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UBC Theses and Dissertations

Biological nitrification and denitrification in a modified activated sludge process Dew, Harvey Peter 1979

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BIOLOGICAL NITRIFICATION AND DENITRIFICATION IN A MODIFIED ACTIVATED SLUDGE PROCESS by HARVEY PETER DEW B.E. (Metallurgy), U n i v e r s i t y of Melbourne, 1968. A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (The Department of C i v i l Engineering) We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October 1 9 7 9 (c) Harvey Peter Dew, 1 9 7 9 • In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Depa rtment The University of Brit ish Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 - i i -BIOLOGICAL NITRIFICATION AND DENITRIFICATION IN A MODIFIED ACTIVATED SLUDGE PROCESS ABSTRACT A 40 L/day continuous reactor, c o n s i s t i n g of 5 basins arranged i n an a l t e r n a t i n g anoxic-aerobic sequence ("modified Bardenpho process") was operated at low temperatures on municipal e f f l u e n t to determine the rate and e f f i c i e n c y of nitrogen transformations and removal. Total nitrogen removal ranged from 95% at 18°C to 79% at 6°C. The average BOD and t o t a l phosphorus removals remained i n excess of 91% and 81% r e s p e c t i v e l y . The maximum un i t n i t r i f i c a t i o n rates were 1.76, 1.44, 0.38 and 0.42 mg oxidized N/gm MLSS/hr at 18°C, 14°C, 10°C and 6°C r e s p e c t i v e l y . The maximum u n i t rates f o r endogenous d e n i t r i f i c a t i o n and with waste-water substrate were 0.95, 0.86, 0.60, 0.31 and 1.52, 0.88, 0.71, 0.36 mg oxidized N/gm MLSS/hr at 18°C, 14°C, 10°C and 6°C. For the system studied, rates and performance appear s i g n i f i c a n t l y influenced by BOD, C:N r a t i o , sludge age, substrate concentration and p o s s i b l y pH and t o x i c i t y . The necessary consensus among inve s t i g a t o r s on standardized techniques for reporting v i a b l e biomass and nitrogen concentration remains to be attained. KEY WORDS Activated Sludge; Advanced Waste Treatment; D e n i t r i f i c a t i o n ; Extended Aeration; N i t r i f i c a t i o n . - i i i -TABLE OF CONTENTS ABSTRACT . ( i i ) LIST OF TABLES (x) LIST OF FIGURES (xi) ACKNOWLEDGEMENTS ( x i i i ) CHAPTER PAGE 1 INTRODUCTION 1 1.1 Eutrophication of Lakes 1 1.1.1 Man's cont r i b u t i o n to eutrophication 2 1.1.2 Problems associated with eutrophication . . . . 2 1.2 Add i t i o n a l Concerns Associated With Aqueous Nitrogen. . 3 1.3 Available Processes f o r Nitrogen Control i n Water . . . 5 1.3.1 Physical-chemical processes 5 1.3.2 B i o l o g i c a l processes 5 1.3.3 Land a p p l i c a t i o n 6 2 RESEARCH RATIONALE: NUTRIENT REMOVAL VIA THE BARDENPHO PROCESS 7 2.1 Development of the Bardenpho Process 7 2.2 A p p l i c a b i l i t y of the Bardenpho Process 7 2.3 The Bardenpho Process Under Canadian Conditions . . . . 10 2.4 Required Research f o r Canadian A p p l i c a b i l i t y 10 2.5 Experimental Outline 11 2.6 This Thesis 12 3 BACKGROUND TO BIOLOGICAL NITROGEN REMOVAL 13 3.1 Microbial Growth 13 3.2 Waste S t a b i l i z a t i o n K i n e t i c s 14 - i v -3 . 3 T e m p e r a t u r e E f f e c t s o n R e a c t i o n K i n e t i c s 1 5 3 . 3 . 1 T e m p e r a t u r e 1 5 3 . 3 . 2 B i o l o g i c a l p o p u l a t i o n s 1 6 3 . 3 . 3 R e a c t i o n r a t e s 1 6 3 . 4 T h e N i t r o g e n C y c l e 17 3 . 4 . 1 N i t r o g e n b a l a n c e 2 0 4 A M M O N I F I C A T I O N A N D N I T R I F I C A T I O N I N D O M E S T I C W A S T E W A T E R . . 2 2 4 . 1 W a s t e w a t e r C o m p o s i t i o n 2 2 4 . 1 . 1 A m i n o a c i d s a n d p r o t e i n s 2 2 4 . 2 D e a m i n a t i o n a n d A m m o n i f i c a t i o n 2 3 4 . 3 N i t r i f i c a t i o n 2 4 4 . 3 . 1 S u b s t r a t e o x i d a t i o n 2 4 4 . 3 . 2 C l a s s i f i c a t i o n o f n i t r o b a c t e r a n d n i t r o s o m o n a s . 2 5 4 . 3 . 3 E n e r g y y i e l d s a n d s y n t h e s i s 2 5 4 . 3 . 4 A l k a l i n i t y c o n s u m p t i o n 2 5 4 . 3 . 5 E n v i r o n m e n t a l f a c t o r s o f i m p o r t a n c e i n n i t r i f i c a t i o n 2 6 4 . 3 . 5 . 1 D i s s o l v e d o x y g e n 2 6 4 . 3 . 5 . 2 E f f e c t o f a n a e r o b i c s t o r a g e o n n i t r i f y i n g a c t i v a t e d s l u d g e 2 7 4 . 3 . 5 . 3 E f f e c t o f p H 2 7 4 . 3 . 5 . 4 T e m p e r a t u r e 2 8 4 . 3 . 5 . 5 E f f e c t o f l i g h t 2 9 4 . 3 . 5 . 6 E f f e c t o f s o l i d s u r f a c e s a n d t u r b u l e n c e 2 9 4 . 3 . 5 . 7 M i c r o n u t r i e n t s 3 0 4 . 4 I n h i b i t i o n o f N i t r i f i c a t i o n 3 0 4 . 4 . 1 A c c l i m a t i o n 3 2 4 . 4 . 2 C h l o r i n a t i o n . 3 2 4 . 4 . 3 S u b s t r a t e a n d p r o d u c t i n h i b i t i o n 3 2 4 . 4 . 4 O r g a n i c m a t t e r 3 3 4 . 5 K i n e t i c s o f N i t r i f i c a t i o n 3 3 4 . 5 . 1 R e p o r t e d n i t r i f i c a t i o n r a t e p a r a m e t e r s . . . . 3 5 4 . 5 . 2 V a r i a t i o n o f n i t r i f i c a t i o n r a t e w i t h t e m p e r a t u r e 3 5 4 . 5 . 3 N i t r i f i c a t i o n i n w a s t e w a t e r 3 7 4 . 5 . 3 . 1 S a f e t y f a c t o r i n d e s i g n 3 8 - v -4 . 5 . 4 F r a c t i o n o f n i t r i f i e r s i n a c t i v a t e d s l u d g e . . . 3 9 4 . 6 D e s i g n A p p r o a c h e s t o N i t r i f i c a t i o n 4 0 4 . 6 . 1 S o l i d s r e t e n t i o n t i m e a p p r o a c h 4 0 4 . 6 . 2 N i t r i f i c a t i o n r a t e a p p r o a c h 4 2 4 . 7 P r o c e s s e s A v a i l a b l e f o r B i o l o g i c a l N i t r i f i c a t i o n . . . 4 2 4 . 7 . 1 S u s p e n d e d g r o w t h s y s t e m s 4 2 4 . 7 . 2 C o m b i n e d a n d s e p a r a t e s l u d g e s y s t e m s 4 4 4 . 7 . 3 P r o s a n d c o n s o f c o m b i n e d a n d s e p a r a t e s l u d g e s y s t e m s 4 5 4 . 7 . 3 . 1 A d v a n t a g e s o f t w o - s t a g e ( s e p a r a t e s l u d g e ) s y s t e m s 4 5 4 . 7 . 3 . 2 D i s a d v a n t a g e s o f t h e s e p a r a t e s l u d g e o p e r a t i o n 4 5 5 N I T R O G E N R E M O V A L O R D E N I T R I F I C A T I O N 4 7 5 . 0 B i o l o g i c a l N i t r o g e n U t i l i z a t i o n 4 7 5 . 1 D i s s i m i l a t i o n 4 7 5 . 1 . 1 R e s p i r a t i o n m o d e s 4 8 5 . 2 E n e r g y , S y n t h e s i s a n d S t o i c h i o m e t r y 4 8 5 . 2 . 1 A l k a l i n i t y p r o d u c t i o n 5 1 5 . 3 F a c t o r s A f f e c t i n g D e n i t r i f i c a t i o n 5 1 5 . 3 . 1 D i s s o l v e d o x y g e n 5 1 5 . 3 . 2 p H 5 2 5 . 3 . 3 T e m p e r a t u r e 5 2 5 . 3 . 4 M i c r o n u t r i e n t s 5 3 5 . 3 . 5 I n h i b i t i o n o f d e n i t r i f i c a t i o n 5 3 5 . 4 K i n e t i c s o f D e n i t r i f i c a t i o n 5 4 5 . 4 . 1 D e n i t r i f i c a t i o n r a t e s 5 4 5 . 4 . 1 . 1 S o l i d s r e t e n t i o n t i m e 5 5 5 . 4 . 1 . 2 S o l i d s c o n c e n t r a t i o n . 5 5 5 . 4 . 1 . 3 T e m p e r a t u r e 5 5 5 . 5 S u b s t r a t e 5 9 5 . 5 . 1 W a s t e w a t e r a s a s u b s t r a t e 5 9 5 . 5 . 2 M e t h a n o l a s a s u b s t r a t e 6 2 5 . 5 . 3 E n d o g e n o u s n i t r a t e r e s p i r a t i o n 6 3 5 . 6 P o s t D e n i t r i f i c a t i o n A e r a t i o n 6 4 - v i -5 . 7 N i t r i t i f i c a t i o n a n d D e n i t r i t i f i c a t i o n 6 5 5 . 8 F l o w S h e e t s f o r B i o l o g i c a l N i t r o g e n R e m o v a l 6 6 5 . 8 . 1 W u h r m a n n d e n i t r i f i c a t i o n s y s t e m ( p o s t - d e n i t r i f i c a t i o n ) 6 6 5 . 8 . 2 L u d z a c k d e n i t r i f i c a t i o n s y s t e m ( p r e - d e n i t r i f i c a t i o n ) 6 7 5 . 8 . 3 B a r d e n p h o p r o c e s s 6 8 5 . 8 . 4 A d s o r p t i o n - b i o - o x i d a t i o n ( A . B . ) p r o c e s s . . . . 6 8 5 . 8 . 5 A l t e r n a t i n g c o n t a c t p r o c e s s 6 9 5 . 8 . 6 A l t e r n a t i n g a n o x i c - a e r o b i c s y s t e m 6 9 5 . 8 . 7 " B i o - d e n i t r o " p r o c e s s 6 9 5 . 8 . 8 O x i d a t i o n d i t c h e s 7 0 6 E X P E R I M E N T A L A P P A R A T U S A N D P R O C E D U R E S 7 2 6 . 1 M o d e l D e s i g n 7 2 6 . 1 . 1 A e r a t i o n 7 2 6 . 1 . 2 M i x i n g 7 4 6 . 1 . 3 P u m p i n g 7 4 6 . 1 . 4 F l o w C o n t r o l 7 4 6 . 1 . 5 F e e d p u m p 7 4 6 . 1 . 6 M i x e d l i q u o r r e c y c l e p u m p 7 4 6 . 1 . 7 S l u d g e r e c y c l e 7 4 6 . 2 B a t c h R e a c t o r s 7 5 6 . 3 F e e d 7 5 6 . 4 S a m p l i n g a n d S a m p l e T r e a t m e n t 7 5 6 . 5 A n a l y t i c a l a n d M o n i t o r i n g T e c h n i q u e s . 7 6 6 . 5 . 1 A l k a l i n i t y 7 6 6 . 5 . 2 p H . . 7 6 6 . 5 . 3 D i s s o l v e d o x y g e n ( D O ) 7 7 6 . 5 . 4 F i v e d a y b i o c h e m i c a l o x y g e n d e m a n d ( B O D ) . . . . 7 7 6 . 5 . 5 A m m o n i a 77 6 . 5 . 6 T o t a l K j e l d a h l N i t r o g e n 7 7 6 . 5 . 7 N i t r i t e ( N O ^ ) 7 7 6 . 5 . 8 N i t r a t e ( N O ~ ) 77 6 . 5 . 9 S u s p e n d e d s o l i d s 7 9 - v i i -6.5.10 Temperature 79 6.5.11 Flow rates 79 6.5.12 Light 79 6.5.13 Solids retention time 79 6.6 Modified Bardenpho Model Operation 80 6.7 Batch Tests 84 7 RESULTS AND DISCUSSION 88 7.1 Startup Operations (Phase 181A) 88 7.2 Overall System performance 88 7.2.1 Phosphorus removal 88 7.2.2 BOD removal 91 7.2.3 Suspended solids removal 91 7.2.4 Volatile suspended solids 91 7.2.5 Heavy metals 91 7.2.6 Nitrite concentrations 92 7.3 Nitrogen Removal (Table 7.1) 92 7.3.1 18°C 92 7.3.2 14°C. 93 7.3.3 10°C (Figure 7.4) 96 7.3.4 6°C (Figure 7.5) 96 7.4 Nit r i f i c a t i o n and Denitrification Rates 96 7.4.1 Batch n i t r i f i c a t i o n tests 96 7.4.2 Nit r i f i c a t i o n rates calculated from a system flow-through mass balance 96 7.4.3 Denitrification rates calculated from a system flow-through mass balance 102 7.4.4 Batch denitrification tests 102 7.4.5 Example batch rate calculation 102 7.4.6 Individual basin operating data 102 7.5 Summary of Results 108 7.6 Discussion of Model Performance 108 7.6.1 Reactor Startup (Phase 181A) 108 7.6.2 Phase 181B and 181C 115 7.6.3 Run 141A 115 - v i i i -7.6.4 Adequate n i t r i f i c a t i o n and d e n i t r i f i c a t i o n achieved 116 7.6.5 Recovery from overheating (141B and 141C) . . . 116 7.6.6 Run 101A 117 7.6.7 Run 182A 117 7.6.8 Run 142A 119 7.6.9 Run 061A 119 7.7 Dependence of N i t r i f i c a t i o n and D e n i t r i f i c a t i o n Rates on Temperature 120 7.8 Factors P o t e n t i a l l y Influencing the Observed Unit Reaction Rates 122 7.8.1 Dissolved Oxygen 122 7.8.2 pH and A l k a l i n i t y 122 7.8.3 Anoxic residence time 122 7.8.4 Combined sludge 122 7.8.5 MLSS concentration 123 7.8.6 Steady-state conditions 123 7.8.7 SRT 123 7.8.8 Fraction of v i a b l e micro-organisms 123 7.8.9 T o x i c i t y and i n h i b i t i o n 124 7.8.10 Substrate l i m i t a t i o n s 125 7.8.10.1 N i t r i f i c a t i o n 125 7.8.10.2 D e n i t r i f i c a t i o n using wastewater substrate (Basin #2) 126 7.8.10.3 Endogenous d e n i t r i f i c a t i o n (Basin #4). 127 7.8.11 Summary of rate l i m i t i n g factors 127 7.8.11.1 N i t r i f i c a t i o n 127 7.8.11.2 Wastewater substrate d e n i t r i f i c a t i o n . 128 7.8.11.3 Endogenous d e n i t r i f i c a t i o n 128 7.9 Minimum Solids Residence Time 129 7.10 E f f e c t of Basin #5 on Nitrogen i n the E f f l u e n t . . . . 129 7.11 Scum Layer 130 7.12 Nitrogen Analysis 131 7.12.1 Alternative monitoring 132 8 CONCLUSIONS 133 - i x -R E F E R E N C E S 135 A P P E N D I C E S . 144 A P P E N D I X 1 145 A P P E N D I X 2 146 A P P E N D I X 3 147 -x-L I S T O F T A B L E S T a b l e N o . T i t l e P a g e 1 . 1 N i t r o g e n R e m o v a l P r o c e s s e s ( A f t e r S u t t o n 1 9 7 4 ) . . . 6 3 . 1 E n e r g y Y i e l d s f r o m N i t r o g e n R e a c t i o n s ( D e l w i c h e 1 9 7 0 ) 2 1 4 . 1 T y p i c a l V a l u e s o f K i n e t i c C o n s t a n t s f o r N i t r i f i e r s ( A f t e r S h a r m a 1 9 7 7 a n d P a i n t e r 1 9 7 7 ) . . 3 4 4 . 2 A r r h e n i u s C o n s t a n t s f o r N i t r i f i c a t i o n 3 6 4 . 3 R a n g e o f A e r o b i c S R T R e p o r t e d f o r N i t r i f i c a t i o n . . 4 1 5 . 1 S t o i c h i o m e t r i c R e p r e s e n t a t i o n s o f D e n i t r i f i c a t i o n R e a c t i o n s ( A f t e r B e e r 1 9 7 8 , M c C a r t y 1 9 6 9 ) 5 0 5 . 2 A r r h e n i u s C o n s t a n t s f o r D e n i t r i f i c a t i o n 5 8 5 . 3 W a s t e w a t e r D e n i t r i f i c a t i o n S u b s t r a t e s 6 0 5 . 4 D e p e n d e n c e o f E n d o g e n o u s N i t r a t e R e s p i r a t i o n o n T e m p e r a t u r e 6 4 6 . 1 M o d e l D i m e n s i o n s a n d C l a r i f i e r D a t a 7 3 6 . 2 C h r o n o l o g y o f M o d e l T e m p e r a t u r e R e g i m e s 8 1 6 . 3 M o d e l H y d r a u l i c D a t a a n d E s t i m a t e d S l u d g e A g e . . . 8 2 6 . 4 F r e q u e n c y o f A n a l y s i s 8 3 7 . 1 O v e r a l l S y s t e m P e r f o r m a n c e 9 0 7 . 2 B a t c h N i t r i f i c a t i o n R a t e s i n #3 B a s i n 1 0 0 7 . 3 N i t r i f i c a t i o n R a t e b y F l o w T h r o u g h M a s s B a l a n c e C a l c u l a t i o n s i n B a s i n #3 . . . . . 1 0 1 7 . 4 D e n i t r i f i c a t i o n R a t e s b y F l o w T h r o u g h M a s s B a l a n c e C a l c u l a t i o n s 1 0 6 7 . 5 B a t c h D e n i t r i f i c a t i o n R a t e s : B a s i n s #2 a n d #4 . . . 1 0 7 7 . 6 R a t i o o f B a t c h R a t e t o C a l c u l a t e d F l o w - T h r o u g h M a s s B a l a n c e R a t e o n S a m e D a y ( D a t a f r o m T a b l e s 7 . 2 t o 7 . 5 ) 1 1 8 7 . 7 E s t i m a t e d M i n i m u m S o l i d s R e s i d e n c e T i m e f o r N i t r i f i c a t i o n a n d D e n i t r i f i c a t i o n 1 2 9 - x i -LIST OF FIGURES Figure No. Titl e Page 2.1 Bardenpho Process (Barnard 1975) 8 2.2 Modified Bardenpho Process (Jank 1978) 8 3.1 Nitrogen Cycle (EPA, 1975) 19 4.1 Ni t r i f i c a t i o n Rates (EPA, 1975) 43 5.1 Endogenous Denitrification Rates: This Work and Others 56 5.2 Denitrification Rates With Wastewater Carbon Source . 57 6.1 Batch Denitrification, Basin #2 at 18°C 86 7.1 System Performance During Startup and Operation at 18°C 89 7.2 Overall System Performance at 14°C (Runs 141 A, B and C) 94 7.3 System and Basin Performance at 14°C (Run 142) 95 7.4 System Performance and #1 Basin Data at 10°C . . . 97 7.5 System Performance and #3 Basin Data at 6°C . . . 98 7.6 Batch Nit r i f i c a t i o n Rates in Basin #3 99 7.7 Calculated N i t r i f i c a t i o n Rate in #3 Basin . . . . 103 7.8 Calculated Denitrification Rate in #4 Basin . . . 103 7.9 Calculated Denitrification Rates Basin #1 and #2 104 7.10 Batch Denitrification Rates in Basins #2 and #4. . 105 7.11 Operating Data for Basins #2, 3 and 4 at 18°C . . 109 7.12 Performance of Basins #2 and #3 at 18°C 110 7.13 Performance of Basin #1 and #2 at 14°C (Run 141) . I l l 7.14 Performance of Basins #3 and #4 at 14°C (Run 141) 112 - x i i -Figure No. Titl e Page 7.15 Operating Data for Basins #2, 3 and 4 at 10°C . . 113 7.16 Performance of Basins #1, #2 and #4 at 6°C . . . . 114 7.17 Nit r i f i c a t i o n Rates: This Work and Others . . . . 121 - x i i i -A C K N O W L E D G E M E N T S M y t h a n k s a r e d u e t o D r . W . K . O l d h a m , F . K o c h a n d t h e s t a f f o f t h e E n v i r o n m e n t a l E n g i n e e r i n g L a b o r a t o r y f o r d i s c u s s i o n , g u i d a n c e a n d a s s i s t a n c e t h r o u g h o u t t h e c o u r s e o f t h i s p r o j e c t . K n i g h t a n d P i e s o l d L t d . p r o v i d e d t h e m a j o r p o r t i o n o f f u n d i n g . R u t h S t . C l a i r e h a s m a g n i f i c e n t l y p e r f o r m e d t h e m o n u m e n t a l t a s k o f t y p i n g t h i s t h e s i s . -1-CHAPTER 1 INTRODUCTION The uncontrolled discharge of nitrogen-containing wastewaters to the aquatic environment has s i g n i f i c a n t aesthetic,^economic, and health consequences, and thus i s a major consideration i n many r e l a t e d decision making processes. In recent years, regulations and technology have been developed to monitor and control such discharges and when implemented they can go a long way toward preventing or reversing the continuing degradation of rec e i v i n g waters. Widespread research continues, aimed at a better understanding of nitrogen's r o l e i n the l i f e process and, among other things, improving the technology of i t s removal from wastewater. 1.1 EutrOphication o f Lakes Most lakes undergo a slow natural t r a n s i t i o n from a low p r o d u c t i v i t y or o l i g o t r o p h i c state, through a mesotrophic state, to that of highly productive eutrophication. T y p i c a l l y , o l i g o t r o p h i c lakes have low nutrient to volume r a t i o s , high dissolved oxygen (DO) l e v e l s and are deep, cold and c l e a r with a d i s t i n c t i v e f l o r a and fauna. Eutrophic lakes have high n u t r i e n t to volume r a t i o s and a d i f f e r e n t c h a r a c t e r i s t i c hierarchy of species. They tend to be warmer, shallow and t u r b i d and : often have areas of low DO. Mesotrophic lakes e x h i b i t intermediate t r a i t s . The natural t r a n s i t i o n of a lake i s slow and complex; influences include the rate of nutri e n t supply, climate ( p r i n c i p a l l y l i g h t i n t e n s i t y and temperature), the depth and the shape of the lake. Some lakes remain o l i g o t r o p h i c over many millenia.(Vallentyne 1974) . -2-T h e t w o m a j o r n u t r i e n t s i n f l u e n c i n g e u t r o p h i c a t i o n a r e n i t r o g e n a n d p h o s p h o r u s . F o s b e r g ( 1 9 7 ? ) i n d i c a t e s t h a t n i t r o g e n i s p r o b a b l y g r o w t h l i m i t i n g i n l a k e s e u t r o p h i e d b y d o m e s t i c s e w a g e , w h i l e p h o s p h o r u s i s u s u a l l y g r o w t h l i m i t i n g i n o l i g o t r o p h i c w a t e r s . I n a f e w i n s t a n c e s o r g a n i c c a r b o n m a y b e l i m i t i n g . T h e a b i l i t y o f s o m e a l g a e t o f i x n i t r o g e n f r o m t h e a i r g a v e r i s e t o t h e c o n v e n t i o n a l w i s d o m t h a t p h o s p h o r u s w a s m o s t f r e q u e n t l y l i m i t i n g ( H o m e 1 9 7 7 ) . 1 . 1 . 1 M a i i - ' . s c o n t r i b u t i o n t o e u t r o p h i c a t i o n : M a n c a n h a s t e n t h e e u t r o p h i c a t i o n o f w a t e r b o d i e s , m o s t o f t e n b y i n c r e a s i n g t h e r a t e o f n u t r i e n t i n p u t . S o u r c e s o f s u c h n u t r i e n t s i n c l u d e : ( i ) M u n i c i p a l a n d i n d i v i d u a l ( t i l e f i e l d ) . s e w a g e d i s c h a r g e s ; ( i i ) I n d u s t r i a l w a s t e d i s c h a r g e ; ( i i i ) A g r i c u l t u r a l r u n o f f f r o m a n i m a l f e e d l o t s a n d f r o m f e r t i l i z e r a p p l i e d t o f i e l d s ; ( i v ) I n c r e a s e d s i l t a t i o n f r o m f o r e s t r y , m i n i n g , a g r i c u l t u r a l , c o n s t r u c t i o n a n d f l o o d c o n t r o l o p e r a t i o n s . 1 . 1 . 2 P r o b l e m s a s s o c i a t e d w i t h e u t r o p h i c a t i o n : ( i ) W i t h h i g h n u t r i e n t l e v e l s , " b l o o m s " o f a l g a e o r o f a q u a t i c p l a n t s m a y o c c u r ; ( i i ) S u c h b l o o m s g i v e r i s e t o d i u r n a l c h a n g e s i n D O , p H a n d a l k a l i n i t y , t h u s s t r e s s i n g u n a d a p t e d e x t a n t s p e c i e s a n d a l t e r i n g i o n i c c o n c e n t r a t i o n s ; ( i i i ) T h e i n c r e a s e d t u r b i d i t y a n d s h a d e a s s o c i a t e d w i t h s u c h b l o o m s d e c r e a s e s l i g h t i n t e n s i t y t o t h e l a k e w a t e r , f u r t h e r c h a n g i n g t h e h a b i t a t o f e x i s t i n g s p e c i e s . -3-( i v ) T h e d e a t h a n d d e c a y o f b l o o m i n g s p e c i e s r e c y c l e s t h e n u t r i e n t s , c a u s e s h i g h DO d e m a n d a n d l o c a l d e p l e t i o n , f u r t h e r s t r e s s i n g e x t a n t f a u n a ; ( v ) F r o m a n a e s t h e t i c a n d r e c r e a t i o n a l p o i n t o f v i e w , t h e f l o a t i n g m a t s o f w e e d s o r a l g a e a r e u n d e s i r a b l e f o r s w i m m i n g a n d b o a t i n g . N e w a n d c o a r s e r f i s h s p e c i e s b e c o m e d o m i n a n t . R o t t i n g p l a n t m a t e r i a l g i v e s r i s e t o c o l o u r , o d o u r a n d t a s t e p r o b l e m s ; ( v i ) N a t u r a l c h a n n e l s b e c o m e o b s t r u c t e d , t h u s r e s t r i c t i n g d r a i n a g e . W a t e r i n l e t p i p e s m a y b e b l o c k e d . W a t e r t r e a t m e n t c o s t s i n c r e a s e b e c a u s e o f t h e n e c e s s i t y t o r e m o v e c o l o u r , o d o u r a n d t a s t e , o r t o d r a w w a t e r f r o m m o r e e x p e n s i v e s o u r c e s . 1.2 A d d i t i o n a l C o n c e r n s A s s o c i a t e d W i t h A q u e o u s N i t r o g e n A p a r t f r o m t h e i r i m p o r t a n t r o l e i n e u t r o p h i c a t i o n , n i t r o g e n c o m p o u n d s i n w a t e r a r e o f c o n c e r n f r o m p u b l i c h e a l t h , e c o l o g i c a l , i n d u s t r i a l a n d p r a c t i c a l p o i n t s o f v i e w : ( i ) P r i o r t o d e v e l o p m e n t o f t h e c o l i f o r m t e s t , a h i g h r a t i o o f r e d u c e d t o o x i d i z e d n i t r o g e n f o r m s i n w a t e r w a s t a k e n t o i n d i c a t e r e c e n t p o l l u t i o n b y s e w a g e a n d t h u s d a n g e r o f w a t e r - b o r n e d i s e a s e t r a n s m i s s i o n ( S a w y e r 1978). ( i i ) M c K e e (1963) i n d i c a t e s t h a t n i t r a t e c o n c e n t r a t i o n s o v e r 100 m g / L - N r e n d e r t h e c o l i f o r m t e s t u n r e l i a b l e . ( i i i ) N i t r a t e c o n c e n t r a t i o n s i n e x c e s s o f 50 m g / L i n d o m e s t i c w a t e r m a y g i v e r i s e t o m e t h e m o g l o b i n e m i a ( a b l o o d o x y g e n d e f i c i e n c y ) i n i n f a n t s ( S h u v a l 1977). N i t r i t e p r o d u c e d b y r e d u c i n g c o n d i t i o n s i n t h e s t o m a c h f o r m s m e t h e m o g l o b i n w h i c h p r e v e n t s o x y g e n t r a n s f e r -4-i n t h e b l o o d , g i v i n g r i s e t o t h e c h a r a c t e r i s t i c b l u e c o l o u r a t i o n o f s u f f o c a t i o n . S u c h a p r o b l e m i s o f m o s t c o n c e r n w h e r e s h a l l o w w e l l s a r e u s e d t o p r o v i d e p o t a b l e w a t e r . ( i v ) T h e r o l e o f n i t r o s a m i n e s a n d o t h e r n i t r o g e n c o m p o u n d s a s c a r c i n o g e n s i s d i s c u s s e d b y M i r v i s h ( 1 9 7 7 ) . ( v ) F r e e a m m o n i a i s t h e m o s t t o x i c t o a q u a t i c f a u n a o f t h e n i t r o g e n c o m p o u n d s a s s o c i a t e d w i t h d o m e s t i c s e w a g e ( M c K e e 1 9 6 3 ) . T h e t o x i c i t y i s s t r o n g l y r e l a t e d t o p H , t e m p e r a t u r e a n d D O . I n h i g h c o n c e n t r a t i o n s , o t h e r n i t r o g e n f o r m s a l s o e x h i b i t t o x i c i t y ( C a i r n s 1 9 7 5 ) . ( v i ) W h e r e e f f l u e n t , r i c h i n r e d u c e d n i t r o g e n , i s d i s c h a r g e d t o r e c e i v i n g w a t e r s w i t h l o w d i l u t i o n , s u b s e q u e n t n i t r i f i c a t i o n m a y c a u s e s i g n i f i c a n t o x y g e n d e p l e t i o n . T h i s n i t r o g e n o u s o x y g e n d e m a n d ( N O D ) a d d s t o t h e r e q u i r e m e n t f o r o x y g e n s u p p l y i n b i o l o g i c a l s e w a g e t r e a t m e n t . I t m a y a l s o ' c o n t r i b u t e t o h i g h r e s u l t s i n t h e s t a n d a r d B O D t e s t ( B i s h o p 1 9 7 6 ) . ( v i i ) W h e n b r e a k p o i n t c h l o r i n a t i o n o f d r i n k i n g w a t e r o r e f f l u e n t s i s c a r r i e d o u t , r e a c t i o n s o c c u r b e t w e e n a m m o n i a a n d h y p o c h l o r i t e i o n s , w i t h t h e f o r m a t i o n o f c h l o r a m i n e s . H i g h c o n c e n t r a t i o n s o f a m m o n i a w i l l i n c r e a s e t h e c o n s u m p t i o n o f c h l o r i n e p r i o r t o t h e f o r m a t i o n o f t h e d e s i r a b l e c h l o r i n e r e s i d u a l a n d t h u s d e t r a c t f r o m t h e p r o c e s s e c o n o m i c s . ( v i i i ) T h e r e d u c t i o n o f o x i d i z e d n i t r o g e n t o n i t r o g e n g a s i n a n o x i c r e g i o n s o f s l u d g e s e t t l i n g t a n k s m a y c a u s e r i s i n g s l u d g e , d u e t o g a s b u b b l e e n t r a i n m e n t i n t h e s e t t l i n g f l o e a n d t h u s l o w e r t h e e f f i c i e n c y o f s o l i d s r e m o v a l , ( i x ) I n s e v e r a l i n d u s t r i e s ( e g . b r e w i n g a n d d y e i n g ) , n i t r a t e s a n d -5-n i t r i t e s a r e h a r m f u l t o t h e p r o c e s s o r t h e p r o d u c t , w h i l e i n o t h e r s t h e y m a y b e d e s i r a b l e ( e g . m e t a l c o r r o s i o n p r o t e c t i o n i n b o i l e r s ) . 1 . 3 A v a i l a b l e P r o c e s s e s f o r N i t r o g e n C o n t r o l i n W a t e r T h e m o s t g e n e r a l l y u s e d c o n t r o l i s t o t r e a t t h e w a t e r s t r e a m c a r r y i n g t h e n i t r o g e n . D e p e n d i n g o n t h e a p p l i c a b l e r e g u l a t i o n s o r s p e c i f i c a t i o n s , p r a c t i c e m a y e n t a i l o n l y o x i d a t i o n o f r e d u c e d n i t r o g e n f o r m s ( n i t r i f i c a t i o n ) o r r e m o v a l o f a l l n i t r o g e n f o r m s f r o m t h e e f f l u e n t ( n i t r o g e n r e m o v a l ) . T h e a v a i l a b l e p r o c e s s e s m a y b e c l a s s i f i e d a s b i o l o g i c a l o r p h y s i c a l - c h e m i c a l ( T a b l e 1 . 1 ) . 1 . 3 . 1 P h y s i c a l - c h e m i c a l p r o c e s s e s a r e r e l a t i v e l y u n a f f e c t e d b y t e m p e r a t u r e o r t o x i c i t y , t w o b a n e s o f b i o l o g i c a l s y s t e m s . H o w e v e r , t h e y o f t e n d o n o t r e m o v e a l l t h e f o r m s o f n i t r o g e n p r e s e n t , a n d t h e y a r e m o s t l y h i g h t e c h n o l o g y , e n e r g y - i n t e n s i v e p r o c e s s e s w i t h i n d i v i d u a l i d i o s y n c r a s i e s r e s t r i c t i n g t h e i r u s e f u l n e s s o r e c o n o m i c c o m p e t i t i v e n e s s t o n a r r o w a r e a s o f a p p l i c a b i l i t y . 1 . 3 . 2 B i o l o g i c a l p r o c e s s e s m a y e m p l o y p l a n t s p e c i e s o r m i x e d c u l t u r e s o f a l g a e o r m i c r o b e s t o e f f e c t n i t r o g e n t r a n s f o r m a t i o n s a n d r e m o v a l s . T h e a v a i l a b i l i t y o f s e v e r a l b i o l o g i c a l t r e a t m e n t s y s t e m s , s u c h a s t r i c k l i n g f i l t e r s , a c t i v a t e d s l u d g e u n i t s , r o t a t i n g b i o l o g i c a l d i s c s , o x i d a t i o n d i t c h e s , e t c . g i v e s g r e a t f l e x i b i l i t y t o t h e d e s i g n f o r n i t r o g e n r e m o v a l . C a r e f u l e n v i r o n m e n t a l c o n t r o l m u s t , h o w e v e r , b e e x e r c i s e d t o m a i n t a i n t h e d e s i r e d m i c r o b i a l p o p u l a t i o n s a n d t h u s t h e p r o c e s s e f f i c i e n c y . - 6 -T A B L E 1..1 N I T R O G E N R E M O V A L P R O C E S S E S ( A f t e r S u t t o n 1 9 7 4 ) P R O C E S S R E F E R E N C E P h y s i c a l - C h e m i c a l P r o c e s s e s A m m o n i a S t r i p p i n g B r e a k p o i n t C h l o r i n a t i o n I o n E x c h a n g e U s i n g C l i n o p t i l a l i t e E l e c t r o d i a l y s i s E l e c t r o c h e m i c a l R e v e r s e O s m o s i s D i s t i l l a t i o n L a n d A p p l i c a t i o n B i o l o g i c a l P r o c e s s e s A e r o b i c N i t r i f i c a t i o n / A n a e r o b i c D e n i t r i f i c a t i o n W a t e r P l a n t H a r v e s t i n g ( H y a c i n t h ) A c t i v a t e d A l g a e E P A ( 1 9 7 5 ) E P A ( 1 9 7 5 ) E P A ( 1 9 7 5 ) S u t t o n ( 1 9 7 4 ) P o o n ( 1 9 7 5 ) S u t t o n ( 1 9 7 4 ) S u t t o n ( 1 9 7 4 ) E P A ( 1 9 7 7 ) E P A ( 1 9 7 5 ) D i n g e s ( 1 9 7 8 ) R e g a n ( 1 9 7 7 ) M c G r i f f ( 1 9 7 2 ) L a g o o n s a n d O x i d a t i o n P o n d s E P A ( 1 9 7 3 ) 1 . 3 . 3 L a n d a p p l i c a t i o n o f s e w a g e r e l i e s o n a c o m b i n a t i o n o f b i o l o g i c a l a n d p h y s i c a l - c h e m i c a l p r o c e s s e s t o s t a b i l i z e w a s t e w a t e r . B a c t e r i a l a n d p l a n t l i f e t r a n s f o r m n i t r o g e n s p e c i e s , w h i l e c l a y s i n t h e s o i l a r r e s t t h e m o v e m e n t o f a m m o n i a . D e s i g n e r s o f s u c h s y s t e m s m u s t c o n s i d e r t h e p o s s i b i l i t y o f p u b l i c h e a l t h p r o b l e m s , n i t r a t e i n f i l t r a t i o n t o g r o u n d -w a t e r s a n d t h e e f f e c t s o f s e a s o n a l c l i m a t i c v a r i a t i o n s . - 7 -C H A P T E R 2 R E S E A R C H R A T I O N A L E : N U T R I E N T R E M O V A L V I A T H E B A R D E N P H O P R O C E S S 2 . 