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Combined treatment of landfill leachate and domestic sewage Raina, Sanjay 1984

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COMBINED TREATMENT OF LANDFILL LEACHATE AND DOMESTIC SEWAGE by SANJAY RAINA B. Tech., Indian Institute of Technology, Kanpur, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in FACULTY OF GRADUATE STUDIES Department of Civil Engineering We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1984 ® Sanjay Raina, 1984 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the THE UNIVERSITY OF BRITISH 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 or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Civil Engineering THE UNIVERSITY OF BRITISH C O L U M B I A 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: October. 1984 ABSTRACT Leachate generation from a sanitary landfill site often causes a serious pollution problem. Amongst the various options available to the engineer, collection and subsequent treatment of leachate is gaining wide acceptance. This study investigated the feasibility of treating leachate in combination with domestic sewage. Conventional activated-sludge units were operated at SRT's of 5, 10 and 20 days. A continuous-flow reactor and two fill-and-draw reactors, each with a reactor volume of 5 L, were operated at different organic loadings and temperatures. One fill-and-draw system was fed once a day, while the other was fed the same amount of food in two feeding operations. The organic loadings applied corresponded to sewage:leachate mixtures of 80:20 and 60:40, by volume. The temperatures studied were 22° C (average room temperature), 10° C, and 6°C. Leachate used in the experiment was collected, in one sampling, from a landfill site, while sewage was collected on a weekly basis from the U B C pilot-plant influent feed tank. The COD of the landfill leachate was 3530 mg/L, whereas the average COD of the domestic sewage was 275 m g / L The first set of steady-state runs were conducted with a sewage:leachate ratio of 80:20, corresponding to an average influent feed COD of approximately 800 mg/L. COD removal efficiency ranged from 85.7 percent to 92.8 percent, for all the conditions investigated. Settling properties of the biomass, as reflected by the effluent suspended solids and SVI, improved as the sludge age was increased from 5 days to 20 days. However, due to endogenous respiration, cell lysis occurred in all the systems during the 20-day SRT and this caused the average effluent COD to increase. The continuous-flow system experienced the largest increase in the effluent C O D since it was in an endogenous respiration state at all times. At the higher SRT's, the once-a-day system was found to be more efficient in treatment as compared to the twice-a-day system, while at the lower SRT, the reverse was true. ii T h e s e c o n d se t o f s t e a d y - s t a t e r u n s , w i t h a 6 0 : 4 0 s e w a g e : l e a c h a t e r a t i o a n d a n a v e r a g e i n f l u e n t C O D o f a p p r o x i m a t e l y 1 2 0 0 m g / L , p e r f o r m e d b e t t e r i n t e r m s o f C O D r e m o v a l e f f i c i e n c y . T h e c o n t i n u o u s - f l o w r e a c t o r p e r f o r m e d b e s t a t t h e 2 0 - d a y S R T w i t h a t r e a t m e n t e f f i c i e n c y o f 9 5 . 0 p e r c e n t . A t t h e 5 - d a y S R T , h o w e v e r , t h e o n c e - a - d a y s y s t e m p r o d u c e d t h e b e s t q u a l i t y e f f l u e n t (93 .3 p e r c e n t C O D r e m o v a l ) . T h e b i o m a s s c o n t i n u e d t o s h o w g o o d s e t t l i n g p r o p e r t i e s f o r a l l t h e c o n d i t i o n s s t u d i e d . H o w e v e r , i n t h e fill-and-draw s y s t e m s , at t h e 2 0 - d a y S R T , s l u d g e b u l k i n g w a s o b s e r v e d d u e t o the l o w F / M r a t i o s . T h i s w a s r e f l e c t e d b y t h e i n c r e a s e d S V I v a l u e s as w e l l as 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 . F r e q u e n t s l u d g e s e t t l i n g p r o b l e m s w e r e e n c o u n t e r e d a t t h e l o w e r o p e r a t i n g t e m p e r a t u r e s o f 1 0 ° C a n d 6 ° C . A d e c r e a s e i n t h e t r e a t m e n t e f f i c i e n c y , w i t h t e m p e r a t u r e , w a s c l e a r l y i n d i c a t e d f o r a l l t h r e e s y s t e m s . A t 1 0 ° C , t he c o n t i n u o u s - f l o w s y s t e m w a s l eas t e f f i c i e n t d u e t o a h i g h o r g a n i c l o a d i n g (72 .7 p e r c e n t C O D r e m o v a l ) . H o w e v e r , at 6 ° C , a l l t h r e e s y s t e m s p e r f o r m e d p o o r l y , i n d i c a t i n g s y s t e m f a i l u r e a t t h a t t e m p e r a t u r e . A e r o b i c t r e a t m e n t o f a c o m b i n e d s e w a g e : l e a c h a t e w a s t e s t r e a m w a s f o u n d t o b e f e a s i b l e , e v e n a t h i g h o r g a n i c l o a d i n g s . A d e t a i l e d s t u d y o f t h e s e t t l i n g c h a r a c t e r i s t i c s i n d i c a t e d t h a t s e t t l i n g is g o v e r n e d b y t h e f o l l o w i n g p a r a m e t e r s : f o o d / m i c r o o r g a n i s m ( F / M ) r a t i o , o r g a n i c l o a d i n g , 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 ) , a n d t e m p e r a t u r e . In t h i s s t u d y , m o s t o f t h e s t e a d y - s t a t e r u n s i n d i c a t e d a p r o p e r l y s e t t l i n g s l u d g e . i i i Tahle of Contents A B S T R A C T ii L I S T O F T A B L E S v i i L I S T O F F I G U R E S v i i i A C K N O W L E D G E M E N T x 1. I N T R O D U C T I O N 1 2. L I T E R A T U R E R E V I E W 4 2.1 C o m p o s i t i o n o f L a n d f i l l L e a c h a t e s a n d D o m e s t i c W a s t e w a t e r s 4 2.2 A e r o b i c B i o s t a b i l i z a t i o n o f L e a c h a t e 7 2.2.1 G e n e r a l P r o c e s s D e s c r i p t i o n 7 2.2.2 T r e a t m e n t S t u d i e s 10 2.2.2.1 P u r e L e a c h a t e 10 2.2.2.2 C o m b i n e d W a s t e w a t e r s 13 2.3 K i n e t i c P a r a m e t e r s 14 2.3.1 L e a c h a t e 14 2.3.2 C o m b i n e d W a s t e w a t e r s 16 2.4 F a c t o r s a f f e c t i n g A e r o b i c S t a b i l i z a t i o n 17 2.4.1 T r a c e M e t a l s 17 2.4.2 N u t r i e n t R e q u i r e m e n t s 18 2.4.3 T e m p e r a t u r e E f f e c t s 20 2.5 S y s t e m P e r f o r m a n c e 21 2.5.1 S e t t l i n g C h a r a c t e r i s t i c s 21 2.5.2 O x y g e n U p t a k e R a t e s 2 9 3. E X P E R I M E N T A L M E T H O D S A N D A N A L Y S I S 32 3.1 E x p e r i m e n t a l S e t U p .-. 32 3.1.1 R e a c t o r T y p e s 32 3.1.2 A p p a r a t u s U s e d 33 iv 3.1.3 R e a c t o r O p e r a t i o n 33 3.1.3.1 C o n t i n u o u s F l o w R e a c t o r 33 3.1.3.2 F i l l - a n d - D r a w R e a c t o r s 36 3.2 E x p e r i m e n t a l R u n s a n d S t a r t U p P r o c e d u r e s 37 3.2.1 R u n s C o n d u c t e d 37 3.2.2 S t a r t U p a n d A c c l i m a t i z a t i o n 4 0 3.3 A n a l y t i c a l P r o c e d u r e s 43 3.3.1 S o l i d s a n d C h e m i c a l O x y g e n D e m a n d 43 3.3.2 O x y g e n U p t a k e R a t e 43 3.3.3 D i s s o l v e d O x y g e n a n d p H 4 4 3.3.4 S l u d g e V o l u m e I n d e x a n d S e t t l i n g 4 4 3.3.5 T o t a l K j e l d a h l N i t r o g e n a n d T o t a l P h o s p h o r u s 4 4 3.3.6 T r a c e M e t a l s 4 5 4. R E S U L T S A N D D I S C U S S I O N 4 6 4.1 F e e d C h a r a c t e r i s t i c s 4 6 4.2 R e s u l t s f r o m t h e P r e l i m i n a r y E x p e r i m e n t 4 8 4.3 R e s u l t s f r o m t h e 8 0 : 2 0 E x p e r i m e n t a l R u n s 51 4.3.1 M i x e d - L i q u o r C h a r a c t e r i s t i c s 51 4.3.2 E f f l u e n t C h a r a c t e r i s t i c s 64 4.3.3 C o m p a r i s o n o f D i f f e r e n t R e a c t o r T y p e s 6 9 4.4 R e s u l t s f r o m t h e 6 0 : 4 0 E x p e r i m e n t a l R u n 7 9 4.4.1 M i x e d - L i q u o r C h a r a c t e r i s t i c s 7 9 4.4.2 E f f l u e n t C h a r a c t e r i s t i c s 88 4.4.3 C o m p a r i s o n o f D i f f e r e n t R e a c t o r T y p e s 93 4.5 R e s u l t s f r o m t h e C o l d T e m p e r a t u r e S t u d y 9 9 4.5.1 R e s u l t s f r o m t h e 1 0 ° C T e m p e r a t u r e R u n 9 9 4.5.2 R e s u l t s f r o m t h e 6 ° C T e m p e r a t u r e R u n 108 v 5. C O N C L U S I O N S A N D R E C O M M E N D A T I O N S 115 5.1 C O N C L U S I O N S 115 5.2 R E C O M M E N D A T I O N S 119 BIBLIOGRAPHY :. 121 vi LIST OF TABLES 2 - 1 . C o m p o s i t i o n o f T y p i c a l L e a c h a t e s 5 2 - 2 . C o m p o s i t i o n o f T y p i c a l D o m e s t i c W a s t e w a t e r .-. 8 2 - 3 . K i n e t i c P a r a m e t e r s f o r V a r i o u s L e a c h a t e s 15 2 - 4 . K i n e t i c P a r a m e t e r s f o r a P a r t i c u l a r L e a c h a t e a n d a C o m b i n e d W a s t e w a t e r 15 2- 5. C o m m o n l y O c c u r r i n g F i l a m e n t o u s O r g a n i s m s 23 3- 1. S t e a d y - S t a t e E x p e r i m e n t a l P r o g r a m 42 4 - 1. L e a c h a t e C h a r a c t e r i s t i c s 47 4 - 2 . D o m e s t i c S e w a g e C h a r a c t e r i s t i c s 47 4 - 3 . P r e l i m i n a r y E x p e r i m e n t R e s u l t s 4 9 4 - 4 . O p e r a t i o n a l C h a r a c t e r i s t i c s f o r t h e 8 0 : 2 0 E x p e r i m e n t a l R u n 5 4 4 - 5 . E f f e c t o f S R T o n S o l i d s a n d S P O U R V a l u e s f o r t h e 8 0 : 2 0 R u n 61 4 - 6 . E f f l u e n t C h a r a c t e r i s t i c s f o r t h e 8 0 : 2 0 E x p e r i m e n t a l R u n 66 4 - 7 . O p e r a t i o n a l C h a r a c t e r i s t i c s f o r t h e 6 0 : 4 0 E x p e r i m e n t a l R u n 80 4 - 8 . E f f e c t o f S R T o n S o l i d s a n d S P O U R V a l u e s f o r t h e 6 0 : 4 0 R u n 87 4 - 9 . E f f l u e n t C h a r a c t e r i s t i c s f o r t h e 6 0 : 4 0 E x p e r i m e n t a l R u n 9 0 4 - 1 0 . C h a r a c t e r i s t i c s f r o m t h e 1 0 ° C T e m p e r a t u r e R u n 102 4 - 1 1 . C h a r a c t e r i s t i c s f r o m t h e 6 ° C T e m p e r a t u r e R u n 109 vii 1.1ST O F F I G U R E S 2 - 1 . S V I as a F u n c t i o n o f T e m p e r a t u r e 28 2 - 2 . S V I as a F u n c t i o n o f S l u d g e A g e .'. 28 2 - 3 . S V I a s a F u n c t i o n o f F e e d S t r e n g t h 28 2 - 4 . O x y g e n U p t a k e R a t e V e r s u s S l u d g e A g e 3 0 2- 5. O x y g e n U p t a k e R a t e as a F u n c t i o n o f T i m e f o r S e m i b a t c h R e a c t o r s 3 0 3- 1. F i l l - a n d - D r a w S y s t e m 3 4 3 - 2 . C o n t i n u o u s F l o w S y s t e m 3 4 3- 3. S c h e m a t i c O p e r a t i o n o f a F i l l - a n d - D r a w S y s t e m 38 4 - 1. S P O U R V s T i m e f o r t h e F i l l - a n d - D r a w S y s t e m s - P r e l i m i n a r y E x p e r i m e n t 5 0 4 - 2 . S P O U R V s T i m e f o r t h e C o n t i n u o u s - F l o w S y s t e m - P r e l i m i n a r y E x p e r i m e n t 5 0 4 - 3 . V a r i a t i o n o f I n f l u e n t F e e d C O D w i t h T i m e 53 4 - 4 . F / M R a t i o V s S R T - 8 0 : 2 0 E x p e r i m e n t a l R u n 56 4 - 5 . M i x e d - L i q u o r S o l i d s - 8 0 : 2 0 E x p e r i m e n t a l R u n 58 4 - 6 . M L S S V s D a y s i n S t e a d y S ta te - 8 0 : 2 0 E x p e r i m e n t a l R u n 5 9 4 - 7 . S P O U R V s S R T - 8 0 : 2 0 E x p e r i m e n t a l R u n 62 4 - 8 . S P O U R V s D a y s i n S t e a d y S ta te - 8 0 : 2 0 E x p e r i m e n t a l R u n 63 4 - 9 . p H V s D a y s i n S t e a d y S ta te - 8 0 : 2 0 E x p e r i m e n t a l R u n 65 4 - 1 0 . E f f l u e n t C h a r a c t e r i s t i c s V s S R T - 8 0 : 2 0 E x p e r i m e n t a l R u n 67 4 - 1 1 . P e r c e n t M L V S S V s S R T - 8 0 : 2 0 E x p e r i m e n t a l R u n 71 4 - 1 2 . S P O U R V s T i m e (5 D a y s S R T ) - 8 0 : 2 0 E x p e r i m e n t a l R u n 7 2 4 - 1 3 . S P O U R V s T i m e ( 2 0 D a y s S R T ) - 8 0 : 2 0 E x p e r i m e n t a l R u n 7 4 4 - 1 4 . D . O . V s T i m e ( 2 0 D a y s S R T ) - 8 0 : 2 0 E x p e r i m e n t a l R u n 77 4 - 1 5 . F / M R a t i o V s S R T - 6 0 : 4 0 E x p e r i m e n t a l R u n '. 82 4 - 1 6 . M i x e d - L i q u o r S o l i d s - 6 0 : 4 0 E x p e r i m e n t a l R u n 84 4 - 1 7 . M L S S V s D a y s i n S t e a d y S ta te - 6 0 : 4 0 E x p e r i m e n t a l R u n 85 4 - 1 8 . S P O U R V s S R T - 6 0 : 4 0 E x p e r i m e n t a l R u n 8 9 viii 4 - 1 9 . E f f l u e n t C h a r a c t e r i s t i c s V s S R T - 6 0 : 4 0 E x p e r i m e n t a l R u n . . . . 92 4 - 2 0 . P e r c e n t M L V S S V s S R T - 6 0 : 4 0 E x p e r i m e n t a l R u n . 94 4 - 2 1 . S P O U R V s T i m e (5 D a y s S R T ) - 6 0 : 4 0 E x p e r i m e n t a l R u n 96 4 - 2 2 . S P O U R V s T i m e ( 2 0 D a y s S R T ) - 6 0 : 4 0 E x p e r i m e n t a l R u n 97 4 - 2 3 . L i q u i d T e m p e r a t u r e V s D a y s i n S t e a d y S t a t e - 1 0 ° C T e m p e r a t u r e R u n 101 4 - 2 4 . M L S S V s D a y s i n S t e a d y S ta te - 1 0 ° C T e m p e r a t u r e R u n 103 4 - 2 5 . S P O U R V s T i m e f o r t h e F i l l - a n d - D r a w S y s t e m s - 1 0 ° C T e m p e r a t u r e R u n . . . 1 0 6 4 - 2 6 . M L S S V s D a y s i n S t e a d y S ta te - 6 ° C T e m p e r a t u r e R u n I l l 4 - 2 7 . S P O U R V s T i m e f o r t h e F i l l - a n d - D r a w S y s t e m s - 6 ° C T e m p e r a t u r e R u n 113 ix A C K N O W I F D G F M F N T T h e a u t h o r s i n c e r e l y t h a n k s h i s s u p e r v i s o r , D r . D . S . M a v i n i c , f o r h i s g u i d a n c e , g e n u i n e i n t e r e s t a n d c o n s t a n t e n c o u r a g e m e n t d u r i n g t h i s s t u d y . T h e a u t h o r a l s o a c k n o w l e d g e s t h e v a l u a b l e a d v i c e a n d a s s i s t a n c e r e c e i v e d f r o m P r o f . J . W . A t w a t e r a n d D r . K J . H a l l o n v a r i o u s a s p e c t s o f t h e r e s e a r c h . M u c h a s s i s t a n c e w a s r e c e i v e d f r o m S u e J a s p e r , S u s a n L i p t a k a n d P a u l a P a r k i n s o n 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 . I w o u l d a l s o l i k e to t h a n k S a m T u r k , f e l l o w g r a d u a t e s t u d e n t , f o r h i s f r e q u e n t h e l p d u r i n g l a b o r a t o r y w o r k . F i n a n c i a l s u p p o r t f o r t h i s w o r k o r i g i n a t e d f r o m t h e N a t u r a l S c i e n c e s a n d E n g i n e e r i n g R e s e a r c h C o u n c i l o f C a n a d a . x 1. INTRODUCTION Sanitary landfills are still considered by many to be the most popular and economically viable means of solid waste disposal. They are also regarded as one of the safest methods of disposal. Leachate generation, from water seeping through the landfill can, however, often cause a serious pollution problem at the site. In order to keep the landfill environmentally safe, site selection, proper design and operation must be given special attention. The problem of leachate generation pan be handled in different ways depending on the hydrogeological characteristics of the site. In some cases it is possible to minimize leachate production at the site. This would normally require extensive sealing of the site. A clay liner is often best suited for sealing the bottom of a landfill. Use of synthetic liners is also common. A landfill designed to produce minimum leachate would be completely sealed after the filling is completed. Recirculation of the leachate is yet another means of minimizing the total volume produced. Since leachate production is usually minimal in low rainfall areas, such efforts to minimize leachate produced is very common in these particular areas. Another method of controlling pollution due to leachate is by collecting and treating the leachate produced. It is nearly impossible to completely eliminate leachate production at any site, since a landfill cannot be sealed perfectly from all sides (thereby allowing for some infiltration). Therefore, collection and subsequent treatment of leachate is gaining wide acceptance. Most landfills built today have extensive leachate collection and treatment systems. The types of treatment systems used vary from place to place and are usually site specific. The treatment methodology is also site specific. Aerobic biological treatment of most leachates has emerged as a viable means of treatment (Cook and Foree 1974, Boyle and Ham 1974, Chian and Dewalle 1977, Uloth and Mavinic 1977, Temoin and Mavinic 1978, Zapf-Gilje and Mavinic 1981). In a few cases in Germany, on site leachate treatment using oxidation ditches and aerated lagoons is being practised. Some studies (Boyle and Ham 1974) also 1 2 i n d i c a t e t h e e f f e c t i v e u s e o f a n a e r o b i c p r o c e s s e s f o r l e a c h a t e t r e a t m e n t , e s p e c i a l l y i f t h e l e a c h a t e is " y o u n g " ( i .e. h i g h B O D j / C O D r a t i o a n d h i g h o r g a n i c c o n t e n t ) . T h e u s e o f p h y s i c a l - c h e m i c a l m e t h o d s h a s b e e n f o u n d to b e r e s t r i c t e d a n d e x p e n s i v e ( C h i a n a n d D e w a l l e 1977 ) . P h y s i c a l - c h e m i c a l t r e a t m e n t p r o c e s s e s a r e m o s t e f f e c t i v e i n t r e a t i n g l e a c h a t e s f r o m s t a b i l i z e d l a n d f i l l s ( i .e . o l d l e a c h a t e ) o r i n f u t h e r r e m o v i n g o r g a n i c m a t t e r i n t h e e f f l u e n t o f b i o l o g i c a l u n i t s t r e a t i n g l e a c h a t e ( C h i a n a n d D e w a l l e 1 9 7 7 , C o o k a n d F o r e e 1 9 7 4 , W o n g a n d M a v i n i c 1982 ) . M o s t l a b o r a t o r y l e a c h a t e t r e a t m e n t s t u d i e s h a v e b e e n c o n d u c t e d b y d i l u t i n g t h e l e a c h a t e w i t h d i s t i l l e d w a t e r o r b y u s i n g r a w l e a c h a t e as t h e i n f l u e n t f e e d . H o w e v e r , l e a c h a t e t r e a t m e n t w i t h d i f f e r e n t r a t i o s o f d o m e s t i c w a s t e w a t e r h a s r e c e i v e d v e r y l i t t le a t t e n t i o n . L e a c h a t e c h a r a c t e r i s t i c s h a v e b e e n k n o w n t o v a r y a g r e a t d e a l a n d q u i t e o f t e n a l e a c h a t e is f o u n d t o b e n u t r i e n t d e f i c i e n t i n t e r m s o f e i t h e r n i t r o g e n a n d / o r p h o s p h o r u s . D o m e s t i c w a s t e w a t e r is s i g n i f i c a n t l y richer i n n u t r i e n t s a n d its c o m b i n a t i o n w i t h l e a c h a t e c o u l d r e s u l t i n a m o r e d e s i r e a b l e n u t r i e n t c o m p o s i t i o n i n t h e c o m b i n e d was t e . A l s o , d o m e s t i c w a s t e w a t e r h a s o f t e n c o n s i d e r a b l y l o w e r C O D a n d B O D 5 v a l u e s c o m p a r e d t o m o s t l e a c h a t e s a n d m i x i n g o f t h e t w o w a s t e s t r e a m s w o u l d r e s u l t i n a n e f f e c t i v e d i l u t i o n o f t h e l e a c h a t e a n d s u b s e q u e n t l y " e a s i e r " t r e a t m e n t . D i f f e r e n t t y p e s o f b i o - r e a c t o r s o p e r a t i n g u n d e r i d e n t i c a l c o n d i t i o n s c o u l d r e s u l t , h o w e v e r , i n v a r y i n g p e r f o r m a n c e e f f i c i e n c i e s . F o r e x a m p l e , fill-and-draw r e a c t o r s h a v e b e e n k n o w n to c a u s e p r o b l e m s d u e t o t h e s h o c k l o a d i n g s o n t h e s y s t e m ( Z a p f - G i l j e a n d M a v i n i c 1 9 8 2 ) . T h e r e f o r e , o p e r a t i o n o f fill-and-draw r e a c t o r s , u n d e r d i f f e r e n t o r g a n i c l o a d i n g s c o u l d r e s u l t i n a d i f f e r e n c e i n p e r f o r m a n c e e f f i c i e n c e s . T h i s d i f f e r e n c e c o u l d b e s e e n i n t e r m s o f t h e e f f l u e n t c h a r a c t e r i s t i c s o f t h e s y s t e m . F o r a fill-and-draw r e a c t o r , i n c r e a s e d o r g a n i c l o a d i n g s h a v e r e s u l t e d i n a h i g h e r c o n c e n t r a t i o n o f o r g a n i c m a t t e r i n t h e e f f l u e n t ( D a i g g e r a n d G r a d y 1 9 7 7 , Z a p f - G i l j e a n d M a v i n i c 1982 ) . 3 T h e p u r p o s e o f t h i s i n v e s t i g a t i o n w a s t o s t u d y t h e b i o l o g i c a l t r e a t a b i l i t y o f a c o m b i n e d w a s t e s t r e a m o f d o m e s t i c w a s t e w a t e r a n d l e a c h a t e , a n d t o s t u d y t h e p e r f o r m a n c e o f d i f f e r e n t r e a c t o r t y p e s . A c o n t i n u o u s f l o w r e a c t o r a n d t w o d i f f e r e n t l y f e d f i l l - a n d - d r a w r e a c t o r s w e r e o p e r a t e d a t r o o m t e m p e r a t u r e ( 2 1 - 2 3 ° C ) . T h e d i f f e r e n c e i n p e r f o r m a n c e o f t h e s e r e a c t o r s w a s s t u d i e d b y c o m p a r i n g v a r i o u s p a r a m e t e r s . T h e p a r a m e t e r s i n v e s t i g a t e d w e r e e f f l u e n t C h e m i c a l O x y g e n D e m a n d ( C O D ) , e f f l u e n t s o l i d s , o x y g e n u p t a k e r a t e s , m i x e d l i q u o r s o l i d s , S l u d g e V o l u m e I n d e x ( S V 1 ) , p H a n d t r a c e m e t a l s . A l l t h r e e r e a c t o r s w e r e s t u d i e d f o r d i f f e r e n t o r g a n i c l o a d i n g s a n d d i f f e r e n t s o l i d s r e t e n t i o n t i m e s ( a l s o c a l l e d s l u d g e age ) . T h e t h r e e s y s t e m s w e r e a l s o o p e r a t e d b r i e f l y at l o w e r t e m p e r a t u r e s , t o s t u d y t h e t e m p e r a t u r e e f f e c t s o n t h e t r e a t m e n t e f f i c i e n c i e s o f t h e r e a c t o r s . 2. LITERATURE REVIEW 2.1 COMPOSITION OF LANDFILL LEACHATES AND DOMESTIC WASTEWATERS One of the most difficult aspects of a study involving leachate treatment is attempting to define the "characteristics" of the leachate which is to be treated. Leachate characteristics vary so widely that attempts to define a typical composition must include such broad concentration ranges of the various contaminants as to be virtually meaningless for treatability studies. Composition of typical leachates are shown in Table 2.1. This composition range is the result of several investigations done in the past (Chian and Dewalle 1976). There are several known factors that contribute to the variation in leachate composition; factors like refuse characteristics, site hydrogeology, seasons, climate, height and moisture content of the refuse. These all determine the leachate quality leaving the refuse at any given site. These factors are extremely difficult to quantify due to their complexity (Boyle and Ham 1974). Age of the landfill, and thus the degree of solid waste stabilization, has a significant effect on the composition of leachate (Chian and Dewalle 1976). Other factors such as landfill geometry and interaction of leachate with its environment prior to sample collection, also contribute to the spread of data. Leachate frequently contains such high concentrations of a large variety of substances that many analytical techniques are in error because of interferences, and results are not necessarily comparable. Also, depending on the leachate flow and sampling systems, the apparent leachate quality may be changed appreciably. COD concentrations in a landfill leachate are a major concern in terms of treatment. COD concentrations may reach as high as 89,520 mg/L (Chian and Dewalle 1974). COD is an indirect measure of the total organic matter in the leachate (Sawyer and McCarty 1978). Due to their biodegradable nature, the organic compounds decrease rapidly with increasing age of the landfill (Chian and Dewalle 1976). The COD of the 4 TABLE 2-1 Composition of Typical Leachates ( Chian and Dewalle 1976 ) P a r a m e t e r R a n g e o f C o n c e n t r a t i o n s * C O D 4 0 - 8 9 , 5 2 0 B O D 5 81 - 3 3 , 3 6 0 T O C 2 5 6 - 2 8 , 0 0 0 p H 3.7 - 8.5 T o t a l S o l i d s 0 - 5 9 , 2 0 0 T o t a l D i s s o l v e d S o l i d s 5 8 4 - 4 4 , 9 0 0 T o t a l S u s p e n d e d S o l i d s 10 - 7 0 0 S p e c i f i c C o n d u c t a n c e 2 ,810 - 1 6 , 8 0 0 A l k a l i n i t y ( C a C 0 3 ) 0 - 2 0 , 8 5 0 H a r d n e s s ( C a C O , ) 0 - 2 2 , 8 0 0 T o t a l P h o s p h o r u s 0 - 1 3 0 O r t h o P h o s p h o r u s 6.5 - 85 A m m o n i a - N 0 - 1,106 N i t r a t e + N i t r i t e - N 0.2 - 10 .29 C a 6 0 - 7 ,200 C I 4.7 - 2 ,467 N a 0 - 7,70 K 28 - 3 ,770 S u l f a t e 1 - 1,558 M n 0 .09 - 125 M g 17 - 1 5 , 6 0 0 F e 0 - 2 ,820 Z n 0 - 3 7 0 C u 0 - 9.9 C d 0 .03 - 17 P b l ess t h a n 0 .10 • A l l v a l u e s i n m g / L e x c e p t p H i n p H u n i t s a n d S p e c i f i c C o n d u c t a n c e i n m i c r o m h o s / c m . 6 l e a c h a t e , t h e r e f o r e , w i l l t e n d t o d e c r e a s e w i t h t h e a g e o f t h e l a n d f i l l . T h e 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 5 ) test i s p r e d o m i n a n t l y a b i o l o g i c a l test a n d it r e f l e c t s t h e b i o d e g r a d a b i l i t y o f t h e o r g a n i c m a t t e r i n l e a c h a t e . It is , t h e r e f o r e , i n i t s e l f a d i r e c t m e a s u r e o f t h e t r e a t a b i l i t y o f l e a c h a t e b y b i o l o g i c a l p r o c e s s e s . T h e B O D 5 / C O D r a t i o d e c r e a s e s a s t h e a g e o f t h e l a n d f i l l i n c r e a s e s , t h e r e b y i n d i c a t i n g t h a t a n o l d e r l e a c h a t e is m o r e d i f f i c u l t t o t rea t b y b i o l o g i c a l p r o c e s s e s . A s s u c h , p h y s i c a l - c h e m i c a l t r e a t m e n t m a y b e t h e o n l y f e a s i b l e m e a n s . I n a n y b i o l o g i c a l p r o c e s s , a c e r t a i n B O D 5 : N : P r a t i o is r e q u i r e d f o r t r e a t a b i l i t y . F o r m u n i c i p a l w a t e w a t e r s , t h e r e c o m m e n d e d r a t i o is 1 0 0 : 5 : 1 ( M e t c a l f a n d E d d y 1972 ) . S t u d i e s d o n e b y T e m o i n a n d M a v i n i c ( 1 9 8 1 ) a n d W o n g a n d M a v i n i c ( 1 9 8 2 ) s h o w e d t h a t f o r l e a c h a t e t r e a t m e n t a 1 0 0 : 3 . 