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Two-stage anaerobic digestion of hog wastes Duncan, Adrian C. 1975

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TWO-STAGE ANAEROBIC DIGESTION OF HOG WASTES  BY  ADRIAN C. DUNCAN B . A . S c , U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1970  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  i n the Department of C i v i l Engineering  We accept t h i s thesis as conforming  to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA  August, 1975  In p r e s e n t i n g  this  thesis  an advanced degree at the I  Library shall  f u r t h e r agree  for  scholarly  by h i s of  this  written  make  it  British  freely available  that permission  for  the requirements  Columbia,  I agree  r e f e r e n c e and  f o r e x t e n s i v e copying o f  this  for  It  financial  is understood gain s h a l l  that  not  C-l\/lL  U n i v e r s i t y of B r i t i s h  2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5  t ^ 6 Af ^ ff, /A;' Q /  Columbia  copying or  for  that  study. thesis  purposes may be granted by the Head of my Department  permission.  Department of The  fulfilment of  the U n i v e r s i t y of  representatives. thesis  in p a r t i a l  or  publication  be allowed without my  ABSTRACT  The present trend towards concentrated land-use animal farming has given r i s e to a number of new animal waste disposal problems due to the very high strength of l i q u i d wastes from such f a c i l i t i e s . One treatment alternative applicable to these wastes i s anaerobic digestion.  A study was undertaken to determine the anaerobic digestion  c h a r a c t e r i s t i c s of waste from a high-density hog-raising f a c i l i t y .  Earlier  work had provided treatment e f f i c i e n c y data for a single-stage, laboratoryscale anaerobic reactor, as well as giving certain design c r i t e r i a for anaerobic lagoons.  The present study was intended to provide a measure of the increase i n treatment e f f i c i e n c y obtained through use of a two-stage anaerobic reactor, again on a laboratory scale, and to give information regarding biodegradab i l i t y of the settled sludge.  The effect of variations i n temperature and  detention time was included i n the study, as was an investigation of volat i l e acids, t o t a l organic carbon, and copper t o x i c i t y due to the use of brass f i t t i n g s i n test apparatus.  Conclusions reached on the basis of this study were that the twostage system gives a s l i g h t l y higher loading capacity, due to improved s e t t l i n g c a p a b i l i t y , but the effluent from the second c e l l i s s t i l l of higher strength than i s often desirable for discharge to receiving waters. The settled solids were found to be degradable to a limited extent only, and thus most of them w i l l require physical removal from a lagoon. s i g n i f i c a n t correlation was found between BOD,  COD,  and TOC and copper levels  were found to reach s i g n i f i c a n t l e v e l s i n the reactors. ii  No  This report was based on laboratory findings only.  No c o r r e l a t i o n  between laboratory-scale and f i e l d results was attempted i n the study.  iii  TABLE OF CONTENTS  ABSTRACT  i i  LIST OF TABLES  vi  LIST OF FIGURES  vii .  ACKNOWLEDGEMENT  viii •  CHAPTER 1.  CHAPTER 2.  INTRODUCTION  1  1.1  General Discussion  1  1.2  Fundamentals of Anaerobic Digestion  3  1.3  Need f o r Further Research  4  1.4  Separation of Settled Solids and Supernatant  6  1.5  Sludge Build-up and Gas Production  7  EXPERIMENTAL PROCEDURE  9  2.1  General Discussion  9  2.2  Establishment and Operation of the Batch Systems ... 10  2.3  Establishment and Operation of the Two-Stage Systems  CHAPTER 3.  13  2.4  Testing Procedure f o r the Influents and Effluents .. 15  2.5  Testing Procedure f o r the Evolved Gases  18  2.6  Summary  18  RESULTS OF BATCH TESTS  20  3.1  Introduction  20  3.2  General Discussion of Procedure  20  3.3  Gas Production and Analysis  21  3.4  Relationship of Methane Production to BOD and COD Removal  24  Relationship of Methane Production to V o l a t i l e Solids Removal  29  3.5  iv  CHAPTER 4.  CHAPTER 5.  TWO-STAGE DIGESTER RESULTS  35  4.1  Introduction  35  4.2  General Discussion  35  4.3  Effectiveness of Modifications to C e l l  36  4.4  Overall Treatment E f f i c i e n c y  42  4.5  S e t t l i n g vs. B i o l o g i c a l Degradation  43  4.6  Relative Importance of 1st and 2nd C e l l  48  4.7  Single-Stage vs. Two-Stage System  49  4.8  Copper Concentrations  55  VOLATILE ACIDS AND  TOTAL ORGANIC CARBON RESULTS  5.1  Introduction  59  5.2  V o l a t i l e Acids and pH Levels i n Anaerobic Systems ...  59  5.3  V o l a t i l e Acids and pH i n the Two-Stage Digesters ....  61  5.4  Total Organic Carbon Measurements i n the Two-Stage Digesters  69  CHAPTER 6.  CONCLUSIONS AND RECOMMENDATIONS  74  6.1  Introduction  74  6.2  Conclusions from Batch Test Results  74  6.3  Conclusions from Two-Stage Continuous-Feed Results  6.4  6.5  6.6  Digester 75  Conclusions Regarding Two-Cell Vs. One-Cell Systems  75  Conclusions from Copper, V o l a t i l e Acids, pH and Total Organic Carbon Tests  76  Recommendations  77  BIBLIOGRAPHY APPENDIX A.  59  79 Sample Calculations  81;  v  LIST OF TABLES  TABLE TABLE TABLE  TABLE  I.  Average Raw Waste C h a r a c t e r i s t i c s  36  I I . Average E f f l u e n t C h a r a c t e r i s t i c s I I I . Comparison of P e r c e n t Removals i n O r i g i n a l M o d i f i e d 12.5 £ C e l l IV.  37 25 I  C e l l and  Comparison of Mass Removed Per U n i t C e l l Volume f o r 25 S i n g l e - S t a g e C e l l and 12.5 I F i r s t C e l l of D o u b l e - C e l l Digester  38 I 39  TABLE  V.  Percentage BOD Removals  44  TABLE  VI.  Percentage COD Removals  44  TABLE  VII.  Percentage V o l a t i l e S o l i d s Removals  45  TABLE V I I I .  Percentage T o t a l  45  TABLE  Percentage BOD Removals Due t o S e t t l i n g and Bacteriological Action  46  Percentage COD Removals Due to S e t t l i n g and Bacteriological Action  46  Percentage V o l a t i l e S o l i d s Removal Due t o S e t t l i n g and Bacteriological Action  47  TABLE  TABLE  TABLE  IX.  X.  XI.  XII.  Percentage T o t a l  Solids  Solids  Removals  Removal Due to S e t t l i n g and  Bacteriological Action  47  TABLE X I I I .  Comparison o f S i n g l e -  and Two-Stage Systems (LDT=50 d a y s ) . 50  TABLE  XIV.  Comparison of S i n g l e -  and Two-Stage Systems (LDT=25 d a y s ) . 50  TABLE  XV..  TABLE  XVI.  Comparison of 1 s t C e l l Only Vs. 1 s t and 2nd C e l l s a t 25-Day LDT  52  Copper C o n c e n t r a t i o n s i n Two-Stage D i g e s t e r C e l l s  56  vi  LIST OF FIGURES  FIGURE 1.1  Mechanism o f Anaerobic  FIGURE 2.1  S i n g l e - S t a g e D i g e s t e r , Showing P o s s i b i l i t y of S h o r t C i r c u i t i n g During Feeding  11  FIGURE 2.2  Two-Stage D i g e s t e r , Showing Flow P a t t e r n During Feeding  12  FIGURE 3.1  Methane P r o d u c t i o n Rate Vs. Time  22  FIGURE 3.2  Cumulative  23  F i g u r e 3.3  COD Values Vs. Time  25  FIGURE 3.4  BOD V a l u e s Vs. Time  26  FIGURE 3.5  COD Removal Vs. Methane P r o d u c t i o n  28  FIGURE 3.6  BOD Removal Vs. Methane P r o d u c t i o n  30  FIGURE 3.7  Volatile  S o l i d s Vs. Time (Batch T e s t s )  31  FIGURE 3.8  Volatile  S o l i d s Reduction  33  FIGURE 5.1  V a r i a t i o n of V o l a t i l e A c i d C o n c e n t r a t i o n  60  FIGURE 5.2  V o l a t i l e A c i d s V s . Time f o r Two-Stage D i g e s t e r Number 1 (30°C)  62  V o l a t i l e A c i d s Vs. Time f o r Two-Stage D i g e s t e r Number 2 (23°C)  63  FIGURE 5.3  FIGURE 5.4  Sludge D i g e s t i o n  Methane P r o d u c t i o n Vs. Time  Vs. Gas P r o d u c t i o n  5  V o l a t i l e A c i d s Vs. Time f o r Two-Stage D i g e s t e r Number 3 (10°C)  64  FIGURE 5.5  pH Vs. Time f o r Two-Stage D i g e s t e r Number 1 (30°C)  65  FIGURE 5.6  pH Vs. Time f o r Two-Stage D i g e s t e r Number 2 (23°C)  66  FIGURE 5.7  pH Vs. Time f o r Two-Stage D i g e s t e r Number 3 (10°C)  67  FIGURE 5.8  BOD Vs. TOC f o r Raw Feed and D i g e s t e r E f f l u e n t s  71  FIGURE 5.9  COD Vs. TOC f o r D i g e s t e r E f f l u e n t  72  vii  ACKNOWLEDGEMENT  The  author i s deeply  for h i s assistance, patience study.  g r a t e f u l t o h i s s u p e r v i s o r , Dr. W.K. Oldham,  and encouragement d u r i n g  the course o f the  The author i s a l s o g r a t e f u l f o r t h e h e l p r e c e i v e d from L i s a McDonald,  Gary B i r t w h i s t l e , David Bond, and R i c h a r d  Brun.  S p e c i a l thanks go t o  L i n d a B l a i n e f o r h e r e x c e l l e n t t y p i n g of t h e f i n a l  This thesis i s dedicated  report.  t o t h e a u t h o r ' s f a t h e r , Dr. J.P. Duncan,  w i t h o u t whose encouragement i t might never have been w r i t t e n .  Vancouver, B.C. August, 1975 viii  1 CHAPTER 1.  1.1  INTRODUCTION  General Discussion During the l a s t f i f t e e n years or so there has been a marked trend  among farmers involved i n the breeding and r a i s i n g of animals towards concentration of their stock on ever-decreasing areas of land.  This process,  while bringing considerable economic benefits to the farmer, has l e d to cert a i n new a g r i c u l t u r a l problems, not the least of which i s that of animal waste disposal.  Previously, wastes could be spread on arable land as f e r t i -  l i s e r , but c l e a r l y t h i s concept i s not applicable, except i n special instances, i n the case of concentrated land-use animal farms.  Today i t i s generally  accepted that some form of b i o l o g i c a l waste treatment system i s a prerequis i t e i n the design of such farms''"'"''. B i o l o g i c a l treatment takes many forms, but b a s i c a l l y there are two major c l a s s i f i c a t i o n s : a) Aerobic_treatment —  employs micro-organisms which require  dissolved oxygen to obtain their energy.  In this instance some  indirect means must c l e a r l y be found of supplying and d i s t r i b u t i n g s u f f i c i e n t oxygen throughout the system to keep the bacteria fully  active.  b) Anaerobic_treatment —  employs micro-organisms which do not  require dissolved oxygen, but employ fermentation, or anaerobic . respiration,  to obtain t h e i r energy.  In this case, there exists  no oxygen supply problem, which greatly s i m p l i f i e s matters from a mechanical standpoint.  2 From these b r i e f observations i t becomes clear that anaerobic treatment does offer several advantages over aerobic treatment when considered for use i n farming.  For a t y p i c a l treatment f a c i l i t y , such as a  lagoon, the anaerobic system w i l l give a lower i n i t i a l cost, and usually a lower maintenance cost, as i t does not require the aeration and mixing equipment essential to the aerobic process, and also requires no power to function. Maintenance time, also, w i l l be minimal with the anaerobic system, as mechanic a l parts are reduced to the bare minimum, a few valves and pipes being a l l that are required.  However, the anaerobic system, f o r a l l i t s s i m p l i c i t y ,  does have i t s drawbacks, among which may be counted the odor problem often associated with anaerobic treatment.  This i s due to the production of hydro-  gen sulphide gas which accompanies the digestion process.  The anaerobic sys-  tem also tends to give a somewhat i n f e r i o r effluent quality compared to an  [2] aerobic system  .  Thus i t i s not uncommon to find an aerobic pond  following .an anaerobic pond i n situations where a very high effluent quality i s a requirement.  The effluent quality problem i s o f f s e t , however,  by the fact that anaerobic systems operate under a very high loading rate, which i s important when one considers the high strength of the animal wastes with which farmers are concerned. Thus i t may be seen that both methods have their drawbacks, and careful thought must be given i n any design project to the choice of system, having due regard to the type and strength of waste, the location and size of the f a c i l i t y , and the quality of effluent required.  This study concerns  i t s e l f with investigations into the anaerobic system only. Anaerobic lagooning i s at f i r s t sight a very a t t r a c t i v e proposition.  A l l that i s required i s an area near the farm buildings s u f f i c i e n t to  3  accommodate a lagoon or group of lagoons large enough to handle the waste output of the farm and produce an e f f l u e n t of quality acceptable to the appropriate regulatory agencies. required.  No mixing of air-supply equipment i s  I f the lagoon i s i n i t i a l l y well constructed, maintenance costs  w i l l be largely determined by the frequency at which accumulated to be removed from the bottom of the lagoons.  sludge has  The rate of sludge build-up  i s thus of great importance, and a primary objective of the research proj e c t under discussion was to learn something of the degree to which sludge i s b i o l o g i c a l l y degraded i n such a lagoon.  A knowledge of this would enable  an estimate to be made regarding maintenance costs f o r many years ahead, as sludge which i s not b i o l o g i c a l l y degraded w i l l eventually have to be physic a l l y removed.  Clearly the anaerobic lagoon i s the simplest possible treatment f a c i l i t y for a high-concentration a g r i c u l t u r a l operation, and such lagoons [3] have been widely used with success  . A good example of an operation of  this kind,' using the anaerobic lagoon system, i s to be found at Abbotsford, B.C.,  i n the Fraser Valley.  pig-raising f a c i l i t y . for  Here the National Hog Center has a large indoor  The treatment system on that farm provided the wastewater  this present study, as well as giving a check on performance  under actual,  as opposed to laboratory, operating conditions. 1.2  Fundamentals of Anaerobic Digestion The mechanism of anaerobic sludge digestion i s shown i n Figure 1.1.  There are two d i f f e r e n t groups of bacteria involved i n the anaerobic chain. The f i r s t group are known as the "acid-forming bacteria".  