1 D e v e l o p m e n t o f t h e B a r d e n p h o P r o c e s s T h e B a r d e n p h o P r o c e s s ( B A R n a r d - D E N i t r i f i c a t i o n - P H O s p h o r u s r e m o v a l ) u t i l i z e s b i o l o g i c a l a c t i v i t y a l o n e t o r e m o v e n i t r o g e n a n d p h o s p h o r u s f r o m w a s t e w a t e r a n d t o s t a b i l i z e o r g a n i c c a r b o n i n a m o d i f i e d , e x t e n d e d a e r a t i o n , a c t i v a t e d s l u d g e o p e r a t i o n . T h e d e v e l o p m e n t o f t h i s p r o c e s s i n S o u t h A f r i c a , f r o m t h e w o r k o f L u d z a c k ( 1 9 6 2 ) , i s o u t l i n e d b y B a r n a r d ( 1 9 7 5 b ) . I n t h e " L u d z a c k " r e a c t o r ( s e e S e c t i o n 5 . 8 . 2 ) , n i t r i f i e d m i x e d l i q u o r i s r e c y c l e d t o a n a n o x i c t a n k a n d m i x e d w i t h i n c o m i n g r a w s e w a g e . N i t r a t e i s r e d u c e d t o n i t r o g e n b y a v a i l a b l e c a r b o n i n t h e w a s t e w a t e r a n d l e a v e s t h e s y s t e m . T h e m i x e d l i q u o r o v e r f l o w s t o a n a e r o b i c c e l l w h e r e t h e n i t r i f i c a t i o n a n d c a r b o n s t a b i l i z a t i o n o c c u r , . . B a r n a r d a d d e d a t h i r d b a s i n , w h e r e u n d e r a n o x i c c o n d i t i o n s , e n d o g e n o u s n i t r a t e r e s p i r a t i o n r e m o v e d t h e n i t r a t e n o t e l i m i n a t e d i n t h e f i r s t b a s i n ( S e c t i o n 5 . 8 . 2 ) . F o r n i t r o g e n s t r i p p i n g , f i n a l a m m o n i a o x i d a t i o n , r e a e r a t i o n a n d s l u d g e s t a b i l i z a t i o n p r i o r t o s e t t l i n g , a f i n a l a e r o b i c b a s i n w a s a d d e d ( F i g u r e 2 . 1 ) . A M o d i f i e d B a r d e n p h o P r o c e s s ( F i g u r e 2 . 2 ) w a s d e v e l o p e d , b y t h e a d d i t i o n o f a n i n i t i a l a n a e r o b i c r e a c t o r ( n o o x y g e n o r n i t r a t e ) p r i o r t o t h e w a s t e w a t e r d e n i t r i f i c a t i o n s t e p , t o " c o n d i t i o n " t h e s l u d g e f o r s u b s e q u e n t b i o l o g i c a l p h o s p h o r u s r e m o v a l . 2 . 2 A p p l i c a b i l i t y o f t h e B a r d e n p h o P r o c e s s B a r n a r d ( 1 9 7 5 a ) o u t l i n e s t h e r e s u l t s o f h i s w o r k o n a S o u t h A f r i c a n p i l o t p l a n t i n w h i c h u p t o 9 4 % t o t a l n i t r o g e n a n d 9 0 % C O D ( a v e r a g e ) Feed FeedW, Mixed L iquor R e c y c l e Anoxic Basin Denitrification 2 nr. M Aerobic Basin Nitr i f icat ion BOD Removal 6hr. Anoxic Basin Denitrification 6hr. I Aerobic Basin S t r ipp ing and Reaerat ion 2 hr. S l u d g e R e c y c l e I : I FIG.2.1 B A R D E N P H O PROCESS (Barnard 1975) M i x e d L i q u o r R e c y c l e 1 Anaerobic Basin Anoxic Bosin Aerobic Bosin Anoxic Basin #1 # 2 # 3 # 4 Denitrification Denitrification BOD Removal Denitrification P Removal N i t r i f i ca t ion Condi t ion! ng S l u d g e R e c y c l e Effluent S ludge Wasteoge i co Aerobic Bosin # 5 Stripping and Reaerat ion U C l a r i f i er Ef f luent Sludge Wasteoge FIG.2.2 MODIFIED BARDENPHO PROCESS ( Jank 1978) -9-removals and l e s s than a 1 mg/L t o t a l phosphorus r e s i d u a l were achieved. A mixed l i q u o r recycle of 4:1 and a sludge return of 1:1 were used. Feed COD of 340, TKN of 81 and system MLSS i n the 4500 to 6000 mg/L range were reported. Operational temperatures were between 18°C and 25°C. The system nominal hydraulic retention time (HRT) was about 16 hours and the s o l i d s r e t e n t i o n time (SRT) was generally between 18 and 25 days. N i c h o l l s (1975), Venter (1976), Osborn (1978) describe modifications' to f u l l scale extended aeration plants and p i l o t plants i n the Johannesburg area, which when operated i n the Bardenpho mode, r e g u l a r l y achieved t o t a l nitrogen removals i n excess of 80%. The reported operating temperatures were generally i n excess of 17°C; BOD:TKN i n excess of 7:1; MLSS i n the 3000-6000 mg/L range; system SRT greater than 20 days and system HRT greater than 20 hours. McLaren (1976) , i n P r e t o r i a , reported 76% t o t a l nitrogen removal from a p i l o t plant operated i n the modified Bardenpho mode and optimized fo r phosphorus removal. Barnard (1978) indicated that the endogenous basin may not be necessary, except where: (i) the raw sewage i s highly nitrogenous, i n which case high removal e f f i c i e n c i e s i n the f i r s t anoxic reactor would s t i l l leave high n i t r a t e r e s i d u a l s ; or ( i i ) where low BOD (eg. from weak sewage) could l i m i t f i r s t stage d e n i t r i f i c a t i o n rates due to carbon d e f i c i e n c y . Barnard indicated that cold-weather, second-stage d e n i t r i f i c a t i o n rates could be increased by a c o n t r o l l e d methanol or ethanol addition to t h i s nominally endogenous reactor. The South A f r i c a n experience i s so encouraging that most new plants there are using the Bardenpho process (Burdick 1978). P a r t i c u l a r l y i n the Johannesburg area, fresh water i s scarce and r e c e i v i n g waters are -10-generally impounded and reused f o r potable water supply, i r r i g a t i o n and r e c r e a t i o n . The c i t y has a long established p o l i c y of n u t r i e n t reduction i n sewage e f f l u e n t s i n order to retard r e s e r v o i r eutrophication. The Bardenpho process at present i s the n u t r i e n t removal process of choice (Venter 1976). Recently the c i t y of Palmetto, F l o r i d a has chosen to i n s t a l l a Bardenpho plant f o r nitrogen and phosphorus removal. Burdick (1978) out l i n e s the r e l a t i v e costs and other factors that saw t h i s process chosen. 2.3 The Bardenpho Process Under Canadian Conditions The P r o v i n c i a l Government of B r i t i s h Columbia (B.C.) has imposed r e s t r i c t i o n s and deadlines on the l e v e l s of n u t r i e n t discharge that may be made to the Okanagan lake system by bordering m u n i c i p a l i t i e s . These r e s t r i c t i o n s w i l l require the upgrading of e x i s t i n g waste-water treatment f a c i l i t i e s or the cessation of e f f l u e n t discharge to surface waters. Because operating temperatures i n c e n t r a l B.C. are lower than those encountered i n South A f r i c a , evaluation of the Bardenpho process f o r B.C. operation requires i n v e s t i g a t i o n at the lower temperatures and weaker sewage strengths more t y p i c a l of Canadian conditions. Such research w i l l be of increased value because very l i t t l e published data i s a v a i l a b l e on the low temperature operation of any b i o l o g i c a l n u t r i e n t removal systems. 2.4 Required Research f o r Canadian A p p l i c a b i l i t y Any research programme w i l l be seeking answers to several general but basic questions. F o r a g i v e n s e w a g e w i t h i t s e x p e c t e d r a n g e o f c o n c e n t r a t i o n s a n d f l o w r a t e s : ( i ) W h a t e f f i c i e n c y o f n i t r o g e n , p h o s p h o r u s a n d B O D r e m o v a l c a n b e a n t i c i p a t e d a t t h e l o w e s t e x p e c t e d o p e r a t i n g t e m p e r a t u r e a n d w h a t w i l l b e t h e r e m o v a l r a t e f o r t h e s e c o n s t i t u e n t s ? ( i i ) H o w m a y t h e r a t e b e o p t i m i z e d t o m a i n t a i n t h e e f f i c i e n c y o r q u a l i t y o f e f f l u e n t , b u t t o m i n i m i z e t h e c a p i t a l c o s t ( e g . t a n k v o l u m e ) a n d t h e o p e r a t i n g c o s t ( e g . p o w e r / c h e m i c a l a d d i t i o n / p e n a l t y c h a r g e s ) o f t h e s y s t e m ? ( i i i ) H o w w i l l r a t e s a n d e f f i c i e n c i e s v a r y w i t h s e a s o n a l t e m p e r a t u r e c y c l e s ? ( i v ) W h a t f a c t o r s w i l l b e m o s t c r i t i c a l i n t h e i r e f f e c t s o n e a c h o f n i t r i f i c a t i o n , d e n i t r i f i c a t i o n , p h o s p h o r u s a n d B O D r e m o v a l a n d e f f l u e n t s o l i d s , a n d h o w s i g n i f i c a n t w i l l s u c h e f f e c t s b e ? ( v ) W h i c h o f t h e p a r a m e t e r s r e s t r i c t e d b y a d i s c h a r g e p e r m i t i s t h e m o s t l i k e l y t o e x c e e d t h i s l i m i t a t i o n a n d h o w m u c h m o r e l i k e l y i s i t t h a n a n y o t h e r p a r a m e t e r ? ( i v ) H o w w i l l l o w t e m p e r a t u r e s e f f e c t t h e s e t t l i n g a n d h a n d l i n g p r o p e r t i e s o f t h e p r o c e s s m i x e d l i q u o r a n d s l u d g e ? 2 . 5 E x p e r i m e n t a l O u t l i n e : B a s e d o n t h e a b o v e c o n s i d e r a t i o n s t h e f o l l o w i n g e x p e r i m e n t a l p r o g r a m w a s u n d e r t a k e n : 1. A 5 0 l i t r e m o d e l o f t h e m o d i f i e d B a r d e n p h o p r o c e s s w a s o p e r a t e d i n a t e m p e r a t u r e c o n t r o l l e d r o o m i n t h e E n v i r o n m e n t a l E n g i n e e r i n g L a b o r a t o r y o f t h e D e p a r t m e n t o f C i v i l E n g i n e e r i n g a t t h e 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 ( U . B . C ) . -12-2. T e s t i n g w a s u n d e r t a k e n a t 18°C, 14°C, 10°C a n d 6°C. 3. P h y s i c a l a n d c h e m i c a l d a t a w e r e c o l l e c t e d i n o r d e r t o u n d e r s t a n d a n d d e s c r i b e t h e o p e r a t i o n o f t h e p r o c e s s . 4. R e m o v a l e f f i c i e n c i e s o f n i t r o g e n , p h o s p h o r u s a n d B O D w e r e d e t e r m i n e d . 5. N i t r i f i c a t i o n a n d d e n i t r i f i c a t i o n r a t e s w e r e m e a s u r e d . 6. F a c t o r s t h a t l i m i t e d o r a f f e c t e d r a t e s a n d e f f i c i e n c i e s w e r e i d e n t i f i e d . 7. E x p e r i e n c e w a s g a i n e d i n t h e d e s i g n , p l a n n i n g a n d e x e c u t i o n o f a n e x p e r i m e n t u s i n g a s m a l l , c o m p l e x c o n t i n u o u s - f l o w b i o l o g i c a l r e a c t o r , w i t h n u m e r o u s i n t e r - r e l a t i o n s h i p s a m o n g v a r i a b l e s a n d m a n y s i g n i f i c a n t o u t p u t p a r a m e t e r s . 2 .6 T h i s T h e s i s T h i s w o r k s u m m a r i z e s s o m e o f t h e a v a i l a b l e l i t e r a t u r e o n b i o l o g i c a l n i t r i f i c a t i o n a n d n i t r o g e n r e m o v a l t h a t i s r e l e v a n t t o w a s t e - w a t e r t r e a t m e n t . T h a t p a r t o f t h e o u t l i n e d e x p e r i m e n t a l w o r k , r e l a t i n g t o n i t r o g e n t r a n s f o r m a t i o n a n d r e m o v a l a n d t o t h e a c t u a l o p e r a t i o n o f t h e m o d e l l e d s y s t e m , i s a l s o d i s c u s s e d . - 1 3 -C H A P T E R 3 B A C K G R O U N D T O B I O L O G I C A L N I T R O G E N R E M O V A L 3 . 1 M i c r o b i a l G r o w t h U n d e r t h e c i r c u m s t a n c e s o f m o s t r e l e v a n c e t o b i o l o g i c a l w a s t e t r e a t m e n t , a n o r g a n i s m r e p r o d u c e s b y b i n a r y f i s s i o n i n t o t w o c e l l s , e a c h w i t h a n e q u a l m e t a b o l i z i n g a b i l i t y . E a c h s u c h e v e n t o c c u r s w i t h i n a t i m e i n t e r v a l k n o w n a s , t h e " g e n e r a t i o n t i m e " . T h e l i f e c y c l e o f a n i s o l a t e d b a c t e r i a l p o p u l a t i o n o r o f a n a c t i v e b i o m a s s c a n b e b r o k e n i n t o t h r e e p h a s e s : a r a p i d ( l o g a r i t h m i c ) i n c r e a s e , a l e v e l l i n g o f f a n d a d e c l i n e . D u r i n g t h e l o g g r o w t h p h a s e , t h e r a t e a t w h i c h b o t h t h e p o p u l a t i o n a n d t h e b i o m a s s g r o w i s r e s t r i c t e d o n l y b y t h e r a t e a t w h i c h s u b s t r a t e i s m e t a b o l i z e d a n d b y t h e g e n e r a t i o n t i m e . W i t h t h e r i s i n g p o p u l a t i o n a n d b i o m a s s c o n c e n t r a t i o n , c o m p e t i t i o n f o r t h e a v a i l a b l e f o o d i n c r e a s e s a n d b o t h r a t e s b e g i n t o d e c l i n e a n d t h e n t o l e v e l o f f . T h e v i a b l e p o p u l a t i o n b e g i n s t o f a l l a t a n a c c e l e r a t i n g r a t e a s a n i n c r e a s i n g f o o d s h o r t a g e l o w e r s t h e g r o w t h r a t e a n d r a i s e s t h e d e a t h r a t e , l e a d i n g u l t i m a t e l y t o t h e " d e a t h " o f t h e c o l o n y . T h e b i o m a s s u n d e r g o e s a l e s s s p e c t a c u l a r d e c l i n e . A s t h e a v a i l a b l e f o o d d e c r e a s e s t h e a u t o - c o n s u m p t i o n o f c e l l u l a r p r o t o p l a s m i n c r e a s e s ( e n d o g e n o u s m e t a b o l i s m ) t o g e t h e r w i t h c o n s u m p t i o n o f t h e c e l l u l a r c o n t e n t s o f d e a d ( l y s e d ) b a c t e r i a . W i t h p r o l o n g e d m a i n t e n a n c e o f t h e e n d o g e n o u s p h a s e , a h i g h d e g r e e o f w a s t e s t a b i l i z a t i o n i s a c h i e v e d . I n t h e d e s i g n o f a b i o l o g i c a l s y s t e m t h e l o g g r o w t h p h a s e a p p e a r s a d v a n t a g e o u s d u e t o t h e r a p i d w a s t e s t a b i l i z a t i o n r a t e . P r a c t i c a l d i f f i c u l t i e s o c c u r , h o w e v e r , i n m e e t i n g t h e n e c e s s a r y o x y g e n - 1 4 -d e m a n d a n d m a i n t a i n i n g h i g h s u b s t r a t e c o n c e n t r a t i o n s . F u r t h e r p r o b l e m s a r e a s s o c i a t e d w i t h h i g h s l u d g e p r o d u c t i o n . G e n e r a l l y t h i s p h a s e i s p a s s e d o v e r f o r d e s i g n a n d t h e m o r e e a s i l y c o n t r o l l e d d e c l i n i n g o r e n d o g e n o u s g r o w t h p h a s e s a r e c h o s e n . 3 . 2 W a s t e S t a b i l i z a t i o n K i n e t i c s T w o e m p i r i c a l r e l a t i o n s h i p s f o r m t h e b a s i s f o r a n u n d e r s t a n d i n g o f t h e k i n e t i c s o f t h e b i o l o g i c a l s y s t e m r e s p o n s i b l e f o r s t a b i l i z i n g a n o r g a n i c w a s t e o r s o m e c o m p o n e n t o f t h a t w a s t e . ( i ) A r e l a t i o n s h i p b e t w e e n s u b s t r a t e u t i l i z a t i o n a n d b i o m a s s g r o w t h : ( i i ) A M o n o d t y p e r e l a t i o n s h i p ( S c h r o e d e r , 1 9 7 7 ) i n d i c a t i n g t h e r a t e o f s u b s t r a t e u t i l i z a t i o n : ( k X S ) / ( K + S ) s b i o m a s s c o n c e n t r a t i o n ( M / V ) n e t b i o m a s s g r o w t h r a t e ( M / V T ) y i e l d ( b i o m a s s p e r a m o u n t o f s u b s t r a t e u t i l i z e d ( M / M ) ) r a t e o f s u b s t r a t e u t i l i z a t i o n b y b i o m a s s ( M / V T ) b i o m a s s d e c a y c o e f f i c i e n t ( T ^") m a x i m u m r a t e o f w a s t e u t i l i z a t i o n p e r u n i t w e i g h t o f b i o m a s s ( M / M T ) w a s t e c o n c e n t r a t i o n a t w h i c h r a t e o f u t i l i z a t i o n i s 0 . 5 k ( M / V ) w a s t e c o n c e n t r a t i o n s u r r o u n d i n g b i o m a s s ( M / V ) [ 3 . 2 ] w h e r e : d F d t d F ( — ) b K s - 1 5 -U s i n g t h e s e t w o e q u a t i o n s ( o r s l i g h t m o d i f i c a t i o n s ) a n d a m o d e l f o r a c o m p l e t e m i x r e a c t o r , a s e r i e s o f r e l a t i o n s h i p s c a n b e d e r i v e d t o d e s c r i b e t h e o p e r a t i o n a n d c o n t r o l o f a c o n t i n u o u s b i o l o g i c a l p r o c e s s , s u c h a s t h e B a r d e n p h o o p e r a t i o n . ( S e e , f o r e x a m p l e , L a w r e n c e ( 1 9 7 0 ) o r M e t c a l f a n d E d d y ( 1 9 7 9 ) f o r a d e t a i l e d d i s c u s s i o n . T w o o f t h e s e e q u a t i o n s a r e o f m a j o r c o n c e r n h e r e : ( i ) S o l i d s R e t e n t i o n T i m e ( S R T ) o r S l u d g e A g e : [ 3 . 3 ] 9 c = X ' / d X ' = 1/u ( i i ) A r e l a t i o n s h i p b e t w e e n S R T a n d t h e r a t e o f w a s t e u t i l i z a t i o n : [ 3 . 4 ] l / 6 m = Y k - k c d w h e r e X " = S o l i d s I n v e n t o r y (M) d X ' = S o l i d s W a s t a g e p e r U n i t T i m e ( M / T ) y = S p e c i f i c g r o w t h r a t e ( l n . 2 / d o u b l i n g t i m e ) ( T ~S 3 m c = M i n i m u m . S E T t o m a i n t a i n a n a d e q u a t e v i a b l e b i o m a s s a b l e t o p e r f o r m t h e r e q u i r e d b i o l o g i c a l s t a b i l i z a t i o n ( T ) k ^ = D e c a y C o e f f i c i e n t ( T ^ ) U n l e s s a s l u d g e a g e i n e x c e s s o f i s m a i n t a i n e d , d e c a y w i l l e x c e e d g r o w t h f o r t h e p o p u l a t i o n i n q u e s t i o n a n d " w a s h o u t " w i l l o c c u r . 3 . 3 T e m p e r a t u r e E f f e c t s o n R e a c t i o n K i n e t i c s 3 . 3 . 1 T e m p e r a t u r e : T e m p e r a t u r e h a s t w o s i g n i f i c a n t e f f e c t s o n b i o l o g i c a l r e a c t i o n s : f i r s t l y , i t a f f e c t s t h e t y p e s o f b i o l o g i c a l p o p u l a t i o n p r e s e n t a n d , s e c o n d l y , i t i n f l u e n c e s t h e r a t e a t w h i c h r e a c t i o n s p r o c e e d . -16-3.3.2 B i o l o g i c a l Populations: According to the temperature range i n which they survive, b a c t e r i a may be c l a s s i f i e d as: (Sutton 1974) psychrophiles <20°C mesophiles 20-50°C thermophile s >5 0°C These categories are f l e x i b l e but, generally, b a c t e r i a acclimated to one temperature environment w i l l be severely i n h i b i t e d or k i l l e d by a r a d i c a l thermal change. 3.3.3 Reaction Rates: The Arrhenius equation or one of several modifications have been used to model the v a r i a t i o n of reaction rates with temperature (Sawyer 1978): k = A exp (-E/RT) or d (lnk)/dT = E/RT 2 - (change i n rate constant k with temperature) i n t e g r a t i n g E (T-T.. ) [3.5] 'ln(k / k ) = where: 2' 1 R T 2 T i T = Absolute Temperature (°K) k^,k£ = Reaction Rate Constants at T^ and T^ (1/time) . A = Frequency Factor (constant) E = A c t i v a t i o n Energy (cal/gm-mole) R = Universal Gas Constant (cal/gm-mole/°K) Where the temperature range i s small, Equation 3.5 may be written: In ^ 2/\) = 9(T 2 - T ) or k2 = k ! e x P ( 0 ^ T 2 ~ T l ^ ^  -17-where 9 i s a constant. Further s i m p l i f i c a t i o n (Metcalf 1979) replaces exp9 with a constant 9' (the thermal c o e f f i c i e n t ) such that: k2 = k i e , ( T 2 " T l ) Sutton (1974) discusses the C> concept, with Q, „ being the r a t i o 10 10 of the rate a t temperature T to the rate at T" = T - 10°C. The van't Hoff r u l e (Sawyer 1978) i n d i c a t e s a doubling i n re a c t i o n rate f or a 10°C temperature r i s e ( i e . Q 1 Q = 2.0). In a l l instances these rate-temperature r e l a t i o n s h i p s are empirical and v a l i d only for the s p e c i f i c system tested over r e l a t i v e l y narrow temperature ranges. 3.4 The Nitrogen Cycle A i r by weight i s 79% nitrogen and yet, paradoxically, a nitrogen, shortage l i m i t s the growth of plants and, thus, the world's food supply. Before i t i s a v a i l a b l e f o r use by most plants, nitrogen must be combined with another element (usually hydrogen or oxygen), a state r e f e r r e d to as "fixed nitrogen". Nitrogen gas, p a r t i c u l a r l y near "room" temperature, i s remarkedly i n e r t . This i s due both to i t s slow reaction k i n e t i c s i n otherwise thermo-dynamically favourable reactions (eg. nitrogen:hydrogen reactions) and to the unfavourable p o s i t i v e free energy of formation of, f o r example, i t s oxides (and thus t h e i r i n t r i n s i c i n s t a b i l i t y with respect to nitrogen and oxygen (Mahan 1969)). Nontheless, f i x a t i o n may be achieved i n the atmosphere by high energy phenomena such as l i g h t n i n g . However, the main source of combined nitrogen i s a few dozen marine and t e r r e s t r i a l organisms that are -18-b i o l o g i c a l l y able to f i x nitrogen (Painter 1977, Home 1977). The best known are those of the genus rhizobium which form symbiotic r e l a t i o n -ships with leguminous p l a n t s . Free l i v i n g nitrogen f i x e r s are found i n numerous environments i n the s o i l , the water,and even the gut of c e r t a i n i n s e c t s . Aerobes, anaerobes and phototrophs have been documented as, nitrogen f i x e r s ( B r i l l 1977) . Man, mostly v i a the high temperature and pressure HABER process, but also by extensive legume pla n t i n g and i n d u s t r i a l technology, makes a con t r i b u t i o n of f i x e d nitrogen approaching the natural production p r i o r to modern farming (Delwich 1970)) . He thus i s making a s i g n i f i c a n t i n t r u s i o n i n t o the "Nitrogen Cycle" i n terms of the sum t o t a l of a l l the forms of nitrogen and t h e i r i n t e r - r e l a t i o n s h i p s i n the ecosphere (Figure 3.1). Much of the complexity of t h i s cycle i s due to the wide range of oxidation states exhibited by nitrogen (ranging from —3 to +5), to the numerous mi c r o b i a l populations that u t i l i z e the energy released during transformation from one oxidation state to another> and to the e s s e n t i a l part played by nitrogen i n l i v i n g matter, as a constituent of n u c l e i c acids and c e l l u l a r p r o t e i n . In plant and animal ti s s u e nitrogen i s present i n i t s most reduced form (-3) as amino acids (protein constituents) or as the ammonium ion. In natural aerobic s o i l s and waters i t mostly occurs i n the +5 state as the n i t r a t e i o n . Both these ions are suitable f o r a s s i m i l a t i o n (incorporation i n t o plant tissue) although the n i t r a t e ions u s u a l l y must f i r s t be reduced. In s o i l s , ammonium ions tend to be trapped on c l a y p a r t i c l e s due to t h e i r e l e c t r o n i c charge and thus must f i r s t be oxidized to the highly mobile n i t r a t e form,unless they are already i n close Volcanism Deamination Ammonification Hydrolysis / Bacterial Lysis / Decomposition Bacterial Oxidation (Nitratification) U3 Deep Sediments Ground Wa te r FIG.3.1 NITROGEN C Y C L E ( E P A , 1 9 7 5 ) - 2 0 -p r o x i m i t y t o p l a n t r o o t s . U n l i k e p l a n t s , a n i m a l s a r e u n a b l e t o s y n t h e s i z e m a n y o f t h e i r e s s e n t i a l n u t r i e n t s a n d m u s t r e l y o n t h e i r d i e t t o p r o v i d e t h e s e . W h e n p l a n t o r a n i m a l t i s s u e i s c o n s u m e d b y a n i m a l s , m u c h o f t h e p r o t e i n i s b r o k e n d o w n i n t o a m i n o a c i d s a n d r e a s s e m b l e d i n t o n e w t i s s u e f o r m s o r e l s e m e t a b o l i z e d f o r e n e r g y . U l t i m a t e l y , m o s t o f t h e n i t r o g e n l o c k e d u p i n p r o t e i n i s r e t u r n e d t o t h e s o i l o r w a t e r a s b o d y w a s t e o r d e a d t i s s u e a n d i s t h e r e b r o k e n d o w n i n t o a m i n o a c i d s , u r e a , a m m o n i a a n d o r g a n i c r e s i d u a l s b y a s e r i e s o f b i o l o g i c a l a c t i o n s . O r g a n i s m s o f t h e g e n u s n i t r o s o m o n a s e x t r a c t e n e r g y b y t h e o x i d a t i o n o f a m m o n i u m t o n i t r i t e ; t h o s e o f t h e g e n u s n i t r o b a c t e r c a r r y t h e o x i d a t i o n t h r o u g h t o n i t r a t e . I n a r e a s d e v o i d o f o x y g e n a n d i n t h e p r e s e n c e o f s u i t a b l e r e d u c e d o r g a n i c s u b s t r a t e , f u r t h e r b a c t e r i a ( e g . P s e u d o m o n a s D e n i t r i f i c a n s ) u s e t h e s e o x i d i z e d n i t r o g e n f o r m s a s e l e c t r o n a c c e p t o r s w h i l e e x t r a c t i n g a h i g h e n e r g y y i e l d f r o m t h e o x i d a -t i o n o f t h e s u b s t r a t e . T h e e l e c t r o n a c c e p t o r i s g e n e r a l l y r e d u c e d t o n i t r o g e n g a s a n d r e t u r n e d t o t h e a t m o s p h e r e . N i t r a t e w h i c h i s n o t a s s i m i l a t e d o r r e d u c e d i s a v a i l a b l e f o r c a r r i a g e . t o g r o u n d w a t e r b y i n f i l t r a t i o n b e c a u s e o f i t s h i g h m o b i l i t y i n s o i l s . T a b l e 3 . 1 c o m p a r e s t h e e n e r g y y i e l d s f r o m s o m e o f t h e r e a c t i o n s i n v o l v e d i n t h e n i t r o g e n c y c l e . 3 . 4 . 1 N i t r o g e n B a l a n c e : D e l w i c h e ( 1 9 7 0 ) i n d i c a t e s t h a t p r i o r t o i n d u s t r i a l f i x a t i o n a n d l a r g e s c a l e l e g u m e - c u l t i v a t i o n " , , n i t r o g e n f i x a t i o n a n d r e d u c t i o n b a l a n c e d o u t . P r e s e n t l y , w i t h f i x a t i o n o u t s t r i p p i n g d e n i t r i f i c a t i o n , t h e p r i n c i p a l o b s e r v e d e f f e c t i s t h a t o f a c c e l e r a t e d e u t r o p h i c a t i o n o f i n l a n d w a t e r s w i t h c a s c a d i n g e c o l o g i c a l c o n s e q u e n c e s . -21-TABLE 3.1 ENERGY YIELDS FROM NITROGEN REACTIONS (Delwiche 1970) Denitrification Respiration Ammonification Ni t r i f i c a t i o n Nitrogen Fixation Kilocalories per mole 5CCH,0Oc +- 24KN0o = 30CO„ + 18H^ O 570 b l z b 3 z 2-(glucose) + 24KOH + 12N2 5S + 6KN03 + 2CaC03 == ^IC^ SO^  + ICe^SO^ 132 + 2CO„ + 3N 2 2 C6 H12°6 + 6 02 = 6 C 0 2 + 6 H 2 ° 6 8 6 2CH2NH2COOH + 30 2 = 2C02 + H20 + NHg 176 2NH3 + 30 2 = HN02 + H20 + H + 66 2KNO„ + 0„ = 2KN0„ 17.5 2 2 3 N2 = 2N (Activation —160 2N + 3H2 = 2NH3 -.12.8 -147.2 * * Requires a net energy input. -22-CHAFTER 4 AMMONIFICATION AND NITRIFICATION IN DOMESTIC WASTEWATER 4.1 Wastewater Composition: Detailed a n a l y s i s of municipal sewages i s presented by Bond (1974), while s p e c i f i c consideration of nitrogen forms has been undertaken by Hanson (1971), Kahn (1964) and Hunter (1965). Nitrogen i n urine occurs mostly as urea, which i s r a p i d l y hydrolyzed to ammonia (ammonification); f a e c a l nitrogen occurs p r i n c i p a l l y as amino a c i d or p r o t e i n , 70% being contained i n b a c t e r i a l c e l l s (Krueger 1973). Bond (1974) reports that a representative raw sewage of medium strength contains about 20 mg/L of organic - N; 30 mg/L of free ammonia - N; 0.2 mg/L of n i t r a t e - N. and 0.05 mg/L of n i t r i t e - N . 4.1.1 Amino Acids and Proteins Amino acids are organic molecules i d e n t i f i e d by the presence of an amino group (N^) and a carboxylic a c i d group (COOH). These are linked to a c e n t r a l carbon atom saturated with hydrogen or with a side chain (Krueger 1973). Twenty d i f f e r e n t amino acids (with t h e i r i n d i v i d u a l i t y r e s u l t i n g frprn v a r i a t i o n s i n the hydrogen and side chain configuration) are commonly present i n proteins, being l i n k e d i n a chain by peptide bonds formed by i n t e r a c t i o n between the carboxyl group of one and the amino group of another. One, or numerous chains of amino acids (polypeptides) constitute a protein molecule. Each protein i s distinguished by a constant r a t i o -23-of the constituent amino acids and by a unique configuration i n space; the r e s u l t of numerous bonding i n t e r a c t i o n s between the component sub-molecules. Proteins are r e l a t i v e l y s e n s i t i v e to v a r i a t i o n i n pH and tempera-ture , to rupturing by applied shear forces and to attack by c e r t a i n enzymes. Under such adverse conditions "denaturing" or l o s s of the c h a r a c t e r i s t i c protein configuration occurs, with an accompanying break, down i n t o smaller polypeptide chains. 4.2 Deamination and Ammonification Painter (1970) discusses three ways of producing ammonia from o r g a n i c a l l y bound nitrogen: (i) E x t r a - c e l l u l a r deamination, whereby exoenzymes from a c e l l break down organic molecules remote from the c e l l with the eventual formation of ammonia which may then be reassimilated; ( i i ) Endogenous r e s p i r a t i o n , where stored or expendable i n t e r n a l components of the c e l l i n c l u d i n g amino acids are broken down, r e s u l t i n g i n c e l l shrinkage and the release of byproduct ammonia i n the form of urea (deamination); ( i i i ) Death or l y s i s , where c e l l contents, i n c l u d i n g unassimilated ammonia are discharged to the surrounding medium. Prasad (1978) showed that the rate of hydrolysis of urea i n waste-water v a r i e d from 3.2 mg/L/hr at 2°C to 10.9 at 2 0°C. He demonstrated that 44% of the v i a b l e b a c t e r i a i n a domestic wastewater and 58% i n an activated sludge were u r e o l y t i c ( i e . produce the enzyme urease which brings about urea h y d r o l y s i s ) . Wong-Chong (1975) asserts that the ammonification r e a c t i o n i s a f i r s t order reaction, even up to substrate concentrations exceeding 500 mg/L of convertible organic nitrogen. -24-4.3 N i t r i f i c a t i o n 4.3.1 Substrate Oxidation As i n d i c a t e d by Painter (1970), the production of n i t r a t e or n i t r i t e as a product of b a c t e r i a l a c t i v i t y may be accomplished by autotrophic organisms which extract t h e i r t o t a l energy requirement from the oxidation of ammonia to n i t r i t e and thence to n i t r a t e , and by heterotrophic n i t r i f i e r s that produce oxidized nitrogen forms by reactions which are not ne c e s s a r i l y oxidations, nor the sole energy source f o r the organism. In wastewater treatment, n i t r i f i c a t i o n by autotrophs i s decidedly more important. At a t y p i c a l l y high or low pH value, heterotrophic n i t r i f i c a t i o n may be s i g n i f i c a n t (Focht 1975). N i t r i f i c a t i o n i s generally represented as taking place i n two separate stages (Painter 1977). F i r s t , the oxidation of ammonia to n i t r i t e by Nitrosomonas: [4.1] NH4 + + 1.5 0 2 = N02~ + H 20 + 2H + Second, completion of the oxidation to n i t r a t e by Nitrobacter: [4.2] N02" + 0.5 0 2 = N03~ Biochemically, however, these reactions are a c t u a l l y more complex than merely two sequential oxidations, there being several enzyme systems i n t e g r a l l y involved, and i n the case of ammonia oxidation, a number of intermediate steps. I n h i b i t i o n of the n i t r i f i c a t i o n process i s , i n part, due to interference i n the operation of these intermediate pathways (Delwiche (1956); Painter (1970); Sharma (1977). -25-4.3.2 C l a s s i f i c a t i o n of nitrobacter and riitrosomonas Both genera are s t r i c t l y aerobic and u s u a l l y autotrophic, although Painter (1977) suggests n i t r o b a c t e r may be a f a c u l t a t i v e autotroph. Because energy i s s o l e l y derived from the chemical oxidation of ammonia or n i t r i t e , the organisms are al s o classed as chemolithotrophs. 