m e t r e a t m e n t i n c o n j u n c t i o n w i t h f e r r i c s u l p h a t e t o t r e a t h a r d , t u r b i d , r i v e r water.  He r e p o r t e d no d e c r e a s e i n  f i l t e r r u n s , l e s s a l g a e i n t h e s e t t l i n g b a s i n s and g r e a t e r b a c t e r i a l removal. No c o a g u l a n t r e c y c l e was  attempted.  27 Much l a t e r Lecompte (1966) r e p o r t e d and p a t e n t e d a method o f r e c l a i m i n g p a p e r m i l l wastewaters  by c o a g u l a t i o n w i t h magnesium c a r b o n a t e ,  which i s formed i n s i t u by a d d i n g f i n e magnesium o x i d e t o water c o n t a i n i n g calcium bicarbonate.  T h i s i s i l l u s t r a t e d by t h e f o l l o w i n g r e a c t i o n :  MgO + Ca ( H C 0 ) ^ ; 3  2  MgC0 + C a C 0 + H 0 3  3  2  Then, when t h i s 'make up' water i s combined w i t h t h e i n f l u e n t waste s t r e a m and a s u f f i c i e n t l i m e dosage, a l l t h e M g C 0 i s p r e c i p i t a t e d as M g ( 0 H ) . 3  2  T h i s g e l a t i n o u s f l o e removes suspended m a t e r i a l and c o l o u r b o d i e s as i t settles.  As i n F l e n t j e ' s work, no attempt a t magnesium r e c o v e r y was men-  t i o n e d , a l t h o u g h Lecompte d i d r e c o g n i z e t h a t r e c a r b o n a t i o n o f t h e e f f l u e n t would d i s s o l v e any c a r r y o v e r o f magnesium h y d r o x i d e f l o e i n t h e form o f magnesium b i c a r b o n a t e . O t h e r r e p o r t e d a p p l i c a t i o n s o f magnesium c o a g u l a t i o n i n c l u d e t h e use o f magnesium o x i d e as a f l u o r i d e adjustment agent by t h e AWWA (1971) and a p r o c e s s f o r i r o n removal from groundwater u s i n g magnesium o x i d e r e p o r t e d by O'Connor and Benson (1970).  In t h e f o r m e r , MgO i s u s u a l l y added  i n t h e form o f a l i m e t h a t i s h i g h i n magnesium c o n t e n t .  Both t h e f l u o r i d e s  and t h e p r e c i p i t a t e d magnesium h y d r o x i d e a r e removed by s e t t l i n g and then discarded.  The l a t t e r p r o c e s s i n v o l v e s t h e r a p i d m i x i n g o f s m a l l q u a n t i t i e s  o f MgO i n t o a e r a t e d w a t e r , g i v i n g a l m o s t complete i r o n removal.  However,  i n t h i s p r o c e s s , MgO i s d i s s o l v e d w i t h o u t t h e f o r m a t i o n o f M g ( 0 H ) , s o t h e 2  i r o n removal may n o t be s t r i c t l y by c o a g u l a t i o n . O f t e n magnesium h y d r o x i d e forms i n a l k a l i n e s y s t e m s , a i d i n g s o l i d s removal as i t s e t t l e s , (Culp and Culp ( 1 9 7 1 ) ) .  It i s likely that,  i n t h i s way, many o f t h e t r e a t m e n t systems u s i n g l i m e a r e enhanced c o n s i d e r a b l y by M g ( 0 H )  2  precipitation.  A l t h o u g h an i n - d e p t h r e v i e w o f t h e l i t e r a t u r e would  undoubtedly  28 r e v e a l o t h e r s p e c i f i c a p p l i c a t i o n s o f magnesium f o r c o a g u l a t i o n i t i s s a f e t o say t h a t i t s ' use has n o t been w i d e s p r e a d .  In g e n e r a l , i t can be  s a i d t h a t , a l t h o u g h magnesium compounds a r e e f f e c t i v e c o a g u l a n t s , t h e y have not been used e x t e n s i v e l y because o f t h e i r h i g h c o s t s . Both magnesium s u l p h a t e and magnesium c h l o r i d e are more e x p e n s i v e than alum.  So c a l l e d  " b a s i c magnesium c a r b o n a t e " ( 4 M g C 0 . M g ( 0 H ) . 5 H 0 ) i s e x t r e m e l y e x p e n s i v e , 3  2  2  and the t r i h y d r a t e form, MgCOy 3 H 0 , i s c u r r e n t l y u n a v a i l a b l e . 2  T h i s was the s i t u a t i o n around 1970. was a cheap s o u r c e o f magnesium i o n s .  C l e a r l y , what was  needed  E a r l i e r , Monis (1956) had l i s t e d  f o u r major s o u r c e s o f magnesium c a r b o n a t e . 1.  From d o l o m i t i c l i m e s t o n e  2.  From deepwell b r i n e s  3.  From b i t t e r n s o r "mother" l i q u o r s o b t a i n e d from s o l a r evaporation o f sea water f o r s a l t  4.  From sea w a t e r w i t h o u t e v a p o r a t i o n , u s i n g l i m e t o p r e c i p i t a t e o u t magnesium  The l a t t e r method has been r e c e n t l y i n v e s t i g a t e d a t Nova S c o t i a Research F o u n d a t i o n (NSRF) ( r e p o r t e d by Rapson e t a l (1973)) as t h e b a s i s f o r c l a r i f i c a t i o n o f p u l p m i l l wastes.  T h i s p r o c e s s may p r o v i d e c o a s t a l  f a c i l i t i e s w i t h cheap magnesium h y d r o x i d e formed i n s i t u and may  even  produce some e x c e s s magnesium s a l t s f o r s a l e . But such a p r o c e s s , even i f proven f e a s i b l e , w i l l have l i m i t e d a p p l i c a t i o n because o f i t s l o c a t i o n requirements.  However, a c o m b i n a t i o n o f t h i n g s now i n d i c a t e t h a t magnesium  s h o u l d be g i v e n f u r t h e r c o n s i d e r a t i o n as a c o a g u l a n t . 1.  Alum i s i n a p o s i t i o n o f i n c r e a s i n g d i s f a v o u r because o f s l u d g e d i s p o s a l problems.  2.  W a t e r - s o f t e n i n g s l u d g e e l i m i n a t i o n i s now mandatory i n many a r e a s .  29 3.  The most p r a c t i c a l d i s p o s a l o f w a t e r - s o f t e n i n g s l u d g e s l e a d s t o the r e c o v e r y o f l a r g e q u a n t i t i e s o f i n e x p e n s i v e magnesium c a r b o n a t e as ( M g C O g . 3 ^ 0 ) .  T h i s means a^ new l o s t c o s t s o u r c e  o f magnesium. U s i n g t h e s e t e r m s . o f r e f e r e n c e and B l a c k ' s f o u r b a s i c d i s c o v e r i e s : (1) s e p a r a t i o n o f magnesium h y d r o x i d e from c a l c i u m c a r b o n a t e ; (2) f l o t a t i o n o f c a l c i u m c a r b o n a t e from raw water i m p u r i t i e s ; (3) t h e use o f magnesium as a r e c y c l e d c o a g u l a n t ; and (4) t h e p r o d u c t i o n o f magnesium c a r b o n a t e f r o m s l u d g e s o f w a t e r s h i g h i n magnesium c o n c e n t r a t i o n , a new  technology  f o r water t r e a t m e n t has been d e v e l o p e d and d e s c r i b e d by Thompson, S i n g l e y and B l a c k (1972); i t i s f u r t h e r o u t l i n e d i n an EPA r e p o r t (1971). The b a s i s o f t h i s new s y s t e m can be d e s c r i b e d b r i e f l y as f o l l o w s , and w i l l be d i s c u s s e d i n more d e t a i l l a t e r .  Lime i s added t o a water  which  c o n t a i n s magnesium b i c a r b o n a t e o r has had magnesium c a r b o n a t e added. p r e c i p i t a t e s magnesium h y d r o x i d e and c a l c i u m c a r b o n a t e a t pH > 1 1 .  This The  r e s u l t i n g s l u d g e i s c a r b o n a t e d t o s o l u b i l i z e t h e magnesium as magnesium b i c a r b o n a t e , which can be r e c o v e r e d by vacuum f i l t r a t i o n , the f i l t r a t e b e i n g r e c y c l e d and r e u s e d .  The f i l t e r cake ( c o n t a i n i n g CaCC^ and  suspended  s o l i d s ) * c a n be e a s i l y h a n d l e d and d i s p o s e d o f as l a n d f i l l o r r e c a l c i n e d , as economics  d i c t a t e . A l t h o u g h o r i g i n a l l y d e v e l o p e d as a water  treatment  p r o c e s s , t h e tremendous p o t e n t i a l o f such a r e c y c l e d c o a g u l a n t i s immedi a t e l y obvious. To d a t e , t h e r e have been t h r e e EPA funded p r o j e c t s r e l a t e d to the Magnesium Carbonate P r o c e s s .  The f i r s t was a l a b o r a t o r y s t u d y a t  G a i n e s v i l l e , F l o r i d a by EPA (1971).  The second c o n s i s t e d o f f u l l - s c a l e  d e m o n s t r a t i o n p r o j e c t s a t Montgomery, Alabama and Melbourne,  F l o r i d a re-  p o r t e d by B l a c k , Crow and E i d s n e s s Inc. (1974) and t h e t h i r d p r o j e c t was f o r t h e t r e a t m e n t o f m u n i c i p a l and i n d u s t r i a l w a s t e s (DuBose 1973).  30 From the water t r e a t m e n t s t u d i e s , a number o f s i g n i f i c a n t advantages o v e r the alum p r o c e s s have been i d e n t i f i e d .  The p r i m a r y  advantage  i s t h a t t h e e x i s t i n g problem o f s l u d g e d i s p o s a l can be e l i m i n a t e d o r at l e a s t g r e a t l y reduced ('.depending on whether l i m e r e c a l c i n a t i o n i s economical).  A l l water i s r e c y c l e d w i t h i n t h e p r o c e s s , a l o n g w i t h the t h r e e  b a s i c water t r e a t m e n t c h e m i c a l s ; dioxide.  O t h e r advantages  l i m e ; magnesium b i c a r b o n a t e ; and carbon  found were;  (1) i n c r e a s e d f l o e s e t t l i n g r a t e s ;  (2) s i m p l i c i t y o f o p e r a t i o n and c o n t r o l ; (3) reduced c o s t s when s l u d g e t r e a t m e n t and d i s p o s a l c o s t s a r e c o n s i d e r e d ; (4) more complete  disinfection;  and (5) reduced c o r r o s i o n r a t e . With r e s p e c t to advanced t r e a t m e n t o f m u n i c i p a l w a s t e s , magnesium i s known t o a f f e c t phosphorus  removal by l i m e p r e c i p i t a t i o n .  Ferguson  and McCarty (1971) f o u n d t h a t i f t h e pH o f c o a g u l a t i o n i s below 9.0, p r e s e n c e o f magnesium d e c r e a s e s phosphorus moval was enhanced by magnesium.  the  removal but a t h i g h pH, r e -  V i n c e n t (1974) found phosphorus  removals  o f 90-95% from p u l p m i l l e f f l u e n t c o n t a i n i n g i n i t i a l c o n c e n t r a t i o n s r a n g i n g from .7 to 31.5 mg/1  (as P ) .  DuBose (1973) c a r r i e d out p i l o t p l a n t t r e a t m e n t o f raw m u n i c i p a l w a s t e s o f v a r i o u s s t r e n g t h s , r a n g i n g from t o t a l COD < 400 to t o t a l COD  >800.  H i s d a t a showed t h a t 10% t o 30% more t o t a l COD and much g r e a t e r r e d u c t i o n i n phosphate, suspended s o l i d s and c o l o u r c o u l d be removed by c o a g u l a t i o n w i t h r e c y c l e d magnesium b i c a r b o n a t e and l i m e than c o u l d be a t t a i n e d by lime treatment alone.  T h i s s t u d y a l s o demonstrated  t h a t .the s u p e r i o r i t y  of magnesium p l u s l i m e o v e r l i m e a l o n e was even more pronounced  as the  s t r e n g t h o f the waste i n c r e a s e d and recommended f u r t h e r s t u d i e s on i n d u s t r i a l wastes o r d i g e s t e r s u p e r n a t a n t . A c c o r d i n g t o B l a c k , Crow and E i d s n e s s ( 1 9 7 4 ) , t h e U.S.A. EPA has completed some a n a l y s i s o f t r a c e m e t a l s i n both alum and magnesium t r e a t e d  waters.  31 The magnesium t r e a t e d w a t e r showed metal c o n c e n t r a t i o n s a t l e a s t  50% l o w e r than t h o s e f o u n d i n t h e alum t r e a t e d w a t e r s .  T h e r e were no  s i g n i f i c a n t c o n c e n t r a t i o n s o f m e t a l s f o u n d i n e i t h e r , however.  As an  example, c o p p e r was 17 p a r t s p e r b i l l i o n (ppb) i n t h e alum t r e a t e d w a t e r and 9 ppb i n t h e magnesium t r e a t e d w a t e r .  Z i n c was 190 ppb i n alum t r e a t e d  w a t e r and 76 ppb i n t h e magnesium t r e a t e d water.  These r e s u l t s a r e m e r e l y  an i n d i c a t i o n o f t h e p o t e n t i a l o f magnesium c o a g u l a t i o n f o r removal o f t r a c e m e t a l s , whether from w a t e r , m u n i c i p a l sewage o r i n d u s t r i a l w a s t e w a t e r . T h i s s h o u l d be i n v e s t i g a t e d i n more d e t a i l . To date t h e o n l y major i n d u s t r i a l a p p l i c a t i o n s o f magnesium c o a g u l a t i o n r e p o r t e d have been i n p p u l p and p a p e r m i l l c l a r i f i c a t i o n .  Lecompte's  work, m e n t i o n e d p r e v i o u s l y , has formed t h e b a s i s o f a lime-magnesium s y s t e m f o r r e n o v a t i o n o f p a p e r m i l l w a s t e w a t e r s a t K i m b e r l e y - C l a r k ' s m i l l i n Huntsv i l l e , O n t a r i o , (Gropp and Montgomery, 1972).  80-100% o f t h e p r o c e s s  w a t e r i s t r e a t e d w i t h dosages as low as 5-10 mg/1 M g  + +  and 150 mg/1 CaO  and r e c y c l e d t o t h e p a p e r machine. Preliminary i n v e s t i g a t i o n s o f k r a f t pulp mill decolourization by B l a c k , Crow and E i d s n e s s (1974) and V i n c e n t (1974) i n d i c a t e t h a t a comb i n a t i o n o f l i m e and magnesium would p r o v i d e s e v e r a l advantages o v e r conv e n t i o n a l l i m e t r e a t m e n t . The f o r m e r r e s e a r c h e r s f o u n d t h a t l i m e dosages o f about 400 mg/1 as C a ( 0 H ) a l o n g w i t h 60-90 mg/1 o f M g 2  + +  r e s u l t e d i n 90%  c o l o u r r e m o v a l , and 72% COD removal f r o m t o t a l k r a f t m i l l e f f l u e n t c o n t a i n i n g 530 C U . o f c o l o u r and 592 mg/1 COD.  Preliminary laboratory studies  by V i n c e n t i n Quebec i n d i c a t e t h a t 500 mg/1 o f l i m e and 30-60 mg/1 magnesium have about t h e same d e c o l o u r i z i n g e f f e c t on k r a f t m i l l e f f l u e n t s as 1000 mg/1 o f l i m e a l o n e and r e s u l t s i n s m a l l e r volumes o f s l u d g e t o h a n d l e .  With  a l l t y p e s o f e f f l u e n t examined, t h e use o f magnesium h y d r o x i d e formed " i n s i t u " a l l o w e d much l o w e r l e v e l s o f l i m e t o be used than i f l i m e were used alone.  32 From t h e s e v e r y p r e l i m i n a r y s t u d i e s , i t a p p e a r s t h a t magnesium enhanced l i m e t r e a t m e n t has s e v e r a l advantages o v e r c o n v e n t i o n a l l i m e decolourization processes.  These i n c l u d e , (1) e a s i e r s l u d g e h a n d l i n g ,  (2)  l o w e r c o a g u l a t i o n pH o f about 11.3, thus r e s u l t i n g i n a l o w e r c a l c i u m l o s s i n the d e c o l o u r i z e d e f f l u e n t and l e s s time r e q u i r e d f o r n a t u r a l pH s t a b i l i z a t i o n a f t e r d i s c h a r g e ; (3) chemical c o s t s b e i n g s u b s t a n t i a l l y l e s s , (4) p o s s i b l y b e t t e r removal e f f i c i e n c i e s f o r c o l o u r and o t h e r p a r a m e t e r s ; and (5) h o p e f u l l y , t o x i c i t y b e i n g e l i m i n a t e d , a l t h o u g h t h i s remains t o be shown. As p r e v i o u s l y - m e n t i o n e d ,  MgCO^.SH^O i s n o t a v a i l a b l e i n q u a n t i t i e s  a t t h i s ' time; however, a c c o r d i n g to B l a c k (1975) i t soon w i l l be.  I f the  pr.iice i s as low (5<£/lb) as a n t i c i p a t e d , t h i s c h e a p e r s o u r c e o f magnesium i o n s would make c o n s i d e r a b l e improvements i n the c o s t p i c t u r e o f any magnesium c o a g u l a t i o n system.  T h i s appears t o be an added i n c e n t i v e f o r  c u r r e n t and f u t u r e r e s e a r c h , a l t h o u g h use o f o t h e r magnesium s o u r c e s ( p a r t i c u l a r l y MgO o r d o l o m i t i c l i m e ) c o u l d be j u s t i f i e d i n some c a s e s . I t s h o u l d be e v i d e n t t h a t the r e s e a r c h to date has m e r e l y s c r a t c h e d the s u r f a c e o f p o s s i b l e a p p l i c a t i o n s o f magnesium c o a g u l a t i o n . The p o t e n t i a l f o r p u l p and p a p e r w a s t e t r e a t m e n t i s o n l y one p o s s i b l e a p p l i c a t i o n and s h o u l d be s t u d i e d i n d e t a i l .  I t seems l i k e l y t h a t s i m i l a r  b e n e f i t s would a r i s e i n t r e a t m e n t o f o t h e r c o l o u r e d e f f l u e n t s , such as t e x t i l e w a s t e s , as w e l l as i n t r e a t m e n t o f f l u o r i d e w a s t e s , removal o f t r a c e metals from m u n i c i p a l and i n d u s t r i a l w a s t e s , and s i l i c a removal t o meet i n d u s t r i a l w a t e r t r e a t m e n t r e q u i r e m e n t s ,  t o mention a few.  I t i s , t h e r e f o r e , i m p o r t a n t t h a t t h i s new t e c h n o l o g y be e v a l u a t e d o v e r a wide range o f a p p l i c a t i o n s and be a p p l i e d where b e n e f i c i a l .  33 4.2  T h e o r e t i c a l C o n s i d e r a t i o n s o f Magnesium Treatment  4.2.1  Magnesium S o l u b i l i t y The water-works p r o f e s s i o n has l o n g been i n t e r e s t e d i n magnesium  s o l u b i l i t y i n w a t e r because o f i t s c o n t r i b u t i o n t o w a t e r h a r d n e s s . nesium i s p r e s e n t t o some e x t e n t i n a l m o s t a l l n a t u r a l w a t e r s .  Mag-  It is  found p r e d o m i n a n t l y i n c o n j u n c t i o n w i t h a n i o n s such as c a r b o n a t e , b i c a r b o n a t e , h y d r o x i d e , c h l o r i d e , s u l p h a t e and n i t r a t e , depending on the p a r t i c u l a r e n v i r o n m e n t a l c o n d i t i o n s . The s o l u b i l i t y o f magnesium i s known t o depend on pH, t e m p e r a t u r e , a l k a l i n i t y and t o t a l i o n i c s t r e n g t h o f the solution. Stumm and Morgan (1970) s t u d i e d the e q u i l i b r i u m o f a s y s t e m c o n t a i n i n g o n l y magnesium, carbon d i o x i d e , and water.  In such a s y s t e m ,  f o u r s o l i d phases o f magnesium can be f o u n d i n v a r i o u s c o n c e n t r a t i o n s , depending m a i n l y on pH.  These a r e M g ( 0 H ) , ( B r u c i t e ) ; MgC0 ( M a g n e s i t e ) ; 2  3  MgC0 .3H 0 ( N e s g u e h o n i t e ) ; and M g ( C 0 ) ( 0 H ) . 3 H 0 ( H y d r o m a g n e s i t e ) . 3  2  4  3  2  Fig-  2  ure 4 shows the p H - s o l u b i l i t y r e l a t i o n s h i p o f t h i s s y s t e m f o r a t o t a l c a r bonate c o n c e n t r a t i o n o f 10  M.  MgC0 .3H 0 i s l e s s s o l u b l e t h a n MgC0 f o r 3  a l l pH v a l u e s ; t h u s , MgC0 i s n o t shown. 3  2  3  I t can be seen t h a t f o r pH v a l u e s  up t o 7.5, M g C 0 3 H 0 i s the l e a s t s o l u b l e . Between pH 7.5-pH 9.0 M g ( C 0 ) 3  3  2  4  3  ( O H ) - 3 H 0 . control's, s o l u b i l i t y and a t pH above 9.0, M g ( 0 H ) i s by f a r 2  2  2  the l e a s t s o l u b l e . Because l i m e - s o d a w a t e r s o f t e n i n g e f f i c i e n c y i s d i r e c t l y r e l a t e d t o t h e s o l u b i l i t y o f magnesium h y d r o x i d e , c o n s i d e r a b l e e f f o r t has gone i n t o d e t e r m i n i n g the s o l u b i l i t y p r o d u c t c o n s t a n t f o r Mg(0H) -  The EPA  2  (1971)  s t u d y r e v i e w e d the l i t e r a t u r e and f o u n d many v a l u e s o f p k p f o r M g ( 0 H ) , g  r a n g i n g f r o m 10.31 to 11.38 a t t e m p e r a t u r e s around 25-30°C.  2  T a b l e 2,  from B l a c k ( 1 9 6 6 ) , shows c a l c u l a t e d v a l u e s f o r the t h e o r e t i c a l o f M g ( 0 H ) a t 25°C based on a k 2  g p  = 2.5 x l o  - 1 1  .  solubility  L a r s o n e t a a l (1959) used  the s o l u b i l i t y p r o d u c t c o n s t a n t o f I r a v e r s and Nouvel (1929) t o i l l u s t r a t e  34 TABLE 2 SOLUBILITY OF M g ( 0 H ) AT 25°C •11 ks = 2.5 x l o 2  Solubility pH  mg/1 moles/1  gm/l As CaC0  10.56  1.84 x l O "  4  1.07  X  lO"  10.70  1.0  x lO"  4  5.8  X  10"  10.80  6.3  x 10"  5  3.6  X  10.90  4.0  x 10"  5  2.3  11.00  2.5  X  lO"  11.10  1.6  X  10"  X  10"  11.20  ,  2.8  As. Mg  3  18.4  4.4  3  10.0  2.4  10"  3  6.3  1.5  X  10"  3  4.0  1.0  1.4  X  10"  3  2.5  0.6  5  9.1  X  lO"  4  1.6  0.4  5  1.6  X  lO"  4  0.3  0.07  5  2  B l a c k (1966)  +  o  the i n f l u e n c e o f t e m p e r a t u r e and pH on t h e s o l u b i l i t y o f magnesium i n a w a t e r o f 50 mg/1 a l k a l i n i t y as shown i n F i g u r e 5.  I t has been p o i n t e d o u t  t h a t f o r e f f i c i e n t p r e c i p i t a t i o n , a h i g h e r pH i s needed w i t h c o l d w a t e r t h a n w i t h warm w a t e r .  The w e l l known s e n s i t i v i t y o f pH t o t e m p e r a t u r e i s  a l s o i n d i c a t e d b u t t h e e f f e c t s o f a l k a l i n i t y and t o t a l d i s s o l v e d s o l i d s are n o t shown.  I f t h e o t t a l a l k a l i n i t y were 25 mg/1, t h e pH a t 167° w o u l d  be .14 l o w e r ; w i t h a t o t a l a l k a l i n i t y o f 100 mg/1, the pH a t 167° would be .16 pH u n i t s h i g h e r , a c c o r d i n g t o the work o f L a n g l i e r ( 1 9 4 6 ) . A c c o r d i n g t o t h e d a t a o f Naesaenen ( 1 9 4 1 ) , i f t h e t o t a l d i s s o l v e d m i n e r a l s was i n c r e a s e d f r o m 200 mg/1 t o 600 mg/1, t h e s o l u b i l i t y would i n c r e a s e by about 30 p e r c e n t . In summary i t can be s a i d that: 1.  An i n c r e a s e i n pH means a d e c r e a s e i n M g ( 0 H )  9  solubility  FIGURE 4. SOLUBILITY DIAGRAM FOR MAGNESIUM IN WATER AT ATMOSPHERIC CONDITIONS. TOTAL CARBONATE = 1 0 " M. 3  (STUMM  AND  MORGAN , 1970)  36  12.0  11.0  vN  -10 -20 -40 -100 -200  SJ  •N  10.0 X Q.  9.0  8.01 30  50  70  90  0  130  150  170  190  210  TEMPERATURE (°F) MAGNESIUM SOLUBILITY (as parts per million C a C 0 ) B A S E D O N T H E SOLUBILITY PRODUCT CONSTANTS O F TRAVERS A N D N O U V E L . (1929) 3  pH  VARIATION  FIGURE 5. TEMPERATURE INFLUENCE ON MAGNESIUM SOLUBILITY ( L A R S O N E T A L , 1959)  37 2.  An i n c r e a s e i n a l k a l i n i t y means a d e c r e a s e i n Mg(0H)2 s o l u b i l i ty  3.  An i n c r e a s e i n t e m p e r a t u r e means a d e c r e a s e i n MgCOH)^ solubility  4.  An i n c r e a s e i n t o t a l d i s s o l v e d s o l i d s means an i n c r e a s e i n Mg(0H)2 s o l u b i l i t y .  In p r a c t i c e , t h e amount o f Mg(0H)2 s o l u b l e under g i v e n d i t i o n s has been found t o be h i g h e r than p r e d i c t e d by t h e o r y .  con-  This i s  i l l u s t r a t e d i n F i g u r e 6, taken from r e c e n t s t u d i e s a t Montgomery, Alabama by B l a c k , Crow and E i d s n e s s (1974).  T h i s d i f f e r e n c e a r i s e s from t h e f a c t  that conditions p r e v a i l i n g i n c o n t r o l l e d l a b o r a t o r y studies are seldom found i n l a r g e s c a l e o p e r a t i o n .  D e t e n t i o n time i n p r a c t i c e i s o f t e n l o n g e r  than i n j a r t e s t s g i v i n g more time f o r MgCOg.Sr^O t o r e s o l u b i l i z e . The t i m e - s o l u b i l i t y r e l a t i o n s h i p o f MgCO^-SH^O i s shown i n F i g u r e 7. i t i o n , Stumm and Morgan (1970) s t a t e t h a t c o m p l e x a t i o n  In add-  o f t h e magnesium,  w i t h both i n o r g a n i c and o r g a n i c l i g a n d s , i n c r e a s e s t h e s o l u b i l i t y as does the f o r m a t i o n o f i o n p a i r s .  ( I n i o n p a i r s , t h e metal i o n and base a r e  s e p a r a t e d by one o r more w a t e r m o l e c u l e s ; i n a complex, t h e l i g a n d i s immediately  a d j a c e n t t o t h e metal c a t i o n ) .  These a u t h o r s r e p o r t t h a t ,  w h i l e complex formers p r e s e n t i n a s o l u t i o n may o f t e n have l i t t l e o r no e f f e c t on t h e s o l u b i l i t y o f s o l i d s , they may a f f e c t t h e k i n e t i c s o f n u c l e a t i o n and o f growth and d i s s o l u t i o n o f c r y s t a l s . In p r a c t i c e t h e s o l u b i l i t y r e l a t i o n s h i p i,s used t o d e t e r m i n e r e c o v e r y e f f i c i e n c i e s and c o s t estimates f o r various treatment  conditions.  S a t i s f a c t o r y t r e a t m e n t o f a w a t e r r e q u i r e s a s p e c i f i c amount o f magnesium h y d r o x i d e .  The s o l u b i l i t y r e l a t i o n s h i p d e v e l o p e d f o r t h a t  w a t e r o r w a s t e w a t e r determines  t h e amount o f magnesium s a l t t h a t must be  added t o p r e c i p i t a t e t h i s amount a t v a r i o u s c o a g u l a t i o n pH's.  JAR TESTS PILOT  1  1  i  [  1  1  i  1  10.50 10.60 10.70 10.80 10.90 11.00 11.10 COAGULATION  1  1  PLANT  1  11.20 11.30 11.40 11.50  pH  FIGURE 6.COMPARISON OF T H E O R E T I C A L SOLUBILITY O F M g ( O H ) WITH O B S E R V E D JAR TEST AND PILOT P L A N T VALUES. TBLACK enow & EIDSNESS 1 9 7 4 ) 2  39  24 H  2CH T3 CD  16  '  Cd O  A  T3 O C 12 W 03  o  I X  c? o  o •1—  o o a •  X  cn  Heated to 103 C for 1 hr. as M g C 0 - 3 H 0 200°C for 2 hrs. as M g C 0 3 H 0 200°C for 2 hrs. as M g C 0 2 H 0 Air dried as M g C 0 - 3 H O 3  3  3  2  3  2  2  2  4T  cn —i—  i  —i—  8  4  10  TIME FIGURE 7 . S O L U B I L I T Y TIME  OF  FOR THE  2  INDICATED  AS A FUNCTION  HYDRATE  FORMS  ( E P A , 1971)  A L K A L I N I T Y (mg/i as C a C 0 ) 3  F I G U R E 8. L I M E R E Q U I R E D A  T O R A I S E T H E p H T O 11 A S  FUNCTION OF THE  ALKALINITY  18  16  (min.)  MgC0 -XH 0 3  12  —i—  14  RAW  WASTEWATER  (TCHOBANOGLOUS ,1970)  OF  40 4.2.2  Chemical  Reactions  The c h e m i s t r y o f magnesium c o a g u l a t i o n i s a r e l a t i v e l y combination  o f w a t e r s o f t e n i n g and c o n v e n t i o n a l  coagulation.  simple  Lime i s  added t o r a i s e t h e pH t o about 11.1-11.3, s o t h a t any magnesium p r e s e n t i s p r e c i p i t a t e d as magnesium h y d r o x i d e . HCOg must be c o n v e r t e d  Remembering t h a t a l l C 0 and 2  t o C 0 b e f o r e t h e OH" 3  c o n c e n t r a t i o n can i n c r e a s e ,  the well-known s o f t e n i n g r e a c t i o n s a r e summarized below. C0  2  + Ca"(0H) ~* CaC0 f + H 0 2  3  (1)  2  C a ( H C 0 ) + Ca(0H) ->- 2 C a C O ^ + 2H 0 3  2  2  With f u r t h e r a d d i t i o n o f l i m e , magnesium b i c a r b o n a t e nesium hydroxide  (2)  2  i s c o n v e r t e d t o mag-  by t h e f o l l o w i n g two r e a c t i o n s .  M g ( H C 0 ) + C a ( 0 H ) - > MgC0 + CaCOgf + 2 H 0  (3)  MgC0 + C a ( 0 H ) - * - M g ( 0 H ) |  (4)  3  2  3  2  2  3  2  2  CaC0 | 3  When magnesium i s p r e s e n t as MgCT,, o r MgSO^ ( i . e . , non c a r b o n a t e  hardness)  a r e a c t i o n such as (5) o c c u r s . MgS0 + C a ( 0 H ) 4  2  Mg(0H) i+ C a S 0 2  4  (5)  I t s h o u l d be p o i n t e d o u t t h a t , when magnesium c a r b o n a t e  i s used  as a c o a g u l a n t , no i n c r e a s e i n t o t a l d i s s o l v e d s o l i d s r e s u l t a c c o r d i n g t o reaction (4).  Whereas a d d i t i o n o f s a l t s o t h e r than magnesium  carbonate,  would r e s u l t i n an i n c r e a s e i n n o n c a r b o n a t e h a r d n e s s ( a n d TDS) p r o p o r t i o n a l to t h e amount o f make-up s a l t added as shown i n r e a c t i o n ( 5 ) . From t h e s e r e a c t i o n s , i t would seem t h a t t h e amount o f l i m e r e q u i r e d f o r t h e removal o f f r e e c a r b o n d i o x i d e , b i c a r b o n a t e  (usually the  t o t a l ) a l k a l i n i t y and magnesium ( n o n c a r b o n a t e ) h a r d n e s s f r o m a p a r t i c u l a r w a t e r o r waste c o u l d be c a l c u l a t e d s t o i c h i o m e t r i c a l l y . However, i n p r a c t i c e i t has been found t h a t such c a l c u l a t i o n s c a n n o t be used t o d e t e r m i n e t h e l i m e r e q u i r e m e n t s f o r magnesium p r e c i p i t a t i o n . S e v e r a l e m p e r i c a l r e l a t i o n s h i p s , such as t h e graph, shown i n F i g u r e 8, have been used t o e s t i m a t e  41  the l i m e r e q u i r e d t o r e a c h a g i v e n pH v a l u e under v a r i o u s a l k a l i n i t y conditions. In magnesium c o a g u l a t i o n s t u d i e s , Thompson e t a l (1972) i l l u s t r a t e d t h e n o n - s t o i c h i o m e t r i c r e q u i r e m e n t s o f l i m e by t h e f o l l o w i n g example. "A w a t e r , c o n t a i n i n g both o r g a n i c c o l o u r and t u r b i d i t y , has an a l k a l i n i t y o f 40 ppm and c o n t a i n s 30 ppm magnesium as CaCOo. J a r t e s t s show t h a t t h e minimum e f f e c t i v e amount o f Mg(0H) t o be p r e c i p i t a t e d w i l l be p r o v i d e d by a dosage o f 60 mg/1 MgC0 .3rL0. The most e c o n o m i c a l t r e a t ment o f t h i s water r e q u i r e s t h a t t h e e n t i r e dosage o f 60 mg/1 MgC0 .3rL0 be added and t h a t v e r y l i t t l e o f t h e 30 ppm o f magnesium p r e s e n t i n t h e w a t e r be used. Tfois r e s u l t s from f o u r r e a s o n s : (a) The dosage o f l i m e r e q u i r e d f o r t h e p r e c i p i t a t i o n o f t h e r e q u i r e d amount o f Mg(0H) from 90 mg/1 o f M g C 0 . 