These take the  organic materials i n the waste, which are f i r s t l i q u i f i e d by e x t r a - c e l l u l a r  4  enzymes, and convert them t o v o l a t i l e a c i d s , such as a c e t i c , p r o p i o n i c and butyric.  The second group o f micro-organisms a r e known as the "methane-  forming b a c t e r i a " .  They take the v o l a t i l e a c i d s a l r e a d y produced by the  a c i d - f o r m i n g b a c t e r i a and ferment them f u r t h e r t o form gaseous the main c o n s t i t u e n t s o f which a r e methane and carbon d i o x i d e .  products, Some n i t r o g e n  and hydrogen s u l p h i d e a r e a l s o produced a t t h i s s t a g e , due t o r e d u c t i o n o f n i t r a t e s and s u l p h a t e s , e t c .  However, these a r e present o n l y as t r a c e gases  i n a w e l l - o p e r a t i n g system t h a t does not have t o t r e a t wastes h i g h i n n i t r a t e s or sulphates.  O b v i o u s l y both  l i n k s . i n the c h a i n a r e e q u a l l y important,  a c i d s formed i n t h e f i r s t stage s t i l l waters.  e x e r t BOD and COD on the r e c e i v i n g  The t r u e r e d u c t i o n of the waste o c c u r s o n l y i n the second  Thus i t becomes important and  as the  t o understand  the response o f both  gas-formers to changing c o n d i t i o n s .  stage.  acid-formers  I t i s g e n e r a l l y assumed t h a t t h e  r a t e of r e a c t i o n i s c o n t r o l l e d by the r a t e a t which v o l a t i l e a c i d s a r e con-  [2] v e r t e d t o methane and carbon d i o x i d e  .  Thus, system f a i l u r e , which  occurs  when t h e r e i s an imbalance i n the p r o c e s s , r e s u l t s i n a b u i l d - u p o f i n t e r mediate v o l a t i l e a c i d s .  To check on t h i s , the v o l a t i l e a c i d s and pH were  c a r e f u l l y monitored i n t h i s study, as they a r e important  i n d i c a t o r s of how  w e l l the second phase i s p r o c e e d i n g .  1.3  Need.for F u r t h e r Research  During of  the summer and f a l l  o f 1970, the C i v i l E n g i n e e r i n g  The U n i v e r s i t y o f B r i t i s h Columbia undertook r e s e a r c h intended  Department  to provide  more d e t a i l e d i n f o r m a t i o n r e g a r d i n g the d e s i g n and o p e r a t i o n o f a n a e r o b i c  [4] lagoons than had p r e v i o u s l y been a v a i l a b l e ber of s i n g l e - s t a g e a n a e r o b i c  .  The program employed a num-  d i g e s t e r s , each o f t w e n t y - f i v e l i t r e s  capacity,  5  SLUDGE INSOLUBLE ORGANIC MATERIAL  EXTRACELLULAR ENZYMES  SOLUBLE ORGANIC MATERIAL  ACID-FORMING BACTERIA  VOLATILE ACIDS  +  CO.  H„  FIGURE 1.1  +  co  2  +  BACTERIAL CELLS  ENDOGENOUS >RESPIRATION TO OTHER PRODUCTS  GAS-FORMING BACTERIA  INTERMEDIATE PRODUCTS  CH. 4  OTHER PRODUCTS  BACTERIA CELLS  Mechanism o f A n a e r o b i c Sludge  Digestion.  6  which were f e d w i t h samples of raw waste o b t a i n e d from the p r e v i o u s l y mentioned  N a t i o n a l Hog  Center at A b b o t s f o r d , B.C.  A l l the important  opera-  t i o n a l and t r e a t m e n t - e f f i c i e r i c y ' i n d i c e s were monitored, and the e f f e c t the system o f changes i n o p e r a t i n g c o n d i t i o n s was  investigated.  on  As a r e s u l t  of t h i s work, c e r t a i n recommendations f o r d e s i g n of a n a e r o b i c lagoons were o u t l i n e d , and a number of recommendations  f o r f u t u r e s t u d i e s were made.  The p r e s e n t study i s based on t h r e e of those recommendations.  1.4  S e p a r a t i o n of S e t t l e d S o l i d s and  The t o p i c was  Supernatant  recommended f o r f u r t h e r study i n the p r e v i o u s  [4] report  .  I t was  felt  that much of the e f f i c i e n c y of treatment was  due  to  s e t t l i n g out of the s o l i d s i n the waste, and t h a t b i o l o g i c a l d e g r a d a t i o n was of secondary  importance  i n the p r o d u c t i o n of a h i g h - q u a l i t y e f f l u e n t .  any i n c r e a s e i n s e t t l i n g e f f i c i e n c y s h o u l d prove worthwhile.  The  Thus  problem  [4] encountered w i t h the s i n g l e - s t a g e d i g e s t e r s used i n the p r e v i o u s study was  t h a t gas l e n s e s would form i n the s l u d g e a t the bottom, and would  eventually u p l i f t suspended  the s o l i d s , m i x i n g them w i t h the s u p e r n a t a n t .  These r e -  s o l i d s would be f l u s h e d out w i t h the e f f l u e n t , c o n t r i b u t i n g to  lower o v e r a l l e f f i c i e n c y . work, a s e r i e s of two-stage the two-stage  I t was  t h e r e f o r e d e c i d e d t o b u i l d , f o r the p r e s e n t  d i g e s t e r s , approximating on a l a b o r a t o r y  lagoon arrangement used i n the A b b o t s f o r d o p e r a t i o n .  l a t t e r case, the main lagoon was  scale In the  f o l l o w e d by a s m a l l e r lagoon s e r v i n g  as a f i n a l s e t t l i n g and p o l i s h i n g chamber.  The p a i r s o f c e l l s used i n  the l a b o r a t o r y were b o t h o f the same c a p a c i t y , twelve and o n e - h a l f l i t r e s each, g i v i n g an i d e n t i c a l t o t a l volume t o the s i n g l e - s t a g e u n i t s  [4]  used i n the p r e v i o u s r e s e a r c h . The f i r s t c e l l would t r a p the b u l k of the s o l i d s by s e t t l i n g , and much of the b i o l o g i c a l a c t i v i t y would occur  7  here.  The  supernatant  from t h i s c e l l would be run i n t o a second  c e l l which  would not e x h i b i t as much b i o l o g i c a l a c t i v i t y , but which would s e r v e as a s e t t l i n g chamber, as i t would be l e s s s u b j e c t e d to the s e l f - m i x i n g p r o c e s s already described.  Thus it;;was expected  t h a t some i d e a of the e f f e c t  i n c r e a s e d s e t t l i n g e f f i c i e n c y would be o b t a i n a b l e from the  1.5  Sludge B u i l d - u p and Gas  of  study.  Production  These t o p i c s were recommended f o r f u r t h e r i n v e s t i g a t i o n s i n recommen[4] d a t i o n s B and D of the p r e v i o u s study  .  u n d e r t a k i n g such an i n v e s t i g a t i o n .  f i r s t of these was  percentage  The  There were a number of reasons f o r  on the bottom of the  e v e n t u a l l y h a v i n g to be removed m e c h a n i c a l l y .  of  what  of the s e t t l e d s o l i d s were " f i x e d " , t h a t i s , would not respond  b i o l o g i c a l treatment, but would accumulate  above, was  to determine  The  second,  t h a t a major o b j e c t i v e of the p r e s e n t work was  the r e l a t i v e importance  the d e g r a d a t i o n p r o c e s s . a v a i l a b l e was l i n k e d t o COD,  lagoon,  outlined  to g a i n some i d e a  of s e t t l i n g as opposed to b i o l o g i c a l a c t i v i t y i n The  o n l y measure of b i o l o g i c a l a c t i v i t y  gas p r o d u c t i o n and BOD  as  to  readily  a n a l y s i s ; thus gas p r o d u c t i o n had  and v o l a t i l e s o l i d s removal.  to be  F i g u r e s e x i s t e d f o r these  v a l u e s f o r domestic wastes, but they would not n e c e s s a r i l y a p p l y to concent r a t e d animal wastes. [4] To o b t a i n t h i s i n f o r m a t i o n , i t was of  b a t c h t e s t s be undertaken,  etc.,  recommended  that a s e r i e s  w i t h the v a r i o u s parameters such as BOD,  measured i n a f u l l y mixed c o n d i t i o n .  The  temporal  COD,  reduction i n solids  and oxygen demand c o u l d then be g r a p h i c a l l y l i n k e d to the amount of  gas  formed, and u n i t p r o d u c t i o n f i g u r e s o b t a i n e d from these.  propor-  t i o n of s o l i d s remaining  A l s o , the  i n the c e l l s a f t e r b i o l o g i c a l d e g r a d a t i o n  was  essentially  complete would g i v e the d e s i r e d i n f o r m a t i o n r e g a r d i n g the  p r o p o r t i o n of " f i x e d " s o l i d s . remainder of the p r e s e n t  study.  T h i s recommendation formed the b a s i s f o r  9  CHAPTER 2.  2.1  EXPERIMENTAL PROCEDURE  General Discussion  I n i t i a l l y , much time was saved by the use of m a t e r i a l and e q u i p -  [4] ment from t h e former experiments used were s t i l l  .  The s i n g l e - s t a g e d i g e s t e r s p r e v i o u s l y  i n o p e r a t i o n , and hence s t i l l  contained v i a b l e  organisms.  These organisms were used as seed f o r the ongoing r e s e a r c h program. the  s i n g l e - s t a g e a c r y l i c d i g e s t e r s were used as the c o n t a i n e r s f o r the b a t c h  experiments. two-stage  The new two-stage u n i t s had t o be c o n s t r u c t e d .  Three o f these  u n i t s were b u i l t . For  the b a t c h t e s t s , i t was d e c i d e d f o r s e v e r a l reasons t o r u n two  c o n c u r r e n t experiments. of  Two o f  F i r s t l y , a comparison  c o u l d be made on t h e r e s u l t s  one t e s t a g a i n s t those o f the o t h e r , g i v i n g a g r e a t e r degree o f c e r t a i n t y  about the r e s u l t s . been u s i n g Acti-Zyme  Secondly, the N a t i o n a l Hog Center had f o r some months , an enzyme a d d i t i v e i n t e n d e d t o s t i m u l a t e b i o l o g i c a l  a c t i v i t y and prevent s l u d g e b u i l d - u p s a t the i n l e t s t o the lagoons.  This  [4] m a t e r i a l had not been p r e s e n t i n the samples but i t would be p r e s e n t i n the samples  taken f o r t h e p r e v i o u s t e s t s  ,  used f o r the new s e r i e s o f t e s t s .  Thus, some i d e a o f i t s e f f e c t , i f any, on the a n a e r o b i c a c t i v i t y would be useful.  The b a t c h t e s t s were a c c o r d i n g l y f i l l e d w i t h waste o b t a i n e d , by  s p e c i a l arrangement, w i t h Acti-Zyme  One o f the b a t c h t e s t s was  treated  a c c o r d i n g t o t h e manufacturers i n s t r u c t i o n s , and t h e o t h e r was  l e f t untreated. half l i t r e  f r e e from Actizyme.  Each b a t c h t e s t u n i t was f i l l e d  level initially.  t o the twenty-four and one-  As samples were taken weekly,  Allowance was made f o r t h i s i n a l l c a l c u l a t i o n s .  the volume d e c r e a s e d .  The b a t c h t e s t s were both  Manufactured by Actizyme Co., Box 188, Three R i v e r s , C a l i f o r n i a , U.S.A.  10  run a t room temperature, which h e l d f a i r l y  c o n s t a n t a t around 22° C e l s i u s .  The two-stage systems were s p e c i a l l y designed t o prevent c a r r y over o f suspended  s o l i d s from t h e f i r s t  the second c e l l t o the e f f l u e n t . at the same l e v e l .  c e l l t o the second c e l l ,  o r from  The o l d c e l l s had i n l e t and o u t l e t  valves  Thus s h o r t c i r c u i t i n g o f some o f the i n f l u e n t waste t o  the e f f l u e n t v a l v e was v e r y p o s s i b l e  ( F i g u r e 2.1).  The new d i g e s t e r s had  b a f f l e s i n f r o n t o f the t r a n s f e r p i p e i n both f i r s t and second-stage T h i s e f f e c t i v e l y prevented any s h o r t - c i r c u i t i n g of t h i s k i n d  cells.  ( F i g u r e s 2.2  and 2.3).  The t h r e e two-stage u n i t s were r u n a t 30° C e l s i u s , room t u r e , and 10° C e l s i u s r e s p e c t i v e l y .  tempera-  Thermostatically controlled heating  tapes were used to heat the high-temperature system, w h i l e the low-temperature system was equipped w i t h a s e t of c o o l i n g c o i l s i n each c e l l .  Thermostats  s i m i l a r t o those used i n the high-temperature u n i t c o n t r o l l e d the pumping o f c o l d water through these c o i l s .  An immersion r e f r i g e r a t i o n u n i t kept the  c o o l i n g water r e s e r v o i r a t around 4° C e l s i u s , and s u b m e r s i b l e e l e c t r i c pumps were used f o r water c i r c u l a t i o n .  Thermometers i n t h e d i g e s t e r  lids  enabled a check on temperature t o be kept a t a l l times.  The o b j e c t i v e o f the study was t o use t h i s and o t h e r l a b o r a t o r y equipment t o o b t a i n t h e n e c e s s a r y d a t a f o r a l l o b j e c t i v e s of the i n v e s t i g a tion.  The e x p e r i m e n t a l procedure may be broken down c o n v e n i e n t l y as  follows.  2.2  E s t a b l i s h m e n t and O p e r a t i o n of the Batch Systems  As p r e v i o u s l y mentioned,  t h e c e l l s from the p r e v i o u s s i n g l e - s t a g e  11  FIG. 2 - I S I N G L E - S T A G E DIGESTE R, SHOWING POSSIBILITY OF SHORT-CIRCUITING DURING FEEDING.  o Outlet  Inlet  12  FIG. 2 - 2 T W O - S T A G E DIGESTER,SHOWING FLOW PATTERN DURING FEEDING.  FIG. 2 - 3 P L A N OF FLOW DURING FEEDING  13  t e s t s were s t i l l  s e t up i n the l a b o r a t o r y , and s t i l l  contained sludge.  Although gas p r o d u c t i o n had f a l l e n o f f t o p r a c t i c a l l y n i l , s a f e t o assume t h a t a v i a b l e c u l t u r e o f b a c t e r i a sludge.  The two d i g e s t e r s t o be used  still  i t was  fairly  existed i n this  f o r the b a t c h t e s t s were t h e r e f o r e  d r a i n e d u n t i l o n l y an i n c h o r so o f sludge remained.  F r e s h raw waste  from  the A b b o t s f o r d farm was then used t o r e - f i l l t h e d i g e s t e r s up t o the twentyf o u r and o n e - h a l f l i t r e  level.  D i g e s t e r number 1 was f i l l e d w i t h wastewater  which was s p e c i a l l y c o l l e c t e d t o be f r e e o f Acti-Zyme,  w h i l e d i g e s t e r number 2  was t r e a t e d w i t h an Acti-Zyme c o n c e n t r a t i o n o f 0.00625% as recommended by the  manufacturer.  I t may be s t a t e d t h a t the use o f Acti-Zyme on t h e farm had proved e f f e c t i v e i n keeping p i p e blockages and sludge b u i l d - u p s on the lagoons t o a minimum.  