4.3.3 Energy y i e l d s and synthesis In a d d i t i o n to d e r i v i n g energy from the oxidation of reduced nitrogen species (Table 3.1), n i t r i f y i n g b a c t e r i a synthesize new c e l l t issue from some of the nitrogen present. Using the empirical c e l l composition CglL^C^N (Porges 1956) , and considering these reactions i n aqueous solution with carbonate system a l k a l i n i t y , EPA (1975) proposed the following synthesis equations: Synthesis of Nitrosomonas: [4.3] 13NH4+ + 23HC03~ = 8H 2C0 3 + 10N02~ + 3 0 ^ 0 ^ + 19*^0 Synthesis of Nitrobacter: [4.4] NH„ + + 10NO~ + 4H„C0. + HC0~ = 10NO~ + 3H-0 + C cH_0„N 1 Z z 3 i o £ o l 2. Using y i e l d c o e f f i c i e n t s of 0.15 f o r n i t r a t e nitrogen and 0.02 fo r n i t r i t e nitrogen, EPA (1975) presents an o v e r a l l oxidation plus synthesis equation: [4.5] NH.+ + 1.83 CL + 1.98HCO~ = 0.021 C r iX.NC' + 0.98NO~ 4 2 3 D / 2 3 + 1.041 H 20 + 1.88 H 2C0 3 4.3.4 A l k a l i n i t y Consumption Combining Equations 4.1 and 4.2 i n the context of the carbonate a l k a l i n i t y system, the following i s obtained: [4.6] NH.+ + 20„ + 2HC0~ = NO," + 2H„C0, .+ H„0 -26-It can be calculated that the removal of 1 mg/L of ammonia w i l l consume 7.14 mg of alkalinity (as CaCO^), or using Equation 4.5f the consumption w i l l be only 7.07 due to the incorporation of some ammonia into c e l l biomass. In practice EPA (1975) reports an observed range of 6.0 to 7.1 mg alkalinity per mg ammonia. Benninger (1978) determined that the consumption ratio was lower at increased SRT, probably due to changes in microbial chemical composition, shift in the predominant species or to augmentation of alka l i n i t y by denitrification in the settler. Sherrard (1976b) asserted:, that wastewater BOD:N:P ratios and sludge age. influence the amount of alkalinity destroyed. Higher BOD:N ratio and longer sludge age give increased;destruction. Thus, to an extent determined mainly by the buffering capacity of the system, n i t r i f i c a t i o n in an aqueous system destroys alkalinity and lowers the pH, which may in turn decrease the n i t r i f i c a t i o n rate (EPA 1975) . 4.3.5 Environmental factors of importance in n i t r i f i c a t i o n 4.3.5.1 Dissolved Oxygen From Equations 4.6,which neglects synthesis,and 4.5 which includes synthesis, NOD's of 4.57 mg/L and 4.33 mg/L respectively per mg/L of ammonia oxidation are calculated. This difference i s reportedly due to oxygen release during carbon fixation, as part of the overall synthesis reaction (Painter, 1970). Other researchers (Sharma 1977) indicate that variations are explained by the oversimplification of the reaction chemistry implicit in Equations 4.1 through 4.6. Additionally, in any practical biological n i t r i f y i n g system, further demands for oxygen w i l l be made by other oxidizing reactions, principally the stabilization of organic carbon. -27-Sharma ( 1 9 7 7 ) , Painter ( 1 9 7 0 ) and Downing (1964a) h a v e compiled extensive data from the literature on the effects of dissolved oxygen concentration on n i t r i f i c a t i o n in both pure and mixed cultures. While there i s ample evidence that low DO values inhibit n i t r i f i c a t i o n , there i s no precisely defined upper level at which n i t r i f i c a t i o n rates become independent of oxygen concentration. Painter ( 1 9 7 0 ) found evidence that nitrobacter i s more sensitive to oxygen depletion than i s nitrosomonas. Downing (1964a), indicates that "some of the differences in the reported effects of DO on the n i t r i f y i n g a b i l i t y of activated sludge may be due to the local oxygen lack because of the respiration of other (hetero-trophic) organisms". In using a Monod model for the effect of DO on n i t r i f i c a t i o n rate, EPA (1975) advocates a Michaelis-Menten (half-rate) constant of 1.3 mg/L. Thus, i f a DO of 2.0 mg/L i s maintained in solution, the observed n i t r i f i c a -tion rate should exceed 60% of the peak rate. Further work i s required to determine other factors affecting the half-rate constant and thus the most economical DO level for n i t r i f i c a t i o n . McHarness (1975), in a pure oxygen submerged f i l t e r , found no effect on n i t r i f i c a t i o n at DO levels as high as 60 mg/L. 4.3.5.2 Effect of Anaerobic Storage on Nitrifying Activated Sludge It has been established that maintaining a n i t r i f y i n g sludge under anaerobic conditions for up to 4 hours does not lower i t s n i t r i f y i n g a b i l i t y as measured by n i t r i f i c a t i o n rate (Downing, 1 9 6 4 a ; Wuhrmann, 1 9 6 8 ; J a n k , 1 9 7 8 ) . A conclusive investigation of longer anaerobic periods and factors- such as sludge a g e , sludge type and temperature remains to be carried out. 4.3.5.3 Effect of pH Sharma ( 1 9 7 7 ) indicated that pH effects on n i t r i f i c a t i o n may be looked at from three angles: -28-(i) E f f e c t of pH on n i t r i f i c a t i o n by e x i s t i n g c e l l s ; ( i i ) Adaption of n i t r i f i e r s to adverse pH; ( i i i ) Growth of n i t r i f i e r s . A consensus i s that n i t r i f i c a t i o n rates follow a b e l l curve r e l a t i o n s h i p , with pH being optimum i n the s l i g h t l y a l k a l i n e range (Focht 1975; Painter 1970). As shown by Painter (1970), i n pure culture studies, d i f f e r e n t s t r a i n s of nitrosomonas and n i t r o b a c t e r exhibited various optimum pH values spanning the range 6 to 9.3. EPA (1975) presents a r e l a t i o n s h i p between observed n i t r i f i c a t i o n r a te, peak rate and pH for use when the pH i s l e s s than 7.2: [4.7] N i t r i f i c a t i o n Rate = Peak Rate (1 - 0.833 (7.2 - pH) For pH between 7.2 and 8.0 the rate i s assumed constant. A pH higher than 8.0 i s unusual i n domestic wastewater n i t r i f i c a t i o n . Painter (1970) reported that i n a n i t r i f y i n g a c t i v a t e d sludge t r e a t i n g a poorly buffered domestic waste, n i t r i f i c a t i o n had ceased before the pH decreased to 6.3. Prakasam (1972) indi c a t e d that n i t r i f i c a t i o n rates were unaffected up to pH 11.0, provided un-ionized ammonia concentra-tions were held below 0.02 mg/L. Generally, the upper optimum pH i s l e s s than 9.0 (Focht, 1975), due to i n h i b i t i o n by un-ionized ammonia. EPA (1975) reports on work that showed a rapid increase i n e f f l u e n t ammonia when the pH was quickly changed from 7.2 to 5.8. When the i n i t i a l pH was abruptly restored, a rapid improvement ensued, i n d i c a t i n g that the low pH was only i n h i b i t o r y and not t o x i c . Haug, as reported by EPA (1975), was able to acclimate n i t r i f i e r s to pH 5.5 i n a submerged f i l t e r . - 2 9 -4 . 3 . 5 . 4 T e m p e r a t u r e : P a i n t e r ( 1 9 7 7 ) i n d i c a t e s t h a t n i t r i f i c a t i o n p r o c e e d s i n t h e t e m p e r a t u r e r a n g e 4 ° C - 4 5 ° C . T h e o p t i m u m f o r n i t r o s o m o n a s i s a b o u t 3 5 ° C ; t h a t f o r n i t r o b a c t e r 3 5 - 4 2 ° C . T h u s , f r o m a t e m p e r a t u r e p o i n t o f v i e w , w a s t e w a t e r n i t r i f i c a t i o n i s u s u a l l y o p e r a t e d u n d e r s u b - o p t i m a l c o n d i t i o n s . S h a r m a ( 1 9 7 7 ) r e p o r t s t h e r m a l d e a t h o f a p u r e n i t r o s o m o n a s c u l t u r e b e t w e e n 5 4 ° c a n d 5 8 ° c . H a u g ( 1 9 7 2 ) w a s a b l e t o m a i n t a i n n i t r i -f i c a t i o n i n a p u r e o x y g e n s u b m e r g e d f i l t e r d o w n t o 1 ° C . R i m e r ( 1 9 7 2 ) r e p o r t e d d i f f i c u l t y i n e s t a b l i s h i n g a n i t r i f y i n g f l o r a i n a c t i v a t e d s l u d g e a t 1 0 ° C , b u t n o d i f f i c u l t y i n m a i n t a i n i n g a n e x i s t i n g c u l t u r e . A t 5 ° C P a i n t e r ( 1 9 7 0 ) n o t e d t h a t n i t r i f i c a t i o n c o u l d c o n t i n u e , b u t t h a t t h e r e w a s m i n i m a l g r o w t h o f n e w b a c t e r i a . 4 . 3 . 5 . 5 E f f e c t o f L i g h t : S h a r m a ( 1 9 7 7 ) a n d P a i n t e r ( 1 9 7 0 ) i n d i c a t e t h a t l i g h t i n h i b i t s t h e a c t i v i t y o f n i t r i f i e r s i n p u r e c u l t u r e , b u t d o n o t e x p l a i n t h e m e c h a n i s m . 4 . 3 . 5 . 6 E f f e c t o f S o l i d S u r f a c e s a n d T u r b u l e n c e P a i n t e r ( 1 9 7 0 ) s u p p o r t s t h e i d e a t h a t p a r t i c l e s o r s u r f a c e s a r e n o t n e c e s s a r y f o r n i t r i f i e r g r o w t h . S h a r m a ( 1 9 7 7 ) c o n t e n d s t h a t t h e e f f e c t o f s u r f a c e s , o f s u r f a c e t y p e a n d o f t u r b u l e n c e i s n o t y e t c l e a r , a n d t h u s c a n n o t b e d i s c o u n t e d . K h o l d e b a r i n ( 1 9 7 7 ) s h o w s a n i n c r e a s e i n n i t r i f i c a t i o n r a t e w i t h i n c r e a s e d s u s p e n d e d s o l i d s c o n c e n t r a t i o n i n s u r f a c e w a t e r s . I n n a t u r a l s y s t e m s , n i t r i f i e r s a p p e a r t o b e c o n c e n t r a t e d i n s e d i m e n t s o r a t i n t e r f a c e s w i t h r e s p e c t t o s u r f a c e w a t e r s ( S h a r m a 1 9 7 7 ) . S h a r m a r e p o r t s o n t h e e n h a n c e m e n t o f n i t r i f i c a t i o n i n a n a e r a t i o n u n i t w i t h t h e a d d i t i o n o f z e o l i t e p a r t i c l e s . B e s i k ( 1 9 7 7 ) d e s c r i b e s a m o d i f i e d a c t i v a t e d s l u d g e p r o c e s s i n w h i c h r e a c t i o n r a t e s a r e e n h a n c e d b y p o w d e r e d a n d g r a n u l a t e d a c t i v a t e d c a r b o n a d d i t i o n s . ( S e e S e c t i o n 5 . 8 . 4 ) -30-4.3.5.7 Micronutrients: Apart from a carbon source (carbonate system), substrate or electron donor (ammonium for nitrosomonas, n i t r i t e f o r nitrobacter) and an electron acceptor (dissolved oxygen), small q u a n t i t i e s of other elements are e s s e n t i a l n u t r i e n t s for n i t r i f i e r growth. While the requirements may d i f f e r f o r generator species, Painter (1970) shows the following elements to be b e n e f i c i a l i n various pure c u l t u r e s : P; Ca; K; Mg; Cu; S; Fe; Mo; Na. Usually i n domestic sewage, such nutrients are present i n adequate quantities (Bond 1974) . Sharma (1977) presents d e t a i l e d tabulations of stimulatory and i n h i b i t o r y substances and suggests that some of the inconsistencies i n n i t r i f i c a t i o n work may be r e l a t e d to the presence or absence of adequate micro-nutrient concentrations. 4.4 I n h i b i t i o n of N i t r i f i c a t i o n In an activated sludge process, n i t r i f i c a t i o n can be severely c u r t a i l e d or halted by the introduction of i n h i b i t o r y or t o x i c materials or conditions. Downing (1964b) i n d i c a t e s three general manifestations of t o x i c i t y : (i) Death of the n i t r i f y i n g b a c t e r i a (Toxicity) ( i i ) Decreased organism growth rate (Inhibition) ( i i i ) Temporary i n h i b i t i o n of r e s p i r a t i o n ( n i t r i f i c a t i o n ) with a return to near normal rates a f t e r removal of the i n h i b i t o r y conditions. I n h i b i t o r s act e i t h e r on the general c e l l metabolism or on one of the primary oxidation reactions (Painter 1977). The most commonly reported data are from short term screening t e s t s -31-that compare n i t r i f i c a t i o n rates with and without the a d d i t i o n of t e s t i n h i b i t o r y materials (Hockenbury,. 1977b; Stensel,1976; Loveless, 1968). Numerous f a c t o r s a f f e c t the extent to which n i t r i f i c a t i o n i s i n h i b i t e d , i n c l u d i n g pH, temperature, DO, acclimation, MLSS, culture type (pure or mixed), nature of the t o x i c a n t / i n h i b i t o r , method of addition (slug or continuous), other i o n i c species present and t h e i r concentrations, s y n e r g i s t i c and antagonistic reactions, and hydraulic regime (Downing 1964b; Hockenbury 1977b). Wide v a r i a t i o n s i n reported i n h i b i t i o n data are caused by these f a c t o r s and make i t impossible to develop s p e c i f i c q u antitative r e l a t i o n s h i p s between t o x i c materials and the behaviour of n i t r i f y i n g b a cteria (Loveless 1968; Stensel 1976). Autotrophs are much more susceptible to i n h i b i t i o n than hetero-trophs. The ammonia oxi d i z e r s are more susceptible than the n i t r i t e o x i d i z e r s (Painter 1977) . Pure c u l t u r e s are affected by lower concentra-t i o n s than are mixed (activated sludge) cultures which, i n turn,are more se n s i t i v e than acclimated sludges (Tomlinson 1966; Painter 1977). The most potent i n h i b i t o r s are a family of nitrogenous organo-sulphur compounds including thiourea and thioacetamide. In pure culture, thiourea i s 75% i n h i b i t o r y at 0.08 mg/L but i n the same sludge a f t e r acclimation, 3.5 mg/L had no e f f e c t . Cyanide i s a strong toxicant at l e s s than 1 ppm (Barth 1965). In pure c u l t u r e , Skinner (1961) reports Ni and Cr i n h i b i t o r y at 0.25 mg/L and Cu at 0.5 ppm. Loveless (1968) reports Zn and Co i n h i b i t o r y at 0.5 mg/L. Tomlinson (1966) demonstrated that the same degree of i n h i b i t i o n i n acclimated sludge, as i n a pure culture, needed a concentration of i n h i b i t a n t two or three logarithmic u n i t s greater. Downing (1964b) showed that sludges acclimated to low l e v e l s of continuous heavy metal exposure may become i n h i b i t e d due to metal accumulation i n the sludge. -32-4.4.1 Acclimation Two major mechanisms allow a n i t r i f y i n g sludge to b u i l d up a resistance to i n h i b i t i o n : (i) Adaptation with time of the n i t r i f i e r population to the agent, ( i i ) Development of an associated heterotrophic population capable of metabolizing the toxicant. 4.4 .2 C h l o r i n a t i o n Strom (1977) demonstrated that chlorine doses up to 50 mg/L i n recycled sludge d i d not a f f e c t the rate of n i t r i f i c a t i o n or the BOD removal i n an activated sludge. N i t r i f i e r s were more r e s i s t a n t to c h l o r i n a t i o n than were E. C o l i or f e c a l s t r e p t o c o c c i . 4.4.3 Substrate and Product I n h i b i t i o n Painter (1970) indicated that both nitrosomonas and n i t r o b a c t e r are i n h i b i t e d by t h e i r own nitrogen substrates and more so by the substrate of the other. The reported concentrations at which i n h i b i t i o n occurred were one or two orders of magnitude greater than those normally found i n municipal wastewater treatment. The degree of i n h i b i t i o n was a f f e c t e d by the environmental conditions i n c l u d i n g pH, temperature and acclimation (Sharma 1977). The work of Prakasam (1972), Anthonisen (1976) and Verstraete (1977) demonstrated that free ammonia and free nitrous a c i d concentrations, rather than ammonium or n i t r i t e ion concentrations, i n h i b i t n i t r i f i c a t i o n . Anthonisen (1976) developed an operating chart r e l a t i n g pH, n i t r i t e ion - n i t r o u s a c i d equilibrium and t o t a l ammonia -free ammonia equilibrium. I n h i b i t o r y concentrations were dependent on the pH, which, as i t increased, displaced the ammonia equilibrium toward free ammonia, and, at lower pH, the n i t r i t e equilibrium toward nitrous acid. Free ammonia was i n h i b i t o r y toward n i t r o b a c t e r beginning at 0.1 mg/L -33-to.1.0 mg/L and toward nitrosomonas beginning between 10 and 150 mg/L. Free nitrous acid i n h i b i t i o n toward n i t r i f i e r s began at concentrations between 0.2 and 2.8 mg/L. Cairns (1975) showed that, f o r a temperature increase from 10°C to 20°C, the percentage of un-ionized ammonia increased by a f a c t o r of 1.3 to 1.6 depending on the pH. Poduska (1975) c i t e s evidence that ammonium ion, n i t r i t e and n i t r a t e are not i n h i b i t o r y at concentrations normally encountered i n domestic wastewater treatment. Problems may occur, however, with high strength industrial.or- a g r i c u l t u r a l wastes. 4.4.4 Organic Matter Organic matter per se i s not i n h i b i t o r y . However, i n the presence of high organic concentrations, the heterotrophs may slow down n i t r i f i c a t i o n by reducing the available DO to a suboptimal concentration (Painter 1977). 4.5 K i n e t i c s of N i t r i f i c a t i o n EPA (1975) and Wang-Chong (1975) modelled n i t r i f i c a t i o n reactions using a Monod-type r e l a t i o n s h i p . Generally, because the required k i n e t i c data (Table 4.1) i s gathered from pure cultures or from c o n t r o l l e d laboratory experiments, the model accuracy i s l i m i t e d i n p r e d i c t i n g f u l l scale n i t r i f i c a t i o n performance (Beer 1978; EPA 1975). A consensus has the o v e r a l l wastewater n i t r i f i c a t i o n rate being l i m i t e d by the rate of ammonia oxidation to n i t r i t e , ( G u j e r 1975; Poduska 1975). Where the ammonia concentration exceeds 2-3 mg/L, the rate i s frequently accepted as being "zero order" or independent of the ammonia concentration (Wild 1971,. Sutton 1974). As the concentration f a l l s , an accelerating reduction i n the ammonia u t i l i z a t i o n rate i s observed (Heide 1977; EPA 1975). - 3 4 -T A B L E 4 . 1 T Y P I C A L V A L U E S O F K I N E T I C C O N S T A N T S F O R N I T R I F I E R S ( A f t e r S h a r m a 1 9 7 7 * a n d P a i n t e r . 1 9 7 7 ) C o n s t a n t N i t r o s o m o n a s N i t r o b a c t e r H e t e r o t r o p h s C e l l Y i e l d Y ( w t c e l l s / w t e n e r g y s u b s t r a t e ) 0 . 0 3 - 0 . 1 3 * 0 . 0 2 - 0 . 0 8 * 0 . 3 7 - 0 . 7 9 * M a x S p e c i f i c G r o w t h R a t e u . ( d a y - 1 ) 2 . 2 ( 3 0 ° C ) 0 . 4 6 - 2 . 2 * 1 . 3 9 ( 3 2 ° C ) 0 . 2 8 - 1 . 4 4 * 7 . 2 - 1 7 . 0 * M i c h a e l i s - M e n t e n C o n s t a n t s ( m g / L ) E n e r g y S u b s t r a t e 0 . 0 6 - 5 . 6 * i o ' ( 3 o°o 3 . 5 ( 2 5 ° C ) 1 . 2 ( 2 0 ° C ) 0 . 0 6 - 8 . 4 * 8 ( 3 2 ° C ) 5 ( 2 5 ° C ) <1 - 1 8 1 * E l e c t r o n A c c e p t o r ( o x y g e n ) m g / L 0 . 3 - 1 . 3 * 0 . 5 ( 3 0 ° C ) 0 . 3 ( 2 0 ° C ) 0 . 2 5 - 1 . 3 * 1 . 0 ( 3 0 ° C ) 0 . 2 5 ( 1 8 ° C ) < 0 . 1 * ( -35-Painter (1970) and EPA (1975) indicate that the maximum specific growth rates in activated sludges are from 60% to 85% less than those observed in pure culture, due principally to the less favourable and uncontrolled environment. 4.5.1 Reported Nit r i f i c a t i o n Rate Parameters The lack of generally accepted procedures and consistent nomenclature for determining and reporting n i t r i f i c a t i o n rates frequently precludes comparison of data from different investigators. Biomass i s variously reported as MLSS, MLVSS, cellular TKN and " n i t r i f i e r s " or else l e f t i ll-defined. Rates are expressed either as "substrate u t i l i z a -tion" or "product increase" with such parameters as TKN (total and soluble), ammonia, oxygen uptake rate, n i t r i t e and nitrate being monitored by one investigator or another. Further complication i s introduced by such factors as ammonia assimilation, stripping, endogenous oxidation, n i t r i t e build up and other environmental or process considerations which may influence results, but are seldom documented. 4.5.2 Variation of Nitrification Rate with Temperature Few useful studies of temperature effects on the n i t r i f i c a t i o n rate of domestic wastewater have been reported in the literature. Lawrence (1970) and Sutton (1977b) have found n i t r i f i c a t i o n to be more sensitive than denitrification or carbon oxidation. (Sayigh (1978) showed a heterotrophic BOD stabilizing population with a three day sludge age to be substantially temperature independent in the 4°C to 31°C range.) Focht ( 1 9 7 5 ) and EPA ( 1 9 7 5 ) discuss the strong temperature depend-ence of specific growth rates and half-rate constants for n i t r i f i e r s . As a general rule, an Arrhenius type of relationship adequately models -36-most of the observed v a r i a t i o n s i n rates (Sutton 1977a; Wild 1971; Mulbager 1971). In Table 4.2 values of some experimentally determined temperature c o e f f i c i e n t s are l i s t e d together with source references. The wide v a r i a t i o n i n data i s generally a t t r i b u t a b l e to d i f f e r e n t experimental techniques and v a r i a t i o n s i n environmental conditions other than temperature. (See Section 4.5.1.) TABLE 4.2 ARRHENIUS CONSTANTS FOR NITRIFICATION Temperature (°C) % 0 ' 1 e Arrhenius E (cal/mole) Reference 10-20 2.2 Wild (1971) 20-30 3.3 Painter (1970) 0.075 12,730* Sutton (1978a) 2.1 12,000* Sutton (1978b) 10-20 3.3 20,570 a Ibid 10-20 2.1 12,000 a Ibid 10-20 2.4 15,400 a Ibid 10-20 2 .6 le^oo*1 Ibid Notes: Nomenclature: See Chapter 3.2.3. * Combined n i t r i f i c a t i o n - d e n i t r i f i c a t i o n (7-25°C) fc Separate n i t r i f i c a t i o n (8-23°C) a Combined n i t r i f i c a t i o n - c a r b o n oxidation (5-30°C) Other References , (Data not included): Wong-Chong (1975); Sharma (1977) ; Mulbager (1971); Sutton (1975b), (1977b). - 3 7 -Focht ( 1 9 7 5 ) indicated that at temperatures below 10° or 1 5 ° C , other p h y s i c a l f a c t o r s such as reduced s o l u b i l i t y and lower d i f f u s i o n rates exert an increasing influence, thus r a i s i n g Q values. P a r t i c u l a r l y at low substrate l e v e l s , Q values were d i r e c t l y proportional to substrate concentration. Sutton (1975b) showed that the TKN removal rate became l e s s s e n s i t i v e to temperature at higher sludge ages. In a s e r i e s of e x p e r i -ments with a combined sludge system using sludge ages of 4,7 and 10 days and varying the temperature from 5 ° C t o 20 ° C a l i n e a r (and not Arrhenius) dependency of n i t r i f i c a t i o n rate on temperature was observed by Sutton (1975b). 4.5.3 N i t r i f i c a t i o n i n Wastewater Both reduced nitrogen (TKN) and reduced carbon (BOD) e x i s t together i n normal domestic wastewater. The oxidation of carbon by heterotrophs i s more rapid than autotrophic n i t r i f i c a t i o n and the y i e l d c o e f f i c i e n t i s also higher (see Table 4.1). Unless c e r t a i n conditions are met, the heterotroph population w i l l increase at the expense of the n i t r i f i e r s and n i t r i f i c a t i o n w i l l not occur. In order to maintain n i t r i f i c a t i o n i t i s necessary that the actual growth rate of n i t r i f i e r s , u , under the environmental conditions of the system, be equal to or greater than that of the associated heterotrophs, u (Lawrence 1970). H Recalling that growth rate = 1/sludge age (Equation 3.3), the minimum sludge age to maintain n i t r i f i c a t i o n can be established by c a l c u l a t i o n or by experiment and a design sludge age 6 (design) can be used i n the system such that: -38-[4.8] 6,. . . > e m ( d e s i g n ) - c F r o m E q u a t i o n 3.4 [4.9] - i - = u = Y T T q - b 0 , , . , H H H ( d e s i g n ) ( w h e r e t h e s u b s c r i p t H r e f e r s t o t h e h e t e r o t r o p h i c c a r b o n o x i d i z e r s ) . A s b o t h Y a n d b a r e n o m i n a l l y c o n s t a n t , c o n t r o l o f t h e h e t e r o t r o p h H H g r o w t h r a t e c a n b e a c h i e v e d b y c o n t r o l o f t h e r e m o v a l r a t e q o f o r g a n i c H s u b s t r a t e , w h e r e q m a y b e e x p r e s s e d a s : H [ 4 - 1 0 ] * H = x ^ l ) ( S q a n d S g a r e t h e i n f l u e n t a n d e f f l u e n t o r g a n i c c a r b o n s u b s t r a t e c o n c e n t r a t i o n s a s s o c i a t e d w i t h t h e n i t r i f i c a t i o n r e a c t o r , X i s t h e b i o m a s s c o n c e n t r a t i o n ( M L V S S ) a n d H R T t h e r e a c t o r h y d r a u l i c r e t e n t i o n t i m e . ) B y i n c r e a s i n g t h e M L V S S o r t h e H R T o r b y l o w e r i n g t h e i n f l u e n t s u b s t r a t e c o n c e n t r a t i o n , . . t h e r e q u i s i t e s l u d g e a g e t o h o l d d o w n t h e h e t e r o t r o p h i c g r o w t h r a t e a n d t h u s m a i n t a i n n i t r i f i c a t i o n c a n b e o b t a i n e d . T h e u s e o f a p r i o r o r g a n i c c a r b o n r e m o v a l s t e p i s o n e p r o c e d u r e u s e d t o l o w e r t h e o r g a n i c i n f l u e n t c o n c e n t r a -t i o n ( W i l d 1971). 4.5.3.1 S a f e t y F a c t o r i n D e s i g n : A s d i s c u s s e d b y L a w r e n c e (1970), a s a f e t y f a c t o r ( S F ) f o r n i t r i f i -c a t i o n m a y b e d e f i n e d a s : g [4 111 S F - P Q s i g 1 1 s o l i d s r e t e n t i o n t i m e _ ( d e s i g n ) M i n i m u m S R T f o r n i t r i f i c a t i o n g m c S u c h a f a c t o r a l l o w s a t e m p o r a r y i n h i b i t i o n o f n i t r i f i e r g r o w t h r a t e t o o c c u r w i t h o u t c a u s i n g w a s h o u t o f t h e n i t r i f y i n g o r g a n i s m s . I n a d d i t i o n , a n o p e r a t i n g p l a n t u n d e r g o e s a d i u r n a l v a r i a t i o n i n f l o w r a t e s a n d t h u s i n - 3 9 -H R T a n d f r e q u e n t l y i n t h e B O D / T K N r a t i o ( E P A 1 9 7 5 ) . W h e r e a n a d e q u a t e s a f e t y f a c t o r i s p r o v i d e d , s i g n i f i c a n t a m m o n i a b r e a k t h r o u g h f r o m t h e n i t r i f i c a t i o n s t a g e w i l l n o t o c c u r . A s a g e n e r a l r u l e E P A ( 1 9 7 5 ) r e c o m m e n d s t h e s a f e t y f a c t o r b e t h e r a t i o o f p e a k T K N c o n c e n t r a t i o n t o m e a n T K N c o n c e n t r a t i o n . 4 . 5 . 4 F r a c t i o n o f N i t r i f i e r s i n A c t i v a t e d S l u d g e I n a n i t r i f y i n g a c t i v a t e d s l u d g e o n l y a f r a c t i o n , f , o f t h e b i o m a s s ( M L S S ) o r ( M L V S S ) a r e n i t r i f i e r s , t h e r e s t m o s t l y h e t e r o t r o p h s . T h u s t h e o b s e r v e d n i t r i f i c a t i o n r a t e o f a s l u d g e , r ( p o u n d s a m m o n i a o x i d i z e d p e r p o u n d M L V S S p e r d a y ) , c a n b e r e l a t e d t o q ( l b N H ^ o x i d i z e d p e r p o u n d o f n i t r i f i e r s i n t h e s l u d g e p e r d a y ) a s f o l l o w s : r = q * f N o r m a l l y , a l t h o u g h q m a y b e c a l c u l a t e d t h e o r e t i c a l l y f o r a p u r e o r m i x e d c u l t u r e , t h e a c t u a l r a t e ' r ' i s d e t e r m i n e d e x p e r i m e n t a l l y . E P A ( 1 9 7 5 ) i n d i c a t e s t h a t f m a y b e a p p r o x i m a t e d b y u s i n g : f = M+m w h e r e M i s t h e m a s s o f n i t r i f i e r s g r o w n t h r o u g h a m m o n i a o x i d a t i o n = Y ( N - N ) N o e m i s t h e m a s s o f h e t e r o t r o p h s g r o w n t h r o u g h c a r b o n o x i d a t i o n = Y ( S - S ) H o e w h e r e t h e e f f l u e n t T K N a n d B O D a r e s m a l l : U s i n g E q u a t i o n 4 . 1 2 w i t h y i e l d c o e f f i c i e n t s o f 0 . 1 5 a n d 0 . 5 5 f o r T K N a n d BODp. r e s p e c t i v e l y , E P A ( 1 9 7 5 ) e s t i m a t e s t h e f o l l o w i n g n i t r i f i e r f r a c t i o n s : -40-BOD/TKN f BOD/TKN f 0.5 0.35 4.0 0.064 1.0 0.21 6.0 0.043 2.0 0.12 8.0 0.033 I t i s apparent that the n i t r i f i c a t i o n rate of ac t i v a t e d sludge i s strongly dependent on the BOD:TKN r a t i o of the feed. Srinath (1976) proposed that the n i t r i f i e r population could be estimated by using c e l l u l a r TKN instead of MLVSS as a measure of a c t i v e biomass. The n i t r i f y i n g a b i l i t y of a t e s t sample can be compared to that of a pure standard sample on a un i t biomass basis and the f r a c t i o n of n i t r i f i e r s thus determined. Painter (1970) and Sharma (1977) indi c a t e however that numerous factors d i c t a t e lower n i t r i f i c a t i o n rates per u n i t of n i t r i f i e r biomass i n activated sludge compared t o pure c u l t u r e , and not jus t the percentage of biomass that i s comprised of n i t r i f i e r s . 