3 r L 0 i s s i g n i f i c a n t l y l e s s than t h a t r e q u i r e d t o p r e c i p i t a t e a l l o f t n e Mg(0H) from t h e 30 mg/1 o f MgCO, p r e s e n t p l u s 30 mg/1 added, and t h e pH i s s i g n i f i c a n t l y l o w e r . (b; The amount o f C0p r e q u i r e d t o r e d i s s o l v e t h e Mg(0H) from the s l u d g e w i l l be t h e same i n e i t h e r c a s e , b u t , t h e amount o f (XL r e q u i r e d t o r r e e a r b o n a t e t h e h i g h pH w a t e r o f t h e s e c o n d p r o c e d u r e w i l l be much g r e a t e r than t h e amount r e q u i r e d from t h e lower pH w a t e r o f t h e f i r s t procedure. ( c ) A f t e r a few c y c l e s , a pH v a l u e i s i d e n t i f i e d a t which comp l e t e r e c o v e r y and r e c y c l i n g o f c o a g u l a n t i s a c h i e v e d , a f t e r which no new c o a g u l a n t i s added. (d) The unused 30 ppm o f magnesium r e m a i n i n g i n t h e w a t e r r e p r e s e n t s r e s e r v e c o a g u l a n t which can be used i f n e c e s s a r y by i n c r e a s e d lime a d d i t i o n " . 2  3  3  2  3  2  2  F o r any p a r t i c u l a r t r e a t m e n t s y s t e m an e c o n o m i c a n a l y s i s i s r e q u i r e d t o i d e n t i f y optimum o p e r a t i n g c o n d i t i o n s .  I t seems t h a t more  e x p e r i e n c e i s r e q u i r e d , o v e r a wide range o f c o n d i t i o n s , t o d e v e l o p a good method f o r d e t e r m i n i n g minimum l i m e dosages r e q u i r e d . A n o t h e r dosage t h a t must be d e t e r m i n e d i s t h e amount o f magnesium r e q u i r e d t o p r o v i d e s u f f i c i e n t Mg(0H) f l o e f o r t r e a t m e n t . 2  t e s t s a r e used t o i d e n t i f y c o a g u l a n t dosage r e q u i r e m e n t s .  Usually, j a r However, Thompson  e t a l (1972) have d e v e l o p e d an e q u a t i o n f o r e s t i m a t i n g t h e r e q u i r e d magnesium dosage f o r w a t e r t r e a t m e n t , u s i n g s t e p w i s e l i n e a r r e g r e s s i o n t e c h n i q u e s . Minimum magnesium dosage was dependent on o r g a n i c c o l o u r and t o a l e s s e r e x t e n t on t u r b i d i t y , a l k a l i n i t y and hardness o f t h e w a t e r as shown by t h e following equation:  42 Minimum magnesium dosage (mg/1  o f MgCO-j.Sr^O) =  8.33  + 0.03  ( t u r b i d i t y i n JTU) + 0.46  (organic colour in  - 0.03  ( t o t a l a l k a l i n i t y as mg/1  CaC0 )  + 0.14  ( t o t a l h a r d n e s s as mg/1  3  CaC0 ) 3  I t may be p o s s i b l e t o develop s i m i l a r e q u a t i o n s w a t e r o r w a s t e w a t e r t o be t r e a t e d . required to simultaneously  CU.)  f o r any  given  In any c a s e , e x t e n s i v e j a r t e s t i n g i s  o p t i m i z e the two chemical  dosage r e q u i r e m e n t s  ( i . e . , l i m e and magnesium). 4.2.3  Magnesium R e c o v e r y A t p r e s e n t t h e r e are f o u r p o s s i b l e methods b e i n g c o n s i d e r e d  r e c o v e r i n g magnesium v a l u e s .  a.  for  These a r e :  a.  Selective softening  b.  Centrifugation  c.  Leaching of c a l c i n e d sludge  d.  Sludge  carbonation  S e l e c t i v e s o f t e n i n g can be employed t o s e p a r a t e magnesium hy-  d r o x i d e from l i m e - s o d a w a t e r s o f t e n i n g s l u d g e s but i t i s a cumbersone method t h a t r e q u i r e s m a j o r s o f t e n i n g p l a n t changes and more operating conditions.  complicated  T h i s would be l i m i t e d to magnesium r e c o v e r y  from  w a t e r s o f t e n i n g s l u d g e s and w o u l d not be a p p l i c a b l e f o r g e n e r a l use i n coagulation systems. b.  P h y s i c a l s e p a r a t i o n o f s l u d g e i n t o i t s components by c e n t r i -  f u g a t i o n has been i n v e s t i g a t e d .  Early studies y i e l d e d negative  But w i t h improved equipment and t e c h n i q u e s ,  r e c e n t s t u d i e s by  r e p o r t s u c c e s s f u l s e p a r a t i o n o f C a C 0 from M g ( 0 H ) and 3  :(Phundstein  e t a l 1974).  2  results. Dorr-Oliver  inorganics,  Lime s l u d g e s f r o m t e r t i a r y t r e a t m e n t  as w e l l as s l u d g e s p r o d u c e d from w a t e r s o f t e n i n g p r o c e s s e s  facilities  have been  43 c l a s s i f i e d u s i n g a combined a p p l i c a t i o n o f the d i s c n o z z l e , and the s o l i d bowl c e n t r i f u g e . The use o f t h e d i s c n o z z l e c e n t r i f u g e p r o v i d e s w a s h i n g . o f t h e s l u d g e t o c l a s s i f y magnesium h y d r o x i d e , h y d r o x y a p a t i t e and o r g a n i c m a t e r i a l t o produce r e l a t i v e l y c l e a n C a C 0 f o r c a l c i n a t i o n . 3  Sludge i s  a l s o t h i c k e n e d i n t h i s s t a g e , to a l l o w optimum f e e d t o t h e s o l i d bowl c e n t r i f u g e , where f u r t h e r c l a s s i f i c a t i o n and d e w a t e r i n g o c c u r s .  High  r e j e c t i o n s o f Mg(0H)2 and i n e r t s a r e r e p o r t e d a l o n g w i t h h i g h r e c o v e r y o f CaC0 . 3  I f t h i s e q u i p m e n t s t a n d s up t o f u r t h e r f i e l d t e s t i n g , then c e n t r i f u g a l s e p a r a t i o n o f magnesium h y d r o x i d e from c a l c i u m c a r b o n a t e may p r o v i d e a v i a b l e method f o r magnesium r e c o v e r y . c.  L e a c h i n g o f c a l c i u m c a r b o n a t e from i n c i n e r a t e d s l u d g e , c o n t a i n -  i n g CaO and MgO, has been p r o p o s e d by Rapson e t a l (1973) a t t h e Nova S c o t i a Research F o u n d a t i o n (NSRF) as a method o f r e c o v e r i n g magnesium v a l u e s from t h e s e a w a t e r - l i m e t r e a t m e n t system.  The m i x t u r e o f c a l c i u m  and magnesium o x i d e s from t h e k i l n i s t o be t r e a t e d w i t h s e a w a t e r , t o d i s s o l v e t h e l i m e and t o p r e c i p i t a t e more magnesium h y d r o x i d e .  The l i m e  s o l u t i o n i s p a r t i a l l y n e u t r a l i z e d w i t h a c i d and r e t u r n e d t o t h e f l o c c u l a t i o n tank w h i l e t h e m a g n e s i u m - h y d r o x i d e can be c a l c i n e d t o produce a h i g h q u a l i t y ( ? 98% MgOj p r o d u c t f o r s a l e .  I t s h o u l d be p o i n t e d o u t t h a t t h i s  method has n o t y e t been proven e f f e c t i v e .  However, s t u d i e s a r e p r e s e n t l y  underway by NSRF t o e v a l u a t e i t s f e a s i b i l i t y . d.  The main magnesium r e c o v e r y p r o c e s s , w h i c h p r o m i s e s to;;.make c o -  a g u l a t i o n w i t h magnesium an e c o n o m i c a l l y f e a s i b l e p r o c e s s , i s t h a t o f s l u d g e c a r b o n a t i o n ( d i s c o v e r e d by B l a c k and E i d s n e s s (1957) and b r i e f l y discussed e a r l i e r ) .  T h i s method can be used f o r e i t h e r o f two p u r p o s e s ;  1) t o produce magnesium c a r b o n a t e t r i h y d r a t e (MgC0 -3H20) from l i m e - s o d a 3  w a t e r s o f t e n i n g s l u d g e s f o r use as a c o a g u l a n t , and; 2) t o r e c o v e r  44 magnesium from c o a g u l a t i o n systems u s i n g such s a l t s , thus p r o v i d i n g a r e c y c l e d M g ( H C 0 ) t h a t can be r e u s e d i n t h e p r o c e s s . 3  2  P r o d u c t i o n o f magnesium c a r b o n a t e from t h e c a r b o n a t e d involves:  sludge  ( i ) t h e s e l e c t i v e removal o f t h e M g ( 0 H ) from t h e p r i m a r y s l u d g e , 2  by k i l n s t a c k gas c o n t a i n i n g 19-21 p e r c e n t C 0 o r by pure C 0 , a n d ; ( i i ) 2  2  removal o f t h e s o l i d - p h a s e CaCO^ by e i t h e r s e t t l i n g o r f i l t r a t i o n a n d the r e c o v e r y o f p r o d u c t magnesium c a r b o n a t e from t h e c l a r i f i e d l i q u o r by h e a t i n g and a e r a t i o n . The f o l l o w i n g r e a c t i o n s a p p l y . Sludge  Carbonation:  Mg(0H) + 2C0 2  Mg(HC0 )  2  3  Mg(0H ) + C 0 + 2 H 0 2  2  3  MgC0 .3H 0  2  MgC0 .3H 0 + C 0 2  (1)  2  3  (2a)  2  Mg(HC0 ) + 2H 0  2  3  2  (2b)  2  M g ( 0 H ) + M g ( H C 0 ) + H 0 - > 2 MgC0 .3H 0 2  3  Product  2  2  3  (3)  2  Recovery:  Mg(HC0 ) + 2H 0 3  2  35 - 45°C ->- MgC0 .3H 0 + C 0  2  3  2  2  (4)  I t can be seen t h a t t h e f i r s t t h r e e r e a c t i o n s a r e r e s p o n s i b l e f o r c o n v e r sion o f i n s o l u b l e hydroxide to s o l u b l e bicarbonate.  R e a c t i o n (3) shows  t h a t as time goes o n , t h e r e i s an i n c r e a s i n g tendency f o r i n s o l u b l e MgC0 .3H 0 t o form and be l o s t w i t h C a C O y 3  I t i s therefore necessary to  2  control the feed o f sludge so that a supersaturated s o l u t i o n o f Mg(HC0)  3  i s n o t produced to r e a c t with excess Mg(0H) . 2  F o r p r o d u c t r e c o v e r y , t h e magnesium b i c a r b o n a t e s o l u t i o n , c l a r i f i e d u s u a l l y by f i l t r a t i o n , p a s s e s t o a heat exchange u n i t where i t i s warmed t o 35-45°C a f t e r which i t i s a e r a t e d by compressed i c a l l y mixed b a s i n .  a i r i n a mechan-  The MgC0 .3H 0 p r e c i p i t a t e s r a p i d l y ( - 9 0 min) and 3  2  the r e s u l t i n g p r o d u c t MgC0 .3H 0 i s vacuum f i l t e r e d , d r i e d and bagged f o r 3  2  shipment, h o p e f u l l y t o o t h e r i n s t a l l a t i o n s where i t may be used as a coagulant.  45 In a magnesium c o a g u l a t i o n system, t h e M g  would be added and  ++  the r e s u l t i n g s l u d g e c o u l d be c a r b o n a t e d s i m i l a r l y .  However, i n t h i s c a s e ,  magnesium r e c o v e r y w o u l d s i m p l y r e q u i r e r e c y c l i n g t h e f i l t r a t e , c o n t a i n i n g magnesium b i c a r b o n a t e , t o t h e head o f t h e system.  The c h e m i c a l r e a c t i o n s  d e s c r i b i n g t h e c o a g u l a t i o n p r o c e s s r e s u l t i n g from t h e r e c y c l e d magnesium bicarbonate are: Mg(HC0^) + C a ( 0 H ) - > M g C 0 2  2  3  + CaC0 + 2H 0  MgC0 + C a ( 0 H ) - » - M g ( 0 H ) + C a C 0 3  2  2  3  2  3  T h i s , i n f a c t , i s t h e b a s i s f o r t h e 'magnesium r e c o v e r y ' method i n v e s t i gated i n t h e present research study. 4.3  Practical Considerations From t h e p i l o t and f u l l - s c a l e s t u d i e s , as w e l l as l a b o r a t o r y  s t u d i e s c o n d u c t e d t o d a t e , s e v e r a l g e n e r a l o p e r a t i n g and c o n t r o l p r a c t i c e s have e v o l v e d , which s h o u l d be c o n s i d e r e d d u r i n g f u t u r e i n v e s t i g a t i o n s o r a p p l i c a t i o n s o f magnesium c o a g u l a t i o n p r o c e s s e s .  These a r e summarized as  follows: 1.  Magnesium s h o u l d be added as a s o l u b l e s a l t p r i o r t o a d d i t i o n o f a l i m e s l u r r y , s o t h a t magnesium h y d r o x i d e forms i n s i t u .  2.  ( a ) V i n c e n t (1974) found t h a t l i m e s l u r r y i n water  appeared  to f u n c t i o n b e t t e r than a s l u r r y i n a p o r t i o n o f t h e e f f l u e n t o r a d r y powder when c o n s i d e r i n g r e a c t i o n r a t e (pH s t a b i l i zation). (b)  L o o k i n g a t t h e t y p e o f l i m e used r e l a t i v e t o speed o f  decolourization: (i)  Commercial  q u i c k l i m e , was, by f a r , t h e b e s t when added  as a water s l u r r y . ( i i ) When a s l u r r y i n e f f l u e n t o r a d r y power was used, c a l cium h y d r o x i d e was b e t t e r than t h e o x i d e .  46 These r e s u l t s a r e v e r y p r e l i m i n a r y i n n a t u r e and cannot be g e n e r a l i z e d t o systems t r e a t i n g o t h e r types o f wastes. 3.  C o n t r o l l i n g t h e pH i s t h e key t o s u c c e s s f u l o p e r a t i o n o f magnesium c o a g u l a t i o n systems. (a)  pH c o n t r o l i n t h e f l o c c u l a t o r ( ~ p H 11.0-11.3) p r o -  v i d e s optimum c o n d i t i o n s f o r magnesium h y d r o x i d e f o r m a t i o n . (b)  pH c o n t r o l i n t h e s l u d g e c a r b o n a t o r ( - p H 7.3) p r o v i d e s  optimum r e c o v e r y o f magnesium b i c a r b o n a t e . (c)  pH s t a b i l i z a t i o n o f t r e a t e d e f f l u e n t t o below pH 8.6-8.8  i s n e c e s s a r y t o p r e v e n t c a l c i u m c a r b o n a t e b u i l d i n g up i n t h e filters. S t a n d a r d f i l t e r sand, c o v e r e d w i t h 4 i n c h e s o f 1.2 mm a n t h r a c i t e , p r o v i d e d maximum f i l t e r runs f o r water Diatomateous 5.  treatment.  earth f i l t e r s are also acceptable.  R e c y c l e d s l u d g e s h o u l d be p r o v i d e d i n a l a r g e s c a l e system because: (a)  R e c y c l e d c a l c i u m c a r b o n a t e i n c r e a s e s both r a t e and amount  o f magnesium p r e c i p i t a t i o n . (b)  Some o f t h e magnesium h y d r o x i d e i n t h e r e c y c l e d s l u d g e  r e s o l u b l i z e s t o magnesium c a r b o n a t e , which can be p r e c i p i tated again.  A l t h o u g h some contaminants may a l s o be r e l e a s e d  i n t h e s e r e a c t i o n s , t h e o v e r a l l e f f e c t i s c o n s i d e r e d t o be o f some v a l u e . (c)  C r y s t a l l i n e c a l c i u m c a r b o n a t e , a l r e a d y p r e s e n t , a c t s as  a seed o r n u c l e u s f o r p r e c i p i t a t i o n , p r e v e n t i n g a b u i l d - u p . on equipment. (d)  S l i g h t l y reduced l i m e r e q u i r e m e n t s r e s u l t because o f  the c a u s t i c i ' t y i n t h e h i g h pH (11.2) s l u d g e water.  Small,  47 dense f l o e p a r t i c l e s form r a p i d l y and s e t t l e v e r y w e l l . 6.  Pure carbon d i o x i d e s h o u l d be c o n s i d e r e d f o r use i n s m a l l plants not recoverying lime f o r several reasons. (a)  The r a t e o f s o l u b i l i z a t i o n i s more r a p i d .  (b)  The amount o f magnesium b i c a r b o n a t e d i s s o l v e d by pure  C0  i s c o n s i d e r a b l y more than t h a t d i s s o l v e d by l o w e r p e r -  2  centage C 0 p r o d u c e d by on s i t e g e n e r a t i o n . 2  (c)  Feed o f l i q u i d C 0 i s s i m p l e r , more f l e x i b l e and 2  e a s i e r t o automate. (d) co . 2  Foaming problems a r e more s e v e r e u s i n g low p e r c e n t a g e  48 CHAPTER 5 EXPERIMENTAL MATERIAL AND METHODS 5.1  Selection of E f f l u e n t The m i l l chosen as a s o u r c e o f wastewater f o r t h i s work was  t h e C r e s t b r o o k P u l p and Paper L t d . M i l l a t Skookumchuck, B.C.  This i s  a 400-ton p e r day f a c i l i t y , p r o d u c i n g e s s e n t i a l l y 100% b l e a c h e d k r a f t p u l p f o r e x p o r t , a l t h o u g h some u n b l e a c h e d p u l p i s produced d u r i n g bleach plant interruptions.  Wood f u r n i s h i s e n t i r e l y c h i p s (45% p i n e ,  35% s p r u c e , 13% f i r and l a r c h , and 7% o t h e r ) . C h i p age i s f o u r t o s i x months.  P u l p i n g i s c a r r i e d o u t i n a c o n t i n u o u s Kamyr d i g e s t e r and  b l e a c h i n g i s by a c o n v e n t i o n a l CEDED sequence. Water usage i s a p p r o x i m a t e l y 10,000,000 Imp. g a l / d a y m / s e c ) o r 25,000 Imp gal/AD t o n (114 m /AD t o n ) . 3  3  (.53  I n t a k e i s from the  Skookumchuck R i v e r and d i s c h a r g e i s t o the Upper Kootenay R i v e r , which has a mean monthly f l o w v a r y i n g from 22,000 c f s (623 m / s e c ) d u r i n g 3  e a r l y summer down t o 650 c f s (18 m / s e c ) i n the w i n t e r months. 3  E x t e r n a l t r e a t m e n t i n c l u d e s two p r i m a r y s e t t l i n g ponds o f 2,500,000 Imp. g a l . (11365 m ) 3  r e t e n t i o n a e r a t i o n lagoon.  c a p a c i t y f o l l o w e d by a  seven-day  T y p i c a l u n t r e a t e d and t r e a t e d t o t a l m i l l  e f f l u e n t c h a r a c t e r i s t i c s a r e shown i n T a b l e 3. The r e a s o n s f o r s e l e c t i n g t h i s m i l l as a wastewater included:  source  1) i t i s one m i l l i n B.C. t h a t has a c o l o u r problem and i s  s e e k i n g a v i a b l e d e c o l o u r i z a t i o n method; 2) m i l l p e r s o n n e l were e x t r e m e l y c o - o p e r a t i v e and r e c e p t i v e t o the arrangement;  3) a l a r g e  amount o f background work on c o l o u r removal has been done a t t h i s m i l l , so a comparison o f t h e p r a c t i c a b i l i t y o f t h i s new t e c h n o l o g y t o o t h e r methods may be p o s s i b l e ; and 4) i n - p l a n t c o l o u r b a l a n c e s have  49 been c a r r i e d o u t by m i l l p e r s o n n e l and were a v a i l a b l e , so t h a t a p p r o p r i a t e waste s t r e a m s c o u l d be c h o s e n f o r t r e a t m e n t . TABLE 3 TYPICAL CHARACTERISTICS OF CRESTBROOK PULP AND PAPER LTD. - TOTAL MILL EFFLUENT Parameter  Untreated  Treated  Suspended S o l i d s (mg/1)  300  60  B0D  225  60  6.2  7.2  28  18  2000  2500  5  (mg/1)  pH T e m p e r a t u r e (°C) Colour ( C U . ) Morgan (1975)  Waste s t r e a m s c o n t r i b u t i n g f l o w t o t h e t h r e e main sewers a r e as f o l l o w s : A c i d Sewer:  T-10 T h i c k e n e r E f f l u e n t T-10 Washer E f f l u e n t T-30 E f f l u e n t  C a u s t i c Sewer: T-20 E f f l u e n t Steam P l a n t Recausticizer Chemical P r e p a r a t i o n G e n e r a l Sewer: P u l p i n g Group U n b l e a c h e d White Water Hot Water Tank O v e r f l o w Machine Room B l e a c h Tower D r a i n s  50 The a v e r a g e r e s u l t s o f s e v e r a l i n - p l a n t c o l o u r b a l a n c e s a r e summarized i n T a b l e 4. TABLE 4 AVERAGE RESULTS OF SEVERAL IN-PLANT COLOUR BALANCES AT CRESTBROOK PULP AND PAPER LTD. % of Total M i l l Colour  Source  Major C o n t r i b u t i o n t o C o l o u r i n Sewers  T-20 E f f l u e n t Other T o t a l C a u s t i c Sewer  98.9% o f C a u s t i c Sewer 1.1% o f C a u s t i c Sewer 100%  76.0% 0.9% 76.9%  T-10 T-10 T-30 Total  46% o f A c i d Sewer 27.2% o f A c i d Sewer 26.8% o f A c i d Sewer 100%  5.9% 3.5% 3.5% 12.9%  90.2% o f General 9.8% o f General 100%  9.2% 1.0% 10.2%  Washer Thickener Effluent A c i d Sewer  Unbl. White Water Other T o t a l General Sewer  Crestbrook Personnel  (1975)  These r e s u l t s i n d i c a t e t h a t e f f l u e n t from t h e f i r s t c a u s t i c e x t r a c t i o n tower o f t h e b l e a c h p l a n t (T-20 e f f l u e n t ) i s r e s p o n s i b l e f o r 70 t o 80% o f t h e t o t a l m i l l c o l o u r .  However, t h e c o l o u r  balances  were o b t a i n e d d u r i n g p e r i o d s o f s t e a d y m i l l o p e r a t i o n when t h e r e were no s p i l l s , so t h e l o n g t e r m r e l a t i v e c o n t r i b u t i o n o f T-20 e f f l u e n t , i n r e a l i t y , i s l e s s than shown by t h e s e t e s t s .  In f a c t , e x t e r n a l measure-  ment o f t o t a l m i l l e f f l u e n t d u r i n g e x t e n d e d p e r i o d s o f b l e a c h p l a n t shutdown have shown t h a t o n l y a 50 t o 60% c o l o u r r e d u c t i o n can be a c h i e v e d by c o m p l e t e l y s h u t t i n g down t h e b l e a c h p l a n t .  Therefore, i t  would seem t h a t t r e a t m e n t o f t h e t o t a l m i l l e f f l u e n t w o u l d be n e c e s s a r y  51 t o a c h i e v e a t o t a l c o l o u r r e d u c t i o n i n t h e o r d e r o f 90% a t t h i s m i l l . However, by m o n i t o r i n g and c o n t a i n i n g l i q u o r s p i l l s and i n t e n s i f y i n g other housekeeping  programs, i t may be p o s s i b l e t o a c h i e v e an a c c e p t a b l e  t o t a l m i l l e f f l u e n t c o l o u r by t r e a t i n g o n l y T-20 e f f l u e n t . In any c a s e , i t was d e c i d e d t o t e s t t h i s new t e c h n o l o g y on both t o t a l m i l l b i o l o g i c a l l y t r e a t e d e f f l u e n t (BKME) (-2000 C U . ) and h i g h l y c o l o u r e d c a u s t i c e x t r a c t i o n e f f l u e n t (-16000 C.U.), from T-20 of the bleach plant. 5.2  Sample S t o r a g e A l l samples were s t o r e d a t 4°C. P r i o r t o t e s t i n g t h e  samples were a l l o w e d t o r e a c h room 5.3  Chemical  5.3.1  Lime  temperature.  Preparations  Reagent grade C a ( 0 H )  2  was chosen f o r t h i s s t u d y as t h e  p r e f e r r e d method o f l i m e a d d i t i o n . d r y o r as a s l u r r y , t h e C a ( 0 H )  2  In a l l c a s e s , w h e t h e r i t was added  powder was weighed a c c u r a t e l y on a  S a r t o r i u s Model 2442, f o u r p l a c e b a l a n c e , i m m e d i a t e l y p r i o r t o usage. S e l e c t i o n o f a method f o r l i m e a d d i t i o n i s d i s c u s s e d i n more d e t a i l i n Appendix  A.  5.3.2  Magnesium A s i d e from e a r l y t e s t s , which were c o n d u c t e d u s i n g s t o c k  MgCl .6H 0< (1 ml = 60 M g ) , a l l c o a g u l a t i o n s were performed + +  2  2  s t o c k MgS0it.7H 0 s o l u t i o n (1 ml = 30 mg M g ) . + +  2  with  Both s t o c k s o l u t i o n s  were p r e p a r e d by d i s s o l v i n g an amount o f r e a g e n t grade c h e m i c a l i n d i s t i l l e d water t o g i v e t h e d e s i r e d s t o c k s o l u t i o n c o n c e n t r a t i o n o f Mg  + +  ions.  A more d e t a i l e d d i s c u s s i o n o f t h e s e l e c t i o n o f a magnesium  s o u r c e i s i n c l u d e d i n Appendix  A.  52 5.3.3  Settling Aid An a n i o n i c o r g a n i c polymer, Dow P u r i f l o c A-23, p r o v e d t o be  an e f f e c t i v e s e t t l i n g a i d f o r T-20 c o l o u r s l u d g e .  A working s o l u t i o n  o f t h i s c h e m i c a l (.02%) was p r e p a r e d d a i l y from a s t o c k s o l u t i o n (.2%) a c c o r d i n g t o t h e m a n u f a c t u r e r ' s recommendations,  Dow (1967).  Results  o f T-20 s l u d g e s e t t l i n g t e s t s and polymer s e l e c t i o n t r i a l s a r e shown i n Appendix 5.3.-4  B.  P l a t i n u m - C o b a l t (Pt-Go) S t a n d a r d A 500 c o l o u r u n i t ( C U . ) s t a n d a r d was p r e p a r e d a c c o r d i n g t o  S t a n d a r d Methods (APHA e t a l , 1971). 5.3.5  Lanthanum C h l o r i d e LaCl  2  s t o c k s o l u t i o n f o r magnesium and c a l c i u m d e t e r m i n a t i o n  by a t o m i c a b s o r p t i o n was p r e p a r e d a c c o r d i n g t o APHA e t a l (1971). 5.3.6  Magnesium and C a l c i u m S t a n d a r d s ++  A l l s t a n d a r d s f o r Mg 10,000 mg/1  ++  and Ca  a n a l y s i s were p r e p a r e d from  c e r t i f i e d atomic absorption standards.  The d e s i r e d con-  c e n t r a t i o n s were o b t a i n e d by d i l u t i o n w i t h d i s t i l l e d water and 1% L a C l was added as 10 mis o f 10% s t o c k s o l u t i o n i n 100 ml v o l u m e t r i c 2  flasks. 5.3.7  pH Adjustment  Chemicals  A wide range o f s t a n d a r d s was n e c e s s a r y t o m i n i m i z e the volume change d u r i n g pH a d j u s t m e n t f o r c o l o u r measurement. The d i l u t i o n s o f HCl used f o r pH r e d u c t i o n were c o n c e n t r a t e d H C l , 3N, IN, .5N, .IN, .02N, .01N and .001N.. 5.4  Analytical  Techniques  5.4.1  C o l o u r Measurement After a considerable l i t e r a t u r e search, discussions with  53 s e v e r a l o t h e r r e s e a r c h e r s and p r e l i m i n a r y t e s t i n g i n t h e l a b o r a t o r y , the c o l o u r measurement t e c h n i q u e chosen was t h e one recommended by t h e NCASI (1971) i n t h e U.S. and t h e CPPA (1973) i n Canada.  A detailed  d e s c r i p t i o n o f t h e method has been g i v e n by t h e CPPA (1973) and t h i s p r o c e d u r e was a d o p t e d w i t h o u t s i g n i f i c a n t m o d i f i c a t i o n .  Briefly, this  i n v o l v e d sample d i l u t i o n t o t h e p r o p e r range f o r a b s o r b a n c e measurement, i f n e c e s s a r y ; sample pH a d j u s t m e n t t o pH 7.6 ± .1; f i l t r a t i o n t h r o u g h .8 u membrane p a p e r ; r e a d j u s t m e n t o f pH t o 7.6 ± .1; measurement o f a b s o r b a n c e on a Bausch and Lomb S p e c t r o n i c 600 U.V.  Spectrophotometer  a t a w a v e l e n g t h o f 465 nm; and c o m p a r i s o n o f a b s o r b a n c e t o a p l a t i n u m c o b a l t s t a n d a r d a c c o r d i n g t o APHA e t a l (1971). r e c o r d e d as C U .  (colour units).  are e q u i v a l e n t t e r m s .  C o l o u r u n i t s were  APHA u n i t s , Hazen u n i t s , Pt-Co u n i t s  F o r mass b a l a n c e c a l c u l a t i o n s , c o l o u r masses  r e f e r r e d t o a r e as mg o f P t . 5.4.2  C a l c i u m and Magnesium A f t e r comparing r e s u l t s o f samples r e c e i v i n g no d i g e s t i o n  and samples p r e p a r e d by s e v e r a l d i g e s t i o n methods p r i o r t o a t o m i c a b s o r p t i o n (A.A.) a n a l y s i s , a d r y a s h i n g t e c h n i q u e , d e s c r i b e d below, was s e l e c t e d t o d e s t r o y o r g a n i c compounds t h a t a p p e a r e d t o be t y i n g up Mg  and Ca  .  A l l ashed samples were d i l u t e d t o t h e p r o p e r range w i t h d i s t i l l e d w a t e r , and 1% L a C l , p r i o r t o a n a l y s i s on a P e r k i n Elmer 2  Model 500 A t o m i c A b s o r p t i o n S p e c t r o p h o t o m e t e r , a c c o r d i n g t o APHA e t a l (1971).  A i r and a c e t y l e n e were used as o x i d a n t and f u e l , r e s p e c t i v e l y ,  throughout t h i s research.  54 5.4.3  Dry A s h i n g T e c h n i q u e The d e t a i l s o f t h e d r y a s h i n g method used a r e p r e s e n t e d  below: 1.  The p r e v i o u s l y d r i e d sample was p l a c e d i n a c o l d m u f f l e f u r n a c e and h e a t e d g r a d u a l l y t o 700°C.  2.  The upper t e m p e r a t u r e was m a i n t a i n e d f o r 8 t o 12 h o u r s , or u n t i l t h e specimen was a g r e y i s h w h i t e a s h .  3.  The a s h was c o o l e d , removed and m o i s t e n e d w i t h 1 t o 2 mis d i s t i l l e d w a t e r .  I n i t i a l l y , drops o f concentrated  HCl and HN0 were then added and g e n t l e heat a p p l i e d t o 3  remove e x c e s s m o i s t u r e .  L a t e r i t was found t h a t t h e  HN0 and h e a t i n g was n o t n e c e s s a r y on most samples. 3  4.  When t h e a s h was c o m p l e t e l y decomposed, t h e sample was d i l u t e d w i t h d i s t i l l e d water and 1%  f o r sub-  LaCl2,  sequent A.A. a n a l y s i s . F i l t e r p a p e r s were ashed d i r e c t l y s i n c e t h e y were t h e "ashless" type. U n f i l t e r e d samples o f u n t r e a t e d e f f l u e n t , t r e a t e d e f f l u e n t , c o l o u r s l u d g e , and s u p e r n a t a n t were e v a p o r a t e d t o d r y n e s s i n a 103°C d r y i n g oven p r i o r t o a s h i n g . In. o r d e r t o a v o i d e v a p o r a t i n g and i n c i n e r a t i n g t h e l a r g e q u a n t i t y o f s l u d g e water i n t h e u n t h i c k e n e d f i n a l s l u d g e , t h e s l u d g e sample was f i l t e r e d t h r o u g h a 12.5 cm d i a m e t e r #40 Whatman paper on a Buchner f u n n e l . The paper and e v a p o r a t i o n d i s h were preweighed s o t h a t s l u d g e d r y w e i g h t and a s h w e i g h t c o u l d be d e t e r m i n e d . ++  The v a l u e s o b t a i n e d f o r Mg ash were t a k e n as M g  + +  solids, respectively.  and C a  + +  ++  and Ca  on d i l u t i o n o f t h i s  content o f the dry f i n a l  sludge  55 5.4.4  pH Measurement A l l pH measurements were p e r f o r m e d o n a F i s h e r Aceumet Model  210 pH meter.  B u f f e r s o l u t i o n s o f pH 7.00 and 10.00 were used t o  c a l i b r a t e t h e i n s t r u m e n t a t l e a s t once a d a y . 5.4.5  Total A l k a l i n i t y P r e l i m i n a r y t e s t s by t h e a u t h o r showed t h e i n f l e c t i o n p o i n t  o f t h e t i t r a t i o n c u r v e f o r both t o t a l BKME and T-20 e f f l u e n t t o be a t pH = 4.5. In a l l c a s e s , t o t a l a l k a l i n i t y was d e t e r m i n e d on 20 ml samples, p r e f i l t e r e d t h r o u g h #40 Whatman p a p e r , t i t r a t e d t o a pH o f 4.5 w i t h  H2SO4  i.e.  of appropriate normality. T o t a l BKME ( I n & O u t )  - .02 N H S 0 2  T-20 E f f l u e n t ( I n & O u t ) - l . N  H S0 z  S u p e r n a t a n t (BKME)  - .IN  S u p e r n a t a n t (T-20)  - .2506 N  4  h  tt S0 2  h  H2SO4  T o t a l A l k a l i n i t y = N o r m a l i t y j 50,000 x ml t i t r e 5.4.6  C o n d u c t i v i t y and Temperature A R a d i o m e t e r C o n d u c t i v i t y M e t e r , Model No. CDM3, was used t o  p e r f o r m c o n d u c t i v i t y measurements i n a l l c a s e s , a c c o r d i n g t o t h e manufacturer's i n s t r u c t i o n s .  