I t was i n t e r e s t i n g t o note i n view o f t h i s , t h a t , w h i l e u n i t  number 1 took t w e n t y - f i v e days t o become b i o l o g i c a l l y a c t i v e , number 2 s t a r t e d immediately. curve  A l s o , as may be seen from t h e gas p r o d u c t i o n r a t e  ( F i g u r e 3.1), number 2 had, throughout  tion rate.  the t e s t , a h i g h e r gas produc-  T h i s w i l l be f u r t h e r d i s c u s s e d i n the next c h a p t e r , but c e r t a i n l y  on t h e b a s i s of these i n d i c a t i o n s , t h e use of Acti-Zyme i n systems of t h i s type would seem t o be b e n e f i c i a l .  2.3  E s t a b l i s h m e n t and O p e r a t i o n o f the Two-Stage Systems  In  the case o f the two-stage u n i t s , l i t t l e o r no a c t i v i t y c o u l d  be o b t a i n e d a t f i r s t ,  d e s p i t e the a d d i t i o n o f seed m a t e r i a l from t h e s t i l l  active single-cell units.  The problem was t h a t the a c i d - f o r m i n g b a c t e r i a  began t o work a t once, and produced  enough a c i d t o send t h e pH o f t h e s y s -  tem down t o the r e g i o n o f 6.6 t o 6.8 i n t h e primary c e l l s .  The pH o f the  14  secondary c e l l s h e l d i n the 7.1  - 7.2  range.  P r e v i o u s s t u d i e s have found  t h a t , f o r a b a l a n c e d system to be a c h i e v e d , the optimum pH i s i n the o r d e r of  6.8  to 7.2,  depending  on system o p e r a t i n g c o n d i t i o n s .  In the case under  d i s c u s s i o n , the a c i d - f o r m e r s were f a r o u t p e r f o r m i n g the gas-formers  i n the  p r i m a r y c e l l s and i n d o i n g so were g i v i n g r i s e to a pH range which made i t extremely u n l i k e l y t h a t a b a l a n c e d s t a t e c o u l d be a c h i e v e d . f o u r weeks, i t was lime.  d e c i d e d to r a i s e the pH of the d i g e s t e r c o n t e n t s w i t h  J u s t a f t e r t h i s d e c i s i o n was  taken, however, the 30°C d i g e s t e r  suddenly e x h i b i t e d a r i s e i n pH on i t s own,  and began t o f u n c t i o n w e l l .  The o t h e r two, both o f which were a t room temperature remained  added 0.1  gm.  u n t i l the pH was  a t a time and t h o r o u g h l y mixed: r a i s e d to  about' 7.2.  days to a v o i d shock t o the system. function well.  purposes,  temperature,  c o o l e d down to 10°C  done once a day and was  f u n n e l and s p i g o t mounted i n the l i d .  t h i s p r o c e s s was spread over  Lime continued several  pH, b o t h d i g e s t e r s began t o  g i v e n a f u r t h e r month to become e s t a b l i s h e d , i n a s e r i e s of 1°C  i n o r d e r to g i v e the organisms  Feeding was  r a i s e the pH.  T h i s p r o c e s s was  At the new  The 10°C d i g e s t e r was  d u r i n g which time i t was of  for starting  a t t h e i r former u n f a v o u r a b l e pH l e v e l s , so a f t e r another two weeks  they were t r e a t e d w i t h l i m e (CaCOH)^) to a r t i f i c i a l l y was  Thus, a f t e r  increments  ample time to a c c l i m a t i s e .  accomplished by means of a  No a i r c o u l d pass i n t o the d i g e s t e r  gas space through t h i s , and the o u t l e t i n t o the d i g e s t e r was  a two-opening  one which gave h o r i z o n t a l f l o w i n o p p o s i t e d i r e c t i o n s , thus m i n i m i s i n g s w i r l i n the chamber and d i s t u r b a n c e o f the bottom d e p o s i t s ( F i g u r e I t was  a n t i c i p a t e d t h a t t h i s would tend to reduce s o l i d s t r a n s f e r from the  primary to the secondary cell  2.3).  cell.  E f f l u e n t was  at the time of f e e d i n g . t h e primary c e l l  drawn o f f from the  secondary  to m a i n t a i n a c o n s t a n t l e v e l  i n the d i g e s t e r s and e f f e c t a u n i f o r m t r a n s f e r of supernatant from the '. '  15  primary  to the secondary  of the two  cells,  cells.  To ensure  complete independence of o p e r a t i o n  the t r a n s f e r v a l v e between the two was  kept c l o s e d except  during feed a d d i t i o n .  Initially, primary and  i t had been i n t e n d e d to use a r o t a r y w i r e s c r e e n i n the  c e l l s to d i s t u r b the sludge j u s t s u f f i c i e n t l y t o p r e v e n t  s e l f - m i x i n g as encountered  i n the p r e v i o u s t e s t s .  lensing  However, i t was  found  i m p o s s i b l e w i t h the equipment a v a i l a b l e to run t h i s s c r e e n s l o w l y enough to prevent l e n s i n g w i t h o u t T h i s i d e a was  itself  c a u s i n g r e - s u s p e n s i o n of s o l i d s by  t h e r e f o r e dropped, and  the systems were operated  u n d i s t u r b e d except by s e l f - a c t i o n i n the  2.4  T e s t i n g Procedure  mixing.  entirely  sludge.  f o r the I n f l u e n t s and  Effluents  The raw waste used i n the t e s t s was  o b t a i n e d i n e x a c t l y the same  [4] manner as i n the p r e v i o u s s e r i e s of t e s t s  , with eight-hour  samples b e i n g taken from the manhole c l o s e s t to the lagoons o u t f a l l sewer.  P o l y e t h y l e n e carboys were used  composite  i n the main  as sample c o n t a i n e r s , and  these were s t o r e d i n a r e f r i g e r a t i o n u n i t u n t i l needed f o r f e e d i n g the experimental u n i t s . was  U n f o r t u n a t e l y , d u r i n g the t e s t s , the farm a t A b b o t s f o r d  c l o s e d down and evacuated  due  t o an outbreak  of v i r u s d i s e a s e among the  hog p o p u l a t i o n , and so enough waste t o supply the second h a l f of the had  t o be gathered and  s t o r e d a t once, w h i l e t h e r e was  p r o d u c i n g p o p u l a t i o n i n the farm. throughout.the  still  tests  a waste-  The raw waste samples v a r i e d i n s t r e n g t h  t e s t s , but t h e r e were no marked a b n o r m a l i t i e s among the  c h a r a c t e r i s t i c s of the long-term s h o r t - t e r m s t o r a g e ones.  s t o r a g e samples, as opposed t o the p r e v i o u s .  The o n l y problem was  the f i n a l s t a g e s of the experiment,  a shortage of feed d u r i n g  which l i m i t e d the scope of the work  16  somewhat.  1  Grab samples were used t o t e s t the d i g e s t e r e f f l u e n t .  from both p r i m a r y and secondary c e l l s of the two-stage T e s t s were performed weekly f o r most parameters, d i t i o n s o n l y f o r t h e remainder.  Effluent  systems was t e s t e d .  and under e q u i l i b r i u m  con-  The o b j e c t of the experiment was t o a c h i e v e  an e q u i l i b r i u m s t a t e a t each o f s e v e r a l f e e d i n g r a t e s , and t o r u n a l l r e l e vant t e s t s t o measure d i g e s t e r performance  a t these f e e d i n g r a t e s .  Feeding  r a t e s used were 0.5 A/day, 1.0 it/day, and 1.5 H/day, g i v i n g a s i m i l a r of d e t e n t i o n times t o t h a t used i n the p r e v i o u s r e s e a r c h  range  [4]  Both mixed raw waste and d i g e s t e r supernatant were t e s t e d .  I n the  case o f the b a t c h t e s t s , the c o n t e n t s o f the d i g e s t e r were f u l l y mixed b e f o r e t e s t i n g , as a c t u a l q u a n t i t i e s , not c o n c e n t r a t i o n s , were r e q u i r e d i n t h i s Initially,  case.  some i r r e g u l a r i t y was found i n t h e b a t c h t e s t r e s u l t s , b u t e x t e n -  s i o n and s t a n d a r d i s a t i o n of the pre-sampling mixing time s o l v e d t h i s p r o blem.  All Standard  t e s t s were c a r r i e d out a c c o r d i n g to the procedures g i v e n i n  M e t h o d s ^ , and f u r t h e r e x p l a i n e d i n Chemistry f o r S a n i t a r y  Engineers^"'.  I n t h e case o f both the b a t c h t e s t s and the two-stage  d i g e s t e r s , t e s t s run r o u t i n e l y on t h e e f f l u e n t s were:  1) PH 2) B i o c h e m i c a l Oxygen Demand (BOD) 3) Chemical Oxygen Demand (COD) 4) T o t a l and V o l a t i l e S o l i d s  (TS and VS)  5) K j e l d a h l N i t r o g e n , both T o t a l and O r g a n i c .  D i l u t i o n o f the samples was n e c e s s a r y , due t o t h e h i g h s t r e n g t h o f  17  the waste.  These were a r r i v e d at u s i n g  m o d i f y i n g the  f i g u r e s through r e p e a t e d  In the i n f l u e n t and  case of the  the p r e v i o u s work as a b a s i s trials.  two-stage d i g e s t e r s ,  effluent i n addition  and  t e s t s run  r o u t i n e l y on  the  to the above were:  6) V o l a t i l e A c i d s 7) T o t a l O r g a n i c Carbon.  The as  v o l a t i l e acids  d a t a were expected to be  i n d i c a t o r s of m i c r o - b i o l o g i c a l  A c i d s a n a l y s i s was  conditions  accomplished u s i n g  chromatograph w i t h a s i x - f o o t by  1/8  i n the  of great  test units.  interest  /  Volatile  a Hewlett-Packard Model 5752 B  gas  i n c h diameter s t a i n l e s s s t e e l column  packed w i t h Porapack Q 50 - 80 Mesh p a c k i n g , c o n t a i n i n g  2 percent phosphoric  acid.  T o t a l O r g a n i c Carbon was T o t a l Organic Carbon A n a l y s e r . a c o r r e l a t i o n between BOD,  COD  The and  determined u s i n g  a Beckman Model  d a t a generated was TOC.  I t i s f e l t by  i n t e n d e d to p r o v i d e some t h a t TOC  some time, become a s t a n d a r d t e s t , perhaps even s u p p l a n t i n g l e n g t h y and  involved  to a s s i s t a l i n k - u p  BOD  and  COD  to p o s s i b l e  tests  8) T o t a l Phosphate 9) Copper C o n c e n t r a t i o n  11) A l k a l i n i t y .  may,  at  comparatively also  included  future r e s u l t s .  or at e q u i l i b r i u m o n l y were:  Nitrate  the  Hence t h i s t e s t was  In a d d i t i o n to the t e s t s p r e v i o u s l y  10)  915  mentioned, t e s t s run  occasionally  18  For the purposes of t h i s study, n u t r i e n t v a l u e s were of  little  importance, as they were s t u d i e d i n some d e t a i l i n the p r e v i o u s experiments. A check was  kept on them i n the p r e s e n t case, but no more.  c e n t r a t i o n was  of i n t e r e s t , because i t was  felt  The copper con-  t h a t d i s s o l v e d copper from  the b r a s s f i t t i n g s i n the d i g e s t e r s , and a l s o from the copper c o i l s i n the c o l d d i g e s t e r , might r e a c h c o n c e n t r a t i o n s s u f f i c i e n t  t o have a h a r m f u l  e f f e c t on the o p e r a t i o n of the d i g e s t e r s .  2.5  T e s t i n g Procedure f o r the E v o l v e d Gases  The e v o l v e d gases were a n a l y z e d b o t h q u a l i t a t i v e l y and The Hewlett-Packard gas chromatograph These r e s u l t s would  was  quantitatively.  used to o b t a i n gas c o m p o s i t i o n f i g u r e s .  enable methane p r o d u c t i o n t o be c a l c u l a t e d and t h i s  to be r e l a t e d to s o l i d s and BOD  removal.  was  A l s o they gave some i n d i c a t i o n as  to the s t a b i l i t y of the system.  To o b t a i n volumes o f e v o l v e d gas, the same water-displacement [4] tubes used i n the p r e v i o u s work  were employed.  L a t e r , a p a i r of Alexander  Wright and Co., Model M 809 LT Hyde P a t t e r n wet-meters were o b t a i n e d used f o r t h i s purpose.  Gas p r o d u c t i o n f o r the two-stage u n i t s was  o n l y a f t e r e q u i l i b r i u m had been a c h i e v e d . was  and  measured  Continuous use of the wet-meters  not c o n s i d e r e d a d v i s a b l e from a c o r r o s i o n s t a n d p o i n t . Samples f o r gas c o m p o s i t i o n a n a l y s i s were taken by means of  s y r i n g e s from sampling p o r t s i n s t a l l e d the treatment u n i t to the gas  2.6  i n the gas o u t l e t l i n e which  connected  meter.  Summary  No g r e a t d i f f i c u l t i e s , o t h e r than the shortage of feed near the  19  end of the t e s t , were encountered  d u r i n g the course of the experiment.  equipment worked w e l l , and s u f f i c i e n t d a t a was o b t a i n e d . d a t a and d i s c u s s i o n o f r e s u l t s i s p r e s e n t e d  All  The a n a l y s i s of this,  i n the f o l l o w i n g c h a p t e r s .  20  CHAPTER 3.  3.1  RESULTS OF BATCH TESTS  Introduction  The f i r s t  o b j e c t i v e i n the case o f the b a t c h t e s t s was  to q u a n t i t a -  t i v e l y r e l a t e the r a t e o f methane p r o d u c t i o n to the r a t e s of r e d u c t i o n of s o l i d s , BOD  and COD.  The second o b j e c t i v e was  of b i o l o g i c a l d e g r a d a t i o n of the accumulated  to study the r a t e and  solids.  degree  Such u n d e r s t a n d i n g  would enable a good e s t i m a t e to the made both of the r e l a t i v e importance  of  b i o - d e g r a d a t i o n as opposed t o s e t t l i n g , and o f the p r o p o r t i o n of s o l i d s which would e v e n t u a l l y have to be removed from the lagoon by p h y s i c a l means. [21 Eckenfelder  , among o t h e r s , g i v e s f i g u r e s f o r the r e l a t i o n s h i p between gas  p r o d u c t i o n and r e d u c t i o n of s o l i d s , BOD the p a r t i c u l a r waste was 3.2  felt  G e n e r a l D i s c u s s i o n of  and COD,  to be n e c e s s a r y .  Procedure  Gas p r o d u c t i o n was  measured on a c u m u l a t i v e b a s i s by t a k i n g the  twenty-four hour p r o d u c t i o n , c o n v e r t i n g to STP temperature  (having r e g a r d to l a b o r a t o r y  and p r e s s u r e ) and adding to the p r e v i o u s day's c u m u l a t i v e  Hence the t o t a l amount of gas produced was of the gas was was  but a check on these f o r  checked  at a l l times  known at any time.  a l s o at weekly i n t e r v a l s .  total.  Composition  Thus methane p r o d u c t i o n  monitored.  To check the r e d u c t i o n o f s o l i d s , BOD,  COD,  mixed c o n t e n t s were sampled and a n a l y s e d weekly.  e t c . , the  fully  Knowing the c o n c e n t r a t i o n s ,  and the volume remaining i n the digester,, the a c t u a l q u a n t i t y of s o l i d s , BOD,  and COD  remaining c o u l d e a s i l y be c a l c u l a t e d .  o b t a i n e d , i t was  From the d a t a thus  easy to check the p u b l i s h e d f i g u r e s f o r methane p r o d u c t i o n ,  21  v e r s u s BOD, COD and s o l i d s  3.3  removal.  