4.6 Design Approaches to N i t r i f i c a t i o n : EPA (1975) and Sutton (1977a) indi c a t e two approaches for designing activated sludge n i t r i f i c a t i o n systems: (a) S o l i d s Retention Time approach. (b) N i t r i f i c a t i o n Rate approach. 4.6.1 S o l i d s Retention Time Approach: By experiment (Sutton 1978a, Lawrence 1976), or by ca l c u l a t i o n , using the estimated environmental conditions (EPA 1975, Downing 1964a), the minimum SRT necessary for n i t r i f i c a t i o n i s determined. The a p p l i c a t i o n of a sui t a b l e safety f a c t o r determines the design SRT. The use of equation:.:4.9 r e l a t e s t h i s SRT to the carbonaceous substrate concentration and i t s removal rate, allowing a suitable process MLSS and HRT to be determined. - 4 1 -T A B L E 4 . 3 R A N G E O F A E R O B I C S R T R E P O R T E D F O R N I T R I F I C A T I O N T e m p e r a t u r e S R T R a n g e ( M i n i m u m ) 5 ° C 1 0 - 2 0 d a y s 7 - 8 ° C 4 - 9 . 5 d a y s 1 0 ° C 1 0 d a y s 1 4 = 1 6 ° C 6 - 1 0 d a y s 2 0 ° C 1 . 3 - 4 d a y s 2 3 ° C 3 - 4 d a y s 2 4 - 2 6 ° C 1 . 6 - 4 . 5 d a y s R e f e r e n c e s : B a l a k r i s h n a n ( 1 9 6 9 a ) R e b b u n ( 1 9 7 8 ) H o r s t k o t t e ( 1 9 7 4 ) S h e r r a r d ( 1 9 7 7 ) L a w r e n c e ( 1 9 7 0 , 1 9 7 6 ) S u t t o n ( 1 9 7 5 b , 1 9 7 8 a ) W i l s o n ( 1 9 7 7 ) S t o v e r ( 1 9 7 6 ) T a b l e 4 . 3 s u m m a r i z e s s o m e o f t h e S R T d a t a r e p o r t e d i n t h e l i t e r a t u r e . I n s i n g l e s l u d g e n i t r i f i c a t i o n - d e n i t r i f i c a t i o n s y s t e m s t h e S R T u s e d f o r n i t r i f i c a t i o n i s e q u a l t o t h e s y s t e m S R T t i m e s t h e f r a c t i o n o f M L S S u n d e r a e r o b i c c o n d i t i o n s ( S u t t o n 1 9 7 8 a ) . E P A ( 1 9 7 5 ) i n d i c a t e s t h a t t h e r e t e n t i o n t i m e a p p r o a c h i s m o s t c o m m o n l y u s e d f o r c o m b i n e d s l u d g e s y s t e m s . J a n k ( 1 9 7 8 ) s u g g e s t s i t i s t h e p r e f e r r e d a p p r o a c h o f t h e t w o d e s i g n m e t h o d s . -42-4.6.2 N i t r i f i c a t i o n Rate Approach: By experiment, i d e a l l y i n a p i l o t plant operation, the u n i t n i t r i f i c a t i o n rate of a sludge i s measured. By using an appropriate safety f a c t o r , suitable MLSS and HRT data, the use of Equation 4.9 w i l l provide a design SRT. However, as previously demonstrated, the u n i t rate depends on the SRT and on the f r a c t i o n of n i t r i f i e r s present, which i s determined by the BOD:TKN r a t i o . Sutton (1977a) asserts that the wide v a r i a t i o n i n u n i t rates as observed i n h i s work and by others (reported by EPA 1975) i s a t t r i b u t a b l e mostly to C:N v a r i a t i o n s (Figure 4.1). Sutton (1977a) also found i n a combined sludge system that the n i t r i f i c a -t i o n rates at a given SRT decreased as the MLVSS increased. Lawrence (1976) discounts the n i t r i f i c a t i o n rate approach by ass e r t i n g that " s p e c i f i c oxidation rate of ammonia i s meaningless because the predominant f r a c t i o n of VSS c o n s i s t s of carbonaceous heterotrophs". 4.7 Processes Available f o r B i o l o g i c a l N i t r i f i c a t i o n A wide range of b i o l o g i c a l processes are a v a i l a b l e f o r n i t r i f i c a t i o n of wastewaters containing reduced nitrogen. Only those systems using some modification of the activated sludge process are elaborated upon here. Some other systems are referenced i n Chapter 1. 4.7.1 Suspended Growth Systems Sherrard (1976b) characterizes activated sludge operations by SRT: SRT ' Activated Sludge V a r i a t i o n <3 days High Rate 5-10 days Conventional >20 days Extended Aeration -43-0 . 4 o •o \ (A) 0 0 > T3 r s i O to I O rr 0 . 3 0 . 2 c o - 0 . o B0D/TKN = 3.0 pH = 8.4 1 8 12 16 T e m p e r a t u r e °C 20 24 FIG.4.1 NITRIFICATION RATES ( E P A , 1 9 7 5 ) -44-As a general r u l e , EPA (1975) indicates that extended aeration p l a n t s , i n c l u d i n g oxidation ditches, are capable of n i t r i f i c a t i o n even at cold temperatures. Conventional plants including complete mix, plug flow, step aeration and high p u r i t y oxygen modifications may n i t r i f y at warm temperatures but usu a l l y not at c o l d (Lawrence 1976; Khararjian 1978). High rate plants, including contact s t a b i l i z a t i o n (CS.) and modified act i v a t e d sludge v a r i a t i o n s , are generally poor n i t r i f i e r s (EPA 1975; Zoltek 1976). 4.7.2 Combined and Separate Sludge Systems Suspended sludge n i t r i f i c a t i o n systems are s u b c l a s s i f i e d as combined systems when the same sludge c a r r i e s out both n i t r i f i c a t i o n and BOD removal. Separate sludge systems use a d i f f e r e n t (specialized) sludge f o r each operation. Further d i v e r s i f i c a t i o n occurs when combined sludges carry out BOD removal and then n i t r i f i c a t i o n i n sequential tanks, or when the sludge undergoes a period of anaerobiasis f o r d e n i t r i f i c a t i o n purposes . (Barnard 1975a). Separate systems may use a f i x e d biomass ( t r i c k l i n g f i l t e r or r o t a t i n g b i o l o g i c a l contactor) f o r one or several of the operating stages (Balakrishnan 1969b),. Increasing d i v e r s i t y i s added by the use of primary chemical treatment f o r BOD or phosphorus removal (Rebbun 1978;. Horskotte 1974) by modification of environmental conditions to enhance b i o l o g i c a l phosphorus removal, or by the use of oxidation d i t c h systems which often bypass primary treatment and simultaneously c a r r y out BOD removal, n i t r i f i c a t i o n and d e n i t r i f i c a t i o n , (Matsche 1977a). - 4 5 -4 . 7 . 3 P r o s a n d C o n s o f C o m b i n e d a n d S e p a r a t e S l u d g e S y s t e m s T h e e a r l y d e v e l o p m e n t o f n i t r i f i c a t i o n s l u d g e t h e o r y b y D o w n i n g ; . ( 1 9 6 4 a ) u s e d a c o m b i n e d s y s t e m . E u r o p e a n e n g i n e e r s p e r s e v e r e d w i t h t h i s s y s t e m w h i l e t h e N o r t h A m e r i c a n t h r u s t t e n d e d t o w a r d t w o s l u d g e s y s t e m s , p r i n c i p a l l y t o o v e r c o m e t h e p r o b l e m s c a u s e d b y l o s s o f n i t r i f i c a t i o n d u r i n g l o w t e m p e r a t u r e w i n t e r o p e r a t i o n s ( W i l d 1 9 7 1 , M u l b a g e r 1 9 7 1 ) . 4 . 7 . 3 . 1 A d v a n t a g e s o f T w o - S t a g e ( S e p a r a t e S l u d g e ) S y s t e m s ( i ) O p t i m i z a t i o n a n d e a s i e r c o n t r o l o f t h e s e p a r a t e d c a r b o n o x i d a t i o n a n d n i t r i f i c a t i o n f u n c t i o n s ; ( i i ) L o w e r B O D : T K N r a t i o s i n t h e n i t r i f i e r t a n k a l l o w t h e b u i l d u p o f l a r g e r n i t r i f i e r p o p u l a t i o n a n d t h u s h i g h e r c o n v e r s i o n r a t e s ; ( i i i ) L o w e r o v e r a l l S R T a n d H R T i n t h e s y s t e m ; ( i v ) A b i l i t y t o n i t r i f y i n a l l s e a s o n s ; ( v ) T h e p r i o r c a r b o n o x i d a t i o n s t a g e p r o v i d e s a b u f f e r a g a i n s t t o x i c a g e n t s t h a t m a y a f f e c t t h e s e n s i t i v e n i t r i f i e r s . S o m e o r g a n i c t o x i c a n t s m a y b e b i o x i d i z e d a n d t h u s a l l o w n i t r i f i c a t i o n o f a n e f f l u e n t t h a t c o u l d n o t o t h e r w i s e b e t r e a t e d . 4 . 7 . 3 . 2 D i s a d v a n t a g e s o f t h e S e p a r a t e S l u d g e O p e r a t i o n ( i ) A g r e a t e r c a p i t a l , o p e r a t i n g a n d m a i n t e n a n c e e x p e n d i t u r e w i t h d u a l t a n k s a n d c l a r i f i e r s . ( i i ) A h i g h e r t o t a l s l u d g e p r o d u c t i o n d u e t o l o w e r S R T a n d t h u s l e s s e n e d e n d o g e n o u s b i o m a s s d e c a y . ( i i i ) D u p l i c a t i o n o f t h e m a j o r o p e r a t i n g p r o b l e m - t h e c l a r i f i e r . ( i v ) I f t h e B O D : T K N r a t i o i s t o o l o w , t h e d a i l y l o s s o f b i o m a s s i n t h e c l a r i f i e r o v e r f l o w m a y s u r p a s s t h e t o t a l d a i l y b i o m a s s p r o d u c t i o n i n t h e n i t r i f y i n g r e a c t o r , l e a d i n g t o n i t r i f i e r w a s h o u t . -46-(v) The use of a high rate f i r s t stage i n order to keep an adequate BOD:TKN r a t i o i n the second stage can lead to poor f i r s t stage s e t t l i n g c h a r a c t e r i s t i c s . Lawrence (1976) discounts many of the advantages of the two stage system. Most re c e n t l y published work on activated sludge n i t r i f i -c a t i o n and d e n i t r i f i c a t i o n systems indicates a movement away from these multi-sludge systems toward combined systems (Barnard 1975a;Jank 1978; Besik 1977). In part, t h i s must be due to the development of improved knowledge about, and an adequate data base f o r , single sludge design at a l l temperatures. Increased c a p i t a l , labour and energy costs and a consequent trend toward simpler systems probably also play a r o l e . Lawrence (1976) and Sutton (1975b) observed no apparent d i f f e r e n c e s i n the e f f i c i e n c y or the performance of one and two stage n i t r i f y i n g systems operated under the same growth and temperature conditions. Jank (1978) found s i m i l a r n i t r i f i c a t i o n performances f o r both systems i n n i t r i f i c a t i o n reactors using a combined sludge that was also performing d e n i t r i f i c a t i o n and phosphorus removal functions under d i f f e r e n t environmental conditions. The comparison was based on s i m i l a r aerobic SRT's. -47-CHAPTER 5 NITROGEN REMOVAL OR DENITRIFICATION 5.0 B i o l o g i c a l Nitrogen U t i l i z a t i o n Micro-organisms active i n wastewater use n i t r a t e e i t h e r by as s i m i l a t i o n or by d i s s i m i l a t i o n (Painter 1977). Ass i m i l a t i o n processes reduce n i t r a t e to ammonia and then incorporate i t i n t o c e l l u l a r organic nitrogen. D i s s i m i l a t i o n or "n i t r a t e r e s p i r a t i o n " u t i l i z e s the oxygen of the n i t r a t e as a f i n a l e l e ctron acceptor, during the oxidation of organic substrate by heterotrophic microbes i n an oxygen free (anoxic) environment. From an engineering point of view, d i s s i m i l a t i o n i s the more important because most of the i n f l u e n t nitrogen may be e n t i r e l y removed from the system by t h i s route. 5.1 D i s s i m i l a t i o n D i s s i m i l a t i o n i s generally represented as a two stage process (Table 5.1): f i r s t l y , n i t r a t e reduction to n i t r i t e and secondly, reduction to nitrogen gas. However, as discussed by Delwiche (1956) and Painter (1970), the reduction involves various other intermediates and the f i n a l product depends on the ba c t e r i a and environmental conditions. Moore (1970) in d i c a t e s that a greater v a r i e t y of microbes are av a i l a b l e i n sewage to reduce n i t r a t e to n i t r i t e than to reduce n i t r i t e to (di)nitrogen. Some species are capable of reducing both n i t r a t e and n i t r i t e ; others are more s e l e c t i v e . The term " D e n i t r i f i c a t i o n " i s used to describe a process which provides f i n a l products of n i t r i c oxide, nitrous oxide or dinitrogen (Painter 1977). -48-Unlike n i t r i f y i n g organisms, most other bacteria i n sewage or activ a t e d sludge are capable of n i t r a t e d i s s i m i l a t i o n . (Christensen 1977a). The bulk of these d e n i t r i f y i n g species are f a c u l t a t i v e chemo-organohetero-trophs, d e r i v i n g both energy and carbon from reduced organic substrate but being capable of using oxygen, n i t r a t e , n i t r i t e or, i n some cases, sulphate ions as a f i n a l e l e c t r o n acceptor. In any d e n i t r i f y i n g system, the v a r i e t y and numbers of species present are determined by environmental conditions and by changes i n these conditions (Davies 1971). The plethora of p o t e n t i a l d e n i t r i f i e r s i n a sewage treatment plant and the a b i l i t y of populations to change with environmental conditions i s a major reason f o r the wide range of observed d e n i t r i f y i n g responses to factors such as pH and temperature (Dodd 1975). 5.1.1 Respiration Modes: Respiration i s c l a s s i f i e d as aerobic or anoxic according to whether oxygen or n i t r a t e i s the f i n a l e l e c t r o n r e c e i v e r . The biochemical pathways are i d e n t i c a l except f o r one enzyme at the f i n a l e l e c t r o n t r a n s f e r i n t e r f a c e (Painter 1970). The f a c u l t a t i v e organisms are thus able to switch r a p i d l y between the two r e s p i r a t i o n modes. However, because the energy y i e l d from aerobic r e s p i r a t i o n i s greater, (Table 3.1) n i t r a t e r e s p i r a t i o n i s severely c u r t a i l e d i n the presence of oxygen. Dodd (1975) indicates that the oxygen i n h i b i t s the synthesis of enzymes capable of c a t a l y z i n g the d e n i t r i f i c a t i o n r eaction ( i e . n i t r a t e r e s p i r a t i o n ) . 5.2 Energy, Synthesis and Stoichiometry In a p r a c t i c a l d e n i t r i f y i n g system,there are several reactions that influence nitrogen removal: biomass (new c e l l ) synthesis> -49-n i t r a t e r e s p i r a t i o n with an e x t r a - c e l l u l a r carbon source, endogenous n i t r a t e r e s p i r a t i o n , and aerobic respiration,(which w i l l occur u n t i l the DO l e v e l s are very low) (Painter 1970). From Table 5.1, Equations 5.1 to 5.4 represent " h a l f - c e l l " reactions f o r oxygen and n i t r a t e r e s p i r a t i o n . H a l f - c e l l reactions f o r methanol and domestic sewage oxidation, using the C2.0 H19°3 N w a s t e w a t e r d e s c r i p t i o n of Christensen and McCarty (1975), are shown by Equations 5.5 and 5.6. Over a l l energy equations f o r methanol, wastewater and endogenous ( c e l l t i s sue) substrates with oxygen or n i t r a t e e l e c t r o n acceptors are represented by Equations 5.7 to 5.12. I t i s noted that where the substrate contains nitrogen, ammonia i s released. This w i l l be discharged i n the system e f f l u e n t unless assimilated i n t o biomass or else oxidized i n a subsequent aerobic step. Except in the case of endogenous r e s p i r a t i o n where biomass i s being oxidized, the synthesis of new biomass occurs simultaneously with energy production. Synthesis i s represented by Equations 5.13 f o r a methanol substrate (McCarty 1969) and 5.14 f o r wastewater sub-strate (Beer 1978) . Equations of greater accuracy and complexity, which include phosphorus and consider v a r i a t i o n s i n the c e l l composition with sludge age, are a v a i l a b l e i n the l i t e r a t u r e (Sherrard 1976a). The complete p i c t u r e of substrate u t i l i z a t i o n must combine equations f o r synthesis and for r e s p i r a t i o n . For t h i s , the r e l a t i v e proportions of substrate used i n energy production and i n biomass synthesis must be known. Beer (1978) derived an energy:synthesis r a t i o of 35:65 f o r aerobic and 65:35 f o r anoxic synthesis using the r e s u l t s of McCarty (1969), Barnard (1975a) and Porges (1956) for T A B L E 5 . 1 HALF CELL REDUCTION REACTIONS S T O I C H I O M E T R I C R E P R E S E N T A T I O N S O F D E N I T R I F I C A T I O N R E A C T I O N S ( A f t e r B e e r 1 9 7 8 , M c C a r t y 1 9 6 9 ) BIOMASS SYNTHESIS REACTIONS Nitrate Respiration 7sH20 + VioN 2 + 75 OH Oxygen Respiration Ho2 + H + + e" = >iH20 (5.1) (5.2) - (5.3) (5.4) HALF CELL SUBSTRATE OXIDATION Methanol VeCHjOH + '/6H20 = '/6C02 + H + + e" Domestic Wastewater (5.5) V50C 1 0H 1 9O 3N + 9/25H20 = 9AoC0 2 + VsoNH,, + V50HCO3 + H + e" (5.6) OVERALL ENERGY EQUATIONS  Methanol Substrate - Oxygen Electron Receiver - (5.7) Methanol Substrate - Nitrate Electron Receiver SCHjOH + 6NO3 = 3N2 + 5C02 + 7H20 + 60H~ Wastewater Organic Substrate - Oxygen Electron Receiver C10 H19°3 N + 1 2 - 5 02 = 1 0 c o 2 + 8 H 2 ° + m 3 Wastewater Organic Substrate - Nitrate Electron Receiver C10 H19°3 N + 1 0 N 0 3 = 1 0 0  Endogenous Oxygen Respiration C 5H 70 2N + 5 0 2 = 5C0 2 + NH3 + 2H20 Endogenous Nitrate Respiration C 5H 70 2N + 4NOj = 5C02 + NH3 + 2N2 + 40H~ (5.8) (5.9) - (5.10) (5.11) - (5.12) Methanol Substrate 14CH3OH + C0 2 + 3NO3 + 3H + = 3C 5H 70 2N + 19H20 Wastewater Substrate C10 H19°3 N + 1-5NH3 + 2.5C02 = 2.5C 5H 70 2N = 3H20 OVERALL SUBSTRATE REMOVALS (5.13) (5.14) Aerobic Respiration - Methanol Substrate 0.93CH3OH + 0.056NO3 + 0 2 = 0.056CsH7NO2 + 1.04H2O + 0.59H2CO3 + O.O56HCO3 Nitrate Respiration - Methanol Substrate I.O8CH3OH + NO3 + H + = 0.065C5H7O2N + 0.47N2 + 0.76CO2 + 2.44H20 Aerobic Respiration - Wastewater Substrate C 1 0H, 9O 3N + 4.3750 2 + 0.625NH3 = 1.625C5H702N + 1.875C02 + 4.75H20 Nitrate Respiration - Wastewater Substrate C10 H19°3 N + 6 - 5 N 0 3 = 0.875C5H702N + 0.125NH3 + 3H20 °2 - (5.15) - (5.16) - (5.17) (5.18) I (_n O -51-wastewater carbon removal. Equations 5.17 and 5.18 use these r a t i o s f o r aerobic and n i t r a t e r e s p i r a t i o n r e s p e c t i v e l y . Beer advocates further work to improve the r e l i a b i l i t y of these r a t i o s and of the assumed wastewater composition ( cio H19°3 N^" Equations 5.15 and 5.16, using methanol as the carbon substrate, are based on the work of McCarty (1969) . 5.2.1 A l k a l i n i t y Production These biochemical reactions take place i n aqueous solution and the equations could be modified to r e f l e c t the e f f e c t of changes i n a l k a l i n i t y . From Equation 5.16, 3.57 mg of a l k a l i n i t y (as CaCC>3) are produced per mg of NO^ reduced to dinitrogen. In p r a c t i c e , the actual production i s l e s s than t h i s , due to o v e r s i m p l i f i c a t i o n of the equation and neglect of a s s i m i l a t i o n . EPA (1975) suggests the use of 3.0 mg/mg i n design. J e r i s (1977) observed 2.95 i n a f l u i d bed reactor and suggested the use of a l k a l i n i t y as a c o n t r o l parameter, where an acceptable NO^: a l k a l i n i t y c o r r e l a t i o n i s a v a i l a b l e . Beer (1978) i n d i c a t e s that f o r endogenous n i t r a t e r e s p i r a t i o n (Equation 5.12), a t o t a l of 4.46 mg of a l k a l i n i t y i s produced per mg NO^ reduced because of the a d d i t i o n a l nitrogen i n the biomass. 5.3 Factors A f f e c t i n g D e n i t r i f i c a t i o n 5.3.1 Dissolved Oxygen Christensen (1977a) indicates that d i s s i m i l a t i o n i s i n h i b i t e d by oxygen; a s s i m i l a t i o n i s not. Painter (1970) points out that a few organisms i n pure culture have been shown to d e n i t r i f y under highly aerobic conditions. Where d e n i t r i f i c a t i o n occurs under nominally aerobic conditions (Mulbager 1971), i t i s most probably due to an oxygen gradient, whereby some part of the system i s a c t u a l l y at zero DO (Painter 1977; Dawson 1973). Wuhrmann (1968) asserts that oxygen i s a powerful i n h i b i t o r -52-to n i t r a t e or n i t r i t e r e s p i r a t i o n at pH 6.5 to 7.0, but at lower pH, i n h i b i t i o n i s diminished. Christensen (1977a) suggests that f or d e n i t r i f i c a t i o n , DO should be l e s s than 0.5 mg/L i n suspended c u l t u r e s . Painter (1977) showed that the d e n i t r i f i c a t i o n rate dropped by 50% as conditions were changed from anoxic t o 0.2 mg/L DO. 5.3.2 pH: Delwiche (1956) reports that d e n i t r i f y i n g systems generally function best i n a near neutral pH range. The actual optimum range i s dependent on the cu l t u r e and system under t e s t . Generally, d e n i t r i -f i c a t i o n i s supported i n the 5.8 to 9.2 pH range with a peak rate between 7.0 and 8.2 (Delwiche 1956). EPA (1975) suggests that operation of d e n i t r i f i c a t i o n processes i s optimum from pH 7.0 to 7.5. Dodd (1975) suggests that the s e n s i t i v i t y of a d e n i t r i f y i n g biomass to environmental conditions i s increased as the pH i s r a i s e d above 7.0. 5.3.3 Temperature: Because of the d i v e r s i t y of species present i n a mixed c u l t u r e , d e n i t r i -f i c a t i o n i s generally l e s s s e n s i t i v e to the mixed l i q u o r temperature than i s n i t r i f i c a t i o n , but i s more s e n s i t i v e than carbon oxidation (Sutton 1977b; Focht 1975). Focht (1975) i n d i c a t e s that d e n i t r i f i c a t i o n i s optimal between 65°C - 75°C and ceases at 85°C. Christensen (1977a) suggests an optimum near 40°C and a maximum near 50°C. Painter (1977) summarizes work i n d i c a t i n g that a c t i v e d e n i t r i f i c a -t i o n occurs at temperatures as low as 4°C, and suggests that i t should occur near 0°C but a t reduced r a t e s . Dawson (1972) found rates at 5°C to be only 10% of those at 27°C i n pure c u l t u r e , with d e n i t r i f i c a t i o n ceasing at 3°C. -53-5.3.4 Micronutrients Painter (1970, 1977) itemizes both macro- and micronutrient requirements f o r heterotrophic d i s s i m i l a t i o n ( d e n i t r i f i c a t i o n ) . Apart from an organic substrate, the absence of oxygen and presence of n i t r a t e , the macronutrients S, P, C l , Na, K, Mg and Ca and traces of Mo, Fe, Cu and Mn are required. Some species require ammonia or amino acids for c e l l synthesis. 5.3.5 I n h i b i t i o n of D e n i t r i f i c a t i o n Compared t o n i t r i f i c a t i o n , there i s l i m i t e d data i n the l i t e r a t u r e on i n h i b i t i o n of d e n i t r i f i c a t i o n . A s indicated by Painter (1970), the more d i v e r s i f i e d heterotroph population has a greater resistance to i n h i b i t i o n than i s the case with n i t r i f i e r s . Christensen (1977a) and Moore (1971) show that ammonia, n i t r i t e , methanol, pH and oxygen can be t o x i c . Oxygen and pH are discussed i n Section 5.3.1 and 5.3.2. N i t r i t e may i n h i b i t above 30 mg/L as nitrogen. Dawson (1972) observed that n i t r i t e may accumulate during adaptation of d e n i t r i f i e r s to new conditions. A study of s a l i n i t y additions up to 0.63% was reported by Christensen (1977a) to indic a t e no i n h i b i t o r y e f f e c t s . Painter (1970) itemizes i n h i b i t i o n of pure cultures by such agents as: metal chelating agents (cyanide and " d i t h i o l " ) ; chlorate; Cu II (16% i n h i b i t o r y at 3 mg/L); pyruvic a c i d and hydroxylamine. Focht (1975) suggests that n i t r a t e , or end product i n h i b i t i o n i s of minimal consequence i n d e n i t r i f i c a t i o n . There are i n d i c a t i o n s that d e n i t r i f y i n g sludges require a f i n i t e conditioning period a f t e r aerobiasis before the r e s p i r a t i o n rate reaches a maximum. Painter (1977) suggests 30 to 60 minutes. - 5 4 -5 . 4 K i n e t i c s o f D e n i t r i f i c a t i o n T h e w o r k o f M o o r e ( 1 9 7 0 ) a n d S t e n s e l ( 1 9 7 3 ) ( w h i c h s h o w s t h a t n i t r i t e d o e s n o t n o r m a l l y b u i l d u p i n a d e n i t r i f y i n g s y s t e m ) h a s a l l o w e d t h e p r o c e s s t o b e m o d e l l e d a s a o n e s t e p o p e r a t i o n — n i t r a t e d i r e c t l y t o n i t r o g e n g a s . M o n o d t y p e r e l a t i o n s h i p s h a v e b e e n u s e d b y E P A ( 1 9 7 5 ) , P a s k i n s ( 1 9 7 7 ) , a n d E n g b e r g ( 1 9 7 5 ) t o d e s c r i b e t h e d e p e n d e n c e o f d e n i t r i f i c a t i o n r a t e s o n b o t h n i t r a t e a n d o n o r g a n i c s u b s t r a t e c o n c e n t r a t i o n s . L i t t l e w o r k d i r e c t e d a t d e t e r m i n i n g h a l f - r a t e c o n s t a n t s h a s b e e n r e p o r t e d . M o o r e ( 1 9 7 0 , 1 9 7 1 ) a n d E P A ( 1 9 7 5 ) i n d i c a t e v a l u e s l e s s t h a n 1 m g / L f o r b o t h n i t r a t e a n d m e t h a n o l . P a s k i n s ( 1 9 7 8 ) f o u n d a h a l f - r a t e c o n s t a n t i o f 1 0 . 6 m g / L f o r m e t h a n o l . A s a g e n e r a l r u l e , p r o v i d e d b o t h n i t r a t e a n d m e t h a n o l a r e p r e s e n t i n e x c e s s o f 1 t o 2 m g / L , t h e d e n i t r i f i c a t i o n r a t e i s i n d e p e n d e n t o f e i t h e r c o n c e n t r a t i o n ( E P A 1 9 7 5 ) , ( P a i n t e r 1 9 7 7 ) . D a w s o n ( 1 9 7 2 ) s u g g e s t s c a r b o n i s l i m i t i n g u n l e s s i t i s p r e s e n t i n e x c e s s o f t h e " t h e o r e t i c a l n e e d " f o r c e l l g r o w t h a n d e n e r g y . M u r p h y ( 1 9 7 5 ) a d v o c a t e s a C : N r a t i o i n e x c e s s o f u n i t y a n d a n i t r a t e p l u s n i t r i t e c o n c e n t r a t i o n g r e a t e r t h a n 1 m g / L f o r z e r o o r d e r k i n e t i c s . I n p r a c t i c e , w h e r e t h e a i m i s t o r e d u c e n i t r a t e l e v e l s b e l o w 1 m g / L , n i t r a t e i s u s u a l l y l i m i t i n g ( S u t t o n 1 9 7 5 a , E n g b e r g 1 9 7 5 ) . I n o t h e r s y s t e m s w h e r e a c a r b o n s o u r c e ( e g . m e t h a n o l ) i s n o t u s e d , t h e e n e r g y s u b s t r a t e m a y b e . l i m i t i n g ( S u t t o n 1 9 7 7 b ; S t e n s e l 1 9 7 3 ) . -F o c h t ( 1 9 7 5 ) p o i n t s o u t t h a t d e n i t r i f i c a t i o n k i n e t i c s a r e f a r m o r e c o m p l e x t h a n n i t r i f i c a t i o n a n d a r e n o t w e l l d e v e l o p e d . 5 . 4 . 1 D e n i t r i f i c a t i o n R a t e s D e n i t r i f i c a t i o n r a t e s a r e d e p e n d e n t o n n u m e r o u s f a c t o r s i n c l u d i n g s u b s t r a t e c o m p o s i t i o n a n d c o n c e n t r a t i o n , t e m p e r a t u r e , S R T , p H , -55-sludge density, proportion of d e n i t r i f i e r s i n the biomass, t o x i c i t y , DO, e t c . Because of t h i s , the most common design approach i s v i a experimentally rather than t h e o r e t i c a l l y determined r a t e s . The wide v a r i a t i o n i n reported d e n i t r i f i c a t i o n rates at any temperature i s indicated i n Figures 5.1 and 5.2 f o r endogenous and wastewater carbon sources r e s p e c t i v e l y . Sutton (1978b, 1977b) demonstrated that rates with combined sludge systems were approximately 40% of those with separate sludges. This was explained by a lower f r a c t i o n of d e n i t r i f i e r s i n the combined sludge due to the r e l a t i v e l y lower proportion of time a v a i l a b l e f o r d e n i t r i f i e r growth under anoxic conditions. 5.4.1.1 So l i d s Retention Time; Engberg (1975) and Davies (1971) point out that d e n i t r i f i c a t i o n rates and reaction stoichiometry vary with the SRT because d i f f e r e n t sludge ages a l t e r the environment and thus change the dominant b a c t e r i a l species. Sutton (1974) indicated that the u n i t d e n i t r i f i c a t i o n rate was 1.3 times greater when the SRT was reduced from 6 days to 3 days. I t was suggested that a 6 day minimum SRT at 5°C and 3 day minimum at 20°C was needed to ensure d e n i t r i f i c a t i o n . Stensel (1973) found a doubling i n rate as the SRT was lowered from 7 to 2 days and Moore (1971) a s i m i l a r increase with an SRT reduction from 6 to 3 days. 5.4.1.2 S o l i d s Concentration: Christensen (1977a) presents data showing a decrease, i n u n i t d e n i t r i f i c a t i o n rate with an increase i n s o l i d s concentration. Suggested reasons included lower a c t i v e biomass and increased d i f f u s i o n r e s i s t a n c e . 5.4.1.3 Temperature: S u f f i c i e n t evidence e x i s t s to ind i c a t e that the d e n i t r i f i c a t i o n rate dependence on temperature may be represented by an Arrhenius type -57-0 . 5 3 4 0.14 o " 0 CO t o > > o E •o 0.12 0.10 •o 0 . 0 6 X o $ 0 . 0 4 c o o u Z 0 . 0 2 c a> Q Sutton (1977b) O Peak at I 8 ° C ( R U N 181 B) (This work) Barnard ( I 9 7 5 a ) 10 15 20 T e m p e r a t u r e °C 25 F I G . 5 . 