2 : 1 . 1 r a t i o is s u f f i c i e n t C h i a n a n d D e w a l l e ( 1 9 7 6 ) f o u n d t h a t t h e T o t a l K j e l d a h l N i t r o g e n ( T K N ) v a l u e s f o r l e a c h a t e r a n g e d f r o m 0 t o 1,106 m g / L . I n a r e l a t i v e l y y o u n g l a n d f i l l , t h e C O D ..is u s u a l l y v e r y h i g h a n d t h e T K N is l o w . T h i s c a n r e s u l t i n a n i t r o g e n d e f i c i e n c y i n t h e l e a c h a t e f o r a e r o b i c b i o s t a b i l i z a t i o n . H o w e v e r , f o r a n o l d l a n d f i l l , t h e C O D is l o w a n d t h e T K N is h i g h . S u c h a s i t u a t i o n c a n c a u s e p r o b l e m s i 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 is d e s i r e d , d u e t o l a c k o f a c a r b o n s o u r c e . A s t u d y c o n d u c t e d b y A t w a t e r a n d M a v i n i c ( 1 9 8 3 ) o n a l o w C O D , h i g h T K N l e a c h a t e i n d i c a t e d t h a t a c a r b o n s o u r c e is n e e d e d i n o r d e r to a c h i e v e m o r e c o m p l e t e n i t r o g e n r e m o v a l . T h e p h o s p h o r u s c o n c e n t r a t i o n s i n l e a c h a t e h a s b e e n s h o w n to v a r y f r o m 0 t o 1 3 0 m g / L . T h e l e a c h a t e u s e d i n t h e p r e s e n t i n v e s t i g a t i o n h a d v e r y l o w p h o s p h o r u s l e v e l s , 0 .18 m g / L . H o w e v e r , o n m i x i n g t h e l e a c h a t e w i t h d o m e s t i c w a s t e w a t e r , t h e p h o s p h o r u s c o n c e n t r a t i o n i n t h e c o m b i n e d f e e d w a s i n c r e a s e d t o 0 .45 m g / L . M o s t l e a c h a t e s h a v e b e e n k n o w n t o c o n t a i n h i g h m e t a l c o n c e n t r a t i o n s ( U l o t h a n d M a v i n i c 1 9 7 7 , T e m o i n a n d M a v i n i c 1 9 8 1 , A t w a t e r a n d M a v i n i c 1 9 8 3 , B o y l e a n d H a m 1 9 7 4 ) . C o n c e n t r a t i o n s o f i r o n m a y v a r y f r o m 0 to 2 ,820 m g / L ( C h i a n a n d D e w a l l e 1 9 7 6 ) . Z i n c c o u l d a l s o b e p r e s e n t i n h i g h c o n c e n t r a t i o n s , as h i g h as 3 7 0 7 m g / L . A s s u c h , t h e s e l e a c h a t e s m a y b e d i f f i c u l t t o t r e a t D o m e s t i c w a s t e w a t e r , o n t h e o t h e r h a n d , h a s b e e n s u b j e c t e d to s u c c e s s f u l b i o t r e a t m e n t f o r m a n y y e a r s . A t y p i c a l c o m p o s i t i o n o f d o m e s t i c w a s t e w a t e r , a s p r o v i d e d b y M e t c a l f a n d E d d y ( 1 9 7 2 ) , i s s h o w n i n T a b l e 2.2. A l t h o u g h t h e C O D v a l u e s f o r s e w a g e a r e c o n s i d e r a b l y l o w e r ( c o m p a r e d t o l e a c h a t e ) , s e w a g e c a n b e s i g n i f i c a n t l y r i c h e r i n p h o s p h o r u s a n d c o n t a i n a m o r e f a v o r a b l e c a r b o n : n i t r o g e n : p h o s p h o r u s r a t i o . M i x i n g t h e t w o t y p e s o f was t e , t h e r e f o r e , m i g h t p r o v e t o b e a d v a n t a g e o u s f r o m a t r e a t m e n t p o i n t o f v i e w . 2.2 AEROBIC BIOSTABILIZATION OF LEACHATE 2.2.1 G E N E R A L P R O C E S S D E S C R I P T I O N R e m o v a l o f o r g a n i c m a t e r i a l f r o m w a s t e w a t e r , b y b i o l o g i c a l o x i d a t i o n , p r o c e e d s v i a a c o n v e r s i o n o f t h e o r g a n i c w a s t e i n t o b i o m a s s , e n e r g y a n d i n e r t e n d p r o d u c t s . I n a n o r m a l a e r o b i c b i o l o g i c a l t r e a t m e n t p r o c e s s , r o u g h l y t w o t h i r d s , o n a n o x y g e n e q u i v a l e n t b a s i s , o f t h e i n f l u e n t o r g a n i c w a s t e is u s e d f o r c e l l m a s s s y n t h e s i s . T h e r e m a i n i n g o n e t h i r d is c o n v e r t e d t o e n e r g y w h i c h is t h e n u t i l i z e d f o r c e l l s y n t h e s i s a n d m a i n t e n a n c e . W h i l e t h e b a c t e r i a a r e o f p r i m a r y i m p o r t a n c e , m a n y o t h e r m i c r o o r g a n i s m s t a k e p a r t i n t h e s t a b i l i z a t i o n o f t h e o r g a n i c was t e . B i o l o g i c a l t r e a t m e n t u n i t s a r e o f t e n c o m p o s e d o f c o m p l e x , i n t e r r e l a t e d , m i x e d b i o l o g i c a l p o p u l a t i o n s , w i t h e a c h p a r t i c u l a r m i c r o o r g a n i s m i n t h e s y s t e m h a v i n g i ts o w n g r o w t h ra te . T h e p a r t i c u l a r g r o w t h r a t e d e p e n d s o n t h e f o o d a n d n u t r i e n t s a v a i l a b l e a n d o n e n v i r o n m e n t a l f a c t o r s s u c h a s t e m p e r a t u r e , p H , a n d w h e t h e r t h e s y s t e m is a e r o b i c o r a n a e r o b i c . B a c t e r i a g e n e r a l l y r e p r o d u c e b y b i n a r y fission. B a c t e r i a l g r o w t h ' p a t t e r n h a s f o u r m o r e o r l ess d i s t i n c t p h a s e s . T h e l a g p h a s e r e p r e s e n t s t h e t i m e r e q u i r e d f o r t h e o r g a n i s m s to a c c l i m a t e t o t h e i r n e w e n v i r o n m e n t . S u c h a p h a s e w o u l d b e s e e n 8 TABLE 2-2 Composition of Typical Domestic Wastewater ( Metcalf and Eddy 1972 ) P a r a m e t e r R a n g e o f C o n c e n t r a t i o n s C O D 5 0 0 B O D 5 2 0 0 T O C 2 0 0 T o t a l S o l i d s 7 0 0 T o t a l D i s s o l v e d S o l i d s 5 0 0 T o t a l S u s p e n d e d S o l i d s 2 0 0 S e t t l e a b l e S o l i d s 10 A l k a l i n i t y ( C a C 0 3 ) 1 0 0 T o t a l N i t r o g e n 4 0 A m m o n i a - N 25 t o t a l P h o s p h o r u s 10 C h l o r i d e s 5 0 • A l l v a l u e s i n m g / L . 9 i n a b a t c h o p e r a t i o n b u t n o t i n a c o n t i n u o u s o p e r a t i o n . L o g - g r o w t h p h a s e is t he p e r i o d d u r i n g w h i c h t h e c e l l s d i v i d e a t a r a t e d e t e r m i n e d b y t h e i r g e n e r a t i o n t i m e a n d t h e i r a b i l i t y t o p r o c e s s f o o d . T h i s p h a s e is c h a r a c t e r i z e d b y e x c e s s subs t r a t e a v a i l a b l e t o t h e m i c r o o r g a n i s m s . T h e s t a t i o n a r y p h a s e i n v o l v e s n o n e t g r o w t h o f t h e o r g a n i s m s ; t h e to ta l p o p u l a t i o n r e m a i n s c o n s t a n t R e a s o n s f o r t h i s p h e n o m e n a a r e (a ) t h a t t h e c e l l s h a v e e x h a u s t e d t h e s u b s t r a t e o r n u t r i e n t s n e c e s s a r y f o r g r o w t h , a n d ( b ) t h a t t h e g r o w t h o f n e w c e l l s is o f f s e t b y t h e d e a t h o f o l d ce l l s . In t h e l o g d e a t h p h a s e , t h e b a c t e r i a l d e a t h r a t e is u s u a l l y a f u n c t i o n o f t h e v i a b l e p o p u l a t i o n a n d e n v i r o n m e n t a l c h a r a c t e r i s t i c s . In s o m e c a s e s , t h e l o g d e a t h r a t e is t h e i n v e r s e o f t h e l o g g r o w t h ra te . G r o w t h p a t t e r n s c a n a l s o b e i n t e r p r e t e d i n t e r m s o f t h e v a r i a t i o n o f t h e " m a s s " o f m i c r o o r g a n i s m s w i t h t i m e . S u c h a g r o w t h p a t t e r n c o n s i s t s o f t h r e e p h a s e s : l o g g r o w t h p h a s e , d e c l i n i n g g r o w t h p h a s e , a n d t h e e n d o g e n o u s p h a s e . T h e l o g g r o w t h p h a s e ex is ts w h e n t h e s u b s t r a t e is i n excess . T h e l a t t e r t w o p h a s e s a r e c h a r a c t e r i z e d b y l i m i t a t i o n s i n t h e f o o d s u p p l y . D u r i n g t h e e n d o g e n o u s p h a s e , a p h e n o m e n a k n o w n as " l y s i s " c a n o c c u r , i n w h i c h t h e n u t r i e n t s r e m a i n i n g i n t h e d e a d c e l l s d i f f u s e o u t t o f u r n i s h t h e r e m a i n i n g ce l l s w i t h f o o d . T o e n s u r e t h a t t h e m i c r o o r g a n i s m w i l l g r o w , t h e y m u s t b e a l l o w e d t o r e m a i n i n t h e s y s t e m l o n g e n o u g h t o r e p r o d u c e . T h i s p e r i o d d e p e n d s o n t h e i r g r o w t h r a t e , w h i c h is r e l a t e d d i r e c t l y t o t h e r a t e at w h i c h t h e y m e t a b o l i z e o r u t i l i z e t h e was t e . L a w r e n c e a n d M c C a r t y ( 1 9 7 0 ) p r o p o s e d a n e m p i r i c a l k i n e t i c m o d e l , d e s c r i b i n g t h e a s s i m i l a t i o n o f s o l u b l e o r g a n i c m a t t e r . T h e r e a r e t w o b a s i c e q u a t i o n s w h i c h d e s c r i b e t h e r e l a t i o n s h i p b e t w e e n b i o l o g i c a l g r o w t h a n d s u b s t r a t e u t i l i z a t i o n . E q u a t i o n 1 d e s c r i b e s t h e r e l a t i o n s h i p b e t w e e n t h e n e t r a t e o f g r o w t h a n d ra te o f s u b s t r a t e u t i l i z a t i o n : 10 f - vf - b X (1) w h e r e = n e t g r o w t h r a t e o f m i c r o o r g a n i s m s / r e a c t o r v o l u m e , m a s s / v o l u m e - t i m e Y = g r o w t h y i e l d c o e f f i c i e n t , m a s s / m a s s d F - j — = r a t e o f s o l u b l e s u b s t r a t e u t i l i z a t i o n / v o l u m e , m a s s / v o l u m e - t i m e d t b = m i c r o o r g a n i s m d e c a y c o e f f i c i e n t , time1 X = m i c r o b i a l m a s s c o n c e n t r a t i o n , m a s s / v o l u m e M o n o d ( 1 9 4 9 ) p r o p o s e d t h a t 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 is p r o p o r t i o n a l t o b o t h t h e m i c r o o r g a n i s m c o n c e n t r a t i o n a n d t h e s u b s t r a t e c o n c e n t r a t i o n : d F _ K S X d t ~ K + S" s • (2) w h e r e K = m a x i m u m s u b s t r a t e u t i l i z a t i o n / w t o f m i c r o o r g a n i s m s , t i m e - 1 S = s u b s t r a t e c o n c e n t r a t i o n , m a s s / v o l u m e K g = h a l f - v e l o c i t y c o e f f i c i e n t ( d e f i n e d as t h e s u b s t r a t e c o n c e n t r a t i o n at w h i c h t h e s u b s t r a t e u t i l i z a t i o n r a t e is o n e - h a l f t h e m a x i m u m ) , m a s s / v o l u m e T h e s e t w o m o d e l s f o r m t h e b a s i s f o r d e s i g n a n d o p e r a t i o n o f m o s t b i o l o g i c a l t r e a t m e n t u n i t s . T h e d e s i g n o f t h e a c t i v a t e d s l u d g e p r o c e s s is a l s o b a s e d o n t h e s e m o d e l s . 2.2.2 TRFATMFNT STUDIES 2.2.2.1 P u r e L e a c h a t e 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 h a s b e e n e x t e n s i v e l y i n v o l v e d i n t h e field o f l e a c h a t e t r e a t m e n t o v e r t h e las t 10 y e a r s ( T e m o i n a n d M a v i n i c 1 9 7 8 , U l o t h a n d M a v i n i c 1 9 7 7 , Z a p f - G i l j e a n d M a v i n i c 1 9 8 1 , G r a h a m a n d M a v i n i c 1 9 7 9 , 11 W o n g a n d M a v i n i c 1 9 8 2 ) . V a r i o u s o t h e r s t u d i e s i n v o l v i n g a e r o b i c b i o l o g i c a l t r e a t m e n t o f l e a c h a t e s h a v e a l s o b e e n c o n d u c t e d ( B o y l e a n d H a m 1 9 7 4 , C o o k a n d F o r e e 1 9 7 4 , C h i a n a n d D e w a l l e 1 9 7 6 , P a l i t a n d Q a s i m 1977 ) . T h e s t u d y c o n d u c t e d b y C o o k a n d F o r e e ( 1 9 7 4 ) i n d i c a t e d t h a t a e r o b i c b i o l o g i c a l t r e a t m e n t w a s a v e r y e f f e c t i v e m e a n s o f s t a b i l i z i n g s a n i t a r y l a n d f i l l l e a c h a t e . T h e b e s t o p e r a t i o n a l c o n d i t i o n w a s a d e t e n t i o n t i m e o f 10 d a y s , w i t h a 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 ) c o n c e n t r a t i o n o f 4 , 4 0 0 m g / L . W i t h a n i n f l u e n t C O D o f 1 5 , 8 0 0 m g / L , a C O D s t a b i l i z a t i o n e f f i c i e n c y o f g r e a t e r t h a n 9 7 p e r c e n t w a s a c c o m p l i s h e d . T h e m i x e d - l i q u o r w a s c h a r a c t e r i z e d b y v e r y g o o d s e t t l i n g p r o p e r t i e s ; e f f i c i e n t n u t r i e n t r e m o v a l o f n i t r o g e n ( e f f l u e n t T K N v a l u e s as l o w as 13 m g / L ) a n d p h o s p h o r u s ( e f f l u e n t t o t a l p h o s p h o r u s as l o w as 0 .14 m g / L ) w a s a l s o a c c o m p l i s h e d . B o y l e a n d H a m ( 1 9 7 4 ) a l s o u n d e r t o o k a l e a c h a t e t r e a t m e n t s t u d y u s i n g a e r o b i c r e a c t o r s . It w a s f o u n d t h a t a e r o b i c t r e a t m e n t o f l e a c h a t e w a s p o s s i b l e , w i t h B O D 5 r e m o v a l e f f i c i e n c i e s o f m o r e t h a n 9 0 p e r c e n t O r g a n i c l o a d i n g s w e r e k e p t l o w e r t h a n 0 .48 k g B O D 5 / d a y / c u m f o r a n e f f i c i e n t p e r f o r m a n c e . F o a m i n g a n d p o o r s o l i d s - l i q u i d s s e p a r a t i o n o c c u r r e d i n t h e b e n c h - s c a l e un i t s . T h e c a u s e s f o r t h e p o o r s e t t l i n g w e r e a t t r i b u t e d t o h i g h o r g a n i c l o a d i n g s a n d h i g h f o o d / m i c r o o r g a n i s m ( F / M ) r a t i o s . C h i a n a n d D e w a l l e ( 1 9 7 7 ) f o u n d t h a t a h i g h - s t r e n g t h l e a c h a t e , w i t h a C O D o f 5 7 , 9 0 0 m g / L , c o u l d b e t r e a t e d , w i t h 93 t o 96 .8 p e r c e n t o r g a n i c m a t t e r r e m o v a l . C o m p l e t e l y m i x e d , f i l l - a n d - d r a w r e a c t o r s w i t h n o c e l l u l a r r e c y c l e , s i m u l a t i n g a e r a t e d l a g o o n s , w e r e u s e d w i t h d e t e n t i o n t i m e s v a r y i n g f r o m 7 d a y s to 85 .7 d a y s . It w a s a l s o c o n c l u d e d t h a t h i g h e r d e t e n t i o n t i m e s l e a d t o a l o w e r p h o s p h o r u s r e q u i r e m e n t . F o r t h e 3 0 d a y u n i t s , C O D : P r a t i o s o f a t l eas t 300 :1 w e r e r e q u i r e d . U n i t s w i t h r e t e n t i o n t i m e s o f 6 0 to 85 .7 d a y s c o u l d h a v e a C O D : P r a t i o as l o w as 1 5 4 0 : 1 . L o w e r r e t e n t i o n t i m e u n i t s , w i t h C O D : P r a t i o s less t h a n 12 165:1, s h o w e d a n i n c r e a s e i n e f f l u e n t o r g a n i c m a t t e r , a d e c r e a s e i n t h e b i o l o g i c a l M L V S S a n d a d e t e r i o r a t i o n o f s l u d g e s e t t l i n g ra tes . H i g h m e t a l r e m o v a l r a t e s w e r e o b s e r v e d i n a l l u n i t s f o r i r o n (>99.9%), z i n c (99.9%), c a l c i u m (99.3%) a n d m a g n e s i u m (75.9%). P a l i t a n d Q a s i m (1977) u s e d a b e n c h - s c a l e , c o n t i n u o u s - f l o w a c t i v a t e d s l u d g e u n i t f o r t r e a t i n g l e a c h a t e (365 m g / L C O D ) . It w a s c o n c l u d e d t h a t l a n d f i l l l e a c h a t e c a n b e t r e a t e d b i o l o g i c a l l y i n a n a c t i v a t e d s l u d g e p l a n t H o w e v e r , s l u d g e b u l k i n g p r o b l e m s w e r e e n c o u n t e r e d s e v e r a l t i m e s d u r i n g t h e e x p e r i m e n t a t i o n . N u t r i e n t d e f i c i e n c y i n t h e l e a c h a t e r e s u l t e d i n p o o r e r p l a n t e f f i c i e n c y . U l o t h a n d M a v i n i c (1977) f o u n d t h a t l e a c h a t e C O D r e m o v a l e f f i c i e n c i e s f r o m 96.8 t o 99.2 p e r c e n t c o u l d b e o b t a i n e d , w i t h s l u d g e a g e s f r o m 10 d a y s t o 60 d a y s , r e s p e c t i v e l y . T h e i n f l u e n t C O D c o n c e n t r a t i o n s r a n g e d b e t w e e n 44,000 m g / L a n d 52,000 m g / L . M o s t o f t h e m e t a l s i n t h e m i x e d - l i q u o r w e r e r e m o v e d b y t h e s e t t l i n g b i o l o g i c a l f l o e ; t h i s r e m o v a l w a s a i d e d b y h i g h p H a n d h i g h M L V S S c o n c e n t r a t i o n s . F o r t h e p a r t i c u l a r l e a c h a t e u s e d , a s l u d g e a g e o f at l e a s t 20 d a y s w a s r e c o m m e n d e d a n d t h e F / M r a t i o t o b e k e p t b e l o w 0.15 k g B O D j / k g M L V S S / d a y . Z a p f - G i l j e a n d M a v i n i c (1981) s t u d i e d t h e a e r o b i c b i o s t a b i l i z a t i o n o f l e a c h a t e (19,000 m g / L C O D ) a t d i f f e r e n t t e m p e r a t u r e s . R e m o v a l s b e t t e r t h a n 95 p e r c e n t f o r C O D a n d 99 p e r c e n t f o r B O D 5 w e r e a c h i e v e d f o r a l l t h e t e m p e r a t u r e s i n v e s t i g a t e d . T h e p o o r s o l i d s - l i q u i d s e p a r a t i o n o b t a i n e d t h r o u g h o u t t h e s t u d y w a s a t t r i b u t e d t o t h e s h o c k i m p o s e d b y t h e i n t e r m i t t e n t f e e d i n g o p e r a t i o n o f a fill-and-draw s y s t e m . A n o t h e r s t u d y o n l e a c h a t e t r e a t m e n t 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 w a s c o n d u c t e d b y W o n g a n d M a v i n i c (1982). T h e p u r p o s e o f t h i s p r o j e c t w a s to e v a l u a t e t h e t r e a t a b i l i t y o f a m e d i u m s t r e n g t h l e a c h a t e ( B O D } = 8090 m g / L ) at a n u t r i e n t l o a d i n g o f B O D 5 : N : P = 100:3.2:1.1, at d i f f e r e n t t e m p e r a t u r e s . BOD5 13 r e m o v a l s o f a t l eas t 9 9 . 4 p e r c e n t a n d C O D r e m o v a l s g r e a t e r t h a n 96 .4 p e r c e n t w e r e a c h i e v e d . T h e n u t r i e n t l o a d i n g w a s f o u n d t o b e s u f f i c i e n t . S e t t l i n g p r o b l e m s w e r e a l s o e n c o u n t e r e d i n t h i s s t u d y . 2.2.2.2 C o m b i n e d W a s t e w a t e r s V e r y f e w s t u d i e s h a v e b e e n c o n d u c t e d to s t u d y t h e e f f e c t o f m i x i n g l e a c h a t e a n d d o m e s t i c w a s t e w a t e r ( B o y l e a n d H a m 1 9 7 4 , T e m o i n a n d M a v i n i c 1981 ) . T h e s t u d y c o n d u c t e d b y B o y l e a n d H a m ( 1 9 7 4 ) i n v o l v e d t h e u s e o f a n e x t e n d e d a e r a t i o n p r o c e s s . T h e p e r c e n t a g e o f l e a c h a t e i n t h e d o m e s t i c w a s t e w a t e r - l e a c h a t e m i x t u r e was v a r i e d f r o m 0 to 2 0 p e r c e n t o n a v o l u m e b a s i s , w i t h l o a d i n g s v a r y i n g f r o m 5.7 to 7 7 . 6 l b s B O D j / d a y / 1 0 0 0 c u ft . E f f l u e n t q u a l i t y w a s n o t s i g n i f i c a n t l y a f f e c t e d u p t o 5 p e r c e n t l e a c h a t e a d d i t i o n b y v o l u m e , a p p r o x i m a t e l y 2 4 l b s B O D 5 / d a y / 1 0 0 0 c u ft. In exces s o f 5 p e r c e n t v o l u m e t r i c a d d i t i o n s , d e t e r i o r a t i o n o f s l u d g e s e t t l e a b i l i t y r e s u l t e d i n p o o r e f f l u e n t q u a l i t y . T h e C O D o f t h e e f f l u e n t a n d t h e S V I v a l u e s f o r t h e s l u d g e r o s e s h a r p l y a b o v e 5 p e r c e n t a d d i t i o n s . T h e a u t h o r s c o n c l u d e d t h a t l e a c h a t e c o u l d b e a d d e d to d o m e s t i c w a s t e w a t e r i n a n 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 p l a n t at a l e v e l o f a t l eas t 5 p e r c e n t b y v o l u m e ( l e a c h a t e C O D = 1 0 , 0 0 0 m g / L ) w i t h o u t s e r i o u s l y i m p a i r i n g e f f l u e n t q u a l i t y . A t g r e a t e r t h a n 5 p e r c e n t b y v o l u m e , l e a c h a t e a d d i t i o n s r e s u l t e d i n s u b s t a n t i a l s o l i d s p r o d u c t i o n , i n c r e a s e d o x y g e n u p t a k e ra tes , a n d p o o r e r m i x e d l i q u o r s e p a r a t i o n . ' T e m o i n a n d . M a v i n i c ( 1 9 8 1 ) f o u n d t h a t a c o m b i n a t i o n o f h i g h - s t r e n g t h l e a c h a t e a n d d o m e s t i c w a s t e w a t e r c o u l d b e s u c c e s s f u l l y t r e a t e d i n a n a e r a t e d l a g o o n , s i m u l a t e d i n the l a b o r a t o r y b y a c o m p l e t e l y - m i x e d , n o c e l l u l a r r e c y c l e , s i n g l e s t age s y s t e m , w i t h a 2 0 d a y d e t e n t i o n t i m e . A g o o d q u a l i t y e f f l u e n t w a s a c h i e v e d w i t h a n i n f l u e n t c o n s i s t i n g o f 2 0 p e r c e n t l e a c h a t e a d d i t i o n , w h i c h c o r r e s p o n d s to a n i n f l u e n t B O D 5 o f 3 ,650 m g / L . B O D j r e m o v a l e f f i c i e n c i e s g r e a t e r t h a n 9 9 p e r c e n t 14 were achieved. When the BODj/P ratio in the feed dropped below 100:0.29, the effluent TKN concentrations rose to 13.4 mg/L, while the TKN values in all other instances never exceeded 2.8 mg/L. It was thought that the low phosphorus loading inhibited the ability of the mixed-liquor to assimilate nitrogen. Phosphorus, like nitrogen, is an essential nutrient for biological growth. Lack of phosphorus could inhibit growth and hence the microorganisms would not use up the nitrogen in the feed. 2.3 KINETIC PARAMETERS 2.3.1 LEACHATE The main parameters of interest in understanding the kinetics of a biological growth system are the following - the maximum rate of substrate utilization (K), the half velocity coefficient (Kg ), the microorganism decay coefficient (b), and the growth yield coefficient (Y). A summary of all the kinetic parameters from various leachate treatment studies are presented in Table 2-3 (Mavinic 1984). These kinetic parameters are compared with the kinetic parameters for domestic wastewater. The maximum rate of substrate utilization, K, in all cases is lower than that for domestic wastewater, and seems to be decreasing with increasing leachate strength. This supports the conclusion of most authors that there is a certain degree of inhibition due, in part, to the presence of trace metals in the leachate ( Neufeld 1976, Wong and Mavinic 1982, Uloth and Mavinic 1977). Palit and Qasim (1977) carried out a study to obtain the values of the kinetic parameters for leachate. The value of the decay coefficient, b, was found to be considerably higher than that for domestic wastewater. In all probability, this was due to the deficiency of nutrients such as nitrogen and phosphorus in the 15 T A B L E 2-3 Kinetic Parameters for Various Leachates ( Mavinic 1984 ) R e f e r e n c e F e e d S t r e n g t h Y ( m g / m g ) b ( d a y s " 1 ) K ( d a y s " 1 ) K s ( m g / L ) ( m g / L ) M e t c a l f a n d E d d y 1 9 7 2 S e w a g e - 2 5 0 B O D 5 0.67 0.07 5.6 22 P a l i t a n d Q a s i m 1 9 7 7 C O D - 3 6 5 0 .59 0 .1150 1.8 182 L e e 1 9 7 9 B O D 3 -• 1,000 0 .59 0.04 4.5 9 9 W o n g a n d M a v i n i c 1 9 8 3 B O D s -• 8 ,090 0 .49 0 .009 1.16 81 .8 Z a p f - G i l j e a n d M a v i n i c 1981 B O D 5 -1 3 , 6 4 0 0 .39 0.022 0.77 20 .4 C o o k a n d F o r e e 1 9 7 4 C O D - 1 5 . 8 0 0 0 .40 0.05 0 .60 175 U l o t h a n d M a v i n i c 1 9 7 7 B O D 5 -3 6 , 0 0 0 0 .33 0 .0025 0 .75 2 0 0 T A B L E 2-4 Kinetic Parameters for a Particular Leachate and a Combined Wastewater ( Temoin 1980 ) I n f l u e n t • T y p e Y b K K s ( m g / m g ) ( d a y s - ' ) ( d a y s 1 ) ( m g / L ) L e a c h a t e 0 .525 0 .0025 0 .75 2 0 0 C o m b i n e d W a s t e w a t e r 0 .525 0 .0025 0 . 1 7 4 139 16 feed. Lack of the essential nutrients can prevent biological growth and cause microorganisms to die off. The value of the decay coefficient obtained by Palit and Qasim was also very high compared to other studies (Table 2-3). Uloth and r Mavinic (1977) attribute the low value of the decay coefficient to the high substrate concentration available to the biomass. The authors concluded that no endogenous respiration took place and hence the low value of the decay coefficient Wong and Mavinic (1982) also concluded that the low decay coefficient values were due to the presence of continuing log gTowth phase. The growth yield coefficient for domestic wastewater is approximately 0.67 mg VSS /mg BOD5. This value has been found to be lower for leachates. Uloth and Mavinic (1977) state that this may be due, in part, to biological inhibition caused by the trace metals. Wong and Mavinic (1982) also found that the growth yield coefficient is dependent on the strength of the leachate feed, as well as the complexity of the waste. The half-velocity coefficient has been observed to vary with the type of waste (Uloth and Mavinic 1977). As the complexity of the waste increases or the biodegradability of the waste decreases, the half-velocity coefficient value increases. A very high value suggests that very high MLVSS concentrations are necessary to get reasonable reductions in the influent leachate BOD5. 2.3.2 COMBINED WASTEWATERS The only known study to evaluate kinetic parameters of a combined wastewater was done by Temoin (1980). The values of the parameters are provided in Table 2-4. According to the author, only one sludge age was used during the experiment and as such the data presented should not be construed as absolute in accuracy. It is simply indicative of a 'trend' in the kinetic evaluation of these reactors. 