A l l c o n d u c t i v i t y v a l u e s were r e c o r d e d i n  m i c r o Siemens ( y s ) , e q u i v a l e n t t o m i c r o Mhos.  A t e m p e r a t u r e com-  p e n s a t i o n probe was a v a i l a b l e , b u t s i n c e a l l t e s t s were c o n d u c t e d between 20 t o 25°C, no c o m p e n s a t i o n was r e q u i r e d . However, t e m p e r a t u r e was measured m a n u a l l y and r e c o r d e d . 5.4.7  Percent S o l i d s o f Sludges In a l l c a s e s , r e p r e s e n t a t i v e samples o f s l u d g e s were t r a n s -  f e r r e d by wide mouth p i p e t t e t o preweighed gooch c r u c i b l e s , and  56 f i l t e r e d under s l i g h t vacuum t h r o u g h Reeve A n g e l , g l a s s - f i b r e , f i l t e r paper. R e w e i g h i n g o f t h e c r u c i b l e , a f t e r d r y i n g a t 103°C f o r a t l e a s t one hour and a c o o l i n g f o r a t l e a s t 15 m i n u t e s i n a d e s i c c a t o r , gave s o l i d s c o n c e n t r a t i o n , a f t e r a p p l y i n g t h e a p p r o p r i a t e d i l u t i o n factor.  lo ssoollii dd ss =  1  m g / 1  solids  1 0 j 0 0 0 x  s  g  <  assuming s.g. -1.0 t h e n y/o s so o lids 1 1 d s  = mg/1 d r y s o l i d s 10,000  57 CHAPTER 6 RESULTS AND  DISCUSSION  6.1  Results of T e s t i n g with Fresh  6.1.1  Jar Test Results  6.1.1.1  General.  Chemicals  To e v a l u a t e the c o l o u r removal e f f i c i e n c y o f  v a r i o u s l i m e and magnesium d o s a g e s , i t was n e c e s s a r y t o d e f i n e an o b j e c t i v e f o r r e s i d u a l c o l o u r i n t h e t r e a t e d wastes.  I t was f e l t t h a t  t h i s t e c h n o l o g y s h o u l d p r o v i d e a l e v e l o f d e c o l o u r i z a t i o n equal t o o r b e t t e r than e x i s t i n g l i m e t r e a t m e n t f a c i l i t i e s a t a s i m i l a r o r l e s s e r cost.  With t h i s i n mind, a c o l o u r r e d u c t i o n o b j e c t i v e o f 90 t o 95%  was s e l e c t e d .  In most k r a f t m i l l s , t h i s would mean a r e s i d u a l c o l o u r  o f 500 t o 1 ,000 C U . CU.  f o r c a u s t i c e x t r a c t i o n e f f l u e n t and 100 t o 200  f o r t o t a l m i l l e f f l u e n t . These v a l u e s c o r r e s p o n d e d t o r e s i d u a l s  o b t a i n e d w i t h l i m e t r e a t m e n t i n the p u b l i s h e d l i t e r a t u r e and seemed l i k e r e a s o n a b l e c r i t e r i a f o r t h e s e l e c t i o n o f t e n t a t i v e optimum dosage l e v e l s o f l i m e and magnesium f o r use d u r i n g the subsequent b a t c h t e s t s in t h i s study. Two o t h e r c r i t e r i a c o n s i d e r e d i n t h e f i n a l s e l e c t i o n o f c h e m i c a l dosages were: i)  t h e d e c o l o u r i z e d e f f l u e n t pH s h o u l d be k e p t as low as p o s s i b l e to minimize recarbonation c o s t s ;  ii)  a cursory look at chemical c o s t s i n d i c a t e d t h a t a minimum usage o f l i m e would be d e s i r e d .  I t s h o u l d be emphasized  t h a t the r e s u l t s o f these j a r t e s t s  a r e p r e l i m i n a r y . A more d e t a i l e d e v a l u a t i o n s h o u l d be c a r r i e d out o v e r a w i d e r range o f raw waste c h a r a c t e r i s t i c s t o d e t e r m i n e t h e most economic dosages f o r any l a r g e s c a l e use.  6.1.1.2  BKME.  58 R e s u l t s o f p r e l i m i n a r y 100 ml c o a g u l a t i o n t e s t s o f  the t o t a l m i l l b i o l o g i c a l l y t r e a t e d e f f l u e n t a r e shown i n T a b l e s 5, 6, 7 and 8. The d a t a i n T a b l e 5 f o r Time a d d i t i o n o n l y , and i n T a b l e s 6 and 7 f o r i n c r e a s i n g l i m e d o s a g e s a t t h e c o n s t a n t M g  + +  l e v e l s o f 30  mg/1 and 60 mg/1, r e s p e c t i v e l y , were used t o c o n s t r u c t t h e graphs i n F i g u r e 9. From t h e s e r e s u l t s , i t c a n be seen t h a t 91 t o 92% c o l o u r removal was a c c o m p l i s h e d  by 2,000 mg/1 C a ( 0 H )  2  (1,500 mg/1 CaO) a l o n e  o r by u s i n g h a l f a s much l i m e (750 mg/1 CaO) i n c o n j u n c t i o n w i t h 30 mg/1 M g .  A Mg  ++  + +  a d d i t i o n o f 60 mg/1, p r e c i p i t a t e d by o n l y 500 mg/1  C a ( 0 H ) 2 (375 mg/1 CaO) a l s o p r o v i d e d 92% improvement.  F i g u r e 9 i l l u s t r a t e s t h a t a c o m b i n a t i o n o f low magnesium and l i m e dosages a c h i e v e d g r e a t e r c o l o u r removal e f f i c i e n c i e s than d i d a much h i g h e r l i m e dosage by i t s e l f . The e f f e c t o f i n c r e a s i n g t h e M g  + +  dosage w h i l e h o l d i n g t h e  l i m e dosage a t 375 mg/1 as CaO i s shown i n T a b l e 8. With no magnesium, c o l o u r removal was an u n a c c e p t a b l e , 73.3%, w h i l e a d d i t i o n o f 30 and 60 mg/1 o f M g  + +  y i e l d e d 86.7 and 9 1 . 9 % c o l o u r r e m o v a l s , r e s p e c t i v e l y . A t  t h i s low l i m e l e v e l , f u r t h e r a d d i t i o n s o f t h e a c i d i c magnesium s u l p h a t e s o l u t i o n gave o n l y m a r g i n a l improvement, p r o b a b l y because o f t h e d e c r e a s e i n pH o u t o f t h e optimum range f o r M g ( 0 H ) p r e c i p i t a t i o n . 2  T h i s a n t a g o n i s t i c e f f e c t on pH caused by t h e a c i d i c magnesium s o l u t i o n and t h e c a u s t i c l i m e i s an i m p o r t a n t f a c t o r when t r y i n g t o a r r i v e a t an optimum s e t o f c o n d i t i o n s f o r c o a g u l a t i o n o f a p a r t i c u l a r w a s t e . As noted e a r l i e r , Thompson e t a l (1972) i d e n t i f i e d a pH o f T l . l t o 11.4 as t h e optimum c o a g u l a t i o n pH f o r t r e a t i n g s u r f a c e w a t e r s , based on a d e t a i l e d economic e v a l u a t i o n .  TABLE 5 JAR TESTS WITH FRESH CHEMICALS EFFLUENT TYPE - BKME I n i t i a l C o l o u r = 2100 I n i t i a l pH = 7.12  J a r No.  Magnesium mg/1 as Mg  06-01-1 06-01-2 06-01-3 06-01-4 06-01-5 06-01-6  0 0 0 0 0 0  + +  Lime mg/1 as C a ( 0 H ) CaO 2  500 750 1000 1500. 2000 3000  375 560 750 1125 1500 . 2250  pH  Cglgur  11.62 11.84 11.94 12.12 12.21 12.33  600 400 320 225 180 150  % Removal 71.4 80.9 84.8 89.3 91.4 92.9  TABLE 6 JAR TESTS WITH FRESH CHEMICALS BKME I n i t i a l C o l o u r = 2100 I n i t i a l pH = 7 . 1 0  J a r No.  Magnesium mg/1 as Mg  06-02-7 06-02-8 06-02-9 06-02-10 06-02-11 06-02-12  30 30 30 30 30 30  + +  Lime mg/1 as C a ( 0 H ) CaO 2  100 250 400 500 750 1000  75 190 300 375 560 750  pH 9.10 10.62 11.10 11.47 11.72 11.90  Colour  % Removal  N.A. N.A. 410 315 215 170  V e r y Poor Poor 80.5 85.0 89.8 91.9  60 TABLE 7 JAR TESTS WITH FRESH CHEMICALS BKME I n i t i a l C o l o u r = 2200  J a r No. 06-05-1 06-05-2 06-05-3 06-05-4 06-05-5 06-05-6 06-05-7 06-05-8  I n i t i a l pH = 7.10 Magnesium Lime mg/1 as mg/1 as .. ++ Ca(0H) CaO Mg  PH  2  60 60 60 60 60 60 60 60  100 200 300 400 500 600 750 1000  75 150 225 300 375 450 . 560 750  9.35 10.00 10.68 10.85 11.21 11.45 11.71 11.91  Cglflur.  % Removal  N.A. N.A. 810 300 175 140 115 105  Very Poor Very Poor 63.2 86.4 92.0 93.6 94.7 95.2  Colour c. u.  %. Removal  TABLE 8 JAR TESTS WITH FRESH CHEMICALS BKME I n i t i a l C o l o u r .= 2285*  J a r No. 06-06-1 06-06-2 06-06-3 06-06-4 06-06-5 06-06-6 06-06-7 06-06-8  I n i t i a l pH = 7.30 Magnesium Lime mg/1 as mg/1 as Mg Ca(0H) CaO 9  0 15 30 45 60 75 90 120  500 500 500 500 500 500 500 500  375 375 375 375 375 375 375 375  PH 11.60 11.50 11.42 11.25 11.10 11.00 10.90 10.64  610 356 303 285 184 165 154 161  73.3 84.4 86.7 87.5 91.9 92.8 93.3 93.0  * Note: T h i s was t h e same sample as i n t h e t h r e e p r e v i o u s t a b l e s . Note t h a t t h e c o l o u r o f t h i s sample i n c r e a s e d o v e r t h e s i x d a y s . T h i s was b e c a u s e t h e sample was s t o r e d a t room t e m p e r a t u r e d u r i n g t h i s e a r l y p e r i o d o f t h e s t u d y . A f t e r t h i s samples were s t o r e d a t 4°C.  o  100 n  LU  80  cr rr  ZD  O _J o  o  6040-  h-  ~Z. 2 0 LU o cc 0 LU  A--  o—  0  LIME LIME •o LIME A  500  ALONE + 60 m g / i M g + 30 m g / i Mg++ + +  — i  T  2000  1000  3000  Ca (0H) mg// 2  FIGURE 9. LIME Vs PERCENT COLOUR REMOVAL AT THREE MAGNESIUM LEVELS-BKME  CXi  62 Results o f these p r e l i m i n a r y j a r t e s t s i n d i c a t e d that the r e l a t i o n s h i p between M g  + +  d o s a g e , l i m e d o s a g e , pH and c o l o u r removal  e f f i c i e n c y i n k r a f t m i l l e f f l u e n t s i s n o t a s i m p l e one. F o r example, a l t h o u g h 30 mg/1 M g  + +  p l u s 300 mg/1 CaO y i e l d e d a pH o f 11.1, o n l y  80.5% c o l o u r r e d u c t i o n was a c h i e v e d .  A t t h i s low magnesium l e v e l , 750  mg/1 CaO was needed t o p r o v i d e an a c c e p t a b l e e f f l u e n t (91.9% but t h e r e s u l t i n g pH o f 11.90 was q u i t e h i g h .  removal),  A t 60 mg/1 o f M g  + +  and  375 mg/1 CaO a pH o f 11.21 and a c o l o u r r e d u c t i o n o f 92.0% r e s u l t e d . I t a p p e a r e d t h a t i t was n o t t h e r e s u l t i n g pH t h a t was s o i m p o r t a n t , p e r s e . As l o n g a s enough M g  + +  was p r e s e n t , i t formed a  good f l o e above pH 10.8, b u t t h e l i m e was i m p o r t a n t a l s o , s i n c e i n a l l c a s e s , i n c r e a s i n g l i m e dosage c o n t i n u e d t o improve t h e t r e a t e d e f f l u e n t colour.  The l i m e s e r v e d a s more than a s i m p l e pH a d j u s t e r , w i t h f l o e  f o r m a t i o n and s l u d g e s e t t l e a b i 1 i t y i m p r o v i n g as t h e lime:magnesium ratio increased. A more e x t e n s i v e s e t o f j a r t e s t s , i n c l u d i n g measurement o f Mg  + +  and l i m e l o s s e s i n t h e d e c o l o u r i z e d e f f l u e n t , i n c o n j u n c t i o n w i t h  d e t a i l e d economic c o n s i d e r a t i o n s , would be n e c e s s a r y b e f o r e optimum c o n d i t i o n s c o u l d be s e l e c t e d f o r l a r g e s c a l e a p p l i c a t i o n . T h i s was beyond t h e scope o f t h e p r e s e n t  study.  Remembering t h e p r e v i o u s l y s t a t e d c r i t e r i a and c a r e f u l l y e x a m i n i n g t h e t e s t r e s u l t s , a dosage l e v e l o f 60 mg/1 M g mg/1 C a ( 0 H )  2  + +  p l u s 500  (375 mg/1 CaO) was chosen f o r u s e i n t h e d e t a i l e d batch  tests. 6.1.1.3  T-20 E f f l u e n t . T y p i c a l r e s u l t s o f p r e l i m i n a r y (100 ml)  c o a g u l a t i o n t e s t s o f T-20 e f f l u e n t a r e g i v e n i n T a b l e s 9, 10 and 11. V e r y p o o r d e c o l o u r i z a t i o n r e s u l t e d from low l i m e and magnesium l e v e l s ^ i n t h e range s e l e c t e d f o r BKME  treatment.  63  TABLE 9 JAR TESTS WITH FRESH CHEMICALS T-20 E f f l u e n t I n i t i a l C o l o u r = 12,400 I n i t i a l pH = 11.5  J  ^  r  No  -  05-28-1 05-28-2 05-29-3 05-28-4 05-28-5 05-28-6 05-28-7 05-28-8 05-28-9 05-28-10 05-28-11 05-28-12 05-28-13 u ^ - « . o - i u  Magnesium mg/1 a s Mg  Lime mg/1 a s Ca(0H) CaO  + +  ?  1000 lUUU 2500 5000 500 500 1 000 1000 2500 2500 2500 2500 5000 UUUU 5000 5000 00  0 u 0 0 6 600 60 60 6 600 1 80 180 300 300 6 00 600 120 \cu 300 3 00 600 600 6000 6000  For example, 5,000 mg/1 C a ( 0 H ) removal and 2,500 mg/1 C a ( 0 H ) 81.3% r e m o v a l .  2  2  7 50 750 1 875 1875 3750 375 375 7 50 750 1 875 1875 1 875 1875 1875 1875 iQ7c 1875 3750 3750 3750 0 0  pH  •Colour cu.  1 2.15 12.15 1 2.40 12.40 1 2.50 12.50 1 1.75 11.75 1 2.05 12.05 1 2.35 12.35 1 2.20 12.20 1 2 .10 12.10 n ->o 11.78 12.40 1 2.40 12.35 12.35 12.25 1 2.25 9.80 9.80  N.A. N.A. 2280 N.A. N.A. 2320 1060 740 510 1020 580 410 N.A.  % Removal Very Poor Very Poor 81.6 Very Poor Very Poor 81.3 91.5 94.0 95.9 91.7 95.3 96.7 Very Poor  (3,750 mg/1 CaO) a l o n e gave o n l y 81.6% (1,875 mg/1 CaO) p l u s 60 mg/1 M g  + +  gave  However, a t t h e h i g h e r magnesium l e v e l s shown i n T a b l e  10, c o l o u r removal was improved s u b s t a n t i a l l y a t t h e s e l i m e l e v e l s . c o m b i n a t i o n o f 300 mg/1 M g  + +  and 1,875 mg/1 CaO gave 94.0% c o l o u r  r e d u c t i o n a t a c o a g u l a t i o n pH o f 12.10.  Twice t h i s M g  + +  dosage gave  m a r g i n a l l y b e t t e r removal a t a pH o f 11.78, a s d i d t w i c e t h i s l i m e dosage a t a pH o f 12.35.  A  64  TABLE 10 JAR TESTS WITH FRESH CHEMICALS T-20 E f f l u e n t I n i t i a l C o l o u r = 12,900 I n i t i a l pH = 11.45  J a r No.  Magnesium mg/1 a s Mg  05-29-1 05-29-2 05-29-3 05-29-4 05-29-5 05-29-6 05-29-7 05-29-8 05-29-9  180 180 180 300 300 300 600 600 600  Lime mg/1 as Ca(0H) CaO 2  500 1500 3000 500 1500 3000 500 1500 3000  375 1125 2250 375 1125 2250 375 1125 2250  pH 11.22 12.00 12.30 10.70 11.75 12.20 10.40 10.63 11.90  Colour c. u.  % Removal  N.A. 1760 1090 N.A. 1410 760 4020 1110 480  Very Poor 86.4 91.6 V e r y Poor 81.1 94.1 68.8 91.4 96.3  As t h e r e s u l t s i n T a b l e 11 i n d i c a t e , a t a c o n s t a n t M g  T T  l e v e l , i n c r e a s e d l i m e dosages y i e l d e d o n l y m a r g i n a l improvements above a CaO v a l u e o f about 2,000 mg/1.  There appeared t o be l i t t l e  i n a d d i n g more than 2,000 mg/1 CaO. However, as mentioned  benefit  before, a  more e x t e n s i v e j a r t e s t i n g s t u d y would be n e c e s s a r y t o d e t e r m i n e o p t i m a l c h e m i c a l dosages f o r any p a r t i c u l a r e f f l u e n t . I t i s i n t e r e s t i n g t o note t h a t even t h e h i g h l e v e l o f 15,000 mg/1 CaO a l o n e gave o n l y 8 9 . 1 % c o l o u r r e m o v a l .  65  TABLE 11 JAR TESTS WITH FRESH CHEMICALS T-20 E f f l u e n t I n i t i a l C o l o u r = 16,680 I n i t i a l pH = 11.20  J a r No. 06-16-1 06-16-2 06-16-3 06-16-4 06-16-5 06-16-6 06-16-7 06-16-8 06-16-9 06-16-10 06-16-11 06-16-12  Magnesium mg/1 a s Mg 0 0 300 300 300 300 300 450 450 450 450 450  Lime mg/1 a s CaO Ca(0H) 2  10000 20000 2500 3750 5000 6250 7500" 2500 3750 5000 6250 7500  7500 15000 1875 2815 3750 4690 5625 1875 2815 3750 4690 5625  pH  Colour cu.  % Remc  12.55 12.60 12.15 12.30 12.35 12.42 12.45 11.96 12.20 12.31 12.40 12.40  2160 1820 940 700 640 645 550 675 505 425 430 380  87.1 89.1 .94.4 95.8 96.2 96.1 96.7 95.9 97.0 97.5 97.4 97.7  From t h e s e d a t a , and k e e p i n g i n mind t h e p r e v i o u s l y d i s c u s s e d c r i t e r i a , a c o m b i n a t i o n o f 300 mg/1 M g Ca(0H)  2  + +  i n c o n j u n c t i o n w i t h 2,500 mg/1  (1,875 mg/1 CaO) was s e l e c t e d a s t h e t e n t a t i v e optimum dosage  l e v e l s f o r use d u r i n g t h e d e t a i l e d b a t c h t e s t s on T-20 e f f l u e n t . A f t e r t h e f i r s t b a t c h r u n o f T-20 e f f l u e n t , i t became more a p p a r e n t t h a t a s e t t l i n g a i d was needed.  Subsequent t e s t i n g , d i s c u s s e d i n Appendix B,  showed t h a t 1 t o 2 mg/1 o f an a n i o n i c polymer (Dow A-23) s e r v e d t h i s purpose.  I t was, t h e r e f o r e , used i n t h e r e m a i n i n g T-20 r u n s .  66 6.1.2  Batch D e c o l o u r i z a t i o n and Magnesium R e c o v e r y R e s u l t s  6.1.2.1  General.  B e f o r e e x t e n s i v e d a t a c o l l e c t i o n was u n d e r t a k e n ,  a few b a t c h runs were c o n d u c t e d t o g a i n e x p e r i e n c e and d e v e l o p p r o cedures f o r these experiments.  Both BKME and T-20 e f f l u e n t were used  d u r i n g t h e s e r u n s , w i t h d a t a c o l l e c t i o n becoming more e f f i c i e n t as equipment and p r o c e d u r a l m o d i f i c a t i o n s were made. As a l r e a d y m e n t i o n e d , t h e m a j o r o b j e c t i v e o f t h e s e b a t c h t e s t s was t o c a r r y o u t complete c o l o u r , magnesium ( M g ) and c a l c i u m ++  ( C a ) b a l a n c e s around t h e two l o o p s o f t h e p r o c e s s ( i . e . , t h e d e c o l o u r + +  i z a t i o n l o o p and t h e s l u d g e c a r b o n a t i o n l o o p ) . These d a t a were i n t e n d e d t o p r o v i d e t h e answers t o t h e f o l l o w i n g key q u e s t i o n s :  1.  What i s t h e e x t e n t o f t h e c o l o u r r e l e a s e d u r i n g s l u d g e c a r b o n a t i o n ? 2.  How much magnesium c a n be r e c o v e r e d i n t h e s l u d g e s u p e r n a t a n t f o r  r e c y c l e and how much remains i n t h e f i n a l s l u d g e a f t e r c a r b o n a t i o n ? The o t h e r major o b j e c t i v e o f t h e s e b a t c h s t u d i e s was t o m o n i t o r s l u d g e pH and c o n d u c t i v i t y i n c o n j u n c t i o n w i t h measurement o f s l u d g e f i l t r a t e pH, a l k a l i n i t y , c o l o u r , magnesium and c a l c i u m a t i n t e r v a l s d u r i n g sludge carbonation.  These d a t a p r o v i d e d an i n s i g h t i n t o t h e f a c t o r s  a f f e c t i n g c o l o u r r e l e a s e and magnesium r e c o v e r y , a s w e l l a s i d e n t i f y i n g a method o f c o n t r o l l i n g t h e s l u d g e c a r b o n a t i o n i n a l a r g e s c a l e p r o c e s s . Three runs each f o r BKME and T-20 e f f l u e n t were c o n d u c t e d u s i n g f r e s h MgSO.* and C a ( 0 H ) a s c o a g u l a n t s . 2  The e f f l u e n t d e s c r i p t i o n s  and c h e m i c a l dosages used f o r each o f t h e runs a r e summarized i n T a b l e 12.  TABLE 12 BATCH DECOLOURIZATION INITIAL CONDITIONS AND RESULTS UNTREATED EFFLUENT DESCRIPTION Total Spec. jn # Type A l k a l . Cond. C o l o u r PH mg/1 c. u. yS 1 2 7 8 3  4 5 6  Note:  BKME BKME BKME BKME T-20 T-20 T-20 T-20  8.3 7.4 7.5 7.4 10.9 10.4 11.8 11.6  240 240 175 180 1325 1125 1825 1750  14000 16000 13000 13000 49000 52400 68000 68000  2250 2370 1500 1500 16680 17270 16000 16000  Mg mg/1  Ca mg/1  8.30 12.00 4.5 5.4 5.76 4.40 5.80 4.6  65 96 40 40 27 32 34 35  + +  CHEMICAL DOSAGES Lime as Mg Ca(OH) CaO Polymer mg/1 mg/1 mg/1 mg/1 9  L  60 60 60 60 1.50 300 300 300  500 500 500 625 2500 2500 2500 5000  Mg added as a f r e s h s o l u t i o n o f MgS0 .7H20, e x c e p t i n Runs #8 and #6 where i t was added 80% as r e c y c l e d magnesium from t h e p r e v i o u s r u n , p l u s 20% as a s o l u t i o n . o f f r e s h MgS0 .7H 0. 4  A  o  375 375 375 475 1875 1875 1875 3750  0 0 0 0 0 1 2 2  pH 11.21 11.10 11.40 11.40 12.30 12.10 12.25 12.35  TREATED EFFLUENT DESCRIPTION Total Spec. A l k a l . Cond. C o l o u r Mg c. u. mg/1 mg/1 vS 155 135 180 155 1700 1250 1600 2075  18000 19400 17500 15000 84000 74000 80000 80000  220 240 70 100 1450 810 900 940  10.50 5.60 4.25 4.75 3.64 4.70 2.60 3.60  Ca' mg, 78 156 175 93 344 510 390 313  68 The s c h e m a t i c d i a g r a m , F i g u r e 10, shows t h e g e n e r a l s o u r c e s and s i n k s measured f o r t h e m a t e r i a l s b a l a n c e c a l c u l a t i o n s , u s i n g f r e s h chemicals. Where:  IN was t h e mass measured i n t h e u n t r e a t e d w a s t e w a t e r . DOSE was t h e mass o f c h e m i c a l s added. OUT was t h e mass measured i n t h e t r e a t e d e f f l u e n t . C S . was t h e mass measured i n t h e p r i m a r y c o l o u r s l u d g e . OTHER LOSSES (O.L.) were t h e measured c h e m i c a l l o s s e s on equipment, a f t e r d e c o l o u r i z a t i o n . The mass u n a c c o u n t e d f o r i n t h e d e c o l o u r i z a t i o n l o o p (ERRORi) was t h e d i f f e r e n c e between t h e mass c a l c u l a t e d i n t h e C S . minus t h e amount measured i n t h e C S .  A negative result  meant a n e t g a i n o f m a t e r i a l . Between t h e two l o o p s , a sample o f c o l o u r s l u d g e was t a k e n f o r a n a l y s i s ( C S . SAMPLE). C S . t o CARB r e f e r s t o t h e mass o f a g i v e n m a t e r i a l i n t h e colour sludge entering the carbonator.  S l u d g e samples were  t a k e n a t i n t e r v a l s d u r i n g c a r b o n a t i o n and f i l t e r e d . SAMPLES r e f e r s t o t h e mass measured i n t h e f i l t r a t e and FILTERS r e f e r s t o t h e mass measured on t h e f i l t e r p a p e r s . SUPER i n d i c a t e s t h e mass measured i n t h e s u p e r n a t a n t a f t e r c a r b o n a t i o n and f i n a l s l u d g e s e t t l i n g . F.S. i n d i c a t e s t h e mass measured i n t h e f i n a l s l u d g e a f t e r c a r b o n a t i o n and s e t t l i n g . The mass u n a c c o u n t e d f o r i n t h e c a r b o n a t i o n l o o p (ERR0R ) 2  r e f e r s t o t h e d i f f e r e n c e between t h e masses c a l c u l a t e d and measured i n t h e f i n a l s l u d g e .  To c a l c u l a t e t h e mass o f  m a t e r i a l s t h a t would be r e c y c l e d , t h e f o l l o w i n g a s s u m p t i o n s were made:  69 1.  C o l o u r r e c y c l e d = (SUPER + SAMPLES).  2.  Magnesium r e c y c l e d = (SUPER + FILTERS'+ SAMPLES).  3.  C a l c i u m r e c y c l e d = (SUPER + SAMPLES).  4.  Magnesium i n t h e F.S. S o l i d s = ( F . S . ) .  5.  C a l c i u m i n t h e F.S. S o l i d s = ( F . S . + F I L T E R S ) .  O b v i o u s l y , t h e volume o f f i n a l s l u d g e and s u p e r n a t a n t r e c y c l e i s a f u n c t i o n o f the f i n a l sludge s o l i d s concentration achieved. T h e r e f o r e , t h e f i n a l s l u d g e h a n d l i n g method used i n p r a c t i c e would have a s i g n i f i c a n t e f f e c t on t h e mass b a l a n c e s i n t h e s l u d g e c a r bonation loop.  F o r p u r p o s e s o f o b t a i n i n g r e a l i s t i c magnesium r e c o v e r y  v a l u e s and comparing t h e r e s u l t s o f t h e s e t e s t s , two h y p o t h e t i c a l s l u d g e h a n d l i n g methods were e v a l u a t e d : 1.  S u p p o s i n g t h e f i n a l s l u d g e (F.S.) had r e a c h e d 5% s o l i d s . In t h i s c a s e , more s u p e r n a t a n t would be wasted w i t h t h e d i l u t e s l u d g e t h a t would go t o some k i n d o f d i s p o s a l .  2.  S u p p o s i n g t h e f i n a l s l u d g e was dewatered t o 60% s o l i d s for lime recovery i n a k i l n .  Both t h e s e c a s e s were though t o be r e a l i s t i c a l t e r n a t i v e s for f i n a l sludge handling.  However, mass b a l a n c e s f o r o t h e r c a s e s can  be worked o u t f r o m t h e raw d a t a .  An example o f t h e c a l c u l a t i o n s used  to d e r i v e s l u d g e and r e c y c l e volumes f o r s l u d g e o f a g i v e n s o l i d s c o n c e n t r a t i o n i s shown i n Appendix C. S i n c e c o l o u r s l u d g e from t h e d e c o l o u r i z a t i o n system would n o t n o r m a l l y be t h i c k e n e d i n p r a c t i c e , mass b a l a n c e s i n t h e d e c o l o u r i z a t i o n l o o p were c a l c u l a t e d o n l y u s i n g t h e a c t u a l volumes o b t a i n e d during these t e s t s . R e s u l t s o f t h e b a t c h d e c o l o u r i z a t i o n and b a t c h s l u d g e c a r bonation studies are discussed separately i n the f o l l o w i n g sections.  70  r OUT DECOLOURIZATION/ LOOP  \  OTHER  L O S S E S (O.L.)  — T E R R O R  COLOUR  CS.  r  SLUDGE ( C S . )  SAMPLE  C S . TO C A R B .  SAMPLES CARBONATION LOOP  ->-ERROR  FINAL SLUDGE  2  ( F.S.)  FIGURE 10. SCHEMATIC OF MATERIAL SOURCES AND SINKS  71 6.1.2.2  Batch D e c o l o u r i z a t i o n R e s u l t s . A.  Mass b a l a n c e s :  i)  BKME  T a b l e 12 summarizes t h e i n i t i a l c o n d i t i o n s and r e s u l t s o f a l l the batch d e c o l o u r i z a t i o n runs. These b a t c h c o a g u l a t i o n s were e s s e n t i a l l y l a r g e (10 t o 30l i t r e ) j a r t e s t s , s o , as e x p e c t e d , c o l o u r r e m o v a l s were e q u i v a l e n t t o t h o s e o b t a i n e d i n t h e p r e l i m i n a r y j a r t e s t s . The p e r c e n t c o l o u r r e m o v a l s a t t a i n e d and t h e magnesium and c a l c i u m l o s s e s o c c u r r i n g i n the d e c o l o u r i z e d e f f l u e n t d u r i n g a l l t h e r u n s , a r e shown i n T a b l e 13. I t s h o u l d be noted t h a t p e r c e n t c o l o u r removal i n a l l t h e b a t c h  runs  was c a l c u l a t e d on a mass b a s i s ( i . e . % removal =  M a s s  jjjjj ~ ^  s s  0 U T  x 100%); w h e r e a s , i n t h e j a r  t e s t s , i t was c a l c u l a t e d s i m p l y on a c o n c e n t r a t i o n b a s i s (% removal =  C o n c  ' ^ " °j| -  of sludge wasted.  C  c  0 U T  x 100%) w i t h no r e g a r d t o t h e volume  In any c a s e , g r e a t e r than 90% c o l o u r r e d u c t i o n s  were a c h i e v e d i n a l l r u n s .  The r e s i d u a l c o l o u r i n t h e BKME t e s t s  ranged from 7 0 . t o 240 C U . Because t h e p r o c e s s w a t e r used a t t h e C r e s t b r o o k m i l l was from v e r y s o f t s u r f a c e r u n o f f , t h e l e v e l s o f M g  + +  and C a  waste were q u i t e low compared t o t h e dosages employed.  + +  i n t h e raw  The M g  + +  c o n c e n t r a t i o n i n t h e t o t a l m i l l samples ranged from 5.76 t o 12.0 mg/1, r e p r e s e n t i n g 7.9 t o 16.7% o f t h e t o t a l magnesium used i n t r e a t i n g t h i s effluent.  In t h e s e r u n s , e x c l u d i n g t h e r e s u l t s o f Run #1 (because t h e  a n a l y t i c a l method used d u r i n g t h a t r u n d i d n o t i n c l u d e t h e a d d i t i o n o f L a C l ) , 4.25 t o 5.6 mg/1 M g 2  ized effluent.  + +  o r 6.2 t o 7.4% r e m a i n e d i n t h e d e c o l o u r -  72  TABLE 13 SUMMARY OF DECOLOURIZATION LOOP MASS BALANCE RESULTS  Run No.  Percent Colour Removal  1 2 7 8 3 4 5 6  90.8 90.4 95.5 94.8 93.5 97.0 95.1 94.8  P e r c e n t o f t h e T o t a l Mass L o s t ^ourized Effluent Magnesium Calcium  in  D e c o  14.3 7.4 6.2 7.3 1.7 -9 -6 -9  The C a 40 t o 96 mg/1.  the  T T  21.8 40.0 .53.3 23.2 18.5 21.1 8.5 22  c o n c e n t r a t i o n i n the u n t r e a t e d e f f l u e n t ranged from  The w i d e v a r i a t i o n was c a u s e d by t h e C a C 0  adjustment, p r i o r to b i o l o g i c a l treatment at t h i s m i l l .  3  used f o r pH  The measured  c o n c e n t r a t i o n s a c c o u n t e d f o r 12.4 t o 26.2% o f t h e t o t a l C a BKME r u n s .  3  + +  i n the  A g a i n , e x c l u d i n g t h e r e s u l t s o f Run #1 f o r t h e same  reason, the treated e f f l u e n t C a o r 218 t o 245 mg/1 as CaO.  + +  c o n t e n t r a n g e d f r o m 156 t o 175 mg/1  T h i s r e p r e s e n t e d a l o s s o f 40.0 t o 53.3%  to the d e c o l o u r i z e d e f f l u e n t . ii)  T-20 E f f l u e n t  In t h e s e t e s t s , c o l o u r r e d u c t i o n s o f 93.5 t o 97.0% were a t t a i n e d , w i t h r e s i d u a l c o l o u r s r a n g i n g from 810 t o 1 ,450 C U .  The  h i g h e r r e s i d u a l c o l o u r was a d i r e c t r e s u l t o f a l o w e r - t h a n - i n t e n d e d  73 Mg  dosage used i n Run #3.  to a c e r t a i n extent.  T h i s a l s o a f f e c t e d t h e Mg  mass b a l a n c e s  The magnesium and c a l c i u m c o n t r i b u t i o n s o f t h e  u n t r e a t e d e f f l e u n t were even more i n s i g n i f i c a n t f o r t h i s w a s t e w a t e r because o f t h e l a r g e r c h e m i c a l d o s a g e s used. Magnesium c o n c e n t r a t i o n i n t h e raw T-20 e f f l u e n t was between 4.5 t o 5.8 mg/1 o r o n l y 1.1 t o 3.7% o f t h e t o t a l .  Concentrations i n  t h e d e c o l o u r i z e d T-20 e f f l u e n t were even l e s s than i n BKME, v a r y i n g from 2.6 t o 4.7 mg/1.  E x c l u d i n g t h e Run #3 r e s u l t s , t h i s r e p r e s e n t e d  o n l y .6 t o .9% o f t h e t o t a l magnesium i n t h e system. The C a  + +  c o n c e n t r a t i o n i n t h e raw T-20 e f f l u e n t was con-  s i s t e n t l y about 30 mg/1. A t t h e h i g h l i m e d o s a g e s u s e d , t h i s r e p r e s e n t e d o n l y 1.8 t o 2.2% o f t h e t o t a l C a the C a  + +  + +  present.  In t h e s e r u n s ,  c o n t e n t o f t h e d e c o l o u r i z e d e f f l u e n t was between 344 t o 510  mg/1 o r 482 t o 714 mg/1 a s CaO. T h i s r e p r e s e n t e d a l o s s o f 18.5 t o 21.1% o f t h e C a  + +  to the decolourized effluent.  