2 D E N I T R I F I C A T I O N R A T E S W I T H W A S T E W A T E R C A R B O N S O U R C E . -58-curve. Dawson (1972) demonstrated t h i s dependence between 3 C and 27 C. Sutton (1974, 1975a, 1977b, 1978a) presents tables of Arrhenius r e l a t i o n -ship constants f o r d e n i t r i f i c a t i o n (see Table 5.2). Sutton (1978a) showed that the temperature s e n s i t i v i t y of both combined and separate sludge systems was s i m i l a r . The response appeared independent of sludge age (Sutton 1977b). Focht (1975) suggests the values are larger below 15°C than above. Reported rates are dependent on the methods used f o r determining the progress of d e n i t r i f i c a t i o n ( i e . gaseous-product appearance or substrate disappearance). Apart from the work of Sutton, Murphy, Jank, Dawson and others at Burlington, Ontario, very l i t t l e comprehensive work has been published on the r e l a t i o n s h i p s between temperature and d e n i t r i f i c a t i o n r a t e s . The ample v a r i a t i o n reported by these authors suggests the existence of no simple general r e l a t i o n s h i p , but rather one p a r t i c u l a r to the s i t u a t i o n under t e s t . TABLE 5.2 ARRHENIUS CONSTANTS FOR DENITRIFICATION Temperature (°C) Arrhenius E (cal/mole) e 210 *k Reference 6-19 0.02 Christensen 10-2 0 0.05-0.07 (1977a) 15-24 0.07 Ibid 10-40 0.05 Ib i d 18-24 1.094 0.04 Barnard (1975a) 6-25 15,900 1.09 2.5 Murphy (1975) 3-27 16,800 1.12 • Dawson (1972) 10-20 19,500 1.13 3 .3 Stensel (1973) 10-20 19,000 1.15 3.3 Mulbager (1971) 7.26 12,730 1.075 Sutton (1978a) 7-25 15,900 Sutton (1977b) Notes: Nomenclature: see *Rate at T^ = Rate Chapter at T 2 • 3.2.3. i o k ( T i " T 2 } . -59-5 .5 Substrate As indicated i n Section 5.1, d e n i t r i f y i n g b a c t e r i a require a source of reduced carbon f o r energy production and c e l l synthesis. In wastewater treatment, the carbon/energy source i s u s u a l l y one of the f o l l o w i n g : (Painter 1977) (i) R a w Sewage ( i i ) C e l l Tissue (for endogenous n i t r a t e r e s p i r a t i o n ) ( i i i ) External chemical or organic carbon a d d i t i o n . Table 5.3 summarizes the advantages and disadvantages of the various substrates. The work of numerous i n v e s t i g a t o r s such as Dawson (1972), Dodd (1975), Stensel (1973), Christensen (1977a) and McCarty (1969) indicates that both d e n i t r i f i c a t i o n rates and the percentage of nitrogen removed increase p r o p o r t i o n a l l y with carbon substrate additions u n t i l a c e r t a i n r a t i o of carbon to nitrogen i s reached, at which point the values l e v e l o f f . This plateau approximates the stoichiometrically-determinable l e v e l at which s u f f i c i e n t organic carbon i s a v a i l a b l e to s a t i s f y the system needs fo r growth, energy production and oxygen consumption (Barnard 1977). Of these substrates, methanol has been the most widely studied i n North America, while raw sewage and biomass have received the major European a t t e n t i o n (Christensen 1978a). 5.5.1 Wastewater as a Substrate The increased cost of methanol, the cheapness and a v a i l a b i l i t y of raw sewage, together with a greater understanding of the d e n i t r i f i c a t i o n process has increased the i n t e r e s t i n domestic wastewater as a carbon source. D e n i t r i f i c a t i o n with wastewater i s generally regarded as being slower than with methanol addition (EPA 1975, Christensen 1977a). TABLE 5.3 WASTEWATER DENITRIFICATION SUBSTRATES Substrate Advantages D i sadvantage s Reference C e l l Biomass Readily a v a i l a b l e Reduces biomass Temperature i n s e n s i t i v e Low rate Ammonia release Sutton ' (1978b) Christensen (1977a) Raw Sewage Cheap Readily Available Ammonia, organic N release Lower rate than methanol Uncontrolled v a r i a t i o n s i n strength composition & flow Mix of refractory and biodegradable Christensen (1977a) Methanol Chemically simple & pure E a s i l y degraded, nitrogen free Easy monitoring and control Cheap and a v a i l a b l e Small sludge production Toxic to N i t r i f i e r s Escalating price Excess adds BOD to e f f l u e n t EPA (1975) Christensen (1977a) Molasses Cheap and.available i n some areas Slow Rate, Bulking Sludge EPA (1975) Methane Cheap & a v a i l a b l e (Digester) Explosive, few bacteria can use. Rhee (1978) V o l a t i l e Acids Cheap and a v a i l a b l e (Digester) Variable contaminants including NH^ McCarty (1969) Brewery Waste Local A v a i l a b i l i t y High Rate High Solids Production Wilson (1973) Ethanol Less to x i c than Methanol More expensive McCarty (1969) Other - - Christensen (1977a) -61-Paskins (1978) in d i c a t e s that raw sewage with i t s numerous d i f f e r e n t organic constituents (few of them i n high concentrations) i s most probably a carbon l i m i t i n g substrate. Sutton (1978a) determined that organic carbon would be l i m i t i n g unless "3 mg of f i l t e r e d COD are a v a i l a b l e for each mg of nitrogen according to stoichiometric c a l c u l a t i o n s " . (Based on the equation: mg/L methanol =1.91 N03~N +1.14 N02~N + 0.67 DO and a conversion f a c t o r from methanol to COD of 1.5). Christensen (1977b) suggests a BOD^^O^-N r a t i o from 3 to 6 i s desir a b l e ; Bishop (1976) a COD:TKN greater than 10:1. Barnard (1977) ... indicates 11.5 COD mass u n i t s to one nitrogen u n i t i s d e s i r a b l e . Recent p u b l i c a t i o n s by Sutton (1978a) and Barnard (1977) have highlighted the value of raw sewage as a d e n i t r i f i c a t i o n substrate. Sutton demon-strated that d e n i t r i f i c a t i o n r a t e s , under p a r a l l e l batch conditions were equal f o r methanol and raw sewage. Barnard (1977) analyzed the three separate zero order d e n i t r i f i c a t i o n rates observed i n h i s batch d e n i t r i f i c a t i o n t e s t s using raw sewage ad d i t i o n s : A r a p i d i n i t i a l (5-15 minutes) rate of 60 mg/gm .MLSS/hr; An intermediate rate of 16 mg/gm ;MLSS/hr; A slow, long term rate of 5.4 mg/gm MLSS/hr. The i n i t i a l r a p i d rate was brought about by the oxidation of highly reduced organic compounds i n the wastewater. (The extent of such material i n raw sewage depends on the p a r t i c u l a r system under examination.) This rapid rate continued u n t i l the d i f f e r e n c e i n redox p o t e n t i a l s between the mixed l i q u o r and raw sewage was removed. The intermediate rate was that commonly observed under steady state conditions with wastewater substrate and lasted u n t i l a l l the -62-av a i l a b l e carbon was depleted, at which time the slow or endogenous rate was abruptly apparent. Barnard (1977) indicated that methanol addi t i o n was equivalent to the intermediate r a t e . At the highest r a t e , d e n i t r i f i c a t i o n could normally be completed extremely r a p i d l y - say f i v e minutes. In h i s endogenous d e n i t r i f i c a t i o n studies, Barnard (1977) observed only the two slower r a t e s . The existence of t h i s r apid i n i t i a l rate of d e n i t r i f i c a t i o n (or oxygen uptake) could p o s s i b l y be u t i l i z e d to economic advantage when designing nitrogen removal systems to t r e a t highly sep t i c wastewater. 5.5.2 Methanol as a Substrate Methanol has been used extensively i n North America to provide a r e a d i l y a v a i l a b l e carbon source i n d e n i t r i f i c a t i o n systems with low carbon a v a i l a b i l i t y i n the n i t r a t e r e s p i r a t i o n reactor, (EPA 1975; Sutton 1974; Mulbager 1971; McHarness 1973) . McCarty (1969) defined a Consumption Ratio as: Quantity of Organics Consumed During D e n i t r i f i c a t i o n  Stoichiometric Organic Requirement f or Ni t r a t e , N i t r i t e , and Oxygen Removal Experimentally, t h i s r a t i o was determined as 1.3 f o r methanol by McCarty (1969) and 1.26 by Stensel (1973). Using t h i s r a t i o and a knowledge of the biomass synthesis, McCarty (1969) determined the required methanol addi t i o n as: ( A l l data i n mg/L) Methanol = 2.47(N03~N) + 1.53(N02~N) + 0.87 (DO) Biomass production can al s o be c a l c u l a t e d : Biomass = 0.53(NO3~N) + 0.32(N02~N) + 0.19(DO) EPA (1975) suggests that 3.0 mg methanol added per mg n i t r a t e i s s u f f i c i e n t i n p r a c t i c e . Stensel (1973) suggests that an excess of 1 mg/L i n the e f f l u e n t allows d e n i t r i f i c a t i o n without carbon l i m i t a t i o n . Horskotte -63-(1974) ind i c a t e s d i f f i c u l t y i n c o n t r o l l i n g methanol l e v e l s i n a f u l l scale operation. Numerous authors point out that excess methanol addition may add BOD to the e f f l u e n t unless subsequent removal i s p r a c t i s e d , (Wuhrmann 1973; Murphy 1975; Barnard 1975a; .Sutton 1977b). 5.5.3 Endogenous Nitrate Respiration Wuhrmann (1968) indicated that the endogenous carbon reserves i n b acteria are s u f f i c i e n t to maintain n i t r a t e r e s p i r a t i o n u n t i l a l l the oxidized nitrogen i s reduced i n normal domestic wastewater treatment. The nitrogen removal rate i s l i m i t e d only by the endogenous decay r a t e . Beer (1978) pointed out that endogenous n i t r a t e r e s p i r a t i o n i s slower than oxygen r e s p i r a t i o n . The r e a c t i o n rate i s zero order with respect to substrate, electron acceptor and biomass. From Equation 5.12, a biomass destruction of 2 mg i s indicated for each mg of n i t r a t e removed, with a t o t a l a l k a l i n i t y production of 4.4 mg;3.57 from n i t r a t e reduction, the r e s t from biomass conversion to n i t r a t e and subsequent reduction. Sutton (1978a) points out the wide v a r i a t i o n i n reported endogenous d e n i t r i f i c a t i o n rates (Figure 5.1). There i s no good agreement among inv e s t i g a t o r s on the extent to which temperature a f f e c t s rates (Table 5.4). Sutton (1978a, 1978b) found that temperature had a minor e f f e c t on rate i n the 7°C to 26°C range at s i m i l a r SRT. Changing SRT's had a s i g n i f i c a n t e f f e c t , with the endogenous d e n i t r i f i c a t i o n rate decreasing by 80% as the SRT was r a i s e d from 2 to 32 days. This was explained by the dependence of the d e n i t r i f i c a t i o n rate on the release of organic carbon from l y s i n g c e l l s . The number of v i a b l e c e l l s decreases with increasing SRT and thus the rate of carbon release diminishes. On the other hand, Marais (1975) concluded that the unit rate of endogenous d e n i t r i f i c a t i o n was constant at any temperature for a l l SRT As,.. - 6 4 -T A B L E 5 . 4 D E P E N D E N C E O F E N D O G E N O U S N I T R A T E R E S P I R A T I O N O N T E M P E R A T U R E ^ T - 2 0 T e m p e r a t u r e : R a t e r e l a t i o n s h i p R^, = R^ 0 N o t e s : 2 0 0 . 0 4 5 * 0 . 0 4 0 . 0 0 7 - 0 . 0 1 * 1 . 2 1 . 0 6 0 . 0 0 6 - 0 . 0 4 ( S u b s t a n t i a l l y i n d e p e n d e n t o f t e m p e r a t u r e ) R e f e r e n c e B a r n a r d ( 1 9 7 4 ) B e e r ( 1 9 7 8 ) C h r i s t e n s e n ( 1 9 7 7 a ) S u t t o n ( 1 9 7 8 a ) R T = r e m o v a l r a t e ( l b N 0 3 - N / l b M L V S S / d a y ) a t T ° C . * a s s u m e s M L V S S = 7 0 % M L S S . 5 . 6 . 1 P o s t D e n i t r i f i c a t i o n A e r a t i o n : T h e i m p o s i t i o n o f a s h o r t p e r i o d o f a e r o b i c t r e a t m e n t b e t w e e n d e n i t r i f i c a t i o n a n d s e t t l i n g h a s s e v e r a l p r o c e s s a d v a n t a g e s ( E P A 1 9 7 5 ; B a r n a r d 1 9 7 5 a ; H o r s t k o t t e 1 9 7 4 ) . ( i ) N i t r o g e n g a s i s s t r i p p e d f r o m t h e b i o m a s s a l l o w i n g a l o w e r S S i n t h e d i s c h a r g e d e f f l u e n t . a n d i m p r o v e d s l u d g e s e t t l i n g . ( i i ) T h e a m m o n i a r e l e a s e d d u r i n g e n d o g e n o u s r e s p i r a t i o n a n d . a n y e x c e s s c a r b o n s o u r c e a d d i t i o n s a r e o x i d i z e d . ( i i i ) D e n i t r i f i c a t i o n i s h a l t e d a n d t h e r e s i d u a l D O p r e v e n t s n i t r o g e n f o r m a t i o n i n t h e c l a r i f i e r , w i t h i t s c o n s e q u e n t r i s i n g s l u d g e p r o b l e m s . ( i v ) S l u d g e s t a b i l i z a t i o n i s i n c r e a s e d b y e n d o g e n o u s o x y g e n r e s p i r a t i o n , t h u s l o w e r i n g t h e B O D p e r u n i t o f b i o m a s s i n t h e e f f l u e n t . H o w e v e r s u c h s t a b i l i z a t i o n a l s o l o w e r s t h e d e n i t r i f y i n g a b i l i t y - 6 5 -o f t h e s l u d g e b y r e d u c i n g t h e h e t e r o t r o p h p o p u l a t i o n , t h u s r e q u i r i n g a l a r g e r a n o x i c r e a c t o r o r l o n g e r H R T t o e f f e c t d e n i t r i f i c a t i o n . R e t e n t i o n t i m e s s t u d i e d a n d r e p o r t e d i n t h e l i t e r a t u r e r a n g e f r o m 1 0 t o 1 2 0 m i n u t e s ( C h r i s t e n s e n 1 9 7 7 a ) . H o r s t k o t t e ( 1 9 7 4 ) i n d i c a t e s t h a t o n e h o u r i s g e n e r a l l y a d e q u a t e . E P A ( 1 9 7 5 ) s u g g e s t s t h a t a s h o r t p e r i o d o f m i l d t u r b u l e n c e b e t w e e n t h i s a e r a t i o n a n d c l a r i f i c a t i o n w i l l i m p r o v e s e t t l i n g b y a l l o w i n g f l o c c u l a t i o n t o o c c u r . 5 . 7 N i t r i t i f i c a t i o n a n d D e n i t r i t i f i c a t i o n A s o u t l i n e d b y P r a k a s a m ( 1 9 7 2 ) t h e s e t e r m s a r e u s e d t o d e s c r i b e a m m o n i a o x i d a t i o n t o n i t r i t e o n l y a n d d i r e c t r e d u c t i o n o f n i t r i t e t o g a s e o u s p r o d u c t s . P r a k a s a m , i n t r e a t i n g h i g h l y n i t r o g e n o u s p o u l t r y w a s t e , e x p e r i e n c e d a n i t r i t e b u i l d u p d u r i n g a n i t r i f i c a t i o n p r o c e s s , d u e t o n i t r o b a c t e r b e i n g i n h i b i t e d b y t h e h i g h a m m o n i a c o n c e n t r a t i o n s . B y d e n i t r i t i f y i n g t h e p a r t i a l l y n i t r i f i e d l i q u o r , h e w a s a b l e , i n a s u b s e q u e n t s t e p t o c o m p l e t e l y c o n v e r t t h e r e m a i n i n g a m m o n i a t o n i t r a t e . T h e d e m o n s t r a -t i o n t h a t t h e n i t r i t i f i e d l i q u o r c o u l d b e c o m p l e t e l y d e n i t r i f i e d o f f e r e d s e v e r a l a d v a n t a g e s : ( i ) N i t r o b a c t e r i n h i b i t i o n b y a m m o n i a w a s n o l o n g e r a p r o b l e m . ( i i ) H i g h e r l o a d i n g r a t e s a n d s i m p l e f l o w s h e e t s w e r e p o s s i b l e a s c o m p l e t e c o n v e r s i o n t o n i t r a t e w a s n o t n e c e s s a r y . ( i i i ) D e n i t r i t i f i c a t i o n w a s m o r e r a p i d t h a n n i t r a t e r e d u c t i o n ( d e n i t r i f i c a t i o n ) . ( i v ) L e s s e n e r g y a n d s u b s t r a t e w e r e n e e d e d ( o x y g e n a n d m e t h a n o l ) . ( v ) H i g h s t r e n g t h w a s t e s c o u l d b e s i m p l y t r e a t e d . V o e t s ( 1 9 7 5 ) d e t e r m i n e d t h a t d e n i t r i t i f i c a t i o n o c c u r r e d u n d e r b o t h a e r o b i c a n d a n a e r o b i c c o n d i t i o n s . T h e n i t r i t e c a n a l s o b e c h e m i c a l l y r e m o v e d b y -66-a c i d i f i c a t i o n , plus urea or sulfamic a c i d a d d i t i o n . 5.8 Flow Sheets f o r B i o l o g i c a l Nitrogen Removal Numerous process configurations have been proposed or used f o r the b i o l o g i c a l d e n i t r i f i c a t i o n of municipal sewage (see Sutton 1974; EPA 1975; Christensen 1977a; Beer 1978;. Sharma 1977; Jank 1978 f o r summaries). The d i s t i n g u i s h i n g c h a r a c t e r i s t i c s of the various systems include the following: (i) Attached or suspended biomass; ( i i ) ; Combined or separate sludges; ( i i i ) The number of dis t i n g u i s h a b l e process basins; (iv) Extent and nature of d e n i t r i f i c a t i o n substrate ad d i t i o n ( i f any); (v) Sequence of operations and recycle ( i f any); (vi) Other associated chemical and b i o l o g i c a l operations. For the purpose of t h i s review, only suspended biomass, combined sludge systems with wastewater or c e l l biomass carbon sources are relevant. The basic p r i n c i p l e s on which many of these systems are based a r i s e from the work of ei t h e r Wuhrmann (see Christensen 1977a) or Ludzack (1962). 5.8.1 Wuhrmann D e n i t r i f i c a t i o n System ( P o s t - d e n i t r i f i c a t i o n ) Wuhrmann made use of a two reactor system with BOD removal and n i t r i f i c a t i o n c a r r i e d out simultaneously i n the f i r s t and endogenous d e n i t r i f i c a t i o n i n the second. Mixed l i q u o r was apparently not recy c l e d . Using a MLVSS of approximately 5.3 gm/L and an anoxic HRT varying between 2.2 and 2.8 hours, the calculated endogenous d e n i t r i f i c a t i o n rates were -67-1.7 mg -N/gm MLVSS/hour at 17°C and 0.7 at 13.6°C. Up to 90% t o t a l nitrogen removal was achieved. Subsequent researchers c i t e d i n Christensen (1977a) were generally unable to duplicate these r e s u l t s due, p r i m a r i l y to poor n i t r i f i c a t i o n or to an i n s u f f i c i e n t anoxic HRT to allow adequate d e n i t r i f i c a t i o n . Christensen (1977b) was able to match Wuhrmann's r e s u l t s i n a system with a BOD:total nitrogen r a t i o of between 4 and 6 i n the anoxic reactor. Beer (1978) and Christensen (1977a,b) discuss f a c t o r s that influence endogenous d e n i t r i f i c a t i o n and present design considerations for "Wuhrmann" systems. 5.8.2 Ludzack D e n i t r i f i c a t i o n System ( P r e - d e n i t r i f i c a t i o n ) Ludzack (1962) u t i l i z e d the organic carbon i n wastewater as an ele c t r o n donor f o r b i o l o g i c a l d e n i t r i f i c a t i o n . In a sing l e reactor, anoxic, aerobic and s e t t l i n g zones were established by the use of b a f f l e s . Wastewater and recycled sludge, together with n i t r i f i e d mixed liquor, were fed to the anoxic zone where up to 60% t o t a l nitrogen removal was achieved. The rate of n i t r a t e removal increased as the mixed l i q u o r recycle increased. Barnard (1975b) was able to achieve up to 80% nitrogen removal by increasing the underflow sludge recycle or by mixed l i q u o r recycle from the aerobic to the anoxic stage. The important influence of recycle r a t i o on d e n i t r i f i c a t i o n e f f i c i e n c y i s discussed further by Beer (1978) and Faup (1978). Design considerations f o r "Ludzack" reactors are discussed by Beer (1978), Faup (1978), Marais (1975) and Christensen (1977a). In i t s most general form, the d e n i t r i f y i n g reactor detention time i s -68-determined by: „ . .. • . Nitrate from Aerobic Reactor x Recycle Ratio Detention Time = : : : Unit D e n i t r i f i c a t i o n Rate x MLSS 5.8.3 Bardenpho Process The Bardenpho Process, which uses both wastewater and biomass as carbon sources f o r d e n i t r i f i c a t i o n i n separate parts of the operation, i s discussed i n Chapter 2. Heide (1977) describes a process s i m i l a r to the Bardenpho process i n which nitrogen i s removed by d e n i t r i f i c a t i o n and phosphorus by lime ad d i t i o n . 93% COD and 85% t o t a l nitrogen removals were achieved at 10°C using a MLSS recycle of between 2 and 4 and a sludge recycle of 1:1 (based on incoming feed). The nominal system HRT was 40 hours. Design procedures of relevance to the Bardenpho process are discussed by Barnard (1974), Beer (1978), Christensen (1977b) and Marais (1975) . 5.8.4 Adsorption-Bio-oxidation (A.B.) Process Besik (1977) describes a high-rate, single stage, activated sludge process capable of 90% soluble nitrogen removal. I t u t i l i z e s a mixed l i q u o r c o n s i s t i n g of granular and powdered charcoal with both attached and f r e e l y suspended biomass, i n a non-aerated reactor. A i r l i f t s c o n t i n u a l l y recycle mixed l i q u o r from the reactor bottom to the top, where contact i s made with incoming raw feed. Organics are adsorbed to the biomass and charcoal, then oxidized as the MLSS moves downward. The required oxygen i s obtained i n the a i r l i f t and from oxidized nitrogen. Processed wastewater is.drawn from the base of the reactor i n t o a c l a r i f i e r where s o l i d s are separated and recycled to the reactor top a f t e r undergoing reaeration. - 6 9 -T h e s y s t e m M L S S , i n c l u d i n g c h a r c o a l , r a n g e d b e t w e e n 4 . 5 a n d 9 . 0 : g m / L w i t h l o a d i n g r a t e a n d H R T r a n g i n g f r o m 0 . 1 4 t o 0 . 1 6 l b BOD/lb M L S S / d a y a n d 4 _ • t o 9 h o u r s r e s p e c t i v e l y . R e c y c l e r a t i o s v a r i e d f r o m 3 t o 5 . 5 . 8 . 5 A l t e r n a t i n g C o n t a c t P r o c e s s T h i s p r o c e s s , a s d e s c r i b e d b y M . H . C h r i s t e n s e n ( 1 9 7 5 ) , h a s b e e n s u c c e s s f u l l y t e s t e d i n D e n m a r k u n d e r b o t h p i l o t p l a n t a n d f u l l - s c a l e c o n d i t i o n s u p t o 1 . 5 m g d ( 0 . 0 6 7 m 3 / s e c ) . T w o r e a c t o r s i n s e r i e s a n d a c l a r i f i e r a r e u t i l i z e d a n d o p e r a t e d i n a s e q u e n c e t h a t a l t e r n a t e s t h e t a n k s b e t w e e n a e r o b i c a n d a n o x i c e n v i r o n m e n t s . R a w s e w a g e , t o g e t h e r w i t h r e t u r n s l u d g e , i s a d d e d t o t h e a n o x i c t a n k , w i t h t h e c l a r i f i e r b e i n g f e d f r o m t h e a e r o b i c t a n k , t h u s m a i n t a i n i n g a n a n o x i c - a e r o b i c -s e t t l i n g f l o w s e q u e n c e . F o r a s h o r t p e r i o d b e t w e e n c h a n g e o v e r , b o t h t a n k s a r e o p e r a t e d a e r o b i c a l l y . T h i s a l t e r n a t i n g m o d e s i m u l a t e s a h i g h d e g r e e o f M L S S r e c i r c u l a t i o n . T h e a u t h o r ' s p a p e r p r e s e n t s a d e t a i l e d d e s i g n m o d e l . 5 . 8 . 6 A l t e r n a t i n g A n o x i c - A e r o b i c S y s t e m B i s h o p ( 1 9 7 6 ) d e s c r i b e s t h i s p r o c e s s a t B l u e P l a i n s ( W a s h i n g t o n , D . C . ) w h e r e a 1 5 0 m / d a y p i l o t p l a n t w a s u s e d . T w o i d e n t i c a l b a s i n s , - p r o v i d e d w i t h n o n - a e r a t i n g m i x e r s a r e o p e r a t e d i n s e r i e s w i t h a i r b e i n g s u p p l i e d a l t e r n a t e l y i n t h i r t y m i n u t e s e q u e n c e s . F e e d i s t o t h e h e a d o f o n e b a s i n w h i l e o v e r f l o w f r o m t h e o t h e r b a s i n p a s s e s t o a c l a r i f i e r a f t e r a b r i e f p e r i o d o f r e a e r a t i o n . R e c y c l e d s l u d g e e n t e r s w i t h t h e f e e d . N o m i x e d l i q u o r i s r e c y c l e d . N i t r o g e n r e m o v a l s o f 8 4 % w e r e a c h i e v e d u n d e r s u m m e r o p e r a t i n g c o n d i t i o n s . 5 . 8 . 7 " B i o - d e n i t r o " P r o c e s s T h o l a n d e r ( 1 9 7 7 ) a n d B u n d g a a r d ( 1 9 7 8 ) r e p o r t e d o n a 2 1 , 0 0 0 c u b i c m e t e r d a i l y e x t e n d e d a e r a t i o n p l a n t u s e d i n D e n m a r k . T h i s d e n i t r i f i c a t i o n -70-process c o n s i s t s of four complete mix ditches, the f i r s t being a preaeration u n i t with a 1.25 hour HRT; the other three being u n i t s with 5.5 hour HRT's and v a r i a b l e operating c h a r a c t e r i s t i c s . Wastewater i s fed without primary s e t t l i n g . The MLSS i s about 4.1 gm/L and a SRT of 12 days i s used. T h e three ditches are operated i n serie s with a b i l i t y to alternate the flow d i r e c t i o n s and to maintain aerobic, anoxic or non-stirred conditions to achieve n i t r i f i c a t i o n , carbon oxidation, d e n i t r i f i c a t i o n or s e t t l i n g as required. Automatic DO c o n t r o l i s p r a c t i s e d . Simultaneous phosphorus p r e c i p i t a t i o n i s c a r r i e d out using f e r r i c c h l o r i d e . Cycle time i s about eight hours. Tholander (1977) reports 90% removal of nitrogen. 5.8.8 Oxidation Ditches The oxidation d i t c h was developed by Pasveer (see Matsche 1977b) for BOD removal and subsequently modified to carry out d e n i t r i f i c a t i o n (EPA 1975, Heide 1977). Va r i a t i o n s of the system are known by several names: Pasveer d i t c h ; Orbal, Carousel or Bio-denitro p l a n t s . Generally, a l l are characterized by continuous endless channels, high recycle rates and a long SRT. The major d i f f e r e n c e s include the s i z e and arrangement of di t c h e s , the type, l o c a t i o n and number of the aerators and of the mixing equipment. As indicated by Matsche (1977a,b) d e n i t r i f i c a t i o n i n large carousel type plants i s achieved by c o n t r o l l i n g the l e v e l of oxygen input at each aerator, thus allowing alternate aerobic and anoxic zones to develop between aerators. A s e r i e s of simultaneous carbon oxidation, n i t r i f i c a t i o n and d e n i t r i f i c a t i o n reactions thus occurs along the reactor length, using i n i t i a l l y raw sewage and l a t t e r l y endogenous ( c e l l t issue) - 7 1 -c a r b o n s o u r c e s f o r d e n i t r i f i c a t i o n . I n o p e r a t i o n , o x i d a t i o n d i t c h e s u s u a l l y h a v e a d e q u a t e M L S S a n d S R T l e v e l s t o e f f e c t g o o d c o l d w e a t h e r d e n i t r i f i c a t i o n . B e e r ( 1 9 7 8 ) s u g g e s t s e f f i c i e n c y c o u l d b e i m p r o v e d b y s t e p - f e e d i n g r a w s e w a g e a l o n g t h e r e a c t o r l e n g t h , t h u s m a k i n g b e t t e r u s e o f t h e c a r b o n f o r d e n i t r i f i c a t i o n . A s d i s c u s s e d b y B e e r ( 1 9 7 8 ) , V . d . G e e s t ( 1 9 7 7 ) a n d D r e w s ( 1 9 7 3 ) , a d v a n t a g e s o f o x i d a t i o n d i t c h s y s t e m s i n c l u d e : ( i ) L o w e r c a p i t a l c o s t s t h a n b o t h 2 a n d 3 s l u d g e d e n i t r i f i c a t i o n s y s t e m s d u e t o s i m p l i c i t y o f c o n s t r u c t i o n ; ( i i ) A b i l i t y t o b y p a s s p r i m a r y t r e a t m e n t o r t o i n c l u d e c h e m i c a l p r e c i p i t a t i o n . ( i i i ) H i g h e r B O D a n d T K N r e m o v a l s t h a n c o n v e n t i o n a l e x t e n d e d a e r a t i o n d u e t o h i g h M L S S r e c y c l e . ( i v ) L o w s l u d g e y i e l d a n d p r o d u c t i o n o f a s t a b i l i z e d s l u d g e . S i m i l a r l y , d i s a d v a n t a g e s i n c l u d e : ( i ) D i f f i c u l t y i n s e p a r a t i n g a n d c o n t r o l l i n g t h e m i x i n g a n d a e r a t i o n o p e r a t i o n s a n d t h u s d i f f i c u l t y i n h a n d l i n g p e a k f l o w s o r v a r i a t i o n s i n c o n c e n t r a t i o n ; ( i i ) A l a r g e r c l a r i f i e r c a p a c i t y i s n e e d e d , d u e t o t h e h i g h M L S S ; ( i i i ) B u l k i n g a n d f l o a t i n g s l u d g e c a n o c c u r ; ( i v ) I n e f f i c i e n t u s e o f r a w s e w a g e a s a c a r b o n s o u r c e u n l e s s s t e p f e e d i n g i s u s e d . ( v ) R e l a t i v e l y l o w o x y g e n t r a n s f e r e f f i c i e n c y a n d t h e r e f o r e h i g h e r p o w e r c o s t s , a n d v o l u m e n e e d s . ( v i ) T o t a l n i t r o g e n r e m o v a l e f f i c i e n c i e s a r e l o w e r t h a n m o d i f i e d a c t i v a t e d s l u d g e p r o c e s s e s . -72-CHAPTER 6 EXPERIMENTAL APPARATUS AND PROCEDURES 6.1 Model Design The reactor model consisted of five rectangular tanks and a cylindrical c l a r i f i e r arranged in the Modified Bardenpho Configuration (see Figure 2.2)'.. Construction was of clear 0.25 inch perspex, with a maximum system volume of 50 l i t r e s . (See Table 6.1 for tank and c l a r i f i e r dimensions.) Flow was by gravity from tank #1 through to tank #5 and then to the c l a r i f i e r . Each tank was f i t t e d with a fixed baffle 2 cm from the discharge end and extending vertic a l l y from the surface to 12 cm from the tank floor. Discharge was through a single pipe in the end wall. The c l a r i f i e r consisted of a vertical cylinder with an inverted conical base. Inflow was downward through a narrow vertical central cylinder extending to the line of intersection of the cone and major cylinder. Effluent discharge was at the surface through a single 1 cm diameter discharge pipe in the outer wall. Sludge was removed through a single 0.5 cm outlet at the apex of the cone. Tank #1 was f i t t e d with a fixed cover, while tanks #2 and #4 were fi t t e d with close f i t t i n g , floating polyurethane covers to minimize the transfer of atmospheric oxygen to the mixed liquor. The mixing and aeration regimes aire outlined in Table 6.1. 6.1.1 Aeration Air injection into tanks #3 and #5 was via Fisher 12C Fritted Glass Air F i l t e r s , with the flow rate being manually controlled via a needle valve and pressure regulator linked into the building compressed air supply. TABLE 6.1 MODEL DIMENSIONS Basin Basin Length (cm) Dimensions Width (cm) Height (cm) Available Minimum Experimental (Litres) Volumes maximum Mixing Regime Oxygen Status #1 15.9 9.8 31.8 2.0 3.0- 4.0 intermittent Anaerobic #2 32.1 9.8 31.8 4.0 6.0 8.0 continuous Anoxic #3 55.9 9.8 31.8 7.2 11.0 14.0 continuous Aerobic #4 55.9 9.8 31.8 7.0 10.5 14.0 intermittent Anoxic #5 24 .1 9.8 31.8 3.0 4.5 6.0 intermittent Aerobic CLARIFIER DATA Volume (litre) Diameter (outside) (inside) (cm) (cm) Surface Area (cm2) Hydraulic Residence Time (hours) Upflow Rate (meters/day) 4.5 12.7 3.2 118.8 2 .25 4.0 Note: C l a r i f i e r Residence Time and Upflow Rates are based on 2 l i t r e per hour nominal flow. - 7 4 -6 . 1 . 