17 2.4 FACTORS AFFECTING AEROBIC STABILIZATION 2.4.1 TRACE METALS A s t u d y w a s c a r r i e d o u t b y B a r t h et al. ( 1 9 6 5 ) t o d e t e r m i n e t h e e f f e c t s o f t r a ce m e t a l s o n a c o n v e n t i o n a l a c t i v a t e d s l u d g e p r o c e s s . T h e m e t a l s a n a l y z e d w e r e c h r o m i u m , c o p p e r , n i c k e l a n d z i n c . T h e b i o m a s s w a s a c c l i m a t i z e d f o r t w o w e e k s b e f o r e a n y a n a l y s i s w a s d o n e . A c o n t i n u o u s d o s e o f c o p p e r , w i t h a c o n c e n t r a t i o n o f 1 m g / L , w a s f o u n d to s i g n i f i c a n t l y r e d u c e t h e t r e a t m e n t e f f i c i e n c y . It w a s o b s e r v e d t h a t a to ta l h e a v y m e t a l c o n c e n t r a t i o n o f 1 0 m g / L c o u l d b e t o l e r a t e d b y t h e b i o m a s s . N e u f e l d a n d H e r m a n n ( 1 9 7 5 ) s t u d i e d t h e e f f e c t s o f m e r c u r y , c a d m i u m a n d z i n c o n t h e a c t i v a t e d s l u d g e p r o c e s s . T h e t h r e s h o l d c o n c e n t r a t i o n f o r c a d m i u m w a s a b o u t 25 m g / L a n d 8 m g / L f o r z i n c . N o t h r e s h o l d e f f e c t w a s o b s e r v e d f o r m e r c u r y a n d i t w a s c o n c l u d e d t h a t b i o l o g i c a l i n h i b i t i o n b y m e r c u r y c o u l d b e t o t a l l y c o u n t e r a c t e d b y i n c r e a s i n g t h e c o n c e n t r a t i o n o f t h e o r g a n i c s u b s t r a t e . A l t h o u g h v a r i o u s s t u d i e s o n t h e e f f e c t s o f m e t a l s h a v e i n d i c a t e d a n i n h i b i t o r y e f f e c t o n . t h e b i o m a s s , s e v e r a l l e a c h a t e t r e a t m e n t s t u d i e s h a v e s h o w n t h a t t h e a c t i v a t e d s l u d g e p r o c e s s c a n e f f e c t i v e l y r e m o v e t r a c e m e t a l s ( C o o k a n d F o r e e 1 9 7 4 , U l o t h a n d M a v i n i c 1 9 7 7 , T e m o i n a n d M a v i n i c 1 9 8 1 , Z a p f - G i l j e a n d M a v i n i c 1981 ) . T h e i n f l u e n t l e a c h a t e f e e d u s e d b y C o o k a n d F o r e e ( 1 9 7 4 ) h a d a n i r o n c o n c e n t r a t i o n o f 2 4 0 m g / L . M o s t o f t h e i r o n w a s r e m o v e d f r o m t h e 1 0 - d a y u n i t s . T h i s l a r g e i r o n r e m o v a l , w i t h t h e final e f f l u e n t h a v i n g l ess t h a n 10 m g / L i r o n , w a s a t t r i b u t e d m a i n l y to c h e m i c a l p r e c i p i t a t i o n a t t h e h i g h p H t h a t w a s m a i n t a i n e d i n t h e 1 0 - d a y u n i t s . S i g n i f i c a n t r e m o v a l o f c a l c i u m a n d m a g n e s i u m w a s a l s o o b s e r v e d d u r i n g t h e s t u d y . . 18 T e m o i n a n d M a v i n i c ( 1 9 8 1 ) u s e d a l e a c h a t e f e e d c o n t a i n i n g a w i d e r a n g e o f m e t a l s . A l u m i n i u m , c a d m i u m , c h r o m i u m , i r o n , l e a d , m a n g a n e s e a n d z i n c w e r e s t u d i e d . T h e 2 0 - d a y s l u d g e a g e w a s v e r y e f f e c t i v e i n r e m o v i n g m e t a l s d o w n to a b a s e v a l u e , w e l l b e l o w t o x i c l e v e l s . N o c o r r e l a t i o n w a s f o u n d b e t w e e n m e t a l r e m o v a l a n d n u t r i e n t l o a d i n g . H o w e v e r , t h e r e w a s g o o d c o r r e l a t i o n b e t w e e n t h e to ta l s u s p e n d e d s o l i d s l e v e l a n d t h e m e t a l c o n c e n t r a t i o n i n t h e s e t t l e d e f f l u e n t T h e r e m o v a l o f t r a ce m e t a l s w i t h a e r o b i c t r e a t m e n t w a s a l s o s t u d i e d b y U l o t h a n d M a v i n i c ( 1 9 7 7 ) . It w a s f o u n d t h a t m o s t o f t h e m e t a l s i n t h e m i x e d l i q u o r s w e r e r e m o v e d b y t h e s e t t l i n g b i o l o g i c a l f l o e . T h e h i g h p H v a l u e s ( g r e a t e r t h a n 8.5) w e r e f o u n d t o a i d m e t a l r e m o v a l , as d i d t h e h i g h M L V S S c o n c e n t r a t i o n s . T h e r e w a s n o i n d i c a t i o n o f d i g e s t e r i n s t a b i l i t y a t t r i b u t a b l e to t h e s e m e t a l s . H o w e v e r , a n a n a l y s i s o f t h e k i n e t i c p a r a m e t e r s i n d i c a t e d t h a t t h e h i g h m e t a l c o n c e n t r a t i o n s i n t h e m i x e d l i q u o r s p r o b a b l y h e l p e d t o i n h i b i t t h e a c t u a l b i o l o g i c a l r e m o v a l o f o x y g e n d e m a n d i n g m a t e r i a l f r o m th i s l e a c h a t e . Z a p f - G i l j e a n d M a v i n i c ( 1 9 8 1 ) a l s o s t u d i e d t h e e f f e c t s o f m e t a l s o n b i o l o g i c a l t r e a t m e n t . It w a s f o u n d t h a t m o s t m e t a l s w e r e r e d u c e d i n c o n c e n t r a t i o n b y m o r e t h a n 9 0 p e r c e n t T h i s w a s a t t r i b u t e d t o t h e p r e c i p i t a t i o n o f m e t a l h y d r o x i d e s w i t h s u b s e q u e n t e n t r a p m e n t i n b i o l o g i c a l f l oes , s o r p t i o n b y o r g a n i c s o l i d s , a n d c o n s u m p t i o n b y b i o m a s s . M e t a l r e d u c t i o n w a s f o u n d t o b e i n d e p e n d e n t o f t e m p e r a t u r e a n d l o a d i n g ra tes . 2.4.2 N I J T R I F . N T R F.OI TIR F . M F . N T S T h e r a w l e a c h a t e u s e d b y C o o k a n d F o r e e ( 1 9 7 4 ) h a d a T K N c o n c e n t r a t i o n o f 2 4 0 m g / L , w i t h a n a m m o n i a - n i t r o g e n c o n c e n t r a t i o n o f 10 m g / L . T h i s c o r r e s p o n d e d t o a 4 3 : 1 r a t i o o f B O D 5 : N . T h e B O D ^ P r a t i o w a s f o u n d to b e 4 3 0 : 1 . T h e r e f o r e , n i t r o g e n a n d p h o s p h o r u s w e r e a d d e d i n c o n c e n t r a t i o n s o f 500 m g / L a n d 1 0 0 m g / L , r e s p e c t i v e l y . H o w e v e r , t he r e s u l t s f r o m t h i s s t u d y s h o w e d 19 t h a t n u t r i e n t a d d i t i o n s w e r e n o t n e e d e d f o r s u c c e s s f u l b i o l o g i c a l t r e a t m e n t E f f i c i e n t n u t r i e n t r e m o v a l w a s a c c o m p l i s h e d d u r i n g t h e e x p e r i m e n t P a l i t a n d Q a s i m ( 1 9 7 7 ) f o u n d t h a t t h e l e a c h a t e t h e y u s e d w a s a l s o n u t r i e n t d e f i c i e n t T h e m a x i m u m C O D o f t h e f e e d w a s a b o u t 3 0 , 0 0 0 m g / L , w h i l e t h e T K N v a l u e w a s o n l y 13 m g / L a n d t h e p h o s p h o r u s c o n c e n t r a t i o n w a s a p p r o x i m a t e l y 1 m g / L . T h e k i n e t i c p a r a m e t e r s e v a l u a t e d d u r i n g t h e e x p e r i m e n t i n d i c a t e d a h i g h d e c a y c o e f f i c i e n t f o r t h e l e a c h a t e . T h i s w a s a t t r i b u t e d t o t h e d e f i c i e n c y o f n u t r i e n t s . T h e r e s i d u a l p h o s p h o r u s w a s less t h a n 0 .25 m g / L , a n d the m i c r o b i a l g r o w t h w a s l i m i t e d t o s o m e e x t e n t , d u e t o t h i s d e f i c i e n c y . A s t u d y c o n d u c t e d s p e c i f i c a l l y t o e v a l u a t e t h e n u t r i e n t r e q u i r e m e n t s f o r l e a c h a t e w a s d o n e b y T e m o i n a n d M a v i n i c ( 1 9 8 1 ) . T h e s t u d y c o n c l u d e d tha t , f o r a n e x t e n d e d a e r a t i o n s y s t e m w i t h a s l u d g e a g e o f 2 0 d a y s , t h e r e q u i r e d n u t r i e n t s c a n b e s i g n i f i c a n t l y r e d u c e d t o as l o w as 1 0 0 : 3 . 1 9 : 0 . 5 , w h i l e s t i l l p r o d u c i n g a g o o d q u a l i t y e f f l u e n t A l o w e r n u t r i e n t l o a d i n g r e s u l t e d i n a p o o r l y s e t t l i n g , b u l k i n g s l u d g e . H o w e v e r , at a l o w e r v o l u m e t r i c B O D 5 l o a d i n g , t h i s n u t r i e n t r a t i o c o u l d b e r e d u c e d f u r t h e r . W o n g a n d M a v i n i c ( 1 9 8 2 ) a l s o f o u n d t h a t a B O D j : N : P l o a d i n g o f 1 0 0 : 3 . 2 : 1 . 1 w a s " a d e q u a t e " f o r t r e a t m e n t R e a c t o r s undeT t h i s l o a d i n g c o m p a r e d f a v o r a b l y w i t h a c o n v e n t i o n a l n u t r i e n t l o a d i n g o f 1 0 0 : 5 : 1 . N u t r i e n t s w e r e a d d e d i n a l l u n i t s i n o r d e r to m a i n t a i n t h e r e q u i r e d l o a d i n g s . T h e e f f e c t o f t e m p e r a t u r e w a s n o t s i g n i f i c a n t i n th i s r e s p e c t , e x c e p t f o r t h e 5 - d a y S R T , 5 ° C r e a c t o r s . Z a p f - G i l j e a n d M a v i n i c ( 1 9 8 1 ) c a r r i e d o u t a s t u d y f o r a e r o b i c b i o - t r e a t m e n t o f l e a c h a t e a n d u s e d a s t a n d a r d n u t r i e n t l o a d i n g o f 1 0 0 : 5 : 1 f o r a l l t h e e x p e r i m e n t s . T h i s w a s f o u n d t o b e s u f f i c i e n t a t a l l t i m e s a n d n o p r o b l e m s w e r e e n c o u n t e r e d i n t h i s r e g a r d . U l o t h a n d M a v i n i c ( 1 9 7 7 ) a l s o c o n d u c t e d a s t u d y f o r l e a c h a t e t r e a t m e n t u s i n g a e r o b i c r e a c t o r s . T h e B O D 5 : N : P r a t i o o f t h e f e e d w a s 1 0 0 : 3 . 3 : 0 . 5 5 . N u t r i e n t s 2 0 w e r e a d d e d t o t h e f e e d , t o p r o v i d e a r a t i o o f 1 0 0 : 6 . 4 : 3 . 1 d u r i n g t h e " e x t e n d e d - a e r a t i o n " s t u d y . T h i s a d d i t i o n w a s f o u n d t o b e " e x c e s s i v e " , as h i g h e f f l u e n t c o n c e n t r a t i o n s w e r e o b s e r v e d f o r b o t h n i t r o g e n a n d p h o s p h o r u s . A r a t i o o f 1 0 0 : 5 : 1 , w h i c h w a s p r o v i d e d d u r i n g t h e l a t e r p a r t o f t h e s t u d y , i m p r o v e d t h e e f f l u e n t q u a l i t y w i t h o u t a d v e r s e l y a f f e c t i n g t h e b i o l o g i c a l e f f i c i e n c y . 2.4.3 T E M P E R A T T FR F E F F E C T S A s m e n t i o n e d e a r l i e r , m o s t l e a c h a t e t r e a t m e n t s t u d i e s h a v e b e e n c o n d u c t e d a t r o o m t e m p e r a t u r e s . H o w e v e r , a f e w s t u d i e s h a v e a l s o b e e n d o n e at l o w e r t e m p e r a t u r e s ( W o n g a n d M a v i n i c 1 9 8 2 , Z a p f - G i l j e a n d M a v i n i c 1981 ) . Z a p f - G i l j e a n d M a v i n i c ( 1 9 8 1 ) s t u d i e d a t e m p e r a t u r e r a n g e f r o m 9 t o 2 5 ° C . T h i s r a n g e s e e m e d t o h a v e m i n i m a l e f f e c t s o n t h e b i o s t a b i l i z a t i o n p r o c e s s o f l e a c h a t e . C O D r e m o v a l e f f i c i e n c y g r e a t e r t h a n 9 7 p e r c e n t w a s o b s e r v e d d u r i n g m o s t o f t h e e x p e r i m e n t s . T h e M L V S S c o n c e n t r a t i o n s i n c r e a s e d w h e n t h e t e m p e r a t u r e w a s d e c r e a s e d , a n d t h i s w a s a t t r i b u t e d t o t h e s l o w e r b i o l o g i c a l a c t i v i t y a t l o w e r t e m p e r a t u r e s . T h e i d e a l o p e r a t i n g t e m p e r a t u r e o f t h e d o m i n a t i n g b i o l o g i c a l c o m m u n i t y w a s s p e c u l a t e d t o b e s o m e w h e r e b e t w e e n 9 ° C a n d 2 5 ° C . T h e r e m o v a l o f m e t a l i o n s w a s n o t a f f e c t e d b y t e m p e r a t u r e . I r o n , m a n g a n e s e , a n d z i n c r e m o v a l r e m a i n e d u n c h a n g e d . R e s u l t s o b t a i n e d f o r o t h e r e l e m e n t s s e e m e d t o v a r y r a n d o m l y . T h e s t u d y c o n d u c t e d b y W o n g a n d M a v i n i c ( 1 9 8 2 ) o p e r a t e d a t t e m p e r a t u r e s r a n g i n g f r o m 5 ° C t o 2 5 ° C . P r o b l e m s o f p o o r s l u d g e s e t t l i n g w e r e e n c o u n t e r e d a t t h e l o w e r t e m p e r a t u r e s . T h e l o w e s t s l u d g e a g e r e a c t o r s , at 5 ° C a n d 1 0 ° C , s e e m e d t o h a v e a p o o r e f f l u e n t q u a l i t y , w i t h a C O D r e m o v a l e f f i c i e n c y o f 9 4 p e r c e n t It w a s a l s o o b s e r v e d t h a t t h e t e m p e r a t u r e h a d a m i n i m a l e f f e c t o n t h e r e m o v a l o f m o s t m e t a l s . H o w e v e r , c h r o m i u m a n d n i c k e l r e m o v a l s a p p e a r e d v e r y d e p e n d e n t o n b o t h s l u d g e a g e a n d t e m p e r a t u r e . T h e s t u d y c o n c l u d e d t h a t t h e r e m o v a l o f c o n t a m i n a n t s f r o m l e a c h a t e w e r e o n l y n o m i n a l l y d e p e n d e n t o n t h e t e m p e r a t u r e . 21 2.5 SYSTEM PERFORMANCE 2.5.1 S E T T L I N G C H A R A C T E R I S T I C S M o s t k i n e t i c m o d e l s p r o p o s e d f o r m i c r o b i a l a s s i m i l a t i o n o f o r g a n i c m a t t e r d o n o t i n d i c a t e t h e e f f i c i e n c y w i t h w h i c h b i o l o g i c a l s o l i d s m a y b e s e p a r a t e d f r o m t h e l i q u i d p h a s e . I n t h e d e s i g n s t age , i t is o f t e n a s s u m e d t h a t o n e h u n d r e d p e r c e n t e f f i c i e n c y c a n b e a t t a i n e d f o r s o l i d s - l i q u i d s e p a r a t i o n . T h i s , h o w e v e r , w i l l s e l d o m o c c u r i n p r a c t i c e ( B i s o g n i a n d L a w r e n c e 1971 ) . A c c o r d i n g to P i p e s ( 1 9 6 9 ) , t h e r e a r e s e v e r a l d i f f e r e n t t y p e s o f a c t i v a t e d s l u d g e s w h i c h a r e d i f f i c u l t t o s e p a r a t e f r o m t h e e f f l u e n t T h e p r o d u c t i o n o f e a c h s p e c i f i c t y p e o f s l u d g e , w h i c h s e p a r a t e s p o o r l y , is c a u s e d b y s o m e s p e c i f i c d e f i c i e n c y i n t h e c o m p o s i t i o n o f t h e w a s t e . T h e p o o r s e p a r a t i o n m a y a l s o b e c a u s e d b y c e r t a i n e n v i r o n m e n t a l c o n d i t i o n s l i k e l o w d i s s o l v e d o x y g e n o r e x c e s s t u r b u l e n c e i n t h e a e r a t i o n t a n k . T h e r e a r e d i f f e r e n t c l a s s i f i c a t i o n s f o r p o o r l y s e t t l i n g s l u d g e s c i t e d i n t h e l i t e r a tu r e , ( B i s o g n i a n d L a w r e n c e 1 9 7 1 , P i p e s 1 9 6 9 , N e u f e l d 1976 ) . B i s o g n i a n d L a w r e n c e ( 1 9 7 1 ) s ta te t h a t t h e f a c t o r s w h i c h a f f e c t t h e s e t t l i n g c h a r a c t e r i s t i c s c a n b e d i v i d e d i n t o t w o c a t e g o r i e s ; t h e first o n e is a s s o c i a t e d w i t h c h a n g e s i n t h e b a c t e r i a l o r z o o g l e a l p o p u l a t i o n ' s p h y s i c a l o r b i o c h e m i c a l c h a r a c t e r , w h e r e a s t h e s e c o n d c a t e g o r y i n v o l v e s p o p u l a t i o n s h i f t s f r o m t h e n o r m a l b a c t e r i a l o r z o o g l e a l t y p e s t o a f i l a m e n t o u s t y p e p o p u l a t i o n . B u l k i n g s l u d g e is t h e m o s t c o m m o n l y o c c u r r i n g t y p e o f p o o r l y s e t t l i n g a c t i v a t e d s l u d g e ( B i s o g n i a n d L a w r e n c e 1 9 7 1 , P i p e s 1 9 6 9 , B i e s i n g e r et al. 1 9 8 0 , F r e n z e l 1 9 7 7 , E i k e l b o o m 1 9 7 7 , S e z g i n et al. 1 9 7 8 , P i t m a n 1 9 8 0 , P i p e s 1979 ) . B u l k i n g s l u d g e is d e f i n e d as o n e w h i c h se t t l es s l o w l y a n d c o m p a c t s p o o r l y . P i p e s ( 1 9 6 9 ) a n d S e z g i n et al. ( 1 9 7 8 ) c l a s s i f y t h e t w o t y p e s o f b u l k i n g as n o n - f i l a m e n t o u s a n d f i l a m e n t o u s . N o n - f i l a m e n t o u s b u l k i n g o c c u r s i n n o r m a l z o o g l e a l 22 a c t i v a t e d s l u d g e . H e u k e l e k i a n a n d W e i s b u r g ( 1 9 5 6 ) s tate t h a t t h i s t y p e o f b u l k i n g o c c u r s w h e n t h e a c t i v a t e d s l u d g e o r g a n i s m s sec r e t e a n e x t r a c e l l u l a r m a t e r i a l w i t h a h i g h d e g r e e o f h y d r a t i o n , t h u s p r o d u c i n g a s l u d g e w i t h e x c e s s i v e a m o u n t s o f b o u n d w a t e r . F i l a m e n t o u s b u l k i n g o c c u r s w h e n t h e r e is a n e x c e s s i v e l y l a r g e n u m b e r o f f i l a m e n t o u s o r g a n i s m s i n t h e a c t i v a t e d s l u d g e . I n t h e v a s t m a j o r i t y o f c ases , t h e f i l a m e n t o u s o r g a n i s m i n t h e s l u d g e h a s b e e n i d e n t i f i e d as Sphaerotilus ( P i p e s 1969 ) . I n r e c e n t y e a r s , h o w e v e r , a v a r i e t y o f d i f f e r e n t f i l a m e n t o u s o r g a n i s m s h a v e a l s o b e e n i d e n t i f i e d ( E i k e l b o o m 1 9 7 7 ) . E k e l b o o m c a r r i e d o u t h i s s t u d y t o f i n d o u t t h e m o s t c o m m o n l y o c c u r i n g f i l a m e n t o u s o r g a n i s m s ( T a b l e 2 - 5 ) . Microthrix parvicella a n d T y p e 0 2 1 N h a d b e e n o b s e r v e d m o s t f r e q u e n t l y . It w a s o b s e r v e d t h a t t he p o p u l a t i o n c o m p o s i t i o n a l s o d e p e n d e d o n t h e w a s t e w a t e r q u a l i t y . T h e s a m e f i l a m e n t o u s b a c t e r i a w e r e s e e n i n i n d u s t r i a l p l a n t s as i n p l a n t s r e c e i v i n g d o m e s t i c w a s t e w a t e r . H o w e v e r , a c l e a r d i f f e r e n c e e x i s t e d b e t w e e n t h e p o p u l a t i o n o f f i l a m e n t s i n t h e t w o t y p e s o f p l a n t s . A c c o r d i n g to S e z g i n et al. ( 1 9 7 8 ) , i n o r d e r t o a c h i e v e a g o o d s e t t l i ng s l u d g e , o n e m u s t h a v e t h e c o r r e c t m i c r o b i a l l y - m e d i a t e d p h y s i c a l / c h e m i c a l c o n d i t i o n s . U n l e s s t h e right c o n d i t i o n s f o r m i c r o b i a l a g g r e g a t i o n ex i s t s , p r o p e r a c t i v a t e d s l u d g e f l o e s c a n n o t f o r m . F i l a m e n t o u s a n d z o o g l e a l m i c r o o r g a n i s m s a r e b o t h e s sen t i a l t o t h e i n t e g r i t y o f t h e m a c r o s t r u c t u r e o f t h e a c t i v a t e d s l u d g e f l o e . F i l a m e n t s f o r m a rigid b a c k b o n e f o r t h e f l o e , t o w h i c h f l o c c u l e n t z o o g l e a l o r g a n i s m s a t t a c h l i k e f l e s h o n a b o n e . A n a b s e n c e o f f i l a m e n t s l e a d s t o t h e f o r m a t i o n o f p i n p o i n t f l o e - a w e a k f l o e t h a t s h e a r s i n t o s m a l l a g g r e g a t e s a n d p a r t i c l e s t h a t t e n d to c o n t r i b u t e to s e c o n d a r y e f f l u e n t t u r b i d i t y . A n e x c e s s o f f i l a m e n t s c a u s e s t h e o r g a n i s m s to g r o w o u t o f t h e c o n f i n e s o f t h e b u l k m e d i u m a n d th i s r e s u l t s i n a s l o w l y s e t t l i n g , p o o r l y c o m p a c t i n g s l u d g e . T h e a u t h o r s a l s o p o s t u l a t e d tha t , at l o w D O c o n c e n t r a t i o n s , f i l a m e n t o u s o r g a n i s m s g r o w m o r e r a p i d l y t h a n t h e z o o g l e a l o n e s , w h i l e at h i g h e r D O TABLE 2-5 Commonly Occurring Filamentous Organisms ( Eikelboom 1977 ) N a m e o f F i l a m e n t o u s O r g a n i s m Microthrix parvicella T y p e 0 2 1 N Haliscomenobacter hydrossis T y p e 0 0 9 2 T y p e 1701 T y p e 0 0 4 1 Sphaerotilus nutans T y p e 0581 T y p e 0 8 0 3 T y p e 0 9 6 1 Nostoccxda limicola T y p e 1851 Cyanophyceae Nocardia spp. Fungi spp. T y p e 0 9 1 4 Flexibacter spp. Beggiatoa spp. Thiothrix spp. 24 concentrations the reverse is true. The authors further concluded that a minimum level of 2.0 mg/L for most municipal wastewaters is required for a good settling sludge. Biesinger et al. (1980) also found that low DO is a principal factor in the excessive growth of filamentous organisms. Other factors which also increase the number of filamentous organisms in activated sludge are a low food/microorganism ratio (F/M) and the substrate type. In a study conducted by Sezgin (1980), to explain the role of filamentous organisms in activated sludge settling, it was found that the settling characteristics, as presented by zone settling velocity, reflocculation time and height of the compacted volume, were related to the length of the filamentous organisms present in the sludge. The filaments were also the most important factor affecting the settling characteristics of activated sludge. Deflocculation of the sludge is a state in which the sludge shows no tendency to separate. This produces a uniform turbidity in the supernatant above the settled sludge. Deflocculation is usually the result of a toxic shock such as a sudden temperature change (Dougherty and McNary 1958) or a slug of acid waste (Edwards and Nussberger 1947). Neufeld (1976) conducted experiments to study the toxic effects of mercury, cadmium and zinc on the settling characteristics of the sludge. Shock loadings, of these metals, to activated sludge resulted in the loss of significant quantities of biomass over the effluent weir. Maximum deflocculation seems to occur after 10 to 12 days of intimate contact Pipes (1969) notes that if the toxic conditions are continuous or repeated, the deflocculated state may be established or all of the normal sludge may disappear, thus producing something that looks like dispersed growth. Low dissolved oxygen and low pH are also among the causes of deflocculation (Pipes 1979). Deflocculation has been found to occur at any F/M ratio (Pipes 1979). Bulking, on the other hand, occurs at low F/M ratios. However, bulking and deflocculation can occur simultaneously in an 25 a c t i v a t e d s l u d g e p r o c e s s at F / M r a t i o s g r e a t e r t h a n 0.4 d a y 1 . P i n p o i n t floe r e s u l t s f r o m a l a c k o f s u f f i c i e n t f i l a m e n t s i n t h e b i o m a s s ( S e z g i n et al. 1 9 7 8 ) . P i n p o i n t f l o e c o n s i s t s o f s m a l l , y e t v i s i b l e , f l o e p a r t i c l e s tha t a r e i n t h e s u p e r n a t a n t a f t e r t h e s l u d g e h a s s e t t l ed ( P i p e s 1979 ) . T h e r e a r e a l e a s t t w o d i f f e r e n t t y p e s o f p i n p o i n t floe. O n e t y p e a p p e a r s t o b e n o r m a l a c t i v a t e d s l u d g e p a r t i c l e s o f v e r y s m a l l s i z e ; t h e o t h e r t y p e c o n s i s t s o f w h i t e a m o r p h o u s m a s s e s w h i c h d o n o t e x e r t a n o x y g e n d e m a n d . P i p e s ( 1 9 6 9 ) p o s t u l a t e s t h a t p i n p o i n t f l o e is m o r e l i k e l y t o o c c u r w h e n t h e t e m p e r a t u r e i n t h e a e r a t i o n t a n k is l e ss t h a n 1 5 ° C . E x c e s s t u r b u l e n c e i n t h e a e r a t i o n t a n k c a n a l s o c o n t r i b u t e to the f o r m a t i o n o f a p i n p o i n t floe ( P i p e s 1 9 6 9 , S e z g i n et al. 1978 ) . P i n p o i n t f l o e h a s b e e n o b s e r v e d o n l y i n p r o c e s s e s w i t h l o w o r g a n i c l o a d i n g s , w i t h a n F / M r a t i o less t h a n 0.2 d a y 1 . T h e d e t a i l e d s u m m a r y b y P i p e s ( 1 9 6 9 ) a l s o d e s c r i b e s o t h e r t y p e s o f a c t i v a t e d s l u d g e s w h i c h s e p a r a t e p o o r l y . R i s i n g s l u d g e is o n e w h i c h se t t l es w e l l a n d c o m p a c t s w e l l f o r 3 0 m i n u t e s o r m o r e . H o w e v e r , a f t e r a f e w h o u r s o r s o , t h e s l u d g e rises i n a m a s s t o t h e t o p o f t h e c y l i n d e r . T h e m e c h a n i s m o f rising s l u d g e d e p e n d s o n t h e o c c u r r e n c e o f n i t r i f i c a t i o n i n t h e a e r a t i o n t a n k , d e n i t r i f i c a t i o n i n t h e s e t t l i n g t a n k , a n d e n t r a p m e n t o f n i t r o g e n g a s b u b b l e s i n t h e c o m p a c t e d s l u d g e m a s s . D i s p e r s e d g r o w t h , a n o t h e r c h a r a c t e r i s t i c , s h o w s n o t e n d e n c y t o s e p a r a t e i n a s e d i m e n t a t i o n t ank . T h e w h o l e b i o m a s s is s e e n as o n e w i t h a u n i f o r m t u r b i d i t y . Y e t a n o t h e r p r o b l e m o b s e r v e d i n s l u d g e s e t t l e a b i l i t y is f l o a t i n g s l u d g e . T h i s m e a n s t h a t t h e i n d i v i d u a l s l u d g e p a r t i c l e s h a v e a d e n s i t y l e ss t h a n w a t e r ( P i p e s 1 9 6 9 ) . F l o a t i n g s l u d g e p r o b a b l y c a n b e p r o d u c e d b y a n u m b e r o f d i f f e r e n t b i o l o g i c a l p h e n o m e n a . O v e r a e r a t e d s l u d g e c a n r e s u l t f r o m v i o l e n t a g i t a t i o n i n t h e a e r a t i o n t a n k . T h e a i r b u b b l e s , b r o k e n u p i n t o v e r y s m a l l p a r t i c l e s , a t t a ch t h e m s e l v e s t o t h e s l u d g e a n d float u p t o t h e s u r f a c e . O v e r a e r a t e d s l u d g e is m o r e l i k e l y t o o c c u r i n a n a c t i v a t e d s l u d g e p r o c e s s u s i n g m e c h a n i c a l a e r a t i o n ( P i p e s 26 1969 ) . F o r t e s t i n g s e t t l i n g c h a r a c t e r i s t i c s , h e a v y r e l i a n c e h a s b e e n p l a c e d o n the s u s p e n d e d m a t t e r a n d s e t t l e a b i l i t y tests a n d o n m i c r o s c o p i c e x a m i n a t i o n ( S t a n d a r d M e t h o d s 1 9 8 0 ) . F a c t o r s l i k e s l u d g e v o l u m e i n d e x ( S V I ) , z o n e s e t t l i n g v e l o c i t i e s a n d p e r c e n t d i s p e r s i o n a r e u s e d t o d e f i n e t h e s e t t l i n g c h a r a c t e r i s t i c s o f s l u d g e s . T h e S V I w a s o r i g i n a l l y d e v i s e d as a q u a n t i t a t i v e m e a s u r e o f b u l k i n g ( P e a r s e a n d C o m m i t t e e 1 9 3 7 ) . It m e a s u r e s t h e c o m p a c t i b i l i t y o f t h e s l u d g e . T y p i c a l v a l u e s o f t h e S V I f o r g o o d s e t t l i n g s l u d g e s , i n d i f f u s e d a i r a e r a t i o n p l a n t s , o p e r a t i n g w i t h M L S S c o n c e n t r a t i o n s o f 8 0 0 t o 3 5 0 0 m g / L , r a n g e f r o m 1 5 0 to 35 ( M e t c a l f a n d E d d y 1 9 7 2 ) . S l u d g e t h a t is n o t o f t h e c o n v e n t i o n a l a g e ( 5 - 2 0 d a y s ) o r w h i c h h a s a t e n d e n c y to b e f l u f f y a n d b u o y a n t a n d t h u s to b u l k , w i l l h a v e a n i n d e x g r e a t e r t h a n 150 . T h e v a l u e o f S V I is o f o p e r a t i o n a l i m p o r t a n c e , s i n c e i t r e f l e c t s c h a n g e s i n t h e t r e a t m e n t s y s t e m ( W a n g et al. 1977 ) . T h e r e a r e n u m e r o u s p a p e r s o n t h e i m p o r t a n c e o f S V I m e a s u r e m e n t s . D i c k a n d V e s i l i n d ( 1 9 6 9 ) n o t e t h a t S V I h a s b e e n u s e d as t h e b a s i c m e a s u r e o f s l u d g e s e t t l e a b i l i t y i n t r e a t m e n t p l a n t s . S V I i s a l s o u s e d f o r c o m p a r i n g t h e s e t t l i n g c h a r a c t e r s t i c s o f v a r i o u s s l u d g e s . H o w e v e r , t h e S V I d e f i n e s o n l y o n e p o i n t o n t h e s e t t l i n g c u r v e a n d t h e r f o r e i t i s n o t a p r e c i s e m e a s u r e o f s e t t l i n g c h a r a c t e r i s t i c s . T h e r e a r e v a r i o u s f a c t o r s w h i c h i n f l u e n c e t h e v a l u e o f S V I . T h e r e is n o c o n s i s t e n t r e l a t i o n s h i p b e t w e e n 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 a n d S V I . H o w e v e r , t h e S V I o f a s l u d g e is h i g h l y d e p e n d e n t o n its 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 , w i t h g r e a t e r c o n c e n t r a t i o n s t e n d i n g t o d e c r e a s e t h e S V I . R h e o l o g i c a l c h a r a c t e r i s t i c s l i k e y i e l d s t r e n g t h a n d p l a s t i c v i s c o s i t y a r e n o t a d i r e c t r e f l e c t i o n o f t h e S V I v a l u e ( D i c k a n d E w i n g 1969 ) . N o m e a n i n g f u l c o r r e l a t i o n w a s o b t a i n e d e i t h e r b e t w e e n t h e i n t e r f a c e v e l o c i t y a n d S V I ( R o b e r t s 1 9 4 9 ) . T h e c y l i n d e r d i a m e t e r , i n w h i c h the s e t t l i ng test is c a r r i e d o u t , a l s o a f f e c t s t h e v a l u e o f t h e S V I ( D i c k a n d V e s i l i n d 1969 ) . In c o m p a r i n g t h e S V I v a l u e s o f t h e d i f f e r e n t s l u d g e s , it is t h e r e f o r e 27 important to be consistent with the size of the test cylinder. Temperature effects on the SVI values have also been shown to be significant (Dick and Vesilind 1969). SVI values tend to decrease with increase in temperature (Figure 2-1). Bisogni and Lawrence (1971) found that the SVI varies with the sludge age in a non-linear manner; this variation is shown in Figure 2-2. Another correlation cited in the literature by Hoepker and Schroeder (1979) is the variation of SVI with the organic loading. The relationship, as shown in Figure 2-3, is not direct and is likely to have significant variations from this representation. A study conducted by Pitman (1980) also found that the settling characteristics of a sludge improved with increasing sludge age. The settling properties in this study were characterised by the interface settling velocities. Pitman also found that it is important to maintain aerobic conditions in the reactors to prevent excess filamentous growth. It was postulated that the nutrient removal activated sludge plants, incorporating anoxic zones, run a potential risk of developing slow-settling, filamentous sludges. Sludge settling problems have also been encountered in leachate treatment studies. Boyle and Ham (1974) found that sludge bulking. problems predominate at F/M ratios exceeding 1.5 day1. Zapf-Gilje and Mavinic (1981), who conducted a study on the biostabilization of leachate, found that the settling characteristics were poor throughout the experiment, and deteriorated significantly with increased organic loadings and decreasing temperatures. The cause for the poor settling was speculated to be the severe loadings on the fill-and-draw systems. Both bulking and deflocculation were observed during the study. The high MLSS concentrations probably resulted in a slower settling sludge. 