Gas P r o d u c t i o n and A n a l y s i s  Some d i f f i c u l t y was e x p e r i e n c e d on the gas chromatograph a t f i r s t , s i t u a t i o n a f t e r a time.  i n obtaining consistent readings  but p r a c t i s e i n technique  improved  this  The r e s u l t s showed c o n s i d e r a b l e v a r i a t i o n , so an  average v a l u e was used i n c a l c u l a t i o n s .  Values  o b t a i n e d were as f o l l o w s :  Methane:  56 - 65%  —  avg. 60%  Carbon D i o x i d e :  33 - 42%  —  avg. 38%  Nitrogen:  0.5 - 1.5% —  avg.  1%  Water:  0.5 - 1.5% —  avg.  1%  Hydrogen S u l p h i d e :  trace  Due t o the d i f f i c u l t i e s mentioned p r e v i o u s l y , r e s u l t s were not o b t a i n e d w i t h any c e r t a i n t y near the b e g i n n i n g of the t e s t s , but the above f i g u r e s a r e good f o r the time a t which p r o d u c t i o n was a t a peak and was consistent.  Hence t h e use o f the 60% f i g u r e f o r methane content  j u s t i f i e d , and accords w i t h accepted  figures  seems  T 81  With r e g a r d t o v o l u m e t r i c p r o d u c t i o n , F i g u r e 3.1 shows t h e r a t e of methane p r o d u c t i o n a g a i n s t time, and F i g u r e 3.2 shows the cumulative methane p r o d u c t i o n .  As p r e v i o u s l y mentioned, the enzyme-treated d i g e s t e r  number 2 produced more gas a t a l l times than number 1, which was not so treated.  However, i t may be mentioned t h a t t h e s o l i d s content  initially  p r e s e n t i n number 2 was a p p r e c i a b l y h i g h e r than t h a t i n number 1 due t o d i f f e r e n c e s i n t h e s o l i d s c o n t e n t o f t h e raw waste used and t h i s may have some b e a r i n g on the h i g h e r gas p r o d u c t i o n .  Tl ME  -  DAYS  24  As mentioned e a r l i e r , some d i f f i c u l t y was o b t a i n i n g u n i f o r m r e s u l t s from the c h e m i c a l t e s t s . c o n t e n t s was  initially  encountered  The mixing of the d i g e s t e r  found t o be a t f a u l t and a s t a n d a r d procedure was  adopted  g i v i n g the d i g e s t e r 20 minutes of r a p i d m i x i n g p r i o r to sampling. t h i s , l e s s t r o u b l e was  e x p e r i e n c e d and  in  of  After  so the cumulative gas p r o d u c t i o n p l o t  was  s t a r t e d from the f i r s t  day of t h i s s t a n d a r d procedure,  and  c o n c l u s i o n s drawn from the t e s t s taken a f t e r t h i s  The gas r a t e curve e x h i b i t s a f a i r l y  and a l l f i g u r e s  time.  t y p i c a l form.  If i t i s  assumed t h a t the gas p r o d u c t i o n r a t e i s an i n d i c a t o r of b a c t e r i a l p o p u l a t i o n , then one would expect d u c t i o n near  the curve seen on F i g u r e 3.1.  The resurgence  the end of the t e s t , at around the 50-day mark, may  of p r o -  be due  to  a change-over of the system to endogenous r e s p i r a t i o n as the s u b s t r a t e becomes d e p l e t e d .  In any  case, endogenous r e s p i r a t i o n i s c e r t a i n l y a f a c t o r  i n the c l o s i n g phases of a b a t c h t e s t such as t h i s one, from t h i s p o r t i o n of the curve may to a continuous  3.4  be suspect as f a r as t h e i r  system i s concerned.  subsequent s e c t i o n s of the p r e s e n t  F i g u r e s 3.3  and  3.4  chapter.  i n t r o d u c e d , the COD  i n e f f l u e n t BOD  respectively.  application  T h i s w i l l be f u r t h e r r e f e r r e d to i n  R e l a t i o n s h i p of Methane P r o d u c t i o n to BOD  The decreases  and hence r e s u l t s  and COD  and COD  Removal  w i t h time are shown i n  Even a f t e r s t a n d a r d i s e d s t i r r i n g  t e s t r e s u l t s showed c o n s i d e r a b l e f l u c t u a t i o n .  was This  due  l a r g e l y to the n a t u r e of the waste.  and  s t r i n g , sawdust, and l a r g e lumps of s o l i d s u r f a c e c r u s t were a l l p r e s e n t  i n the d i g e s t e r c o n t e n t s . can s i g n i f i c a n t l y a f f e c t  The presence the COD  would be the case i f i t were not  Wood c h i p s , s m a l l p i e c e s of  was  cloth  of a s m a l l p i e c e of wood, f o r example,  t e s t , c a u s i n g a h i g h e r v a l u e to be read present.  than  FIG.3-3 COD VALUES VS. TIME  25  10,000  TIME -  DAYS  27  To a l l o w somewhat f o r these f l u c t u a t i o n s , a f i t t e d through  curve was drawn  the p o i n t s o b t a i n e d f o r b o t h d i g e s t e r s , p l a c i n g more emphasis on t h e  p o i n t s o b t a i n e d from d i g e s t e r number 1, which e x h i b i t e d f a r l e s s than number 2.  However, the p o i n t s from number 2 l a y f a i r l y  fluctuation  close to t h i s  l i n e a l s o , w i t h the e x c e p t i o n of some towards the end of the t e s t .  Using  the gas p r o d u c t i o n d a t a and c a l c u l a t i n g the amount o f COD  removed by b a c t e r i a l a c t i o n as i n Appendix A, F i g u r e 3.5 was developed show COD removal v e r s u s methane p r o d u c t i o n .  to  The f i t t e d COD curve o f  F i g u r e 3.3 was used i n c o n j u n c t i o n w i t h the mean methane p r o d u c t i o n from the two t e s t s , r e p r e s e n t i n g an average o f both COD removal and gas p r o d u c t i o n [9] from the two u n i t s .  A l i n e h a v i n g t h e s l o p e g i v e n by Lawrence and McCarty  3 of 5.62 f t .  o f methane per l b . of COD d e s t r o y e d  (35.15 I o f methane per  100 gm. o f COD destroyed) was drawn f o r comparison.  The Lawrence and  McCarty f i g u r e i s based on t h e o r e t i c a l as w e l l as e x p e r i m e n t a l tions.  considera-  The l i n e o b t a i n e d from the average o f the two t e s t s c o r r e l a t e d q u i t e  w e l l w i t h t h i s t h e o r e t i c a l s l o p e , w i t h a tendency toward a s l i g h t l y p r o d u c t i o n o f methane p e r u n i t o f COD d e s t r o y e d .  lower  The l i n e s o b t a i n e d  from  the i n d i v i d u a l gas p r o d u c t i o n f i g u r e s from the two d i g e s t e r s a r e shown a l s o on F i g u r e 3.5, showing t h a t u n i t number 2 a p p a r e n t l y reduced per u n i t of methane produced than number 1.  much l e s s  COD  However, due t o t h e e r r a t i c  n a t u r e o f the COD r e s u l t s , the approach o f t a k i n g the average v a l u e f o r gas p r o d u c t i o n and a p p l y i n g i t t o t h e f i t t e d COD curve seems t o be j u s t i f i e d . On t h e b a s i s o f t h e s e f i n d i n g s , i t can be s t a t e d t h a t t h e use o f the f i g u r e o f 0.35 mi methane per mg o f COD d e s t r o y e d  i  i s perfectly  justified  o o  0  100  200 COD  Reduced  Biologically  300 -  grams  i n c a l c u l a t i o n s i n v o l v i n g the p a r t i c u l a r waste under t e s t . a c c o r d i n g l y employed i n subsequent  BOD  The  two  removal and gas p r o d u c t i o n .  a l o n g w i t h the l i n e o b t a i n e d above  L  J  .  f o l l o w e d i n c a l c u l a t i n g BOD  The  curve o b t a i n e d  i s shown i n F i g u r e  from the Lawrence and McCarty  o n l y , and  COD  removal as  t e s t s were a g a i n averaged out w i t h r e g a r d  T h i s s h o u l d h o l d good f o r BOD^  b a c t e r i a remove BOD  was  calculations.  An i d e n t i c a l procedure was r e l a t e d to gas p r o d u c t i o n .  This figure  (  B o r >  i s the sum  u  i )  a  s  w  t  e  l l  of the BOD  i-l  a  figure s  COD,  and  3.6,  given  s i n c e the  those  consti-  Li  tuents which can be c h e m i c a l l y o x i d i s e d o n l y .  In the case of the BOD than w i t h the COD  r e s u l t s , as the s m a l l p i e c e s of wood, hog  not r e a d i l y b i o - d e g r a d a b l e the COD  test.  r e s u l t s , much more c o n s i s t e n c y was  As may  be  and  thus do not a f f e c t the BOD  seen from F i g u r e 3.6,  obtained  h a i r s , e t c . , are  t e s t as they would  the r e s u l t s agreed  quite well  [91 w i t h the f i g u r e g i v e n by Lawrence and McCarty out.  Thus, i t may  a g a i n be  use of the f i g u r e 0.35  3.5  of BOD  destroyed  is fully  the  justified  the hog waste i n q u e s t i o n .  R e l a t i o n s h i p of Methane P r o d u c t i o n to V o l a t i l e S o l i d s Removal  V o l a t i l e s o l i d s removal was all  e s p e c i a l l y when averaged  s t a t e d t h a t , on the b a s i s of these r e s u l t s ,  ml methane per mg  i n c a l c u l a t i o n s concerning  .,  c a l c u l a t e d as i n Appendix A.  samples were taken f u l l y mixed, the c o n c e n t r a t i o n of the samples  Since was  the same as the o v e r a l l c o n c e n t r a t i o n i n the d i g e s t e r , e n a b l i n g the weight of v o l a t i l e s o l i d s i n the d i g e s t e r to be c a l c u l a t e d f o r the date of F i g u r e 3.7  shows the v o l a t i l e s o l i d s c o n c e n t r a t i o n i n the two  p l o t t e d a g a i n s t time,  s t a r t i n g from the b e g i n n i n g  the d i g e s t e r s f o r sampling  purposes.  sampling.  digesters  of the improved m i x i n g  in  To a l l o w f o r the f l u c t u a t i o n s i n the  to  BOD  FIG.3-6 REMOVAL VS. METHANE  PRODUCTION.  FIG. 3 - 7 VOLATILE SOLIDS VS. TIME (BATCH T E S T S ) .  Vo  - sanos  3iIIVIOA  32  results, fitted  curves were drawn through the p o i n t s o b t a i n e d , and these  were used t o o b t a i n t h e f i g u r e s f o r v o l a t i l e s o l i d s r e d u c t i o n as r e l a t e d t o methane p r o d u c t i o n .  F i g u r e 3.8 shows the gas p r o d u c t i o n r e l a t e d to the removal of v o l a t i l e s o l i d s , w i t h t h e p u b l i s h e d range of v a l u e s p l o t t e d f o r comparison. Eckenfelder  [2]  3 g i v e s a range of 17 to 20 f t . of gas produced per l b . of VS  d e s t r o y e d w i t h a methane content  of around 65%.  T h i s i s e q u i v a l e n t t o 69 t o  81 £ of methane produced per 100 gm. of VS d e s t r o y e d . E c k e n f e l d e r notes  t h a t these v a l u e s a r e a maximum, assuming complete  s i o n of v o l a t i l e s o l i d s to methane. initially although destroyed  In the same work,  T h i s may e x p l a i n why the s l o p e  converobtained  f o r d i g e s t e r number 2 i s lower than the E c k e n f e l d e r f i g u r e s  [21  ,  the same d i g e s t e r gave a h i g h e r gas p r o d u c t i o n per u n i t of BOD than the Lawrence and McCarty  figure  [91  , as seen from F i g u r e 3.6.  V o l a t i l e s o l i d s may be d e s t r o y e d by c o n v e r s i o n to v o l a t i l e a c i d s , w i t h no  [21 p r o d u c t i o n of methane and no r e d u c t i o n i n BOD probably  .  The low i n i t i a l  slope i s  t h e r e f o r e due t o a l a g i n e f f i c i e n c y of t h e methane-forming b a c -  t e r i a as opposed t o the a c i d - f o r m i n g b a c t e r i a .  on the curve,  A f t e r the f i r s t  two p o i n t s [2]  the s l o p e steepens t o match t h a t g i v e n by E c k e n f e l d e r  r e s u l t s from d i g e s t e r number 1 agreed  q u i t e w e l l w i t h the E c k e n f e l d e r  .  The  value.  E c k e n f e l d e r ' s f i g u r e was" a c c o r d i n g l y used i n f u r t h e r c a l c u l a t i o n i n v o l v i n g the hog waste under t e s t . With r e g a r d t o s o l i d s d e g r a d a t i o n in 19%  i n the b a t c h u n i t s used  the t e s t s , o v e r a l l v o l a t i l e s o l i d s r e d u c t i o n from s t a r t f o r d i g e s t e r number 1 and 22% f o r d i g e s t e r number 2.  t i o n had f a l l e n o f f t o n e a r l y zero jLn both  to f i n i s h was Since gas produc-  cases a t the c o n c l u s i o n of  t e s t i n g , any f u r t h e r v o l a t i l e . s o l i d s r e d u c t i o n would be of an  extremely  FIG.3-8  33  34  long-term n a t u r e .  The v o l a t i l e / t o t a l s o l i d s r a t i o i n b o t h cases  out a t approximately 69% a t the end of the t e s t , i n d i c a t i n g  averaged  that at l e a s t  30% of the remaining s o l i d s were d e f i n i t e l y non-degradable i n n a t u r e .  Thus,  a l l o w i n g a d i g e s t e r or lagoon to stand unfed w i l l not prove of much v a l u e i n r e d u c i n g sludge a c c u m u l a t i o n s .  35  CHAPTER 4.  4.1  Introduction  The  primary o b j e c t i v e o f t h e flow-through  knowledge c o n c e r n i n g tem  TWO-STAGE DIGESTER RESULTS  experiment was t o a c q u i r e  the r e l a t i v e performance o f a t w o - c e l l a n a e r o b i c  sys-  as compared t o a s i n g l e - s t a g e system o f the type employed i n p r e v i o u s [4]  research Detention mination  .  Results obtained  from the two systems a t c o r r e s p o n d i n g  Times (LDT) were compared.  A f u r t h e r a r e a o f study was the d e t e r -  of t h e manner and degree o f t h e c o n t r i b u t i o n of each o f the two  c e l l s i n a two-stage system t o the o v e r a l l treatment 4.2  Liquid  General  efficiency.  Discussion  As p r e v i o u s l y mentioned, the one problem encountered d u r i n g the t e s t program was a shortage ment.  A f t e r completion  o f feed d u r i n g the l a t t e r stages  of the t e s t s f o r the 50-day and 25-day LDT s t a g e s ,  i t was r e a l i s e d t h a t i n s u f f i c i e n t schedule  o f the e x p e r i -  feed remained t o complete the whole  o f t e s t i n g on a l l u n i t s .  A d e c i s i o n was t h e r e f o r e made t o r u n t h e  f i n a l 17-day LDT t e s t on the 30°C and 10°C d i g e s t e r s o n l y .  Even w i t h  l i m i t a t i o n , o n l y 13 days o f f e e d i n g c o u l d be completed w i t h  the remaining  feed.  this  Thus t h e r e i s c o n s i d e r a b l e doubt t h a t e q u i l i b r i u m was a c h i e v e d o r  even approached on the 17-day LDT. s o l i d s v a l u e s were s t i l l of the t e s t .  r i s i n g , although  not r a p i d l y , a t the c o n c l u s i o n  Hence the r e s u l t s f o r percentage removals on the 17-day LDT  are p r o b a b l y  a little  The degradation  I n f a c t , the e f f l u e n t BOD, COD and  high.  amounts o f methane produced by the immediate  (24-hour)  of the feed m a t e r i a l , and by the c o n t i n u i n g d e g r a d a t i o n  of the  36  accumulated sludge were .determined by m u l t i p l y i n g the t o t a l methane produc-  ts t i o n by percentages determined i n p r e v i o u s strate.  