2 M i x i n g : E a c h t a n k w a s e q u i p p e d w i t h a S a r g e n t - W e l c h c o n e - d r i v e s t i r r e r a n d a s i n g l e s t a i n l e s s s t e e l o r p l a s t i c m i x i n g p r o p e l l o r . T a n k s #2 a n d #3 w e r e s t i r r e d c o n t i n u o u s l y , t h e o t h e r s i n t e r m i t t e n t l y o n a r e g u l a r c y c l e . A i r i n j e c t i o n a l o n e w a s u n a b l e t o p r e v e n t s e t t l i n g i n t h e a e r o b i c t a n k s . 6 . 1 . 3 P u m p i n g : A l l p u m p i n g w a s v i a C o l e - P a r m e r v a r i a b l e s p e e d p e r i s t a l t i c p u m p s u s i n g C o l e - P a r m e r s i l i c o n e t u b i n g , t y p e 6 4 1 1 . T h e p u m p s p e e d s w e r e c o n t r o l l e d b y C o l e - P a r m e r M a s t e r f l e x C o n t r o l l e r s . 6 . 1 . 4 F l o w C o n t r o l : P u m p O N : O F F c y c l e s w e r e c o n t r o l l e d b y E a g l e S i g n a l F l e x o p a u s e T i m e r s . E a c h t i m e r a c t i v a t e d t w o e l e c t r i c a l c i r c u i t s a l l o w i n g t h e s i m u l t a n e o u s o p e r a t i o n o f b o t h a p u m p a n d a m i x e r . 6 . 1 . 5 F e e d P u m p : T h i s p u m p t r a n s f e r r e d r a w s e w a g e f r o m t h e r e f r i g e r a t e d f e e d s t o r a g e t a n k s t o #1 b a s i n . S i m u l t a n e o u s l y w i t h p u m p o p e r a t i o n t h e s e s t o r a g e t a n k s a n d #1 b a s i n w e r e s t i r r e d . 6 . 1 . 6 M i x e d L i q u o r R e c y c l e P u m p : R e c y c l e t o o k p l a c e f r o m t h e b o t t o m c o r n e r a t t h e d i s c h a r g e e n d o f b a s i n #3 t o b a s i n # 2 . 6 . 1 . 7 S l u d g e R e c y c l e : S l u d g e w a s r e c y c l e d f r o m t h e c l a r i f i e r t o t h e #1 b a s i n . S o l e l y a s a c o n v e n i e n c e , #5 b a s i n w a s s t i r r e d o n l y d u r i n g t h e a c t i v e p h a s e o f t h i s p u m p i n g c y c l e . I n o r d e r t o m i n i m i z e s u r g e s , t h e p u m p s w e r e g e n e r a l l y r u n b e t w e e n 1 0 a n d 2 0 t i m e s p e r h o u r . -75-6 . 2 B a t c h R e a c t o r s B a t c h t e s t s w e r e c o n d u c t e d i n s e p a r a t e 1 2 l i t r e p e r s p e x c y l i n d e r s w i t h m a g n e t i c s t i r r e r s . A f l o a t i n g c o v e r w a s u s e d i n d e n i t r i f i c a t i o n e x p e r i m e n t s . . D O , t e m p e r a t u r e a n d p H w e r e c o n t i n u o u s l y m o n i t o r e d . 6 . 3 F e e d A t t w o w e e k i n t e r v a l s , f r e s h u n s e t t l e d s e w a g e w a s o b t a i n e d f r o m t h e L u l u I s l a n d t r e a t m e n t p l a n t o f t h e G r e a t e r V a n c o u v e r R e g i o n a l D i s t r i c t a n d s t o r e d i n t w o s t a i n l e s s s t e e l , 5 0 g a l l o n d r u m s a t 3 ° C . T h e d r u m c o n t e n t s w e r e s t i r r e d o n l y d u r i n g t h e t i m e t h a t f e e d w a s p u m p e d t o t h e m o d e l . • T h i s f e e d w a s p a s s e d t h r o u g h a 1 / 1 6 i n c h s q u a r e m e s h a s i t l e f t t h e s t o r a g e d r u m s . O h t w o o c c a s i o n s w h e n B O D l e v e l s w e r e b e l o w 8 0 m g / L t h e f e e d w a s s p i k e d w i t h s y n t h e t i c s e w a g e . A p p e n d i x 1 s u m m a r i z e s t y p i c a l a n a l y s e s f o r t h e r a w s e w a g e a n d f o r t h e s y n t h e t i c s e w a g e . T h i s p a r t i c u l a r s o u r c e o f s e w a g e w a s c h o s e n b e c a u s e : ( i ) R e l a t i v e l y l i t t l e i n d u s t r i a l w a s t e e n t e r e d t h e s e w a g e s t r e a m . ( i i ) T h e s e w e r a g e s y s t e m i s . s e p a r a t e f r o m t h e s t o r m w a t e r s y s t e m , a n d i s r e l a t i v e l y n e w . ( i i i ) P h o s p h o r u s a n d n i t r o g e n c o n c e n t r a t i o n s w e r e h i g h e r t h a n i n s e w a g e f r o m o t h e r a v a i l a b l e s o u r c e s . ( i v ) T h e m e c h a n i c s o f s e w a g e c o l l e c t i o n w e r e r e l a t i v e l y s i m p l e . 6 . 4 S a m p l i n g a n d S a m p l e T r e a t m e n t A l l s a m p l e s w e r e g r a b s a m p l e s , t a k e n f r o m r e a c t o r b a s i n o v e r f l o w • l i n e s o r f r o m p u m p d i s c h a r g e o u t l e t s ( f e e d a n d s l u d g e r e c y c l e ) . W h e r e r e q u i r e d f o r t h e p a r t i c u l a r a n a l y s i s , s a m p l e s w e r e i m m e d i a t e l y f i l t e r e d t h r o u g h a W h a t m a n #4 p a p e r . A n a l y s i s w a s c a r r i e d o u t w i t h i n t w o h o u r s , -76-otherwise samples were stored at 3 C. With the exception of heavy metal determinations, preservatives were not used. As a general r u l e analyses were made within eight hours, with a l l samples and reagents being at room temperature. In order to minimize suspended s o l i d s interferences, a l l oxidized nitrogen determinations were made on samples f i l t e r e d through a Whatman #4 paper, i n order to eliminate problems associated with poor c l a r i f i e r performance. When large sample quantities were used, a s i g n i f i c a n t proportion of the s o l i d s retained during f i l t e r i n g was returned to the reactor. 6.5 A n a l y t i c a l and Monitoring Techniques 6.5.1 A l k a l i n i t y : The a l k a l i n i t y was measured on u n f i l t e r e d and unsettled samples, s t i r r e d magnetically, and with 0.02N sulphuric a c i d to an end point at pH 4.3. Results were reported as mg/L of CaCO^. Preliminary i n v e s t i -gation indicated a wide v a r i a t i o n between f i l t e r e d and u n f i l t e r e d : samples of both mixed l i q u o r and recycled sludge probably because of b i o l o g i c a l a c t i v i t y . Such v a r i a t i o n was not apparent with feed and e f f l u e n t samples (Appendix 2). 6.5.2 pH_: A l l pH determinations were made using a v a i l a b l e glass electrodes (eg. VANLAB 34106-022) referenced to a saturated calomel electrode (Fisher Calomel Reference Electrode 13-639-51), with readings being made on a Fisher Accumet Model 210 pH meter. C a l i b r a t i o n , before use, was made with buffer solutions of pH 7.0 and pH 4.0. -77-6.5.3 Dissolved Oxygen (DO) DO was monitored with a Yellow Springs Instrument Company Model 54A meter and a submersible probe. The probe c a l i b r a t i o n was checked weekly by using a water sample of known DO as determined by the Azide modification of the Iodometrie Method (APHA 1976). 6.5.4 Five Day Biochemical Oxygen Demand (BOD) BOD was determined according to "Standard Methods" (APHA 1976) . DO was determined using a BOD probe with an attached s t i r r e r boot. Samples were unseeded with preliminary t e s t s i n d i c a t i n g seeding-to be unnecessary. Nitrogenous oxygen demand was not suppressed. 6.5.5 Ammonia Ammonia was determined using the "Preliminary D i s t i l l a t i o n Step" and "Acidimetric T i t r a t i o n " of Standard Methods (APHA 1976) . No dechlorinating agent was used. 6.5.6 Total Kjeldahl Nitrogen (TKN) The TKN (organic nitrogen plus ammonia) was determined using Standard Methods f o r di g e s t i o n , and f o r acid i m e t r i c t i t r a t i o n using boric a c i d (APHA 1976). 6.5.7 N i t r i t e (N02~ ) N i t r i t e was determined using a Technicon Auto Analyzer II according to the methodology of Technicon I n d u s t r i a l Method 100-70w. Samples were m i c r o f i l t e r e d through a 45 micron element, d i l u t e d to the <2 mg/L range and determined i n duplicate with each p a i r separated by a d i s t i l l e d water blank. 6.5.8 Nitrate (N03~) Three methods were used f o r n i t r a t e a n a l y s i s : - 7 8 -( i ) S p e c i f i c I o n E l e c t r o d e ( i i ) U l t r a v i o l e t S p e c t r o p h o t o m e t r y ( i i i ) C a d m i u m R e d u c t i o n ( i ) S p e c i f i c I o n E l e c t r o d e A n O r i o n M o d e l 9 2 - 0 7 e l e c t r o d e w a s i n v e s t i g a t e d w i t h t h e i d e a o f i n s i t u m o n i t o r i n g o f b a s i n n i t r a t e l e v e l s . E x t e n s i v e i n i t i a l e x p e r i m e n t a t i o n w i t h r a w s e w a g e a n d w i t h m i x e d l i q u o r ( f i l t e r e d a n d u n f i l t e r e d ) p r o v e d u n s a t i s f a c t o r y b e c a u s e o f a s t e a d y d r i f t a n d t h e i n a b i l i t y t o o b t a i n r e p r o d u c i b l e r e s u l t s , e v e n w i t h s p i k e d a n d f i l t e r e d s a m p l e s . U s e o f t h e s p e c i f i c i o n e l e c t r o d e w a s a b a n d o n e d . ( i i ) U l t r a v i o l e t S p e c t r o p h o t o m e t r y A P y e U n i c a m S P 8 - 1 0 0 U l t r a v i o l e t S p e c t r o p h o t o m e t e r w a s u s e d a c c o r d i n g t o S t a n d a r d M e t h o d s ( A P H A 1 9 7 6 ) . A f t e r f i l t r a t i o n t h r o u g h a 4 5 m i c r o n e l e m e n t , s a m p l e s w e r e a n a l y z e d a s i s , o r w h e n n e c e s s a r y , d i l u t e d t o l e s s t h a n - 3 m g / L . T h e o n l y c o r r e c t i o n m a d e w a s f o r d i s s o l v e d o r g a n i c s . ( i i i ) C a d m i u m R e d u c t i o n T h e i n s t r u m e n t a t i o n a n d m e t h o d o l o g y a r e d e s c r i b e d i n S e c t i o n 6 . 5 . 7 . T h e c h e m i s t r y i s o u t l i n e d i n S t a n d a r d M e t h o d s ( A P H A 1 9 7 6 ) . P e a k s t a b i l i t y w a s e n h a n c e d b y a d d i n g 1 0 d r o p s o f E D T A t o t h e a m m o n i u m c h l o r i d e s o l u t i o n w h i c h w a s n e u t r a l i z e d t o p H 7 . 0 b y N a O H a d d i t i o n . T h e c a d m i u m c o l u m n r e d u c e s n i t r a t e t o n i t r i t e a n d t h u s g i v e s a t o t a l o x i d i z e d n i t r o g e n r e s u l t . N i t r a t e n i t r o g e n w a s d e t e r m i n e d b y d i f f e r e n c e b e t w e e n t o t a l a n d n i t r i t e n i t r o g e n . - 7 9 -A b r i e f o u t l i n e o f p r o b l e m s a s s o c i a t e d w i t h n i t r o g e n a n a l y s i s i s i n c l u d e d i n S e c t i o n 7 . 1 2 . 6 . 5 . 9 S u s p e n d e d S o l i d s M i x e d L i q u o r S u s p e n d e d S o l i d s ( M L S S ) , f e e d s u s p e n d e d s o l i d s a n d e f f l u e n t s u s p e n d e d s o l i d s w e r e d e t e r m i n e d a s f o r " T o t a l N o n f i l t r a b l e R e s i d u e " i n S t a n d a r d M e t h o d s ( A P H A 1 9 7 6 ) , w h i l e M i x e d L i q u o r V o l a t i l e S u s p e n d e d S o l i d s ( M L V S S ) w e r e d e t e r m i n e d a s f o r " T o t a l V o l a t i l e R e s i d u e " . 6 . 5 . 1 0 T e m p e r a t u r e A m e r c u r y i n g l a s s t h e r m o m e t e r a n d a t h e r m o c o u p l e b u i l t i n t o t h e D O p r o b e ( q . v . ) w e r e u s e d t o m o n i t o r t e m p e r a t u r e . T h e r e a c t o r w a s l o c a t e d i n a t e m p e r a t u r e c o n t r o l l e d r o o m . 6 . 5 . 1 1 F l o w R a t e s F l o w r a t e s w e r e d e t e r m i n e d u s i n g a g r a d u a t e d c y l i n d e r a n d s t o p -w a t c h t o d e t e r m i n e t h e v o l u m e o f l i q u i d d e l i v e r e d p e r p u m p i n g c y c l e , a n d t h u s p e r u n i t t i m e . 6 . 5 . 1 2 L i g h t A s a g e n e r a l r u l e t h e r e a c t o r w a s o p e r a t e d i n n e a r d a r k n e s s . 6 . 5 . 1 3 S o l i d s R e t e n t i o n T i m e T h e t o t a l s y s t e m M L S S i n v e n t o r y w a s b a s e d o n t h e M L S S C o n c e n t r a -t i o n i n b a s i n #3 ( a s s u m e d t o r e p r e s e n t t h e a v e r a g e s y s t e m v a l u e ) a n d t h e k n o w n t o t a l v o l u m e o f t a n k a g e , i g n o r i n g t h e c l a r i f i e r . C o r r o b o r a t i v e t e s t w o r k i n d i c a t e d t h a t u p t o ± 1 5 % v a r i a t i o n n o r m a l l y o c c u r r e d b e t w e e n b a s i n s . D a i l y s o l i d s w a s t a g e c o n s i s t e d o f t h e e f f l u e n t s u s p e n d e d s o l i d s p l u s a n e x t r a a v e r a g e d v o l u m e t o a c c o u n t f o r s p i l l a g e , s a m p l i n g , d e l i b e r a t e w a s t a g e , l o s s e s t o s c u m a n d a n y s l u d g e r e t u r n e d t o t h e s y s t e m a f t e r a n a l y s i s . B e c a u s e o n l y t h e e f f l u e n t s o l i d s w e r e a c t i v e l y m o n i t o r e d , t h e r e p o r t e d S R T ' s f o r t h e s y s t e m a r e b e s t e s t i m a t e s . -80-6.6 Modified Bardenpho Model Operation The model was operated at four temperatures (18, 14, 10 and 6°C) over a 15 month period, which included a four month phase necessary to e s t a b l i s h an adequate SRT to allow the development of a n i t r i f y i n g sludge (Table 6.2). Hydraulic data i n c l u d i n g sludge and l i q u i d retention times, feed and recycle rates are summarized i n Table 6.3. The SRT was not a c t i v e l y c o n t r o l l e d at a s p e c i f i c value, except as necessary to ensure an adequate l e v e l for n i t r i f i c a t i o n and d e n i t r i f i c a t i o n . The reported SRT values are estimates only (Section;6.5.13). A comprehensive monitoring, sampling and a n a l y s i s programme (Table 6.4) allowed o v e r a l l system performance, n i t r i f i c a t i o n and d e n i t r i f i c a t i o n rates to be determined. Removal e f f i c i e n c i e s were determined by comparing u n f i l t e r e d feed with f i l t e r e d e f f l u e n t because of the v a r i a b l e c l a r i f i e r e f f i c i e n c y . N i t r i f i c a t i o n and . d e n i t r i f i c a t i o n rates were determined.by c a l c u l a t i o n using a " n i t r a t e " ( t o t a l oxidized nitrogen) balance i n the relevant basin over a f i n i t e time i n t e r v a l : For the purposes of these c a l c u l a t i o n s , and a l s o those f o r batch rate determinations, n i t r i t e concentrations were assumed constant and thus acted as neither a sink f o r , nor a source of oxidized nitrogen. between 1.5 and 4 mg/L except during periods of process f a i l u r e or adjustment. In basins #1, #2 and #4 the DO was l e s s than 0.2 mg/L, except during unexpected process upsets. To maintain an adequate pH buffering capacity i n the system, the feed storage drum was spiked with [6.1] Rate (mg'N'/gm MLSS/hr) Dissolved oxygen l e v e l s i n basins #3 and #5 were maintained at -81-T A B L E 6 . 2 C H R O N O L O G Y O F M O D E L T E M P E R A T U R E R E G I M E S R u n ° C P h a s e E n d E l a p s e d T i m e ( D a y s ) R e m a r k s 1 8 1 A f c 1 8 S e p t . 1 2 , 1 9 7 7 1 2 0 S t a r t u p 1 8 1 B 1 8 D e c . 1 8 0 S t a b i l i z a t i o n o f N r e m o v a l 1 8 1 C 1 8 F e b . 3 6 0 S t e a d y S t a t e 1 4 1 A 1 4 M a r c h 2 4 * 4 9 S t a b l e 1 4 ° C r u n 1 4 1 B 1 4 A p r i l 2 0 2 7 P a r t i a l r e c o v e r y a f t e r o v e r h e a t i n g 1 4 1 C 1 4 M a y 2 2 3 0 N i t r i f i c a t i o n r e t u r n i n g 1 0 1 A 1 0 J u n e 1 6 2 5 S y s t e m s t i l l r e c o v e r i n g 1 8 2 A 1 8 J u l y 1 4 2 5 S e c o n d 1 8 ° C R u n ( R e c o v e r y C o m p l e t e d ) 1 4 2 A 1 4 J u l y 2 4 9 S e c o n d 1 4 ° C R u n -- n o n . s t e a d y - s t a t e 0 6 1 A 6 A u g . 1 0 , 1 9 7 8 1 8 6 C R u n N o t e s : *~ T h e l e t t e r s A , B , C d i v i d e e a c h r u n i n t o s i g n i f i c a n t p h a s e s * O n M a r c h 2 4 , m u c h o f t h e b i o m a s s w a s a p p a r e n t l y d e s t r o y e d w h e n t h e r e a c t o r l i q u i d t e m p e r a t u r e w a s a c c i d e n t l y r a i s e d t o 6 0 ° C f o r t h r e e h o u r s . -82-TABLE 6.3 MODEL HYDRAULIC DATA AND ESTIMATED SLUDGE AGE Run Days Flow Rates (L/hr) Hours Model Reaction Basin' (Fig. 2.2) Feed MLSS Recycle Sludge Recycle Days System 1 2 3 4 5 CLA 181A 100 1-2 6-12 • 1-3 HRT SRT 20-30 2-3 H 4-6 ighly 5-8 Varis 5-8 ible 3-4 N.D. 181B 140 1.5 6.5 2.1 HRT SRT 23 15-60 3 2-7 4 3-10 7 5-18 7 5-18 3 2-8 3 N.D. 181C HRT SRT 24 50-70 3 2-7 5 4-14 7 6-19 7 6-18 3 5-8 3 N.D. 182A. 0-11 1.7 6.7 2.2 HRT SRT 24 38 2 4 5 7 8 12 6 12 3 4 2 N.D. 11-25 2.0 11.7 2.2 HRT SRT 18-22 37 2 4 4 7 6-7 11 5-7 11 1 4 2 N.D. 141A B C 0-98 1.7 6.2 2.7 HRT SRT 23 18-68 2 2-7 5 4-15 7 5-20 6 5-19 3 2-8 2 N.D. 98- . 108 HRT SRT 25 29 2 3 5 6 9 10 6 8 3 3 2 N.D. 142A 0-5 2.0 ...1.7 11.4 3.2 HRT SRT 18-23 47 2 5 3-5 10 5-7 14 5-6 13 2-3 6 2 N.D. 5-8 1.7 9.5 2.3 HRT SRT 24 73 2 7 5: 14 7 19 6-8 25 3 8 2 N.D. 101A 0-10 1.7 7.3 2.3 HRT SRT 25 • 33 2 3 5 6 8 11 6 8 3 4 2 N.D. 0-25 HRT SRT 25 40 2 4 5 8 8 13 6 11 3 4 2 N.D. 061A 0-13 1.0 5.7 1.1 HRT SRT 46 98 4 9 8 18 15 31 15 31 5 10 4 N.D. 13-18 1.9 10.7 3.4 HRT SRT 24 64 2 5 4 10 7 18 7 18 2 6 2 N.D. Notes: CLA: HRT: SRT: C l a r i f i e r N.D.: Not Determined Nominal Hydraulic Retention Time (Based on feed only) Feed [L/hr] Actual HRT = Nominal HRT x M T C ( ; , Feed + Sludge (+ MLSS) Solids Retention Time (days) - estimate only - 8 3 -T A B L E 6 . 4 F R E Q U E N C Y O F A N A L Y S I S P A R A M E T E R F R E Q U E N C Y ( T i m e s W e e k l y ) S A M P L I N G P O I N T S A l k a l i n i t y 1 - 3 m o s t P H 1 - 3 m o s t O x y g e n B O D 1 f e e d , e f f l u e n t B O D i r r e g u l a r a l l DO 3 - 4 m o s t C O D i n f r e q u e n t f e e d S u s p e n d e d S o l i d s M L S S 2 - 3 # 3 , e f f l u e n t M L S S i r r e g u l a r a l l M L V S S i n f r e q u e n t m o s t N i t r o g e n T K N 1 - 2 f e e d , e f f l u e n t T K N v a r i a b l e a l l A m m o n i a i n f r e q u e n t m o s t N i t r a t e 1 - 3 a l l N i t r i t e v a r i a b l e m o s t P h o s p h o r u s T o t a l 1 f e e d , e f f l u e n t S o l u b l e 1 m o s t T e m p e r a t u r e c o n t i n u o u s a i r t e m p e r a t u r e F l o w R a t e s . 1 - 2 a l l p u m p s N o t e : T o t a l a v a i l a b l e s a m p l i n g p o i n t s w e r e : f e e d , 5 r e a c t i o n b a s i n s , e f f l u e n t , s l u d g e r e t u r n . -84-sodium carbonate when the e f f l u e n t a l k a l i n i t y f e l l below 70 mg/L. BOD l e v e l s i n the feed were maintained at 150 mg/L or over by s t i r r i n g the feed drums to increase the feed suspended s o l i d s , or i n other instances by spiking the storage drums with an a r t i f i c i a l sewage (Appendix 1). For t h i s work, the MLSS l e v e l i n #3 basin was used to represent the average system MLSS. 6.7 Batch Tests Batch n i t r i f i c a t i o n and d e n i t r i f i c a t i o n t e s t s were made on 6 to 9 l i t r e s of mixed l i q u o r to v e r i f y the r e s u l t s of flow-through mass balance c a l c u l a t i o n s , and to ascertain the extent, i f any, of unused capacity or of substrate d e f i c i e n c y . Spikes of KNO^ were made to the batches from #2 and #4 basins, r a i s i n g the n i t r a t e l e v e l to between 15 and 30 mg/L of N. Small amounts of raw sewage were added to #2 a l i q u o t s , to provide s u f f i c i e n t external carbon source during d e n i t r i f i c a t i o n . No sewage was added to #4. The TKN l e v e l i n #3 ( n i t r i f i c a t i o n ) was ra i s e d by spiking with ammonium c h l o r i d e . In several instances, the #3 a l k a l i n i t y was raised by spiking with sodium carbonate. Usually between 15 and 30 minutes a f t e r the mixed l i q u o r t r a n s f e r to the batch reactor, a zero time sample was withdrawn f o r a n a l y s i s , followed by further samples at regular i n t e r v a l s . Batch reactors were monitored f o r between one and eight hours. In a l l cases the pH and a l k a l i n i t y were determined at zero time and at the end of a run. Nit r a t e l e v e l s were determined at measured time i n t e r v a l s . MLSS was determined i n t r i p l i c a t e at completion. During batch t e s t i n g of the contents of #3 basin, one or both of TKN and ammonia were determined at the s t a r t and f i n i s h of each run. - 8 5 -T h e t o t a l o x i d i z e d n i t r o g e n ( n i t r a t e + n i t r i t e ) w a s p l o t t e d a g a i n s t t i m e ; b y t h e m e t h o d o f l e a s t s q u a r e s , t h e l i n e o f b e s t f i t w a s d e t e r m i n e d , a s w a s t h e r e l e v a n t a v e r a g e n i t r i f i c a t i o n o r d e n i t r i f i c a t i o n r a t e ( F i g u r e 6 . 1 ) . B e c a u s e o f t h e r a n d o m v a r i a t i o n i n r a t e s d u r i n g m o s t b a t c h t e s t s , a m a x i m u m r a t e w a s a l s o d e t e r m i n e d b y u s i n g t h a t p a i r o f a d j a c e n t d a t a p o i n t s w i t h t h e g r e a t e s t v a r i a t i o n i n c o n c e n t r a t i o n p e r u n i t t i m e . F o r t h i s p u r p o s e , d a t a f r o m t h e f i r s t h o u r w a s n o t u s e d , d u e t o i t s w i d e l y s c a t t e r e d n a t u r e . A s c a n b e s e e n f r o m F i g u r e 6 . 1 t h e s l o p e o f t h e N O ^ - N r e m o v a l l i n e i s g r e a t e r t h a n t h a t o f t h e t o t a l o x i d i z e d n i t r o g e n l i n e d u e t o t h e b u i l d u p o f n i t r i t e . I n t h i s i n s t a n c e , a n d i n a l l o t h e r i n s t a n c e s w h e r e b o t h n i t r a t e a n d n i t r i t e a n a l y s e s w e r e a v a i l a b l e , i t w a s a p p a r e n t t h a t t h e u s e o f n i t r a t e d a t a a l o n e w o u l d g i v e a g r e a t e r d e n i t r i f i c a t i o n r a t e t h a n u s e o f n i t r a t e p l u s n i t r i t e d a t a . B e c a u s e t h e p u r p o s e o f d e n i t r i f i c a t i o n i s t h e t o t a l r e m o v a l o f o x i d i z e d n i t r o g e n , t h e r a t e s r e p o r t e d a r e t h o s e f o r n i t r a t e p l u s n i t r i t e . I n t h e c a s e o f n i t r i f i c a t i o n , t h e n i t r i t e p l u s n i t r a t e l i n e i s s t e e p e r t h a n t h a t f o r n i t r a t e a l o n e . I n t h i s i n s t a n c e , t h e s t e e p e r l i n e w a s u s e d b e c a u s e t h e s u b s e q u e n t d e n i t r i f i c a t i o n p r o c e s s d o e s n o t r e q u i r e t h e n i t r o g e n t o b e t o t a l l y o x i d i z e d t o n i t r a t e . W h e r e t o t a l o x i d i z e d n i t r o g e n d a t a w e r e a v a i l a b l e f r o m b o t h s p e c t r o p h o t o m e t r i c a n d c a d m i u m r e d u c t i o n a n a l y s e s , t h e c a l c u l a t e d r a t e s v a r i e d b y u p t o 1 5 % d e p e n d i n g o n t h e s o u r c e o f n i t r o g e n d a t a u s e d f o r c a l c u l a t i o n . I n d e n i t r i f i c a t i o n w o r k , t h e s p e c t r o p h o t o m e t r i c a l l y d e t e r m i n e d c o n c e n t r a t i o n d e c r e a s e d m o r e r a p i d l y a n d t h u s t h e r a t e r e p o r t e d w o u l d b e h i g h e r ( F i g u r e 6 . 1 ) . T h e c o n v e r s e a p p l i e d i n n i t r i f i c a t i o n w o r k . T h e s e o b s e r -v a t i o n s w e r e n o t u n e x p e c t e d b e c a u s e t h e a u t o a n a l y z e r r e d u c e s a l l n i t r a t e t o n i t r i t e a n d r e p o r t s t h e t o t a l N O „ + N O a s N , w h e r e a s t h e s p e c t r o p h o t o m e t e r -86-20i B A S I N # 2 MLSS = 2990 mg/L I 8 '^f~Spe c t rop ho t o m e t r ie N 0 3 - N ... \ (N0 2 +N0 3 )N E 8 Slope [mg(N02+ N0 3)N/hr] = 1.79 (By Least Squares). D e n i t r i f i c a t i o n Rate = Slope/MLSS = 1.79/2.99 = 0.98 mg (NC^ + NO^J/N/gm MLSS/hr (N0 2 : )N H o u r s FIG.6.1 B A T C H D E N I T R I F I C A T I O N , B A S I N # 2 AT I 8 ° C -87-a n a l y z e s f o r n i t r a t e o n l y , w i t h n i t r i t e b e i n g d i s c o u n t e d a s o n l y a n a d d i t i v e i n t e r f e r e n c e . W h e n a v a i l a b l e , t o t a l o x i d i z e d n i t r o g e n v a l u e s r e p o r t e d a r e d e t e r m i n e d b y c a d i u m r e d u c t i o n , u n l e s s o t h e r w i s e i n d i c a t e d . - 8 8 -C H A P T E R 7 R E S U L T S A N D D I S C U S S I O N 7 . 1 S t a r t u p O p e r a t i o n s ( P h a s e 1 8 1 A ) : I n i t i a l o p e r a t i o n b e g a n a t r o o m t e m p e r a t u r e , u s i n g r a w s e w a g e w i t h o u t r e c y c l e , u n t i l w a l l g r o w t h w a s a p p a r e n t . T h e t e m p e r a t u r e w a s t h e n l o w e r e d t o 1 8 ° C a n d r e c y c l e o f " s l u d g e " a n d " M L S S " i n i t i a t e d . T h e r e a c t o r w a l l s a n d t u b i n g w e r e b r u s h e d t o a i d i n t h e i n i t i a l M L S S b u i l d u p . A p p r o x i m a t e l y t w e l v e w e e k s w e r e n e e d e d t o a c h i e v e a n M L S S c o n c e n t r a t i o n a b o v e 5 0 0 m g / L . S h o r t l y a f t e r t h e i n s t a l l a t i o n o f a n i m p r o v e d c l a r i f i e r ( D a y 1 0 0 , F i g u r e 7 . 1 ) t h e M L S S r e a c h e d 1 0 0 0 m g / L . W i t h s t a b l e M L S S c o n c e n t r a t i o n s , g o o d D O c o n t r o l b e c a m e p o s s i b l e a n d t h e b a s i n s c o u l d b e m a i n t a i n e d a n o x i c o r a e r o b i c a s r e q u i r e d . B O D r e m o v a l r e a c h e d 9 0 % w i t h i n s i x w e e k s o f s t a r t u p . A f t e r n i n e t y d a y s , T K N c o n v e r s i o n a p p r o a c h e d 5 0 % , i n d i c a t i n g a n i n i t i a t i o n o f n i t r i f i e r b u i l d u p . A f u r t h e r t w o m o n t h s e l a p s e d b e f o r e 9 0 % c o n v e r s i o n a n d a 2 m g / L T K N c o n c e n t r a t i o n i n t h e p r o c e s s e f f l u e n t w a s o b t a i n e d ( F i g u r e 7 . 1 ) . 7 . 2 O v e r a l l S y s t e m P e r f o r m a n c e T a b l e 6 . 2 s u m m a r i z e s t h e f e e d a n d r e c y c l e r a t e s ; h y d r a u l i c a n d e s t i m a t e d s o l i d s r e t e n t i o n t i m e s u s e d i n a l l r u n s a n d t e s t s . T h e p e r c e n t a g e r e m o v a l s o f B O D , T K N a n d t o t a l N i t r o g e n , t o g e t h e r w i t h t h e e f f l u e n t q u a l i t y a r e p r e s e n t e d i n T a b l e 7 . 1 . 7 . 2 . 1 P h o s p h o r u s R e m o v a l : W h i l e t h e o v e r a l l a v e r a g e p h o s p h o r u s r e m o v a l n e v e r e x c e e d e d 8 9 % , a t e a c h t e m p e r a t u r e s t a b l e o p e r a t i n g p e r i o d s a v e r a g i n g 9 3 % r e m o v a l w e r e o b t a i n e d . Fl 6.7.1 S Y S T E M PERFORMANCE DURING STARTUP AND OPERATION AT I8°C. TABLE 7.1 OVERALL SYSTEM PERFORMANCE System Removal Percentages System Eff l u e n t Quality (mg/L) Total N TKN BOD N0 3 TKN SS Run Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range 181B 55 31-87 84 46-96 96 92-99 9.7 2.0-25.8 7.0 1.7-22.8 50 21-260 18 IC 81 65-95 95 93-98 94 87-97 5.5 0.4-10.5 2.1 1.5-2 .5 54 23-102 182A 92 83-94 96 95-97 95 84-99 2.6 1.0-6.8 1.7 1.4-2.2 49 28-80 141A 87 79-93 93 83-96 91 83-97 2.3 1.2-4.8 3 .3 1.6-7.7 78 22-110 141B No Data Available No Data Available 141C 67 62-72 70 65-73 91 87-95 1.5 0.2-1.5 13.9 12-16 101 69-142 142A 83 82-86 95 91-96 99 99 4.7 3.8-5.9 2.4 1.7-3.6 39 25-54 101A 50 48-54 53 52-56 93 85-97 1.4 0.8-2 .8 23 22-24 81 5 0-110 061A 70 61-79 80 64-87 ' 91 91 3.9 1.0-7.8 7.9 4.4-14 40 18-72 * See Table 6.2 for explanation. -91-7.2.2 BOD Removal: At a l l temperatures, the BOD removal averaged over 91% and no i n d i v i d u a l value l e s s than 83% was recorded. Under the "extended a e r a t i o n " conditions of the model,high removals would be expected. Lower values recorded are most l i k e l y due to the exertion of a nitrogenous oxygen demand i n the e f f l u e n t , as n i t r i f i c a t i o n i n h i b i t i o n was not pra c t i s e d i n the BOD t e s t s . 7.2.3 Suspended Solids Removal: From Table 7.1, i t i s apparent that the c l a r i f i e r was not capable of producing an e f f l u e n t of generally acceptable suspended s o l i d s q u a l i t y . Several f a c t o r s are suggested as major causes: (i) Scale (size) e f f e c t s ( i i ) Carry over of the "scum" present on a l l tanks (Section 7.11). ( i i i ) Dispersion of b i o f l o c s by aeration and s t i r r i n g i n the f i n a l aeration basin (Tank #5). (iv) D e n i t r i f i c a t i o n i n the c l a r i f i e r causing f l o a t i n g sludge. No r e l a t i o n s h i p between the system MLSS and the e f f l u e n t suspended s o l i d s was apparent. 7.2.4 V o l a t i l e Suspended Sol i d s : MLVSS was determined as 80% of MLSS. This f a c t o r i s used to compare rate data from t h i s work (based on MLSS) with other data based on MLVSS (eg. Figures 5.1 and 5.2). 7.2.5 Heavy Metals: A comprehensive a n a l y s i s , spanning three months i s attached as Appendix 3. Nickel ranged from 0.04 to 0.39 mg/L i n the feed and was determined at 1.4 mg/L i n the MLSS. Chromium i n the feed was 0.1 to 0.71 mg/L and 3.8 i n the MLSS. - 9 2 -7.2.6 N i t r i t e Concentrations While n i t r i t e concentrations were not monitored r e g u l a r l y , concentrations of between 1 and 3 mg/L were observed during several batch t e s t s . During periods of poor o v e r a l l n i t r i f i c a t i o n performance, n i t r i t e concentrations i n basins #3 and #5 sometimes approached the n i t r a t e l e v e l s . 