28 3 0 0 Temperature, °C Figure 2-1 : SVI as a function of temperature (Rudolfs and Lacy 1934) Sludge age, days Figure 2-2 : SVI as a function of Sludge age (Bisogni and Lawrence 1971) 110 o c — ma -E s "3 DA 35 Semi-Batch Operation Batch Operation —i 1 1 1 1 1 1 i 160 120 4 8 0 6 4 0 8 0 0 9 6 0 1120 1 2 8 0 C, (g/m3 as TOC) Figure 2-3 : SVI as a function of feed strength. Batch and semibatch operation (Hoepker and Schroeder 1979) 29 A n o t h e r l e a c h a t e t r e a t m e n t s t u d y , c a r r i e d o u t b y W o n g a n d M a v i n i c ( 1982 ) , e n c o u n t e r e d p r o b l e m s d u e t o p o o r s e t t l i n g . T h e e x c e s s i v e o r g a n i c l o a d i n g was t h o u g h t t o b e a p o s s i b l e c a u s e o f s l u d g e b u l k i n g . A l l r e a c t o r s w i t h b u l k i n g p r o b l e m s h a d a F / M r a t i o h i g h e r t h a n 0 .17 d a y s 1 . R e a c t o r s w i t h F / M r a t i o s l o w e r t h a n t h i s v a l u e d i d n o t h a v e a n y s e t t l i n g p r o b l e m s . W o n g a n d M a v i n i c a l s o f o u n d t h a t t h e s l u d g e s e t t l e a b i l i t y g r e w p r o g r e s s i v e l y w o r s e as t h e t e m p e r a t u r e s d e c r e a s e d . 2.5.2 O X Y G E N I J P T A K F R A T E S T o e v a l u a t e t h e a e r o b i c t r e a t a b i l i t y o f a w a s t e w a t e r , i t i s n e c e s s a r y to d e v i s e a b i o l o g i c a l r e a c t o r w h i c h c o n t a i n s t h e w a s t e , n u t r i e n t s a n d the m i c r o o r g a n i s m s a n d t o f o l l o w s o m e c h a r a c r t e r i s t i c p r o p e r t y o f t h a t s y s t e m f o r a p e r i o d o f t i m e . O n e o f t h e eas i e s t t e c h n i q u e s is t h e o b s e r v a t i o n o f t he O x y g e n U p t a k e R a t e ( O U R ) ( W a n g et al.,1911). G r e e n a n d S h e l e f ( 1 9 8 1 ) c o n c l u d e d t h a t t h e v i a b i l i t y o f t h e s l u d g e c a n b e d e t e r m i n e d b y o b s e r v i n g t h e O U R v a l u e s . O x y g e n u p t a k e r a t e i n c r e a s e s w i t h i n c r e a s i n g g r o w t h r a t e u n d e r s u b s t r a t e s a t u r a t i o n c o n d i t i o n s . It w a s , h o w e v e r , a s s u m e d t h a t a n y c h a n g e i n O U R is t h e r e s u l t o f c h a n g e s i n t h e s l u d g e v i a b i l i t y . It w a s a l s o a s s u m e d t h a t a n i n c r e a s e i n t h e V S S c o n c e n t r a t i o n is d u e t o a n i n c r e a s e i n t h e v i a b l e c e l l c o n c e n t r a t i o n . O U R d a t a c a n b e u s e d t o s h o w a n a v e r a g e , " r e l a t i v e " m e t a b o l i c a c t i v i t y o f t h e m i c r o o r g a n i s m s at e a c h v a l u e o f t h e s l u d g e a g e ( B i s o g n i a n d L a w r e n c e . 1 9 7 1 ) . T h e r e l a t i o n s h i p b e t w e e n O U R a n d s l u d g e a g e is s h o w n i n F i g u r e 2 - 4 . F o r a s y s t e m i n s t e a d y - s t a t e , t h e o x y g e n u p t a k e r a t es t e n d to d e c r e a s e w i t h i n c r e a s i n g s l u d g e a g e . I n a e r o b i c a c t i v a t e d s l u d g e s y s t e m s , o x y g e n is u s e d as a n e l e c t r o n a c c e p t o r i n t h e b i o l o g i c a l o x i d a t i o n r e a c t i o n . T h u s , t h e O U R c a n a l s o b e u s e d to r e p r e s e n t t h e r e s p i r a t i o n r a t e o f t h e s y s t e m ( W a n g et a/ . ,1977) . O U R v a l u e s c a n a l s o b e 160 0 1 1 1 1 — T — 0 2 4 6 8 10 Sludge Age, days Figure 2-4 : Oxygen uptake rate Versus Sludge age (Bisogni and Lawrence 1971) Figure 2-5 : Oxygen uptake rate as a function of time for semibatch reactors (Hocpker and Schroeder 1979) 31 u s e d to m o n i t o r t h e a c c l i m a t i z a t i o n o f a s l u d g e ( W a n g et al.,\911). W h e n t h e O U R a p p r o a c h e s a c o n s t a n t v a l u e , t h e s l u d g e c a n b e c o n s i d e r e d w e l l a c c l i m a t e d . H o e p k e r a n d S c h r o e d e r ( 1 9 7 9 ) s t u d i e d t h e e f f e c t o f l o a d i n g ra te o n t h e e f f l u e n t q u a l i t y o f a b a t c h a c t i v a t e d - s l u d g e s y s t e m . H i g h o x y g e n u p t a k e ra tes w e r e o b s e r v e d d u r i n g t h e f i l l p h a s e (as c o u l d b e p r e d i c t e d i n t u i t i v e l y ) f o r a s e m i b a t c h o p e r a t i o n w i t h a n 8 h o u r f i l l c y c l e . A t t h e e n d o f t h e f i l l p h a s e , t h e O U R v a l u e s s t a r t e d to d r o p a n d g r a d u a l l y l e v e l e d o u t at t h e m i n i m u m v a l u e ( F i g u r e 2-5). A l e a c h a t e t r e a t m e n t s t u d y i n v o l v i n g O U R a c t i v i t y w a s c o n d u c t e d b y B o y l e a n d H a m ( 1 9 7 4 ) u s i n g a n e x t e n d e d a e r a t i o n p r o c e s s w i t h a 23 h o u r d e t e n t i o n t i m e . T h i s s t u d y s h o w e d t h a t i n c r e a s e d o r g a n i c l o a d i n g r e s u l t e d i n h i g h e r O U R v a l u e s . It w a s s p e c u l a t e d t h a t a c o n v e n t i o n a l a c t i v a t e d s l u d g e p r o c e s s m a y r e s p o n d m o r e s e v e r e l y t o l e a c h a t e i n p u t s w i t h a h i g h e r o x y g e n u p t a k e ra te . 3. EXPERIMENTAL METHODS AND. ANALYSIS EXPERIMENTAL SET UP 3.1.1 R E A C T O R T Y P E S T h e p u r p o s e o f t h i s r e s e a r c h w a s to s t u d y t h e t r e a t a b i l i t y o f a c o m b i n e d was t e s t r e a m o f l e a c h a t e a n d d o m e s t i c s e w a g e . T h e t w o m o s t c o m m o n t y p e o f r e a c t o r s u s e d f o r b i o l o g i c a l t r e a t m e n t a r e t h e c o m p l e t e l y - m i x e d , c o n t i n u o u s f l o w r e a c t o r a n d t h e p l u g f l o w r e a c t o r . T h e l a b o r a t o r y s c a l e m o d e l o f t h e c o m p l e t e - m i x , c o n t i n u o u s f l o w r e a c t o r w a s s i m u l a t e d b y u s i n g a s c a l e d d o w n e d v e r s i o n o f t h e s a m e , w i t h a r e a c t o r v o l u m e o f 5 - L a n d a c l a r i f i e r v o l u m e o f 1 - L T h e p l u g f l o w s y s t e m w a s s i m u l a t e d w i t h a fill-and-draw r e a c t o r . T h e v o l u m e o f t h i s r e a c t o r w a s a l s o c h o s e n as 5 - L . S i n c e t h e o p e r a t i o n o f a p l u g f l o w s y s t e m , o n a l a b o r a t o r y s c a l e , i s d i f f i c u l t , m o s t r e s e a r c h w o r k f o r a p l u g f l o w s y s t e m is d o n e w i t h a fill-and-draw t y p e o f o p e r a t i o n ( Z a p f - G i l j e a n d M a v i n i c 1 9 8 2 , D a i g g e r a n d G r a d y 1 9 7 7 ) . T h e k i n e t i c m o d e l f o r a p l u g f l o w r e a c t o r is a l s o s i m i l a r . V a r i o u s r e l a t e d s t u d i e s p e r f o r m e d 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 h a v e m a d e u s e o f fill-and-draw s y s t e m s . H o w e v e r , t h e s t u d y c o n d u c t e d b y Z a p f - G i l j e a n d M a v i n i c ( 1 9 8 2 ) i n d i c a t e d t h e p o s s i b l e e f f e c t s o f s h o c k l o a d i n g i n a fill-and-draw r e a c t o r . I n t h i s s t u d y , t w o d i f f e r e n t t y p e s o f fill-and-draw r e a c t o r s w e r e se t u p , i n o r d e r t o s t u d y t h e p o s s i b l e e f f e c t s o f s h o c k l o a d i n g s o n t h e s y s t e m . O n e r e a c t o r w a s f e d o n c e a d a y w h i l e t h e o t h e r w a s f e d t h e s a m e a m o u n t o f i n f l u e n t f e e d o v e r t w o l o a d i n g s , i n a s i n g l e d a y . T h e p e r f o r m a n c e o f t h e fill-and-draw r e a c t o r s w a s t h e n c o m p a r e d w i t h t h e c o m p l e t e - m i x , c o n t i n u o u s f l o w r e a c t o r . A l l t h r e e r e a c t o r s w e r e o p e r a t e d u n d e r s i m i l a r c o n d i t i o n s t h r o u g h o u t t h e e n t i r e r u n . 32 33 3.1.2 A P P A R A T U S U S E D T h e t w o fill-and-draw s y s t e m s w e r e i d e n t i c a l i n a l l r e s p e c t s . I n v e r t e d 1 0 - L g l a s s j a r s w e r e u s e d as r e a c t o r s . T h e n e c k s o f t h e g l a s s j a r s w e r e t i g h t l y fitted w i t h r u b b e r s t o p p e r s . T h e b o t t o m o f t h e g l a s s j a r s w a s r e m o v e d . C o a r s e b u b b l e d i f f u s e r s t o n e s w e r e F i t ted t h r o u g h t h e r u b b e r s t o p p e r s a t t h e b o t t o m o f t h e r e a c t o r s . T h e r e a c t o r s w e r e k e p t c o m p l e t e l y m i x e d w i t h t h e h e l p o f c o n s t a n t s p e e d s t i r r e r s . A i r w a s s u p p l i e d t h r o u g h t h e d i f f u s e r b y t h e l a b o r a t o r y ' s filtered, c o m p r e s s e d a i r s y s t e m . A s c h e m a t i c o f t h e fill-and-draw s y s t e m is s h o w n i n F i g u r e 3 - 1 . T h e c o n t i n u o u s f l o w r e a c t o r , u n l i k e t h e fill-and-draw o n e s , w a s m a d e o f p e r s p e x . T h e r e a c t o r h a d a r e c t a n g u l a r c r o s s s e c t i o n a n d t h e b o t t o m e d g e s o f t h e r e a c t o r w e r e s m o o t h e d t o a v o i d s h o r t - c i r c u i t i n g o r d e a d s p o t s i n t h e r e a c t o r . T h e r e a c t o r w a s a t t a c h e d to a c l a r i f i e r u n i t o f 1-*L v o l u m e . T h e c l a r i f i e r w a s c y l i n d r i c a l l y s h a p e d w i t h a c o n e s h a p e d b o t t o m . A c y l i n d r i c a l i n f l u e n t c h a m b e r was a l s o p r o v i d e d f o r t h e c l a r i f i e r s o a s t o d i r e c t t h e s o l i d s t o t h e b o t t o m . A c o n s t a n t s p e e d s t i r r e r w a s p r o v i d e d i n t h e r e a c t o r t o k e e p t h e b i o m a s s c o m p l e t e l y m i x e d . A c o a r s e b u b b l e a i r d i f f u s e r w a s a l s o fitted i n t h e r e a c t o r . M a s t e r f l e x p u m p s , w i t h s i l i c o n t u b i n g w e r e u s e d f o r t h e i n f l u e n t l i n e f e e d a n d t h e s o l i d s r e c y c l e . A 1 0 - L t a n k w a s u s e d f o r the i n f l u e n t f e e d . T h e f e e d w a s s t i r r e d i n t e r m i t e n d y to k e e p t h e s o l i d s i n s u s p e n s i o n . T h e c o n t i n u o u s f l o w s y s t e m is s h o w n i n F i g u r e 3 - 2 . 3.1.3 REACTOR OPERATION 3.1.3.1 C o n t i n u o u s F l o w R e a c t o r T h e i n f l u e n t f e e d w a s p r e p a r e d b y m i x i n g a c e r t a i n p r o p o r t i o n o f d o m e s t i c s e w a g e a n d l e a c h a t e , d e p e n d i n g o n t h e p a r t i c u l a r e x p e r i m e n t a l r u n . T h e t w o was te s t r e a m s w e r e m i x e d o n t h e b a s i s o f v o l u m e o n l y . A c o n s t a n t i n f l u e n t f l o w ra te o f 5 - L / d a y w a s m a i n t a i n e d t h r o u g h o u t t h e e n t i r e s t u d y . S i n c e t h e p u m p s a v a i l a b l e 34 c i i » > STIRRER AEROBIC REACTOR AIR SUPPLY Figure 3-1: FILL-AND-DRAW SYSTEM. AEROBICS-REACTOR INFLUENT FEED TANK t \7 c > EFFLUENT CLARIFIER <+ ^ V RECYCLE Figure 3-2: CONTINUOUS FLOW SYSTEM. 35 w e r e n o t a b l e t o p u m p a t a l o w f l o w r a t e o f 5 - L / d a y , t h e i n f l u e n t f e e d p u m p w a s s e t o n a t i m e r . T h e t i m e r w a s o p e r a t e d o n a n o n / o f f c y c l e o f a p p r o x . 10 m i n u t e s . T h e ' O n ' p e r i o d f o r o n e c y c l e w a s 6.5 m i n u t e s . T h e i n f l u e n t f e e d p u m p w a s o p e r a t e d a t i ts s l o w e s t f l o w r a t e o f 8.6-L/day. T h e r e c y c l e p u m p w a s o p e r a t e d e i t h e r c o n t i n u o u s l y o r o n a t i m e r , d e p e n d i n g o n t h e s o l i d s b u i l d u p i n t h e c l a r i f i e r . T h e r e a s o n f o r d o i n g t h i s w a s t o e n s u r e c o m p l e t e s o l i d s r e c y c l e t o t h e r e a c t o r . S i n c e t h e r e c y c l e ra te v a r i e d f r o m r u n t o r u n , t h e h y d r a u l i c r e t e n t i o n t i m e i n t h e c l a r i f i e r a l s o v a r i e d . F o r t h i s r e a s o n , i t w a s d e c i d e d to e v a l u a t e t h e e f f l u e n t q u a l i t y o f t h e c o n t i n u o u s f l o w r e a c t o r b y p e r f o r m i n g 1 h o u r s e t t l i n g tests o n t h e b i o m a s s . T h e S R T i n t h e c o n t i n u o u s f l o w s y s t e m w a s m a i n t a i n e d b y w a s t i n g t h e a p p r o p r i a t e a m o u n t o f m i x e d l i q u o r d i r e c t l y f r o m t h e a e r o b i c r e a c t o r . W a s t a g e w a s d o n e o n a o n c e a d a y b a s i s . T h e v o l u m e o f m i x e d l i q u o r w a s t e d w a s r e p l a c e d b y d i s t i l l e d w a t e r . T h i s p r o c e d u r e i n v o l v e d t h e r e m o v a l o f s o m e s o l u b l e o r g a n i c f o o d a l o n g w i t h t h e b i o m a s s . T h e a m o u n t o f f o o d w a s t e d w a s a c c o u n t e d f o r i n t h e o r g a n i c l o a d i n g s t o t h e r e a c t o r . A l s o , i t w a s a n t i c i p a t e d t h a t s e t t l i ng p r o b l e m s w o u l d b e e n c o u n t e r e d d u r i n g s o m e o f t h e r u n s . S u c h a p r o b l e m w o u l d m a k e i t d i f f i c u l t t o r e p l a c e t h e o r g a n i c f o o d t h a t i s w a s t e d a l o n g w i t h t h e m i x e d l i q u o r . I n o r d e r t o m a i n t a i n u n i f o r m i t y d u r i n g t h e e n t i r e e x p e r i m e n t a l r u n , i t w a s d e c i d e d t o w a s t e a c c o r d i n g to t h e a b o v e m e n t i o n e d p r o c e d u r e d u r i n g a l l s t e a d y - s t a t e r u n s . C o m p l e t e l y - m i x e d c o n d i t i o n s w e r e o b t a i n e d w i t h t h e h e l p o f c o n s t a n t s p e e d s t i r r e r s a n d t h e a i r f l o w . T h e a i r f l o w w a s k e p t s u f f i c i e n t l y h i g h i n t h e r e a c t o r s o a s t o k e e p t h e b i o m a s s a e r o b i c ( D O 2 p p m ) . D u e to t h e s t i r r i n g , s o m e w a t e r w a s l o s t d u e t o e v a p o r a t i o n . H o w e v e r , i n a c o n t i n u o u s f l o w s y s t e m , t h e r e is n o n e e d t o r e p l a c e t h i s l o s t w a t e r s i n c e t h e c o n t i n u o u s f e e d w o u l d b r i n g t h e l e v e l i n t h e r e a c t o r u p t o v o l u m e . T h e a m o u n t o f w a t e r l o s t d u e t o e v a p o r a t i o n w a s c a l c u l a t e d b y t a k i n g t h e d i f f e r e n c e b e t w e e n t h e i n f l u e n t v o l u m e a n d t h e e f f l u e n t v o l u m e . 36 F r o m p a s t e x p e r i e n c e , i t w a s a n t i c i p a t e d t h a t d o m e s t i c s e w a g e u s e d i n th i s e x p e r i m e n t w o u l d c o n t a i n n u t r i e n t s i n e x c e s s . T h e l e a c h a t e , h o w e v e r , w a s e x p e c t e d t o b e n u t r i e n t d e f i c i e n t i n e i t h e r o n e o r b o t h o f t h e e s s e n t i a l n u t r i e n t s , n i t r o g e n a n d p h o s p h o r u s . S i n c e d o m e s t i c s e w a g e w a s a d d e d t o l e a c h a t e i n s i g n i f i c a n t l y l a r g e p r o p o r t i o n s , i t w a s d e c i d e d n o t t o a d d a n y n u t r i e n t s to t h e i n f l u e n t f e e d . T h e n u t r i e n t l e v e l s w e r e s p o t c h e c k e d d u r i n g t h e e n t i r e s t u d y a n d i n f l u e n t a n d e f f l u e n t n u t r i e n t l e v e l s w e r e m o n i t o r e d f o r t h e w o r s t c o n d i t i o n . 3.1.3.2 F i l l - a n d - D r a w R e a c t o r s F i l l - a n d - d r a w r e a c t o r s a r e c o m m o n l y u s e d f o r e x p e r i m e n t a l w o r k d u e to t h e i r e a s e o f o p e r a t i o n a n d t h e i r a b i l i t y to s i m u l a t e a p l u g f l o w r e a c t o r . T w o r e a c t o r s o f t h i s k i n d w e r e o p e r a t e d w i t h t h e i n t e n t i o n o f s t u d y i n g t h e e f f e c t o f d i f f e r e n t o r g a n i c l o a d i n g s o n t h e r e a c t o r s . O n e r e a c t o r w a s f e d o n c e a d a y o n l y , w h e r e a s t h e o t h e r r e a c t o r w a s f e d t w i c e a d a y . T h e t w o r e a c t o r s w e r e f e d the s a m e a m o u n t o f s u b s t r a t e . W a s t a g e f r o m t h e fill-and-draw r e a c t o r s w a s d o n e b y w a s t i n g a c e r t a i n v o l u m e o f t h e m i x e d l i q u o r , d e p e n d i n g o n t h e S R T r e q u i r e d . A c o n s t a n t v o l u m e , 1 - L , o f i n f l u e n t f e e d w a s a d d e d d a i l y d u r i n g the e n t i r e r u n . S i n c e t h e v o l u m e to b e w a s t e d v a r i e d a c c o r d i n g t o t h e S R T r e q u i r e d , m a i n t a i n i n g a c o n s t a n t to ta l v o l u m e o f 5 - L i n t h e r e a c t o r p r o v e d to b e c o m p l i c a t e d . T o g e t a r o u n d th i s p r o b l e m , t h e f o l l o w i n g e l a b o r a t e m e t h o d w a s a d o p t e d : F i r s t i y , t o m a i n t a i n t h e r e q u i r e d S R T , t h e v o l u m e t o b e w a s t e d was r e m o v e d f r o m t h e r e a c t o r . R e m o v a l o f m i x e d l i q u o r f r o m a l l t h e r e a c t o r s w a s d o n e b y u s i n g a v a c u u m i n g s y s t e m . F o r t h e 5 d a y S R T r u n s , t h e v o l u m e to b e w a s t e d w a s 1 - L , a n d t h e r e f o r e t h e i n f l u e n t f e e d o f 1 - L c o u l d b e a d d e d t o m a k e u p t h e to ta l v o l u m e i n t h e r e a c t o r . F o r t h e t w i c e - a - d a y r e a c t o r , t h e i n f l u e n t f e e d w a s a d d e d i n t w o d o s e s o f 5 0 0 m i s . e a c h . F o r t h e 10 d a y a n d 20 d a y S R T r u n s , t h e w a s t e d v o l u m e w a s less t h a n 1 - L . T h e r e f o r e , d u r i n g t h e s e r u n s a n a d d i t i o n a l 37 1-L ( a p p r o x i m a t e l y ) o f m i x e d l i q u o r w a s r e m o v e d f r o m t h e r e a c t o r a n d a l l o w e d to se t t l e . T h e s o l i d s w e r e p o u r e d b a c k i n t o t h e r e a c t o r w h i l e a n a p p r o p r i a t e a m o u n t o f t h e s u p e r n a t a n t w a s w a s t e d . T h e C O D o f t h e s u p e r n a t a n t w a s a c c o u n t e d f o r i n t h e o r g a n i c l o a d i n g c a l c u l a t i o n s . T h e i n f l u e n t f e e d o f 1-L w a s t h e n a d d e d to t h e r e a c t o r . T h e a b o v e m e n t i o n e d p r o c e d u r e is s c h e m a t i c a l l y s h o w n i n F i g u r e 3-3. W a t e r w a s a l s o l o s t t o e v a p o r a t i o n i n t h e F i l l - a n d - d r a w r e a c t o r s . T h i s l o s s o f w a t e r w a s a d j u s t e d i n t h e s u p e r n a t a n t w a s t a g e d e s c r i b e d a b o v e . A t t h e e n d o f e a c h f e e d i n g o p e r a t i o n , t h e l e v e l i n t h e r e a c t o r s w a s k e p t a t 5-L. T h e d i s s o l v e d o x y g e n l e v e l s i n t h e f i l l - a n d - d r a w r e a c t o r s w e r e k e p t s u f f i c i e n t l y h i g h ( D O 2 p p m ) s o as t o k e e p t h e b i o m a s s a e r o b i c a t a l l t i m e s . T h e a i r f l o w w a s k e p t c o n s t a n t w i t h t i m e a n d i t w a s n o t v a r i e d o v e r a f e e d i n g c y c l e . 3.2 E X P E R I M E N T A L R U N S A N D S T A R T U P P R O C E D U R E S 3.2.1 RUNS CONDUCTED B a s e d o n p r e v i o u s r e s e a r c h c o n d u c t e d i n t h i s field ( B o y l e a n d H a m 1974, C o o k a n d F o r e e 1974, Z a p f - G i l j e a n d M a v i n i c 1981, U l o t h a n d M a v i n i c 1977, P a l i t a n d Q a s i m 1977), i t w a s d e c i d e d t o o p e r a t e t h e t h r e e r e a c t o r s w i t h S R T ' s o f 5, 10 a n d 20 d a y s . T h i s w o u l d c o v e r t h e r a n g e o f c o n v e n t i o n a l a c t i v a t e d s l u d g e p r o c e s s e s . T h e c o n t i n u o u s f l o w r e a c t o r w a s o p e r a t e d at a l l t i m e s w i t h a 24 h o u r n o m i n a l h y d r a u l i c r e t e n t i o n t i m e ( H R T ) . N o m i n a l H R T is d e f i n e d as t h e r e a c t o r v o l u m e d i v i d e d b y t h e i n f l u e n t f l o w . T h i s i s a f a i r l y h i g h r e t e n t i o n t i m e f o r c o n v e n t i o n a l a c t i v a t e d s l u d g e p r o c e s s e s ( M e t c a l f a n d E d d y 1972). T h e r e a s o n s f o r k e e p i n g a h i g h n o m i n a l H R T i n t h e c o n t i n u o u s f l o w r e a c t o r w e r e t h e f o l l o w i n g : - l e a c h a t e is o f t e n f o u n d t o c o n t a i n h i g h m e t a l c o n c e n t r a t i o n s , w h i c h m a y i n h i b i t t h e b i o l o g i c a l a c t i v i t y a n d s u b s e q u e n t u p t a k e o f t h e o r g a n i c m a t t e r . Waste volume required to maintain SRT (a) 38 Remove approximately I litre of Mixed Liquor (b) (e) Figure 3-3: SCHEMATIC OPERATION OF A FILL-AND-DRAW SYSTEM. 