Measured c h e m i c a l l o s s e s on equipment d u r i n g both BKME and T-20 e f f l u e n t b a t c h d e c o l o u r i z a t i o n t e s t s were n o r m a l l y about 1%. Most o f t h e s e l o s s e s were r e c o v e r e d from t h e w a l l s o f t h e v e s s e l used f o r t h e c o a g u l a t i o n and c l a r i f i c a t i o n , p o i n t i n g t o t h e p o s s i b i l i t y o f s c a l e b u i l d u p on equipment i n a l a r g e s c a l e a p p l i c a t i o n o f t h e p r o cess. The e r r o r s i n t h e d e c o l o u r i z a t i o n l o o p mass b a l a n c e s showed a p e r c e n t a g e v a r i a t i o n between .6 and 6.7%. T h i s was w i t h i n t h e a c c u r a c y o f t h e volume measurements and a n a l y t i c a l p r o c e d u r e s B.  F a c t o r s a f f e c t i n g t h e mass b a l a n c e s :  i)  General  In t h e c o l o u r removal  used.  s t e p , t h e a i m was t o m i n i m i z e t h e  74 c o l o u r , magnesium, and c a l c i u m c o n c e n t r a t i o n s i n t h e d e c o l o u r i z e d effluent.  The f i r s t v a r i a b l e i s a measure o f t h e t r e a t m e n t e f f i c i e n c y ,  w h i l e t h e l a t t e r two r e p r e s e n t c h e m i c a l l o s s e s from t h e system, ++ Ca  although  c a n be r e c o v e r e d a t a c o s t by r e c a r b o n a t i n g t h e d e c o l o u r i z e d  effluent. The main f a c t o r s w h i c h a f f e c t e d t h e s e c o n c e n t r a t i o n s were the u n t r e a t e d e f f l u e n t c h a r a c t e r i s t i c s , and t h e dosages o f t h e two c h e m i c a l s used i n t h e t r e a t m e n t . c o a g u l a t i o n pH r e a c h e d .  These, i n t u r n , determined the f i n a l  Other c o n s i d e r a t i o n s d i s c u s s e d here i n c l u d e  r a p i d m i x i n g and f l o c c u l a t i n g t i m e s and speeds, s e t t l i n g t i m e , use o f s e t t l i n g a i d s , and c o l o u r s l u d g e s o l i d s c o n c e n t r a t i o n , ii)  C o a g u l a t i o n pH The f i n a l pH a c h i e v e d d u r i n g c o a g u l a t i o n has been  i d e n t i f i e d by Thompson e t a l (1972) as t h e key v a r i a b l e i n c o l o u r removal w i t h M g  + +  and l i m e .  However, i t must be remembered t h a t t h i s  pH i s a f u n c t i o n o f t h e l i m e and magnesium dosages u s e d , a s w e l l as the i n i t i a l pH and a l k a l i n i t y o f t h e raw w a s t e .  During these batch  r u n s , t h e dosages used t o t r e a t BKME y i e l d e d a pH between 11.1 and 11.4 g i v i n g a c o l o u r r e d u c t i o n o f >90%. A l t h o u g h s m a l l d a r k f l o w p a r t i c l e s were v i s i b l e a f t e r M g  + +  a d d i t i o n t o T-20 e f f l u e n t , w i t h i n i t i a l pH j u s t above 11, no a p p r e c i a b l e c o l o u r removal r e s u l t e d u n t i l enough l i m e had been added t o a c h i e v e a f i n a l pH above 12. F u r t h e r i n v e s t i g a t i o n o f t h e optimum pH f o r c o a g u l a t i o n i s r e q u i r e d t o i d e n t i f y t h e mechanism(s) o f c o l o u r removal by t h e M g ( 0 H ) + C a C 0 p r e c i p i t a t e formed d u r i n g c o a g u l a t i o n o f t h e s e 2  3  effluents. The i n f l u e n c e o f t h e u n t r e a t e d e f f l u e n t a l k a l i n i t y on t h e amount o f l i m e r e q u i r e d t o r e a c h a g i v e n pH l e v e l c a n be seen from t h e  75 l i m i t e d d a t a i n T a b l e 12. The l o w e r i n i t i a l a l k a l i n i t y i n Run #7 (180 mg/1), r e s u l t e d i n a h i g h e r pH (11.4) than i n Runs #1 and 2 ( a l k a l i n i t y = 240 mg/1) where t h e f i n a l . pH was 11.21 and 11.1, r e s p e c t i v e l y . Howe v e r , i t i s d i f f i c u l t t o s a y what e f f e c t t h i s had on t h e p e r c e n t c o l o u r removal because t h e i n i t i a l c o l o u r i n Run #7 was o n l y 1 ,500 C U . comp a r e d t o about 2,300 C U . i n Runs #1 and 2. The r e s u l t s o f Runs #4 and 5 a r e an a p p a r e n t anomaly t o t h i s a l k a l i n i t y - lime requirement r e l a t i o n s h i p .  Run #4 had an i n i t i a l a l k a -  l i n i t y o f 1,125 mg/1, b u t t h e f i n a l pH was o n l y 12.1 compared t o 12.25 i n Run #5 which had an i n i t i a l a l k a l i n i t y o f 1,825 mg/1. The i n c r e a s e d polymer dosage i n Run #5 may p a r t i a l l y e x p l a i n t h i s d i f f e r e n c e . The e f f e c t o f a l k a l i n i t y on l i m e r e q u i r e m e n t s became more a p p a r e n t d u r i n g t e s t i n g w i t h r e c y c l e d magnesium and i s d i s c u s s e d f u r t h e r in that s e c t i o n . The pH - magnesium s o l u b i l i t y r e l a t i o n s h i p has been d i s cussed e a r l i e r .  A comparison o f t h e r e s u l t s o f t h e runs w i t h BKME a t  a pH o f 11.1 t o 11.4, t o t h o s e w i t h T-20 e f f l u e n t a t a pH o f 12.1 12.25, i l l u s t r a t e s t h i s pH e f f e c t on magnesium l o s s e s . A t t h e lower pH, 4.25 t o 5.6 mg/1 o f M g  + +  remained i n t h e d e c o l o u r i z e d BKME e f f l u e n t  whereas o n l y 2.6 t o 4.7 mg/1 M g  + +  remained i n t h e t r e a t e d T-20 e f f l u e n t .  C a l c i u m l o s s e s a r e more d i f f i c u l t t o e x p l a i n on t h e b a s i s o f solubility  a l o n e because o t h e r f a c t o r s p l a y i m p o r t a n t r o l e s as w e l l .  However, t h e l o s s e s a t pH 12.1 t o 12.25 were a p p r o x i m a t e l y t w i c e t h o s e a t pH 11.1 t o 11.4. iii)  M i x i n g Times and Speeds  These v a r i a b l e s were m o n i t o r e d d u r i n g most o f t h e b a t c h d e c o l o u r i z a t i o n r u n s , t o e n s u r e t h a t pH s t a b i l i z a t i o n had o c c u r r e d before allowing the sludge t o s e t t l e .  The pH u s u a l l y s t a b i l i z e d  76  w i t h i n f i v e m i n u t e s , as i t d i d i n t h e p r e l i m i n a r y j a r t e s t s o f t h e two e f f l u e n t types.  No improvement i n c o l o u r removal e f f i c i e n c y r e s u l t e d  f r o m c o n t i n u i n g f l o c c u l a t i o n f o r more than 5 t o 10 m i n u t e s . The e f f e c t s o f r a p i d m i x i n g and f l o c c u l a t i o n on M g Ca  + +  l o s s e s were n o t s t u d i e d e x t e n s i v e l y d u r i n g t h i s work.  + +  and  However,  i n d i c a t i o n s were t h a t e x t e n d e d m i x i n g t i m e s (beyond 15 m i n u t e s ) and f a s t e r m i x i n g speeds o n l y cause f l o e d e s t r u c t i o n . cause p o o r e r s e t t l i n g and i n c r e a s e d M g  + +  and C a  + +  T h i s would i n t u r n losses i n floe carry  over. iv)  S l u d g e S e t t l e a b i T i t y and S o l i d s  Concentration  S e t t l i n g t i m e s i n t h e s e t e s t s v a r i e d from two hours t o o v e r n i g h t , i n some c a s e s , so no d i r e c t c o m p a r i s o n c a n be made between tests.  In g e n e r a l , s l u d g e from BKME s e t t l e d w e l l and y i e l d e d a f a i r l y  c l e a r e f f l u e n t i n l e s s than an hour.  On t h e o t h e r hand, T-20 e f f l u e n t  s l u d g e s e t t l e d p o o r l y , r e q u i r i n g s e v e r a l hours t o a c h i e v e a f i n a l s l u d g e volume o f 25 t o 4 0 % o f t h e o r i g i n a l volume.  This poor s e t t l e -  a b i l i t y would have r e s u l t e d i n l a r g e amounts o f f l o e c a r r y o v e r i n t h e two hours a l l o t t e d f o r s e t t l i n g . However, t h e r e s u l t s o f p r e l i m i n a r y e v a l u a t i o n o f s e t t l i n g a i d s (Appendix B) showed t h a t s e t t l i n g t i m e s c o u l d be r e d u c e d t o l e s s than two hours by a d d i t i o n o f an a n i o n i c polymer. ++ o f Mg over.  I t was e x p e c t e d ++ and Ca  t h a t polymer use would d e c r e a s e t h e l o s s e s  t o t h e d e c o l o u r i z e d e f f l u e n t by l i m i t i n g f l o e c a r r y  T h i s was n o t t h e c a s e .  The C a  + +  l o s s i n Run #5 (2 mg/1 Dow A-  23) was h i g h e r than i n Run #3 (no p o l y m e r ) and Run #4 (1 mg/1 Dow A23) had t h e h i g h e s t M g runs.  + +  and C a  + +  l o s s e s o f a l l t h e T-20 e f f l u e n t  From t h e r e s u l t s o f Run #4, i t a p p e a r e d t h a t t o o l i t t l e p o l y m e r  77 was worse t h a n none a t a l l because s m a l l l i g h t f l o e  agglomerations  f o r m e d , but some f a i l e d t o s e t t l e w i t h the f l o e b l a n k e t . As i n the p r e l i m i n a r y j a r t e s t s , c o l o u r removal was improved s i g n i f i c a n t l y by polymer usage. o f 2 mg/1  not  So, w h i l e the polymer dosage  r e s u l t e d i n good s l u d g e s e t t l i n g , no o t h e r b e n e f i t s c o u l d be  seen from t h e s e l i m i t e d d a t a . The s o l i d s c o n t e n t o f the c o l o u r s l u d g e from BKME t r e a t m e n t ranged from 1.20 t o 1.60% and from 1.20 to 2.04% treatment.  i n T-20 e f f l u e n t  However, the method o f l i q u i d - s o l i d s s e p a r a t i o n i n t h e s e  b a t c h t e s t s was not v e r y e f f i c i e n t .  With timed s l u d g e w a s t i n g , i n a  l a r g e s c a l e system a c o l o u r sludge concentration approaching c o u l d l i k e l y be a t t a i n e d .  5% s o l i d s  T h i s would mean a s l i g h t l y l a r g e r volume o f  d e c o l o u r i z e d e f f l u e n t and hence s l i g h t l y h i g h e r c o l o u r , Mg  and Ca  l o s s e s i n t h a t e f f l u e n t . However, as d i s c u s s e d i n the next s e c t i o n , t h e o v e r a l l e f f e c t o f an i n c r e a s e d s o l i d s c o n c e n t r a t i o n i n the c o l o u r s l u d g e may be a p o s i t i v e one. 6.1.2.3  Batch S l u d g e C a r b o n a t i o n A. i)  Results  Mass b a l a n c e s : General  P e r t i n e n t s l u d g e c a r b o n a t i o n r e s u l t s from each run have been summarized i n T a b l e 14.  P a r t 1 o f t h i s t a b l e g i v e s the r e s u l t s as a  p e r c e n t o f the t o t a l mass i n the c o l o u r removal s y s t e m , so t h a t o v e r a l l m a t e r i a l r e c o v e r i e s and l o s s e s can be seen f o r the two assumed s l u d g e d i s p o s a l methods.  P a r t 2 g i v e s the r e s u l t s as a p e r c e n t o f the mass  o f m a t e r i a l s c a r b o n a t e d , a l l o w i n g a more d i r e c t c o m p a r i s o n o f the s l u d g e c a r b o n a t i o n e f f i c i e n c i e s from t h e v a r i o u s r u n s .  Not shown i n  t h i s t a b l e a r e the measured l o s s e s on the equipment w h i c h were <1% i n  most c a s e s .  The e r r o r s i n t h e c a r b o n a t i o n l o o p Mg  b a l a n c e s were ± 3 t o 6% i n most c a s e s .  and Ca  78 mass  Run #1 had l a r g e r e r r o r s (20  t o 30%) because t h e a n a l y t i c a l methods were n o t f u l l y d e v e l o p e d a t t h a t time.  O t h e r w i s e , e r r o r s ranged from z e r o i n Run #7 f o r C a  + +  to  10% i n Run #5 f o r M g . ++  I n f o r m a t i o n on t h e s u p e r n a t a n t r e c y c l e q u a l i t y , o b t a i n e d i n each o f t h e r u n s , i s g i v e n i n T a b l e 15, f o r c o m p a r i s o n w i t h t h e c o r r e s p o n d i n g u n t r e a t e d and t r e a t e d e f f l u e n t v a l u e s shown i n T a b l e 12. i i) 1.  Colour BKME.  In t h e t e s t s o f t o t a l m i l l e f f l u e n t w i t h f r e s h  c h e m i c a l s , 22.7 t o 36.3% o f t h e t o t a l c o l o u r mass i n t h e s y s t e m was contained i n the supernatant r e c y c l e . This represented a colour r e l e a s e from t h e c o l o u r s l u d g e d u r i n g c a r b o n a t i o n o f 25.0 t o 38.1%. W i t h t h i s amount o f c o l o u r b e i n g r e c y c l e d , t h e r e s u l t a n t c o l o u r mass d i s p o s e d o f i n t h e f i n a l s l u d g e o f t h e b a t c h s y s t e m v a r i e d f r o m 56.4 t o 68.1% o f t h e t o t a l , b u t t h i s w o u l d be h i g h e r when f l o w t h r o u g h e q u i l i b r i u m c o n d i t i o n s were e s t a b l i s h e d i n a c o n t i n u o u s system. The r e c y c l e d c o l o u r was c o n c e n t r a t e d i n o n l y 4.9 t o 6.4% o f t h e o r i g i n a l volume (as shown i n T a b l e 1 6 ) , meaning t h a t , i n a l l c a s e s , t h e c o l o u r c o n c e n t r a t i o n o f t h e s u p e r n a t a n t was h i g h e r than i n t h e o r i g i n a l u n t r e a t e d e f f l u e n t ( i . e . , 5,575 t o 9,400 C U . compared t o 1 ,500 t o 2,300 C U . i n t h e u n t r e a t e d w a s t e ) . The e f f e c t o f r e c y c l i n g t h i s h i g h l y c o l o u r e d s u p e r n a t a n t i s d i s c u s s e d i n t h e s e c t i o n on t h e use o f r e c y c l e d magnesium. 2.  T-20 e f f l u e n t . C o r r e s p o n d i n g r e s u l t s f o r t h e c a u s t i c  e x t r a c t i o n e f f l u e n t t e s t s w i t h f r e s h c h e m i c a l s showed, g e n e r a l l y , a l o w e r p e r c e n t o f t h e c o l o u r i n t h e r e c y c l e . The s u p e r n a t a n t , a f t e r  TABLE 14  ( P a r t 1)  SUMMARY OF CARBONATION LOOP MASS BALANCE RESULTS  Run No.  Actual Percent Solids C.S. t o Carb. F.S. 99  3.65  46 1. 26 2. 24 1. 70 1. 20 2. 04 4. 03  2.10 3.19 6.33 3.83 3.45 2.60 31.10  Percent o f the Total In The Supern a t a n t R e c y c l e i t F.S. = 5% S o l i d s * I f F.S. = 60% S o l i d s I f F.S. Colour Mg Ca Colour Mg Ca Colour + +  22.7 32.5 29.9 25.4 16.0 25.1 18.7 16.2  *  67.7 73.7 74.1 61.0 71.3 82.4 71.0 58.3  Note:  + +  2.3 9.5 2.0 1.0 24.5 30.7 11.5 5.2  + +  26.1 34.0 36.3 34.4 19.5 28.8 24.8 17.2  78.4 77.2 89.3 80.2 87.3 94.5 93.3 61.9  Run #8 F.S. = 6.33%  + +  2.7 10.0 2.5 1.3 30.2 35.1 15.5 5.5  68.1 57.9 65.6 69.4 77.5 71.9 76.4 78.6  Mass In The F i n a l = 5% S o l i d s Mg Ca + +  34.0 8.8 26.2 34.4 29.7 27.0 42.7 39.8  + +  51.7 39.9 44.8 71.3 53.6 50.5 57.9 80.0  Sludae  I f F.S. = 60% S o l i d s Colour Mg Ca + +  64.7 56.4 59.2 60.4 74.0 68.2 70.3 77.6  23.1 5.5 11.5 15.2 13.2 14.9 20.4 36.4  + +  51.5 39.2 44.3 70.9 47.8 46.0 53.8 79.7  Run #6 F.S. = 31. 1% ^1  <JD  TABLE 14 ( P a r t 2) SUMMARY OF CARBONATION LOOP MASS BALANCE RESULTS  Run No. 1 2 7  8 3 4 5  6  P e r c e n t o f t h e Mass C a r b o n a t e d In t h e S u p e r n a t a n t R e c y c l e In t h e F i n a l S l u d g e I f F.S. = 5% S o l i d s * I f FS = 6 0 % S o l i d s I f FS = 5% S o l i d s * I f FS = 6 0 % S o l i d s ++ ++ Colour Mg Ca C o l o u r Mg - C a C o l o u r Mg Ca Colour Mg • C a + +  25.0 35.9 31.4 26.8 17.0 26.9 19.6 17.0  79.1 85.9 75.6 62.6 72.9 79.1 68.0 56. 7  + +  13.0 17.9 4.4 1.3 33.0 39.3 15.8 6.2  ++  28.8 37.6 38.1 36.2 20.8 29.7 26.1 18.2  91.5 90.0 91.1 82.3 89.3 90.7 89.3 .60.2  + +  3.5 18.8 5.0 1.8 40.8 45.0 21.5 6.7  * Note:  + +  75.0 64.1 68.6 73.2 83.0 73.1 80.4 83.0  39.7 10.3 26.7 35.3 30.4 25.9 40.9 38.8  65.8 74.5 97.0 91.7 72.2 64.8 79.8 96.7  Run #8 F.S. = 6.33%  71.2 62.4 59.2 63.8 79.2 70.3 73.9 81.9  27.0 6.4 11.7 15.6 13.4 14.3 19.5 35.3  + +  65.4 73.6 96.0 91.2 64.4 59.1 74.1 96.3  Run #6 F.S. = 3 1 . 1 %  Percent o f the I n c i n e r a t e d F.S. MgO 7.1 2.9 5.2 3.7 2.9 6.8 8.9 4.8  ^ f\ 1 T A c OU 1 1 Ub  CaO  64.8 88.4 73.9 80.0 74.9 81.4 79.9 82.2  Ma c c rlobb  Other 28.1 8.7 20.9 16.3 20.9 11.9 11.2 13.0  81  TABLE 15 CARBONATION SUPERNATANT CHARACTERISTICS  Run No. 1 2 7 8 3 4 5 6  Unfiltered Filtered pH pH N.A. N.A. 7.7 7.6 7.2 7.3 7.7 N.A.  7.3 7.0 7.8 7.8 7.5 7.3 7.9 7.7  Total Alkalinity mg/1 C a C 0  3  2250 1400 3650 4375 6578 N.A. 6830 5765  Specific Conductance yS  Colour CU.  Mg mg/1  N.A. 28000 43500 43000 90000 61000 91000 80000  5575 3790 9400 13500 12825 11810 16000 12550  525 263 960 980 552 734 1250 900  Ca mg/1 93 192 135 110 1750 1240 1050 865  s l u d g e c a r b o n a t i o n , was found t o c o n t a i n 16,0 t o 28.J3% o f t h e t o t a l c o l o u r mass.  T h i s r e p r e s e n t e d a c o l o u r r e l e a s e from t h e c o l o u r s l u d g e  o f 17.0 t o 29.7 %.  With t h e s e p e r c e n t a g e s o f c o l o u r b e i n g r e c y c l e d ,  t h e r e s u l t a n t c o l o u r mass i n t h e f i n a l s l u d g e was h i g h e r than f o r BKME r u n s ( i . e . , 68.2 t o 78.6% o f t h e t o t a l m a s s ) . S i n c e a much l a r g e r c o l o u r s l u d g e volume was g e n e r a t e d i n t h e s e r u n s t h a n i n BKME t e s t s , t h e r e c y c l e volumes were a l s o h i g h e r (16.9 t o 39.1% o f t h e o r i g i n a l volume).  The r e s u l t a n t c o l o u r con-  c e n t r a t i o n s were g e n e r a l l y about t h e same as t h e i n f l u e n t c o l o u r , as seen by comparing T a b l e s 12 and 15.  TABLE 16 SUMMARY OF THE BATCH TEST VOLUME BALANCE  Run No.  1 2 7 8 3 4 5 6  Total Vol ume (litres) 10 10 30 26 10 10 10 6.52  In 99.8 99.8 96.3 91.3 99.5 93.0 88.0 69.9  Dose  Out  .2 .2 3,7 8.7 .5 7.0 12.0 30.1  *  93.8 93.5 94.0 94.8 74.2 60.4 77.2 78.2  Note:  CS. 6.2 6.5 6.0 5.2 25.8 39.6 22.8 21.8  RESULTS  P e r c e n t o f t h e T o t a l Volume I f F.S. = 5% S o l i d s * Recycle F.S. 5.3 5.9 4.9 3.8 20.9 34.1 16.9 19.3  Run #8 F.S. = 6.33%  .9 .6 1.1 1.4 4.9 5.8 5.9 2.5  I f F.S. = 60% S o l i ds F S Recvcle • o I  6.1 6.4 5.9 5.05 25.9 39.1 22.3 20.5  .1 .1 .1 .15 .4 .5 .5 1.3  Run #6 F.S. = 31.1% CO  ro  83 iii) 1.  Magnesium BKME. O v e r a l l magnesium r e c o v e r y , i n BKME t e s t s w i t h  f r e s h c h e m i c a l s , ranged from 67.7 t o 8 9 . 3 % o f t h e t o t a l mass i n t h e system.  T h i s was 75.6 t o 91.5 % o f t h e magnesium p r e s e n t i n t h e  sludge entering the carbonation stage. Recovery o f t h i s m a g n i t u d e was c o u p l e d w i t h measured magnesium l o s s e s i n t h e f i n a l s l u d g e , v a r y i n g from a low o f 5.5% t o a h i g h o f 34.0% o f t h e t o t a l mass i n t h e system o r 6.4 t o 39.7% o f t h e mass carbonated.  T h i s amount o f magnesium i n t h e f i n a l s l u d g e  accounted  f o r 2.9 t o 7.1% o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s mass, c a l c u l a t e d as MgO. Magnesium c o n c e n t r a t i o n i n t h e c a r b o n a t i o n r e c y c l e v a r i e d from 263 t o 980 mg/1, depending on t h e s u p e r n a t a n t volume. 2.  T-20 e f f l u e n t . In c a r b o n a t i o n o f t h e T-20 c o l o u r  s l u d g e , s l i g h t l y b e t t e r o v e r a l l magnesium r e c o v e r y was a c h i e v e d i n most c a s e s because l o s s e s i n t h e d e c o l o u r i z e d e f f l u e n t became l e s s s i g n i f i c a n t a t t h e h i g h e r magnesium d o s a g e l e v e l used.  With f r e s h  c h e m i c a l s , 71.0 t o 9 4 . 5 % o f t h e t o t a l mass was r e c o v e r e d i n t h e supernatant.  However, t h e 68.0 t o 90.7% r e c o v e r e d from t h e mass  c a r b o n a t e d was j u s t e q u i v a l e n t o r s l i g h t l y l e s s than r e c o v e r y i n BKME runs.  Measured magnesium l o s s e s t o t h e f i n a l s l u d g e were 13.2 t o  42.7% o f t h e t o t a l mass o r 13.4 t o 4 0 . 9 % o f t h e c a r b o n a t e d mass. As MgO, t h i s a c c o u n t e d f o r 2.9 t o 8.9% o f t h e i n c i n e r a t e d f i n a l  sludge  s o l i d s mass. Magnesium c o n c e n t r a t i o n i n t h e r e c y c l e from t h e s e runs a l s o v a r i e d g r e a t l y , depending on d i l u t i o n , and dosage l e v e l , r a n g i n g from 552 mg/1 i n Run #3 t o 1,250 mg/1 i n Run #5.  84 i v) 1.  Calcium BKME.  While magnesium i n the s u p e r n a t a n t r e c y c l e was a  r e c o v e r y , c a l c i u m i n t h a t s t r e a m was c o n s i d e r e d a l o s s . variation in C a  + +  A wide  l o s s e s t o the r e c y c l e was o b s e r v e d d u r i n g t h e s e  t e s t s , d e p e n d i n g on the f a c t o r s d i s c u s s e d i n the n e x t s e c t i o n . In BKME runs w i t h f r e s h c h e m i c a l s , 2.0 t o 10.0% o f t h e t o t a l c a l c i u m i n the system appeared i n the c a r b o n a t i o n s u p e r n a t a n t .  This  was 3.0 t o 18.8% o f t h e mass i n t h e c a r b o n a t e d c o l o u r s l u d g e .  On t h e  o t h e r hand, o v e r a l l C a  + +  r e c o v e r y i n the f i n a l s l u d g e ranged from o n l y  39.2 t o 51.7% o f t h e t o t a l mass i n t h e system. r e s e n t e d 68.4 t o 97.0% o f t h e C a  + +  T h i s , however, r e p -  s e n t to the c a r b o n a t o r .  This  amount o f c a l c i u m i n the f i n a l s l u d g e a c c o u n t e d f o r 64.8 t o 88.4% o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s mass as CaO, l e a v i n g 8.7 t o 28.1% unaccounted f o r by MgO o r CaO i n t h e s e t e s t s .  Unburned o r g a n i c s i n  t h e e a r l y runs a t lower t e m p e r a t u r e s a l o n g w i t h s u l p h a t e , c h l o r i d e and o t h e r i n o r g a n i c o x i d a t i o n m a t e r i a l s c o u l d make up t h e d i f f e r e n c e . F u r t h e r i n v e s t i g a t i o n i s r e q u i r e d t o a c c o u n t f o r t h e e n t i r e mass o f the r e c a l c i n a t e d lime.  Calcium c o n c e n t r a t i o n i n the supernatant  v a r i e d between 93 and 192 mg/1 2.  T-20 e f f l u e n t .  during these t e s t s . O v e r a l l calcium l o s s e s i n the c a r -  b o n a t i o n s u p e r n a t a n t d u r i n g T-20 e f f l u e n t runs w i t h f r e s h c h e m i c a l s were much h i g h e r than i n BKME runs because i n c o m p l e t e m i x i n g and  C0  2  t r a n s f e r was a c h i e v e d ; 11.5 t o 35.1% o f the t o t a l mass was f o u n d i n t h a t stream.  T h i s amounted t o 15.8 t o 45.0% o f t h e c a l c i u m i n i t i a l l y  p r e s e n t i n the c a r b o n a t e d c o l o u r s l u d g e .  These l a r g e l o s s e s i n the  r e c y c l e d supernatant, coupled with l o s s e s i n the d e c o l o u r i z e d e f f l u e n t , r e s u l t e d i n poor o v e r a l l l i m e r e c o v e r y i n t h e f i n a l s l u d g e .  Only  46.0  85 to 57.9% o f t h e t o t a l C a  i n t h e system ended up i n t h e f i n a l s l u d g e .  + +  L o o k i n g a t t h e c a r b o n a t i o n l o o p a l o n e , t h e r e c o v e r y from t h e mass e n t e r i n g t h e c a r b o n a t o r was a l s o lower than i n BKME t r e a t m e n t  (i.e.,  59.1 t o 79.8%).  sludge  T h i s amount o f c a l c i u m ( a s CaO) i n t h e f i n a l  r e p r e s e n t e d 74.9 t o 81.4% o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s mass l e a v i n g 11.2 t o 20.9% unaccounted  f o r by t h e sum o f MgO and CaO.  These r e s u l t s were s i m i l a r t o t h o s e o b t a i n e d i n t h e BKME r u n s .  Calcium  c o n c e n t r a t i o n i n t h e s u p e r n a t a n t r e c y c l e ranged from 1,050 t o 1,750 mg/1 i n t h e s e t e s t s w i t h f r e s h c h e m i c a l s . B.  F a c t o r s a f f e c t i n g t h e mass b a l a n c e s :  i)  General  Simply s t a t e d , the aim o f carbonating t h e primary c o l o u r s l u d g e i s t o r e c o v e r t h e maximum amount o f s o l u b l e M g n a t a n t , w h i l e m i n i m i z i n g t h e f i n a l c o l o u r and C a same r e c y c l e stream.  + +  + +  i n the super-  release into the  As o u t l i n e d p r e v i o u s l y , t h i s M g  + +  recovery  method r e l i e s on t h e pH - magnesium s o l u b i l i t y r e l a t i o n s h i p .  Reducing  the pH o f t h e c o l o u r s l u d g e by C 0 gas a d d i t i o n , from t h e i n i t i a l pH 2  o f 11 o r 12, t o a f i n a l pH near 7.5 r e s u l t s i n e s s e n t i a l l y complete s o l u b i l i z a t i o n o f Mg(0H) while causing very l i t t l e d i s s o l u t i o n o f the 2  CaC03 p r e c i p i t a t e i n t h e time a l l o w e d .  The r e a c t i o n s and r a t e con-  s t a n t s c o n t r o l l i n g C 0 n e u t r a l i z a t i o n have been g i v e n by C o t t o n and 2  Wilkinson  (1972). The n e u t r a l i z a t i o n o f C 0 o c c u r s by two p a t h ways. 2  A t pH  >10, t h e p r e d o m i n a n t r e a c t i o n i s t h e d i r e c t r e a c t i o n o f C 0 •+ 0H~: 2  C0 then  2  + OH" = H C 0 " (slow)  HCO3"  3  + OH" = C 0 " + H 0 ( I n s t a n t a n e o u s ) 2  3  2  (1) (2)  86 where t h e r a t e law i s -d[C0 ] —^ 2  and  k -  =  k - [OH ] [ C 0 ] 2  = 8500 s e c "  Q H  (3)  -  Q H  (mol/1)"  1  1  For pH <8 t h e p r i n c i p a l mechanism i s d i r e c t h y d r a t i o n o f C 0 : 2  C0 + H 0 = H C0 2  then  2  2  (slow)  3  H C 0 + OH" = H C 0 " 2  3  (4)  + H 0 (instantaneous)  3  (5)  2  where t h e r a t e law i s pseudo - 1 s t o r d e r -d[C0 ] —nt~ 2  and  K  CQ  2  =  k  [C0 ]  C 0 2  (6)  2  = 0.03 s e c "  1  In t h e pH range 8 t o 10, b o t h mechanisms a r e i m p o r t a n t h y d r a t i o n r e a t i o n (1) and ( 4 ) , t h e r e i s a c o r r e s p o n d i n g  and f o r each dehydration  reaction. H C0 2  3  H 0 + C0 2  where k ^ Q Q  =  (7)  2  20 s e c "  1  and HG0 " -»• C 0 + OH" 3  (8)  2  where k HC0 - =_ 2 „x 10 -t u r n  0  s e-c i  n n  3  From t h e f i r s t s e t o f e q u a t i o n s , i t can be seen t h a t , i n i t i a l l y , t h e r a t e o f d i s s o l u t i o n o f M g ( 0 H ) w i l l be governed by a l k a l i n i t y and 2  C 0 s o l u b i l i t y , which i n t u r n i s a f f e c t e d by t e m p e r a t u r e , as shown i n 2  T a b l e 17. As t h e pH d r o p s below 8, o n l y C 0  solubility controls.  2  I t i s w e l l known t h a t H C 0 + C a C 0 can r e a c t t o g i v e s o l u b l e 2  3  3  C a ( H C 0 ) , so t h a t a f t e r r e a c t i o n (4) has taken p l a c e , some C a C 0 3  2  3  d i s s o l u t i o n c o u l d be a n t i c i p a t e d a t pH below 8, a l t h o u g h t h i s r e a c t i o n w i l l have t o compete w i t h t h e d e h y d r a t i o n  reaction (7).  87  TABLE 17 Temp °C  Carbon Dioxide a*  q  0 1 2 3 4  1.713 1.646 1.584 1.527 1.473  0.3346 0.3213 0.3091 0.2978 0.2871  5  9  1.424 1.377 1.331 1.282 1.237  0.2774 0.2681 0.2589 0.2492 0.2403  10 11 12 13 14  1.194 1.154 1.117 1.083 1.050  0.2318 0.2239 0.2165 0.2098 0.2032  15 16 17 18 19  1.091 0.985 0.956 0.928 0.902  0.1970 0.1903 0.1845 0.1789 0.1737  20 21 22 23 24  0.878 0.854 0.829 0.804 0.781  0.1688 0.1640 0.1590 0.1540 0.1493  25 26 27 28 29  0.759 0.738 0.718 0.699 0.682  0.1449 0.1405 0.1366 0.1327 0.1292  30 35 40 45 50  0.665 0.592 0.530 0.479 0.436  0.1257 0.1105 0.0973 0.0860 0.0761  6  7 8  60  0.359 0.0578 (Lange & F o r k e r , 1967) The column headed " a " g i v e s t h e volume o f gas r e d u c e d t o s t a n d a r d c o n d i t i o n s (0°C a n d 760 riim) d i s s o l v e d i n one volume o f w a t e r when t h e p r e s s u r e o f t h e gas ( w i t h o u t t h e aqueous t e n s i o n ) i s 760 mm; t h i s v a l u e " a " i s t h e a b s o r p t i o n c o e f f i c i e n t " . The column headed "q" g i v e s t h e w e i g h t o f gas i n grams d i s s o l v e d i n 100 grams o f w a t e r a t a t o t a l p r e s s u r e ( p a r t i a l p r e s s u r e o f t h e gas p l u s t h e aqueous t e n s i o n a t t h e s t a t e d t e m p e r a t u r e ) o f 760 mm.  88 B l a c k and E i d s n e s s (1957), c a r b o n a t i n g a s l u d g e c o n t a i n i n g M g ( 0 H ) and 36 g/1 o f C a C 0 w i t h 11% C 0 , found t h a t o n l y 80 mg/1 2  3  of  2  C a C 0 was d i s s o l v e d a f t e r 30 m i n u t e s ' c a r b o n a t i o n , a t a gas f l o w f i v e 3  t i m e s t h a t r e q u i r e d t o d i s s o l v e a l l o f the M g ( 0 H ) p r e s e n t . 2  According  t o J o h n s t o n (1915), who s t u d i e d the s o l u b i l i t y o f c a l c i u m and magnesium c a r b o n a t e s i n n a t u r a l w a t e r s , the e q u i l i b r i u m r a t i o a t 16°C i s [ M g ] ++  [Ca }> = 14,000, when the p a r t i a l p r e s s u r e o f C 0 ++  2  g r e a t enough t o p r e v e n t p r e c i p i t a t i o n o f M g ( 0 H ) . 2  i n the atmosphere i s Another explanation  f o r t h e s e phenomena i s t h a t a s a t u r a t e d s o l u t i o n o f C a ( H C 0 ) 2 has a 3  lower pH than a s a t u r a t e d s o l u t i o n o f M g ( H C 0 ) . 3  2  As c a r b o n a t i o n  p r o c e e d s , the pH i s b u f f e r e d a t a pH o f a p p r o x i m a t e l y 7.5, due t o the Mg(HC0 ) , a l l o w i n g l i t t l e of the calcium to d i s s o l v e . 