7.3 Nitrogen Removal (Table 7.1) 7.3.1 18°C At 18°C,up to 98% TKN conversion and 95% t o t a l nitrogen removal was achieved. Run 18IB (Figure 7.1) This designation coincided with the period during which complete TKN conversion and nitrogen removal was being established. As a consequence,, r e l a t i v e l y low average TKN removals (84%) and t o t a l nitrogen removals (55%) are reported (Table 7.1). Run 18IC (Figure 7.1) A r b i t r a r i l y begun when both n i t r i f i c a t i o n and d e n i t r i f i c a t i o n were s a t i s f a c t o r i l y established, t h i s run exceeded 93% TKN conversion throughout. Total nitrogen removal averaged 81%, reaching a 95% maximum. Several periods with r e l a t i v e l y high n i t r a t e concentrations i n the e f f l u e n t were responsible f o r lowering the o v e r a l l nitrogen removal. These periods corresponded with low system feed BOD values (less than 90 mg/L). Run 182A (Table 7.1) During t h i s repeat run at 18°C, TKN oxidation and t o t a l nitrogen removals equal to or better than performance during 181C were achieved. Periods of low system performance again coincided with low feed BOD l e v e l s (less than 100 mg/L). -93-7.3.2 14°C At 14°C,TKN oxidation up to 96% and t o t a l nitrogen removals up to 94% were achieved. Run 141A (Figure 7.2) During t h i s run, which coincided with the period p r i o r to f a i l u r e of the system (as a r e s u l t of catastrophic overheating),, t o t a l nitrogen removal averaged 87% and TKN conversion was 93%. Several short periods of poor performance, which .lowered the averages, r e s u l t e d from mechanical f a i l u r e s i n the reactor pumping and feeding systems. Run 141B (Figure 7.2) Minimal data was c o l l e c t e d during t h i s run which was the period immediately a f t e r system f a i l u r e , i n which n i t r i f i c a t i o n d i d not occur. Run 141C (Figure 7.2) This run began when some n i t r i f i c a t i o n a b i l i t y had apparently returned to the system. The o v e r a l l performance was poor, mostly due to the slow and incomplete r e s t o r a t i o n of n i t r i f i c a t i o n . TKN concentrations i n the e f f l u e n t remained i n excess of 12 mg/L. Nitr a t e l e v e l s remained low, i n d i c a t i n g that the d e n i t r i f y i n g a b i l i t y was at l e a s t equal to the n i t r i f i c a t i o n capacity. This run was terminated before a s a t i s f a c t o r i l y n i t r i f y i n g sludge had redeveloped i n the system. Run 142A (Figure 7.3) During t h i s run, a short bridging period between operations at 18°C and at 6°C, a steady state condition was not achieved. However TKN conversions up to 96% and t o t a l nitrogen removals up to 86% were obtained; values comparable to the best obtained during run 141A. 0 10 2 0 3 0 4 0 7 0 8 0 9 0 100 110 Operat ing days FIG.7.2 O V E R A L L SYSTEM PERFORMANCE AT I4°C (RUNS 141 A , B AND C) Bas in N 0 3 - N - m g / I T K N or N 0 3 - mg/1 — OJ 4^  O OJ <r> O cn O m b b o> 0 0 1 D e n i t r i f i c a t i o n Rate N i t r i f i c a t i o n Rate mg• N.0 3 -N/g MLSS /h r . mg N 0 3 - N / g MLSS /hr . -S6-- 9 6 -7.3.3 10°C (Figure 7.4) At 10°C, TKN conversions up to 56% and t o t a l nitrogen removals up to 54% were achieved. O v e r a l l , at t h i s temperature, performance was steady but poor, p r i n c i p a l l y as a r e s u l t of an uns a t i s f a c t o r y n i t r i f y i n g a b i l i t y (apparently a legacy of i t s incomplete r e s t o r a t i o n during the.immediately preceding run, 141C). However, as was the case during 141C, the d e n i t r i f i -cation a b i l i t y was s u f f i c i e n t to maintain low e f f l u e n t n i t r a t e l e v e l s . 7.3.4 6°C (Figure 7.5) At 6°C, TKN conversion reached 8 7 % and t o t a l nitrogen removal reached 7 9 % . E f f l u e n t n i t r a t e l e v e l s were i n i t i a l l y high, as a r e s u l t of r e l a t i v e l y poor removal during the l a t e stages of run 142A'. However, the concentration f e l l with time at 6°C, due to the d e t e r i o r a t i n g n i t r i f i c a t i o n a b i l i t y of the system r e l a t i v e to d e n i t r i f i c a t i o n . From Figure 7.5, i t appears probable that the n i t r i f i c a t i o n c a p a b i l i t y was s t e a d i l y f a i l i n g and that the run was terminated before t h i s trend could be v e r i f i e d . As a consequence, the reported average e f f i c i e n c i e s are probably somewhat high. Nonetheless, the data in d i c a t e s that good nitrogen removal can be maintained f o r a s i g n i f i c a n t period of time at such a reduced mixed l i q u o r temperature. 7.4 N i t r i f i c a t i o n and D e n i t r i f i c a t i o n Rates 7.4.1 Batch n i t r i f i c a t i o n t e s t s : N i t r i f i c a t i o n rates i n basin #3 as determined from batch t e s t s are summarized i n Table 7.2. The v a r i a t i o n of these rates with temperature i s shown i n Figure 7.6. 7.4.2 N i t r i f i c a t i o n rates c a l c u l a t e d from a system flow-through  mass balance: Table 7.3 summarizes the ca l c u l a t e d n i t r i f i c a t i o n rates using basin #3, while the v a r i a t i o n with temperature i s shown i n Figure 7 . 7 . -97-S Y S T E M A T 10° C 0 5 10 15 2 0 2 5 Operating days FIG.7.4 SYSTEM PERFORMANCE AND # I BASIN DATA AT IO°C. - 9 8 -0 5 10 15 20 Opera t ing days FIG.7.5 S Y S T E M P E R F O R M A N C E A N D # 3 B A S I N DATA AT 6 ° C . -99-5 10 15 18 T e m p e r a t u r e °C FIG.7.6 BATCH NITRIFICATION RATES IN BASIN # 3. -100-TABLE 7.2 BATCH NITRIFICATION RATES IN #3 BASIN Run Day Temp °C MLSS .'TKN (sol) BOD Feed N i t r i f i c a t i o n Rate mg (N03 + N0 2 - N) /hr/gm MLSS pH Range A A l k a l i n i t y : TKN , mg/L maximum^ •average 181 220 18 2410 14.9 150 3.3* 3.3* 7.0-6.8 ND 182 6 18 3500 18.2 + 140 1.33 .87/.8*- 6.6-5.6 • 6.67 182 16 18 4020 27.2 + 2 90 147 1.03 °8.9-7.1 7.63 141 98 14 3370 47 .6 200 0.30* 0.23* 7.1-7.0 ND 141 106 14 3470 25 .2 2 00 .44/.36* .42/.32* 7 .2-6.8 ND 142 9 14 3540 19.3 + 160 1.21 1.08 °8.6-7.1 8.08 101 10 10 3290 44.3 180 .38/.19* .38/.19* 7.2-7.1 ND 101 20 10 4160 41.2 240 0.2 0.2 7 .2-7.0 ND 061 9 6 3870 25 ,0 + 140 0.29 0.29 7.3-7.0 7.43 Ammonia only Spectrophotqmetric n i t r a t e a n a l y s i s Ratio of A l k a l i n i t y consumed to Nitr a t e produced The maximum observed rate between two sampling times Not Determined I n i t i a l a l k a l i n i t y spike made - 1 0 1 -T A B L E 7 . 3 N I T R I F I C A T I O N R A T E B Y F L O W T H R O U G H M A S S B A L A N C E C A L C U L A T I O N S I N B A S I N #3 [ m g ( N O ~ + N O , ) - N / h o u r / g r a m M L S S ] R u n T e m p e r a t u r e M e a n L o w H i g h N u m b e r o f O b s e r v a t i o n s 1 8 1 A 1 8 ° C No N i t r i f i c a t i o n -1 8 1 B * 1 8 ° C 4 . 9 0 . 7 2 1 4 . 5 1 0 1 8 1 C 1 8 ° C 1 . 2 6 0 . 7 5 1 . 7 6 9 1 8 2 A 1 8 ° C 1 . 0 4 0 . 5 2 1 . 5 0 1 3 1 8 ° A v e r a g e 1 . 1 5 0 . 5 2 1 . 7 6 2 2 1 4 1 A 1 4 ° C 0 . 5 7 0 . 4 0 0 . 8 6 6 1 4 1 B 1 4 ° C N o N i t r i f i c a t i o n - • 1 4 1 C * 1 4 ° C 0 . 3 4 0 . 2 2 0 . 4 6 1 1 1 4 2 A 1 4 ° C 0 . 9 6 0 . 7 3 1 . 4 4 8 o 1 4 A v e r a g e 0 . 7 9 0 . 4 0 1 . 4 4 1 4 1 0 1 A 1 0 ° C 0 . 1 7 0 . 1 3 0 . 2 6 6 0 6 1 A 6 ° C 0 . 3 3 0 . 2 5 0 . 4 2 5 * N o t i n c l u d e d i n m e a n d u e t o u n s t a b l e o p e r a t i n g c o n d i t i o n s . -102-7.4.3 D e n i t r i f i c a t i o n rates c a l c u l a t e d from a system flow-through  mass balance: In Table 7.4 the c a l c u l a t e d d e n i t r i f i c a t i o n rates for basin #1, #2 and #4 are summarized. The data f o r basin #1 have mostly been estimated by using average values f o r n i t r a t e concentrations i n the raw sewage and #1 basin overflow (which were generally very low) when actu a l n i t r a t e analyses were unavailable. Because a good c o r r e l a t i o n was found between the n i t r a t e concentration i n the system e f f l u e n t and i n the recycled sludge, the former was used to give a conservative estimate..of the n i t r a t e returning to basin #1 when no ac t u a l return sludge data was a v a i l a b l e . Figures 7.8 and 7.9 i l l u s t r a t e the v a r i a t i o n i n d e n i t r i f i c a t i o n rates with temperature. 7.4.4 Batch D e n i t r i f i c a t i o n Tests: Table 7.5 summarizes the d e n i t r i f i c a t i o n rates c a l c u l a t e d from batch t e s t s f or basins #2 and #4. In Figure 7.10, the v a r i a t i o n i n d e n i t r i f i c a t i o n rates with temperature i s shown. 7.4.5 Example Batch Rate Ca l c u l a t i o n Figure 6.1 shows a t y p i c a l v a r i a t i o n of n i t r i t e and n i t r a t e concentration with time, as observed i n a batch d e n i t r i f i c a t i o n t e s t . The accompanying c a l c u l a t i o n i l l u s t r a t e s the way i n which the batch rates were ca l c u l a t e d . 7.4.6 Individual Basin Operating Data As summarized i n Sections 7.4.2 and 7.4.3, the n i t r a t e l e v e l s were frequently monitored i n most basins and from t h i s data, plus a knowledge of basin HRT and MLSS, a mass balance was c a r r i e d out and i n d i v i d u a l n i t r i f i c a t i o n or d e n i t r i f i c a t i o n rates were c a l c u l a t e d . Some of t h i s monitoring data i s summarized i n Figures 7.3, 7.4, 7.5 and - 1 0 3 -. 1.5 JZ CO CO _l 2 I 1.0 Cf> <U M p 0.5 O CP E B A S I N # 3 Max. Observed Rate 10 T e m p e r a tu re ° C 15 18 F I G . 7 . 7 C A L C U L A T E D N I T R I F I C A T I O N R A T E I N # 3 B A S I N . ( F L O W - T H R O U G H B A S I S ) 1.5, BASIN # 4 k_ x: \ CO CO _1 s \ - 1 0 Z XJ (O 1 ° 5 X O C" E T e m p e r a t u r e P C F I G . 7 . 8 C A L C U L A T E D D E N I T R I F I C A T I O N R A T E I N # 4 B A S I N . 5 - 1 0 4 -B A S I N #1 T e m p e r a t u r e °C Tempera tu re °C FIG.7.9 CALCULATED DENITRIFICATION RATES BASIN#I AND #2. -105-l . 5 i B A S I N # 2 CO to _l ' 1.0 z T3 <U Nl i§ 0.5] X o E Max. O b s e r v e d R a t e A v e r a g e Rate —o M i n . R a t e 10 T e m p e r a t u r e ° C 18 to to B A S I N #4 1.0 CP •o | 0.5 X O CP E M a x . R a t e .x / A v e r a g e Rate x —Q>-~' M i n . R a t e 10 T e m p e r a t u r e ° C 15 8 FIG.7.10 B A T C H D E N I T R I F I C A T I O N R A T E S IN B A S I N S # 2 A N D # 4 . -106-TABLE 7.4 DENITRIFICATION RATES BY FLOW THROUGH MASS BALANCE CALCULATION [mg(NO + NO ) -N (hour/gram MLSS] Run,, #1 Basin*" #2 Basin #4 Basin Mean Low High Mean Low High Mean Low High 181A 181B* 181C 182A 18°C Mean. No l! 4.0 0.7 7.8 .0.8 0.1 1.2 0.34 <0.1 0.93 0.53 <0.1 1.2 l i t r i f i c a t i o n Occurrir 3.8 -0.4 17.8 0.54 0.15 1.09 0.92 0.55 1.52 0.73 0.15 1.52 0.65 0.17 1.96 0.61 0.32 0.95 0.42 0.26 0.54 0.52 0.26 0.95 141A 141B 14 IC* 142A 14°C Mean 0.5 0.3 1.07 Negligi] 0.43 0.35 0.45 0.87 0.48 1.16 0.70 0.3 1.16 0.44 0.31 0.68 ale N i t r i f i c a t i o n :0cc\ 0.29 0.07 0.34 0.56 0.12 0.83 0.50 0.12 0.83 0.22 0.16 0.36 i r r i n g 0.15 0.11 0.26 0.34 0.08 0.47 0.28 0.08 0.47 101A 061A 0.25 0.2 0.41 0.35 0.23 0.77 0.18 0.06 0.3 0.2 0.12 0.36 0.08 0.06 0.11 0.14 0.07 0.18 * Data not included f o r determination of mean due to lack of steady state conditions. Estimated (See Section 7.4.3) -107-TABLE 7.5 BATCH DENITRIFICATION:"RATES: BASINS #2 AND #4 Basin #2 (Wastewater- Carbon Source) Batch Day Temp °C MLSS Feed BOD D e n i t r i f i c a t i o n Rate (mg N/hour/gm MLSS) pH Range A Alk/ N0 3 (mg/L) Maximum^ Average 181 256 18 2720 80 0.63* 0.60* 7.2-7.4 5.3 182 6 18 2990 100 0:. 98/1.14* 0.60/0.72* 6.9-7.0 3.3 182 17 18 3450 230 0.79 0.77 7.1-7.2 3 .8 141 14 14 3170 190 0.82* 0.59* 6.9-8.2 2.3 141 98 14 3352 195 0.88* 0.72* 7.2-7.3 2.5 141 106 14 3210 205 0.86/1.0* 0.80/0.89* 7.1-7.2 4.0 142 9 14 3280 160 0.60 0.51 7.2-7.5 3 .9 101 17 10 3390 187 0.45 0.45 7.1-7.3 3 .5 101 23 10 3 940 200 0.71 0.60 7.1-7.2 4.9 061 9 6 3 090 140 0.27 0.18 6.9-7.0 2 .0 Basin #4 (Endogenous D e n i t r i f i c a t i o n ) 181 262 18 3780 - 0.7 9* 0.73* 7.0-7.1 5.38 182 6 18 3630 - 0.53/0.63* 0.41/0.53* 6.7-6.8 4.78 182 17 18 3670 - 0.80 0.64 7.1-7.2 3.18 141 25 14 2890 - 0.86* ' 0.56* . 6.7-6.9 2 .61 141 106 14 3210 - 0.57/0.68* 0.42/0.50* . 7.1-7.2 3 .88 142 9 14 3540 - 0.39 0.38 7.1-7.2 3.46 101 17 10 3570 - 0.30 0.30 7.1-7.3 3.84 101 23 10 3650. - 0.6 0.33 7.1 4.83 161 9 6 3440 - 0.31 0.19 6.9-7.0 4.05 Notes: * Spectrophotometry n i t r a t e a n a l y s i s used. fc The maximum observed rate between two adjacent sampling times. ^ Ratio of a l k a l i n i t y produced to n i t r a t e consumed. For the d e n i t r i f i c a t i o n rate 'N' i s N0„ pl u s NO,. -108-Figures 7.11 to 7.16 and gives an i n s i g h t into the f l u c t u a t i o n s i n basin and hence system performance. 7 .5 Summary of Results The process e f f i c i e n c i e s and rates reported i n Sections 7.2 through 7.4 are summarized below. The rates are the maximum observations taken from the pooled batch and flow through data. Process Removal E f f i c i e n c i e s (%) Temperature Total N TKN Total P BOD °C Mean Max Mean Max Mean Max Mean Max 18 92 95 95 98 87 96 95 99 14 87 93 93 96 88 97 91 99 10 50 54 53 56 89 94 93 97 6 70 79 80 87 81 93 91 91 Maximum Observed N i t r i f i c a t i o n or D e n i t r i f i c a t i o n Rates (mg oxidized N/gm MLSS/hr) Temperature °C N i t r i f i c a t ion D e n i t r i f i c a t i o n Wastewater Substrate Endogenous 18 1.52 (14.5)* 1.52 (14.5)* 0.95 (1.96)* 14 1.44 0.88 0.86 10 0.38 0.71 0.60 6 0.42 0.36 0.31 * This peak rate was observed during the establishment of n i t r i f i e r and d e n i t r i f i e r populations but not subsequently. (See Section 7.6.2) 7.6 Discussion of Model Performance 7.6.1 Reactor Startup (Phase 181A) The startup phase could have been s i g n i f i c a n t l y reduced by using an acti v a t e d sludge from a secondary treatment plant or by i n i t i a l l y using the model as a draw and f i l l reactor and growing a s u i t a b l e mixed l i q u o r on the sewage being tested. - 1 0 9 -2.0 CO CO _l 5 2 0 , CD fM X O E 20 PHASE 181 B /VNo; PHASE 181 C BASIN # 4 o—' Denitrification Rate \ BASIN # 2 Denitrification Rate A / \ ^ N 0 3 BASIN # 3 Nitrification Rate 20 10 0 20 E I 0 -o X O 20 10 0 10 140 170 2 0 0 Operat ing d a y s 2 3 0 2 6 0 FIG.7.II OPERATING DATA FOR BASINS #2,3 AND 4 AT I8°C. -110-5 0 0 0 4 5 0 0 4 0 0 0 3 5 0 0 E co CO _ l 3 0 0 0 2 5 0 0 2 0 0 0 5 0 0 I 0 0 0 I 8 ° C RUN I82A System MLSS Nitrification Rate # 3 .Denitrification Rate # 2 5 10 15 20 O p e r a t i n g day s f rom s tar tup .6 co CO I 5 I-2 I 1.0 • -X O E 0.8 0.6 25 FIG.7.12 PERFORMANCE OF BASINS #2 AND #3 AT I8°C. O p e r a t i n g day s FIG.7.13 PERFORMANCE OF BASIN #1 AND # 2 AT I4°C(RUN 141) -«=0.5 o> co — CO S i0A C c ~ 2 0.3 L B A S I N # 4 o i o • r o itrif ° 0 . 2 c CD cn Q e o . i •j o <u CO o CO or _J c o z o 1 CJ r o O Z cn Z E \ C P E 4 • i r o O 2 2 c w rS o 0.8 r -0 .4 H o I4IC 'N i t r i f i ca t ion Rate Bas in N 0 3 Denitrification Rate x-" B A S I N # 3 Basin T K N ^ ^ 14 £ E 13 £ CO < m 0 3 0 cn E 120 • z P rocess fai lure o / \ 10 co < / 0 10 20 30 40 70 Operat ing days 80 90 100 10 110 FIG 7.14 PERFORMANCE OF BASINS # 3 AND #4 AT I4°C (RUN 141 ) -113-.0 0.5 cn E l z' <V N X O 0 0.5 2.5 0 .5 B A S I N # 2 H 0 . I B A S I N # 4 H 0 . 2 i Den i t r i f i ca t ion Rate X- X* """" — o— — o — ^ " ^ Ho B A S I N # 3 Ho.25 N i t r i f i c a t i o n Rate 0.3 0.2 CO CO T3 fM X o cn E H O . 1 5 H 0 . 0 5 5 10 15 20 O p e r a t i n g days FIG.7.I50PERATING DATA FOR BASINS #2,3 AND 4 AT I0°C. -114-0 . 5 c o CO I 0.4 X J 0> .2 0 .2 X J X O CP E 0.2 R U N 06 IA B A S I N # Denitrification rate •1-N 0 3 BAS IN # 2 \ \ BAS IN # 4 2.0 I .0 4.0 cn E-X J CP IM 2.0 2 X O 4.0 2 .0 10 15 O p e r a t i n g days 20 FIG.7I6 PERFORMANCE OF BASINS # l , # 2 AND #4 AT 6°C -115-Th e presence of a more e f f i c i e n t c l a r i f i e r to provide a higher percentage of s o l i d s recycle would also have shortened the startup time. 7.6.2 Phase 181B and 181C During the establishment of the n i t r i f i e r population (181B) the observed n i t r i f i c a t i o n rates were p e r i o d i c a l l y an order of magnitude greater than any rate achieved during the subsequent 181C and 182A phases (Figure 7.11; Table 7.3). Coincident with these high r a t e s , the system e f f l u e n t TKN's were above 3 mg/L, while during the periods of lower average rates they were below 3 mg/L (Figure 7.1). This supports the theory that n i t r i f i c a t i o n rates are dependent of substrate concentra-t i o n below the 2-3 mg/L l e v e l . Even though the observed n i t r i f i c a t i o n rates were low at these smaller TKN concentrations, they were adequate to maintain the desired low TKN concentrations (Table 7.1). A batch n i t r i f i c a t i o n t e s t c a r r i e d out l a t e i n run 181C (Table 7.2) showed that the a v a i l a b l e n i t r i f i c a t i o n capacity of the mixed l i q u o r was at l e a s t three times greater than a c t u a l l y being u t i l i z e d at t h i s time (Table 7.3). Also during 181B, both d e n i t r i f i c a t i o n rates (endogenous and waste-water carbon substrate) had s i g n i f i c a n t l y higher peak values than those subsequently observed during phases 181C and 182A (Figure 7.11). However, i n t h i s instance, the lower rates were f i r m l y established as "normal", p a r t i c u l a r l y f or basin #2, while the n i t r a t e l e v e l i n the system was s t i l l excessive at 12 mg/L. At t h i s time, the BOD concentrations i n the raw sewage were quite low (<100 mg/L) and probably the d e n i t r i f i c a -t i o n rate was l i m i t e d by the shortage of r e a d i l y a v a i l a b l e short chain hydrocarbons i n basin #2. 7.6.3 Run 141A The addition of BOD spikes near the end of run 181C and e a r l y i n run 141A brought about a rapid decline i n the o v e r a l l n i t r a t e l e v e l s , -116-the concentration in the effluent being reduced to 1 mg/L and the total nitrogen removal exceeding 90% (Figure 7.2; Table 7.1). Because at this time the rates were not monitored, no conclusions can be drawn as to the effect of BOD supplementation on the denitrification rate. 7.6.4 Adequate Nitr i f i c a t i o n and Denitrification Achieved Onee.the i n i t i a l n i t r i f i e r and denit r i f i e r populations were established and an adequate external carbon source was available for denitrification, the unit reaction rates f e l l to low values, because of the conservative design of the system. Both mechanisms performed at the rates demanded by the loads imposed on them and a high level of nitrogen removal was maintained. 7.6.5 Recovery from Overheating (141B and 141C) Both BOD removal and denitrification a b i l i t y appeared relatively unaffected by the catastrophic overheating, or else recovered rapidly. However, the TKN conversion, 4 days after the event, was only 31% in contrast to the 93% average before. When run 141C was terminated two months later, the TKN removal had reached only 70% (Figure 7.2). Calculated n i t r i f i c a t i o n rates from batch tests and from flow-through data were similar, tending to show that the poor TKN conversion was due to a low n i t r i f i e r population in the sludge rather than to any substrate concentration limitations. Both of these n i t r i f i c a t i o n rates were significantly lower than the flow-through calculations made during 141A prior to overheating (Table 7.2 and 7.3). During 141C, the denitrification rates calculated from flow-through mass balances were only half those determined before "overheating" (Run 141A). However, the maximum rates calculated from batch tests during both 141C and 141A were similar, indicating the existence of unused denitrification capacity during 141C; unused because of the poor n i t r i f i c a -- 1 1 7 -t i o n p e r f o r m a n c e , c o n s e q u e n t l o w n i t r a t e l e v e l s a n d , t h u s , m i n i m a l n e e d f o r d e n i t r i f i c a t i o n ( T a b l e s 7 . 4 a n d 7 . 5 ) . 7 . 6 . 6 R u n 1 0 1 A A t 1 0 ° C , r e l a t i v e l y c o n s t a n t p e r f o r m a n c e w a s m a i n t a i n e d , p a r t i c u l a r l y w i t h r e g a r d t o T K N t r a n s f o r m a t i o n w h i c h s t a y e d f i x e d i n t h e 5 0 % t o 5 5 % r a n g e . T h e a e r o b i c b a s i n S R T a p p e a r e d a d e q u a t e t o p r e v e n t n i t r i f i e r w a s h o u t ( T a b l e s 4 . 3 a n d 6 . 2 ) . B O D c o n c e n t r a t i o n s a n d B O D : T K N r a t i o s r e m a i n e d h i g h a n d u n f a v o u r a b l e t o a n i t r i f i e r p o p u l a t i o n i n c r e a s e . T h e t w o b a t c h n i t r i f i c a t i o n t e s t s c a r r i e d o u t y i e l d e d c o n f l i c t i n g i n f o r m a t i o n . I n t h e f i r s t , t h e r a t e c a l c u l a t e d f r o m t h e b a t c h d a t a w a s 2 . 7 t i m e s g r e a t e r t h a n t h e f l o w - t h r o u g h c a l c u l a t e d r a t e o n t h e s a m e d a y , w h i l e i n t h e s e c o n d , b o t h c a l c u l a t i o n s g a v e a s i m i l a r r a t e ( T a b l e 7 . 6 ) . T h i s s e c o n d t e s t g a v e t h e e x p e c t e d r e s u l t . T h e p o o r n i t r i f i c a t i o n p e r f o r m a n c e w a s m o s t p r o b a b l y d u e t o t h e l o w n i t r i f i e r f r a c t i o n i n t h e s l u d g e , a n d n o t d u e t o a s u b s t r a t e d e f i c i e n c y . T h e f i r s t r e s u l t , h o w e v e r , s u g g e s t s a p o s s i b l e p r o b l e m w i t h p o o r T K N h y d r o l y s i s i n t h e c o n t i n u o u s r e a c t o r , a t t h e t i m e o f t e s t i n g . F r o m T a b l e 7 . 6 , i t c a n b e s e e n t h a t t h e d e n i t r i f y i n g c a p a c i t y o f t h e b i o m a s s w a s u p t o 5 . 7 t i m e s g r e a t e r i n b a t c h t e s t s t h a n w a s a c t u a l l y b e i n g u t i l i z e d i n t h e f l o w - t h r o u g h r e a c t o r . A s a c o n s e q u e n c e , n i t r a t e l e v e l s t h r o u g h o u t t h i s r u n w e r e k e p t l o w ( F i g u r e s 7 . 4 a n d 7 . 1 5 ) . 7 . 6 . 7 R u n 1 8 2 A W i t h i n o n e d a y o f r a i s i n g t h e t e m p e r a t u r e f r o m 1 0 ° C t o 1 8 ° C , t h e T K N c o n v e r s i o n r o s e f r o m 5 0 % t o 70% a n d r e a c h e d 9 5 % w i t h i n 4 d a y s . B o t h t h e n i t r i f i c a t i o n a n d d e n i t r i f i c a t i o n r a t e s i n c r e a s e d s t e a d i l y f o r t h e d u r a t i o n o f t h i s r u n ( s e e F i g u r e 7 . 1 2 ) . T h e b a t c h a n d t h e m a s s b a l a n c e T A B L E 7 . 6 R A T I O O F B A T C H R A T E T O C A L C U L A T E D F L O W - T H R O U G H M A S S B A L A N C E R A T E O N S A M E D A Y ( D A T A F R O M T A B L E S 7 . 2 T O 7 . 5 ) B a s i n #2 B a s i n #4 B a s i n #3 R u n • R a t i o N0 3 R u n R a t i o NO3 R u n R a t i o T K N M a x . A v g . M g / L M a x . A v g . M g / L M a x . A v g . M g / L 0 6 1 1 . 9 1 . 3 3 . 0 0 6 1 1 . 9 1 . 2 0 . 4 0 6 1 1 . 5 1 . 2 1 1 . 5 1 0 1 2 . 6 - 2 . 6 0 . 1 1 0 1 4 . 3 4 . 3 0 . 1 1 0 1 2 . 7 2 . 7 2 5 . 2 1 0 1 3 . 4 2 . 9 0 . 4 1 0 1 5 . 7 3 . 1 0 . 2 1 0 1 1 . 2 1 . 0 2 3 . 5 1 4 1 2 . 1 1 . 5 0 . 2 1 4 1 - 1 . 0 * 2 . 0 * 1 4 1 1 . 1 1 . 0 < 3 . 0 1 4 1 3 . 3 2 . 7 0 . 4 1 4 1 3 . 8 2 . 8 0 . 2 1 4 1 1 . 2 0 . 9 1 6 * 1 4 1 ' 2 . 3 2 . 2 0 . 2 1 4 2 0 . 9 0 . 9 2 . 0 1 4 2 1 . 4 1 . 3 1 3 * 1 4 2 0 . 8 0 . 7 3 . 7 1 8 1 0 . 9 0 . 8 1 . 1 1 8 1 2 . 7 2 . 7 2 . 0 1 8 1 0 . 8 0 . 7 0 . 8 1 8 2 1 . 8 1 . 4 0 . 5 1 8 2 2 . 2 1 . 5 2 . 0 1 8 2 1 . 6 1 . 0 0 . 7 1 8 2 2 . 0 1 . 6 0 . 3 1 8 2 1 . 4 1 . 0 •<4.0 1 8 2 0 . 5 0 . 5 , 0 . 5 N o t e s : * E s t i m a t e d M a x i m u m a n d A v e r a g e r e f e r t o t h o s e r a t e s d e t e r m i n e d i n b a t c h t e s t s ( T a b l e s 7 . 2 a n d 7 . 4 ) . -119-rates stayed i n close agreement (see Table 7.6). With the rapid increase i n n i t r i f i c a t i o n a b i l i t y , the n i t r a t e l e v e l s i n the e f f l u e n t rose appreciably, due to the rapid use of the excess d e n i t r i f y i n g capacity observed at 10°C and an apparent "lag-time" needed f o r growth of a d d i t i o n a l d e n i t r i f i e r s to respond to t h i s n i t r a t e surge. Although the feed c h a r a c t e r i s t i c s during t h i s run were more favourable to n i t r i f i e r growth than at 10°C, i t i s apparent that-there was a large d i f f e r e n c e i n the system behaviour between operation at 18°C and 10°C. Because t h i s run was not monitored during the f i r s t few days at 18°C, i t i s not possible to comment on the existence of high peak rates s i m i l a r to those achieved during 181B. Generally the rates and performance achieved confirmed those obtained during 181C. 7.6.8 Run 142A The r e s u l t s exceeded those obtained during the previous 14°C period. A good performance was expected because the detrimental e f f e c t s of overheating had been completely erased by the time of t h i s run. Because of the enhanced n i t r i f i c a t i o n performance, unlike 141C, there was no .excess d e n i t r i f i c a t i o n capacity (Table 7.6). For the duration of 142A,;a comparison of the batch and the flow-through mass balance c a l c u l a t i o n s showed no unused d e n i t r i f i c a t i o n capacity to be present and only a small excess n i t r i f i c a t i o n - capacity, probably.carrying over from 182A. 7.6.9 Run 061A During t h i s short run at 6°C, an e f f o r t was made to s t r e s s the system to the point of f a i l u r e by lowering the HRT i n each basin. Because the short duration of the run and several changes i n operating parameters allowed i n s u f f i c i e n t time to f u l l y evaluate the steady-state performance, the r e s u l t s are t e n t a t i v e , but informative. -120-Figure 7.5 shows a marked build-up i n TKN concentration i n basin #3 and i n the e f f l u e n t , together with a s l i g h t but perceptible decline i n the n i t r i f i c a t i o n r a t e. Table 7 . 6 shows the n i t r i f i c a t i o n rate c a l c u l a t e d from a batch t e s t to be s l i g h t l y higher than from a flow-through mass balance c a l c u l a t i o n ; perhaps r e s u l t i n g from ammonia being more r e a d i l y a v a i l a b l e i n the batch reactor (due to spiking) than i n the model, where, at 6°C organic nitrogen hydrolysis has slowed down. Tables 4 . 3 and 6 . 3 show that the estimated s o l i d s retention time should be s u f f i c i e n t to maintain n i t r i f i c a t i o n . The n i t r a t e concentrations f e l l from i n i t i a l l y higher values and then remained low i n d i c a t i n g the existence of an adequate d e n i t r i f i c a t i o n capacity (see Figures 7.5 and 7 . 1 6 ) . From Table 7 . 6 , adequate reserve nitrogen removal c a p a b i l i t y i s apparent. An unanswered question remains as to how the system performance would have looked at 6°C given several more weeks of operation under the high feed-rate conditions imposed s h o r t l y before shut-down. Such long-term performance at low temperature could be important under some c l i m a t i c conditions i n B r i t i s h Columbia. 7 . 7 Dependence of N i t r i f i c a t i o n and D e n i t r i f i c a t i o n Rates on Temperature In Figure 7 . 1 7 , an envelope of the maximum and minimum u n i t n i t r i f i c a t i o n rates observed i n t h i s study i s compared to the r e s u l t s of other i n v e s t i g a t i o n s i n the 4°C to 25°C temperature range. S i m i l a r l y , Figures 5 . 1 and 5.2 compare r e s u l t s f o r endogenous and waste-water carbon substrate d e n i t r i f i c a t i o n r e s p e c t i v e l y . It i s immediately apparent that the n i t r i f i c a t i o n r e s u l t s determined i n t h i s work are s i g n i f i c a n t l y lower than most data previously reported i n the l i t e r a t u r e . The endogenous d e n i t r i f i c a t i o n rates compare w e l l , but are s l i g h t l y lower while the rates using sewage substrate are s i m i l a r to some reported work, but s i g n i f i c a n t l y lower than the data of Barnard. -121-4 10 15 20 25 T e m p e r a t u r e ° C FIG .7.17 NITRIFICATION RATES » THIS WORK AND OTHERS. (See FlG.4.1 for References ). -122-An examination of the factors regarded as having s i g n i f i c a n c e i n e s t a b l i s h i n g rates may provide an explanation f o r t h i s discrepancy. 7.8 Factors P o t e n t i a l l y Influencing the Observed Unit Reaction Rates 7.8.1 Dissolved Oxygen; Only r a r e l y d i d "aerobic" DO concentrations leave the 1-4 mg/L range, or anoxic concentrations exceed 0.2 mg/L, and thus oxygen had minimal e f f e c t on the observed average u n i t r a t e s . 7.8.2 pH and A l k a l i n i t y In basin #3, the observed p H ranged between 6.5 and 7.3 over the course of the experiment, with basins #2 and #4 u s u a l l y being 0.2 to 0.3 units higher. Using Equation 4.7 and an average p H of 6.7, the n i t r i f i c a -t i o n rate at p H 6.7 would be 58% of the maximum rate at p H 7.2 (EPA 1975). Thus i n t h i s work, the low system p H has probably lowered the maximum possible n i t r i f i c a t i o n r a t e . The p H has probably had n e g l i g i b l e e f f e c t on d e n i t r i f i c a t i o n due to the adequately high values. 7.8.3 Anoxic Residence Time At no time i n t h i s work was the actual anoxic HRT d e l i b e r a t e l y maintained above three hours i n the model (see Table 6.3). Thus/...according to Section 4.3.5 n i t r i f i c a t i o n a b i l i t y should have remained unaffected. However, during batch d e n i t r i f i c a t i o n t e s t s or system malfunction, t h i s l i m i t was exceeded and may have caused some biomass m o r t a l i t y . 7.8.4 Combined Sludge As ind i c a t e d by Sutton (1978a), a combined sludge performing carbon oxidation, n i t r i f i c a t i o n and d e n i t r i f i c a t i o n operations w i l l e x h i b i t lower substrate removal rates per u n i t of biomass than a separate sludge performing only one of these operations. Where u n i t rates are being -123-compared, the type of sludge i s a major, indeed probably the most important consideration. 