39 - t h e h i g h o r g a n i c s t r e n g t h o f t h e f e e d w o u l d r e s t r i c t t h e i n f l u e n t f l o w ra te to a l o w v a l u e o f 5 - L / d a y , s o as t o m a i n t a i n " a c c e p t a b l e " o r g a n i c l o a d i n g s to the s y s t e m . T h i s i n t u r n w o u l d r e q u i r e t h a t t h e r e a c t o r s i z e b e s m a l l , t o k e e p the n o m i n a l H R T i n t h e r e a c t o r t o a r e a s o n a b l e v a l u e . A n a e r o b i c r e a c t o r o f 5 - L c a p a c i t y w a s c h o s e n f o r t h i s p u r p o s e . - a l a b o r a t o r y s c a l e m o d e l w o u l d n o r m a l l y r e q u i r e a r e a c t o r o f a t l e a s t 5 - L c a p a c i t y . D u r i n g a s t e a d y - s t a t e r u n , a s i g n i f i c a n t a m o u n t o f m i x e d l i q u o r is r e m o v e d f o r a n a l y s i s a n d i t w o u l d b e u n d e s i r a b l e t o h a v e a m u c h s m a l l e r r e a c t o r . - a c o n v e n t i o n a l a c t i v a t e d s l u d g e p r o c e s s w o u l d n o t h a v e a h i g h s t r e n g t h o r g a n i c f e e d a n d a s s u c h a l o w e r n o m i n a l H R T w o u l d b e s u f f i c i e n t to r e m o v e the o r g a n i c m a t t e r . I n t h e fill-and-draw r e a c t o r s , t h e h y d r a u l i c r e t e n t i o n t i m e w a s v e r y h i g h d u e t o t h e v e r y n a t u r e o f i ts o p e r a t i o n . I n t h i s e x p e r i m e n t , 1 - L o f t he i n f l u e n t w a s a d d e d e v e r y d a y , t o m a i n t a i n a c o n s t a n t H R T o f 5 d a y s . T h e to ta l v o l u m e i n t h e r e a c t o r w a s m a i n t a i n e d at 5 - L , b y w a s t i n g t h e a p p r o p r i a t e a m o u n t o f m i x e d - l i q u o r a n d s u p e r n a t a n t f r o m t h e r e a c t o r . E a c h s l u d g e a g e w a s s t u d i e d f o r t w o d i f f e r e n t r a t i o s o f d o m e s t i c w a s t e w a t e r a n d l e a c h a t e . T h e l e a c h a t e u s e d h a d a n i n i t i a l C O D o f 3 5 3 0 m g / L . T h e d o m e s t i c w a s t e w a t e r u s e d , f r o m t h e U B C p i l o t p l a n t ' s i n f l u e n t f e e d t a n k , h a s a C O D v a l u e i n t h e r a n g e o f 2 0 0 - 3 0 0 m g / L . T h e r a t i o s o f s e w a g e : l e a c h a t e u s e d w e r e 8 0 : 2 0 a n d 6 0 : 4 0 , b y v o l u m e . T h i s r e s u l t e d i n a p p r o x i m a t e i n f l u e n t C O D c o n c e n t r a t i o n s o f 9 0 6 m g / L a n d 1562 m g / L , r e s p e c t i v e l y . T h e f e e d c o n c e n t r a t i o n s , h o w e v e r , v a r i e d t h r o u g h o u t t h e s t u d y p e r i o d ( b u t n o t s i g n i f i c a n d y ) . T h e C O D v a l u e s f o r t h e i n f l u e n t f e e d w e r e a n a l y s e d d u r i n g e v e r y s t e a d y - s t a t e r u n . A f t e r t h e r o o m t e m p e r a t u r e ( 2 1 - 2 3 ° C ) r u n s w e r e c o m p l e t e d , t h e r e a c t o r s w e r e o p e r a t e d u n d e r l o w e r t e m p e r a t u r e s . S R T o f 10 d a y s w a s m a i n t a i n e d i n a l l t h r e e r e a c t o r s , d u r i n g b o t h c o l d t e m p e r a t u r e s t u d i e s . T h e first c o l d t e m p e r a t u r e r u n 40 h a d a s e w a g e r l e a c h a t e r a t i o o f 8 0 : 2 0 . T h i s c o r r e s p o n d e d to a n a v e r a g e i n f l u e n t C O D o f 9 0 5 m g / L . T h e r o o m t e m p e r a t u r e m a i n t a i n e d f o r t h i s r u n w a s 1 0 ° C , w i t h a 8 ° C l i q u i d t e m p e r a t u r e . T h i s t e m p e r a t u r e w a s s e l e c t e d d u e to t h e e n v i r o n m e n t a l c o n s t r a i n t s e x i s t i n g i n t h e l a b o r a t o r y . P e r h a p s a s l i g h t l y h i g h e r t e m p e r a t u r e o f 12 - 1 4 ° C w o u l d h a v e b e e n m o r e d e s i r a b l e f o r t h i s f i r s t c o l d t e m p e r a t u r e r u n , b u t t h e l o g i s t i c s o f t h i s w e r e n o t a t t a i n a b l e . T h e s e c o n d c o l d t e m p e r a t u r e r u n i n v o l v e d a f u r t h e r d r o p i n t h e r o o m t e m p e r a t u r e t o 6 ° C , w i t h a c o r r e s p o n d i n g 5 ° C l i q u i d t e m p e r a t u r e . H o w e v e r , s i n c e th i s d r o p i n t e m p e r a t u r e w a s n o t a s i g n i f i c a n t o n e , i t w a s d e c i d e d t o i n c r e a s e the o r g a n i c l o a d i n g i n t h e r e a c t o r s t o a 6 0 : 4 0 s e w a g e : l e a c h a t e r a t i o . T h e a v e r a g e i n f l u e n t C O D f o r t h i s s t e a d y - s t a t e r u n w a s 1 8 3 0 m g / L . A p r e l i m i n a r y r u n w a s a l s o c o n d u c t e d w i t h n o l e a c h a t e a d d i t i o n s t o t h e i n f l u e n t d o m e s t i c w a s t e w a t e r . P r o b l e m s o f l o w M L V S S w e r e o b s e r v e d at t h e 5 d a y a n d 1 0 d a y S R T ' s , w h i l e s e r i o u s s e t t l i n g p r o b l e m s w e r e e n c o u n t e r e d a t t h e 2 0 d a y S R T r u n . T h e l o w M L V S S v a l u e s w e r e a d i r e c t r e s u l t o f t h e l o w o r g a n i c l o a d i n g s t o t h e t h r e e s y s t e m s . T h e n o m i n a l H R T w a s f i x e d a t 2 4 h o u r s , a n d t h i s w a s t o o l o n g f o r t h e l o w o r g a n i c f e e d . T h e b u l k i n g s l u d g e i n t h e 2 0 d a y S R T r u n w a s a r e s u l t o f t h e d e n i t r i f i c a t i o n t a k i n g p l a c e i n t h e c l a r i f i e r . P o o r c l a r i f i e r o p e r a t i o n , d u r i n g t h e e a r l y s t ages o f t h e e x p e r i m e n t a t i o n , p r e v e n t e d q u i c k r e m o v a l o f t h e s l u d g e f r o m t h e b o t t o m o f t h e c l a r i f i e r . T h i s f u r t h e r e n h a n c e d t h e p r o b l e m o f d e n i t r i f i c a t i o n , d u e to t h e a n a e r o b i c c o n d i t i o n s c r e a t e d i n t h e c l a r i f i e r . L i m i t e d r e s u l t s a r e p r e s e n t e d i n t h e l a t e r c h a p t e r s t o h e l p s e r v e as a b a s i s f o r c o m p a r i s i o n w i t h o t h e r s t e a d y - s t a t e r u n s . 3.2.2 S T A R T U P A N D A C C T J M A T T Z A T T O N A c t i v a t e d s l u d g e w a s c o l l e c t e d f r o m t h e U B C p i l o t p l a n t a e r o b i c r e a c t o r . T h e M L S S o f t h e a c t i v a t e d s l u d g e w a s 1 9 9 0 m g / L a t t he t i m e o f c o l l e c t i o n . S i n c e 41 t h e p r e l i m i n a r y r u n w a s o p e r a t e d w i t h o n l y d o m e s t i c s e w a g e as t h e i n f l u e n t f e e d , t h e r e w a s n o n e e d t o s e e d o r a c c l i m a t i z e t h e b i o m a s s . T h e t h r e e r e a c t o r s w e r e filled w i t h 5 - L o f t h e a c t i v a t e d s l u d g e a n d t h e o p e r a t i o n w a s s t a r t e d as d e s c r i b e d e a r l i e r . T h e s o l i d s l e v e l i n t h e r e a c t o r w a s c h e c k e d d a i l y , t o k e e p t r a c k o f t h e s t a b i l i t y o f t h e s y s t e m . T h e b i o m a s s i n a l l t h r e e r e a c t o r s d r o p p e d s h a r p l y , d u e to t h e l o w o r g a n i c l o a d i n g s o n t h e r e a c t o r s . T h e r e a c t o r s w e r e o p e r a t e d u n d e r t h e s a m e c o n d i t i o n s f o r a d u r a t i o n o f a p p r o x i m a t e l y 6 w e e k s ; t h e S R T f o r t h e first r u n w a s k e p t a t 2 0 d a y s . S t e a d y - s t a t e c o n d i t i o n s w e r e a s s u m e d w h e n t h e s o l i d s l e v e l i n t h e r e a c t o r s b e c a m e f a i r l y c o n s t a n t T h e M L S S f r o m a l l t h r e e r e a c t o r s w a s c h e c k e d a t t he t i m e o f w a s t i n g . I n t h e f o l l o w - u p s t u d i e s , d o m e s t i c s e w a g e , c o l l e c t e d o n a w e e k l y b a s i s f r o m t h e U B C p i l o t p l a n t , w a s m i x e d w i t h the l e a c h a t e b e f o r e b e i n g u s e d as i n f l u e n t f e e d . T h e l e a c h a t e f o r t h e e n t i r e s t u d y w a s c o l l e c t e d f r o m t h e P r e m i e r L a n d f i l l i n N o r t h V a n c o u v e r , B . C . . A l l t h e l e a c h a t e w a s c o l l e c t e d a t t h e s ta r t o f t h e e x p e r i m e n t a n d s t o r e d a t 4 ° C f o r f u t u r e u s e . T h e s e c o n d se t o f s t e a d y - s t a t e r u n s w a s c o n d u c t e d w i t h a s e w a g e : l e a c h a t e r a t i o o f 8 0 : 2 0 . T h r e e e x p e r i m e n t a l r u n s w e r e s t u d i e d a t S R T ' s o f 5, 10 a n d 2 0 d a y s . T h e first s t e a d y - s t a t e r u n , a t a n S R T o f 5 d a y s , r e q u i r e d a c c l i m a t i z a t i o n o f t h e b i o m a s s t o t h e l e a c h a t e c o m p o n e n t i n t h e f e e d . I n i t i a l l y , 1 0 % l e a c h a t e w a s a d d e d w i t h t h e s e w a g e . T h i s w a s d o n e f o r a p e r i o d o f 10 d a y s . A f t e r 10 d a y s , t h e l e a c h a t e c o m p o n e n t i n t h e f e e d w a s i n c r e a s e d t o 2 0 % . T h e r e a c t o r s w e r e t h e n o p e r a t e d f o r a n a d d i t i o n a l 4 w e e k s . T h e M L S S i n a l l t h e r e a c t o r s r e a c h e d a f a i r l y c o n s t a n t v a l u e w i t h i n 3 w e e k s . T h e a n a l y s e s w e r e t h e n c o n d u c t e d o n t h e v a r i o u s p a r a m e t e r s f o r a f u r t h e r 1 w e e k d u r a t i o n . A t l eas t 3 d a y s o f a n a l y s e s w e r e d o n e f o r e a c h p a r a m e t e r . T h e 10 d a y s a n d 2 0 d a y s S R T r u n s , w i t h a 8 0 : 2 0 f e e d r a t i o , w e r e o p e r a t e d f o r 4 w e e k s a n d 6 w e e k s , r e s p e c t i v e l y . A s e x p l a i n e d e a r l i e r , t h e d u r a t i o n 4 2 o f e a c h r u n w a s g o v e r n e d b y t h e s o l i d s l e v e l i n t h e r e a c t o r s . A t t h e e n d o f e a c h s t e a d y - s t a t e r u n , t h e m i x e d - l i q u o r f r o m a l l t h r e e r e a c t o r s w a s m i x e d t o g e t h e r to e l i m i n a t e a n y b i a s e s d e v e l o p e d d u r i n g a p a r t i c u l a r r u n . T h e n e x t e x p e r i m e n t a l s e q u e n c e w a s o p e r a t e d a t 20 d a y s S R T , w i t h a 6 0 : 4 0 s e w a g e : l e a c h a t e f e e d r a t i o . T h i s r u n s h o w e d t h e h i g h e s t M L S S l e v e l s e n c o u n t e r e d d u r i n g t h e e n t i r e s t u d y , a p p r o x i m a t e l y 8 3 2 0 m g / L f o r t h e c o n t i n u o u s f l o w r e a c t o r . T h e first t w o w e e k s o f t h i s r u n w e r e s p e n t a c c l i m a t i z i n g t h e b i o m a s s to t h e h i g h e r - s t r e n g t h , o r g a n i c f e e d . T h e r u n w a s t h e n c o n d u c t e d f o r a n a d d i t i o n a l 4 w e e k s . T h e last t w o s t e a d y - s t a t e r u n s , w i t h a 6 0 : 4 0 f e e d r a t i o a n d S R T ' s o f 5 a n d 10 d a y s , w e r e o p e r a t e d f o r a t o t a l o f 4 w e e k s , a t t he e n d o f w h i c h t h e s o l i d s l e v e l h a d f u l l y s t a b i l i z e d a n d a n a l y s e s w e r e c o m p l e t e d . A s u m m a r y o f a l l e x p e r i m e n t a l r u n s c o n d u c t e d is p r o v i d e d i n T a b l e 3 - 1 . T a b l e 3-1 S t e a d y S t a t e E x p e r i m e n t a l P r o g r a m S R T ( d a y s ) L e a c h a t e : S e w a g e R a t i o 5 2 0 : 8 0 4 0 : 6 0 10 2 0 : 8 0 4 0 : 6 0 2 0 0 : 1 0 0 2 0 : 8 0 4 0 : 6 0 43 3.3 ANALYTICAL PROCEDURES 3.3.1 S O L I D S A N D C H E M I C A L O X Y G E N D E M A N D T h e 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 ) a n d 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 m e a s u r e d d a i l y d u r i n g t h e e n t i r e r u n . T h e s o l i d s l e v e l w a s u s e d as t h e b a s i s f o r c h e c k i n g t h e s t e a d y - s t a t e c o n d i t i o n s . W h e n t h e b i o m a s s r e a c h e d a f a i r l y s t e a d y v a l u e , i t w a s a s s u m e d t h a t t h e s y s t e m w a s i n s t e a d y - s t a t e . A l l a n a l y s i s o f s o l i d s w a s d o n e c o n f o r m i n g t o t h e p r o c e d u r e 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 ( 1 9 8 0 ) . D u r i n g a s t e a d y - s t a t e r u n , e f f l u e n t s u s p e n d e d s o l i d s a n d v o l a t i l e s u s p e n d e d s o l i d s w e r e a l s o a n a l y s e d . A l l e f f l u e n t s a m p l e s w e r e t a k e n a f t e r a l l o w i n g t h e b i o m a s s t o se t t le f o r 1 h o u r i n a 1 - L g r a d u a t e d c y l i n d e r . S o l i d s l e v e l s , o f t h e w a s t e d s u p e r n a t a n t f r o m t h e f i l l - a n d - d r a w r e a c t o r s , w e r e a l s o a n a l y s e d . C h e m i c a l O x y g e n D e m a n d ( C O D ) v a l u e s w e r e a n a l y z e d d a i l y d u r i n g a s t e a d y - s t a t e r u n . T h i s test w a s a l s o i n a c c o r d a n c e t o t h e S t a n d a r d M e t h o d s p r o c e d u r e . M e r c u r i c s u l f a t e w a s n o t a d d e d t o t h e s a m p l e , as c h l o r i d e l e v e l s i n b o t h l e a c h a t e a n d d o m e s t i c w a s t e w a t e r w e r e v e r y l o w . T h e C O D test w a s p e r f o r m e d o n i n f l u e n t a n d e f f l u e n t s a m p l e s . 3.3.2 OXYGEN UPTAKE RATE T h i s test w a s u s e d a s a m e a n s o f d e t e r m i n i n g t h e v i a b i l i t y o f t h e b i o m a s s . T h e v a l u e o f t h e S p e c i f i c O x y g e n U p t a k e R a t e ( S P O U R ) w a s u s e d f o r c o m p a r i n g t h e p e r f o r m a n c e o f d i f f e r e n t r e a c t o r s a n d t h e v a r i o u s s t e a d y - s t a t e r u n s . T h e O U R m e t e r u s e d w a s a Y e l l o w S p r i n g s I n s t r u m e n t s C o . L t d . , M o d e l 5301 m e t e r . A s a m p l e v o l u m e o f 3 m l w a s u s e d f o r e a c h r e a d i n g . O U R v a l u e s w e r e a n a l y z e d f o r a l l s t e a d y - s t a t e c o n d i t i o n s . F o r e v e r y i n d i v i d u a l s t e a d y - s t a t e s i t u a t i o n , O U R v a l u e s w e r e a l s o a n a l y z e d o v e r a 2 4 h o u r p e r i o d . T h i s w a s d o n e p u r p o s e f u l l y to s t u d y t h e d i f f e r e n c e i n t h e p e r f o r m a n c e o f t h e t w o fill-and-draw r e a c t o r s . 4 4 3.3.3 D I S S O L V E D O X Y G E N A N D P H B o t h d i s s o l v e d o x y g e n a n d p H v a l u e s w e r e s p o t c h e c k e d d u r i n g t h e e n t i r e s t u d y . T h e d i s s o l v e d o x g e n l e v e l s w e r e k e p t m o r e t h a n 2 m g / L a t a l l t i m e s i n a l l r e a c t o r s . T h e r e w a s n o s t r i c t m o n i t o r i n g o f t h e d i s s o l v e d o x y g e n l e v e l s , b u t c a r e w a s t a k e n t o p r e v e n t t h e r e a c t o r s f r o m g o i n g a n a e r o b i c . F o r a f e w s t e a d y - s t a t e r u n s , d i s s o l v e d o x y g e n v a l u e s w e r e o b s e r v e d o v e r a 2 4 h o u r p e r i o d f o r the t w o fill-and-draw r e a c t o r s . A Y e l l o w S p r i n g s I n s t r u m e n t s C o . L t d . , M o d e l 5 4 A O x y g e n m e t e r w a s u s e d f o r m e a s u r i n g t h e d i s s o l v e d o x y g e n l e v e l s . T h e p H m e t e r u s e d f o r the a n a l y s i s w a s a F i s h e T A c c u m e t M o d e l 3 2 0 E x p a n d e d S c a l e R e s e a r c h p H m e t e r . 3.3.4 S L U D G E V O L U M E I N D E X A N D S E T T L I N G T h e S l u d g e V o l u m e I n d e x ( S V I ) w a s m e a s u r e d b y a l l o w i n g t h e b i o m a s s to se t t le f o r h a l f a n h o u r a n d o b s e r v i n g t h e m l o f s l u d g e s e t t l e d i n t h e c y l i n d e r . S e t t l i n g w a s c a r r i e d o u t i n a 1 - L g r a d u a t e d c y l i n d e r . T h e S V I i s d e f i n e d as the v o l u m e i n m l o c c u p i e d b y 1 g m o f a c t i v a t e d s l u d g e a f t e r s e t t l i n g the a e r a t e d l i q u o r f o r 3 0 m i n u t e s . T h e b i o m a s s w a s t h e n a l l o w e d t o se t t le f o r a f u r t h e r h a l f h o u r a n d t h e s u p e r n a t a n t f r o m t h e s e t t l i n g w a s d e c a n t e d as t h e e f f l u e n t s a m p l e . T h e o n e h o u r s e t t l i n g p r o c e d u r e w a s u s e d as a s t a n d a r d f o r c o m p a r i s i o n b e t w e e n s t e a d y - s t a t e s . 3.3.5 T O T A L K J E L D A H L N I T R O G E N A N D T O T A L P H O S P H O R U S T o t a l K j e l d a h l N i t r o g e n ( T K N ) a n d T o t a l P h o s p h o r u s ( T P ) w e r e a l s o a n a l y s e d f r o m t i m e to t i m e , d u r i n g a s t e a d y - s t a t e r u n . A n a l y s i s f o r t h e s e t w o p a r a m e t e r s w a s d o n e o n t h e i n f l u e n t a n d t h e e f f l u e n t s a m p l e s . T h e m a i n p u r p o s e f o r d o i n g T K N a n d T P w a s t o c h e c k f o r a n y n u t r i e n t l i m i t a t i o n s d u r i n g the s t e a d y - s t a t e r u n s . T h e tests w e r e c a r r i e d o u t a c c o r d i n g to t h e T e c h n i c o n M a n u a l 45 (1974), and the instrument used was a Technicon Auto Analyser II S.C. Colorimeter. 3.3.6 TRACE METALS For each steady-state run, metal analyses were performed on the sludge samples from each reactor. The metals analyzed were - Iron, Copper, Chromium, Zinc, Cadmium, and Lead. These metals have been known to inhibit the activity of activated sludge microorganisms (Neufeld 1976). An attempt was made to correlate the bioaccumulation of metals in the sludge to the process efficiency. Firstly, the sludge samples were centrifuged and dried; then they were ground and 'wet-ash' digested according to the recommended EPA procedure (March 1979). An Atomic Absorption (AA) Spectrophotometer, a Jairell Ash A A (Model 810), was used for all metal analyses. 4. RESULTS AND DISCUSSION 4.1 FEED CHARACTERISTICS L e a c h a t e u s e d i n t h i s i n v e s t i g a t i o n w a s c o l l e c t e d f r o m t h e P r e m i e r S t r ee t L a n d f i l l s i t u a t e d i n N o r t h V a n c o u v e r , B r i t i s h C o l u m b i a . T h e P r e m i e r L a n d f i l l l e a c h a t e is t h e s u b j e c t o f s e v e r a l i n v e s t i g a t i o n s 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 ; c u r r e n t w o r k i n v o l v e s s t u d y i n g t h e b i o l o g i c a l t r e a t a b i l i t y o f t h i s l e a c h a t e u s i n g o n - s i t e r o t a t i n g b i o l o g i c a l c o n t a c t o r s , a n d t h e a n a e r o b i c t r e a t m e n t o f l e a c h a t e u s i n g a n u p f l o w filter. A p p r o x i m a t e l y 3 5 0 - L o f l e a c h a t e w e r e c o l l e c t e d f r o m t h e s i te at t h e s tar t o f t h e e x p e r i m e n t . T h i s w a s s t o r e d i n 2 0 - L p o l y e t h y l e n e c o n t a i n e r s , w i t h a i r t i g h t c a p s , at 4 ° C , t h r o u g h o u t t h e s t u d y . T h e i n v e s t i g a t i o n w a s c a r r i e d o u t f o r a d u r a t i o n o f t e n m o n t h s . T h e c h a r a c t e r i s t i c s o f t h e l e a c h a t e a r e s h o w n i n T a b l e 4 - 1 . T h e C O D o f the l e a c h a t e w a s c h e c k e d f r o m t i m e t o t i m e a n d n o s i g n i f i c a n t d e c r e a s e i n C O D v a l u e w a s o b s e r v e d d u r i n g t h e e x p e r i m e n t I n i t i a l l y , B O D 5 tests w e r e c a r r i e d o u t b u t t h e v a r i a t i o n i n t h e B O D s v a l u e s i n d i c a t e d t h a t t h i s c o u l d n o t b e u s e d as a r e l i a b l e m e a s u r e o f o r g a n i c m a t t e r . T h e u s e o f B O D 5 , as a p a r a m e t e r w a s , t h e r e f o r e , d i s c o n t i n u e d i n t h e e x p e r i m e n t a l r u n s . T h e d o m e s t i c s e w a g e u s e d i n t h i s e x p e r i m e n t w a s o b t a i n e d f r o m t h e i n f l u e n t f e e d t a n k o f t h e p i l o t - p l a n t , 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 . S e w a g e w a s c o l l e c t e d o n a w e e k l y b a s i s a n d s t o r e d a t 4 ° C . T h e v a r i a t i o n i n t h e d o m e s t i c s e w a g e q u a l i t y w a s r e f l e c t e d i n t h e c o m b i n e d i n f l u e n t f e e d C O D c o n c e n t r a t i o n s . H o w e v e r , t h i s v a r i a t i o n w a s n o t f o u n d t o b e s i g n i f i c a n t ( d e t a i l e d l a te r ) . C O D v a l u e s f o r e a c h b a t c h o f d o m e s t i c s e w a g e c o l l e c t e d w e r e o b t a i n e d , t h u s k e e p i n g t r a c k o f t h e v a r i a t i o n i n t h e i n f l u e n t f e e d . A v e r a g e c h a r a c t e r i s t i c s o f t h e d o m e s t i c s e w a g e a r e s h o w n i n T a b l e 4 - 2 . 4 6 T A B L E 4-1 Leachate Characteristics P a r a m e t e r C o n c e n t r a t i o n C O D 3 5 3 0 B O D 5 1698 p H 6.1 T o t a l S o l i d s 3 2 4 6 S p e c i f i c C o n d u c t a n c e 3 0 6 2 A l k a l i n i t y (as C a C O , ) 3 2 5 8 T o t a l P h o s p h o r u s 0.18 T o t a l K j e l d a h l N i t r o g e n 53 C a 265 C d 0 .13 C r less t h a n 0.02 C u 0.4 F e 185 M g 4 9 P b less t h a n 0.02 Z n 0.42 • A l l c o n c e n t r a t i o n s i n m g / L , e x c e p t p H i n p H u n i t s a n d S p e c i f i c C o n d u c t a n c e i n m i c r o m h o s / c m . TABLE 4-2 Sewage Characteristics P a r a m e t e r C o n c e n t r a t i o n C O D 2 2 0 B O D 5 119 p H 7.2 T o t a l K j e l d a h l N i t r o g e n 2 4 T o t a l P h o s p h o r u s 4.2 • A l l c o n c e n t r a t i o n s i n m g / L , e x c e p t p H i n p H u n i t s . 4 8 4.2 RESULTS F R O M T H E PRELIMINARY EXPERIMENT A p r e l i m i n a r y e x p e r i m e n t w a s c o n d u c t e d to d e v e l o p a n i d e a o f s e w a g e c h a r a c t e r i s t i c s a n d s y s t e m p e r f o r m a n c e . T h i s e x p e r i m e n t i n v o l v e d t h e u s e o f o n l y d o m e s t i c s e w a g e a s i n f l u e n t f e e d . It w a s a l s o e x p e c t e d t o s e r v e a s a b a s i s f o r c o m p a r i s o n w i t h t h e o t h e r e x p e r i m e n t a l r u n s . A l l r u n s w e r e p e r f o r m e d at r o o m t e m p e r a t u r e ( 2 1 - 2 3 ° C ) . I n i t i a l l y , t h e b i o r e a c t o r s w e r e o p e r a t e d a t a S R T o f 5 d a y s . T h e 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 ) l e v e l s i n t h e f i l l - a n d - d r a w r e a c t o r s d r o p p e d t o less t h a n 1 0 0 m g / L . I n o r d e r t o b u i l d u p t h e b i o m a s s , i t w a s d e c i d e d t o i n c r e a s e t h e S R T to 2 0 d a y s . H o w e v e r , t h i s i n c r e a s e i n S R T c a u s e d a d e c r e a s e i n t h e f o o d / m i c r o o r g a n i s m ( F / M ) r a t i o t o l ess t h a n 0.2 d a y s 1 , w h i c h c o r r e s p o n d e d t o a n e n d o g e n o u s p h a s e i n t h e s y s t e m . T h e r e f o r e , t h e b i o m a s s at 2 0 d a y s S R T w a s a l s o v e r y l o w ( T a b l e 4 - 3 ) . T h e b i o m a s s l e v e l s i n t h e f i l l - a n d - d r a w r e a c t o r s w e r e c o n s i d e r a b l y l o w e r t h a n t h e c o n t i n u o u s - f l o w r e a c t o r d u e t o t h e l o w o r g a n i c l o a d i n g s t o t h e s e s y s t e m s . V a l u e s o f v a r i o u s p a r a m e t e r s o b t a i n e d f o r t h i s r u n a r e a l s o p r o v i d e d i n T a b l e 4 - 3 . A l l t h r e e r e a c t o r s i n d i c a t e d a v e r a g e e f f l u e n t C O D ' s i n t h e r a n g e o f 2 5 t o 35 m g / L , c o r r e s p o n d i n g t o t r e a t m e n t e f f i c i e n c i e s f r o m 83.1 p e r c e n t to 87 .6 p e r c e n t S e t t l i n g c h a r a c t e r i s t i c s f o r a l l t h r e e s y s t e m s w e r e p o o r a n d p i n - p o i n t f l o e w a s o b s e r v e d t h r o u g h o u t t h e g r a d u a t e d c y l i n d e r . T h i s c o u l d h a v e b e e n d u e t o t h e v e r y l o w M L S S v a l u e s , t h u s r e s u l t i n g i n a p o o r l y s e t t l i n g f l o e . S p e c i f i c o x y g e n u p t a k e r a t e ( S P O U R ) v a l u e s t a k e n o v e r a 2 4 - h o u r p e r i o d ( F i g u r e 4 - 1 ) s h o w e d t h a t a m a x i m u m S P O U R v a l u e w a s r e a c h e d i n e a c h fill-and-draw r e a c t o r a f e w h o u r s a f t e r f e e d i n g . It was a l s o n o t e d t h a t t h e m a x i m u m S P O U R v a l u e i n t h e o n c e - a - d a y r e a c t o r o c c u r r e d 2 to 3 h o u r s a f t e r t h e t w i c e - a - d a y s y s t e m . T h i s s e e m s t o i n d i c a t e t h a t t h e t w i c e - a - d a y r e a c t o r t o o k u p t h e s u b s t r a t e m o r e e f f i c i e n t l y . H o w e v e r , d u e to t h e u n s t a b l e n a t u r e o f t h e s y s t e m s , i t w a s d i f f i c u l t t o a s c e r t a i n a n y d e f i n i t e r e l a t i o n s h i p o r t r e n d f r o m t h i s se t o f d a t a . T h e S P O U R 49 TABLE 4-3 Preliminary Experiment Results R e a c t o r T y p e I n f l u e n t F e e d ( m g / L C O D ) O r g a n i c L o a d i n g ( k g C O D / m 3 - d a y ) M L S S ( m g / L ) E f f l u e n t C O D ( m g / L ) % T r e a t m e n t S l u d g e S e t d i n g ( m i s ) C o n t . F l o w R e a c t o r 2 1 0 0 .210 2 5 3 35 83.1 2 0 - 25 O n c e -a - d a y F e e d 2 1 0 0 .042 85 33 84.5 5 - 5 T w i c e -a - d a y F e e d 2 1 0 0 .042 96 2 6 87 .6 5 - 5 Figure 4-1: SPOUR Vs Time for the Fill-and-Draw Systems -Preliminary Experiment 10 -u 1 1 1 1 1 r 1 2 3 4 5 6 7 Days in Steady State Figure 4-2: SPOUR Vs Time for the Continuous-Flow System -Preliminary Experiment 51 v a l u e s f o r t h e c o n t i n u o u s - f l o w r e a c t o r w e r e a l s o o b t a i n e d . S a m p l e s f r o m t h e c o n t i n u o u s - f l o w s y s t e m w e r e t a k e n d a i l y . A p l o t o f SPOUR a g a i n s t d a y s , i n s t e a d y s ta te o p e r a t i o n , s h o w e d t h a t t h e v a r i a t i o n w a s q u i t e s i g n i f i c a n t a n d t h e s y s t e m w a s u n s t a b l e ( F i g u r e 4 - 2 ) . T h e d a t a o b t a i n e d f r o m t h i s e x p e r i m e n t a l r u n c l e a r l y i n d i c a t e d t h a t t h i s r u n d i d n o t p e r f o r m w e l l . It i s f e l t t h a t f o r s u c h a w e a k i n f l u e n t t h e SRT s h o u l d n o t h a v e b e e n i n c r e a s e d t o 2 0 d a y s . P e r h a p s , a t a n SRT o f 1 0 d a y s o r l ess , t h e s y s t e m w o u l d h a v e p e r f o r m e d b e t t e r . A n o t h e r i m p o r t a n t f a c t o r , as m e n t i o n e d e a r l i e r , w a s t h e s i g n i f i c a n d y h i g h h y d r a u l i c r e t e n t i o n t i m e (HRT) i n t h e b i o r e a c t o r s ( 2 4 h o u r s f o r t he c o n t i n u o u s - f l o w r e a c t o r ) . M e t c a l f a n d E d d y ( 1 9 7 2 ) r e c o m m e n d a n HRT o f 4 to 8 h o u r s i n a c o n v e n t i o n a l a c t i v a t e d s l u d g e p l a n t T h i s h i g h HRT p r o b a b l y r e s u l t e d i n t h e s u b s t r a t e b e i n g u s e d u p v e r y q u i c k l y a n d t h e s u b s e q u e n t d i e o f f o f t h e m i c r o o r g a n i s m i n t h e e n d o g e n o u s p h a s e . A l t h o u g h s u c h a h i g h HRT w a s r e q u i r e d f o r t h e a e r o b i c b i o l o g i c a l t r e a t m e n t o f a h i g h s t r e n g t h w a s t e l i k e l e a c h a t e ( d i s c u s s e d e a r l i e r ) , i t w a s fe l t , t h a t t h i s p a r t i c u l a r e x p e r i m e n t a l s e t - u p w a s n o t f e a s i b l e f o r a d o m e s t i c s e w a g e i n f l u e n t f e e d . In o r d e r t o h a v e a s i g n i f i c a n t l y h i g h e r b i o m a s s f o r t h e 2 0 d a y s SRT, e i t h e r t h e f l o w r a t e h a d t o b e i n c r e a s e d ( t h e r e b y i n c r e a s i n g t h e o r g a n i c l o a d i n g ) o r t h e r e a c t o r s i z e h a d t o b e r e d u c e d ( to d e c r e a s e t h e HRT). The f l o w r a t e , h o w e v e r , c o u l d n o t b e i n c r e a s e d s i n c e t h e r e w a s l i m i t e d a m o u n t o f f e e d a v a i l a b l e . A r e a c t o r s i z e o f 5 L is c o n s i d e r e d t o b e t h e m i n i m u m r e c o m m e n d e d s i ze f o r l a b o r a t o r y w o r k ( d i s c u s s e d e a r l i e r ) , a n d h e n c e a s m a l l e r r e a c t o r s i z e a l s o w a s n o t u s e d . 