research  w i t h s i m i l a r sub-  The c h a r a c t e r i s t i c s o f the raw feed and e f f l u e n t s r e s p e c t i v e l y a r e  shown i n T a b l e s I and I I .  These data form the b a s i s f o r r e s u l t s  discussed  herein. TABLE I .  4.3  Average Raw Waste C h a r a c t e r i s t i c s .  THEORETICAL LDT DAYS  BOD,, ppm  COD ppm  50  4410  24,100  T V  2.964 2.146  25  6185  25,232  T V  2.696 1.508  17  4113  20,500  T V  2.049 1.459  E f f e c t i v e n e s s of M o d i f i c a t i o n s  The  SOLIDS %  to C e l l  two-stage flow-through d i g e s t e r s had two c e l l s each o f 12.5 Z  c a p a c i t y , g i v i n g the same 25 Z c a p a c i t y o f the p r e v i o u s l y used  single-stage  [4] units  .  The f i r s t  cell  o f the two-stage system c o u l d be c o n s i d e r e d  h a l f - s i z e s i n g l e - s t a g e u n i t f o r comparison purposes. mance should  thus be a c h i e v e d  i n a given  as a  Comparative p e r f o r -  s i n g l e - c e l l r e a c t o r used i n p r e -  [4] vious  research  and the f i r s t  cell  o f a two-stage r e a c t o r b e i n g  h a l f the d a i l y r a t e o f the s i n g l e - c e l l  f e d at  reactor.  Percentage removal f i g u r e s f o r t h e t w o - c e l l types a r e shown i n T a b l e I I I and mass removal f i g u r e s i n T a b l e IV.  37  TABLE I I . Average E f f l u e n t  Characteristics.  BOD ppm TEMP  30°C  23°C  10°C  LDT DAYS^\^^  1st  CELL  2nd  CELL  1st  CELL  2nd  CELL  1st  CELL  2nd  CELL  50  565  470  777  578  3583  2266  25  1035  850  1735  1352  5966  5680  17  1450  850  4100  4660  COD ppm TEMP LDT^ \. DAYS^v.  1st CELL  50  6780  5203  7630  6120  10,626  7,983  25  6995  5750  7680  6190  12,710  11,363  17  7690  6330  11,020  10,200  30°C  23°C  10°C  S  2nd  CELL  1st  CELL  2nd  CELL  1st  CELL  2nd  CELL  TOTAL AND V()LATILE SOL IDS % TEMP LDT^v. DAYS^V.  5 0  25 °  1 7  30°C 1st  CELL  23°C  2nd  CELL  1st  CELL  10°C  2nd  CELL  1st  CELL  2nd  CELL  T V  0.657 0.400  0.545 0.320  0.661 0.402  0.651 0.362  0.717 0.467  0.631 0.408  T V  0.676 0.411  0.569 0.329  0.728 0.450  0.617 0.366  0.769 0.492  0.705 0.438  T V  6.730 0.455  0.629 0.379  0.909 0.629  0.780 0.525  TABLE I I I .  Comparison o f P e r c e n t Removals i n O r i g i n a l 25 I C e l l and M o d i f i e d 12.5 £ C e l l .  12.5 DAY LDT UNIT  25 I CELL  12.5 I CELL  (MODIFIED)  Temp °C  30  23  10  30  23  % BOD Rem.  84.0  80.5  27.0  83.2  72.0  3.6  % COD Rem.  77.0  78.0  52.0  72.2  69.6  49.6  % VS Rem.  : 79.0  80.5  74.5  72.7  73.0  67.4  % TS Rem.  74.0  74.0  69.5  74.9  73.0  71.5  10  25 DAY LDT UNIT Temp  25 I CELL C  12.5  CELL  (MODIFIED)  30  23  10  30  23  10  % BOD Rem.  88.0  85.0  43.5 "  87.2  82.4  18.7  % COD Rem.  82.5  81.5  64.5  71.9  68.3  55.7  % VS Rem.  79.5  81.0  79.0  81.4  81.2  78.2  % IS Rem.  73.5  74.0  73.0  77.8  77.6  75.8  0  TABLE IV.  Comparison o f Mass Removed Per U n i t C e l l Volume f o r 25 I S i n g l e - s t a g e C e l l and 12.5 I F i r s t C e l l o f Double-Cell Digester.  25 DAY LDT UNIT Temp °C  25 I CELL  12.5 I MODIFIED CELL  30  23  10  30  23  10  344  332  169  153  145  33  COD Removed  985  976  769  692  658  538  VS Removed  661  674  657  698  697  671  TS Removed  829  834  823  922  921  898  * BGT> Removed 5  12.5 DAY LDT UNIT  25 I CELL  12.5 £ MODIFIED CELL  30  23  10  30  23  10  334  320  107  206  178  8  COD Removed  1009  1022  681  729  702  500  VS Removed  601  612  566  438  423  406  TS Removed  803  803  754  808  787  770  Temp °C  * B0D Removed 5  A l l removals i n mg/Jt o f c e l l / d a y .  40  P o i n t s t o note were:  a) Percentage BOD removals were almost i d e n t i c a l a t the 30°C temperature, but dropped o f f much more s h a r p l y w i t h d e c r e a s i n g temperature I n t h e case o f the f i r s t 12.5 £ c e l l of the twostage system.  On a mass b a s i s , t h e removal o f t h e 12.5 £ c e l l  never approached  t h a t of the 25 £ c e l l .  T h i s may be due t o the  f a c t t h a t the BOD of the m a t e r i a l used as feed f o r the 12.5 £ c e l l was v e r y much lower than t h a t used f o r the 25 £ c e l l .  The  r e s u l t i n g decrease i n the amount o f a v a i l a b l e s u b s t r a t e p e r u n i t o f c e l l volume c o u l d g i v e r i s e t o the lower mass removal figures obtained. of  the c e l l would  A l s o , any s h o r t - c i r c u i t i n g d u r i n g  feeding  lower the a c t u a l mass f e e d i n g r a t e f o r t h e  c e l l i n terms o f raw waste f e e d , as the amount o f raw waste remaining i n the c e l l a f t e r f e e d i n g would be lower. f a v o u r t h e s i n g l e - s t a g e d i g e s t e r s , as designed t o a v o i d s h o r t - c i r c u i t i n g .  This  would  the two-stage c e l l s were  However, t h i s e f f e c t  would  be o f f s e t t o an i n d e t e r m i n a t e degree by t h e i n c r e a s e i n e f f l u e n t s t r e n g t h due t o t h e s h o r t - c i r c u i t e d raw f e e d .  b) COD removal, b o t h on a percentage and mass b a s i s , was g r e a t l y s u p e r i o r f o r t h e 25 £ c e l l as compared t o the 12.5 £ two-stage cell.  A g a i n the two-stage c e l l  type f e l l o f f i n removal  e f f i c i e n c y much more w i t h d e c r e a s i n g temperature than d i d t h e 25 £ c e l l .  T h i s decrease i n e f f e c t i v e n e s s o f treatment w i t h  d e c r e a s i n g temperature noted a l s o f o r BOD, can o n l y be due t o decrease o f b i o l o g i c a l a c t i v i t y w i t h d e c r e a s i n g temperature. Since both two-stage and s i n g l e - s t a g e systems were s u b j e c t e d t o s i m i l a r temperature v a r i a t i o n s , the f a c t t h a t the two-stage system responded more n o t i c e a b l y can o n l y be due t o a d i f f e r e n c e  41  In t h e n a t u r e o f the b a c t e r i a l p o p u l a t i o n  i n the c e l l .  The  b a c t e r i a i n the t w o - c e l l system were l e s s t o l e r a n t o f temperat u r e changes. in  Since no b a c t e r i o l o g i c a l s t u d i e s were undertaken  the course o f t h i s r e s e a r c h ,  present  t h e a c t u a l n a t u r e o f the b a c t e r i a  i n b o t h cases i s unknown.  c) T o t a l s o l i d s removal was, on a percentage b a s i s ,  slightly  b e t t e r f o r the 12.5 £ two-stage type o f c e l l ,  and was  c a n t l y b e t t e r on a mass b a s i s f o r t h i s c e l l .  V a r i a t i o n with  temperature was o n l y s l i g h t  signifi-  i n the case of t o t a l s o l i d s removal.  V o l a t i l e s o l i d s removal was s l i g h t l y b e t t e r f o r the 12.5 £ c e l l at  t h e 25-day LDT, but was not as good at the 12.5-day LDT as  that obtained  w i t h the 25 £ c e l l .  From the t o t a l s o l i d s removal f i g u r e s , i t can be s t a t e d t h a t the modified The  c e l l does g i v e somewhat improved s e t t l i n g e f f i c i e n c y as p r e d i c t e d .  v a r i a t i o n i n removal e f f i c i e n c i e s o f the other parameters can be  attri-  buted t o d i f f e r e n c e s i n the c o m p o s i t i o n o f the f e e d m a t e r i a l , which was cons i d e r a b l e i n t h e case o f BOD c o n t e n t , and t o s h o r t - c i r c u i t i n g i n the 25 £ c e l l s . The  BOD c o n c e n t r a t i o n  o f the feed u s e d . i n  t h e two-stage c e l l s was l e s s than [4]  h a l f t h a t used i n the s i n g l e - s t a g e experiments r e a d i l y degradable m a t e r i a l p r e s e n t .  and thus there was much l e s s  T h i s would not a f f e c t parameters such  as t o t a l s o l i d s removal, which a r e dependent l a r g e l y on s e t t l i n g , but c o u l d appreciably  a f f e c t parameters such as BOD which c a n be expected t o be more  dependent on b a c t e r i o l o g i c a l a c t i o n . present for  feeding  of the 25 £ c e l l s would g i v e b e t t e r apparent r e s u l t s  t h e s e c e l l s due t o t h e a c t u a l f e e d i n g  level. this  during  S h o r t - c i r c u i t i n g , which was p r o b a b l y  These p o i n t s w i l l be d i s c u s s e d  thesis.  r a t e being  lower than the t h e o r e t i c a l  f u r t h e r i n t h e subsequent s e c t i o n s o f  42  4.4  Overall  Treatment  The r e s u l t s two-cell units,  Efficiency  o b t a i n e d from p e r c e n t a g e removal i n each c e l l o f the  and f o r the o v e r a l l system, a r e shown i n T a b l e s V - V I I I .  R e s u l t s noted were:  a) Removal e f f i c i e n c y decreased w i t h d e c r e a s i n g LDT:  this  effect  was more marked from 25 days t o 17 days than from 50 days t o 25 days. of  The d e c r e a s e was  not n e a r l y so pronounced  s o l i d s removal as i n the cases of COD  BOD.  T h i s seems t o i n d i c a t e  p o r t i o n of the COD bacteriological  and,  i n the case  particularly,  t h a t much o f t h e BOD  and a  certain  i s of a n o n - s e t t l e a b l e n a t u r e , depending on  action  f o r removal.  The f i g u r e s  d i g e s t e r , which showed minimal b a c t e r i o l o g i c a l  f o r the 10°C  action,  support  t h i s view, as a v o l a t i l e s o l i d s removal of 64% was o b t a i n e d w i t h e s s e n t i a l l y no BOD  removal a t the 17—day LDT.  s i o n h e r e i s t h a t most of the s e t t l e a b l e  The  conclu-  v o l a t i l e s o l i d s are [4]  essentially  non-degradable, as found i n the e a r l i e r r e s e a r c h  and i n the b a t c h t e s t s b) A s i m i l a r  d i s c u s s e d i n Chapter 3.  e f f e c t was n o t i c e d f o r the d e c r e a s e i n  e f f i c i e n c y w i t h decreased temperature. i n s o l i d s removal was  A g a i n the decrease  somewhat l e s s pronounced  i n COD  removal, and v e r y much l e s s pronounced  i n BOD  removal.  S i n c e the only f a c t o r  than the d e c r e a s e  i n the treatment p r o c e s s s i g n i f i c a n t l y  by temperature i s b i o l o g i c a l a c t i o n , s o l i d s and much of the COD  than t h e d e c r e a s e  i t may  affected  be concluded t h a t most of the  a r e removed by s e t t l i n g , but t h a t s u p e r n a t a n t  43  b i o l o g i c a l action removes most of the BOD.  This conclusion i s further  examined i n the following section.  4.5  Settling vs. B i o l o g i c a l Degradation Tables IX - XII show the percentage BOD removal figures broken down  into removals due to immediate b a c t e r i o l o g i c a l action and removals due to settling.  These figures were arrived at by taking the 24-hour methane produc-  t i o n due to the raw feed addition and multiplying t h i s by the appropriate c o e f f i c i e n t as discussed i n Chapter 3 to obtain the amount of each parameter b i o l o g i c a l l y degraded each day.  Knowing the feed and effluent c h a r a c t e r i s t i c s ,  the t o t a l removal per day could be simply calculated, and from this the removal due to s e t t l i n g was obtained. A l l figures were then converted to percentages. Points to note were: a) Immediate b a c t e r i o l o g i c a l degradation of v o l a t i l e s o l i d s was of very small importance compared to the s e t t l i n g e f f e c t .  Removal  due to b a c t e r i o l o g i c a l degradation never exceeded 13% of the t o t a l removal, and this was only achieved at the 30°C temperature.  b) The proportion of COD removal due to b a c t e r i o l o g i c a l action was somewhat higher than that found f o r s o l i d s , reaching a maximum of 19.3% of the t o t a l removal, also at the 30°C temperature, but again the settlement factor predominated.  c) BOD removal was f a r more dependent on immediate b a c t e r i o l o g i c a l degradation than either solids or COD.  At the 30°C temperature,  TABLE V.  \ . LDT  TEMP \. DAYS^X.  Percentage BOD Removals.  1st CELL  2nd CELL  30  23  10  50  87.2  82.4  18.7  25  83.2  72.0  3.6  17  64.7  0  TABLE VI.  30  OVERALL  23  10  30  23  10  2.1  4.5  29.8  89.3  86.9  48.5  \ 4.1  6.2  4.6  87.3  78.2  8.2  0  79.4  14.7  0  Percentage COD Removals.  TEMP LDT^\ DAYS^\.  1st CELL 30  23  10  30  23  10  30  23  10  50  71.9  68.3  55.9  6.5  6.3  11.0  78.4  74.6  66.9  25  72.2  69.6  49.6  4.9  5.6  5.3  77.1  75.2  54.9  17  62.5  46.3  6.6  3.9  69.1  2nd CELL  OVERALL  50.2  45  TABLE V I I .  Percentage V o l a t i l e  1st  TEMP°C  CELL  Solids  Removals.  2nd CELL  OVERALL  LDT 30  23  10  30  23  10  30  23  10  50  81.4  77.6  78.2  3.7  0.4  2.7  85.1  78.0  80.9  25  72.7  73.0  67.4.  5.5  4.1  3.6  78.2  77.1  71.0  17  68.9  56.9  5.2  7.1  74.1  DAYS  TABLE V I I I .  Percentage T o t a l S o l i d s  1st  TEMP°C LDT ^ " v . DAYS  CELL  Removals.  OVERALL  2nd CELL  30  23  10  30  64.0  23  10  30  23  10  50  r  77.8  77.6  75.8  5.8  0.4  2.9  83.6  78.0  78.7  25  •74.9'  73.0  71.5  7.4  4.1  2.4  82.3  77.1  73.9  17  64.4  55.7  13.6  6.3  78.0  62.0  TABLE IX.  N. TEMP°C LDT DAYS  >°1  Percentage BOD Removals Due t o S e t t l i n g and Bacteriological Action.  1st CELL 23  10  30  23  10  30  23  10  75.3 11.9  61.2 21.2  12.0 6.7  0 2.1  3.1 1.4  0 29.8  75.3 14.0  64.3 22.6  12.0 36.5  34.1 37.9  3.3 0.3  4.1 0  2.4 3.8  0 4.6  47.9 38.9  36.5 41.7  3.3 4.9  0 0  8.6 6.1  0 0  66.2 13.2  s  44.6 38.6  1  s  57.6 7.1 B = Bacteriological  TABLE X.  OVERALL  30  »  7  2nd CELL  0 0  S = Settling  Percentage COD Removals Due t o S e t t l i n g and Bacteriological Action.  TEMP°C  1st CELL  2nd CELL  OVERALL  LDT DAYS  »  30  s  «I »  s  , 23  10  30  23  10  30  23  10  13.8 58.1  11.2 57.1  2.2 53.7  0 6.5  0.6 5.7  0 11.0  13.8 64.6  11.8 62.8  2.2 64.7  10.9 61.3  8.4 61.2  0.8 48.8  1.0 3.9  0.6 5.0  0 5.3  11.9 65.2  9.0 66.2  0.8 54.1  0.9 45.4  1.7 4.9  0 3.9  13.3 55.8  11.6 50.9  0.9 49.3  47  TABLE X I .  Percentage V o l a t i l e S o l i d s Removal Due t o S e t t l i n g and Bacteriological Action.  