3  2  From r e c e n t l a r g e s c a l e magnesium r e c o v e r y t e s t s on w a t e r t r e a t m e n t s l u d g e s , upper l i m i t s o f 20,000 t o 25,000 mg/1  a l k a l i n i t y at  20 t o 25°C have been found t o be the p r a c t i c a l v a l u e s t o l e r a b l e i n s l u d g e c a r b o n a t i o n , a t the p a r t i a l p r e s s u r e s when u s i n g pure C 0 ; 2  s o l u b i l i z a t i o n has not been s i g n i f i c a n t u n t i l the pH d r o p s below 6.6 (Thompson, 1975). However, t h e s e p r a c t i c a l v a l u e s were unknown t o the a u t h o r a t t h e t i m e o f t e s t i n g , and c l o s e m o n i t o r i n g d u r i n g s l u d g e c a r b o n a t i o n was c a r r i e d o u t t o g a i n a b e t t e r u n d e r s t a n d i n g o f t h e p r o c e s s and i d e n t i f y p r a c t i c a l c o n t r o l methods f o r use i n f u t u r e p i l o t p l a n t operation. T a b l e s 1 t o 8 i n A p p e n d i x D show the r e s u l t s o f a l l the sludge carbonation monitoring runs.  These d a t a , a l o n g w i t h the r e s u l t s  p r e s e n t e d i n T a b l e 14, p r o v i d e d much u s e f u l i n f o r m a t i o n on the f a c t o r s a f f e c t i n g the sludge carbonation process.  89 In g e n e r a l , t h e r e was l i t t l e d i f f e r e n c e i n t h e r e s u l t s o b t a i n e d i n t h e t r e a t m e n t o f t h e two e f f l u e n t t y p e s w i t h f r e s h c h e m i c a l s . The f a c t o r s f o u n d t o a f f e c t t h e outcome o f t h e s l u d g e c a r b o n a t i o n were e s s e n t i a l l y t h e same f o r t o t a l m i l l e f f l u e n t as f o r c a u s t i c e x t r a c t i o n effluent.  The p a r a m e t e r s i d e n t i f i e d as h a v i n g a s i g n i f i c a n t i n f l u e n c e  on t h e mass b a l a n c e r e s u l t s were:  f i n a l s l u d g e volume; f i n a l c a r b o n a t i o n  pH; t i m e ; c o l o u r s l u d g e and f i n a l s l u d g e s o l i d s c o n c e n t r a t i o n ; and mixing.  D i s c u s s i o n o f each f o l l o w s under t h e a p p r o p r i a t e h e a d i n g s , ii)  F i n a l s l u d g e volume  The r e a s o n i n g and m e t h o d o l o g y f o r c a l c u l a t i n g t h e c a r b o n a t i o n l o o p mass b a l a n c e s , on t h e b a s i s o f assumed v a l u e s o f 5% and 60% s o l i d s i n t h e f i n a l s l u d g e , has been d i s c u s s e d e a r l i e r .  If calculations  were made on t h e b a s i s o f 5% s o l i d s i n t h e f i n a l s l u d g e , t h e v a l u e s o f c o l o u r , magnesium and c a l c i u m i n t h e r e c y c l e were lower than on t h e b a s i s o f 60% s o l i d s because o f t h e l o s s e s i n t h e l i q u i d p o r t i o n o f t h e d i l u t e (5%) s l u d g e .  F o r example, r e s u l t s o f BKME t e s t s w i t h f r e s h  c h e m i c a l s showed t h a t o v e r 90% o f t h e magnesium s e n t t o t h e c a r b o n a t o r would be r e c o v e r e d i f t h e f i n a l s l u d g e was d e w a t e r e d t o 60% s o l i d s , whereas o n l y 75 t o 85% r e c o v e r y would be o b t a i n e d i f t h e f i n a l s l u d g e was o n l y 5% s o l i d s .  On t h e o t h e r hand, about 3% more c o l o u r and 1%  more c a l c i u m were r e c y c l e d a t t h e h i g h e r s o l i d s c o n t e n t . R e s u l t s o f T-20 t e s t s show more o f a d i f f e r e n c e i n mass b a l a n c e r e s u l t s because o f t h e l a r g e r volume o f s l u d g e p r o d u c e d . A t 60% s o l i d s , 90% magnesium r e c o v e r y r e s u l t e d , b u t a t 5% s o l i d s o n l y 68 to 79% o f t h e magnesium i n t h e c a r b o n a t o r was r e c o v e r e d i n t h e r e c y c l e . In t h e s e t e s t s , 3 t o 5% more c o l o u r and about 6% more c a l c i u m was recycled a t the higher sludge concentration.  90 O b v i o u s l y , t h e magnesium l o s s e s and c a l c i u m r e c o v e r i e s i n the f i n a l s l u d g e a r e a f f e c t e d i n a s i m i l a r manner.  Several final  h a n d l i n g methods a r e a v a i l a b l e and t h e one chosen f o r a l a r g e s c a l e a p p l i c a t i o n w i l l have s i g n i f i c a n t e f f e c t s on t h e c h e m i c a l r e c o v e r i e s achieved. iii)  C a r b o n a t i o n pH  U n d o u t e d l y , pH was t h e most i m p o r t a n t f a c t o r a f f e c t i n g t h e outcome o f t h e s l u d g e c a r b o n a t i o n p r o c e s s .  A f i n a l c a r b o n a t i o n pH  below 7.5 was s e l e c t e d f o r t h e f i r s t runs w i t h s a m p l i n g a t v a r i o u s time i n t e r v a l s d u r i n g c a r b o n a t i o n .  S l u d g e pH i n t h e c a r b o n a t o r and  s l u d g e f i l t r a t e pH were both measured.  The f i l t r a t e pH was c o n s i s -  t e n t l y h i g h e r (.1 t o 1 pH u n i t ) than t h e s l u d g e pH i n t h e c a r b o n a t o r and i t soon became a p p a r e n t t h a t c o n t i n u o u s pH measurement i n t h e c a r b o n a t i o n c y l i n d e r would p r o v i d e t h e b e s t i n d i c a t i o n o f t h e c a r bonation progress.  A l l f u r t h e r runs were m o n i t o r e d i n t h i s manner,  w i t h CO2 gas f l o w b e i n g v a r i e d m a n u a l l y and s h u t o f f when a s l u d g e pH of 7.5 was r e a c h e d .  The r e s u l t s o f a l l c a r b o n a t i o n m o n i t o r i n g runs  a r e p r e s e n t e d i n T a b l e s 1 t o 8 o f Appendix D. T y p i c a l pH v s . c o l o u r , M g  + +  and C a  + +  i n the supernatant f o r  BKME and T-20 e f f l u e n t c o l o u r s l u d g e c a r b o n a t i o n w i t h f r e s h c h e m i c a l s a r e shown g r a p h i c a l l y i n F i g u r e s 11 and 12. S e v e r a l g e n e r a l o b s e r v a t i o n s c a n be made from t h e s e r e s u l t s . C o l o u r and magnesium r e l e a s e were v e r y c l o s e l y r e l a t e d during a l l tests.  L i t t l e r e l e a s e o f t h e s e m a t e r i a l s o c c u r r e d above pH  10.5, w i t h t h e b u l k o f t h e c o l o u r and M g  + +  b e i n g r e l e a s e d between pH  10.0 and pH 8.5. In a l l r u n s , a d e f i n i t e . l e v e l l i n g o f f t r e n d i n c o l o u r and M g  + +  c o n c e n t r a t i o n was n o t e d as t h e pH d e c r e a s e d below 8.5.  91  11  9  10  8  7  PH IGURF11 p H V s C O L O U R , M g and C a I N T H E S U P E R N A T A N T F R O M A T Y P I C A L B K M E S L U D G E C A R B O N A T I O N USING F R E S H CHEMICALS. + +  *-  CHANGE  IN C O N C E N T R A T I O N  AND  + +  pH  DURING  SLUDGE  SETTLING  92  r 16000  14000  120CH  1000  800  400  200  r  IGURE 12 pH Vs COLOUR , M g + + , C a . IN THE SUPERNATANT FROM A TYPICAL T-20 SLUDGE CARBONATION USING FRESH CHEMICALS. ++  *  CHANGE  IN C O N C E N T R A T I O N  A N D pH DURING  SLUDGE  SETTLING  In some c a s e s the measured c o l o u r o f the s u p e r n a t a n t even s l i g h t l y a t pH's below 8.0.  93 decreased  T h i s was t h o u g h t t o be due t o some c a l c i u m  c a r b o n a t e coming o u t o f s o l u t i o n and p o s s i b l e r e p r e c i p i t a t i n g c o l o u r m o l e c u l e s p r i o r t o the c o l o u r d e t e r m i n a t i o n .  Magnesium, on the o t h e r  hand, c o n t i n u e d t o i n c r e a s e s l i g h t l y as the pH approached 7.5.  Mass  d a t a from Runs #3 and 4 showed t h a t magnesium r e c o v e r y c o u l d be s l i g h t l y by c a r b o n a t i n g t o a pH near  improved  7.3.  The c r i t i c a l parameter g o v e r n i n g the a c c e p t a b i l i t y o f t h e magnesium r e c o v e r y p r o c e s s i s t h o u g h t t o be the p e r c e n t MgO i n the i n c i n e r a t e d f i n a l sludge s o l i d s .  A s m a l l amount o f MgO i n t h e r e c a l -  c i n e d l i m e i s d e s i r e d t o a v o i d problems o f magnesium b u i l d u p i n the r e c o v e r y system o f t h e m i l l , because o f i t s a d v e r s e e f f e c t on l i m e r e a c t i v i t y as w e l l as on s e d i m e n t a t i o n and f i l t r a t i o n r a t e s . Average v a l u e s o f MgO i n commercial  high calcium quicklime  and r e b u r n e d l i m e have been g i v e n by J o h n s t o n e t a l (1968) as .3 t o 2.5% and .5 t o 3.0%, r e s p e c t i v e l y , whereas d o l o m i t i c l i m e may c o n t a i n 37 t o 41% MgO a c c o r d i n g t o the N a t i o n a l Lime A s s o c i a t i o n (1951).  In  t h e s e runs u s i n g f r e s h c h e m i c a l s , 2.9 t o 8.9% o f the i n c i n e r a t e d s l u d g e s o l i d s mass was a c c o u n t e d f o r by MgO.  The maximum p e r m i s s i b l e  l e v e l o f MgO i n a l i m e f o r r e u s e i n a k r a f t m i l l w i l l v a r y from m i l l t o m i l l , but i s w e l l above t h i s r a n g e , a c c o r d i n g t o Smook (1975); i n any c a s e , a c c o r d i n g t o Thompson (1975), w i t h o p t i m i z a t i o n o f the p r o c e s s , much b e t t e r l i m e q u a l i t y s h o u l d be a c h i e v a b l e . However, i n a f u l l s c a l e o p e r a t i o n , i f the magnesium c o n t e n t o f the f i n a l s l u d g e i s h i g h e r than the p e r m i s s i b l e l e v e l , t h i s would d i c t a t e c a r b o n a t i n g t o a lower pH. s e r i o u s l y a f f e c t the C a  + +  Such a c o u r s e o f a c t i o n c o u l d  mass b a l a n c e r e s u l t s . The c o n c e n t r a t i o n  94 p r o f i l e f o r C a , as the pH d e c r e a s e d , was q u i t e d i f f e r e n t from t h o s e + +  o f c o l o u r and magnesium, r e f l e c t i n g t h e e f f e c t o f pH on C a C 0 In a l l c a s e s , C a  + +  3  solubility.  c o n c e n t r a t i o n dropped from the upper pH t o a minimum  v a l u e (around 60 mg/1)  between pH 10.5 and 9.5, t h e n i n c r e a s e d g r e a t l y  as t h e pH was l o w e r e d .  Larger incremental increases i n C a  as the pH d e c r e a s e d below 8.0 and l a r g e C a  + +  + +  occurred  l o s s e s r e s u l t e d i n runs  where c a r b o n a t i o n was n o t s t o p p e d as soon as the measured s l u d g e pH r e a c h e d 7.5.  However, as d i s c u s s e d l a t e r , m i x i n g c o n d i t i o n s were such  t h a t a n o n - u n i f o r m pH d i s t r i b u t i o n a c t u a l l y e x i s t e d i n t h e c a r b o n a t o r , p o s s i b l y causing the e x c e s s i v e C a The pH e f f e c t on C a  + +  + +  dissolution.  c o n c e n t r a t i o n i n the s u p e r n a t a n t  was  more n o t i c e a b l e i n t h e T-20 e f f l u e n t t e s t s than i n BKME r u n s , w i t h as much as 40 and 45% C a only d i d these C a  + +  + +  r e l e a s e i n Runs #3 and 4, r e s p e c t i v e l y .  Not  losses represent a direct reduction in recoverable  l i m e i n the f i n a l s l u d g e , but i n the form o f c a l c i u m b i c a r b o n a t e a l k a l i n i t y , t h e y a l s o a d v e r s e l y a f f e c t e d the outcome o f t h e n e x t cycle.  T h i s i s d i s c u s s e d l a t e r i n the s e c t i o n on t h e use o f r e c y c l e d  magnesium. T h e r e f o r e , as i n many e n g i n e e r i n g p r o b l e m s , a t r a d e o f f s i t u a t i o n e x i s t s . While c o l o u r r e l e a s e was e s s e n t i a l l y t h e same between pH 8.0 and 7.5, magnesium r e c o v e r y c o n t i n u e d t o  improve  s l i g h t l y and c a l c i u m l o s s e s i n t o the r e c y c l e r o s e markedly o v e r the same pH range.  From t h e s e r e s u l t s , i t can be seen t h a t an o p e r a t i n g  pH near 7.5 m a i n t a i n e d by e f f i c i e n t m i x i n g and C 0  2  d i f f u s i o n , would be  a good t a r g e t f o r any f u t u r e i n v e s t i g a t i o n s . However, more e x t e n s i v e t e s t i n g on a c o n t i n u o u s b a s i s , t a k i n g i n t o a c c o u n t v a r i o u s economic and t e c h n i c a l c o n s i d e r a t i o n s , i s n e c e s s a r y t o e s t a b l i s h an e x a c t optimum s l u d g e c a r b o n a t i o n pH.  95 iv)  Time  Time, i n t h e s l u d g e c a r b o n a t i o n s t e p o f t h i s bench s c a l e work, was n o t an e f f e c t i v e c o n t r o l v a r i a b l e , because o f t h e nonu n i f o r m f l o w o f CO2 gas a l l o w e d d u r i n g t h e t e s t s . However, time d i d have some a f f e c t on t h e f i n a l s u p e r n a t a n t q u a l i t y a c h i e v e d . i n d i c a t e d i n F i g u r e s 11 and 12, t h e c o l o u r , M g  + +  and C a  + +  As concen-  t r a t i o n s i n t h e s u p e r n a t a n t u s u a l l y changed d u r i n g t h e s l u d g e s e t t l i n g p e r i o d i n t h e s e t e s t s . C o l o u r u s u a l l y d e c r e a s e d s l i g h t l y o r remained about t h e same.  Magnesium, on t h e o t h e r hand, u s u a l l y i n c r e a s e d  s l i g h t l y o r stayed constant.  The most n o t a b l e e f f e c t o f " t i m e " , a f t e r  the C 0 gas had been s h u t o f f , was on t h e c a l c i u m c o n c e n t r a t i o n i n t h e 2  supernatant.  In a l l c a s e s , C a  + +  increased appreciably during the  s l u d g e s e t t l i n g p e r i o d , even though t h e measured pH r o s e s l i g h t l y i n most c a s e s . C0  + H 0 ->  2  2  T h i s p o i n t s t o t h e time dependency o f t h e H2CO3  r e a c t i o n , which p r e c e d e s d i s s o l u t i o n t o C a ( H C 0 ) a s 3  d i s c u s s e d p r e v i o u s l y . Thus, i n o r d e r t o reduce C a i m p o r t a n t t o a l l o w o n l y enough time f o r M g  + +  + +  2  losses, i t i s  t o s o l u b i l i z e , then  s e p a r a t e t h e s o l i d and l i q u i d p o r t i o n s q u i c k l y , so t h a t a minimum o f C a ( H C 0 ) 2 s o l u b i l i z e s i n t h e s u p e r n a t a n t r e c y c l e . A l t h o u g h i t was 3  d i f f i c u l t t o s e p a r a t e t h e e f f e c t s o f time and pH d u r i n g t h e s e t e s t s , the r e s u l t s o f carbonation monitoring i n d i c a t e d t h a t , i f the c a r b o n a t i o n c o n t i n u e d f o r more than 60 m i n u t e s , s u b s t a n t i a l amounts o f Ca  + +  were measured i n t h e s u p e r n a t a n t .  On t h e o t h e r hand, when  c a r b o n a t i o n d u r i n g Run #4 was c a r r i e d o u t i n o n l y 25 m i n u t e s , t h e f i n a l pH o f 7.3 r e s u l t e d i n both t h e h i g h e s t r e c o v e r y o f M g highest loss of C a  + +  + +  and t h e  f o r any o f t h e T-20 e f f l u e n t r u n s ; t h i s p o i n t s t o  the r e l a t i v e p o s i t i v e i m p o r t a n c e o f pH, as compared t o t h e n e g a t i v e importance o f time.  96 v)  Colour Sludge S o l i d s Concentration  The s o l i d s c o n c e n t r a t i o n s o f the c o l o u r s l u d g e s e n t t o c a r b o n a t i o n i n each run a r e shown i n T a b l e 14, a l o n g w i t h t h e f i n a l s l u d g e s o l i d s c o n c e n t r a t i o n s a c h i e v e d and the mass b a l a n c e r e s u l t s . A g a i n , i t was d i f f i c u l t t o s i n g l e o u t the e f f e c t o f t h i s one v a r i a b l e , s i n c e the f i n a l pH and o t h e r v a r i a b l e s were not c o n s t a n t i n a l l t h e runs.  However, e a r l y e v i d e n c e o f t h i s d i l u t i o n e f f e c t was n o t i c e d  a f t e r Runs #1 and 2 u s i n g BKME. t r e a t e d was 10 l i t r e s . sludge f o r carbonation.  In t h e s e t e s t s , the volume o f e f f l u e n t  T h i s p r o v i d e d o n l y 620 t o 650 mis o f c o l o u r (Subsequent runs s t a r t e d w i t h more e f f l u e n t  t o a v o i d s l u d g e d i l u t i o n . ) In o r d e r t o have enough s l u d g e f o r s a m p l i n g d u r i n g c a r b o n a t i o n , the s l u d g e was d i l u t e d t o one l i t r e i n Run #1 and to two l i t r e s i n Run #2, r e s u l t i n g i n p e r c e n t s o l i d s c o n c e n t r a t i o n o f .99% and .46%, r e s p e c t i v e l y . Comparing t h e mass b a l a n c e r e s u l t s o f t h e s e and o t h e r c a r b o n a t i o n runs i n P a r t 2 o f T a b l e 14, a s i g n i f i c a n t l y h i g h e r c o l o u r r e l e a s e o c c u r r e d i n t h e more d i l u t e s y s t e m s .  Ca  + +  l o s s e s i n the s u p e r n a t a n t were a l s o h i g h e r i n the more d i l u t e s l u d g e systems.  Both o f t h e s e f a c t o r s p o i n t t o the a d v a n t a g e o f c a r b o n a t i n g  a more c o n c e n t r a t e d c o l o u r s l u d g e .  Unfortunately, i n these t e s t s ,  magnesium r e c o v e r y a l s o d e c r e a s e d s l i g h t l y when more c o n c e n t r a t e d s l u d g e was  carbonated. I t may be a n t i c i p a t e d from r e s e a r c h o f Swanson e t a l (1973),  and o t h e r s i n v e s t i g a t i n g the mechanisms o f c o l o u r removal by c h e m i c a l p r e c i p i t a t i o n , t h a t c h e m i c a l r e a c t i o n s as w e l l as p h y s i c a l i n t e r actions occur during coagulation. D u r i n g the p r e s e n t s t u d y , i t was not p o s s i b l e t o c o n c l u d e w h e t h e r the r e l e a s e s e n c o u n t e r e d d u r i n g c a r b o n a t i o n were caused by the  97 r e v e r s i o n o f a c h e m i c a l r e a c t i o n between c o l o u r and Mg  , as t h e  Mg(0H)2 r e s o l u b i l i z e d , o r w h e t h e r i t was a s i m p l e p h y s i c a l r e l e a s e o f e n t r a p p e d c o l o u r from the f l o e , which was enhanced by d i l u t i o n and mixing.  E x p e r i m e n t s c o n t r o l l i n g d i l u t i o n , m i x i n g , pH and time s h o u l d  be h e l p f u l i n e l u c i d a t i n g t h e mechanism(s) i n v o l v e d i n magnesium coagulation. vi)  Final Sludge S o l i d s Concentration  The a c t u a l s l u d g e s o l i d s c o n c e n t r a t i o n s a c h i e v e d i n each r u n , a f t e r c a r b o n a t i n g t h e c o l o u r s l u d g e , a r e shown a l o n g w i t h the c o l o u r s l u d g e s o l i d s c o n c e n t r a t i o n s and mass b a l a n c e r e s u l t s i n T a b l e 14.  S i n c e d i l u t e c o l o u r s l u d g e u s u a l l y meant d i l u t e f i n a l s l u d g e , t h e  d i s c u s s i o n o f the e f f e c t s o f c o l o u r s l u d g e s o l i d s c o n c e n t r a t i o n i s a p p l i c a b l e here as w e l l .  In g e n e r a l , a more h i g h l y c o n c e n t r a t e d ,  b e t t e r s e t t l i n g f i n a l s l u d g e r e s u l t e d i n lower c o l o u r r e l e a s e , lower Ca  l o s s e s i n t o the s u p e r n a t a n t , and lower Mg  recovery.  These  r e s u l t s may p a r t i a l l y r e f l e c t the d e c r e a s e d m i x i n g e f f i c i e n c y i n t h e denser  systems. vii)  Mixing  M i x i n g i n t h e s e b a t c h c a r b o n a t i o n t e s t s was n o t as e f f i c i e n t as i t s h o u l d have been.  M i x i n g speed was v a r i e d t h r o u g h o u t t h e c a r -  b o n a t i o n t o t r y t o a c h i e v e good C 0  2  d i f f u s i o n through the sludge  without h i n d e r i n g the formation of the f i n a l sludge f l o e .  T h i s was  d i f f i c u l t t o do i n a s i n g l e v e s s e l and s h o u l d not be a t t e m p t e d i n future tests.  CO2 t r a n s f e r and s l u d g e s e t t l i n g would l i k e l y be  a c c o m p l i s h e d b e t t e r i n a two-stage system c o n s i s t i n g o f a p r o p e r l y d e s i g n e d c a r b o n a t o r w i t h a good d i f f u s e r system and complete m i x i n g p r o v i d e d , f o l l o w e d by a s e p a r a t e s l u d g e t h i c k e n e r .  98 Poor m i x i n g , i n some o f t h e runs w i t h t h i c k e r s l u d g e , p r o b a b l y c a u s e d v a r i a b l e s l u d g e pH and a r e s u l t a n t r e d u c t i o n i n M g  + +  recovery  e f f i c i e n c y ( p o c k e t s o f h i g h e r pH) and e x c e s s i v e C a C 0 d i s s o l u t i o n 3  ( p o c k e t s o f lower p H ) . In a l a r g e s c a l e a p p l i c a t i o n , e s p e c i a l l y i f a combined s l u d g e c a r b o n a t o r - t h i c k e n e r i s u s e d , m i x i n g would become a c r i t i c a l f a c t o r i n t h e outcome o f t h e s l u d g e c a r b o n a t i o n s t e p . 6.2  R e s u l t s o f T e s t i n g w i t h R e c y c l e d Magnesium  6.2.1  J a r Test Results  6.2.1.1  General.  To t h e a u t h o r ' s knowledge, no p r e v i o u s c o l o u r  removal work has been done on k r a f t m i l l e f f l u e n t s u s i n g r e c y c l e d s u p e r n a t a n t as a s o u r c e o f M g . ++  recycled Mg  + +  Thompson e t a l (1972) r e p o r t e d t h a t  was as e f f e c t i v e as f r e s h M g  surface waters.  + +  i n treating coloured  However, i t was n o t known whether t o e x p e c t s i m i l a r  r e s u l t s i n t h e s e t e s t s because o f t h e much more i n t e n s l y c o l o u r e d , h i g h l y a l k a l i n e , s u p e r n a t a n t r e c y c l e o b t a i n e d i n t h e t r e a t m e n t o f BKME and T-20 e f f l u e n t s . In g e n e r a l , i t was n e c e s s a r y t o a s s e s s t h e c o l o u r removal e f f i c i e n c y o f r e c y c l e d s u p e r n a t a n t a l o n e and i n c o m b i n a t i o n w i t h v a r i o u s amounts o f makeup MgSO^, t o compare w i t h r e s u l t s o f t e s t s using fresh chemicals.  The same b a s i c c r i t e r i a were used t o s e l e c t  dosage l e v e l s o f l i m e and magnesium f o r use d u r i n g b a t c h t e s t s , t o d e t e r m i n e any s i g n i f i c a n t e f f e c t s o f u s i n g M g  + +  r e c y c l e on t h e o v e r a l l  d e c o l o u r i z a t i o n - r e c o v e r y mass b a l a n c e s . I n i t i a l work w i t h M g  + +  r e c y c l e was done on T-20 e f f l u e n t  s a m p l e s , so r e s u l t s o f t h e s e t e s t s a r e r e p o r t e d f i r s t .  99 6.2.1.2  T-20 E f f l u e n t . S i n c e i t was n o t known w h e t h e r t h e M g  + +  measured i n t h e s u p e r n a t a n t would a l l be a v a i l a b l e f o r a second p r e c i p i t a t i o n , o r whether t h e r e l e a s e d c o l o u r m o l e c u l e s may i n t e r f e r e i n some way, t h r e e s e t s o f j a r t e s t s were d e s i g n e d t o s e p a r a t e t h e r o l e s of C a ( 0 H ) , f r e s h MgS0 and M g 2  4  + +  r e c y c l e , i n c o l o u r removal.  The c o l o u r removal e f f i c i e n c y o f l i m e a l o n e on t h i s e f f l u e n t ( i n i t i a l c o l o u r = 16,000 C U . ) i s shown i n T a b l e 18. I t c a n be seen t h a t o v e r 20,000 mg/1 C a ( 0 H )  2  (15,000 mg/1 CaO) were n e c e s s a r y t o  a c h i e v e 90% c o l o u r r e d u c t i o n . Treatment o f t h e same waste w i t h l i m e a t 2,500 mg/1  Ca(0H)  2  and v a r i o u s dosages o f f r e s h MgSCt a r e shown i n T a b l e 19. In t h e s e t e s t s , 300 mg/1 M g  + +  p r e c i p i t a t e d by o n l y 2,500 mg/1 C a ( 0 H )  mg/1 CaO) p r o v i d e d 92.6% c o l o u r r e d u c t i o n .  Higher M g  + +  t h i s lime l e v e l provided o n l y s l i g h t l y b e t t e r removals.  2  (1,875  dosages a t These r e s u l t s  c o n f i r m t h o s e found i n t h e p r e v i o u s l y d i s c u s s e d j a r t e s t s u s i n g f r e s h c h e m i c a l s and c a n be compared d i r e c t l y t o t h e r e s u l t s i n T a b l e s 20 and 21. The s u p e r n a t a n t from c a r b o n a t i o n Run #5, u s i n g t h e same T-20 e f f l u e n t , was c o l l e c t e d and used f o r j a r t e s t e v a l u a t i o n o f e f f l u e n t c o l o u r removal u s i n g r e c y c l e d M g . ++  The c h a r a c t e r i s t i c s o f t h i s  e f f l u e n t and t h e r e s u l t i n g s u p e r n a t a n t a r e g i v e n i n T a b l e s 12 and 15, respectively.  The M g  + +  c o n c e n t r a t i o n i n t h e r e c y c l e was 1,250 mg/1.  The s u p e r n a t a n t c o l o u r was t h e same as t h e i n i t i a l e f f l u e n t c o l o u r (16,000 C.U.), so t h e i n i t i a l c o l o u r c o n c e n t r a t i o n o f t h e s e  samples  was n o t changed by r e c y c l e a d d i t i o n . The m a j o r e f f e c t o f t h e s u p e r n a t a n t a d d i t i o n was t o i n c r e a s e t h e u n t r e a t e d sample a l k a l i n i t y  because  o f t h e h i g h (6,800 mg/1) a l k a l i n i t y i n t h e c a r b o n a t i o n s u p e r n a t a n t r e l a t i v e t o t h e 1800 mg/1 i n t h e u n t r e a t e d e f f l u e n t .  TABLE 18 JAR TESTS OF T-20 EFFLUENT WITH LIME ALONE I n i t i a l c o l o u r = 16,000 c u . I n i t i a l pH = 11.75 J a r No. 07-21-1 07-21-2 07-21-3 02-21-4 07-21-5 07-21-6  Magnesium (mg/1 as Mg  + +  0 ' ., .. 0 ,0 •, 0 00 b'  )  Lime mg/1 as C a ( 0 H ) CaO 2  1250 2500 5000 10000 20000 40000  950 1875 3750 7500 15000 30000  A23 (mg/1) pH 12.25 12.40 12.46 12.52 12.53 12.55  (CU.) 9800 9000 3600 1950 1450 1000  „ Colour (Mass I n (Mass O u t ^ g as P t ) jTimg as P t )  •  1440 1440 1440 1440 1440 1440  980 900 360 195 145 100  % Removal 31.9 37.5 75.0 86.0 89.9 93.1  o o  TABLE 19 JAR TESTS T-20 EFFLUENT WITH FRESH MgS0  4  I n i t i a l C o l o u r = 16,000 ' I n i t i a l pH = 11.75 J a r No. 07-21-7 07-21-8 07-21-9 07-21-10 07-21-11 07-21-12 07-21-13 07-21-14  Magnesium ++ (mg/1 Mg ) 30 60 90 120 150 300 600 • 1200  Lime mg/1 as Ca(0H) 2  2500 2500 2500 2900 2500 2500 2500 2500  as CaO 1875 1875 1875 1875 1875 1875 1875 1875  A23 mg/1 2 2 2 2 2 2 2 2  PH  (CU.)  12.40 6350 12.35 3400 12.32 3200 12.34 2600 12.30 1900 12.15 1050 11.80 650 10.48 880  Colour (Massil.'n (Mass o u t nra as P t ) , fn : as P t ) r  g  1420 1420 1420 1420 1420 1410 1390 1390  635 340 320 260 190 105 65 88  55.3 76.1 77.5 81.7 .86.6 92.6 95.3 93.5  TABLE 20 JAR TESTS WITH RECYCLED M g  + +  - T-20 EFFLUENT  I n i t i a l C o l o u r = 16,000 c u . I n i t i a l pH = 1 1 . 7 5 S u p e r n a t a n t pH = 7.85 S u p e r n a t a n t C o l o u r = 16,000 c u .  J a r No. 07-22-1 07-22-2 07-22-3 07-22-4 07-22-5 07-22-6  ** R e c y c l e %  100 80* 80* 80* 80* 80*  Magnesium Recycle. 4 (mg/1 M g ) (mg/1 M g ) M g S 0  T+  300 240 240 240 240 240  ++  0 60 90 120 150 300  Lime as mg/1 Ca(0H) 2  2500 2500 2500 2500 2500 2500  Recycled Supernatant contained io 25 mis ~ 30 mg M g  as • A23 CaO mg/1 1875 1875 1875 1875 1875 1875  2 2 2 2 2 2  pH 10.83 11.40 11.48 11.50 11.50 10.90  (CU.) 10750 7650 6550 4300 2600 1700  Colour (Mass In (Mass O u t ' .mg as P t ) :fig as P t ) % Remo' 1420 1420 1420 1420 1420 1420  1250 mg/1 Mg  + +  80% of t h e o r i g i n a l 300 mg/1 used i n t e s t i n g w i t h f r e s h  chemicals  1075 765 655 430 260 170  24.3 46.1 53.9 69.7 81.7 88.0  TABLE 21 JAR TESTS WITH RECYCLED M g  + +  - T-20 EFFLUENT  I n i t i a l C o l o u r = 16,000 c u . I n i t i a l pH = 11.75 S u p e r n a t a n t pH = 7.85 S u p e r n a t a n t C o l o u r = 16,000 c u .  J a r No. 07-22-7 07-22-8 07-22-9 07-22-10 07-22-11 07-22-12  * Recycle %  100 100 100 80 80 80  Magnesium Lime R e c y c l e MgSOa mg/1 as (mg/1 Mg) (mg/1 Mg) C a ( 0 H ) 2  300 300 300 240 240 240  ;  0 0 0 60 60 60  3750 5000 7500 3750 5000 7500  as CaO 2800 3750 5625 2800 3750 5625  A23 mg/1 2 2 2 2 2 2  pH 11. 83 12. 30 12. 50 12. 23 12. 43 12. 55  (CU.)  6500 1900 620 1800 940 580  * Recycled Supernatant contained  Colour (Mass In (Mass Out ,nig as P t ) -nig as Pt.) 1420 1420 1420 1420 1420 1420 1250 mg/1 Mg  650 190 62 180 94 58  % Removal 54.2 86.6 95.6 87.3 93.4 95.9  TABLE 22 JAR TESTS WITH RECYCLED M g  + +  - BKME  I n i t i a l C o l o u r = 1500 c u . I n i t i a l pH = 7.5 S u p e r n a t a n t pH = 7.7 S u p e r n a t a n t c o l o u r = 9400 c u .  J a r No. 07-24-1 07-24-2 07-24-3 07-24-4 07-24-5 07-24-5 07-24-7  * Recycle  Magnesium Recvcle+-K 9 4 ( f r e s h ) 9 • % (mg/1 M q )  Lime mg/1 as Ca(0H)  CaO  Final pH  60 100 0 250 185 100 60 0 500 375 100 60 0 750 560 80 48 20 12 500 375 80 48 12 20 625 475 80 48 20 12 750 560 Same as 07-24-3 e x c e p t 2 mg/1 o f A23 was added  9.98 10.75 11.49 10.80 11.32 11.40 11.49  %  * +  M  M  S 0  ++  2  Total Colour + 1850 1850 1850 1740 1740 1740 1830  C o l o u r Out % Remo cu. 1800 354 95 296 120 109 98  The s u p e r n a t a n t r e c y c l e c o n t a i n e d 960 mg/1 Mg C o l o u r was t h e c a l c u l a t e d combined c o l o u r o f t h e s u p e r n a t a n t a n d e f f l u e n t , ( c u . )  2.4 80.8 94.8 82.9 93.0 93.7 94.1  o -P=>  105 In e v a l u a t i n g t h e e f f i c i e n c y o f t h e r e c y c l e d M g , t e s t s ++ ++ were c o n d u c t e d a t t h e l e v e l o f 300 mg/1 Mg u s i n g 100% r e c y c l e d Mg , ++  ++  and a t 240 mg/1 r e c y c l e d Mg The 8 0 % r e c y c l e d M g  + +  w i t h v a r i o u s amounts o f makeup MgSOi,.  seemed l i k e a r e a s o n a b l e l e v e l t o work w i t h i n  t h e s e p r e l i m i n a r y t e s t s s i n c e i t was w e l l w i t h i n t h e range o f M g recoveries obtained i n the previous batch t e s t s .  + +  However, t h e volumes  o f s u p e r n a t a n t n e c e s s a r y t o p r o v i d e t h e 80% r e c y c l e d Mg  dosage were  s l i g h t l y l a r g e r than t h e y would be i n a f u l l s c a l e p r o c e s s where b e t t e r s l u d g e t h i c k e n i n g c o u l d be p r o v i d e d .  T h i s meant t h a t o n l y  about 65 t o 70% o f t h e t o t a l volume t r e a t e d i n t h e s e j a r t e s t s was raw waste, 20 t o 25% was r e c y c l e d s u p e r n a t a n t and 10% was l i m e s l u r r y .  In  o r d e r t o compare t h e t e s t r e s u l t s , a l l c o l o u r removals were c a l c u l a t e d on t h e mass b a s i s , b u t no r e g a r d was g i v e n t o t h e volume o f s l u d g e generated. ++  The f i r s t s e t o f r e s u l t s , u s i n g r e c y c l e d Mg  at various  l e v e l s o f makeup MgSO^ p r e c i p i t a t e d by 2,500 mg/1 C a ( 0 H ) , i s shown i n 2  T a b l e 20. These r e s u l t s were f a i r l y d i s a p p o i n t i n g . P o o r e r c o l o u r removals r e s u l t e d i n a l l t e s t s . Even t h e use o f 240 mg/1 r e c y c l e d ++ ++ Mg w i t h 300 mg/1 f r e s h Mg gave o n l y 8 8 % c o l o u r r e m o v a l . T h i s was e q u i v a l e n t t o t h e l e v e l a c h i e v e d by u s i n g o n l y 150 mg/1 o f f r e s h M g  + +  as shown by t h e r e s u l t s i n T a b l e 19. The o b v i o u s r e a s o n was t h e much l o w e r f i n a l pH r e a c h e d i n t h e s e t e s t s compared t o t h e t e s t s on t h e same e f f l u e n t w i t h f r e s h MgS0 ( T a b l e 19). 4  r e a c h e d w i t h 300 mg/1 f r e s h M g  + +  Whereas a pH o f 12.15 was  p l u s 2,500 mg/1 C a ( 0 H ) , a pH o f o n l y  10.83 was r e a c h e d when 100% r e c y c l e d M g  2  + +  was used.  From c a l c u l a t i o n s ,  i t was n o t e d t h a t t h e a l k a l i n i t y o f t h e combined raw waste p l u s c a r b o n a t i o n s u p e r n a t a n t was about 2,900 mg/1, compared t o 1,800 i n t h e  106 e f f l u e n t alone.  T a b l e 21 shows t h e r e s u l t s o f j a r t e s t s aimed a t  d e t e r m i n i n g whether i n c r e a s e d l i m e dosage would improve t h e c o l o u r reduction, or i f possibly the recycled Mg pH l e v e l .  + +  was n o t e f f e c t i v e a t any  F o r t u n a t e l y , e x c e l l e n t r e s u l t s were o b t a i n e d from t h e s e j a r  tests. ++  The r e l a t i v e e f f e c t o f t h e r e c y c l e d Mg  c a n be seen by  comparing t h e r e s u l t s i n T a b l e 21 w i t h t h o s e i n T a b l e 18; 300 mg/1 o f 100% r e c y c l e d M g  + +  w i t h 7,500 mg/1 C a ( 0 H )  2  gave 95.6% c o l o u r removal  compared t o o n l y about 8 0 % removal w i t h t h e same amount o f l i m e a l o n e . In g e n e r a l , when t h e f i n a l c o a g u l a t i o n pH approached 12.3, c o l o u r removals o f 90 t o 9 5 % were a c h i e v e d , both w i t h 100% r e c y c l e d M g  + +  (300  mg/1) and.with 8 0 % r e c y c l e d M g , p l u s 20% makeup MgS0 (300 mg/1 as ++  4  Mg  + +  total). These r e s u l t s were s i m i l a r t o t h o s e o b t a i n e d i n t e s t i n g w i t h  f r e s h c h e m i c a l s and i n d i c a t e t h a t t h e magnesium i n t h e s u p e r n a t a n t r e c y c l e i s i n d e e d a v a i l a b l e and i s an e f f e c t i v e s o u r c e o f M g p r e c i p i t a t i o n with lime. not a major c o n c e r n .  + +  for  The r e l e a s e d c o l o u r i n t h e s u p e r n a t a n t was  However, i n o r d e r t o r e a c h t h i s pH, a l i m e  dosage o f 3,750 t o 5,000 mg/1 Ca(0H)2 was r e q u i r e d t o overcome t h e a l k a l i n i t y i n t h e s e t e s t s compared t o 2,500 mg/1 C a ( 0 H ) fresh  MgSOit  2  when t h e  was used.  I t s h o u l d be n o t e d t h a t t h e polymer dosage o f 2 mg/1 used i n t h e s e t e s t s was a g a i n c r i t i c a l i n a c h i e v i n g good s e t t l i n g .  Monitoring  o f pH d u r i n g c o a g u l a t i o n showed t h a t i t s t a b i l i z e d w i t h i n f i v e m i n t u e s , i n most c a s e s , a s i t d i d d u r i n g t e s t i n g w i t h f r e s h c h e m i c a l s . W h i l e f u r t h e r j a r t e s t i n g would be r e q u i r e d o v e r a w i d e r range o f o p e r a t i n g c o n d i t i o n s , t o a r r i v e a t optimum economic c o n d i t i o n s  107 f o r a l a r g e s c a l e a p p l i c a t i o n , t h e s e r e s u l t s were s u f f i c i e n t t o s e l e c t dosages f o r use i n subsequent  batch t e s t s during t h i s study.  c h e m i c a l dosages chosen f o r use i n Run #6 were 300 mg/1 M g r e c y c l e and 2 0 % MgSO^ makeup) a l o n g w i t h 5,000 mg/1 C a ( 0 H )  2  + +  The (80% (3,750  mg/1 CaO) and 2 mg/1 a n i o n i c p o l y m e r (Dow A-23). 6.2.1.3  BKME.  In t h e s e t e s t s , s u p e r n a t a n t from c a r b o n a t i o n Run #7  was used as t h e s o u r c e  o f magnesium i o n s .  The same i n i t i a l BKME  sample was t r e a t e d i n Run #7, t h e s e j a r t e s t s , and Run #8. The i n i t i a l c h a r a c t e r i s t i c s o f t h i s e f f l u e n t and s u p e r n a t a n t a r e shown i n T a b l e s 12 and 15, r e s p e c t i v e l y . The M g  + +  c o n c e n t r a t i o n i n t h e r e c y c l e was 960 mg/1 and t h e  c o l o u r was 9,400 C U . compared t o 1 ,500 C U . i n t h e u n t r e a t e d waste. T h e r e f o r e , a d d i n g 6.25 mis (100% r e c y c l e d M g ) o f s u p e r n a t a n t t o t h e ++  100 ml j a r s meant a c o l o u r i n c r e a s e from 1 ,500 C U . t o 1 ,850 C U . i n t h e j a r t e s t s . When 8 0 % r e c y c l e and 2 0 % makeup was used, t h i s r e s u l t e d i n a combined i n i t i a l c o l o u r o f 1 ,740 C U . a t a r e c y c l e volume o f 5%. Againi t h i s percentage o f r e c y c l e d M g ++ Mg  + +  was w e l l w i t h i n t h e range o f  r e c o v e r y o b t a i n e d i n t h e b a t c h t e s t s , and t h e 5% volume was c l o s e  to t h a t e x p e c t e d i n p r a c t i c e , a s shown by t h e volume b a l a n c e s i n T a b l e 16. Based on t h e work w i t h T-20 e f f l u e n t , a j a r t e s t was s e t up to d e t e r m i n e t h e i n c r e a s e d l i m e dosage ( i f a n y ) r e q u i r e d t o p r o v i d e t h e same 90 t o 95% c o l o u r removal u s i n g r e c y c l e d M g . ++  R e s u l t s , shown  i n T a b l e 22, were s i m i l a r t o t h o s e o b t a i n e d i n t h e T-20 e f f l u e n t t e s t s w i t h r e c y c l e ( T a b l e 21).  In t h e s e t e s t s t h e same 60 mg/1 and 500 mg/1  C a ( 0 H ) , used i n t e s t s w i t h f r e s h c h e m i c a l s , r e s u l t e d i n f i n a l pH 2  v a l u e s o f o n l y 10.75 and 10.80, p r o v i d i n g c o l o u r r e d u c t i o n s o f 80.8  108 and 8 2 . 9 % when 100% r e c y c l e and 80% r e c y c l e p l u s 20% makeup, r e s p e c t i v e l y , were used.  However, when t h e pH was r a i s e d t o 11.3, by u s i n g 625 mg/1  C a ( 0 H ) , 93.0% c o l o u r removal was a t t a i n e d . 2  A t a h i g h e r l i m e l e v e l , even more c o l o u r was removed.  These  r e s u l t s c a n be compared t o t e s t s o f BKME t r e a t m e n t w i t h l i m e a l o n e and l i m e p l u s f r e s h magnesium i n T a b l e s 5 t o 8. A l t h o u g h s l i g h t l y d i f f e r e n t waste c h a r a c t e r i s t i c s were e v i d e n t i n t h e s e v a r i o u s t e s t s , i t c a n be c o n c l u d e d t h a t t h e r e c y c l e d s u p e r n a t a n t was an e f f e c t i v e s o u r c e o f Mg  . The i n c r e a s e d l i m e r e q u i r e d t o r e a c h a pH n e a r 11.3 c a n be  a t t r i b u t e d t o t h e i n c r e a s e i n i n i t i a l a l k a l i n i t y from 180 mg/1 t o a p p r o x i m a t e l y 360 mg/1 by t h e a d d i t i o n o f 5 m i s o f s u p e r n a t a n t , h a v i n g an a l k a l i n i t y o f 3,650 mg/1. The s l u d g e i n t h e s e t e s t s s e t t l e d w e l l , and i n t h e one r u n where a polymer was u s e d , no improvement i n s e t t l i n g o r c o l o u r removal resulted. From t h e s e r e s u l t s , t h e dosage l e v e l s s e l e c t e d f o r u s e i n the n e x t b a t c h r u n were 60 mg/1 M g a l o n g w i t h 625 mg/1 C a ( 0 H )  2  + +  (80% r e c y c l e and 20% makeup)  (475 mg/1 CaO).  6.2.2  Batch D e c o l o u r i z a t i o n and Magnesium R e c o v e r y R e s u l t s  6.2.2.1  General Batch t e s t s w i t h BKME (Run #8) and T-20 e f f l u e n t (Run #6)  were c a r r i e d o u t u s i n g c a r b o n a t i o n s u p e r n a t a n t from Runs #7 and 5, respectively.  In Runs #7 and 8, BKME from t h e same c o n t a i n e r was  t e s t e d , and i n Runs #5 and 6, T-20 e f f l u e n t from t h e same c o n t a i n e r was used.  T h e r e f o r e , r e s u l t s o f Runs #8 and 7 c a n be compared d i r e c t l y ,  as c a n r e s u l t s o f Runs #6 and 5, t o e v a l u a t e t h e e f f e c t o f r e c y c l e d  109 s u p e r n a t a n t on t h e mass b a l a n c e s t h r o u g h o u t  t h e system. B a s i c a l l y ,  the o b j e c t i v e s were t h e same as f o r t h e b a t c h t e s t s u s i n g f r e s h c h e m i c a l s , o n l y more emphasis was p l a c e d on i d e n t i f y i n g any b e n e f i c i a l or detrimental e f f e c t s the recycled supernatant  had on t h e r e s u l t s .  The same g e n e r a l s o u r c e s and s i n k s as i d e n t i f i e d i n F i g u r e 10 a p p l i e d t o t h e s e r u n s , remembering t h a t DOSE i s now 80% r e c y c l e d Mg  . DOSE a l s o c o n t r i b u t e d t o t h e c o l o u r , Ca  , a l k a l i n i t y and o t h e r  components o f t h e raw e f f l u e n t . The r e s u l t s o f t h e two b a t c h t e s t s w i t h r e c y c l e d M g  + +  are  p r e s e n t e d below and d i s c u s s e d m a i n l y i n t h e l i g h t o f any d i f f e r e n c e s between r e s u l t s o f Runs #7 and 8 (BKME) and Runs #5 and 6 (T-20 e f f l u e n t ) . 6.2.2.2  Batch  Decolourization  A.  Mass b a l a n c e s  i)  BKME  T a b l e 12 shows t h a t i n i t i a l e f f l u e n t c h a r a c t e r i s t i c s and c h e m i c a l d o s a g e s i n Runs #7 and 8 were e s s e n t i a l l y t h e same e x c e p t f o r the h i g h e r l i m e dosage used i n Run #8 (625 mg/1 i n s t e a d o f 500 mg/1 Ca(0H) ). 2  The r e s u l t i n g c h a r a c t e r i s t i c s o f t h e combined  supernatant  and e f f l u e n t a r e n o t shown, b u t as d i s c u s s e d i n t h e j a r t e s t s e c t i o n , combined u n t r e a t e d c o l o u r was a b o u t 1 ,800 C U . and a l k a l i n i t y was approximately  360 mg/1 as C a C 0 . 3  In Run #8, t h e c o a g u l a t i o n pH o f 11.4 was t h e same as i n Run #7, r e s u l t i n g i n 94.8% c o l o u r removal ( r e s i d u a l = 100 C U . ) c a l c u l a t e d from an i n i t i a l c o l o u r o f 1 ,500 C U .  T h i s was e q u i v a l e n t t o t h e 95.5%  removal ( r e s i d u a l = 70 C U . ) a c h i e v e d w i t h f r e s h c h e m i c a l s , i f c a l c u l a t e d from an i n i t i a l c o l o u r o f 1 ,800 C U .  Both e f f l u e n t s were  s l i g h t l y overtreated, according to the c r i t e r i a established f o r this  110 s t u d y , because o f t h e lower than normal i n i t i a l c o l o u r .  I t i s interest!*  to n o t e t h a t c a l c i u m l o s s e s i n t o t h e d e c o l o u r i z e d e f f l u e n t were s i g n i f i c a n t l y lower i n Run #8, u s i n g r e c y c l e d s u p e r n a t a n t , than i n t h e previous run using fresh chemicals.  The 93 mg/1 C a  + +  measured i n Run  #8 was a p p r o x i m a t e l y h a l f t h e 175 mg/1 i n Run #7 and a s a p e r c e n t o f t h e t o t a l mass l o s t , t h i s r e p r e s e n t e d a r e d u c t i o n from 53.4 t o 23.2% in the r e c y c l e run.  T h i s c a n be a t t r i b u t e d t o t h e b e t t e r f l o e formed  and t h e b e t t e r s e t t l i n g s l u d g e t h a t r e s u l t e d i n l e s s C a C 0 f l o e c a r r y 3  o v e r when t h e r e c y c l e d m a t e r i a l was used.  The f a c t t h a t a b e t t e r  c o l o u r s l u d g e was formed i n Run #8 i s v e r i f i e d by t h e h i g h e r s o l i d s c o n c e n t r a t i o n (2.24% s o l i d s compared t o 1.25% i n Run #7), a s shown i n T a b l e 14, and a l s o t h e l o w e r s l u d g e volume p r o d u c e d (5.2% o f t h e o r i g i n a l i n Run #8 compared t o 6.0% i n Run #7), shown i n T a b l e 16. The s m a l l d i f f e r e n c e i n M g  + +  l o s s e s between t h e two runs  (4.75 mg/1 i n Run #8 and 4.25 i n Run #7) i s w i t h i n t h e e x p e r i m e n t a l e r r o r o f t h e a n a l y t i c a l method used f o r M g was no s i g n i f i c a n t d i f f e r e n c e i n M g ii)  + +  + +  determination, so there  losses into the treated effluent,  T-20 E f f l u e n t  A g a i n , T a b l e 12 shows t h a t i n i t i a l e f f l u e n t c h a r a c t e r i s t i c s and c h e m i c a l dosages i n Runs #5 and 6 were a p p r o x i m a t e l y t h e same e x c e p t f o r t h e 5,000 mg/1 Ca(0H)2 used i n Run #6, compared t o 2,500 mg/1 C a ( 0 H )  2  used i n Run #5 w i t h f r e s h NlgSOi*.  Since the colour of the  s u p e r n a t a n t was 16,000 C.U., as was t h e u n t r e a t e d T-20 e f f l u e n t , t h e combined c o l o u r was unchanged.  However, as mentioned i n t h e d i s -  c u s s i o n o f t h e j a r t e s t s , t h e combined u n t r e a t e d a l k a l i n i t y o f Run #6 was about 2,900 mg/1, compared t o about 1,800 mg/1 i n t h e raw waste t r e a t e d i n Run #5.  Ill  The c o a g u l a t i o n pH o f 12.35 r e a c h e d i n Run #6 was s l i g h t l y h i g h e r than t h e pH o f 12.25 i n Run #5, r e s u l t i n g i n a r e s i d u a l c o l o u r o f 940 C U . and 900 C.U., r e s p e c t i v e l y . T h i s d i f f e r e n c e i s a g a i n w i t h i n t h e e x p e r i m e n t a l e r r o r o f t h e c o l o u r d e t e r m i n a t i o n , so c a n n o t be c o n s i d e r e d s i g n i f i c a n t .  On a p e r c e n t mass b a s i s , 94.8% and 9 5 . 1 %  c o l o u r removal r e s u l t e d i n Runs #6 and 5, r e s p e c t i v e l y . In Run #6, t h e C a  l o s s i n t o t h e d e c o l o u r i z e d e f f l u e n t was  + +  lower than i n any o f t h e T-20 e f f l u e n t runs w i t h f r e s h c h e m i c a l s . The Ca  + +  c o n c e n t r a t i o n i n Run #6 was 313 mg/1 compared t o 390 mg/1 i n Run  #5 and because t h e t o t a l mass o f C a  i n Run #6 was h i g h e r , t h e p e r c e n t  + +  l o s t i n Run #6 (8.5%) was much lower t h a n i n Run #5 ( 2 1 . 1 % ) . ++  The r e d u c e d Ca  l o s s e s i n t o t h e t r e a t e d e f f l u e n t c a n be  a t t r i b u t e d t o t h e l a r g e r l i m e dosage u s e d , which r e s u l t e d i n b e t t e r s l u d g e c h a r a c t e r i s t i c s and l e s s C a C 0 f l o e c a r r y o v e r . S l u d g e s e t t l i n g 3  was e x c e l l e n t a t t h e 2 mg/1 polymer dosage used and t h e r e s u l t i n g 4% s o l i d s i n Run #6 c o l o u r s l u d g e was t w i c e t h a t a c h i e v e d i n Run #5 w i t h f r e s h chemicals (Table 14).  R e s u l t a n t s l u d g e volume d e c r e a s e d from  22.8 t o 21.8% o f t h e o r i g i n a l when r e c y c l e d s u p e r n a t a n t was used as the M g  s o u r c e i n Run #6.  + +  The measured M g total.  + +  l o s s i n Run #6 was 3.6 mg/1 o r .9% o f t h e  T h i s was w i t h i n t h e range f o u n d i n t h e t e s t s u s i n g f r e s h  c h e m i c a l s , a l t h o u g h i t was s l i g h t l y h i g h e r than t h e 2.6 mg/1 (.6%) r e s u l t i n g i n Run #5. In a l l r u n s , t h e M g  + +  l o s s was s m a l l , and i t was d i f f i c u l t  t o d e t e r m i n e from t h i s l i m i t e d d a t a whether t h e use o f r e c y c l e d M g made a s i g n i f i c a n t d i f f e r e n c e t o M g effluent.  + +  losses i n the decolourized  + +  112 B.  F a c t o r s a f f e c t i n g t h e mass b a l a n c e s  i)  General  The two r u n s , u s i n g r e c y c l e d s u p e r n a t a n t as a s o u r c e o f M g  + +  t o d e c o l o u r i z e BKME and T-20 e f f l u e n t , g e n e r a l l y c o n f i r m e d t h e f i n d i n g s of the experiments using f r e s h chemicals. U n t r e a t e d waste c h a r a c t e r i s t i c s , f i n a l c o a g u l a t i o n pH, m i x i n g speeds and t i m e s and s l u d g e c h a r a c t e r i s t i c s were i m p o r t a n t factors.  Most o f t h e s e have been mentioned i n t h e p r e c e d i n g s e c t i o n  and r e q u i r e T i t t l e f u r t h e r comment, ii)  C o a g u l a t i o n pH  The e f f e c t o f t h e r e c y c l e d s u p e r n a t a n t c o l o u r and a l k a l i n i t y on e f f l u e n t t r e a t a b i l i t y was t o i n c r e a s e t h e l i m e dosage  requirements  t o a c h i e v e a g i v e n c o a g u l a t i o n pH and c o l o u r r e m o v a l . I f t h e pH o f BKME was r a i s e d above 11.0 by an adequate l i m e dosage, 90 t o 95% c o l o u r removal r e s u l t e d when 60 mg/1 Mg  was p r e s e n t ,  whether i n t h e form o f f r e s h MgS0 s o l u t i o n o r a s Mg(HC0 )2 i n r e c y c l e d 3  4  supernatant. S i m i l a r l y , i f t h e pH o f T-20 e f f l u e n t was r a i s e d above 12.0 by l i m e , 90 t o 9 5 % c o l o u r removal r e s u l t e d when 300 mg/1 M g  + +  was  p r e s e n t whether i n t h e form o f f r e s h o r r e c y c l e d M g . ++  iii)  M i x i n g Speeds and Times  In t h e t r e a t m e n t o f t h e s e e f f l u e n t s w i t h r e c y c l e d m a t e r i a l , s l o w e r m i x i n g speeds and s h o r t e r m i x i n g t i m e s p r o v e d t o be even more i m p o r t a n t than i n t r e a t m e n t w i t h f r e s h c h e m i c a l s .  I f r a p i d mixing ( a t  80 t o 100 rpm) was s t o p p e d one t o two m i n u t e s a f t e r t h e l i m e s l u r r y a d d i t i o n ( o r one minute a f t e r polymer a d d i t i o n , i f used) and f l o c c u l a t i o n ( a t 30 t o 40 rpm) c o n t i n u e d f o r 5 t o 15 m i n u t e s , a good f l o e formed and s e t t l e d w e l l .  In both r e c y c l e r u n s , t h e pH had s t a b i l i z e d  113 a f t e r a f i v e minute f l o c c u l a t i n g time and no improvement i n t h e observed f l o e c h a r a c t e r i s t i c s r e s u l t e d from longer mixing times, iv)  Sludge C h a r a c t e r i s t i c s  The s l u d g e s from runs u s i n g r e c y c l e d M g  + +  settled faster to  a lower volume and h i g h e r p e r c e n t s o l i d s c o n c e n t r a t i o n , p r o b a b l y because o f t h e i r h i g h e r l i m e : magnesium r a t i o .  The main e f f e c t o f  t h i s was t o s i g n i f i c a n t l y r e d u c e t h e c a l c i u m l o s s e s i n t o t h e dec o l o u r i z e d e f f l u e n t by p r e v e n t i n g C a C 0 f l o e c a r r y o v e r . 3  While a p o l y m e r was n o t r e q u i r e d i n t h e t r e a t m e n t o f BKME, i t was an i m p o r t a n t and n e c e s s a r y p a r t o f T-20 e f f l u e n t d e c o l o u r i z a t i o n . A dosage o f 2.0 mg/1 o f an a n i o n i c polymer (Dow A-23) was r e q u i r e d t o p r o v i d e a d e q u a t e f l o e f o r m a t i o n and s e t t l i n g . 6.2.2.3  Batch Sludge Carbonation Results A.  Mass b a l a n c e s  i)  General  F o r c o n v e n i e n c e , t h e mass b a l a n c e r e s u l t s o f t h e runs w i t h r e c y c l e d s u p e r n a t a n t were i n c l u d e d i n t h e same t a b l e s a s r e s u l t s o f the runs w i t h f r e s h c h e m i c a l s ( i . e . , i n A p p e n d i x D and T a b l e 1 4 ) . A l l t h e mass b a l a n c e s were c a l c u l a t e d i n t h e same manner.  The e f f l u e n t  c h a r a c t e r i s t i c s and s u p e r n a t a n t q u a l i t y f o r each r u n c a n be seen i n T a b l e s 12 and 15, r e s p e c t i v e l y , ii) 1.  Colour BKME.  C a l c u l a t e d on t h e b a s i s o f 5% s o l i d s i n t h e  f i n a l s l u d g e , t h e c a r b o n a t i o n s u p e r n a t a n t c o n t a i n e d 25.4% o f t h e t o t a l c o l o u r mass i n t h e system.  T h i s was a c o l o u r r e l e a s e o f 26.8% from  the carbonated c o l o u r sludge.  On t h e b a s i s o f a f i n a l s l u d g e s o l i d s  c o n c e n t r a t i o n o f 60%, t h e s e v a l u e s were i n c r e a s e d t o 34.4% and 36.2%,  114 respectively.  .  These r e s u l t s were i n the range f o u n d i n t e s t s u s i n g  f r e s h c h e m i c a l s , but lower than i n Run #7.  T h i s was a t t r i b u t e d p a r t l y  t o the h i g h e r c o l o u r s l u d g e c o n c e n t r a t i o n i n Run #8 w i t h r e c y c l e . S i n c e l e s s c o l o u r was r e c y c l e d , more was a c t u a l l y d i s p o s e d o f w i t h t h e f i n a l s l u d g e ( i . e . , 60.4 t o 69.4% o f the t o t a l , d e p e n d i n g on the f i n a l sludge s o l i d s concentration). Even though the mass o f c o l o u r i n the c a r b o n a t i o n s u p e r n a t a n t f r o m Run #8 was l e s s t h a n i n Run #7, t h e s u p e r n a t a n t c o l o u r c o n c e n t r a t i o n was h i g h e r .  Due t o t h e h i g h e r f i n a l s l u d g e s o l i d s  c o n c e n t r a t i o n a c t u a l l y a c h i e v e d i n Run #8 (6.33% s o l i d s ) , a lower r e c y c l e volume r e s u l t e d (3.8% o f t h e o r i g i n a l waste volume  treated).  T h i s was lower than i n any o f the o t h e r runs and r e s u l t e d i n a s u p e r n a t a n t c o l o u r o f 13,500 C U . volume i n Run 2.  compared t o 9,400 C U .  i n 4.9% o f t h e  #7. T-20 E f f l u e n t . R e s u l t s o f Run #6 were j u s t as good as  i n any o f t h e runs u s i n g f r e s h c h e m i c a l s and s l i g h t l y b e t t e r than Run #5 on t h e same e f f l u e n t . C o l o u r r e l e a s e was o n l y 16 t o 18%, on t h e b a s i s o f t h e c a l c u l a t i o n .  depending  T h i s meant t h a t g r e a t e r u l t i m a t e  d i s p o s a l o f c o l o u r r e s u l t e d i n t h i s r u n (77.6 t o 78.6% o f t h e t o t a l mass compared t o 70.3 t o 76.4% i n Run  #5).  In t h i s r u n , t h e r e c y c l e volume p e r c e n t a g e was l a r g e r than i n Run #5, due t o the e x t r e m e l y h i g h f i n a l s l u d g e c o n c e n t r a t i o n a c h i e v e d (31.1% s o l i d s ) .  T h i s added d i l u t i o n , a l o n g w i t h the lower  p e r c e n t r e l e a s e , r e s u l t e d i n a lower s u p e r n a t a n t c o l o u r c o n c e n t r a t i o n o f 12,550 C.U., iii) 1.  compared t o 16,000 C U .  i n Run  #5.  Magnesium BKME.  In Run #8, the magnesium r e c o v e r y from t h e  115 c a r b o n a t e d c o l o u r s l u d g e ( T a b l e 14, P a r t 2) was 62.6%, i f t h e f i n a l s l u d g e was 6.33% s o l i d s , o r 8 2 . 3 % i f t h e f i n a l s l u d g e was 60% s o l i d s . T h i s was a d e c r e a s e from t h e 75.6 t o 9 1 . 1 % r e c o v e r y a c h i e v e d i n t h e runs w i t h f r e s h c h e m i c a l s .  I t i s t h o u g h t t h a t a c o m b i n a t i o n o f poor  m i x i n g and h i g h e r s l u d g e s o l i d s c o n c e n t r a t i o n r e s u l t e d i n l o c a l i z e d a r e a s o f h i g h and low pH w h i c h was r e s p o n s i b l e f o r t h i s p o o r e r r e c o v e r y . However, o t h e r f a c t o r s , as d i s c u s s e d l a t e r , may a l s o a d v e r s e l y a f f e c t recovery.  The p o o r e r r e c o v e r y meant t h a t more M g  + +  was l o s t w i t h t h e  f i n a l s l u d g e , a l t h o u g h t h e 15.2 t o 34.4% o f t o t a l mass was n o t t o o much g r e a t e r t h a n t h e 11.5 t o 26.2% l o s t i n Run #7 w i t h f r e s h c h e m i c a l s . I n t e r e s t i n g l y enough, when c a l c u l a t e d a s t h e p e r c e n t o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s , t h e mass o f MgO i n t h e s l u d g e a c c o u n t e d f o r o n l y 3.7% o f t h e t o t a l a s h w e i g h t , compared t o 5.2% i n Run #7. T h i s c a n be e x p l a i n e d by t h e b e t t e r CaO r e c o v e r y i n Run #6, i n c r e a s i n g t h e CaO.MgO r a t i o and d e c r e a s i n g t h e o v e r a l l MgO p e r c e n t o f t h e t o t a l ash w e i g h t . 2.  T-20 E f f l u e n t . Magnesium r e c o v e r y from t h e c a r b o n a t e d  s l u d g e i n Run #6 was 56.7% o r 60.2%, d e p e n d i n g upon whether t h e f i n a l s l u d g e was 3 1 . 1 % o r 6 0 % s o l i d s , r e s p e c t i v e l y . As i n t e s t s w i t h BKME, t h i s was l e s s t h a n t h e 68 t o 9 0 % o b t a i n e d when f r e s h magnesium was used.  A g a i n , t h i s seemed t o be r e l a t e d t o t h e p o o r e r m i x i n g combined  w i t h t h e t h i c k e r c o l o u r s l u d g e ( 4 % s o l i d s ) and t h e e x t r e m e l y dense (31.1% s o l i d s ) f i n a l s l u d g e a c h i e v e d when r e c y c l e d s u p e r n a t a n t was used. In Run #6, t h e p e r c e n t o f t h e t o t a l mass o f M g  + +  i n the  s y s t e m l o s t i n t h e f i n a l s l u d g e was 36.4 t o 39.8, d e p e n d i n g on t h e sludge s o l i d s content.  A l t h o u g h t h i s was h i g h e r than i n runs w i t h  116 f r e s h c h e m i c a l s , t h e MgO p e r c e n t o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s was o n l y 4.8%, compared t o 8.9% i n Run #5 because o f t h e b e t t e r c o n c u r r e n t CaO r e c o v e r y i n t h e r e c y c l e r u n . iv)  Calcium  1.  BKME.  In o r d e r t o i n t e r p r e t t h e mass b a l a n c e p e r c e n t  v a l u e s f o r C a , i t i s n e c e s s a r y t o take i n t o a c c o u n t t h e i n c r e a s e d + +  l i m e usage i n Run #8, a f a c t o r which r a i s e d t h e t o t a l mass o f C a  + +  in  t h e system. However, from T a b l e 14, P a r t 2, i t c a n be seen t h a t o n l y 1.3% o f t h e Ca n a t a n t i n Run #8.  s e n t t o t h e c a r b o n a t o r was r e l e a s e d i n t o t h e s u p e r T h i s was l e s s than h a l f t h a t r e l e a s e d i n any o f t h e  other runs, representing a s i g n i f i c a n t decrease i n C a t u r n meant o v e r 90% C a ++ o f t h e t o t a l Ca  + +  + +  loss.  This i n  r e c o v e r y i n t h e f i n a l s l u d g e o r 60.4 t o 69.4%  i n t h e system.  In Run #8, CaO a c c o u n t e d f o r 80.0% o f t h e mass o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s , compared t o 73.9% i n Run #7.  MgO and  CaO i n Run #8 a c c o u n t e d f o r 83.7% o f t h e f i n a l s l u d g e s o l i d s a s h w e i g h t , l e a v i n g 16.3% unaccounted f o r . T h i s was w i t h i n t h e range o f r e s u l t s found i n o t h e r r u n s .  Runs #7 and 8 can be t h o u g h t o f a s  r e p r e s e n t i n g t h e f i r s t and second c y c l e o f a c o n t i n u o u s p r o c e s s . A comparison o f t h e f i n a l s u p e r n a t a n t q u a l i t y o f t h e s e runs ( T a b l e 1 5 ) , c o n s i d e r i n g t h e volume d i f f e r e n c e s ( T a b l e 16) and t h e i n c r e a s e d l i m e dosage used i n Run #8, i n d i c a t e s t h a t s u p e r n a t a n t q u a l i t y was s t a b i l i z i n g .  The i n c r e a s e d a l k a l i n i t y and c o l o u r con-  c e n t r a t i o n s i n Run #8 c a n be e x p l a i n e d by t h e d e c r e a s e i n c o l o u r s l u d g e p r o d u c t i o n and r e c y c l e volume.  So, on a mass b a s i s , t h e y a r e  about e q u i v a l e n t t o t h e r e s u l t s o f Run #7.  117 In a t h i r d b a t c h c y c l e , no f u r t h e r i n c r e a s e i n l i m e dosage would l i k e l y be r e q u i r e d , b u t more M g  + +  makeup would be needed  because  o f t h e p o o r e r r e c o v e r y i n Run #8. As d i s c u s s e d p r e v i o u s l y , p r o p e r d e s i g n and o p e r a t i o n o f a l a r g e s c a l e s l u d g e c a r b o n a t o r s h o u l d e n a b l e h i g h e r Mg natant.  r e c o v e r y , w h i l e m i n i m i z i n g Ca  l o s s e s i n t o the super-  No s e r i o u s problems have been r e p o r t e d by r e s e a r c h e r s i n  a c h i e v i n g g r e a t e r than 90% M g  + +  r e c o v e r y from water t r e a t m e n t s l u d g e s .  However, o n l y f u r t h e r t e s t i n g o f k r a f t e f f l u e n t s l u d g e s , on a l a r g e r semi-continuous b a s i s , can s a t i s f a c t o r i l y confirm t h i s . 2.  