4.3 R E S U L T S F R O M T H E 80:20 E X P E R I M E N T A L R U N S 4.3.1 M I X E D - L I Q U O R CHARACTERISTICS The p u r p o s e o f c o n d u c t i n g t h i s e x p e r i m e n t w a s t o s t u d y t h e t r e a t a b i l i t y o f a l a n d f i l l l e a c h a t e b y u s i n g d i f f e r e n t r e a c t o r t y p e s . L e a c h a t e w a s m i x e d i n v a r y i n g 52 proportions with the domestic sewage. The 80:20 run corresponds to 20 percent leachate, by volume, in the domestic wastewater. The influent feed strength (as COD) throughout this entire run varied from 804 mg/L to 952 mg/L. This variation was observed due to the fluctuations in the domestic wastewater quality. The day-to-day variation of the influent feed is provided in Figure 4-3. Influent feed strengths and the corresponding loadings are shown in Table 4-4. The organic loadings for the continuous-flow reactor varied from 0.781 to 0.888 kg COD/m 3 -day (48.6 to 55.3 lb COD/1000 cu ft-day). This is within the recommended range of organic loadings for a completely-mixed, activated sludge process (Boyle and Ham 1974, Metcalf and Eddy 1972, Zapf-Gilje and Mavinic 1981). Organic loadings on the fill-and-draw systems ranged from 0.156 to 0.177 kg COD/m 3 -day (9.7 to 11.0 lb COD/1000 cu ft-day). These values are also within the recommended range (Zapf-Gilje and Mavinic 1981). In the continuous-flow reactor, food/microorganism (F/M) values during a particular steady-state run are relatively constant and the F / M value can be used to represent the state of the system at all times. The F / M ratio in a fill-and-draw reactor, however, varies at all times. This is due to the nature of the fill-and-draw operation. Two different fill-and-draw reactors should therefore be compared, on the basis of F / M ratios, only i f the F / M values have been calculated at a particular time during the feed cycle. In a fill-and-draw system, the initial F / M values, corresponding to the time of feeding, are extremely high and they decrease to their lowest value with time. In this experiment, all F / M values are calculated just before feeding, i.e. at the end of a daily feed cycle. As such, the F / M values obtained for the fill-and-draw reactors are their lowest values. These values do not indicate the system's state at all times. However, in most of the steady-state runs, the 'base' value was reached within 4-5 hours of feeding and it is reasonable to assume that this value is perhaps the single most 53 Figure 4-3: Variation of Influent Feed COD with Time 54 TABLE 4-4 Operational Characteristics for the 80:20 Experimental Run (a) Continuous Flow Reactor SRT (davs) Influent Feed Org. Loading Organic MLSS (mg/L) F / M Ratio (mg/L COD) (kg COD Loading (lb (kg COD/kg /m 3-day) COD/1000 cu MLSS -day) ft-day) 5 888 0.888 55.30 331 2.46 10 812 0.812 50.60 1899 0.43 20 781 0.781 48.60 3975 0.20 (b) Once-a-day Reactor SRT (days) Influent Feed Org. Loading (mg/L COD) (kg C O D / m 3 - day) 5 888 0.177 10 812 0.162 20 781 0.156 SRT (days) Influent Feed Org. Loading (mg/L COD) (kg COD /m 3-day) 5 888 0.177 10 812 0.162 20 781 0.156 Organic MLSS (mg/L) F / M Ratio Loading (lb (kg COD/kg COD/1000 cu MLSS -day) ft-day)  11.00 282 0.63 10.10 513 0.32 9.70 987 0.16 Organic MLSS (mg/L) F / M Rauo Loading (lb (kg COD/kg COD/1000 cu MLSS -day) ft-day) 11.00 250 0.71 10.10 532 0.30 9.70 1103 0.14 (c) Twice-a-day Reactor 55 representative F / M value for the particular system. A more representative F / M value for the system might have been an average value calculated over the daily feed cycle. However, it was found difficult to monitor the F / M values at various times during a feed cycle, mainly due to the limited quantity of mixed-liquor available. In all three reactors, it was expected that the F / M ratio would decrease as the SRT. increases. A definite trend towards this was indicated. The relationship between F / M ratio and SRT, for the continuous-flow reactor, is shown in Figure 4-4 (a). The F / M value for the 5-day SRT was 2.46 kg COD/kg MLSS-day. This high F / M value is attributed to the low mixed-liquor suspended solids (MLSS) in the reactor, due to the loss of solids in the effluent and improper clarifier operation. The 5-day SRT was the first steady-state run carried out; a few operational problems were encountered, such as solids accumulating in the clarifier. This led to anaerobic conditions for the biomass in the clarifier and subsequently to some gas formation; this, in turn, resulted in rising sludge and solids loss in the effluent This problem was corrected by changing the operation of the recycle pump to an intermittent 'on-off basis. A slow speed stirrer (1 rpm) was also installed in the clarifier to prevent the sludge from clogging the opening of the recycle line. These modifications worked fairly well and no further operational problems were encountered during the rest of the study. The F / M ratios at different SRTs, for the two fill-and-draw reactors, are compared in Figure 4-4 (b). These 'minimum' F / M values indicate that the 'base' F / M ratio in both fill-and-draw reactors was approximately the same. As expected, both reactors experienced a drop in the F / M ratio with increase in SRT, thereby agreeing with the kinetic model proposed by Lawrence and McCarty (1970). Since the organic loadings did not vary much with the SRTs, for a particular system, it was anticipated that a change in the F / M ratio would also • 1 1 r 5 10 15 20 SRT (days) Figure 4-4: F / M Ratio Vs SRT - 80:20 Experimental Run 57 lead to a change in the MLSS of the system. A decrease in the F / M ratio with increasing SRT implies that the MLSS in the reactors would increase, the organic loading being approximately constant The variation of the MLSS with SRT is shown in Figure 4-5 (a). MLSS values varied slightly during each steady-state run. This variation, however, was much less during the 20-day SRT run (Figure 4-6), thereby indicating a more stable operation. Average values obtained for a particular steady-state run have been used for comparison and calculation purposes. An interesting trend was indicated in the relationship between percent mixed-liquor volatile suspended solids (MLVSS) and the SRTs. The MLVSS percentage is known to vary with the SRT in any biological reactor (Metcalf and Eddy 1972, Zapf-Gilje and Mavinic 1981). The variation, however, seems to be a complex one. On the one hand, percent MLVSS tends to decrease as the SRT is increased, due to the drop in the F / M ratio "(leading to endogenous respiration); this is a result of the limited substrate available to the biomass. The biodegradable portion of the feed is used up completely, whereas the non-biodegradable and inert fractions keep accumulating. The consequence of this is a drop in the percent MLVSS at a higher SRT. This argument holds as long as the feed strength remains the same. However, an increase in the feed strength also increases the total inert content The increase in the biodegradable fraction results in an increase in the activity of the microorganisms and, at a long SRT, this fraction is completely used up. The net result of this is a decrease in the percent MLVSS in the reactor. For a complex waste like leachate, the inert fraction may be a significant amount In such a case, the drop in percent MLVSS with an increase in SRT may not be as large as one might expect, since the inert fraction is already quite high. The percent MLVSS is plotted against the SRT, for all the steady-state runs, in Figure 4-5 (b). For the continuous-flow reactor, the percent MLVSS 00 CO 4000 3500-3000 2500 2000 1500 1000 (0) Legend - A Cont. Flow Reactor • O n c e - a - d a y Feed • Twice-o -doy Feed ______ t __ - - " ' _____ •* . 1 10 15 SRT (days) 20 120 100 (b) If) T3 "6 I/) "O -o C CD CL V) 3 1/1 _0> _5 o > 8 0 -60 -40-20-Cont. Flow Reactor v/t J/'U% V // {'  / A '•' 5 10 20 Twice-o-dcy Feed Legend KX % MLVSS E 2 % MLSS 5 10 20 SRT (days) 5 10 20 Figure 4-5: Mixed-Liquor Solids - 80:20 Experimental Run 400 350 -150 5 Days SRT & Cont. Fiow Reactor • Qnce-o-doy ^ad Q Twice-a-day Teed 4 5 6 7 8 9 Days in Steady State 10 11 Twice—a-day Teed 3 4 5 6 7 3 Days in Steady State ic 4500 4000 f 3500 3000 2500 ^  2000 1500 1000 500 J 1 20 Days SRT Legend A Cont. Flow Reactor • Once-a-day Feed !• Twice—a—day Feed 3 4 5 6 7 Days in Steady State Figure 4-6: MLSS Vs Days in Steady State - 80:20 Experimental Run 60 dropped from 72.8 percent, at a 5-day SRT, to 59.3 percent at a 20-day SRT. A similar pattern, with larger differences, however, was also observed for the two fill-and-draw reactors (Table 4-5 (a)). The Specific Oxygen Uptake Rate (SPOUR) values (expressed as mg/gm VSS-hr) are used to determine the metabolic activity of the microorganisms (Bisogni and Lawrence 1971). In a fill-and-draw system, the SPOUR value varies with time during a feed cycle. This variation, however, is different from the F / M ratio. SPOUR values reach a maximum after a short time period and then decline to their 'base' value, which also corresponds to their lowest value during a feed cycle. In this study, SPOUR values were also obtained just before feeding. Therefore, the SPOUR values in the fill-and-draw systems are their lowest values and the average values would perhaps be higher. However, in most cases, the 'base' values were reached within 4-5 hours, thereby indicating this value to be the single most representative value for the system. Since the procedure for obtaining SPOUR data requires only 3 ml. of the mixed-liquor, it was also possible to obtain SPOUR values over the entire feed cycle. SPOUR values were expected to decrease with an increase in SRT. This was confirmed by the data obtained (Table 4-5 (b)). Variations of SPOUR with SRT, for the three reactors, are shown in Figure 4-7. As the amount of food available to the biomass decreases, due to a longer sludge age, the activity of the biomass is likely to drop. The same trend was observed in all three reactors. This also indicates that, at longer sludge ages, the log growth phase was virtually non-existent, since SPOUR values were quite low. This conforms well to published theory (Metcalf and Eddy 1972). SPOUR values were also monitored on a day-to-day basis, during each steady-state run, for all three reactors. Significant variations were observed in the 5-day SRT run. However, in the 10-day and 20- day SRT runs, SPOUR values 61 T A B L E 4-5 (a) Effect of SRT on Suspended Solids for the 80:20 Run SRT (days) Cont. Flow Reactor Once-a-day Reactor Twice-a-day Reactor MLSS (mg/L) MLVSS MLVSS MLSS (mg/L) (%) (mg/L) MLVSS MLVSS (mg/L) (%) MLSS MLVSS (mg/L) (mg/L) MLVSS (%) 5 331 241 72.8 282 214 75.9 250 188 75.3 10 1899 1178 62.0 513 279 54.4 532 301 56.7 20 3975 2355 59.3 987 504 51.1 1103 605 54.9 (b) Effect of SRT on SPOUR Values for the 80:20 Run SRT (days) Cont. Row Reactor (mg/gm VSS-hr) Once-a-day Reactor (mg/gm VSS-hr) Twice-a-day (mg/gm VSS-Reactor -hr) 5 179 29.2 16.9 10 18.6 16.0 14.2 20 12.1 10.7 8.3 (a) SRT (days) Figure 4-7: SPOUR Vs SRT - 80:20 Experimental Run 20 Days SRT Legend i. Con'. r i ? v » Peoctc • • Once -o -doy £e«d 'C T » ; c e - o - d o v Teed 2 3 Days in Steady State Figure 4-8: SPOUR Vs Days in Steady State - 80:20 Experimental Run 64 were found to be much more consistent (Figure 4-8). This indicates that an increase in the biomass of the system tends to stabilize the activity of the microorganisms, thereby creating a more uniform system, with a lower probability for 'plant upset'. The SPOUR values also conform well with the variation in MLSS values during a particular steady-state operation (Figure 4-6). Values for pH in the reactors were noted for all three steady-state systems, and it was found that at higher SRT's, the pH values were more uniform. pH, however, did not depart at any time out of an acceptable range (6.5 to 8.5) (Figure 4-9). 4.3.2 FFFLTJFNT CHARACTERISTICS The effluent characteristics for this experimental series are summarized in Table 4-6. The average effluent COD, for each of the three reactors, dropped when the SRT was increased from 5 days to 10 days. In the continuous-flow reactor (the system performing most efficiently at the 5-day SRT), the average effluent C O D dropped from 73 mg/L to 58 mg/L at the 10-day SRT (Figure 4-10 (a)). This resulted in a marginal improvement in treatment efficiency from 91.8 percent to 92.8 percent COD removal (Figure 4-10 (b)). This decrease in the effluent COD could be expected due to the decrease in the F / M ratio at the 10-day SRT and, as such, there was less substrate available to the biomass. The fill-and-draw reactors also performed in a similar fashion, with the average effluent C O D in the once-a-day reactor dropping from 83 to 72 mg/L; the twice-a-day reactor had its average effluent C O D reduced from 83 to 62 mg/L. The same trend was expected when the SRT was increased further to 20 days. However, the effluent COD for all three reactors increased, thereby leading to a reduction in the treatment efficiency. The continuous-flow reactor was the 6 7 8 Days in Steady State 10 : Legend Cont. Flow Reactor Figure 4-9: pH Vs Days in Steady State - 80:20 Experimental Run 66 T A B L E 4-6 Effluent Characteristics for the 80:20 Experimental Run ( a ) C o n t i n u o u s F l o w R e a c t o r S R T F / M R a t i o I n f l u e n t E f f l u e n t % E f f . C O D C O D ( d a y s ) ( k g C O D ( m g / L ) ( m g / L ) (%) / k g M L S S - d a y ) 5 2.46 888 73 91 .8 25 312 10 0 .43 812 58 92 .8 23 71 2 0 0 .20 781 112 85 .7 17 42 E f f l . S u s p . S V I S o l i d s ( m g / L ) ( m l / g m ) ( b ) O n c e - a - d a y R e a c t o r S R T F / M R a t i o I n f l u e n t E f f l u e n t % E f f . E f f l . S u s p . S V I C O D C O D S o l i d s ( d a y s ) ( k g C O D ( m g / L ) ( m g / L ) (%) ( m g / L ) ( m l / g m ) / k g M L S S - d a y ) 5 0 .63 888 83 90 .7 57 118 10 0 .32 8 1 2 72 91.1 53 6 0 2 0 0 .16 781 78 9 0 . 0 . 13 56 ( c ) T w i c e - a - d a y R e a c t o r S R T ( d a y s ) 5 10 2 0 F / M R a t i o I n f l u e n t C O D ( k g C O D ( m g / L ) / k g M L S S - d a y ) 0.71 0 .30 0 .14 888 8 1 2 7 8 1 E f f l u e n t C O D ( m g / L ) 83 6 2 9 6 % E f f . (%) 90 .6 9 2 . 4 87 .6 E f f l . S u s p . S V I S o l i d s ( m g / L ) ( m l / g m ) 51 4 6 1 9 1 2 0 61 4 6 (a) 120-1 SRT (days) (b) 94 84 H 4 r 5 10 15 SRT (days) Figure 4-10: Effluent Characteristics Vs SRT Experimental Run 68 least efficient, with an average effluent C O D increasing from 58 mg/L to 112 mg/L; this represented a change in treatment efficiency from 92.8 percent to 85.7 percent The once-a-day and twice-a-day reactors also experienced a deterioration in effluent COD, with increases from 72 to 78 mg/L and 62 to 96 mg/L, respectively ( the reasons for this trend will be discussed later in this section). The effluent suspended solids levels, which are also indicative of effluent quality, however, continued to drop in all reactors. The continuous-flow, once-a-day and twice-a-day reactors had average effluent suspended solids levels of 17, 13 and 19 mg/L, respectively for the 20-day SRT run. This was an improvement over the effluent suspended solids level for the 5-day and 10-day SRT runs (see Table 4-6). Analyses of these two effluent quality parameters lead to the conclusion that there must have been a release of soluble organics at an SRT of 20 days. The F / M ratios for all three reactors indicate that the bioreactors were operating under endogenous respiration, at a 20-day SRT; this is typically characterized by an F / M ratio of less than 0.2 day 1 . It is quite possible, and indeed probable, that cell lysis took place at the low F / M values, resulting in the release of soluble organics to the effluent and thus a lower COD removal efficiency. Since BOD^ values were not determined, it is not known, however, what fraction of these organics were biodegradable. As mentioned earlier, the Sludge Volume Index (SVI) is one of the most common parameters used for estimating effluent quality. SVI values were monitored throughout the entire study. A sludge with a SVI value between 35 and 150 is considered to be a properly settling sludge (Dick and Vesilind 1969). In this set of experiments, the only exception to this range of values was the continuous-flow reactor, during the 5-day SRT run. The SVI value for that particular steady-state system was 312 (see Table 4-6). The reason for this high value was improper clarifier operation (explained earlier), eventually leading to rising sludge and a 69 solids loss in the effluent All the other reactors, under different steady-state conditions, indicate the presence of a properly setding sludge. SVI values, for all three systems, dropped with increasing SRT. This conforms well with the effluent suspended solids level which also dropped with increasing SRT. It can therefore be concluded that the settling properties of the biomass improved with sludge age. However, due to endogenous respiration, cell lysis occurred during the 20-day SRT experimental run and caused the effluent C O D to increase. 4.3.3 COMPARISON OF DIFFERENT REACTOR TYPES One of the main objects of this study was to compare the performance of different reactor types while treating the combined waste. Al l three reactors were operated under similar environmental conditions, at all times. The mixed-liquors were intermixed, to ensure for randomness, before each experimental run. The organic loadings in the two fill-and-draw reactors were kept the same at all SRT's. However, the organic loading in the continuous-flow reactor was approximately 5 times higher. For example, for the 10-day SRT, the fill-and-draw reactors had an organic loading of 0.162 kg COD/m 3 -day, while the continuous-flow reactor had a loading of 0.812 kg COD/m 3 -day. This difference resulted from the operational characteristics of the two reactor types. Even though the difference in the organic loadings between the continuous-flow system and the fill-and-draw systems was 5 times, observed MLSS values were only 4 times higher in the continuous-flow reactor. This might be expected since, at very high substrate concentrations, the ability of the microorganisms to metabolize the substrate in the log growth phase is restricted by their own growth rate. The variation in the percent MLVSS for the different reactor types was also studied in detail (see Table 4-5). As noted earlier, all three reactors indicated a drop in the percent MLVSS with increase in SRT, and the cause was attributed 70 to the limited substrate available per unit of biomass, i.e. a low F / M ratio. However, it is interesting to compare the percent MLVSS, for the same SRT, in the three different reactor types. For example, at the 5-day SRT, the continuous-flow reactor had a MLVSS percentage of 72.8 percent, which is somewhat lower than the percent MLVSS for the two fill-and-draw systems (Figure 4-11). At the 10-day and 20-day SRTs, however, the fill-and-draw systems had a lower MLVSS percentage. This phenomenon can be partially explained by studying the variation in the Specific Oxygen Uptake Rate (SPOUR) over a feed cycle. FOT the 5-day SRT (Figure 4-12), the 'base' SPOUR value for the once-a-day reactor was reached approximately 21 hours after feeding (for a 24-hour feed cycle). Similarly, the twice-a-day reactor reached its 'base' value approximately 9 hours after feeding (for a 12-hour feed cycle). Thus, the biomass exhibited a higher activity, as compared to its 'base' value, during most of the feed cycle. It is, therefore, inferred that there was sufficient food (but not excess) available to the biomass, for the 5-day SRT, at most times of the fill-and-draw feed cycle. In the continuous-flow reactor, at a 5-day SRT, the amount of substrate available was also very high (as indicated by the much higher F / M ratio), but the value of the percent MLVSS in the continuous-flow reactor, although very high at 72.8 percent, was slightly lower than the percent MLVSS in the fill-and-draw system (Table 4-5). It appears then that the biomass, in the continuous-flow reactor, was unable to metabolize the excess substrate, thus suppressing the production of new biomass, and hence lowering the value of the percent MLVSS. The fill-and-draw systems, did not experience "excess substrate" conditions, even at the 5-day SRT, and were therefore able to convert most of the available food into new biomass. Figure 4-11: Percent M L V S S Vs SRT - 80:20 Experimental Run 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) TIME (h) Figure 4-12: SPOUR Vs Time (5 Days SRT) - 80:20 Experimental Run 73 The uptake of food in the 10 and 20-day SRT systems, however, was quite different compared to the 5-day SRT. Figure 4-13 shows the variation of SPOUR with time, for the 20-day SRT (similar for a 10-day SRT). In this case, the 'base' value was reached after approximately 1 hour of feeding. The F / M ratios, during the 20-day SRT, for the once-a-day and twice-a-day reactor were 0.16 and 0.14 day 1 , respectively. This implies that the two fill-and-draw reactors were in the endogenous respiration state for most of the feeding cycle; this, in turn, would lead to a decrease in the percent MLVSS, since most of the biodegradable fraction is used up. The continuous-flow reactor, however, had an F / M ratio of 0.20 day 1 , for the 20-day SRT, throughout the feed cycle; this means more available substrate, greater biomass activity and a percent MLVSS higher than the fill-and-draw systems. A similar explanation would follow the 10-day SRT data. The difference in the average solids levels of the two fill-and-draw reactors was also observed. Since the 5-day and 10-day SRT systems had very low MLSS values (see Table 4-4), it was difficult to ascertain any difference between the solids levels of the two reactors. Wide fluctuations were observed in the MLSS values during the steady-state operation of the 5-day SRT unit (see Figure 4-6), thereby indicating an unstable operation. Variations in the SPOUR values (Figure 4-8) also support the above observations. However, as the SRT was increased to 20 days and the biomass also increased, a definite trend was indicated. At the 20-day SRT, the twice-a-day reactor was found to have a higher average solids level, 1103 mg/L, as compared^ to the once-a-day reactor, 987 mg/L, approximately 12 percent higher (Figure 4-5 (a)). This higher solids level might be due, in part, to a more efficient conversion of the available substrate over a twice-a-day feeding cycle. Figure 4-13: SPOUR Vs Time (20 Days SRT) - 80:20 Experimental Run 75 The F / M ratios in the continuous-flow reactor were higher than the Fill-and-draw systems, for all SRTs. As explained earlier, this was to be expected since the observed F / M values in the continuous-flow reactor were indicative of the average F / M ratio in the system, whereas F / M values in the Fill-and-draw reactors were the 'minimum' F / M values for that system. The "average" value of the F / M ratio for the fill-and-draw reactors would be higher, however, although this average value was not monitored during this study. As such, it was difficult to compare the F / M values between the continuous-flow reactor and the fill-and-draw systems; however, the 'base' F / M values for the two fill-and-draw reactors were compared and they were found to be approximately .equal (see Figure 4-4 (b)). The main basis for comparing the two fill-and-draw systems were the Specific Oxygen Uptake Rate (SPOUR) values. Samples from the mixed-liquor were taken after every few minutes, over a 24-hour period, during each steady-state set of experiments. The variation of SPOUR over 24 hours for both fill-and-draw reactors, is shown in Figures 4-12 & 4-13. Plots are shown for the 5-day and 20-day SRTs, for comparison. During the 20-day SRT run, SPOUR values for the twice-a-day reactor reached a maximum value of 110 mg/gm VSS-hr, whereas the once-a-day reactor attained a maximum of only 85 mg/gm VSS-hr. This clearly indicates that the biomass in the twice-a-day reactor was more active and probably less susceptible to any form of 'shock' loading. Also, at the 20-day SRT (Figure 4-13), the decline in the SPOUR values (after the maximum value was reached), was fairly steep for both reactors, indicating that the substrate was taken up very quickly. The biomass was subsequently in endogenous respiration for the remainder of the cycle; this would eventually result in cell lysis, thereby deteriorating the effluent quality (in terms of effluent COD). 76 The 5-day SRT run, in turn, was characterized by a more gradual decline in the SPOUR values (see Figure 4-12). This indicates that there was excess food available, for the level of biomass, through most of the feeding cycle. At the 5-day SRT, the maximum SPOUR value for the once-a-day reactor, 175 mg/gm VSS-hr, was lower as compared to the twice-a-day reactor, 250 mg/gm VSS-hr. Therefore, in both the 5-day and 20-day SRT runs, the twice-a-day system indicated a more 'active' biomass as compared to the once-a-day system. It was also interesting to note that, in the 5-day SRT, the maximum SPOUR values in both the fill-and-draw reactors were reached anywhere from 1 to 4 hours after feeding. Contrary to this, during the 20-day SRT run, both fill-and-draw reactors showed an almost immmediate oxygen demand (see Figure 4-13). Because of the low F / M ratios observed in the 20-day SRT systems, the biomass would be in the endogenous respiration state at the start of the feeding cycle; in the 5-day SRT systems, however, the endogenous respiration state would not likely be reached. As such, the oxygen demand of the two regimes would be expected to be different The DO levels in the bioreactors were kept greater than 2 ppm at all times. However, during feeding, the DO level in the fill-and-draw systems fell steeply to a very low level. For example, in the 20-day SRT system, the DO level went below 0.2 ppm in the twice-a-day reactor for a duration of few minutes (Figure 4-14). However, aerobic conditions with DO greater than 2 ppm were re-established after a duration of 1 hour. The corresponding DO drop upon feeding, in the once-a-day reactor, was not as great This again confirms the earlier conclusion, based on SPOUR values, that the twice-a-day reactor was more 'active' than the once-a-day system. According to Zapf-Gilje and Mavinic (1982), the DO levels in a fill-and-draw system are characterized by two significant drops during a leachate I Legend |« Qnce-o-doy Teed 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) > i I i i 1 1 1 1 ! 