TEMP°C  1st  CELL  2nd CELL  OVERALL  LDT DAYS  » I  30  23  10  30  23  10  30  23  10  7.9 73.5  6.4 74.8  1.2 77.0  0.0 3.7  0.3 1.5  0.0 2.7  7.9 77.2  6.7 76.3  1.2 79.7  9.3 63.4  7.1 63.1  0.7 66.7  0.9 4.6  0.5  0.0 3.6  10.2 68.0  7.6 68.2  0.7 70.3  0.6 56.3 •  1.2 4.0  0.0 7.1  9.5 ' 64.6  8.3  ' •60.6  B = Bacteriological  TABLE X I I .  0.6 63.4  S = Settling  Percentage T o t a l S o l i d s Removal Due t o S e t t l i n g and Bacteriological Action.  ^ ^ ^ ^ TEMP°C LDT DAYS  ' 1 s t CELL  OVERALL  2nd CELL  30  23  10  30  23  10  30  23  10  *>  s  5.7 72.1  4.6 73.0  0.9 74.9  0.0 5.8  0.2 0.2  0.0 2.9  5.7 77.9  4.8 73.2  0.9 77.8  »  s  5.2 69.7  4.0 69.0  0.4 71.1  0.5 6.9  0.3 3.8  0.0 2.4  5.7 76.6  4.3 72.8  0.4 73.5  »  s  0.5 55.2  0.9 12.7  0.0 6.4  6.8 71.2  .  5.9 58.5  0.5 61.5  48  a maximum o f 84% o f the t o t a l removal was a c h i e v e d in  the s u p e r n a t a n t .  be  s e t t l e a b l e , however, w i t h a maximum o f 41.7% removal due t o  s e t t l i n g being  A fair  by b a c t e r i a  obtained  p o r t i o n o f the BOD d i d appear t o  i n the 10°C r e a c t o r .  The n e g l i g i b l e  removals f o r the 10°C d i g e s t e r a t the 25- and 17-day LDT v a l u e s are p r o b a b l y due to the f a c t t h a t the BOD o f t h e raw feed was decreasing  w i t h time a t the end o f the 25-day LDT and throughout  the 17-day LDT.  T h i s would c l e a r l y g i v e r i s e t o decreased  apparent removal f i g u r e s f o r t h i s d i g e s t e r , e s p e c i a l l y s i n c e the 10°C d i g e s t e r would be the slowest by f a r t o r e a c t to changes i n feed s t r e n g t h .  The decrease i n feed s t r e n g t h would n o t show  as soon i n the e f f l u e n t o f the 10°C d i g e s t e r as i n t h a t o f the others.  Thus the r e s u l t s from the 10°C d i g e s t e r a r e p r o b a b l y  suspect,  and more r e l i a n c e c a n be p l a c e d on the r e s u l t s from  the o t h e r  two u n i t s .  d) At a g i v e n LDT, t o t a l s o l i d s removal by s e t t l i n g was e s s e n t i a l l y independent o f temperature.  Differences  i n t o t a l s o l i d s removal  were mainly due t o b a c t e r i o l o g i c a l r e d u c t i o n volatile solids.  of non-settleable  Much o f the gas produced was due t o the  d e g r a d a t i o n o f s e t t l e d v o l a t i l e s o l i d s , but t h i s was a l l o w e d for  4.6  as p r e v i o u s l y mentioned.  R e l a t i v e Importance o f 1 s t and 2nd C e l l  T a b l e s V - X I I show removal f i g u r e s f o r each c e l l o f the system as w e l l as the o v e r a l l removals. are n o t e d :  From these t a b l e s the f o l l o w i n g  points  49  a) The  first  of the two  c e l l s was  r e s p o n s i b l e f o r the major  p o r t i o n of the removal of a l l parameters. was  The  general  to a g r e a t e r s e c o n d - c e l l c o n t r i b u t i o n at a lower LDT,  would be  l o g i c a l l y expected due  1st c e l l  e f f l u e n t a t lower LDT  the second  the  s u p p l y i n g more f e e d m a t e r i a l  to  cell.  temperature, and  non-existent  the second c e l l was  a t 10°C.  The  c o n t r i b u t i o n of the second c e l l  minimal at  any  c o n t r i b u t i o n of  thus almost e n t i r e l y due  to  settling.  to treatment  efficiency,  a l t h o u g h s m a l l , was  n o n e t h e l e s s s i g n i f i c a n t i n view of the  raw  For a waste of the s t r e n g t h used i n t h i s  feed s t r e n g t h .  experiment, a 1% r e d u c t i o n i n any represents  4.7  which  to the r i s i n g s t r e n g t h of  b) B a c t e r i o l o g i c a l a c t i v i t y i n the second c e l l was  c) The  trend  high  of the important parameters  a worthwhile g a i n i n e f f l u e n t q u a l i t y .  S i n g l e - s t a g e v s . Two-Stage System Two  methods of comparison were employed.  The  f i r s t method  was  [4 to compare r e l a t i v e performance f i g u r e s o b t a i n e d and  from the p r e s e n t  presented  i n Tables  corresponding the 50-day LDT p o i n t was  study a t c o r r e s p o n d i n g X I I I and  LDT's, 50 days and was  The  t h e r e f o r e used a l s o . cell  d i f f i c u l t y here was  i n S e c t i o n 4.3,  short c i r c u i t i n g .  research  These f i g u r e s are that only  25 days, were a v a i l a b l e , and  the p r o b a b i l i t y , d i s c u s s e d  from the f i r s t  values.  the data  r a t h e r incomplete f o r the s i n g l e - s t a g e t e s t .  to feed c h a r a c t e r i s t i c s and was  XIV.  LDT  from the e a r l i e r  two from  A further  of v a r y i n g r e s u l t s due  A second method of  comparison  T h i s e n t a i l e d the c o n s i d e r a t i o n of the r e s u l t s  of the f l o w - t h r o u g h systems as b e i n g - f r o m a  single-stage  TABLE X I I I .  Comparison o f S i n g l e - and Two-Stage Systems.  (LDT = 5 0 days) UNIT  SINGLE-STAGE (25 H)  TWO-STAGE (25 I)  Temp°C  30  23  10  30  23  10  % BOD Removed  89.0  87.0  —  89.3  86.9  48.5  % COD Removed  83.0  80.5  —  78.4  74.6  66.9  % VS Removed  —  85.1  78.0  80.9  % TS Removed  —  83.6  78.0  78.7  TABLE XIV.  Comparison of S i n g l e - and Two-Stage Systems.  (LDT = 25 days) UNIT  SINGLE-STAGE (25 I)  TWO-STAGE (25 £)  Temp°C  30  23  10  30  23  % BOD Removed  88.0  85.0  43.5  87.3  78.2  8.2  % COD Removed  82.5  81.5  64.5  77.1  75.2  54.9  % VS Removed  79.5  81.0  79.0  78.2  77.1  71.0  % TS Removed  73.5  74.0  73.0  82.3  77.1  73.9  10  51  u n i t o f 12.5 I c a p a c i t y .  At a f e e d i n g r a t e o f 0.5 H/day, t h i s gave an LDT o f  25 days, which c o u l d be compared w i t h the r e s u l t s from t h e t o t a l system of two c e l l s a t a f e e d i n g r a t e of 1.0 &/day, g i v i n g a c o r r e s p o n d i n g 25-day LDT. The o n l y problem here would be the p o s s i b i l i t y o f the volume d i f f e r e n c e o f the  two systems g i v i n g r i s e to some s c a l e e f f e c t .  of  25 days, c o u l d be compared.  in  T a b l e XV.  A l s o o n l y one LDT, t h a t  The r e s u l t s f o r t h i s comparison a r e shown  [4] Regarding the comparison o f the o r i g i n a l s i n g l e - s t a g e  tests  and t h e two-stage t e s t s , p o i n t s t o note a r e : a) BOD removal was almost i d e n t i c a l a t the 30°C temperature f o r both systems, but decreased much more r a p i d l y w i t h d e c r e a s i n g temperature a t the same LDT i n the case o f the two-stage  test.  b) The v a r i a t i o n i n COD removal f i g u r e s was somewhat w i d e r , the s i n g l e - s t a g e u n i t g i v i n g c o n s i d e r a b l y b e t t e r removal a t b o t h LDT's.  c) V o l a t i l e s o l i d s removal a t t h e 25-day LDT, t h e o n l y one f o r which comparison was p o s s i b l e , was o f a v e r y s i m i l a r l e v e l a t 30°C, but a g a i n the two-stage u n i t f e l l  o f f i n performance  more r a p i d l y w i t h d e c r e a s i n g temperature.  d) T o t a l s o l i d s removal was c o n s i d e r a b l y b e t t e r f o r the two-stage system a t the two h i g h e r temperatures o f 30°C and 23°C, b u t was almost i d e n t i c a l a t 10°C. off  A g a i n the two-stage u n i t  fell  i n performance w i t h d e c r e a s i n g temperature, w h i l e t h e  s i n g l e - s t a g e u n i t remained e s s e n t i a l l y c o n s t a n t r e g a r d l e s s o f temperature.  TABLE XV.  Comparison o f 1 s t C e l l , O n l y Vs. 1 s t and 2nd C e l l s a t 25-Day LDT.  Percentage B a s i s UNIT  1st CELL (12.5 I)  • TWO-STAGE (25 I)  Temp°C  30  23  10  30  23  % BOD Removed  87.2  82.4  18.7  87.3  78.2  8.2  % COD Removed  71.9  68.3  55.9  77.1  75.2  54.9  % VS Removed  81.4  81.2  7.8.2  78.2  75.8  71.0  % TS Removed  77.8  77.6  75.8  82.3  77.1  73.9  10  Mass Removed B a s i s UNIT k  1st CELL (12.5 I)  TWO-STAGE (25 I)  30  23  10  30  23  10  BOD Removed  153  145  33  213  193  20  COD Removed  692  658  538  779  761  554  VS Removed  698  697  671  471  456  428  TS Removed  922  921  898  850  831  796  Temp°C  *  A l l removals i n mg/1 o f c e l l / d a y .  53  From these o b s e r v a t i o n s , i t may  be s t a t e d t h a t the two-stage  u n i t s d i d g i v e b e t t e r s e t t l i n g e f f i c i e n c y , but v a r i a t i o n s i n the composit i o n of the feed used i n the two t e s t s caused lower e f f i c i e n c i e s t o be r e c o r d e d f o r removal o f parameters other than t o t a l s o l i d s . c o u l d w e l l be e x p l a i n e d i f i t were the c a s e , f o r example, l e s s s e t t l e a b l e BOD  and COD  thus p l a c i n g more emphasis tor.  The  results  that there  i n the waste used f o r the two-stage  was  tests,  on b i o l o g i c a l a c t i o n as the c h i e f removal f a c -  The f a c t t h a t removal f e l l  o f f w i t h temperature f o r the two-stage  system, but d i d no do so to any great e x t e n t i n the s i n g l e - s t a g e system i n d i c a t e s t h a t t h e r e was more dependence the  on b a c t e r i o l o g i c a l a c t i o n f o r  two-stage removals than f o r the s i n g l e - s t a g e .  T h i s would c l e a r l y be  t i e d up w i t h feed c h a r a c t e r i s t i c s such as s e t t l e a b l e v o l a t i l e d i s s o l v e d BOD  o r COD  s e t t l e a b l e , BOD,  COD  as opposed t o s e t t l e a b l e BOD  o r COD.  solids,  Clearly  or v o l a t i l e s o l i d s can o n l y be removed by  non-  bacterial  a c t i o n , so a h i g h e r l e v e l o f these parameters i n s o l u t i o n or s u s p e n s i o n would c e r t a i n l y g i v e r i s e to a more marked temperature e f f e c t .  Thus the  i n d i c a t i o n i s t h a t , a l t h o u g h the two-stage system does g i v e improved s e t t l i n g , as i n d i c a t e d by the t o t a l s o l i d s removal, the p e r c e n t a g e removals of  BOD,  COD  and v o l a t i l e s o l i d s as a r e s u l t of t h i s w i l l be  i n f l u e n c e d by r e l a t i v e l y minor changes i n raw waste  With r e g a r d to the comparison of the f i r s t  considerably  characteristics.  c e l l o n l y a g a i n s t the  t o t a l t w o - c e l l system, b o t h a t 25-day LDT, p o i n t s t o note a r e :  a) On a p e r c e n t a g e b a s i s , BOD  removal was  again, the same a t the  30°C temperature, but f e l l o f f more r a p i d l y f o r the two-stage  54  system w i t h d e c r e a s i n g temperature.  However, the BOD o f the  feed used at 25-day LDT f o r the t w o - c e l l system was h i g h e r than t h a t used f o r the run from which f i g u r e s were o b t a i n e d f o r the f i r s t  cell  considerably  the 25-day LDT  only.  As a r e s u l t of  t h i s , on a mass b a s i s the t w o - c e l l system gave c o n s i d e r a b l y b e t t e r removal f i g u r e s except a t the 10°C temperature, a t which temperature  the BOD removal was v e r y s m a l l i n b o t h c a s e s .  b) On b o t h a percentage and a mass b a s i s , the COD removal f o r the t w o - c e l l system were c o n s i d e r a b l y b e t t e r a g a i n w i t h the except i o n of the 10°C u n i t s , which were almost i d e n t i c a l i n removal efficiency.  c) On a percentage b a s i s , t o t a l s o l i d s removal was v e r y s i m i l a r f o r b o t h systems, a l t h o u g h on a mass b a s i s the f i r s t better results.  cell  a l o n e gave  T h i s can be e x p l a i n e d by the f a c t t h a t the feed  t o t a l s o l i d s c o n c e n t r a t i o n was h i g h e r f o r the f i r s t than f o r the t w o - c e l l system.  cell  only,  I f the percentage o f s e t t l e a b l e  s o l i d s were the same i n both c a s e s , as seems not u n r e a s o n a b l e , then c l e a r l y the lower t o t a l incoming s o l i d s l e v e l f o r the twostage u n i t would r e s u l t  i n a lower t o t a l s o l i d s mass  as found i n t h i s t e s t .  The same o b s e r v a t i o n  removal,  holds true f o r  v o l a t i l e s o l i d s removals, which were f a r lower i n the case o f the  t w o - c e l l system than f o r the f i r s t - c e l l  only.  In t h i s  i n s t a n c e , lower removals were o b t a i n e d both on a percentage and a mass b a s i s f o r the t w o - c e l l  system.  On the b a s i s of these r e s u l t s , i t would appear  that there i s l i t t l e  d i f f e r e n c e i n s e t t l i n g c a p a c i t y o f the t w o - c e l l system and the f i r s t  c e l l of  55  t h a t system working a l o n e . formance on a BOD  - COD  The  t w o - c e l l system gave c o n s i d e r a b l y b e t t e r  removal b a s i s , d e s p i t e the absense of  improved s e t t l i n g , i n d i c a t i n g t h a t , compared to the f i r s t two-stage system i s somewhat more e f f e c t i v e b i o l o g i c a l l y .  appreciably  c e l l alone, Again,  s i t i o n d i f f e r e n c e s appear to have a marked e f f e c t on the r e s u l t s A t r u e e v a l u a t i o n of the r e l a t i v e m e r i t s of the two s e r i e s of c o n c u r r e n t  t e s t s on both s i n g l e - and  same type u s i n g i d e n t i c a l feed m a t e r i a l . w i l l be d i s c u s s e d i n Chapter  4.8  Copper  the  feed compoobtained.  systems would r e q u i r e a  two-stage systems of  These, and  other  the  conclusions,  6.  Concentrations  Towards the end d i g e s t e r s , i t was  decided  l e v e l s of copper p r e s e n t and  per-  copper c o o l i n g c o i l s .  of the s e r i e s of t e s t s made on the to sample the c e l l contents due  and  two-stage  determine  to c o r r o s i o n of the b r a s s d i g e s t e r  T h i s was  the  fittings  not done i n the case of the  earlier  T41  tests  , but  on the BOD  i t would be of i n t e r e s t s i n c e copper has  t e s t , c a u s i n g r e d u c t i o n i n apparent BOD  a significant  v a l u e s , and w i l l  effect also  inhibit bacteriological action. Copper c o n c e n t r a t i o n s were determined by the atomic technique  u s i n g samples of the f u l l y mixed d i g e s t e r c o n t e n t s .  