7.8.5 MLSS Concentration Although Christensen (1977a) showed a decrease i n u n i t d e n i t r i f i c a -t i o n rate with increased MLSS concentration, t h i s work shows no trends i n t h i s r e l a t i o n s h i p . 7.8.6 Steady-state Conditions From the l i t e r a t u r e , i t appears that one to two sludge ages a f t e r a process'change or, two weeks for a temperature change, are adequate to allow s u f f i c i e n t time f o r a system to reach steady-state (Wild 197l; Sutton 1977b). Several runs i n t h i s work f e l l short of t h i s requirement, ( i . e . 101A, 182A, 142A and 061A). 7.8.7 SRT, As indicated i n Section 5.5.3, the d e n i t r i f i c a t i o n rate decreases at higher SRT. N i t r i f i c a t i o n rates increase as the SRT increases (Sutton 1977b). Because of the f a c t that only estimated sludge ages are a v a i l a b l e i n t h i s work, i t i s not possible to comment on any r e l a t i o n s h i p between sludge age and u n i t r a t e . However, as discussed elsewhere i n t h i s chapter (Section 7.5), the SRT i n #3 basin was probably inadequate to allow adequate n i t r i f i e r growth during several runs under the conditions pre-v a i l i n g at the time (eg. runs 141C and 101A). 7.8.8 Fraction of Viable Micro-organisms A major c r i t i c i s m of most published data on u n i t n i t r i f i c a t i o n and d e n i t r i f i c a t i o n rates revolves around the choice of a parameter to quantify the v i a b l e biomass. There i s ample evidence that numerous factors (eg. sludge age, C:N r a t i o and environment) a f f e c t the f r a c t i o n and a c t i v i t y of n i t r i f i e r s i n a sludge. However, most commonly used - 1 2 4 -m e a s u r e m e n t s o f b i o m a s s ( M L V S S , M L S S ) d o n o t a d e q u a t e l y q u a n t i f y t h i s f r a c t i o n , i n d e e d t h e r e i s n e g l i g i b l e e v i d e n c e o f a n y p r a c t i c a l s y s t e m t h a t ( f o r b i o l o g i c a l w a s t e - t r e a t m e n t ) d o e s . T h u s , i n o r d e r t o c o m p a r e u n i t n i t r i f i c a t i o n r a t e s i n a r a t i o n a l w a y a l i t a n y o f o t h e r p r o c e s s v a r i a b l e s s h o u l d p r e s e n t l y b e a t t a c h e d a s q u a l i f i e r s . T h e c a s e f o r d e n i t r i f i c a t i o n i s d i f f e r e n t i n t h a t t h e p o p u l a t i o n i s m o r e d i v e r s i f i e d a n d a d a p t a b l e , w i t h a h i g h e r f r a c t i o n o f p o t e n t i a l n i t r a t e u s e r s , w h i c h a l l o w s u n i t r a t e c o m p a r i s o n s t o b e m a d e w i t h l e s s q u a l i f i c a t i o n . I n t h i s w o r k , s y s t e m S R T v a r i e d r a n d o m l y w i t h t i m e a s d i d B O D : T K N r a t i o s a n d B O D c o n c e n t r a t i o n s . M i x e d l i q u o r a n d s l u d g e f r o m s p i l l a g e , b a t c h t e s t a n d f i l t e r i n g o p e r a t i o n s , a l l w i t h i n d e t e r m i n a t e f r a c t i o n s o f v i a b l e b i o m a s s , w e r e T a l s o r e t u r n e d t o t h e s y s t e m . T h e c r i t e r i a u s e d t o q u a n t i f y t h e b i o m a s s w a s M L S S . T h e u n i t r a t e s o b s e r v e d m u s t t h e r e f o r e b e s e e n i n t h e l i g h t o f t h e s e e x p e r i m e n t a l v a r i a t i o n s a n d t h e f a c t o r s , p r e v i o u s l y d i s c u s s e d , t h a t d e t e r m i n e t h e a c t i v i t y o f t h e r e l e v a n t c o m p o n e n t s o f t h e v i a b l e b i o m a s s . 7 . 8 . 9 T o x i c i t y a n d I n h i b i t i o n N i t r i f i e r s a r e m o r e s u s c e p t i b l e t o i n h i b i t i o n t h a n d e n i t r i f i e r s , w h i c h i n t u r n a r e m o r e s e n s i t i v e t h a n c a r b o n o x i d i z e r s ( S e c t i o n 4 . 4 ) . I n t h i s w o r k p o s s i b l e s o u r c e s o f i n h i b i t o r s o r t o x i c a n t s i n c l u d e d : ( i ) C o m p o n e n t s o f t h e r a w s e w a g e ; ( i i ) P r o d u c t s o f s e w a g e o r s l u d g e b i o d e g r a d a t i o n ; ( i i i ) A n y m a t e r i a l i n c o n t a c t w i t h t h e s e w a g e o r m i x e d l i q u o r ; ( i v ) P l a n t a i r s u p p l y . W h i l e n o d a t a i s a v a i l a b l e o n ( i i ) , ( i i i ) , o r ( i v ) , a n a n a l y s i s o f f e e d a n d m i x e d l i q u o r f o r m e t a l s ( s e e A p p e n d i x 3 ) r e v e a l e d t h e f o l l o w i n g : -125-(i) A build-up of many elements i n the mixed l i q u o r ; ( i i ) The concentration of several metals i n the feed (Zn, Cu, Ni, Cr) and the mixed l i q u o r (Pb) p e r i o d i c a l l y exceeded the "threshold concentration" f o r n i t r i f i c a t i o n i n h i b i t i o n (WPCF 1977). There was, therefore, a p o t e n t i a l f o r i n h i b i t i o n of n i t r i f i c a t i o n by heavy metals, but no data are a v a i l a b l e to in d i c a t e i f i n f a c t i n h i b i t i o n occurred, or i f i t d i d not. 7.8.10 Substrate Limitations 7.8.10.1 N i t r i f i c a t i o n Both the C:N r a t i o and the TKN or ammonia concentration may influence the observed unit n i t r i f i c a t i o n r a t e . Generally, with higher C:N r a t i o s , n i t r i f i e r f r a c t i o n s are smaller, u n i t rates lower, and longer minimum sludge ages are needed to maintain a n i t r i f y i n g sludge. Through-out t h i s work, BOD:TKN r a t i o s i n the raw sewage ranged between 3:1 and 6:1, although passage through basins #1 and #2 accompanied by d i l u t i o n , oxidation, a s s i m i l a t i o n and d i s s i m i l a t i o n events probably changes t h i s r a t i o by basin #3. The r e l a t i v e l y low n i t r i f i c a t i o n rates obtained i n t h i s work r e s u l t , i n part, from the r e l a t i v e l y high C:N r a t i o s . As previously discussed, zero order n i t r i f i c a t i o n rates occur at ammonia concentrations i n excess of 2-3 mg/L. Sutton (1978a) and K e l l e r (1978) show about 2 mg/L of r e f r a c t o r y soluble TKN i n e v i t a b l y passes untransformed i n t o the process e f f l u e n t . TKN i n excess of 4 to 5 mg/L, should thus prevent substrate l i m i t a t i o n of n i t r i f i c a t i o n . For much of t h i s work at 18°C and 14°C, t h i s c r i t e r i a was not met. Table 7.6 compares the r a t i o s of n i t r i f i c a t i o n rates c a l c u l a t e d from batch t e s t s and from flow-through mass balances on the same day. Generally, where the TKN i n basin #3 exceeded 3 mg/L, t h i s r a t i o was r e l a t i v e l y close to unity, which indicates that the system i s operating close to i t s maximum -126-n i t r i f y i n g a b i l i t y . Conversely, at lower TKN concentrations, the r a t i o i s higher, probably showing a substrate shortage i n the model. The high r a t i o s at 18°C (181B and 181C) may well r e s u l t from the growth of a high n i t r i f i e r f r a c t i o n i n the mixed l i q u o r , ( r e s u l t i n g from temporary high TKN concentrations) and i t s gradual d i s s i p a t i o n once low TKN concentrations were established, thus leaving a temporary excess n i t r i f i c a t i o n capacity. The high i n i t i a l r a t i o at 10°C i s l e s s e a s i l y explained, but may be due to a temporary TKN hydrolysis i n h i b i t i o n . 7.8.10.2 D e n i t r i f i c a t i o n Using Wastewater Substrate (Basin #2) Here, one or both of n i t r a t e and wastewater carbon may be l i m i t i n g . For run 142A and generally at 18°C, the batch rates were l e s s than the ca l c u l a t e d flow-through rates, even a t low n i t r a t e concentrations i n basin #2. I t appears that while carbon substrate was c o n t i n u a l l y supplied i n the model by overflow from basin #1, the wastewater spikes in the batch t e s t were inadequate and thus these t e s t s were carbon l i m i t e d . At 10°C and f o r two runs during 141C at 14°, a l l with low reactor n i t r a t e concentrations, and a l l taken when the n i t r i f i c a t i o n performance was inadequate, the batch rates were markedly higher than those c a l c u l a t e d from the flow-through mass balances. Nitrate was most probably l i m i t i n g , in. the reactor, a'l though how much the flow-through, d e n i t r i f i c a t i o n rates could have been increased u n t i l carbon became l i m i t i n g i s not determinable. S i m i l a r l y f o r one run at 14°C, when n i t r i f i c a t i o n was good, the r a t i o , while c l o s e r to u n i t y , s t i l l showed.some d e n i t r i f y i n g capacity unused in•the. reactor model. At 6°C, with an adequate NO., l e v e l i n basin #2, the higher batch rate may be r e l a t e d to factors other than n i t r a t e or carbon substrate (eg. better DO c o n t r o l i n the batch r e a c t o r ) . - 1 2 7 -F r o m T a b l e 7 . 4 , i t c a n b e s e e n t h a t t h e u n i t d e n i t r i f i c a t i o n r a t e s i n b a s i n #1 ( c a l c u l a t e d f r o m a f l o w - t h r o u g h m a s s b a l a n c e ) , a l t h o u g h b a s e d i n s o m e i n s t a n c e s o n e s t i m a t e d d a t a ( s e e S e c t i o n 7 . 4 . 3 ) , a r e o f t e n h i g h e r t h a n i n b a s i n # 2 , e v e n t h o u g h t h e n i t r a t e c o n c e n t r a t i o n s i n #1 b a s i n w e r e g e n e r a l l y e x t r e m e l y l o w ( s e e F i g u r e s 7 . 4 , 7 . 1 4 , 7 . 1 6 ) . P o s s i b l y , i n #1 a l o w e r O . R . P . ( r e s u l t i n g f r o m s e w a g e s e p t i c i t y a n d a n a e r o b i c h y d r o -c a r b o n b r e a k d o w n i n t h a t r e a c t o r ) p r o v i d e s f o r a m o r e r a p i d d e n i t r i f i c a t i o n t h a n i n #2 w h e r e t h e O . R . P . i s r a i s e d b y t h e h i g h r a t e o f r e c y c l e f r o m b a s i n #3 o f a e r o b i c a n d n i t r i f i e d m i x e d l i q u o r . T h i s r e c y c l e w o u l d a l s o d i l u t e t h e s h o r t - c h a i n h y d r o c a r b o n c o n c e n t r a t i o n i n b a s i n # 2 . 7 . 8 . 1 0 . 3 E n d o g e n o u s D e n i t r i f i c a t i o n ( B a s i n #4) F o r e n d o g e n o u s n i t r a t e r e s p i r a t i o n , t h e b i o m a s s p r o v i d e s a n a m p l e c a r b o n s o u r c e ; o n l y n i t r a t e i s o f c o n c e r n . T h e c o n c e n t r a t i o n i n #4 b a s i n w a s u s u a l l y l e s s t h a n 2 m g / L a n d t h u s p o t e n t i a l l y l i m i t i n g . F r o m T a b l e 7 . 6 , i t c a n b e s e e n t h a t w i t h l o w s y s t e m n i t r a t e l e v e l s , b a t c h r a t e s a r e u s u a l l y m u c h h i g h e r t h a n t h o s e c a l c u l a t e d f r o m f l o w - t h r o u g h d a t a , b u t w i t h h i g h s y s t e m n i t r a t e l e v e l s i n t h e m o d e l , t h e r a t e s a r e g e n e r a l l y s i m i l a r . T h e r e i s t h u s a g o o d i n d i c a t i o n t h a t e n d o g e n o u s d e n i t r i f i c a t i o n r a t e s i n t h e f l o w -t h r o u g h s y s t e m m i g h t h a v e b e e n h i g h e r i f a h i g h e r n i t r a t e c o n c e n t r a t i o n e x i s t e d i n t h e #4 r e a c t o r ( a n d t h u s i n t h e p r o c e s s e f f l u e n t ) . 7 . 8 . 1 1 S u m m a r y o f R a t e L i m i t i n g F a c t o r s 7 . 8 . 1 1 . 1 N i t r i f i c a t i o n A s a g e n e r a l r u l e , t h e s y s t e m p e r f o r m e d w i t h t h e m a x i m u m n i t r i f i c a -t i o n r a t e p o s s i b l e , u n d e r t h e c o n d i t i o n s o f d e s i g n a n d o p e r a t i o n . T h e s u p p l e m e n t a t i o n o f p H a n d m i n i m i z a t i o n o f p o t e n t i a l t o x i c i t y p r o b l e m s m a y h a v e i n c r e a s e d t h e u n i t r a t e s t h a t w e r e o b s e r v e d . I m p r o v e d d e s i g n o f t h e e x p e r i m e n t , o p t i m i z a t i o n a n d b e t t e r p r o c e s s c o n t r o l ( e g . S R T ) i n t h e m o d e l w o u l d a l s o h a v e h a d p o s i t i v e b e n e f i t s . -128-However, the apparently superior u n i t rates reported by other i n v e s t i g a t o r s (Figures 4.1 and 7.17) are f o r peak rates i n systems using single stage n i t r i f y i n g sludges with optimum pH, low C:N r a t i o and u n i n h i b i t o r y environments. Such systems possess high f r a c t i o n s of n i t r i f i e r s and thus have a much greater p o t e n t i a l n i t r i f y i n g capacity  per u n i t weight of sludge. 7.8.11.2 Wastewater Substrate D e n i t r i f i c a t i o n Throughout most of t h i s work the d e n i t r i f i c a t i o n rate was l i m i t e d by low n i t r a t e concentrations, due to poor n i t r i f i c a t i o n performance, or to overly long anoxic H R T ' s . However, where low e f f l u e n t n i t r a t e concentra-t i o n i s the operating objective, a less than maximum d e n i t r i f i c a t i o n rate i s i n e v i t a b l e , because of t h i s r e s t r i c t i o n on the electron r e c e i v e r . In some instances at 18°C and 14°C, carbon substrate was apparently l i m i t i n g and may p o s s i b l y have been overcome by adding some raw sewage d i r e c t l y to basin #2. From Figures 5.2 and 5.3, i t i s apparent that many observations of d e n i t r i f i c a t i o n , using wastewater substrate, achieved r e s u l t s comparable to average or good endogenous rates, and t h i s work f i t t e d i n t o the same pattern. Given higher BOD l e v e l s , improved n i t r i f i c a t i o n and a process optimized f o r maximum d e n i t r i f i c a t i o n rate, the observations of Barnard (1975a) may have been approached. 7.8.11.3 Endogenous D e n i t r i f i c a t i o n Some improvement i n the endogenous rates could probably have been obtained by: (i) Maintaining higher n i t r a t e l e v e l s , but thereby s a c r i f i c i n g f i n a l e f f l u e n t q u a l i t y . ( i i ) Operating at a lower SRT i n the endogenous reactor by minimizing - 1 2 9 -t h e e n d o g e n o u s H R T i n a s y s t e m w i t h o p t i m i z e d S R T . 7 . 9 M i n i m u m S o l i d s R e s i d e n c e T i m e A n i n a d e q u a t e d a t a b a s e d o e s n o t a l l o w c o m p a r i s o n s t o b e m a d e b e t w e e n n i t r i f i c a t i o n a n d d e n i t r i f i c a t i o n r a t e s a n d S R T . H o w e v e r , f r o m T a b l e 6 . 2 i t i s p o s s i b l e t o t a b u l a t e t h e e s t i m a t e d m i n i m u m S R T ' s a t w h i c h n i t r i f i c a t i o n a n d d e n i t r i f i c a t i o n w e r e m a i n t a i n e d ( s e e T a b l e 7 . 7 ) . T A B L E 7 . 7 E S T I M A T E D M I N I M U M S O L I D S R E S I D E N C E T I M E F O R N I T R I F I C A T I O N A N D D E N I T R I F I C A T I O N T e m p e r a t u r e ( ° C ) N i t r i f i c a t i o n D e n i t r i f i c a t i o n ( W a s t e w a t e r ) D e n i t r i f i c a t i o n ( E n d o g e n o u s ) 1 8 >5 d a y s 4 d a y s >5 d a y s 1 4 > 1 0 d a y s 4 d a y s >5 d a y s 1 0 > 1 3 d a y s 6 d a y s > 1 0 d a y s 6 3 0 d a y s 1 8 d a y s > 1 8 d a y s A m i n i m u m S R T f o r d e n i t r i f i c a t i o n ( p a r t i c u l a r l y e n d o g e n o u s ) i s s e l d o m r e p o r t e d i n t h e l i t e r a t u r e , p r e s u m a b l y o n t h e a s s u m p t i o n t h a t a h e a l t h y b i o m a s s w i l l b e a b l e t o m o v e f a c u l t a t i v e l y b e t w e e n o x y g e n a n d n i t r o g e n r e s p i r a t i o n a s c i r c u m s t a n c e s d e m a n d . W i t h t h e e x c e p t i o n o f t h e r e c o r d e d v a l u e f o r 6 ° C , t h e m i n i m u m S R T ' s r e p o r t e d h e r e f o r n i t r i f i c a t i o n a g r e e w e l l w i t h t h e d a t a r e p o r t e d i n T a b l e 4 . 3 . 7 . 1 0 E f f e c t o f B a s i n #5 o n N i t r o g e n i n t h e E f f l u e n t I n t h e a e r o b i c b a s i n # 5 , a m m o n i a r e l e a s e d f r o m l y s i n g c e l l s a n d a u t o - o x i d a t i o n i n # 4 b a s i n i s o x i d i z e d t o n i t r a t e ; s o m e T K N n o t t r a n s f o r m e d i n # 3 b a s i n m a y a l s o b e r e m o v e d . A s p o i n t e d o u t b y S u t t o n -130-(1978a) :and K e l l e r (1978), between 1 and 3 mg/L of r e f r a c t o r y soluble TKN i s not removed by normal b i o l o g i c a l treatment. Such was the case here. As a general r u l e , n i t r a t e l e v e l s i n the system e f f l u e n t were increased by 0.5 to 2.0 mg/L over those leaving the endogenous d e n i t r i f i c a t i o n basin, due to the oxidation i n the f i n a l aerobic basin. In t h i s work the aerobic period i n #5 basin has been ignored i n assessing the system aerobic SRT. I t i s suggested that the long SRT i n basin #4 and the good BOD removal i n #3 r e s u l t i n s i g n i f i c a n t endogenous l o s s of both heterotrophs and n i t r i f i e r s i n basin #4 and #5. Any n i t r i f i e r growth i n #5 w i l l at best only replace these losses i n basin #4 and #5. 7.11 Scum Layer: Through most of the experiment (at a l l temperatures), a 1-2 cm thick dark scum remained on the surface of the main aerobic tank (#3). The scum was not dispersed by commercial defoamers (Dow Antifoam C) but could be removed by s t i r r i n g i t i n t o the mixed l i q u o r , when aeration was halted, or by skimming i t o f f . However, i n both instances, the scum r a p i d l y returned a f t e r resumption of aeration. Hadeed (1978) discusses "a dense and somewhat greasy and scummy laye r of deep tan to brown foam" that may i n d i c a t e an o l d or an over-oxidized sludge. Pipes (1978) indicates that "some activated sludge processes develop a p e r s i s t e n t viscous brown scum..." which coincides with the presence of large numbers of actinomycetes. Both overcame the problem by lowering the MLSS, increasing the F/M r a t i o and e f f e c t i v e l y decreasing the sludge age. Because no i n v e s t i g a t i o n was made of the scum i n t h i s instance, nothing can be s a i d about i t s influence, i f any, on nitrogen removal. I t - 1 3 1 -w a s , h o w e v e r , n o t e d t h a t t h e o n s e t o f t h e l a y e r c o i n c i d e d w i t h a n i n c r e a s e d l o a d i n g o f f i s h p a c k i n g w a s t e i n t o t h e s e w a g e s y s t e m f r o m w h i c h t h e p r o c e s s f e e d w a s o b t a i n e d . 7 . 1 2 N i t r o g e n A n a l y s i s : T h e l i t e r a t u r e o n b i o l o g i c a l n i t r i f i c a t i o n a n d d e n i t r i f i c a t i o n i n d i c a t e s a w i d e v a r i a t i o n i n t h e f o r m o f n i t r o g e n m o n i t o r e d a n d i n t h e a n a l y t i c a l t e c h n i q u e s u s e d . T h i s v a r i a t i o n , i n p a r t , r e s u l t s f r o m t h e d i f f i c u l t y o f a c h i e v i n g r a p i d a n d a c c u r a t e d e t e r m i n a t i o n s o f n i t r o g e n v a l u e s i n c o m p l e x s o l u t i o n s , e g . s e w a g e , d u e t o i n t e r f e r e n c e s a n d t o t h e m a n y n i t r o g e n c o n t a i n i n g c o n s t i t u e n t s t h a t m a y b e p r e s e n t . I n t u r n , t h e v a r i e t y o f a n a l y t i c a l t e c h n i q u e s r e f l e c t s e f f o r t s t o o v e r c o m e t h e s e p r o b l e m s . T h u s , a m o n g n u m e r o u s o t h e r f a c t o r s , i t i s i m p o r t a n t t o c o n s i d e r t h e f o r m o f n i t r o g e n a n d t h e m e t h o d o f i t s d e t e r m i n a t i o n w h e n c o m p a r i n g n i t r o g e n t r a n s f o r m a t i o n r a t e s r e p o r t e d i n t h e l i t e r a t u r e . I n t h i s w o r k , n i t r i f i c a t i o n a n d d e n i t r i f i c a t i o n r a t e s w e r e d e t e r m i n e d i n t e r m s o f t h e a p p e a r a n c e a n d d i s a p p e a r a n c e o f " n i t r a t e " - o n t h e s o m e w h a t s u s p e c t a s s u m p t i o n t h a t n i t r i t e c o n c e n t r a t i o n s w e r e n e g l i g i b l e o r a t l e a s t r e m a i n e d c o n s t a n t . D u r i n g t h e c o u r s e o f t h i s w o r k , t h e u s e o f a n i t r a t e p r o b e a n d o f c a d m i u m c o l u m n s w a s h a m p e r e d b y u n k n o w n s o l u b l e m a t e r i a l s i n t h e s e w a g e w h i c h w e r e c a p a b l e o f a f f e c t i n g t h e c a d m i u m p o w d e r a n d t h e p r o b e s e n s i n g h e a d . S p e c t r o p h o t o m e t r i c a n a l y s i s w a s a l s o h a m p e r e d b y n i t r i t e a n d o t h e r i n t e r f e r e n c e s , a n d b y t h e d e v e l o p m e n t o f c o a t i n g s o n s a m p l e c u v e t t e s . M a n y o f t h e s e a n a l y t i c a l p r o b l e m s w e r e i n t e r m i t t e n t , o f v a r y i n g a n d u n p r e d i c t a b l e e f f e c t a n d t h u s d i f f i c u l t t o e l i m i n a t e . - 1 3 2 -7 . 1 2 . 1 A l t e r n a t i v e M o n i t o r i n g W h e n d e t e r m i n i n g n i t r i f i c a t i o n r a t e s , a r e a s o n a b l e a l t e r n a t i v e m i g h t b e t o m o n i t o r s o l u b l e T K N o r a m m o n i a r e m o v a l . I t m u s t b e r e c a l l e d , h o w e v e r , t h a t : ( i ) A m m o n i a w i l l b e a s s i m i l a t e d b y g r o w i n g b i o m a s s ( i i ) A m m o n i a w i l l b e r e l e a s e d f r o m l y s i n g b i o m a s s a n d t h e n o x i d i z e d ( i i i ) I f t h e p H i s h i g h , a e r a t i o n m a y s t r i p o u t a n y f r e e a m m o n i a p r e s e n t ( i v ) A l i m i t a t i o n m a y b e i m p o s e d b y t h e s l o w o r i n c o m p l e t e h y d r o l y s i s o f T K N t o a m m o n i a ( v ) R e l a t i v e l y l a r g e s a m p l e r e q u i r e m e n t s f o r a n a l y s i s m a y u n d u l y s t r e s s s m a l l b e n c h - s c a l e r e a c t o r s . F o r d e n i t r i f i c a t i o n , p o s s i b l e a n a l y s e s a r e l i m i t e d t o n i t r a t e d i s a p p e a r a n c e o r t o d i n i t r o g e n a p p e a r a n c e . A s d i s c u s s e d i n " S t a n d a r d M e t h o d s " ( A P H A , 1 9 7 7 ) , n i t r a t e a n a l y s i s i s d i f f i c u l t a n d p r o n e t o i n t e r f e r e n c e , w h i l e t h e m o n i t o r i n g o f n i t r o g e n e v o l u t i o n i s c o m p l i c a t e d b y p r o b l e m s o f l e a k a g e , o x i d e f o r m a t i o n , s o l u b i l i t y a n d e n t r a i n m e n t , a n d b y t h e h i g h n i t r o g e n c o m p o n e n t o f t h e a i r . I n s u m m a r y , a n y p r o g r a m t o d e t e r m i n e n i t r o g e n t r a n s f o r m a t i o n r a t e s m u s t c a r e f u l l y c h o o s e t h e p a r a m e t e r s t o m o n i t o r a n d m u s t h a v e s u f f i c i e n t r e s o u r c e s a n d m a n p o w e r t o e n a b l e t h e d e v e l o p m e n t o f a s a t i s f a c t o r y a n a l y t i c a l t e c h n i q u e . T h i s p r o g r a m m e w a s h a m p e r e d b y a n i n i t i a l l a c k o f a p p r e c i a t i o n o f t h e d i f f i c u l t i e s a s s o c i a t e d w i t h n i t r o g e n a n a l y s i s a n d b y a n i n a d e q u a t e m a n p o w e r b u d g e t t o d e v e l o p t h e n e c e s s a r y t e c h n i q u e s . A s a c o n s e q u e n c e , n e i t h e r t h e c h o s e n n i t r o g e n p a r a m e t e r n o r t h e a c c u r a c y o f i t s d e t e r m i n a t i o n w e r e f u l l y o p t i m i z e d . - 1 3 3 -C H A P T E R 8 C O N C L U S I O N S A b e n c h s c a l e B a r d e n p h o r e a c t o r a v e r a g e d 9 5 % t o t a l N i t r o g e n r e m o v a l a t 1 8 ° C , 9 3 % a t 1 4 ° C , 5 4 % a t 1 0 ° C a n d 7 9 % a t 6 ° C . A v e r a g e B O D r e m o v a l s i n e x c e s s o f 9 1 % w e r e o b s e r v e d a t a l l t e m p e r a t u r e s . A v e r a g e p h o s p h o r u s r e m o v a l s e x c e e d e d 8 7 % e x c e p t f o r 8 1 % r e c o r d e d a t 6 ° C . T h e m a x i m u m u n i t n i t r i f i c a t i o n r a t e s o b s e r v e d i n t h i s w o r k w e r e 1 . 7 6 , 1 . 4 4 , 0 . 3 8 a n d 0 . 4 2 ( m g o x i d i z e d N / g m M L S S / h r ) , r e c o r d e d a t 1 8 ° C , 1 4 ° C , 1 0 ° C a n d 6 ° C . r e s p e c t i v e l y . T h e m a x i m u m u n i t r a t e s f o r w a s t e w a t e r s u b s t r a t e d e n i t r i f i c a t i o n a n d e n d o g e n o u s d e n i t r i f i c a t i o n w e r e 1 . 5 2 , 0 . 8 8 , 0 . 7 1 , 0 . 3 6 a n d 0 . 9 5 , 0 . 8 6 , 0 . 6 0 , 0 . 3 1 ( m g o x i d i z e d N / g m M L S S / h r ) a t 1 8 ° C , 1 4 ° C , 1 0 ° C a n d 6 ° C r e s p e c t i v e l y . T h e a p p a r e n t l y l o w u n i t n i t r i f i c a t i o n r a t e s r e f l e c t t h e a c t u a l o p e r a t i n g c o n d i t i o n s o f t h i s w o r k a n d o f c o m b i n e d s l u d g e n i t r i f i c a t i o n g e n e r a l l y . T h e m o s t i n f l u e n t i a l f a c t o r s i n c l u d e d : h i g h s y s t e m C : N r a t i o s ( t y p i c a l o f c o m b i n e d s l u d g e s ) , g i v i n g r i s e t o s m a l l n i t r i f i e r f r a c t i o n s i n t h e b i o m a s s ; s u b o p t i m u m s y s t e m p H ; p o s s i b l e h e a v y m e t a l i n h i b i t i o n ; t h e u n r e l i a b i l i t y o f M L S S a n d M L V S S a s a c t i v e - b i o m a s s m o n i t o r i n g p a r a m e t e r s ; a n d n o n - o p t i m i z a t i o n o f t h e s y s t e m o p e r a t i o n a n d c o n t r o l . A t s o l u b l e T K N c o n c e n t r a t i o n s b e l o w 3 t o 4 m g / L , n i t r i f i c a t i o n r a t e s b e c a m e s u b s t r a t e l i m i t e d . T h e o b s e r v e d d e n i t r i f i c a t i o n r a t e s m a y h a v e b e e n i n c r e a s e d b y s h o r t h e r H R T i n t h e a n o x i c r e a c t o r s , h i g h e r n i t r a t e c o n c e n t r a t i o n s a n d h i g h e r B O D c o n c e n t r a t i o n s i n t h e w a s t e w a t e r s u b s t r a t e d e n i t r i f i c a t i o n b a s i n ( # 2 ) . -134-Given higher BOD concentrations i n basin #2 to improve d e n i t r i f i c a -t i o n , n i t r i f i c a t i o n i n basin #3 would probably s u f f e r unless the BOD:TKN r a t i o was decreased to, or maintained at, a low value. Maintenance and co n t r o l of n i t r i f i c a t i o n poses a greater operational d i f f i c u l t y than does d e n i t r i f i c a t i o n . Carbon:Nitrogen r a t i o and sludge age are the key factors i n determining the r e l a t i v e a b i l i t y of a combined sludge to n i t r i f y and d e n i t r i f y . 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" N i t r i f i c a t i o n i n High Sludge-Age Contact S t a b i l i z a t i o n " , Journal W.P.C.F., 48(9), pp. 2183-2189. -144-A P P E N D I C E S -145-APPENDIX 1. LULU ISLAND RAW SEWAGE AND SYNTHETIC SEWAGE COMPOSITION Lulu Island Raw Sewage Component Average Composition BOD COD TKN Ammonia Ni t r a t e N i t r i t e Total Phosphorus Soluble Phosphorus A l k a l i n i t y pH 168 mg/L 43.2 mg/L <0.2 mg/L 0 mg/L 7.5 mg/L 5.6 mg/L 200 mg/L 6.5 - 8.5 Synthetic Sewage Composition Solution A NaCl 12,000 mg KC1 2,800 mg dissolved i n 1 l i t r e NaHCO 67,200 mg Solution B C a C l 2 2,800 mg i n 1 l i t r e Solution C MgS04 2,000 mg i n 1 l i t r e Solution D Nutrient Broth 10 grams i n 5 l i t r e s of feed Solution E Soap 20,000 mg i n 1 l i t r e Solution F Urea 12,000 mg i n 1 l i t r e Solution G Starch 40,000 mg i n 1 l i t r e Solution H Na 2HP0 4 10,000 mg i n 1 l i t r e Solution I A l 2 ( S 0 4 ) 18H 20 10,000 mg i n 1 l i t r e 250 mL of each so l u t i o n d i l u t e d to 5 l i t r e t o t a l gave a t h e o r e t i c a l BOD of 4000 mg/L of synthetic feed. -146-APPENDIX 2 COMPARISON OF DETERMINATIONS ON FILTERED AND UNFILTERED SAMPLES INDICATING THE SIGNIFICANT DIFFERENCES IN THE MEASURED ALKALINITY AND pH .Sample Filtered pH Alkalinity Unfiltered pH Alkalinity Feed 7.1 185 7.1 187 #1 7.2 142 7.15 186 #2 7.3 108 7.12 152 #3 7.1 84 7.0 134 #4 7.1 102 6.9 150 #5 7 .5 96 7.2 142 Effluent 7.4 96 7.2 96 Sludge 7.3 96 7.2 174 APPENDIX 3 METAL ANALYSES (mg/L) Date 10/3 7/4 21/4 21/4 21/4 21/4 5/5 19/5 16/6 M.O.P. Sample Feed Feed Feed Storage E f f l u e n t MLSS Feed Feed Feed Na 59 65 - 81 84 89 - - -K 7.7 7.3 - 7.7 6.9 36.4 - - -Fe 4.9 6.3 5.6 4.0 2.1 85 - - -Zn 0.83 0.54 0.37 ••0.42 0.32 9.64 - - - 0..08 Mg 5.19 3.94 4.7 3.97 3.86 24.4 - - -Cu 0.17 0.25 0.19 0.2 0.14 3.9 - - - 0.005 Ni 0.39 0.29 0.15 0.29 0.25 1.4 0.037 0.08 0.06 0.25 Mn 0.17 0.18 0.17 0.16 0.12 1.5 - - -Cr 0.6 0.18 0.14 0.14 0.12 3.8 0.15 o;io 0.71 0.25 Pb 0.102 0.15 0.137 0.103 0.004 2.39 - - - 0.5 A l 0.82 T..52 0.94 1.15 0.6 21.7 - - -Cd 0.005 0.008 0.004 0.005 0.003 0.120 - - -Ca 14.4 15.4 15.1 13.3 12.2 65.0 - - -Hg 0.0006 0.001 0.0014 0.0012 0.0008 0.0101 - - -NOTES: Feed r e f e r s to a sample of fresh sewage taken immediately p r i o r to cold storage. Storage r e f e r s to a sample taken from the feed l i n e to the reactor model. E f f l u e n t r e f e r s to u n f i l t e r e d e f f l u e n t from the model. MLSS re f e r s to u n f i l t e r e d mixed l i q u o r from basin #3. M.O.P. indicates the minimum threshold concentration for n i t r i f i c a t i o n i n h i b i t i o n . (WPCF, 1977) . A l l analyses were c a r r i e d out using Methods f o r Chemical Analysis of Water and Waste. USEPA Water Quality Lab, Connecticut, Ohio 1971, or modification thereof. 

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