1 1 ! I , 1 ! I I ' i > 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) Figure 4-14: D.O. Vs Time (20 Experimental Run Days SRT) - 80:20 78 feed cycle. The first drop is an immediate one and it takes place due to zero-order metal oxidation in the leachate. The DO levels recover after an hour or so and then a less significant drop takes place; this is attributed to a population shift of the microorganisms from anaerobic to aerobic. In this experiment, the sewage: leachate feed was pre-aerated before being fed into the reactor. Hence it can be assumed that metal oxidation had taken place before feeding. For example, iron would be present in ferrous form in the absence of oxygen; however, oxidation would result in the conversion of ferrous to ferric. The DO drop in this study was thus attributed more to microbial growth. Furthermore, a DO drop, due to metal oxidation, would have resulted in even a higher DO drop for the once-a-day reactor (the maximum SPOUR value for the once-a-day reactor should also have been higher), since the once-a-day system was fed twice the amount of feed at one time as compared to the twice-a-day system. This was not the case, however, and it can be concluded that the biomass in the twice-a-day reactor was basically in a more active state. The effluent characteristics of the three reactors were also compared. The biomass in the continuous-flow reactor did not settle well at the 5-day SRT; however, the settling properties of this particular biomass did improve with SRT, and at a 20-day SRT, the performance of this reactor was better than the other two systems (in terms of SVI values). The average effluent solids levels in the three reactors were comparable (for the 20-day SRT), with each system having an average effluent solids level less than 20 mg/L (see Table 4-6). As mentioned earlier, the continuous-flow reactor experienced the largest increase in effluent COD, when the SRT was increased from 10 to 20 days. The reason for this was probably the existence of an endogenous respiration state (F/M ratio less than 0.2 day"1) during the 20-day SRT reactor operation; essentially, cell lysis took place almost continuously. In the fill-and-draw reactors, however, the 79 endogenous respiration state was achieved only during part of the feed cycle (near the end), the result being much less cell lysis occurring. The twice-a-day reactor proved to be the most active one from all the data obtained. As a result, this system reached an endogenous state earlier, in comparison to the once-a-day system. Cell lysis, therefore, was more prevalent in the twice-a-day system, with corresponding higher C O D values (see Table 4-6). The net result of this appears to be that at very high SRT's (or low F / M ratios), the once-a-day feed system might be expected to produce the best quality effluent for a combined leachate/sewage feed mix. 4.4 RESULTS FROM THE 60:40 EXPERIMENTAL RUN 4.4.1 MIXED-LIQUOR CHARACTERISTICS The 60:40 experimental run corresponds to the presence of 40 percent leachate, by volume, in the influent feed. The feed strengths in this set of steady-state runs were approximately 1200 mg/L. Variations in the influent feed C O D concentrations, for the different SRTs, were not significant (Table 4-7). This run was therefore characterized by a higher organic loading, as opposed to the 80:20 experimental run. The main purpose of setting up this experiment was to study the effect of a higher organic loading on the treatability of the different reactor types. It is, however, important to note that a change in the sewage:leachate ratio also resulted in an 'effective' change in the composition (in terms of concentrations) of the influent feed. This led to significant changes in the performance of the three reactors, as discussed later. The values of the organic loadings and the influent COD's are provided in Table 4-7. In the continuous-flow system, the influent COD varied from 1156 mg/L to 1323 mg/L, which corresponds to organic loadings of 1.16 kg 80 T A B L E 4-7 Operational Characteristics for the 60:40 Experimental Run (a) Continuous Flow Reactor SRT (days) Influent Feed Org. Loading Organic MLSS (mg/L) F / M Ratio (mg/L COD) (kg C O D Loading (lb (kg COD/kg /m 3-day) COD/1000 cu MLSS -day) ft-day) 5 1238 1.238 77.0 3088 0.40 10 1156 1.156 72.0 4939 0.23 20 1323 1.323 82.40 8322 0.16 (b) Once-a-day Reactor SRT (days) Influent Feed Org. Loading (mg/L COD) (kg COD /m 3-day) 5 1297 0.259 10 1160 0.232 20 1304 0.260 SRT (days) Influent Feed Org. Loading (mg/L COD) (kg COD /m 3-day) 5 1273 0.254 10 1140 0.228 20 1304 0.260 Organic MLSS (mg/L) F / M Ratio Loading (lb (kg COD/kg COD/1000 cu MLSS -day) ft-day) 16.1 1029 0.25 14.4 1402 0.17 16.20 1899 0.14 Organic MLSS (mg/L) F / M Ratio Loading (lb (kg COD/kg COD/1000 cu MLSS -day) ft-day) 15.8 1124 0.23 14.2 1547 0.15 16.20 2296 0.11 (c) Twice-a-day Reactor 81 COD/m 3 -day to 1.32 kg COD/m 5 -day. This variation was attributed mainly to the fluctuations in the domestic sewage quality. A similar variation in the influent feed COD's was also observed for the fill-and-draw systems. Due to the nature of the fill-and-draw operation, these reactors had an organic loading 5 times less than the continuous-flow system, varying from 0.228 to 0.260 kg COD/m 3 -day. A study conducted by Zapf-Gilje and Mavinic (1981) recommended the use of a maximum organic loading of 3.2 kg COD/m 3 -day, for a fill-and-draw system. Therefore, all organic loadings during this experimental run were well below this upper limit Food/microorganism (F /M) ratios for the different steady-state runs are also given in Table 4-7. In the continuous-flow reactor, F / M values ranged from 0.16 days', at the 20-day SRT, to 0.40 days"1, at the 5-day SRT. This indicated again that this system was in endogenous phase during the 20-day SRT operation. The F / M values obtained for the fill-and-draw reactors were less than 0.20 days -1 for the 10-day and 20-day SRTs, also indicating an endogenous phase. However, the F / M values for the fill-and-draw reactors were obtained just before feeding, and as such, they represent only the 'base', lowest values in the systems. According to the kinetic model of Lawrence and McCarty (1970), an increase in the SRT is characterized by a decrease in the F / M ratio. The plots of F / M ratios against SRT, for all three reactors, are given in Figure 4-15. As expected, the three reactors showed a decrease in the F / M ratio with increasing SRT. In the previous 80:20 experimental run, it was observed that the difference between the mixed-liquor suspended solids (MLSS) values, for the two fill-and-draw reactors, increased with increasing SRT. At a 20-day SRT, for the 80:20 run, the twice-a-day reactor showed a 12 percent higher MLSS value. However, this difference, in the 60:40 run, was found to be approximately 21 percent at the 20-day SRT, with the twice-a-day reactor having the higher 82 0.45 --0.40 0.35-0.30-1 CO >^  D 3, 0.25-O "5 0.20-0.15-0.10-0.05-0.00 -• 5 0.45 -0.40 -0.35 -0 30 ->-op) 0.25 -O O 0.20 -OC 0.15 -0.10-0.05-0.00 ; Legend i Once-a—day Feed • Twice -a -day Feed 10 15 SRT (days) 20 Figure 4-15: F / M Ratio Vs SRT - 60:40 Experimental Run 83 average value of 2296 mg/L (Table 4-7). The continuous-flow reactor indicated an almost linear increase in MLSS with SRT for the three steady-states (Figure 4-16 (a)). For the 20-day SRT, the average MLSS concentration in the continuous-flow reactor was 8322 mg/L. The linear increase in the MLSS with increase in SRT indicates that biological growth was not inhibited at any SRT during the experimental runs. The MLSS values for the different reactors were obtained daily during a steady-state operation. The variation in the MLSS values during steady-state operations are given in Figure 4-17. The systems showed fairly stable operation, at all SRT's, and the variations in the MLSS values were, for the most part, not significant. Average values were computed for a particular steady-state and these values were used for comparison and calculation purposes. The nature of the fill-and-draw operation-did allow for a more stable operation, on a day-to-day basis; there was no loss of solids over the effluent weir and there was no problem of recycling the solids. This stability is reflected in the MLSS values for the fill-and-draw systems (Figure 4-17). For example, at the 5-day SRT, the once-a-day system experienced a variation from 919 mg/L to 1124 mg/L in the MLSS values, a maximum variation of 10.6 percent from the average computed value of 1028 mg/L. On the other hand, the continuous-flow system, at the 5-day SRT, had a variation from 2839 mg/L to 3568 mg/L in its MLSS value, which corresponds to a maximum variation of 16 percent from the average value of 3080 mg/L. Another significant aspect of this experiment was to study the relationship between percent mixed-liquor volatile suspended solids (MLVSS) and SRT. In the 80:20 experimental run, the percent MLVSS in all three reactors dropped with an increase in SRT. Such a trend, however, could not be predicted for this set of steady-state runs since the organic loadings were significantly higher. As mentioned (a) SRT (days) Figure 4-16: Mixed-Liquor Solids - 60:40 Experimental Run 4000 3000 $ 2000" 1500 1000 500 5 Days SRT A Cont. Flow Reactor j« Once-o-doy Feed :• Twice-o-day Feed 2 3 4 5 6 7 Days in Steady State 85 o 6500 5000 4000 -00 3500 00 _jj 3000 2000 1500 1000 -- i | Legend 10 Days SRT , A Cont. Flow Reactor '• Once-a-doy Feed jn Twice—a-doy Feed ., —B" i — i II 1 2 3 4 5 6 Days in Steady State 10000 7000 _J \ |> 6000 oo : to _J 3 4000 3000 2000 j Legend 20 Days SRT Cont. Flow Reactor i !• Once-o-doy Feed - ID Twice-o-doy Feed ^^^^^ 4 5 6 Days in Steady State Figure 4-17: M L S S Vs Days in Steady State - 60:40 Experimental Run 86 earlier, a complex waste like leachate contains a significant inert fraction and this could reduce the percent MLVSS in all three systems. The values of percent MLVSS obtained for this set of steady-state runs are provided in Figure 4-16 (b) and Table 4-8 (a). Due to the increased organic loadings, the percent MLVSS during the different SRTs, for all three reactors, were much lower as compared to the 80:20 run (see Tables 4-5 (a) and 4-8 (a)). In the continuous-flow reactor, the variation in percent MLVSS with SRT was not significant; this indicates that the inert fraction exerted a significant influence on the resulting reactor characteristics. The fill-and-draw reactors had an organic loading 5 times less than the continuous-flow system. This lower organic loading implies that the inert content in the reactor might be less. At the 5-day SRT, the fill-and-draw reactors did have a higher percent MLVSS as compared to the continuous-flow system (Table 4-8 (a)). However, as the SRT was increased from 5 days to 10 days, and the inert fraction accumulated in the biomass due to the longer sludge age, this inert fraction became significant in all three reactors. As a result, the percent MLVSS were practically the same, albeit at much lower levels. The low F / M ratios support this argument, with the lack of substrate indicating a decrease in the volatile content of the biomass. The examination of the data in this case indicates a somewhat interesting phenomenon. On increasing the SRT further to 20 days, the percent MLVSS values in all three reactors were not expected to change by any significant amount The fill-and-draw reactors were already in endogenous phase at the 10-day SRT and therefore the percent MLVSS was perhaps at its lowest value. As shown in Table 4-8 (a), all three reactors had percent MLVSS values similar to the 10-day SRT systems, thereby confirming the assumption that the inert portion governed at longer sludge ages. Thus, in the continuous-flow reactor, this 87 TABLE 4-8 (a) Effect of SRT on Suspended Solids for the 60:40 Run SRT Corn. Flow Reactor Once-a-day Reactor Twice-a-day Reactor (days)  MLSS (mg/L) MLVSS (mg/L) MLVSS (%) MLSS (mg/L) MLVSS (mg/L) MLVSS (%) MLSS (mg/L) MLVSS (mg/L) MLVSS (%) 5 3088 1371 44.4 1029 580 56.4 1124 596 53.1 10 4939 2211 44.8 1402 631 45.0 1547 705 45.6 20 8322 3981 47.8 1899 896 47.2 2296 1073 46.7 (b) Effect of SRT on SPOUR Values for the 60:40 Run SRT Cont. Flow Reactor Once-a-day Reactor Twice-a-day Reactor (days) (mg/gm VSS-hr) (mg/gm VSS-hr) (mg/gm VSS-hr) 5 6.9 4.9 3.9 10 8.1 6.4 6.7 20 3.9 5.6 4.5 88 inert fraction was significant even at the 5-day SRT, due to the high organic loading; in the fill-and-draw systems, however, this fraction became more significant only at the higher SRT's. Variation of the SPOUR values against SRT is shown in Figure 4-18 (and presented in Table 4-8 (b)), for the three reactors. A l l three reactors showed a decrease in the average SPOUR values when the SRT was changed from 10 days to 20 days. This was expected since the F / M decreases and the substrate available per unit of biomass decreases as well. However, the average SPOUR values increased when the SRT was increased from 5 days to 10 days. The low SPOUR values for the 5-day systems could be due to the high organic loading to the system, coupled with a relatively low level of biomass, thereby resulting in excess substrate in the system. This argument is supported by the high average effluent COD's observed for the 5-day SRT systems (Table 4-9). High C O D values in the effluent implies that total and efficient conversion of the substrate did not take place. pH values in the reactors were spot checked from time to time and they were found to be within the acceptable range of 6.5 to 8.5 pH units. 4.4.2 F.FFTIJFNT CHARACTERISTICS The effluent characteristics for this experimental run are summarized in Table 4-9. The 5-day SRT systems had higher average effluent C O D concentrations, than the 10 or 20-day SRT units, for all reactor types. The continuous-flow reactor had the highest average value, 152 mg/L, for the 5-day SRT. The two fill-and-draw reactors showed lower average effluent COD's. As noted previously, these high C O D values for the 5-day SRT systems could be due, in part, to the high organic loading imposed on these systems. The recommended range of organic 10 15 SRT (days) (b) Legend O n c e - a - d a y Feed • Tw ice -a -day Feed 10 15 20 SRT (days) Figure 4-18: SPOUR Vs SRT - 60:40 Experimental Run 90 T A B L E 4-9 Effluent Characteristics for the 60:40 Experimental Run (a) Continuous Flow Reactor SRT F / M Ratio Influent Effluent % Eff. Effl. Susp. SVI COD C O D Solids (days) (kg C O D (mg/L) (mg/L) (%) (mg/L) (ml/gm) /kg MLSS-day) 5 0.40 1238 152 89.1 31 304 10 0.23 1156 74 94.0 16 52 20 0.16 1323 67 95.0 10 102 (b) Once-a-day Reactor SRT F / M Ratio (days) (kg C O D /kg MLSS-day) 5 0.25 1297 93 93.3 46 50 10 0.17 1160 70 94.3 21 31 20 0.14 1304 86 93.9 35 50 Influent Effluent % Eff. Effl. Susp. SVI COD C O D Solids (mg/L) (mg/L) (%) (mg/L) (ml/gm) (c) Twice-a-day Reactor SRT F / M Ratio Influent Effluent % Eff. Effl. Susp. SVI COD C O D Solids (days) (kg C O D (mg/L) (mg/L) (%) (mg/L) (ml/gm) /kg MLSS-day) 5 0.23 1273 117 91.6 57 38 10 0.15 1140 90 92.7 40 29 20 0.11 1304 85 94.0 41 38 91 loadings for a conventional activated sludge plant are 20 to 40 lb BOD 5/1000 cu ft-day (Metcalf and Eddy 1972). The continuous-flow reactor had an organic loading of 77 lb COD/1000 cu ft-day (Table 4-7). This indicates that the biomass was not able to completely utilize the available substrate and this resulted in a higher effluent C O D value. However, as the SRT was increased from 5 days to 10 days and the biomass also increased, the substrate was used up more efficiently and a lower average effluent C O D was observed for all three systems. The decrease in the F / M ratio also indicates that more substrate was used up during the 10-day SRT. On increasing the SRT further to 20 days, it was expected that the average effluent C O D in all three reactors would drop even further. However, this did not take place. The F / M ratios at the 20-day SRT were lower than 0.20 days 1 for all three systems; therefore, some cell lysis would be expected to occur in the reactors, thus affecting effluent quality. In the continuous-flow reactor, at the 20-day SRT, the F / M ratio was the highest, 0.16 days 1, and it showed only a minor improvement in the treatment efficiency (Figure 4-19 and Table 4-9). The once-a-day reactor observed an actual drop in the treatment efficiency while the twice-a-day reactor had only a marginal improvement in its treatment efficiency. As before, the data seems to indicate a need for 'optimization' of the treatment systems, in terms of organic loadings and F / M ratios. No significant changes in the settling characteristics for all three systems were observed, with the biomass showing good settling properties. However, the continuous-flow system, due to its high organic loading, indicated the presence of a poorly setding sludge at the 5-day SRT. The biomass settied very well, however, during the 10-day and 20-day SRT's. The effluent suspended solids level, in the continuous-flow system, continued to drop with increasing SRT (see Table 4-9). The 20-day SRT had an average 180 160 40 20 H 0 (a) i Legend |A Cont. Flow Reactor I """"~"""~™"~~"~~" |» O n c e - a - d a y Feed !a Twice -a -day Feed —r-10 15 SRT (days) 20 0) 86 H 84 Q O <-> 82 80 (b) Legend I ^ Cont. Flow Reactor '• Once -a -day Feed ILJ Twice-a-day Feed 10 15 20 SRT (days) Figure 4-19: Effluent Characteristics Vs SRT - 60:40 Experimental Run 93 effluent suspended solids level of only 10 mg/L. The fill-and-draw systems, showed a decrease in the average effluent suspended solids levels when the SRT was increased to 10 days; however, a slight deterioration in the average effluent suspended solids level was observed at the 20-day SRT run. SVI values were used as a measure of sludge settleability. All three reactors had a decrease in their SVI values as the SRT was increased from 5 to 10 days (Table 4-9). However, on increasing the SRT further to 20 days, an increase in the SVI values, for all three sludges, was observed. It is speculated that this may be due to the low F / M ratios encountered at the 20-day SRT, thereby resulting in bulking sludge. 4.4.3 COMPARISON OF DIFFERENT RFACTOR TYPES The 60:40 run was operated under similar conditions to the 80:20 run, with the exception of a higher organic loading. The organic loadings in the fill-and-draw systems were 5 times less than the continuous-flow reactor. The MLSS values, however, were approximately 4 times lower than the continuous-flow system. This trend was similar to the one observed in the 80:20 run. As noted earlier, this was attributed to the higher organic loadings in the continuous-flow system. The MLSS levels in the two fill-and-draw reactors were also compared. The 80:20 experimental run had suggested a trend of the twice-a-day reactor having a higher biomass. This trend was also indicated in the 60:40 experimental run. For the 5-day SRT runs, the difference in the MLSS values was 9.2 percent, and this difference was increased to 21 percent for the 20-day SRT run. The percent MLVSS obtained for the different reactors was also compared (Figure 4-20). As mentioned earlier, this steady-state run had significantiy higher organic loadings in the reactors. As such the inert content in the feed was also 70 Reactor Typ Figure 4-20: Percent M L V S S Vs SRT - 60:40 Experimental Run 95 significantly higher. The continuous-flow reactor, with 5 times higher organic loadings, showed the same percent MLVSS for all three SRTs, approximately 45 percent At each particular SRT, the two fill-and-draw reactors had similar percent MLVSS. However, at the 5-day SRT, the percent MLVSS in the fill-and-draw systems was both higher than the continuous-flow system and the 10-day and 20-day SRT fill-and-draw systems. F / M ratios for the continuous-flow reactor were higher in comparison to the fill-and-draw system, at all SRTs. However, the reported F / M ratios for the fill-and-draw systems were their minimum values, and, as such, they do not indicate the state of the system at all times. The fill-and-draw reactors showed a marginal difference between their F / M values, with the once-a-day reactor showing a slightly higher value at all SRTs. This difference was attributed to the lower MLSS levels in the once-a-day reactor. SPOUR values for the fill-and-draw systems were obtained over a 24-hour period. These were used as a basis for comparing the two fill-and-draw systems. For the 5-day SRT, the once-a-day reactor reached a maximum value of 64 mg/ gm VSS-hr, approximately 1 hour after feeding (Figure 4-21). The twice-a-day system reached a maximum of 62 mg/ gm VSS-hr, but only 0.5 hours after feeding. This time difference, which is consistent with the other steady-state runs, clearly indicated that the twice-a-day system was more efficient and faster at utilizing the substrate. Also, the decline in the SPOUR value, for the once-a-day reactor, was gradual. However, the twice-a-day system had a fairly steep decline after the maximum value was reached, indicating, again, a greater affinity for substrate and a higher level of activity. As the SRT was increased further to 20 days, the decline in the SPOUR values, after the maximum was reached, was fairly steep for both the fill-and-draw systems (Figure 4-22). This indicated that, at the 20-day SRT, the 70 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) Figure 4-21: SPOUR Vs Time (5 Days SRT) - 60:40 Experimental Run 5 0 45 4 0 3 5 15 4<i Legend • O n c e - a - d a y Feed yyA ^ • • : > > A - : - . V V . . V A W . • • • • • • • • . — 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 0 21 2 2 2 3 24 TIME (h) 7 0 6 5 6 0 -Jf 55-I 5 0 -45 T 4 0 - * 3 5 A 3 0 2 5 2 0 15 10 5 3 | Legend ; • T w i c e - a - d a y Feed v . v , ' N w . v , v , \ v . ' , 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 2 0 21 2 2 2 3 24 TIME (h) Figure 4-22: SPOUR Vs Time (20 Days SRT) - 60:40 Experimental Run 98 substrate was taken up more quickly due to the lower F / M ratio in these systems. Maximum values were reached just a few minutes after feeding, indicating a high substrate demand. In both fill-and-draw systems, the 'base' value was reached approximately 2 hours after feeding, which shows that the biomass was in the endogenous state for most of the time. The average effluent COD level in the continuous-flow reactor was higher than the two fill-and-draw systems, at all SRTs (Table 4-9). This is attributed to the higher F / M ratios in the continuous-flow system, indicating that the biomass could not metabolize all of the available substrate, thereby producing a higher effluent COD. As expected, the corresponding treatment efficiencies in the continuous-flow system were also lower. The two fill-and-draw systems performed equally well at all SRTs, with the 20-day SRT showing the most efficient performance (in terms of C O D removal). An interesting trend was observed in the settling characteristics of these systems. The average effluent solids dropped in all three reactors as the SRT was increased from 5 days to 10 days. This was expected as the increase in biomass helps improve the settling characteristics. The corresponding SVI values also dropped in all three systems (Table 4-9). However, when the SRT was increased from 10 days to 20 days, the three reactors behaved differently. In the continuous-flow reactor, the average effluent solids levels dropped further, but the SVI value increased. It was speculated that, at a low F / M ratio, sludge bulking took place, thereby increasing the SVI value. Limited sludge bulking is often characterized by a good effluent solids level (Pipes 1969); however, if excessive bulking takes place, due to a still lower F / M ratio, then the effluent quality also deteriorates. This phenomena was observed in the fill-and-draw systems. Both the fill-and-draw systems showed increases in the SVI values and effluent suspended solids levels, when the SRT was increased further to 20 days. 99 Results obtained from this experimental run indicate that aerobic treatment of the combined leachate/sewage waste, at a high organic loading, is feasible. The growth of the biomass in all systems was extensive and a stable operation was achieved. The continuous-flow reactor performed better at the 10-day and 20-day SRTs; at a 5-day SRT, the once-a-day system produced the best quality effluent. The difference in the MLSS levels of the two fill-and-draw systems was more significant in this 60:40 run. It was speculated that, at higher MLSS levels, this difference could be large enough to affect the effluent quality; however, in reality, the two fill-and-draw systems performed equally well (in terms of effluent quality) at all SRTs. 4.5 RESULTS FROM THE COLD TEMPERATURE STUDY 4.5.1 RESULTS F R O M THE 10° C T E M P E R A T U R E R U N After operating the different reactors, under varying conditions, at room temperatures (21-23° C), it was decided to study the effect of lower temperature on the performance of these reactors. The reactors were moved into a temperature controlled room and a temperature of 10° C was set for the study. It would have been desirable to keep the temperature at 12-15°C for the first run. However, this was not possible since the 10° C temperature was required for another experiment being carried out, in the same temperature controlled room, at that time. The SRT for this run was chosen as 10 days. This SRT was chosen due to the 'acceptable' MLSS levels that were encountered during the room temperature runs. This experiment was carried out foT a duration of approximately four weeks. The temperature in the room varied from 9 ° C to 10° C. However, this resulted in a liquid temperature from 7.5 to 8.5° C in the reactors. Ordinarily, one would expect the liquid temperature in the reactors to be higher than the room 100 temperature; however, cold air used for aeration caused a drop in the liquid temperatures. Evaporation from the reactors might also have contributed to the lower liquid temperature values. The liquid temperature was monitored over a 24-hour period and no significant variation was observed in either of the three reactors. Therefore, it was decided to observe the liquid temperature in each reactor just before feeding. Variations in the temperature on a daily basis are shown in Figure 4-23. The organic loading in the reactors corresponded to 20 percent leachate additions, by volume, in the influent feed. The average influent COD in this steady-state run was observed at 905 mg/L. Therefore, the organic loading in the continuous-flow reactor was 0.905 kg COD/m 3 -day (56.4 lb C O D / 1000 cu ft-day), which is in acceptable range according to Zapf-Gilje and Mavinic (1982). The fill-and-draw reactors had organic loadings 5 times less than the continuous-flow system, 0.181 kg COD/m 3 -day (11.3 lb C O D / 1000 cu ft-day) (Table 4-10). The variation in the mixed-liquor suspended solids (MLSS) was observed during the steady-state operation, as shown in Figure 4-24. The variation in the values was not significant at any time and this indicated a fairly stable operation. The continuous-flow reactor showed an average MLSS value of 2066 mg/L (Table 4-10). This value is somewhat higher than the MLSS for the same steady-state run, at room temperature (21-23°C). However, the fill-and-draw reactors showed MLSS levels twice as high as the previous room temperature runs. The F / M ratios, at room temperature, were found to be fairly high in the fill-and-draw systems (see Table 4-4). As mentioned earlier, these F / M values for the fill-and-draw systems represent their lowest values. Therefore it appears that the microorganisms did not convert the organic substrate into biomass efficiently at room temperatures. At the 10° C temperature run. because of the higher solids 101 9 l 7.2-j 7 J , , , , 1 2 3 4 5 6 Days in Steady State Figure 4-23: Liquid Temperature Vs Days in Steady State -10 C Temperature Run 102 T A B L E 4-10 Characteristics from the 8 ° C Liquid Temperature Run Parameter Cont. Flow Reactor Once-a-day Reactor Twice-a-day Reactor SRT (days) 10 Influent C O D (mg/L) 905 Organic Loading 0.905 (kg COD/m 3 -day) Organic Loading 56.4 (lb COD/1000 cu ft-day) F / M Ratio 0.44 (kg COD/kg MLSS-day) MLSS (mg/L) 2066 MLVSS (mg/L) 960 Percent MLVSS (%) 46.3 SPOUR 38.1 (mg/gm VSS-hr) Effluent C O D (mg/L) 220 72.7 Treatment Efficiency (%) Effl. Susp. Solids (mg/L) 58 10 905 0.181 11.3 0.16 1169 566 48.4 29.8 118 85.3 37 10 905 0.181 11.3 0.17 1082 539 49.8 33.6 112 86.1 23 SVI (ml/gm) 75 177 322 103 C7> J , 00 2350 2150-1950 1750 1550 1350 -'150 950 750 10 C Room Temperature 10 Days SRT Legend | A Cont. Flow Reactor j • O n c e - a - d a y Feed !