T-20 E f f l u e n t . Keeping i n mind t h a t t h e C a  + +  level i n  Run #6 i s a l m o s t d o u b l e t h a t i n Run #5, T a b l e 14, P a r t 2 shows a s i g n i f i c a n t decrease i n C a 6.7% o f t h e C a  + +  + +  l o s s i n t o the supernatant.  O n l y 6.2 and  i n t h e c a r b o n a t o r was r e l e a s e d w i t h f i n a l s l u d g e  s o l i d s c o n t e n t s of.31.1 and 6 0 % , r e s p e c t i v e l y . Compared t o t h e 15.8 and 21.5% r e l e a s e i n Run #5, t h i s was a s i g n i f i c a n t improvement t h a t can be a t t r i b u t e d t o t h e b e t t e r f i n a l s l u d g e s e t t l e a b i l i t y (due t o t h e h i g h e r l i m e l e v e l used i n Run #6). These l o w e r l o s s e s meant b e t t e r recovery o f C a  + +  i n t h e f i n a l s l u d g e , (96.3 t o 96.7% compared t o 74.1  t o 79.8% i n Run #5). T h i s r e p r e s e n t e d an o v e r a l l r e c o v e r y o f C a  + +  of  79.7 t o 8 0 . 0 % o f t h e t o t a l mass i n t h e system (much more t h a n any o t h e r r u n because o f t h e l a r g e r t o t a l  mass).  In Run #6, CaO a c c o u n t e d f o r 8 2 . 2 % o f t h e mass o f t h e i n c i n e r a t e d f i n a l s l u d g e s o l i d s , compared t o 79.9% i n Run #5.  This  meant t h a t t h e sum o f MgO and CaO i n Run #6 a c c o u n t e d f o r 8 7 % o f t h e f i n a l s l u d g e s o l i d s a s h w e i g h t l e a v i n g 13% u n a c c o u n t e d f o r . A g a i n , comparing t h e s u p e r n a t a n t c h a r a c t e r i s t i c s r e s u l t i n g from t h e two runs ( r e p r e s e n t i n g t h e f i r s t and second c y c l e o f a  118 c o n t i n u o u s p r o c e s s ) , t h e r e i s e v i d e n c e t h a t an e q u i l i b r i u m p o i n t was being reached.  A l k a l i n i t y and c o l o u r c o n c e n t r a t i o n d e c r e a s e d .  No  i n c r e a s e i n l i m e would l i k e l y be r e q u i r e d f o r the n e x t c y c l e , but a g a i n due t o poor M g  r e c o v e r y a c h i e v e d i n Run #6, more magnesium  + +  makeup w o u l d be needed.  However, t h e same f a c t o r s t h a t a f f e c t e d  t e s t i n g w i t h f r e s h c h e m i c a l s a r e b e l i e v e d t o have c o n t r i b u t e d t o the lower recovery i n t h i s l a b o r a t o r y t e s t . Based on t h e good r e c o v e r i e s i n some o f t h e s e b a t c h t e s t s and t h e s u c c e s s o f r e s e a r c h e r s i n the U.S.A. t r e a t i n g s u r f a c e w a t e r s , t h e r e i s no r e a s o n t o e x p e c t t h a t magnesium and c a l c i u m r e c o v e r y s h o u l d be a s e r i o u s problem i f p r o p e r d e s i g n and o p e r a t i o n o f t h e s l u d g e c a r b o n a t i o n system i s p r o v i d e d .  The e f f e c t s o f m i x i n g , s o l i d s  c o n c e n t r a t i o n , and o t h e r i m p o r t a n t parameters a r e d i s c u s s e d n e x t . B.  F a c t o r s a f f e c t i n g the s l u d g e c a r b o n a t i o n mass b a l a n c e r e s u l t s u s i n g r e c y c l e d Mg  i)  General  Most o f t h e s e f a c t o r s have been d i s c u s s e d i n t h e p r e s e n t a t i o n o f t h e r e s u l t s i n t h e p r e v i o u s s e c t i o n . In g e n e r a l , t e s t s w i t h r e c y c l e v e r i f i e d the i m p o r t a n c e o f t h e f a c t o r s i d e n t i f i e d from the r e s u l t s o f t h e runs u s i n g f r e s h c h e m i c a l s .  Some f u r t h e r comments on t h e s e a r e  made below under the a p p r o p r i a t e h e a d i n g s , ii)  F i n a l Sludge Volume  The f i n a l s l u d g e volume a f f e c t e d t h e mass b a l a n c e c a l c u l a t i o n s . In both runs w i t h r e c y c l e d M g , t h e f i n a l s l u d g e s o l i d s c o n c e n t r a t i o n ++  was o v e r 5%, so t h a t a l l mass b a l a n c e s were c a l c u l a t e d u s i n g two situations:  the volume a t the a c t u a l s o l i d s c o n c e n t r a t i o n ; and t h e  volume a t 60% s o l i d s .  T h i s s h o u l d be kept i n mind when comparing the  r e s u l t s o f a l l the runs.  119 In any c a s e , T a b l e 14 shows t h e e f f e c t o f  d i f f e r e n t f i n a l s o l i d s c o n c e n t r a t i o n on t h e v a r i o u s mass b a l a n c e s , iii)  C a r b o n a t i o n pH  F u r t h e r i n f o r m a t i o n on t h e p r e f e r r e d c a r b o n a t i o n pH c a n be g a i n e d by e x a m i n i n g t h e r e s u l t s o f c a r b o n a t i o n m o n i t o r i n g i n Run #8 on BKME and Run #6 on T-20 e f f l u e n t , shown g r a p h i c a l l y i n F i g u r e s 13 and 14, r e s p e c t i v e l y . The same g e n e r a l c o l o u r , M g , and C a ++  i n t h e runs w i t h f r e s h c h e m i c a l s .  + +  p r o f i l e s r e s u l t e d as  However, t h e magnesium c u r v e s had  n o t l e v e l l e d o f f as c o m p l e t e l y i n Runs #8 and 6 a s t h e y had i n Runs #7 and 5 ( F i g u r e s 11 and 1 2 ) . T h i s p o i n t s t o t h e p o s s i b l e b e n e f i t o f c a r b o n a t i n g t o a pH s l i g h t l y below 7.5 and p a r t i a l l y e x p l a i n s t h e lower M g  + +  r e c o v e r i e s i n these t e s t s ,  iv)  Time  The c o n c e n t r a t i o n s o f c o l o u r , M g  + +  and C a  + +  again u s u a l l y  changed d u r i n g t h e s l u d g e s e t t l i n g p e r i o d , b u t l i t t l e f u r t h e r i n f o r m a t i o n on t h e a f f e c t s o f time c o u l d be g a i n e d from t h e s e two r u n s . v)  C o l o u r S l u d g e and F i n a l S l u d g e S o l i d s C o n c e n t r a t i o n  The i m p o r t a n c e o f t h e s e i n t e r r e l a t e d f a c t o r s became more a p p a r e n t d u r i n g t h e runs w i t h r e c y c l e d m a t e r i a l . The c o l o u r s l u d g e s o l i d s c o n c e n t r a t i o n was a p p r o x i m a t e l y t w i c e t h a t o b t a i n e d i n t h e c o r r e s p o n d i n g runs w i t h f r e s h c h e m i c a l s ( i . e . , 2.24 f o r BKME and 4.03 f o r T-20 e f f l u e n t ) .  The f i n a l s l u d g e  c o n c e n t r a t i o n s were more than t w i c e as h i g h (6.33% i n Run #8 w i t h BKME and an a s t o u n d i n g 3 1 . 1 % i n Run #6 w i t h T-20 e f f l u e n t ) . The e f f e c t o f t h e more c o n c e n t r a t e d c o l o u r s l u d g e f e e d t o t h e c a r b o n a t o r on c o l o u r r e l e a s e was n o t a s s i g n i f i c a n t a s i n d i c a t e d  120  r 14000 of o-  •o  0-  -o  COLOUR Ca +  +  -,+ +  1000-1  800  120  h12000  h-100  10000  8000  H  73  6 D) Q  J ,  600-^  + +  -4000"  400  200  O  o u  o  + +  CL ZD _J  CO  E j?  h6000  •2000  H  L0  F I G U R E 13. p H vs. C O L O U R , M g AND C a IN T H E S U P E R N A T A N T F R O M A B K M E SLUDGE CARBONATION USING RECYCLED MAGNESIUM +  +  + +  * C h a n g e In C o n c e n t r a t i o n A n d p H D u r i n g S l u d g e S e t t i n g  121  r 13000  -,  1-  r  11  10  i  9  8  PH  F I G U R E 14 p H  Vs  COLOUR,  FROM A T-20  M g  SLUDGE  +  +  AND  Ca  +  +  IN  THE  CARBONATION USING  SUPERNATANT RECYCLED  MAGNESIUM. *  C H A N G E IN C O N C E N T R A T I O N A N D p H D U R I N G  SLUDGE  SETTLING  122 by r e s u l t s o f e a r l i e r runs o f more d i l u t e s l u d g e .  The c o l o u r r e l e a s e s  i n Runs #8 and 6 were 2 t o 5% l e s s than i n Runs #7 and 5, i n d i c a t i n g t h a t some b e n e f i t w i t h r e s p e c t t o c o l o u r i s g a i n e d from a c o n c e n t r a t e d s l u d g e f e e d t o the c a r b o n a t o r ; however, t h e r e appears t o be an upper l i m i t t o t h i s ( l i k e l y about 5% s o l i d s ) .  I t was d i f f i c u l t t o s e p a r a t e  the e f f e c t s o f c o l o u r s l u d g e c o n c e n t r a t i o n and f i n a l s l u d g e concent r a t i o n , s i n c e a p o r t i o n o f t h e c o l o u r s l u d g e u l t i m a t e l y becomes f i n a l sludge a f t e r carbonation.  However, i n the two runs w i t h r e c y c l e , t h e  f o r m a t i o n o f a v i s i b l e CaCG"3 s l u d g e b l a n k e t , t h a t t e n d e d t o s e t t l e , even d u r i n g c a r b o n a t i o n , i s b e l i e v e d r e s p o n s i b l e f o r t h e r e d u c e d Mg r e c o v e r i e s i n Runs #8 and 6.  The r e d u c e d C a  + +  l o s s e s i n t o the super-  natant are a l s o a t t r i b u t e d to t h i s denser sludge t h a t hindered mixing, c a u s i n g a n o n - u n i f o r m s l u d g e pH i n t h e c a r b o n a t i o n column, vi)  Mixing  The problems e n c o u n t e r e d w i t h m i x i n g were d i s c u s s e d i n t h e s e c t i o n on f r e s h c h e m i c a l s .  As i n d i c a t e d above, t h e s e problems were  m a g n i f i e d i n t h e t e s t s where v e r y c o n c e n t r a t e d s l u d g e was  carbonated.  I t i s l i k e l y t h a t u n i f o r m pH was not r e a c h e d i n the c a r b o n a t o r , and hence some o f the M g ( 0 H ) d i d not have a chance t o s o l u b i l i z e i n the 2  a r e a s o f h i g h e r pH.  L i k e w i s e , p o c k e t s o f low pH c a u s e d u n e x p e c t e d l y  h i g h C a C 0 d i s s o l u t i o n i n some t e s t s . 3  C a r b o n a t o r d e s i g n and o p e r a t i o n a p p e a r s t o be one o f t h e most i m p o r t a n t c o n s i d e r a t i o n s i n a c h i e v i n g good magnesium and c a l c i u m recovery.  Complete m i x i n g must be p r o v i d e d whether i n a b a t c h o r  c o n t i n u o u s s l u d g e c a r b o n a t i o n system.  C o u p l e d w i t h a good C 0  2  diffuser  d e s i g n , complete m i x i n g s h o u l d a c h i e v e a more u n i f o r m s l u d g e pH, r e s u l t i n g i n more e f f i c i e n t M g  + +  r e c o v e r i e s and lower C a  F u r t h e r t e s t s a r e needed t o v e r i f y t h i s .  + +  losses.  123 CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS 7.1  Conclusions 1.  A c o m b i n a t i o n o f l o w magnesium and low lime dosages can a c h i e v e b e t t e r d e c o l o u r i z a t i o n o f k r a f t m i l l e f l l u e n t s than much g r e a t e r amounts o f l i m e a l o n e .  2.  R e a s o n a b l e dosages o f magnesium and l i m e can p r o v i d e 90-95% d e c o l o u r i z a t i o n o f both c a u s t i c e x t r a c t i o n e f f l u e n t and b i o l o g i c a l l y t r e a t e d combined e f f l u e n t from a b l e a c h e d k r a f t mi 11.  3.  R e c y c l e d s u p e r n a t a n t from c o l o u r s l u d g e c a r b o n a t i o n p r o v i d e s an e f f e c t i v e s o u r c e o f magnesium i o n s , d e s p i t e i t s r e l a t i v e l y h i g h c o l o u r and a l k a l i n i t y .  4.  The magnesium r e c o v e r i e s and r e c a l c i n e d l i m e q u a l i t i e s , a c h i e v e d i n t h i s s t u d y by c a r b o n a t i n g t h e p r i m a r y c o l o u r s l u d g e , show t h a t t h i s p r o c e s s w a r r a n t s f u r t h e r i n v e s t i g a t i o n on a l a r g e r , c o n t i n u o u s b a s i s .  7.2  Recommendations F o r F u t u r e  7.2.1  Bench S c a l e a.  Research  F u r t h e r j a r t e s t i n g i s r e q u i r e d o v e r a wide range o f i n f l u e n t c o n d i t i o n s , t o i d e n t i f y a r e l a t i o n s h i p between waste c h a r a c t e r i s t i c s , c o a g u l a t i o n pH, l i m e and magnesium dosage r e q u i r e ments.  T h i s i n f o r m a t i o n i s e s s e n t i a l f o r o p t i m i z a t i o n o f any  c o n t i n u o u s , magnesium c o a g u l a t i o n s y s t e m . b.  I t i s a n t i c i p a t e d t h a t dosage r e q u i r e m e n t s cfor good s e t t l i n g w i l l be d e c r e a s e d i f t h e u n t r e a t e d waste s o l i d s c o n t e n t i s higher.  T h e r e f o r e , a ' j a r t e s t i n g program s h o u l d be c a r r i e d  out t o e v a l u a t e t h e t r e a t a b i l i t y o f t o t a l BKME b e f o r e and  124 a f t e r p r i m a r y s e t t l i n g , as w e l l as p r i o r t o b i o l o g i c a l t r e a t m e n t and s h o u l d i n c l u d e m o n i t o r i n g o f BOD and SS, in addition to colour. 7.2.2  Pilot Scale C o n c u r r e n t w i t h the l a b o r a t o r y s t u d i e s c o n d u c t e d t h i s y e a r , a  20 Igpm p i l o t , p l a n t has been assembled on p o r t a b l e s k i d s and i s now b e i n g o p e r a t e d a t the Canada C e n t r e f o r I n l a n d Waters (CCIW).  A schematic  d i a g r a m o f the p l a n t i s shown i n F i g u r e 15. a.  I n i t i a l work on t h e p i l o t p l a n t s h o u l d be c o n d u c t e d a t CCIW, u s i n g a p r e p a r e d d y e - l i g n o s o l m i x t u r e as a c o l o u r s o u r c e , to t e s t the o p e r a t i o n and c o n t r o l o f the v a r i o u s u n i t p r o c e s s e s ;  I  i n a d d i t o n , i t c o u l d be used to p o i n t out r e q u i r e d e q u i p ment m o d i f i c a t i o n s p r i o r to f i e l d i n s t a l l a t i o n . b.  The emphasis o f t h e p i l o t p l a n t program s h o u l d be on genera t i n g economic and d e s i g n data f o r a f u t u r e f u l l - s c a l e system.  The key t o economic v i a b i l i t y l i e s i n chemical r e c o v e r y and r e use.  T h e r e f o r e , the main q u e s t i o n s t h a t remain to be answered by p i l o t  scale t e s t i n g are: i)  Is s l u d g e c a r b o n a t i o n a t e c h n i c a l l y and e c o n o m i c a l l y f e a s i b l e method o f magnesium r e c o v e r y f o r reuse?  .ii) Is s l u d g e c a r b o n a t i o n , f o l l o w e d by d e w a t e r i n g and i n c i n e r a t i o n , a t e c h n i c a l l y and e c o n o m i c a l l y f e a s i b l e method o f l i m e recovery f o r reuse? In o r d e r to p r o v i d e answers to t h e s e q u e s t i o n s , i t w i l l be n e c e s s a r y to r e l o c a t e the p i l o t p l a n t a t a k r a f t m i l l f o r a p e r i o d o f s e v e r a l months.  t PRIMARY "COLOUR" CLARIFIER  •  #1  #2  RAW WASTEWATER H«  LIME  #2  FLOCCULATORS  +  # 1  SUPERNATANT [Mg(HC0 ) ] RECYCLE  2  3  DUAL MEDIA FILTERS  CO;  -5> #2  -H RECARBONATION CLARIFIER  SURGELJ TANK FINAL EFFLUENT  C02 2  SLURRY RECYCLE  2  RECARBONATOR  RECARBONATOR  C0  +  RAPID MIXERS  COLOUR SLUDGE [Mg (OH) + C 3 C O 3 + COLOUR]  *1  I  Mg MAKE-UP  RECARBONATION  | PROPOSED SLUDGE *»1 DEWATERING SLUDGE (VACUUM FILTER) and ( CaC0 ) INCINERATION (ROTARY KILN) 3  L_  FINAL | SLUDGE I (CaC03 + I COLOUR)  BATCH SLUDGE CARBONATOR/ THICKENER  SLUDGE RECYCLE  RECOVERED CaO RECYCLED  F I G U R E 15. S C H E M A T I C O F T H E E P S M A G N E S I U M C O A G U L A T I O N P I L O T  PLANT  126 Answering t h e f i r s t q u e s t i o n w i l l i n v o l v e " }")  Testing several sources o f fresh M g  + +  t o f i n d the l e a s t ex-  p e n s i v e make-up c h e m i c a l . These s h o u l d i n c l u d e  i)  MgO o r M g ( 0 H )  ii)  MgC0 .3H 0 3  iii) 2)  2  2  Dolomitic lime  M o n i t o r i n g e f f l u e n t q u a l i t y and M g  + +  makeup  requirements  through a number o f magnesium r e c o v e r y and r e u s e c y c l e s . The q u e s t i o n o f l i m e r e c o v e r y and r e u s e i s one t h a t has not been f o r m a l l y a d d r e s s e d t o t h i s p o i n t .  T h i s w i l l r e q u i r e the a d d i t i o n o f  a sludge handling system to the e x i s t i n g p i l o t p l a n t .  S u i t a b l e equipment  i s a v a i l a b l e a t CCIW f o r f i e l d use. The c a r b o n a t e d f i n a l s l u d g e w i l l p r o b a b l y have a s o l i d s c o n t e n t o f 10-25% on l e a v i n g the b a t c h c a r b o n a t o r - t h i c k e n e r , so f u r t h e r d e w a t e r i n g to 50-60% s o l i d s , on a vacuum f i l t e r p r i o r to i n c i n e r a t i o n , w i l l be needed. R e c a l c i n e d l i m e q u a l i t y s h o u l d be m o n i t o r e d through s e v e r a l c y c l e s o f r e c o v e r y and r e u s e t o check f o r b u i l d u p o f magnesium, c h l o r i d e and o t h e r impurities.  F l u e gas c o n t a i n i n g C 0  2  s h o u l d be e v a l u a t e d f o r e f f l u e n t and  s l u d g e c a r b o n a t i o n , f o r comparison w i t h use o f pure  C0 . 2  The o n - s i t e p i l o t p l a n t s t u d y s h o u l d i n c l u d e i n f l u e n t and e f f l u e n t m o n i t o r i n g f o r such parameters  as BOD, SS, and r e s i n and f a t t y a c i d s , and  t o x i c i t y , i n a d d i t i o n to c o l o u r , s i n c e a s i g n i f i c a n t r e d u c t i o n o f these p o l l u t a n t s can be a n t i c i p a t e d . 7.2.3  Concept f o r F u l l S c a l e  Implementation  I f the p r o p o s e d p i l o t p l a n t t e s t i n g program i s c e n t e r e d around ++ ++ t i g h t mass b a l a n c e s f o r Mg  , Ca  , C o l o u r , SS, e t c . , s u f f i c i e n t d a t a  s h o u l d be a c q u i r e d f o r making more d e t a i l e d e c o n o m i c e s t i m a t e s f o r f u l l -  127 s c a l e use and comparison t o o t h e r p r o c e s s e s . Operation o f a p i l o t p l a n t o f t h i s s i z e should generate s u f f i c i e n t d e s i g n d a t a t o a l l o w s c a l e - u p t o a 10 m i l l i o n g a l l o n / d a y t r e a t m e n t  facility,  a c c o r d i n g t o Lund (1971). I f t e c h n i c a l l y and e c o n o m i c a l l y a c c e p t a b l e , t h e p r o c e s s c o u l d be implemented  i m m e d i a t e l y a t the Skookumchuck M i l l o f C r e s t b r o o k F o r e s t P r o -  d u c t s , s i n c e t h e y a r e c u r r e n t l y under B r i t i s h Columbia P o l l u t i o n C o n t r o l Board o r d e r s t o reduce e f f l u e n t c o l o u r .  Also, according to G r i f f i n  (1975),  t h e r e a r e a t l e a s t two o t h e r m i l l s i n B r i t i s h Columbia t h a t r e q u i r e e f f l u e n t decolourization. In a d d i t i o n , i t s h o u l d be kept i n mind t h a t t h i s magnesium c o a g u l a t i o n p r o c e s s has a b r o a d e r a p p l i c a t i o n than s i m p l y c o l o u r removal. The i n f o r m a t i o n on magnesium and l i m e r e c o v e r y and r e u s e o b t a i n e d from t h i s s t u d y o f h i g h l y - c o l o u r e d , p u l p m i l l e f f l u e n t w i l l p o i n t t o the f e a s i b i l i t y o f p r o c e s s use f o r removal o f o t h e r , l e s s moxious t y p e s o f i m p u r i t i e s , such as f l u o r i d e , s i l i c a t r a c e m e t a l s , p h o s p h o r u s , ?  dye o r suspended  solids,  to name a few. I f removal e f f i c i e n c i e s o f BOD, SS, and t o x i c i t y prove t o be as h i g h as e x p e c t e d , i t i s q u i t e p o s s i b l e t h a t magnesium c o a g u l a t i o n c o u l d be c a p a b l e o f r e p l a c i n g b i o l o g i c a l t r e a t m e n t i n some s i t u a t i o n s . 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C . and C o n n o r s , W.J., - C o l o r o f C o n i f e r o u s L i g n i n " , T a p p i , V o l . 54, No. 2, p. 245 - 251 ( F e b . 1971). P h u n d s t e i n G., P r o b s t m e y e r H. and W a l l , C . J . , C e n t r i f u g a l C l a s s i f i c a t i o n o f C a l c i u m C a r b o n a t e S l u d g e s , p a p e r p r e s e n t e d a t 47th Annual C o n f e r e n c e o f t h e WPCF, Denver, ( O c t o b e r 6-11, 1974). P i l i n s k a y a , N.R., S o l o v ' e n a , E.S., Luk'Yanova, 0.1. and R e b i n d e r , P.A. - " S o r p t i o n o f L i g n o s u l f o n a t e s o f D i f f e r e n t C a t i o n Comp o s i t i o n by t h e S o l i d F o r m a t i o n i n Aqueous S u s p e n s i o n s " C o l l o i d J o u r n a l o f t h e U.S.S.R. ( T r a n s l a t e d from Russian*), p. 260 - 263 (August 1973). P r i h a , S., " L i g n o s u l p h o n a t e s i n Lake P a i j a n n e " , Water J o u r . San. Eng. D i v . , A.S.C.E., 191 - 207, ( A p r i l 1971). Raabe, E.W., - " B i o c h e m i c a l Oxygen Demand and D e g r a d a t i o n o f L i g n i n i n N a t u r a l Waters", J o u r n a l WPCF, V o l . 4 0 , No. 5, P a r t 2, p. 145150, (May 1968). R a n k i n , P.R., Benedek, A. - " L i g n i n A d s o r p t i o n on A c t i v a t e d C a r b o n " , p a p e r p r e s e n t e d a t t h e F o u r t h J o i n t AIChE/CSChE E n g i n e e r i n g C o n f e r e n c e , V a n c o u v e r , Canada ( S e p t . 9 - 12, 1973). Rapson, B., S u l l i v a n , D.P. and B r o t h e r s J.A., "The NSRF SeawaterLime C l a r i f i c a t i o n P r o c e s s f o r K r a f t M i l l E f f l u e n t s " - NSRF P r o j e c t 3041 ( A p r i l 1973). Rush, R . J . a n d Shannon E . E . , "Review o f C o l o u r Removal T e c h n o l o g y i n t h e P u l p and Paper I n d u s t r y " . EPS R e p o r t 3/WP-75 ( S e p t . 1975).  133 S a r k a n e n , K.V,., and Ludwig, C H , , - L i g n i n s , John W i l e y and Sons. I n c . , New York, N,Y. 0 971), S h o t t o n , P.G., H e w l e t t P.C. and James, A.N. - "The P o l y D i s p e r s e Nature o f L i g n o s u l p h o n a t e s " , T a p p i , V o l . 55, No. 3, p. 407 - 415, (March 1972). Smook, G., B r i t i s h Columbia T e c h n i c a l I n s t i t u t e , Vancouver, P e r s o n a l Communication, ( J u l y 1975).  B.C.,  S o u n d a r a r a j a n , T.N., and Wayman, M. - "The D e t e r m i n a t i o n o f t h e M o l e c u l a r Weight and M o l e c u l a r Weight D i s t r i b u t i o n o f Dehydrogenase Polymers o f C o n i f e r y l A l c o h o l and L i g n i n s " , J . Polymer S c i e n c e , P a r t C, No. 30, p. 521 - 531 (1970). S p r u i l l , E.L.., " C o l o u r Removal and S l u d g e Recovery from T o t a l M i l l E f f l u e n t " , T a p p i , V o l . 56, No. 4, p. 98 - 100 ( A p r i l 1973). S p r u i l l , E.L. - "Long Term E x p e r i e n c e w i t h C o n t i n e n t a l Can's C o l o u r Removal System", T a p p i E n v i r o n m e n t a l C o n f e r e n c e (1974). S t o c k n e r , J.G., C l i f f , D.D., Munro, K., "The E f f e c t s c o f P u l p M i l l E f f l u e n t on P h y t o p l a n k t o n P r o d u c t i o n i n B.C. C o a s t a l Waters" F i s h e r i e s and M a r i n e S e r v i c e T e c h n i c a l R e p o r t No. 578, (1975). Stumm, W., and Morgan J . J . , A q u a t i c C h e m i s t r y , Woley - I n t e r s c i e n c e N.Y., N.Y. (1970). Swanson, J.W., D u g a l , H.S., Buchanan, M.A., D i c k e y , E..E. - " K r a f t E f f l u e n t C o l o r C h a r a c t e r i z a t i o n B e f o r e and A f t e r S t o i c h i o m e t r i c Lime T r e a t m e n t s " Env. P r o t . Tech. S e r . , EPA-R2-73-141 (Feb. 1973). T c h o b a n o g l o u s , G., " P h y s i c a l and Chemical P r o c e s s e s f o r N i t r o g e n Removal: T h e o r y and A p p l i c a t i o n s , " p r e s e n t e d a t 12th S a n i t a r y Eng.,.Conf., U n i v e r s i t y o f I l l i n o i s (Feb. 1970). Thompson, C.G., S i n g l e y , J . E . , and B l a c k , A.P., "Magnesium Carbonate A R e c y c l e d C o a g u l a n t " , J o u r n . AWWA P a r t I , p. 11 - 19 ( J a n . 1972). P a r t I I , p. 93 - 99 (Feb. 1972). Thompson, C.G. w i t h B l a c k , Crow and E i d s n e s s I n c . , C o n s u l t i n g E n g i n e e r s , Montgomery Alabama, a P e r s o n a l Communication (Dec. 1975). T r a v e r s A., and N o u v e l . "On t h e S o l u b i l i t y o f Magnesium H y d r o x i d e a t High T e m p e r a t u r e s " Compt. Rend ( F r . ) . 188: 499 (1929). T y l e r , M.A., and F i t z g e r a l d , A.D. - "A Review o f C o l o u r R e d u c t i o n T e c h n o l o g y i n P u l p and Paper M i l l E f f l u e n t s " , P r e s e n t e d a t 58th Annual M e e t i n g , T e c h n i c a l S e c t i o n CPPA (1972).  134 V i n c e n t , D.L. " C o l o u r Removal from B i o l o g i c a l l y T r e a t e d P u l p and Paper M i l l E f f l u e n t s " CPAR P r o j e c t No., 210, F i n a l R e p o r t ( A p r i l 1974), Walden, C C , D i r e c t o r o f B r i t i s h C o l u m b i a R e s e a r c h , V a n c o u v e r , B.C., P e r s o n a l Communication (Dec. 1975).  APPENDIX  A  DEVELOPMENT. OF TEST PROCEDURES  136 1.  General Because c o a g u l a t i o n w i t h magnesium-plus-lime  i s a relatively  new p r o c e s s , many o f t h e l a b o r a t o r y t e s t p r o c e d u r e s had t o be worked o u t as t h e s t u d y p r o g r e s s e d .  C o n s i d e r a b l e time was a l s o s p e n t i n v e r i f y i n g  the a n a l y t i c a l methods used f o r t h e s e s p e c i f i c k r a f t m i l l e f f l u e n t s . I t was t h o u g h t t o be w o r t h w h i l e , t h e r e f o r e , t o o u t l i n e i n some d e t a i l t h e t e s t p r o c e d u r e s d e v e l o p e d d u r i n g t h i s s t u d y , i n t h e hope o f providing a basis f o r future research into this process. 2.  Development o f J a r T e s t P r o c e d u r e s The f a c t o r s e x p e c t e d t o a f f e c t c o l o u r removal e f f i c i e n c y i n -  cluded:  ( i ) time ( o f r a p i d m i x i n g , f l o c c u l a t i o n and s e t t l i n g ) ; ( i i ) speed  ( o f r a p i d m i x i n g and f l o c c u l a t i o n ) ; ( i i i ) pH s t a b i l i z a t i o n d u r i n g coagul a t i o n ; ( i v ) dosage and method o f magnesium i o n a d d i t i o n , and ( v ) dosage and method o f l i m e a d d i t i o n . I t has been f a i r l y w e l l e s t a b l i s h e d by V i n c e n t (1974) t h a t f o r e f f e c t i v e magnesium c o a g u l a t i o n , M g  + +  i o n s must be added i n a s o l u b l e  form, p r i o r t o l i m e a d d i t i o n . D u r i n g p r e l i m i n a r y j a r t e s t i n g , b o t h magnesium and l i m e were added d u r i n g r a p i d m i x i n g f o r f a s t d i s p e r s i o n throughout the wastes. Mg  ++  Lime was added as d r y r e a g e n t grade  Ca(0H) «and 2  was added as a s o l u t i o n o f M g C l - 6 H 0 o r MgS0 .7H 0 i n t h e e a r l i e r 2  2  4  2  t e s t s and dosage l e v e l s used were s i m i l a r t o t h o s e e s t a b l i s h e d by V i n c e n t (1974). The f i r s t j a r t e s t s t u d i e s were c a r r i e d o u t u s i n g 1;00 ml samples i n 150 ml b e a k e r s s t i r r e d on l a b o r a t o r y m a g n e t i c s t i r r e r s . *  These s m a l l  t e s t s were s e l e c t e d i n o r d e r t o c o n s e r v e e f f l u e n t s a m p l e s , s i n c e o n l y 50 -mf was needed f o r c o l o u r a n a l y s i s and because o f t h e i r ease o f p e r f o r m a n c e . *  F i s h e r F l e x a - M i x Model 16  137 M i x i n g speed o f t h e s e m i x e r s was v e r y f a s t ( ^ 1 0 0 rpm on r a p i d m i x i n g ) and f l o c c u l a t i o n was f a s t e r than d e s i r e d f o r good f l o e f o r m a t i o n . To g a i n more c o n t r o l o f m i x i n g speeds a s t a n d a r d Phipps and B i r d L a b o r a t o r y s t i r r e r * was m o d i f i e d s l i g h t l y by r e p l a c i n g t h e custom p a d d l e s w i t h smaller propellers.  T h i s p r o v e d t o be an e x c e l l e n t a p p a r a t u s f o r t h e p u r -  poses o f t h i s s t u d y and gave r e s u l t s comparable t o 1 l i t r e j a r t e s t s and batch d e c o l o u r i z a t i o n t e s t s . I t was e x p e c t e d t h a t r a p i d m i x i n g and f l o c c u l a t i n g r e q u i r e m e n t s w o u l d be m a i n l y dependent on pH s t a b i l i z a t i o n a f t e r t h e l i m e a d d i t i o n . pH m o n i t o r i n g o f s e v e r a l e f f l u e n t s showed t h a t t h e pH u s u a l l y s t a b i l i z e d by t h e e n d o f one minute r a p i d m i x i n g .  F i g u r e s 1 and 2 a r e t y p i c a l pH  s t a b i l i z a t i o n c u r v e s f o r T-20 and BKME. r e s p e c t i v e l y . F u r t h e r t e s t i n g r e v e a l e d t h a t c o l o u r removal e f f i c i e n c y was n o t improved by l o n g e r r a p i d m i x i n g o r f l o c c u l a t i o n t i m e s .  In f a c t , t h e s m a l l  amount o f d a t a , p r e s e n t e d here i n T a b l e s 1 and 2, i n d i c a t e d t h a t p r o l o n g e d r a p i d mix { > } min a f t e r a d d i t i o n o f each c h e m i c a l ) r e d u c e d d e c o l o u r i z a t i o n e f f i c i e n c y as d i d e x c e s s i v e f l o c c u l a t i n g t i m e s ( ^ 1 5 m i n ) . I t appears t h a t t h e magnesium h y d r o x i d e f l o e f o r m a t i o n i s e s s e n t i a l l y i n s t a n t a n e o u s , as t h e pH r e a c h e s about 11, and t h e r e i s no advant a g e t o l o n g e r m i x i n g times as f a r as c o l o u r removal e f f i c i e n c y i s concerned.  On t h e c o n t r a r y , e x c e s s i v e m i x i n g d e s t r o y e d t h e f l o e p r o d u c e d and  r e s u l t e d i n d e c r e a s e d c o l o u r r e d u c t i o n and a p o o r e r s e t t l i n g s l u d g e .  