s e t s of analyses were made, the f i r s t of the experiment and shown i n T a b l e  at t h r e e months from the  absorption Two  separate  conclusion  the second at the c o n c l u s i o n of t e s t i n g .  Results  are  XVI. [2]  Eckenfelder the BOD,,  t e s t w i l l be reduced up  L e v e l s below 1.0 test.  g i v e s data i n d i c a t i n g t h a t the r e s u l t s g i v e n  mg/£  to 50% by  the presence of 4.0  mg/£  copper.  copper have a r e l a t i v e l y i n s i g n i f i c a n t e f f e c t on  However, McKee and Wolfe  s t a t e t h a t the c o n c e n t r a t i o n  by  this  necessary  56  to reduce BOD,, by 50% has been v a r i o u s l y determined a t between 8.4 mg/£ and 35 mg/£. this  Thus t h e r e i s a c o n s i d e r a b l e d i v e r s i t y o f i n f o r m a t i o n r e g a r d i n g  topic.  TABLE XVI.  Copper  Concentrations  i n Two-Stage D i g e s t e r  COPPER CONCENTRATION  Cells  (mg/£ C u ) *  CELL NUMBER Test Number 1 }  2^2 }  1.67 4.30  0.67 1.66  2.80 6.30  4.38 1.53  11.60 3.20  16.12 1.90  30°C  2  3  °  C  } 10°C  Test Number 2  Test Number 1 —  3 months p r i o r t o end o f experiment.  T e s t Number 2 —  a t end of experiment.  *A11 samples f u l l y mixed and a c i d - d i g e s t e d t o ensure a l l copper i n s o l u t i o n .  With r e g a r d to t o x i c i t y o f copper t o micro-organisms, McKee and Wolfe'"'^  r e p o r t t h a t copper c o n c e n t r a t i o n s as low as 0.1 to 0.5 mg/ft a r e  t o x i c t o c e r t a i n micro-organisms.  The Committee on Water Q u a l i t y C r i t e r i a  recorded''"'""'""' t h a t sewage organisms  i n p a r t i c u l a r are inhibited  oxygen u t i l i s a t i o n by 21 ppm copper.  to 50% o f  The copper i n h i b i t s a c t i v i t y by t y i n g  up t h e p r o t e i n s i n t h e key enzyme systems, p r e v e n t i n g these from r e a c t i n g ,, [ 1 2 ] . normally With r e g a r d t o the r e s u l t s o f t h e t e s t s r e p o r t e d h e r e i n , t h e copper c o n c e n t r a t i o n s a r e c e r t a i n l y i n t h e range r e p o r t e d l y r e q u i r e d to cause  57  s i g n i f i c a n t decreases i n the r e s u l t s g i v e n by the BOD i n h i b i t i o n of m i c r o b i o l o g i c a l a c t i v i t y .  t e s t and to cause some  In p a r t i c u l a r , the l e v e l s encountered  i n d i g e s t e r number 3 (!0°C) which had c o o l i n g c o i l s made o f pure copper, were high, enough not o n l y to a f f e c t  the BOD  t e s t , but t o s i g n i f i c a n t l y  a f f e c t u t i l i s a t i o n of oxygen by sewage organisms.  S i n c e no m i c r o b i o l o g i c a l  s t u d i e s were undertaken to c l a s s i f y s p e c i e s of b a c t e r i a p r e s e n t , no e s t i m a t e can be made as to the a c t u a l e f f e c t o f the copper upon the r e s u l t s of these t e s t s , but i t can be s a i d t h a t the r e s u l t s were almost c e r t a i n l y to  some degree.  It i s significant  t h a t the 10° d i g e s t e r showed p r a c t i c a l l y  gas p r o d u c t i o n throughout the t e s t s . from t h i s u n i t was  affected  However, the measured BOD  of the e f f l u e n t  c l o s e t o t h a t of the raw waste, as r e p o r t e d e a r l i e r i n t h i s  c h a p t e r , so i n d i c a t i o n s are t h a t the BOD  t e s t was  not a f f e c t e d to a s e r i o u s  degree. [4] The s i n g l e - s t a g e d i g e s t e r s used i n the e a r l i e r work s t r u c t e d of i d e n t i c a l m a t e r i a l s . the  two,forming  It 3-1, the  Hence, the comparative r e s u l t s between  be s u s p e c t .  s h o u l d a l s o be noted t h a t w i t h the e x c e p t i o n o f c e l l s 2-1  the copper c o n c e n t r a t i o n s i n the o t h e r c e l l s . f e l l t h r e e months between the f i r s t  copper was  were con-  the main b a s i s of t h i s s t u d y , s h o u l d s t i l l be v a l i d , a l t h o u g h  a b s o l u t e v a l u e s may  not going i n t o  and second t e s t s .  This indicates  s o l u t i o n as f a s t as i t had been e a r l i e r .  that This  undoubtedly due to the f o r m a t i o n of a l a y e r o f copper compounds on  the  m e t a l s u r f a c e s which formed a b a r r i e r between the copper and the When the c e l l s were emptied a t the c o n c l u s i o n of  t e s t i n g , a c r u s t of c o r r o s i o n p r o d u c t s was fittings.  and  s i g n i f i c a n t l y over  was  digester contents.  no  i n f a c t found on a l l m e t a l l i c  I t i s r e a s o n a b l e to conclude t h a t o p e r a t i o n over a l o n g e r p e r i o d  58  of time would p r o b a b l y b r i n g copper  c o n c e n t r a t i o n s down t o a c c e p t a b l e  However, the use of b r a s s or copper  fittings  i n experiments  of t h i s  levels.  nature  i s c l e a r l y shown by these r e s u l t s to be u n d e s i r a b l e and p o t e n t i a l l y  ruinous  to the o b t a i n i n g of a c c u r a t e a b s o l u t e v a l u e s f o r e x p e r i m e n t a l d a t a .  Stain-  l e s s s t e e l should be u t i l i s e d whenever p o s s i b l e .  59  CHAPTER 5.  5.1  VOLATILE ACIDS AND TOTAL ORGANIC CARBON RESULTS  Introduction  N e i t h e r V o l a t i l e A c i d s nor T o t a l Organic Carbon (TOC) were [4] s t u d i e d i n depth i n the p r e v i o u s ment.  work  , due t o l a c k o f s u i t a b l e  equip-  However, the n e c e s s a r y instruments were a v a i l a b l e f o r the p r e s e n t  work, and a c c o r d i n g l y  i t was decided  t o study these parameters i n some  detail.  [131 I t has been r e p o r t e d by McGhee batchrfed  systems v a r y  considerably,  reaching  that v o l a t i l e acids l e v e l s i n a peak a p p r o x i m a t e l y 4 hours  a f t e r f e e d i n g and f a l l i n g back t o a base l e v e l a t about 16 hours a f t e r feeding. 5 o r 6. versus  The peak i s t y p i c a l l y g r e a t e r than the base l e v e l by a f a c t o r o f F i g u r e 5.1 shows a t y p i c a l curve o f v o l a t i l e a c i d  concentration  the number o f hours a f t e r f e e d i n g ; the d a t a a r e taken from the work  [131 of McGhee  .  The v o l a t i l e a c i d data presented  herein are base-level  f i g u r e s , s i n c e they were determined immediately p r i o r t o f e e d i n g . 5.2  V o l a t i l e A c i d s and pH L e v e l s  i n A n a e r o b i c Systems  [12] It i s considered i n anaerobic  t h a t a v o l a t i l e a c i d s l e v e l above 2,000 mg/5,  systems i s an i n d i c a t i o n t h a t t r o u b l e i s imminent.  This  rise  i n v o l a t i l e a c i d s can depress pH t o the p o i n t where the methane b a c t e r i a are s e v e r e l y i n h i b i t e d , and thus cannot keep pace w i t h In t h i s s i t u a t i o n , the v o l a t i l e a c i d s w i l l c o n t i n u e will fall  the  acid-formers.  t o r i s e , and t h e pH  f u r t h e r , r e s u l t i n g i n a t o t a l c e s s a t i o n of methane p r o d u c t i o n and  an upset i n the system.  FIG.  60  5-1  VARIATION OF V O L A T I L E ACID (AFTER  McG.HEE  CONCENTRATION. [l  * ) 3  61  V o l a t i l e a c i d s are not b a c t e r i a , as l a b o r a t o r y  s t u d i e s have shown t h a t i t i s p o s s i b l e to operate  a d i g e s t e r at l e v e l s of up i s m a i n t a i n e d above 6.5  i n themselves t o x i c to methane-forming  [12]  to 20,000 mg/£ . I n  methane-formers i s l i m i t e d by  v o l a t i l e a c i d s as long as the  such cases,  the r a t e of matabolism of  the c o n c e n t r a t i o n  pH the  of s o l u b l e c a t i o n s added [12]  w h i l e n e u t r a l i s i n g the v o l a t i l e a c i d s to the d e s i r e d pH  .  commonly used f o r t h i s purpose, and  t h i s experiment  as r e p o r t e d  earlier.  i t was  employed d u r i n g  Lime i s  Lime i s most s u i t a b l e f o r t h i s purpose, as c a l c i u m  is  the l e a s t s o l u b l e c a t i o n u s a b l e i n a n e u t r a l i s i n g s i t u a t i o n , and  thus causes  the l e a s t p o s s i b l e upset to the methane formers; i t i s a l s o v e r y  cheap  and  readily available. 5.3  V o l a t i l e Acids  The  and  i n the Two-stage D i g e s t e r  measured v o l a t i l e a c i d s l e v e l s i n the two-stage d i g e s t e r s  presented i n Figures to  pH  5.2  to 5.4,  w i t h pH d a t a b e i n g  are  presented i n Figures  5.5  5.7.  Points  to note  are:  a) The  v o l a t i l e acids concentrations  i n the 30°C and  d i g e s t e r s were g e n e r a l l y r e l a t i v e l y low,  23°C  i n the 100-600  mg/£  range, i n d i c a t i n g t h a t b o t h b i o l o g i c a l systems were f u n c t i o n i n g i n a s t a b l e manner. a s t a b l e range, b e i n g  The  pH.of these two  of the o r d e r  of 7.2  d i g e s t e r s was - 7.6.  At no  d i d the v o l a t i l e a c i d s l e v e l s of e i t h e r system exceed mg/£,  except f o r number 1-1,  feed r a t e was quick  time 1,200  which went to 3,500 when the  changed from 1.0  to 1.5  £/day.  from t h i s l o a d , however, as the pH  remained at around 7.3,  also i n  Recovery  at t h i s  was  time  i n d i c a t i n g a very w e l l - b u f f e r e d  system.  QIOV  OI130V  SV  9Ji!lsaiov  31I1V10A  QlOv*  0I13DV  S\/  9Ji!l/6"J  SQIDV  31I1V10A  65  FIG. 5 - 5 pH VS. TIME FOR 2 - STAGE DIGESTER  #I(30°C).  O  CM  O X3  m  O O  a  T3  O  CO CO  • >< O  CO  2  c CM  a>  I  o  o  O  CO  CD  'st  CM  Hd  O  o  TJ  CO  CO  CO  CD  68  b) The  second c e l l s of the 30°C and  23°C d i g e s t e r s e x h i b i t e d l e s s  f l u c t u a t i o n i n v o l a t i l e a c i d s than d i d the f i r s t would be  expected, as they were not  l o a d i n g of raw c a t e any  waste.  At no  subject  cells.  to the d i r e c t shock  time d i d these second c e l l s  l i m i t e d , as r e p o r t e d  earlier.  but must have been due further b i o l o g i c a l  to l i m i t e d a v a i l a b i l i t y of s u b s t r a t e  - 6.9  i n t h i s u n i t were not  f e e d r a t e , but  The  very  conditions  to.the  increased  range, i n d i c a t i n g  themselves were i n a s t a t e of  have been due  digesters  values  l i t t l e methane produced  v o l a t i l e acids did r i s e with  the temperature was  two  stated that  remained i n the same g e n e r a l  t h a t the a c i d - f o r m e r s  d) The  I t can be  w i t h pH  conducive to good metabolism of the methane -  i n f a c t t h e r e was  from these c e l l s .  but  range.  pH  V o l a t i l e a c i d s l e v e l s of  2,000 to 3,000 mg/ft were encountered, t o g e t h e r  formers, and  to  degradation.  d i g e s t e r gave r e s u l t s f o r both v o l a t i l e a c i d s and  down i n the 6.8  be  on the b a s i s of these r e s u l t s ,  which i n d i c a t e d upset c o n d i t i o n s .  T h i s may  very  T h i s l i m i t e d a c t i v i t y cannot  a t t r i b u t e d to upset c o n d i t i o n s  10°C  indi-  tendency to u p s e t , a l t h o u g h i t must be borne i n mind  t h a t b a c t e r i o l o g i c a l a c t i v i t y i n the second c e l l s was  c) The  This  inhibition.  copper l e v e l s r e p o r t e d  doubtless  earlier,  a f a c t o r here.  (30°C - 23°C) which operated i n the  range of pH and v o l a t i l e a c i d s v a l u e s had  no  trouble  stable adjusting  to the 1.0  H/day feed r a t e and  the 30°C d i g e s t e r adapted w e l l  to the 1.5  Z/day  u n f o r t u n a t e t h a t l a c k of  rate.  I t was  m a t e r i a l , prevented more e x t e n s i v e  t e s t i n g of the 1.5  feed  Z/day  69  rate.  In t h i s r e g a r d ,  i t would c e r t a i n l y have been most  i n s t r u c t i v e to observe the response of the 23°C d i g e s t e r the 1.5  Z/day  f e e d i n g r a t e , but  the shortage of feed  to  material  at the c l o s e of the t e s t f o r c e d the abandonment of f e e d i n g one  e) The  d i g e s t e r and  recovered  a t the change of feed r a t e to 1.5  q u i c k l y , i n d i c a t i n g e x c e l l e n t system  T o t a l Organic Carbon Measurements i n the Two-Stage  The past  chosen.  30°C d i g e s t e r showed an abrupt jump i n v o l a t i l e  concentration  5.4  the 23°C u n i t was  T o t a l Organic Carbon a n a l y s e r  of  has  acids  H/day,  but  stability.  Digesters  been developed over  the  decade or so i n t o a v e r y p r e c i s e instrument capable of g i v i n g  e x c e l l e n t and effort.  reproducible  A sample can be  r e s u l t s w i t h a minimum e x p e n d i t u r e of time  t e s t e d i n two  minutes q u i t e e a s i l y .  f e l t by many to be a f a r b e t t e r t e s t than the c u r r e n t l y - u s e d  and  Thus, i t i s BOD  and  COD  analyses.  Robbins, Howells, and of r e s e a r c h published  i n t o the use  K r i z have conducted an e x t e n s i v e  of TOC  conclusions''"'"^'"'"'''' may  a) TOC  i n c h a r a c t e r i s a t i o n of swine wastes. be s t a t e d as  i s a more r e p r o d u c i b l e  wastes than e i t h e r BOD  b) The  BOD  or  and  Their  follows:  convenient t e s t f o r swine  COD.  t e s t i n p a r t i c u l a r i s not  t i o n of c o n c e n t r a t e d  program  a p p l i c a b l e to c h a r a c t e r i s a -  swine wastes and  lagoon e f f l u e n t s , due  to the presence of t o x i c s u b s t a n c e s , h i g h s o l i d s contents  and  to e r r o r s a s s o c i a t e d w i t h the h i g h d i l u t i o n requirements f o r  70  testing.  c) No  g e n e r a l B0D/T0C c o r r e l a t i o n was  swine wastes and  effluents,  d i l u t e d by r u n o f f , TOC f i g u r e f o r BOD TOC  found  f o r concentrated  although once the e f f l u e n t s  results  c o u l d be used to y i e l d a  f o r e s t i m a t i n g purposes.  t e s t i s f a r more convenient  were  In a d d i t i o n ,  the  f o r t h i s than the BOD  test.  d) The v a r i a t i o n of the BOD/TOC r a t i o g i v e s an i n d i c a t i o n of presence  of t o x i c m a t e r i a l s , as the BOD  markedly to these, whereas TOC  e) The  actual  the  t e s t responds most  does not.  v a l u e of the BOD/TOC r a t i o g i v e s an i n d i c a t i o n  of  the ease of b i o d e g r a d a t i o n and degree of s t a b i l i s a t i o n of a swine wastewater. except  In g e n e r a l , t h i s r a t i o i s l e s s than  one,  f o r raw wastes or those which a r e not s t a b i l i s e d to a  great degree.  For the p r e s e n t work, TOC feed m a t e r i a l and e f f l u e n t of TOC,  BOD- and COD  data were p l o t t e d  t e s t s were performed r o u t i n e l y  from a l l t h r e e d i g e s t e r s .  v a l u e s was  generated  as shown i n F i g u r e s 5.8  on  Hence, a wide range  f o r comparison purposes. and 5.9  both  f o r BOD  and  COD  These respec-  tively.  The  r e s u l t s f o r BOD  agreed w e l l w i t h the o b s e r v a t i o n s  recorded  r 151 by Robbins et a l  L  J  .  The BOD/TOC r a t i o v a r i e d  a " b e s t - f i t " mean of 0.57. of the copper a f f e c t i n g theory.  The  the BOD  fluctuation  from 1.35  down to 0.22  c o u l d be caused  t e s t , based on the t o x i c i t y  Robbins e t a l ^ " ^ r e p o r t e d r a t i o s r a n g i n g from 0.41  concentrated  effluents.  by the  with  presence  indication to 1.25  for  72  FIG. 5 - 9 COD VS.TOC  FOR DIGESTER  EFFLUENTS.  73  A s i m i l a r v a r i a t i o n was found  f o r COD.  from 1.8 to 3.35 w i t h a " b e s t - f i t " mean of 2.71  The COD/TOC r a t i o  varied  S i n c e no o t h e r work has  a p p a r e n t l y been done on COD and TOC c o r r e l a t i o n s , no comparison can be made h e r e .  I t s h o u l d be noted t h a t a r e g r e s s i o n e q u a t i o n was not o b t a i n e d f o r these c u r v e s , as the wide spread o f r e s u l t s would make t h i s a meaningless exercise.  The c h i e f c o n c l u s i o n i n f a c t i s t h a t due t o a number o f  f a c t o r s not i d e n t i f i e d ,  c o r r e l a t i o n between BOD and COD w i t h TOC i s v e r y  poor f o r c o n c e n t r a t e d swine wastes.  The e f f l u e n t s had BOD/TOC r a t i o s of w e l l under one i n most c a s e s , i n d i c a t i n g t h a t they were w e l l s t a b i l i s e d i n g e n e r a l . d i f f e r e n c e i n d i s t r i b u t i o n between f i r s t and second  There was no marked  c e l l e f f l u e n t s , and  thus these c o u l d n o t m e a n i n g f u l l y be p l o t t e d as s e p a r a t e  graphs.  74  CHAPTER 6. .CONCLUSIONS AND RECOMMENDATION  6.1  Introduction  In The  t h i s c h a p t e r , the b a s i c f i n d i n g s o f the study a r e summarised.  c o n c l u s i o n s reached  as a r e s u l t of t h i s study may c o n v e n i e n t l y be d i s -  t r i b u t e d under s e v e r a l d i s t i n c t  subheadings.  These a r e p r e s e n t e d i n the  following sections.  6.2  C o n c l u s i o n s from Batch T e s t R e s u l t s  a) On t h e b a s i s o f t h e b a t c h t e s t r e s u l t s , the use o f the f i g u r e  [91 g i v e n by Lawrence and McCarty  , 0.35 ml methane  produced  per mg o f COD or BOD^ destroyed, i s f u l l y j u s t i f i e d  i n calcula-  t i o n s i n v o l v i n g a n a e r o b i c d i g e s t i o n s of hog wastes. b) The same t e s t s i n d i c a t e d t h a t the use o f the f i g u r e s p u b l i s h e d [2] by E c k e n f e l d e r of  , 69 t o 81 £ of methane produced  V o l a t i l e S o l i d s destroyed, i s f u l l y j u s t i f i e d  p e r 100 gm  i n calculations  i n v o l v i n g a n a e r o b i c d i g e s t i o n o f hog wastes. c) The p r a c t i s e of a l l o w i n g a lagoon t o stand unfed f o r a p e r i o d of  time i n o r d e r to reduce  s o l i d s build-up i s of l i m i t e d value,  as the m a j o r i t y o f s o l i d s i n hog waste of the type employed i n these t e s t s a r e not r e a d i l y b i o d e g r a d a b l e .  The main b e n e f i t  r e s u l t i n g from a l l o w i n g a lagoon t o stand would be r e d u c t i o n of  sludge volume i n the lagoon r e s u l t i n g from g r a v i t y  consoli-  d a t i o n o f the s o l i d s l a y e r i n the lagoon, which i s o c c u r r i n g anyway whether t h e lagoon i s f e d o r n o t .  Biological  degradation  75  would be o f secondary  6.3  Importance.  C o n c l u s i o n s from Two-Stage Continuous-Feed D i g e s t e r R e s u l t s  a) S e t t l i n g i s the major removal mechanism i n the case of and s o l i d s removal.  However, BOD  COD  removals a r e dependent  b i o l o g i c a l a c t i o n to a c o n s i d e r a b l e e x t e n t .  on  As a r e s u l t of  these o b s e r v a t i o n s , i t i s c l e a r t h a t waste c h a r a c t e r i s t i c s  play  a major r o l e i n g o v e r n i n g treatment e f f i c i e n c y of a system. Based on r e s u l t s p r e s e n t e d i n t h i s r e p o r t , i t may t h a t r e l a t i v e l y minor  be  stated  changes ,in waste c h a r a c t e r i s t i c s can have  an a p p r e c i a b l e e f f e c t on system e f f i c i e n c y .  BOD  removal i n  p a r t i c u l a r i s v e r y s e n s i t i v e to changing c o n d i t i o n s i n both the treatment p r o c e s s and the waste  b) The f i r s t  cell  characteristics.  i n a t w o - c e l l system a c h i e v e s most of the removal  o b t a i n e d i n the system.  The c o n t r i b u t i o n of the second  i s s m a l l by comparison, but w i t h a h i g h - s t r e n g t h waste  cell such as hog  waste, even s m a l l percentage removals a r e s i g n i f i c a n t on a mass basis.  The second c e l l  biological activity, first  c e l l was  i n these t e s t s e x h i b i t e d very  little  i n d i c a t i n g t h a t the supernatant from the  not r e a d i l y b i o - d e g r a d a b l e by the a n a e r o b i c  p r o c e s s d e s p i t e i t s h i g h r e s i d u a l BOD.  S e c o n d - c e l l removals  were almost e n t i r e l y due to s e t t l i n g .  6.4  Conclus ions Regarding Two—Cell Vs. O n e — C e l l Systems  a) The t w o - c e l l system does g i v e improved s e t t l i n g e f f i c i e n c y s o l i d s removal c a p a c i t y .  Whether or not t h i s improves BOD  and or  76  COD  removal s i g n i f i c a n t l y w i l l depend to a g r e a t e x t e n t on  waste c h a r a c t e r i s t i c s such as s e t t l e a b l e BOD BOD  and COD,  and COD,  dissolved  r e l a t i v e percentage of v o l a t i l e and t o t a l s u s -  pended s o l i d s , e t c .  b) The t w o - c e l l system does have a h i g h e r c a p a c i t y f o r removal a mass b a s i s , of BOD  and COD,  based on the comparison  removal e f f i c i e n c y of the f i r s t both c e l l s  on  of  c e l l only against that of  (same t o t a l d e t e n t i o n time i n each system).  Thus,  the u n i t l o a d i n g c a p a c i t y of the t w o - c e l l system i s somewhat higher.  6.5  C o n c l u s i o n s from Copper, V o l a t i l e A c i d s , pH and T o t a l O r g a n i c Tests  Carbon  a) The a n a e r o b i c system can a c c e p t changes i n l o a d i n g r a t e w i t h o u t upset c o n d i t i o n s d e v e l o p i n g , p r o v i d e d temperatures a r e - k e p t up i n a range f a v o u r a b l e t o b i o l o g i c a l a c t i v i t y . the methane-forming  At the 10°C  temperature,  b a c t e r i a a r e a d v e r s e l y a f f e c t e d , and a r e  unable to cope w i t h sudden upswings i n v o l a t i l e a c i d s  concen-  t r a c t i o n s , or i n f a c t to keep up a t a l l w i t h the a c i d  formers,  even a t steady feed  rates.  b) Lack of b i o l o g i c a l a c t i v i t y observed i n the second c e l l s  was  not due t o upset c o n d i t i o n s , and must t h e r e f o r e have been due to l i m i t e d a v a i l a b i l i t y o f substrate,, or some o t h e r f a c t o r not determined.  c) The use of b r a s s or copper f i t t i n g s i n equipment used f o r a n a e r o b i c d i g e s t i o n g i v e s r i s e to s e r i o u s l y h i g h l e v e l s of copper i n the s u b s t r a t e , and i s p o t e n t i a l l y d i s a s t r o u s  from  77  the p o i n t of view of o b t a i n i n g meaningful  results.  d) There i s no r e a d i l y i d e n t i f i a b l e c o r r e l a t i o n between BOD, and  6.6  COD,  TOC.  Recommendat i o n s  a) In the d e s i g n of an a n a e r o b i c lagoon system f o r hog use of two  lagoons  wastes,  of a g i v e n t o t a l volume, r a t h e r than a  s i n g l e lagoon of the same volume, should be c o n s i d e r e d where space p e r m i t s , as l o a d i n g c a p a c i t y and removal e f f i c i e n c y  will  be i n c r e a s e d f o r a v e r y s m a l l i n c r e a s e i n the a r e a of the lagoon  system.  b) In d e s i g n of such a system, waste c h a r a c t e r i s t i c s should  be  t h o r o u g h l y i n v e s t i g a t e d , as they w i l l p l a y a major r o l e i n d e t e r m i n i n g the e f f i c i e n c y of treatment which can be from a g i v e n lagoon system.  The waste should be t e s t e d f o r  such c h a r a c t e r i s t i c s as s e t t l e a b l e BOD s o l i d s , and t r e a t a b i l i t y of the raw from s e t t l i n g out of the s o l i d s . t a n t p a r t of any  c) A n a e r o b i c  and COD,  supernatant  settleable resulting  T h i s should form an  impor-  future laboratory research also.  lagoons w i l l o n l y e x h i b i t worthwhile  a c t i v i t y a t temperatures  above approximately  t h e r e i s p r a c t i c a l l y no a c t i v i t y . o p e r a t i o n , such lagoons o n l y , and  obtained  biological  20°C.  At  Hence, f o r year-round  should be c o n s i d e r e d as s e t t l i n g ponds  the two-stage system i s b e t t e r s u i t e d to t h i s  the s i n g l e - s t a g e system.  10°C,  than  78  d) A l l l a b o r a t o r y equipment used  i n a n a e r o b i c r e s e a r c h should  have s t a i n l e s s s t e e l f i t t i n g s , as copper and b r a s s both cause u n f a v o u r a b l y h i g h l e v e l s of copper  to d i s s o l v e i n  the s u b s t r a t e .  e) C o n s i d e r a t i o n should be g i v e n t o the p o s s i b l e i n treatment lagoon. system  e f f i c i e n c y r e s u l t i n g from a e r a t i o n of the  The supernatant from the f i r s t  second  c e l l of a t w o - c e l l  i s n o t , on the b a s i s of t h i s study, r e a d i l y  by a n a e r o b i c b a c t e r i a , but may ment.  improvements  w e l l respond  degradable  to a e r o b i c t r e a t -  79  BIBLIOGRAPHY [1]  Loehr, R.C.; "The C h a l l e n g e o f Animal Waste Management", Animal Waste Management (1969), C o r n e l l U n i v e r s i t y , pgs. 17-22.  [2]  E c k e n f e l d e r , W.W.; Water Q u a l i t y E n g i n e e r i n g f o r P r a c t i s i n g E n g i n e e r s (1970), Barnes and Noble, I n c . , New York.  [3]  Loehr, R . C ; " E f f l u e n t Q u a l i t y From A n a e r o b i c Lagoons T r e a t i n g F e e d l o t Wastes", J o u r n a l WPCF, V o l . 39, No. 3 (March 1967), pgs. 384-391.  [4]  Nemeth, L.; "Anaerobic Treatment A n a l y s i s o f Concentrated Hog Wastes", M.A.Sc. T h e s i s , U n i v e r s i t y of B r i t i s h Columbia ( A p r i l 1972).  [5]  APHA, AWWA, WPCF; "Standard Methods f o r t h e Examination o f Water and Wastewater" (1965), American P u b l i c H e a l t h A s s o c i a t i o n , I n c . , 12th E d i t i o n .  [6]  Sawyer, C.N. and McCarty, P.L.; "Chemistry f o r S a n i t a r y E n g i n e e r s " (1967), McGraw-Hill, 2nd E d i t i o n , New York.  [7]  Emery, R.M., Welch, E.B., and Christman, R.F.; "The T o t a l Organic Carbon A n a l y z e r and i t s A p p l i c a t i o n t o Water Research", J o u r n a l WPCF, V o l . 43, No. 9 (1971), pgs. 1834-1844.  18]  T a i g i n i d e s , E.P., Baumann, E.R., Johnson, H.P., and Hazen, T.E.; "Anaerobic D i g e s t i o n o f Hog Wastes", J o u r n a l o f A g r i c u l t u r a l E n g i n e e r i n g Research ( B r i t i s h ) , V o l . 8, No. 4 (1963), pgs. 327-333.  [9]  Lawrence, A. and McCarty, P.L.; " K i n e t i c s o f Methane F e r m e n t a t i o n i n A n a e r o b i c Waste Treatment", T e c h n i c a l Report No. 75, Department o f C i v i l Engineering, Stanford U n i v e r s i t y , Stanford, C a l i f o r n i a (1967).  [10]  McKee and Wolfe; "Water Q u a l i t y C r i t e r i a " , C a l i f o r n i a S t a t e Water Resources C o n t r o l Board, P u b l i c a t i o n 3-A (1963).  [11]  "Water Q u a l i t y C r i t e r i a 1972 - A Report o f t h e Committee on Water Q u a l i t y C r i t e r i a " , EPA P u b l i c a t i o n R3-73-033 (March 1973).  [12]  McKinney, R.E.; " M i c r o b i o l o g y f o r S a n i t a r y E n g i n e e r s " , McGraw-Hill (1962).  [13]  McGhee, T . J . ; " V o l a t i l e A c i d C o n c e n t r a t i o n i n Batch Fed A n a e r o b i c D i g e s t e r s " , Water and Sewage Works, V o l . 118, No. 5 (May 1971), pgs. 130-132.  [14]  Robbins, J.W.D., Howells, D.H., and K r i z , G.J.; "Stream P o l l u t i o n From Animal P r o d u c t i o n U n i t s " , J o u r n a l WPCF, V o l . 44, No. 8 (August 1972), pgs. 1536-1544.  80  [15]  Robbins, J.W.D., K r i z , G.J., and Howells, D.H.; " T o t a l Organic Carbon D e t e r m i n a t i o n on Swine Waste E f f l u e n t s " , T r a n s a c t i o n s of the ASAE, V o l . 15 (1972), pgs. 105-109.  APPENDIX A.  Sample  Calculations  a) Amount o f COD removed by b a c t e r i o l o g i c a l a c t i o n i n b a t c h t e s t s  Volume o f l i q u i d  i n d i g e s t e r at s t a r t o f experiment = 23.7 Z  ( a f t e r removal of t e s t sample)  COD a t s t a r t = 30,600  •: T o t a l COD  ppm.  i n d i g e s t e r = 23.7 x 30,600 = 726,000  At  time of next  mg.  sampling:  0.2 Z sample taken, l e a v i n g volume o f 23.5 Z i n d i g e s t e r . COD of sample = average COD i n d i g e s t e r s i n c e sample taken f u l l y mixed.  COD = 27,200  ppm.  COD remaining i n d i g e s t e r = 27,200 x 23.5 = 640,000  mg.  COD removed i n sample = 0.2 x 27,200 = 5,440 mg.  •: COD removed by b a c t e r i o l o g i c a l a c t i o n = Drop i n COD i n d i g e s t e r - COD removed i n sample.  COD removed b a c t e r i o l o g i c a l l y = (726,000 - 640,000 ) - 5,440 mg = 80,560  mg.  b) I d e n t i c a l procedure f o l l o w e d t o c a l c u l a t e BOD and VS removed by bacteriological  action.  

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