Later  t e s t s on both T-20 and BKME v e r i f i e d t h e need f o r s h o r t e r m i x i n g times and less vigorous agitation.  Based on t h e s e f i n d i n g s , t h e f o l l o w i n g p r o c e d u r e  was a d o p t e d f o r magnesium-plus-lime 1.  coagulation testing.  F o r a l l p r e l i m i n a r y c o a g u l a t i o n t e s t s , 100 ml samples o f e f f l u e n t i n 150 ml b e a k e r s were mixed e i t h e r on l a b o r a t o r y  *  Phipps and B i r d I n c . , Richmond V i r g i n i a  138 13  rapid mix  FLOCCULATION  12 mg  +  +  DOSE=  3 0 0 m g / / Mg++ (as Mg C l -6H 0) 2  Lime  Ca(OH)  2  2  D O S E = 2500 mg/i  C (OH) a  2  added  6  8  10  12  14  16  TIME (min)  Fig.1  pH STABILIZATION O F T-20 A F T E R LIME ADDITION.  rapid 12 r m i x  EFFLUENT  -FLOCCULATION ®•  11  mg  10  +  +  PH  DOSE = 60 mg/i M g (as M g C I - 6 H 0 ) +  2  Lime  +  2  DOSE = 5 0 0 mg/i  C (OH) a  2  8 Ca (OH) 0  2  added 6  8  10  12  14  16  T I M E (min)  FIGURE 2. pH STABILIZATION LIME ADDITION.  OF BKME  AFTER  139 TABLE 1 EFFECT OF RAPID MIX .TIME ON COLOUR.REMOVAL E f f l u e n t Type - BKME Magnesium Dose - 60 mg/1 Mg (MgCT .6H 0) Lime Dose - 500 mg/1 C a ( O H ) ?  I n i t i a l C o l o u r = 1900 I n i t i a l pH = 8.2  9 c  9  No. 24-1 24-2 24-3 24-4 24-5 24-6  R a p i d Mix A f t e r Mg Addition !  (Min.) After Ca(0H) Addition c  ?  Flocculation (min)  pH  60 60 60 60 60 60  11.1 11.1 11.1 11.1 11.1 11.1  15 15 15 15 15 15  1/6 1/6 1 1 3 3  1 1 1 1 1  Settling (min)  Colour C U . % Removal 190 170 160 180 200 220  90.0 91.1 91.6 90.5 89.5 88.4  TABLE 2 EFFECT OF FLOCCULATION TIME ON COLOUR REMOVAL E f f l u e n t Type - BKME Magnesium Dose - 60 mg/1 Mg Lime Dose - 500 mg/1 C a ( 0 H )  No. 25-1 25-2 25-3 25-4 25-5 25-6  R a p i d Mix A f t e r Mg Addition  (Min.) After Ca(0H) Addition  2  I n i t i a l C o l o u r = 1900 I n i t i a l pH = 8.2  (MgClp.6rL0) c  L  9  Flocculation (min) 15 15 30 30 60 60  Settling (min) 60 60 60 60 60 60  pH  Colour C U . % Removal 210 200 230 240 240 240  88.9 89.5 87.9 87.4 87.4 87.4  140 m a g n e t i c s t i r r e r s o r on t h e m o d i f i e d P h i p p s and B i r d L a b o r a tory described previously. 2.  In some l a t e r j a r t e s t s , aimed a t more a c c u r a t e e v a l u a t i o n o f p r o c e s s v a r i a b l e s , 1 l i t r e samples o f e f f l u e n t were t e s t e d on an u n m o d i f i e d P h i p p s and B i r d L a b o r a t o r y S t i r r e r .  3.  When magnesium and l i m e were used, t h e y were both added d u r i n g r a p i d m i x i n g (80-100 rpm) 1 minute a p a r t , w i t h mixi n g c o n t i n u i n g f o r 1 minute a f t e r l i m e a d d i t i o n .  When a  s e t t l i n g a i d was a l s o u s e d , i t was added q u i c k l y ( ^ 3 0 s e c o n d s ) a f t e r l i m e a d d i t i o n and r a p i d m i x i n g was c o n t i n u e d f o r 1 minute. 4.  F l o c c u l a t i o n was c a r r i e d o u t a t a speed o f 30-40 rpm f o r 5 minutes i n most t e s t s a l t h o u g h even s l o w e r speeds a r e recommended f o r f u t u r e work.  The t i m e was e x t e n d e d t o 15  minutes i n some e x p e r i m e n t s , b u t t h i s p r o v e d t o be o f l i t t l e v a l u e , so i t was d i s c o n t i n u e d . 5.  S e t t l i n g o f BKME was e s s e n t i a l l y complete a f t e r 30 m i n u t e s , but i n most c a s e s , 1 hour s e t t l i n g was a l l o w e d b e f o r e decant i n g 50 mis f o r pH and c o l o u r measurement.  S l u d g e from  T-20 e f f l u e n t s e t t l e d s l o w l y , b u t 50 mis c o u l d be o b t a i n e d a f t e r 1 hour i n most c a s e s . The optimum m i x i n g c o n d i t i o n s d e r i v e d f o r magnesium-plus-lime c o a g u l a t i o n a r e summarized  below. Time  Speed  Rapid Mixing  1 min + 1 min  80-100 rpm  Flocculation  5-15 min  30-40 rpm  Settling  1 hour  0 rpm  141 T h i s p r o c e d u r e was e s t a b l i s h e d t o develop t e n t a t i v e  chemical  dosage r e q u i r e m e n t s and o p e r a t i n g c o n d i t i o n s f o r use d u r i n g d e t a i l e d b a t c h d e c o l o u r i z a t i o n and magnesium r e c o v e r y s t u d i e s . cant change was made d u r i n g t h e b a t c h s t u d i e s .  Only one s i g n i f i -  S l u d g e s e t t l i n g time i n  these s t u d i e s v a r i e d f r o m 1% hours t o o v e r n i g h t i n one c a s e , t o f a c i l i t a t e c o n c u r r e n t t e s t i n g which had t o be c a r r i e d o u t d u r i n g t h e s e l o n g  runs.  In a l l b u t t h e f i r s t T-20 e x p e r i m e n t s , an a n i o n i c p o l y m e r was added a f t e r the l i m e t o a i d i n s e t t l i n g . 3.  Method o f Magnesium A d d i t i o n I t was supposed t h a t , as l o n g as s o l u b l e magnesium i o n s a r e  a v a i l a b l e i n t h e e f f l u e n t f o r p r e c i p i t a t i o n as Mg(OH),, on l i m e a d d i t i o n , the s o u r c e o f t h e s e i o n s i s i m p o r t a n t o n l y from an economic  viewpoint.  In o r d e r t o v e r i f y t h i s s u p p o s i t i o n and s e l e c t a s u i t a b l e method o f M g addition f o r experimentation,  + +  a b r i e f 1 l i t r e j a r t e s t was c a r r i e d o u t .  The r e s u l t s a r e summarized i n T a b l e 3. T h e r e was e s s e n t i a l l y no d i f f e r e n c e i n c o l o u r removal e f f i c i e n c y between t h e t h r e e cases where t h e M g  + +  was s o l u b l e i n t h e e f f l u e n t .  How-  e v e r , when a s l u r r y o f p r e f o r m e d Mg(0H)2 was u s e d , t h e e f f i c i e n c y was s i g n i f i c a n t l y reduced. is necessary  T h i s c o n f i r m s t h a t MgCOH^ p r e c i p i t a t i o n " i n s i t u "  f o r optimum d e c o l o u r i z a t i o n .  MgS0 .7H 0 s t o c k s o l u t i o n was 4  2  chosen f o r s u b s e q u e n t t e s t s . 4.  Method o f Lime A d d i t i o n In a m i l l s c a l e a p p l i c a t i o n o f t h i s t e c h n o l o g y ,  i t i s almost cer-  t a i n t h a t CaO would be s l a k e d and added as a s l u r r y ; however, s e v e r a l o p t i o n s a r e open f o r s l u r r y i n g w a t e r . technique  In o r d e r t o s e l e c t a l i m e a d d i t i o n  f o r t h e c u r r e n t s t u d y , s e v e r a l methods were compared f o r c o l o u r  removal e f f i c i e n c y . T h e . r e s u l t s o f t h i s b r i e f e v a l u a t i o n a r e shown i n T a b l e 4.  TABLE 3 COLOUR. REMOVAL USING.DIFFERENT. SOURCES OF MAGNESIUM  E f f l u e n t Type: B i o l o g i c a l l y T r e a t e d BKME I n i t i a l C o l o u r : 2254 C U . I n i t i a l pH : 7.30  Magnesium S o u r c e *  Lime S o u r c e ^  MgCl .6H 0 Stock Sol'n  dry Ca(0H)  2  2  2  MgS0 .7H 0 S t o c k Sol'n 4  2  H  II  MgO + H S 0 2  II  " /  4  II  II  II  MgO powder ( 1 0 % s l u r r y A " in d i s t i l l e d H 0) " ?  PH  Colour CU.  - % Removal  11.05 11.09  169 169  92.5 92.5  10.97 11.06  167 161  92.6 92.9  10.98 11.02  167 181  92.6 92.0  11.58 11.56  440 523  80.1 76.8  *  60 mg/1 M g  +  500 mg/1 r e a g e n t C a ( 0 H )  /  MgO was s o l u b l i z e d w i t h H S 0 (1 mg Mg0:2.5 ml H S 0 )  A  S l u r r y mixed 15 minutes p r i o r t o a d d i t i o n - 1000 mis e f f l u e n t + 100 mis e f f l u e n t + 100 m i s s l u r r y , s o c o l o u r c o r r e c t e d f o r d i l u t i o n (x^-)  T T  added i n a l l c a s e s 2  added d r y i n a l l c a s e s 2  4  2  4  143 TABLE 4 COLOUR REMOVAL USING DIFFERENT.SOURCES OF LIME E f f l u e n t Type: B i o l o g i c a l l y T r e a t e d BKME I n i t i a l C o l o u r : 2175 C U . I n i t i a l pH: 7.8 Colour. "r,n.  % Removal  11.30  157  92.8  Reagent C a ( 0 H ) 11.28 (10% s l u r r y i n d i s t i l l e d H 0 )  164  92.5  Reagent C a ( 0 H ) / 11.15 (10% s l u r r y i n h o t raw e f f l u e n t )  168  92.3  T e c h n i c a l grade CaO ( d r y )  11.04  383  82.4  T e c h n i c a l grade CaO - i n 11.80 a 10% s l u r r y o f c o l d d i s t i l led H 0  163  92.5  T e c h n i c a l grade CaO i n a 11.28 10% s l u r r y o f h o t d i s t i l l e d H0  173  92.1  Crushed c a l c i n e r product (dry)  10.75  347  84.1  C r u s h e d c a l c i n e r p r o d u c t i n 10.92 10% s l u r r y o f c o l d d i s t i l led H 0  263  87.9  C r u s h e d c a l c i n e r p r o d u c t i n 10.30 10% s l u r r y o f h o t d i s t i l led H 0  1088  50.0  Magnesium S o u r c e *  Lime S o u r c e  MgS0 .7H 0 S t o c k S o l ' n . 4  2  Reagent C a ( O H )  pH-  +  2  - dry  2  2  2  2  2  A  2  2  * +  60 mg/1 added i n a l l c a s e s 500 mg/1 as C a ( O H ) added i n a l l c a s e s 2  A' C a l c i n e r p r o d u c t f r o m t h e C r e s t b r o o k F l u o s o l i d s C a l c i n e r were crushed i n the l a b . / A l l s l u r r i e s were s t i r r e d 15 m i n u t e s p r i o r t o a d d i t i o n and h o t s l u r r i e s were = 200°F o r 93°C  144 I t can be seen t h a t , when a h i g h p u r i t y r e a g e n t grade Ca(0H)2 was used, i t made l i t t l e d i f f e r e n c e w h e t h e r i t was added d r y , i n a d i s t i l l e d w a t e r s l u r r y o r i n a s l u r r y w i t h t h e raw e f f l u e n t . A s l u r r y o f t e c h n i c a l grade CaO gave equal p e r f o r m a n c e .  In t h i s e x p e r i m e n t , c a l c i n e r  p r o d u c t c r u s h e d i n t h e l a b gave v a r i a b l e r e s u l t s , d e p e n d i n g on method o f addition.  When added d r y o r i n a c o l d w a t e r s l u r r y , c o l o u r removal was  s l i g h t l y l e s s than C a ( 0 H ) o r t e c h . CaO. T h i s i s b e l i e v e d t o be t h e 2  case b e c a u s e o f d i f f i c u l t y i n o b t a i n i n g a f i n e powder from t h e c a l c i n e r product i n the lab.  I t i s a l s o worth n o t i n g t h a t use o f h o t s l u r r i e s  r e s u l t e d i n reduced c o l o u r  removal.  F o r p u r p o s e s o f t h i s r e s e a r c h , d r y r e a g e n t Ca(0H)2 was chosen f o r use i n e a r l y work, f o r c o n v e n i e n c e  and r e p r o d u c i b i l i t y , b u t l a t e r ,  r e a g e n t Ca(0H)2 i n a s l u r r y , w i t h a volume o f d i s t i l l e d w a t e r equal; t o 1 0 % . o f t h e t o t a l volume t r e a t e d , was used; i t was f e l t t h a t l i m e d i s p e r s i o n c o u l d be a c c o m p l i s h e d  w i t h l e s s v i o l e n t m i x i n g and thus improve  sludge s e t t l i n g . 5.  Development o f Batch D e c o l o u r i z a t i o n and Magnesium Recovery Test  Procedure  A l l t h e p r e l i m i n a r y i n v e s t i g a t i o n s d e s c r i b e d s o iar were aimed at e s t a b l i s h i n g appropriate coagulation procedures  and chemical  dosage  l e v e l s , f o r use i n a c h i e v i n g t h e main o b j e c t i v e o f t h i s r e s e a r c h ( t o d e t e r m i n e t h e p e r c e n t magnesium r e c o v e r y and c o l o u r r e l e a s e d u r i n g c a r bonation o f the colour sludge). The b a t c h s t u d i e s were composed o f two c o n s e c u t i v e , y e t s e p a r a t e parts:  1.  approximately  D e c o l o u r i z a t i o n ( a volume o f e f f l u e n t l a r g e enough t o g e n e r a t e 2 l i t r e s o f p r i m a r y " c o l o u r " s l u d g e was t r e a t e d i n a l a r g e  c o n t a i n e r ) and 2. S l u d g e c a r b o n a t i o n ( C 0 gas was b u b b l e d through t h e 2  c o l l e c t e d colour sludge i n a 2 - l i t r e , graduated  C y l i n d e r ) . The main o b j e c -  145 t i v e o f t h e s e b a t c h s t u d i e s was t o o b t a i n mass b a l a n c e s o f c o l o u r , c a l c i u m magnesium around t h e e n t i r e system. The p r o c e d u r e s used i n t h i s phase o f t h e s t u d y a r e based on t h o s e used by Thompson e t a l ( 1 9 7 2 ) , d u r i n g t h e i r t r e a t m e n t o f w a t e r supplies.  Many m o d i f i c a t i o n s i n a p p a r a t u s and p r o c e d u r e s were made d u r i n g  the c o u r s e o f t h e s t u d y .  A l t h o u g h t h e e a r l y t e s t s on b o t h BKME and T-20  e f f l u e n t p r o v i d e d l i t t l e u s e f u l d a t a , each r u n exposed t e c h n i q u e s n e e d i n g improvement  and g r a d u a l l y a w o r k a b l e p r o c e d u r e e v o l v e d . The d e t a i l e d p r o c e d u r e d e v e l o p e d f o r magnesium r e c o v e r y t e s t runs  c o n s i s t e d o f t h e f o l l o w i n g sequence: 1.  P a r t o f a d a y , p r i o r t o a r u n , was used t o p r e p a r e f o r t h e run. This included: (a)  E s t i m a t i n g t h e amount o f sample t o be t r e a t e d s o t h a t  the c o l o u r s l u d g e volume a f t e r 2 hours s e t t l i n g , would be approximately 2 l i t r e s . (b)  D e t e r m i n i n g t h e amount o f M g  + +  s t o c k s o l u t i o n t o be  added. (c)  D e t e r m i n i n g t h e amount o f Ca(0H)2 t o be added.  (d)  P l a c i n g t h e r e q u i r e d e v a p o r a t i n g d i s h e s and gooch  c r u c i b l e s i n t o t h e 103°C d r y i n g oven. (e)  S e t t i n g t h e e f f l u e n t sample o u t o f t h e 4 ° C c o o l e r , t o  a l l o w a slow r e t u r n t o room t e m p e r a t u r e by t h e time o f t h e "main run" t h e n e x t morning. (f) 2.  P r e p a r i n g a l l t h e equipment f o r t h e "main r u n " .  In o r d e r t o c l o s e l y s i m u l a t e s e t t l i n g times t h a t would e x i s t i n a l a r g e s c a l e s y s t e m , i t was d e c i d e d t o a l l o w 2 hours s e t t l i n g f o r c o l o u r and f i n a l s l u d g e .  T h i s would  146 a l l o w a b a t c h d e c o l o u r i z a t i o n , f o l l o w e d (2 hours l a t e r ) by a b a t c h c a r b o n a t i o n o f t h e c o l o u r s l u d g e .  Then a f t e r  2 more hours o f s e t t l i n g , a n a l y s e s o f t h e f i n a l s l u d g e and s u p e r n a t a n t c o u l d be done.  During s e t t l i n g p e r i o d s ,  a n a l y s e s o f raw d e c o l o u r i z e d e f f l u e n t were c a r r i e d o u t . , F i n a l l y , a l l samples f o r a s h i n g were p l a c e d i n a m u f f l e f u r n a c e f o r o v e r n i g h t i n c i n e r a t i o n a t 700°C. The main run u s u a l l y took a t l e a s t 10 hours o f c o n t i n u o u s work.. The d e t a i l s o f t h e main run a r e as f o l l o w s : (a)  Pour i n t o the t r e a t m e n t v e s s e l ( b u c k e t ) an amount o f  c o l o u r e d w a s t e w a t e r to g i v e the d e s i r e d f i n a l volume a f t e r a l l c h e m i c a l a d d i t i o n s , p l u s 500 mis t o be removed f o r analysis. (b)  A f t e r the raw e f f l u e n t had r e a c h e d room, t e m p e r a t u r e  and had been mixed to i n s u r e u n i f o r m i t y , a 500 ml r e p r e s e n t a t i v e sample was e x t r a c t e d f o r a n a l y s i s as u n t r e a t e d e f f l u ent (IN). (c)  pH and a l k a l i n i t y (IN) were d e t e r m i n e d  immediately.  (d)  The c o a g u l a t i o n was then c a r r i e d o u t a c c o r d i n g to the  p r o c e d u r e s a l r e a d y o u t l i n e s and, i n most c a s e s , m o n i t o r e d f o r pH and c o n d u c t i v i t y changes d u r i n g c o a g u l a t i o n . (e)  Immediately  a f t e r f l o c c u l a t i o n , a 25 ml sample was  t a k e n f o r a l k a l i n i t y , and f i l t e r e d t h r o u g h 40 Whatman p a p e r , which was r e t a i n e d f o r a s h i n g . (f)  D u r i n g c o l o u r s l u d g e s e t t l i n g , a n a l y s e s o f (IN) were  completed f o r t e m p e r a t u r e and c o n d u c t i v i t y . Samples were p r e p a r e d f o r c o l o u r and f o r M g  + +  and C a  + +  determination,  147 a f t e r d r y a s h i n g as d e s c r i b e d p r e v i o u s l y . (g)  A f t e r s e t t l i n g f o r 2 hours i n most c a s e s , t h e d e c o l o u r -  i z e d e f f l u e n t was c a r e f u l l y syphoned i n t o a l a r g e c o n t a i n e r and a sample o f t h e composite was taken f o r a n a l y s i s as treated effluent (h)  (OUT).  The pH, a l k a l i n i t y , c o n d u c t i v i t y and t e m p e r a t u r e o f  (OUT) were d e t e r m i n e d i m m e d i a t e l y , w h i l e sample p r e p a r a t i o n for colour, Mg (i)  + +  and C a  + +  was done l a t e r .  The c o l o u r s l u d g e was then mixed w e l l and a sample  t a k e n f o r % s o l i d s d e t e r m i n a t i o n and d r y a s h i n g . The r e m a i n d e r was t r a n s f e r r e d t o a 2 " l i t r e g r a d u a t e d c y l i n d e r for carbonation.  C o l o u r , s l u d g e volume, pH and c o n d u c t i v i t y  i n t h e c y l i n d e r were r e c o r d e d . (j)  In a l l runs e x c e p t #4, t h e s l u d g e was sampled a t i n t e r -  vals during carbonation to monitor a l k a l i n i t y , c o l o u r , M g and C a  + +  changes as t h e pH d e c r e a s e d .  + +  Sludge i n the c y l i n d e r  was c o n t i n u o u s l y m o n i t o r e d f o r pH and c o n d u c t i v i t y .  This  p r o c e d u r e was aimed a t i d e n t i f y i n g some p r a c t i c a l c o n t r o l mechanisms f o r use i n a l a r g e s c a l e i n s t a l l a t i o n , ( i . e . d e t e r m i n e when t o s t o p c a r b o n a t i n g ) . In Run #4, t h e s l u d g e was c a r b o n a t e d t o a p r e d e t e r m i n e d t a r g e t pH (7.5) and i n c l u d e d no s a m p l i n g d u r i n g c a r b o n a t i o n . T h i s was t o s e e how f a s t c a r b o n a t i o n c o u l d be c a r r i e d o u t . COg f e e d r a t e was n o t s t r i c t l y c o n t r o l l e d and appeared t o f l u c t u a t e with time.  T h e r e f o r e , pH, r a t h e r than t i m e , was  a better control v a r i a b l e f o r the process.  D u r i n g runs  where s a m p l i n g was c o n d u c t e d , some samples were syphoned out a t p r e d e t e r m i n e d s l u d g e pH's. Time, s l u d g e c o n d u c t i v i t y  148 and pH were r e c o r d e d .  The sample was i m m e d i a t e l y  filtered  t h r o u g h 40 Whatman p a p e r , pH and a l k a l i n i t y were then d e t e r mined on t h e f i l t r a t e .  Samples o f f i l t r a t e were then s e t  a s i d e f o r p r e p a r a t i o n f o r c o l o u r , M g , and C a ++  + +  analysis.  A l l sample f i l t e r p a p e r s were saved and d r y ashed f o r M g and C a  + +  ++  determination.  In t h e s e r u n s , c a r b o n a t i o n was c o n t i n u e d t o a s l u d g e pH o f 6.5-7.5, i n most cases a t a slow r a t e (1-2 h r s ) t o a l l o w time f o r sample a l k a l i n i t y measurements.  In Run #5 where  no samples were taken,, c a r b o n a t i o n t o a f i n a l s l u d g e pH o f 7.5 took about h hour. (k)  In most c a s e s , F i n a l S l u d g e s e t t l i n g was a l l o w e d 2  hours (sometimes more) b e f o r e c a r e f u l l y s y p h o n i n g o f f t h e supernatant.  S u p e r n a t a n t and F i n a l S l u d g e volume were r e -  corded. (1)  A composite sample o f t h e s u p e r n a t a n t was t a k e n .  A  p o r t i o n was f i l t e r e d f o r pH, a l k a l i n i t y , and c o l o u r , and an u n f i l t e r e d p o r t i o n f o r c o n d u c t i v i t y , t e m p e r a t u r e and d r y ashing, f o r Mg (m)  and C a . + +  F i n a l s l u d g e was sampled f o r % s o l i d s and 10 mis d r y  ashed f o r M g (n)  + +  + +  and C a . + +  C o l o u r d e t e r m i n a t i o n on a l l samples was u s u a l l y s t a r t e d  d u r i n g f i n a l s l u d g e s e t t l i n g and f i n i s h e d s h o r t l y a f t e r , (o)  F i n a l l y , a f t e r o b t a i n i n g d r y w e i g h t o f both s l u d g e s , a l l  samples f o r d r y a s h i n g were p l a c e d i n t h e f u r n a c e and t h e t i m e r s e t t o a l l o w c o o l i n g by morning.  APPENDIX  B  SETTLEABILITY OF T-20 EFFLUENT AND POLYMER SELECTION  150 Because o f t h e p o o r s e t t l e a b i l i t y o f T-20 e f f l u e n t , a few s e t t l i n g a i d s were t e s t e d on t h i s e f f l u e n t .  The r e s u l t s o f s e t t l i n g ,  t e s t s a r e shown i n T a b l e 1. O n l y Dow's a n i o n i c p o l y m e r P u r i f l o c A-23 gave a s i g n i f i c a n t improvement, so f u r t h e r t e s t i n g t o m i n i m i z e t h e dosage r e q u i r e m e n t s were c o n d u c t e d a c c o r d i n g t o t h e m a n u f a c t u r e r ' s d i r e c t i o n s (Dow, 1967).  The  r e s u l t s o f 100 ml s e t t l i n g t e s t s w i t h P u r i f l o c A-23 a r e shown i n T a b l e 2. These t e s t . r e s u l t s were somewhat e r r a t i c , due t o the f a c t t h a t l i m e was added d r y and r a p i d m i x i n g speeds v a r i e d s l i g h t l y between t h e j a r s on t h e m a g n e t i c s t i r r e r s . A f t e r t h i s , l i m e was added as a s l u r r y and 100 ml j>ar t e s t s were c o n d u c t e d on t h e m o d i f i e d s i x - p l a c e  laboratory  stirrer. A p o l y m e r a d d i t i o n o f 1-2 mg/1 a p p e a r e d t o be adequate f o r good s e t t l i n g o f t h e T-20 s l u d g e . F u t u r e j a r t e s t s o f T-20 e f f l u e n t u s e d 2 mg/1 o f A-23 as a s e t t l i n g a i d .  TABLE 1 SETTLEABILITY OF T-20 EFFLUENT WITH VARIOUS SETTLING AIDS A l l j a r s were made up t o 1.0 l i t r e w i t h M g = 300 mg/1 and C a ( 0 H ) = 2500 mg/1* + +  o  J a r No.  0  Observations S l u d g e Volume ( m i s ) A f t e r Time (min) 10 20 30 40 50 60  90  820  400  280  Settling Aid  Dosage  1  B e t z 835 A  10 mg/1  1000  2  Dow P u r i f l o c A-23  10 mg/1  S e t t l e d o u t i m m e d i a t e l y a f t e r r a p i d mix t o 200 m i s .  3  Ca(.0H)  4  Na Si0 .9H 0  5  None  2  2  3  2  590  500  460  430  2500 mg/1  1000  930  880  800  620  540  510  460  300  36.4 mg/1  1000  910  780  680  580  500  490  420  290  1000  960  900  820  630  580  510  460  300  R a p i d Mix (80 rpm)  ( 2 min a f t e r Mg addition) ( 2 min a f t e r C a ( 0 H ) a d d i t i o n ) ( 2 min.after s e t t l i n g a i d addition)  Flocculate (30 rpm)  ( 5 min - 10 rpm)  *  660  14 h r .  2  e x c e p t i n J a r No. 3 where an e x t r a 2500 mg/1 was added as a s e t t l i n g a i d  152 TABLE 2 MINI SETTLING.TESTS USING PURIFLOC A-23 AS A SETTLING AID  ir  * No.  Mg (mg/1)  Ca(0H) (mg/1)  ** 2  A-23 (mg/1).  Observations S l u d g e Volume ( m i s ) a f t e r t i m e (min 0 15 30 45 60 120  1  300  2500  0.1  100  90  80  75  62  43  2  300  2500  0.5  100  79  59  45  40  30  3  300  2500  1.0  100  42  38  35  30  28  4  150  2500  0.5  100  60  45  40  36  30  5  150  2500  1.0  100  82  70  59  48  33  6  150  2500  2.0  100  80  62  50  42  30  +  100 ml b e a k e r s added as t h e d r y powder R a p i d mix was n o t as v i g o r o u s and good f l o e formed d u r i n g t h i s time, r e s u l t i n g i n b e t t e r s e t t l i n g .  APPENDIX  C  EXAMPLE CALCULATION TO DERIVE THE SLUDGE AND SUPERNATANT VOLUME RESULTING FROM SLUDGE DEWATERING TO 5% and 60% SOLIDS  154 Run #7 a)  Test results: C S . volume  =  1.80 1  C S . sample  =  .05 1  C S . t o Carb.  =  1.75 1  Samples (4 x .050)  =  .20 1  =  1.55 1  =  .49 1  =  1.06 1  =  3.19 1  =  .49 1  F i n a l S u p e r n a t a n t (Sp) r + F i n a l S l u d g e (F.S.) F i n a l s l u d g e volume a f t e r settling F i n a l S u p e r n a t a n t Volume A c t u a l % S o l i d s o f F.S. obtained Actual b)  F.S. Volume o b t a i n e d  C a l c u l a t i o n a t any F.S. P e r c e n t S o l i d s F.S. volume a t x% s o l i d s = a c t u a l F.S. v o l . x a c t u a l F.S. % s o l i d s x% s o l i d s R e c y c l e volume F i n a l s u p e r n a t a n t volume + Volume s u p e r n a t a n t samples taken d u r i n g carbonation  c)  C a l c u l a t i o n a t F.S. s o l i d s = 5% F.S. volume a t 5% s o l i d s  d)  S u p e r n a t a n t volume  .49 1 x 3.19% 5% ' 1.237 1  R e c y c l e volume  1.237 1 + .200 1 =  Calculations  a t F.S. s o l i d s  =  ,313 1  1.437 1  60%  F.S. volume a t 60% s o l i d s  .49 1 x 3.19%  S u p e r n a t a n t volume  1.524 1  R e c y c l e volume  1.524 1 + .200 1 =  =  .026 1  1.724 1  APPENDIX  D  SLUDGE CARBONATION MONITORING DATA  156 Run #1 Final Sludge  Colour Sludge  Time Min.  pH o f S l u d g e in Cylinder  3.65  .99  % Solids Sample  .2  1.0  Volume (1)  pH o f Filtrate  Total Alkalinity (CaC0 ) o  C.S.  l  s  F  S  Conductivity JA  ++  C o l o u r mg cu. mg/1  Ca mg/1  S  155  17500  220  10.5  78  7.8  N.A.  N.A.  6260  525  41  6.7  7.4  2400  27000  7175  525  88  N.A.  7.3  2250  27000  5575  525  93  0  11.20  11.20  60  7.1  75 195  Run #2 Colour Sludge Volume (1)  2. 0  Solids  •  %  C.S.  F i n a l SIudge .225 2.1  46  0  11.00  11.1  135  18500  240  5.6  156  s  i  32  8.7  8.9  950  N.A.  4700  248  71  S  2  44  8.0  8.2  750  N.A.  4620  250  68  65  7.5  7.9  1050  N.A.  4545  250  68  S  3  S  4  85  6.5  7.5  1300  N.A.  3750  263  158  S  F  205  N.A.  7.0  1400  28000  3790  263  192  *  e x c e p t SF which i s pH o f u n f i l t e r e d f i n a l s u p e r n a t a n t a f t e r s l u d g e s e t t l i n g  157  .SLUDGE CARBONATION MONITORING DATA Run #3 Colour Sludge  Sample  CS.  Time min.  Final Sludge  Volume (1)  2,0  ,5  % Solids  1.7  3,83  pH o f S l u d g e in Cylinder  *  pH o f Total Filtrate Alkalinity (CaCOo)  Conductivity Colour  Mg  yS  cu.  mg/1  + +  + +  Ca  mg/1  0  12.1  12.3  1775  70400  1450  3.64  344  s  l  16  10.0  10.4  1566  50100  11755  182  410  S  2  36  9.0  9.2  2318  51000  15270  298  250  S  3  64  8.0  8.2  3602  64200  13440  412  610  S  4  90  7.2  7,7  6077  98000  9470  470  1400  S  F  210  7.2  7.55  6578  90000  12825  552  1750  Run #4  CS.  "..: -••  Colour Sludge  Final Sludge  Volume, ,(1)  2.0  .4  % Solids  1.2  3.45  0  11.9  12.1  1250  74000  810  4.7  510  s  l  6  10.5  N.A.  N.A.  42000  N.A.  N.A.  N.A.  S  2  13  9.5  N.A.  N.A.  47800  N.A.  N.A.  N.A.  S  3  16  8,5  N.A.  N.A.  51600  N.A.  N.A.  N.A.  S  4  25  7.5  N.A.  N.A.  61000  N.A.  N.A.  N.A.  S  F  205  7.3  7.3  N.A.  6100  11820  734  1240  *  e x c e p t SF which i s pH o f u n f i l t e r e d f i n a l s u p e r n a t a n t a f t e r s l u d g e s e t t l i n g  158 SLUDGE CARBONATION MONITORING DATA Run #5 Colour Sludge 2.0  Volume (1)  2.04  % Solids  Sample  Time min.  pH o f S l u d g e in Cylinder  Final Sludge 1.0  *  pH o f Filtrate  2.6  Total Alkalinity (CaC0 ) 3  C.S.  ConductColour i vi ty cu. liS  Mg mg/1  mg/'  ea " +  0  12.1  12.1  1600  79500  900  2.6  390  11.5  815  56000  1250  12.5  66  40000  14500  700  200  S  l  16  10.5  S  2  27  9.3  9.65  2445  S  3  47  8.5  8.60  4510  N.A.+  17700  1000  340  S  4  60  8.0  820  5510  N.A.+  17700  1150  540  S  5  80  7.5  7.95  6700  95000  16000  1200  980  S  F  350  7.7  7.9  6830  91000  16000  1250  1050  940  3.6  313  Run #6 Volume (1) % Solids C.S.  Colour Sludge 1.380 4.03  Final Sludge .160 31.1  0  12.32  12.38  2050  10.9  1130  59000  4000  42  107  10100  S  l  16  10.5  S  2  29  9.5  9.75  2130  60000  10150  320  135  S  3  38  8.2  8.45  4135  75000  12100  750  280  S  4  48  7.5  7.88  6580  80000  10150  900  775  S  F  168  N.A.  7.7  5765  80000  12550  900  865  + *  C o n d u c t i v i t y probe p i u g g e d e x c e p t SF which i s pH o f u n f i l t e r e d f i n a l s u p e r n a t a n t a f t e r s l u d g e s e t t l i n g  159 SLUDGE CARBONATION..MONITORING DATA Run #7 Colour Sludge  Sample  C.S.  Volume (1)  1,75  % Solids  1,26  Time min.  pH o f S l u d g e in Cylinder  *  pH o f Filtrate  Final Sludge .490 3.19  Total Alkalinity (CaC0 ) 3  ' Conduct-^ ivity ' C o l o u r ' Mg ^Ca yS cu. mg/1 mg/1 + +  0  11.4  11.4  180  18000  70  4.25  175  S  l  17  10.5  10.75  125  15500  160  5.6  70  S  2  50  9.5  9.7  1150  21000  2800  312.5  70  S  3  69  8.4  8.45  3500  40000  7700  850  90  S  4  73  7.5  8.0  3500  43500  9000  950  100  S  F  223  7.7  7.8  3650  43500  9400  960  135  4.75  93  Run #8 Volume (1) % Solids  C.S.  Colour Sludge 1.30  Final Sludge .350  2.24  6.33  0  11.4  11.4  155  16000  100  10.4  130  13000  460  37.5  75  S  l  10  10.4  S  2  21  9.5  9.65  1475  23000  3900  400  60  S  3  44  8.4  8.5  3525  40000  10600  900  90  S  4  55  7.5  7.8  3825  43000  13600  970  106  S  F  175  7.6  7.8  4375  43000  13500  980  no A,  *  e x c e p t SF which i s pH o f u n f i l t e r e d f i n a l s u p e r n a t a n t a f t e r s l u d g e s e t t l i n g .  

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