• Twice—a—day Feed 2 3 Days in Steady State Figure 4-24: M L S S Vs Days in Steady State - 10° C Temperature Run 104 levels, the fill-and-draw systems had much lower F / M values, thereby indicating that at the end of the feed cycle, most of the substrate had been converted to biomass. Also, the 'base' SPOUR values in the fill-and-draw systems, at 10°C, were much higher, thus supporting the argument that a higher level of activity existed in the 10° C systems over the 24-hour feed cycle. It is possible that a different group of microorganisms (probably psychrophilic) dominated at this temperature, thereby resulting in a more efficient system. However, definitive proof is unavailable from this experimental work. The percent MLVSS levels in all three reactors were almost equal (see Table 4-10). However, these values were lower than the corresponding room temperature run at the 10-day SRT (Table 4-5 (a)). The continuous-flow reactor experienced a sharp decrease in the percent MLVSS from 62.0 to 46.3 percent This could be explained by the much higher SPOUR value in the 10° C system, 38.1 mg/gm VSS-hr. The room temperature run had a SPOUR value of 18.6 mg/gm VSS-hr. This implies that a more "active" biomass, albeit slower responding due to the colder temperature, existed in the continuous-flow system at 10° C, resulting in a lower percent MLVSS value overall. A similar explanation also holds for the two fill-and-draw systems, which also had much higher 'base' SPOUR values (see Tables 4-5 (b) and 4-10). The food/microorganism (F/M) ratios for this steady-state run are also given in Table 4-10. In the continuous-flow system, a high F / M ratio of 0.44 days 1 was observed. In the fill-and-draw reactors, however, the F / M ratios were less than 0.2 days"1, which indicates an endogenous phase operation. The F / M values in the fill-and-draw reactors were obtained just before feeding; therefore, they represent the minimum F / M values in the system. In the low temperature study, the uptake of substrate was expected to take longer, due to the slower response by the microorganisms; hence, it was expected that the substrate would 105 be used up over most of the feed cycle, and not in the initial part, as shown previously. This type of response, if true, would be reflected in the SPOUR values for each system. SPOUR values were obtained for all three reactors during the steady-state operation (see Table 4-10). For the fill-and-draw systems, these values were also obtained over a 24-hour period (Figure 4-25). SPOUR values were also used as a basis for comparing the two fill-and-draw systems. The maximum SPOUR values were also expected to be lower, compared to the room temperature runs, due to the slower response time of the microorganisms. Oxygen uptake was indeed gradual with time (Figure 4-25) and the base values were reached only near the end of the feed cycle. The once-a-day reactor had a maximum SPOUR value of 65 mg/gm VSS-hr, while the twice-a-day system had a maximum value of 84 mg/gm VSS-hr. The twice-a-day reactor showed a maximum value higher than the once-a-day system, as was the case in previous runs. Again, this was attributed to the microorganisms being able to metabolize the substrate faster and more efficiently, thus increasing the maximum SPOUR value. Also, the maximum value for the once-a-day system was reached after approximately 4 hours, as compared to only 2 hours in the twice-a-day system. As expected, the average effluent C O D values showed an increase in all three reactors. The continuous-flow system had a high F / M ratio of 0.44 days 1 and the effluent COD value for this system was expected to be the highest This reactor had an average effluent C O D of 220 mg/L. This resulted in a treatment efficiency of only 72.7 percent The fill-and-draw reactors had organic loadings 5 times less than the continuous-flow system; therefore, the F / M ratio in the fill-and-draw systems was much lower (Table 4-10). The average effluent COD for the once-a-day system was only 118 mg/L, corresponding to a 85.3 percent 90 -i j r r . i i • | . . r . . . . « . i i . i r i . , i n . . . 1 . . . | . . . f . . r . . | 1— • • . 1 ; . 1 | r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) Figure 4-25: SPOUR Vs Time for the Fill-and-Draw Systems -10 C Temperature Run 107 treatment efficiency, while the twice-a-day system had a treatment efficiency of-86.1 percent It is possible, though, that some cell lysis also occurred in the fill-and-draw reactors thereby deteriorating the effluent quality. However, it is speculated that, on the basis of SPOUR values, the endogenous phase occurred only during a small part of the feed cycle and the effect of cell lysis, in this low temperature run, would not be as significant An interesting part of this steady-state run were the settling characteristics. The three reactors showed different characteristics, although each individual system exhibited a uniform pattern. The average effluent suspended solids level in the continuous-flow reactor was 58 mg/L, indicating a relatively poor quality effluent The sludge volume index (SVI) was, however, within the acceptable range of 35 to 150. This indicated that the sludge compacted fairly well. The deterioration in the effluent suspended solids (compared to the room temperature study) levels was probably due to the formation of a pinpoint floe. According to Pipes (1969), pinpoint floe occurs when the temperature in the aeration tank is less than 15° C, and there is a lack of sufficient filamentous growth in the system. A pinpoint floe was observed in this system at these lower temperatures. The two fill-and-draw reactors, on the other hand, experienced a decrease in the effluent suspended solids levels, compared to the corresponding room temperature run (see Tables 4-6 and 4-10). However, SVI values for both systems showed a sharp increase (greater than 150), indicating that bulking took place in the fill-and-draw systems. As mentioned earlier, filamentous growth is controlled by two important parameters : F / M ratio and temperature. Since the F / M ratios in the fill-and-draw systems were low, it appears that some filamentous growth took place in the reactors. However, the low temperature probably restricted the extent of the filamentous growth and hence average effluent suspended solids levels were lower. The continuous-flow system, though, did not have a low F / M ratio. It was 108 also charaterized by a lack of filamentous growth and the formation of pinpoint floe. It appears then that at the 10° C temperature run, the F / M ratio had a more significant effect on filamentous growth, and subsequent settling performance, than did the temperature. The above data also indicates that at lower temperatures, treatment efficiencies in the reactors started to drop. At an operating temperature of 10° C, even though the microorganisms were active, there was a significant reduction in treatment efficiency for all three systems. Since the metabolic activity of the microorganisms is slower, the organic loadings should be lowered for efficient operation, especially when treating leachate. Setding performance also deteriorates with a decrease in temperature, predominandy due to the formation of a pinpoint floe. A system with a F / M ratio less than 0.2 days -1 could also be expected to experience sludge bulking problems at 10° C. 4.5.2 RESULTS F R O M THE 6°C T E M P E R A T U R E R U N The performance of all three reactors was evaluated at 10° C. After that it was decided ' to decrease the temperature further to 6°C. Liquid temperatures varied from 5.0 to 5.5°C, while the air temperatures varied from 6 to 6.5°C. The SRT for this particular run was also maintained at 10 days, so as to serve as a basis for comparison with other temperatures. Since the temperature reduction from the previous run was not as great as hoped for, it was decided to increase the organic loading in this system, in order to study the effect of a higher organic loading at a low temperature. Leachate was added to the domestic wastewater in a ratio of 60:40 sewage:leachate. The average influent C O D for this steady-state was calculated as 1830 mg/L (Table 4-11). Minor variations were observed due to the changes in the domestic wastewater quality. The corresponding organic loading on the 109 T A B L E 4-11 Characteristics from the 5 ° C Liquid Temperature Run Parameter ConL Flow Reactor Once-a-day Reactor Twice-a-day Reactor SRT (days) 10 Influent C O D (mg/L) 1830 Organic Loading 1.830 (kg COD/m 3 -day) Organic Loading 114 (lb COD/1000 cu ft-day) F / M Ratio 0.47 (kg COD/kg MLSS-day) MLSS (mg/L) 3856 MLVSS (mg/L) 1890 Percent MLVSS (%) 49.0 SPOUR 23.6 (mg/gm VSS-hr) Effluent C O D (mg/L) 572 Treatment Efficiency 68.6 (%) Effl. Susp. Solids 63 (mg/L) SVI (ml/gm) 55 10 1830 0.370 22.8 0.19 1919 917 47.8 16.8 515 71.7 106 64 10 1830 0.370 22.8 0.20 2006 987 49.2 17.2 506 72.2 93 46 110 continuous-flow reactor was 1.83 kg COD/m 3 -day (114 lb C O D / 1000 cu ft-day). This was considered to be a fairly high organic loading at a temperature of only 6°C. However, the fill-and-draw systems had 5 times lower organic loadings, 0.37 kg COD/m 3 -day (22.8 lb C O D / 1000 cu ft-day). This loading was within the acceptable range suggested by Zapf-Gilje and Mavinic (1982). Due to the higher organic loadings (compared to the 10° C temperature run), F / M ratios for all three reactors were within the normal range of 0.2 to 0.5 days -1 (Table 4-11). The F / M value of 0.47 days -1 for the continuous-flow system was fairly high, and this resulted in a poorer effluent quality. Again, the F / M values for the fill-and-draw reactors were their minimum values and therefore, these systems were not in an endogenous phase at any time during the feeding cycle. The mixed-liquor suspended solids (MLSS) were observed during the steady-state operation, as shown in Figure 4-26. The solids variation in the continuous-flow reactor was significant and it appears that this system never stabilized. The fill-and-draw systems, on the other hand, seemed to be fairly stable, with insignificant variation in their MLSS values. The average value in the continuous-flow reactor was 3856 mg/L. This was approximately twice as much as the MLSS in the fill-and-draw systems. The once-a-day reactor had an average value of 1919 mg/L, while the twice-a-day reactor had an average value of 2006 mg/L. The continuous-flow system, at the room temperature and same SRT, had a higher MLSS value compared to the 6°C run. It appears that, at this low temperature, biological activity slowed considerably and therefore the microorganisms were not able to use up the organic substrate, especially at such a high loading rate. However, the organic loading in the fill-and-draw systems was 5 times less, and the biomass had sufficient time to use up the organic substrate, thereby resulting in a relatively higher MLSS value. Also, the influent feed strength, at I l l 5000 1500-J ! • : 1 ! 1 ! • ' ! ; : ! 2 3 4 5 6 7 8 9 10 11 12 13 U 15 16 17 Days in Steady State Figure 4-26: M L S S Vs Days in Steady State - 6 C Temperature Run 112 the 6°C, was significantly higher, and this may also have led to the higher solids levels in the reactors. The percent MLVSS values in all three reactors were low, due to the high inert content in the influent feed (Table 4-11). However, these values were marginally higher than the values for the room temperature run (Table 4-8 (a)). This indicates that there was a slower utilization of the organic substrate at 6°C. The SPOUR values were monitored on a daily basis, as well as over a 24-hour period for the fill-and-draw systems. The variation of SPOUR with time for the two fill-and-draw systems is shown in Figure 4-27. A pattern similar to the 10° C run was observed. The maximum SPOUR values were much lower, however, in comparison to the previous run. The once-a-day reactor had a maximum SPOUR value of 42 mg/gm VSS-hr, while for the twice-a-day reactor the maximum value was also 42 mg/gm VSS-hr. In the previous temperature run, the twice-a-day reactor had a maximum SPOUR value of 84 mg/gm VSS-hr, which was greater than the once-a-day value of 65 mg/gm VSS-hr. Even though the high organic loading appeared to adversely affect the metabolic rate in the twice-a-day reactor, all else being equal, the twice-a-day reactor was still as efficient (or more so) at utilizing the substrate as compared to the once-a-day reactor. The maximum value in the once-a-day system was reached approximately 2.5 hours after feeding, while the twice-a-day system reached its maximum value after just 1.5 hours (see Figure 4-27). Perhaps the most conspicuous effect of the lower temperatures was the significant deterioration in the effluent quality for all three systems (see Table 4-11). As mentioned earlier, settling characteristics can be affected either by the F / M ratio or the temperature. The F / M ratios in all three reactors were higher than the previous run (see Tables 4-10 and 4-11). Therefore, it appears that filamentous growth was not extensive in any system. Also, the sull lower 45 Legend 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) 4 5 1 1 1 i l l — I — I — : — i — : — : — I — I — : — r 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 TIME (h) Figure 4-27: SPOUR Vs Time for the Fill-and-Draw Systems -6°C Temperature Run 114 temperature in this experiment would further inhibit filamentous growth. As such, at the 6 ° C temperature, formation of a pinpoint floe was visually observed in all three reactors. High effluent suspended solids were observed in the systems, with the once-a-day reactor having the highest value of 106 mg/L. Since the environmental conditions were not conducive for filamentous growth, no sludge bulking was observed. The SVI values were found to be acceptable for the three systems (Table 4-11). Unlike the 10° C temperature run, it appears that the combination of higher F / M ratios and lower temperatures resulted in the formation of a pinpoint floe (by inhibiting filamentous growth) in all systems, thereby producing a poorer quality effluent. The average effluent C O D in the continuous-flow system was 572 mg/L. This clearly indicated that, at this low temperature and high organic loading, the biomass was not able to metabolize as much of the available substrate. Therefore, it appears that a significantiy lower organic loading would perhaps be more suitable at this low temperature. The effluent COD value corresponded to a treatment efficiency of only 68.6 percent The fill-and-draw reactors also had very high effluent C O D values; the once-a-day reactor had an average effluent COD of 515 mg/L, for a treatment efficiency of 71.7 percent, and the twice-a-day system had an average effluent C O D of 506 mg/L, for a 72.2 percent treatment efficiency. The high effluent suspended solids levels in these two reactors probably contributed, in part, to the high COD value. The 6 ° C temperature run clearly indicated that all three systems failed to treat the influent feed in an effective manner. High values of effluent COD and suspended solids were observed in each reactor. Therefore, at such low operating temperatures, aerobic biotreatment of a combined sewage/leachate mix would require reduced organic loadings on the system, with 'optimization' necessary to maintain the lowest possible effluent levels of organic carbon and suspended solids. 5. CONCLUSIONS AND RECOMMENDATIONS 5.1 CONCLUSIONS 1. Combined treatment of the two waste streams, domestic sewage and leachate, is feasible under various different environmental conditions. Efficient treatment was achieved for most of the steady-state runs using 80:20 and 60:40 mixtures of sewage and leachate. The treatment efficiencies for all three reactors (once-a-day, twice-a-day and continuous feed) were comparable at all times. However, the reactors performed better at the higher organic loadings. The overall best performance, at room temperatures of 21-23° C, was observed in the continuous-flow system, at the 20-day SRT, and an organic loading of 1.323 kg COD/m 3 -day, with an average effluent C O D of 67 mg/L. This corresponded to a treatment efficiency of 95 percent C O D removal, and effluent suspended solids of 10 mg/L. The lowest treatment efficiency of 85.7 percent C O D removal was also observed in the continuous-flow reactor, for a 20-day SRT, but at the lower organic loading of 0.781 kg COD/m 3 -day. Since the influent feed contained a significant portion of domestic sewage, acclimatization of the sewage-fed activated sludge (obtained from the UBC pilot plant) did not take more than 3-4 weeks. The first week was operated with a 10 percent leachate mix, and in the later weeks 20 percent leachate was added to the feed. 2. The most efficient performance of the continuous-flow reactor, at room temperature (21-23° C), was observed at a SRT of 20 days, and an organic loading of 1.323 kg COD/m 3 -day. However, at the lower organic loading of 0.781 kg COD/m 3 -day, the 10-day SRT was found to be the most efficient, for the continuous-flow system. Therefore, it appears that an optimization of the continuous-flow system, in terms of the organic loading and SRT (or F / M ratio), would be required to obtain the most 115 116 efficient operation. 3. The once-a-day feed system performed most efficiendy (in terms of C O D removal) at the 10-day SRT's and 21-23° C temperature, for both the organic loadings, 0.162 and 0.232 kg COD/m 3 -day. A SRT of 20 days was found to be too long at such low organic loadings. However, the longer SRT resulted in higher MLSS values and this improved the sludge settieability, as indicated by the lower effluent suspended solids values. It seems that the once-a-day system could also be optimized in terms of the organic loadings and the SRT. A still higher organic loading would perhaps require a SRT longer than 10 days for the most efficient operation. 4. The twice-a-day system performed differendy as compared to the once-a-day system. The best performance was observed at the 20-day SRT (21-23°C) and the higher organic loading. The higher organic loaded system performed better, as was the case in the once-a-day system. At the lower organic loading, the low F / M ratios probably resulted in cell lysis, further deteriorating the effluent quality. 5. On the basis of SPOUR values, the twice-a-day system was found to be more efficient (21-23° C room temperature) and faster at utilizing the substrate. This was quite significant at the lower SRT of 5-days. At the 20-day SRT, however, both fill-and-draw systems exhibited a similar uptake. Due to the faster utilization of substrate, the microorganisms in the twice-a-day system were in an endogenous respiration state for a longer duration and hence cell lysis was probably more significant in this system. 6. The performance of the two fill-and-draw reactors, in terms of C O D removal, was comparable for most of the steady-state runs at room temperatures (21-23° C). At the 117 lower SRTs, the once-a-day system was found to be marginally better. However, at the longer SRTs, there was no noticeable difference in performance. The MLSS values in the two reactors, however, showed a definite trend with SRT and organic loadings. As the organic loading increased, the difference in the MLSS values of the two fill-and-draw systems also increased, with the twice-a-day reactor indicating a higher value. This difference also increased with increasing SRTs. For example, at the 5-day SRT and an organic loading of 0.177 kg COD/m 3 -day, there were wide variations in the extremely low MLSS values and in fact, the once-a-day system showed an average higher MLSS value of 282 mg/L (a 13 percent higher average value than the twice-a-day system). However, as the SRT was increased to 20 days, the twice-a-day system had a 12 percent higher MLSS value. An organic loading of 0.260 kg COD/m 3 -day resulted in a 21 percent difference in MLSS values, at the 20-day SRT. It appears that, at higher organic loadings and higher MLSS values, this difference could be large enough to affect the effluent quality and a significant difference in the performance of the two systems could result 7. The percent MLVSS values showed interesting trends during the experiments. At low organic loadings and 21-23° C room temperature, percent MLVSS decreased with increasing SRT. However, this variation was not observed at the higher organic loading, presumably due to the high inert content in the influent feed. 8. The cold temperature, steady-state runs clearly indicated a decrease in treatment efficiency with temperature, for all three reactors. The continuous-flow system showed the maximum deterioration in average effluent COD and treatment efficiency, probably due to the higher organic loading. At the 6°C temperature run, however, all three reactors showed a significant decrease (compared to the room temperatures of 21-23° C) in their treatment efficiencies and an increase in their average effluent 118 suspended solids. 9. Even though the metabolic activity of the microorganisms was lower at the decreased operating temperatures, the biomass in all three systems was fairly 'active', with no decrease in MLSS values. It seems that a higher treatment efficiency could be achieved at low temperatures by reducing the organic loadings. 10. The settling characteristics were studied in detail during the experiment The setding properties of a sludge were found to be dependent on various parameters : F / M ratio or SRT, organic loading, MLSS and temperature. For most of the steady-state runs, however, setding characteristics were found to be "acceptable". 11. The continuous-flow system, at the 5-day SRT and 0.781 kg COD/m'-day organic loading (21-23° C), experienced sludge settling problems due to the low MLSS values. However, at the 20-day SRT and 1.323 kg COD/m 3 -day organic loading, the continuous-flow system had an average MLSS value of 8322 mg/L, with hindered settling indicated at this high MLSS value. Therefore, it appears that for a still higher organic loading, setding problems may be encountered at long SRTs. Again, there seems to be a need for optimization of the system with respect to organic loadings, SRT and MLSS values. 12. Sludge bulking was encountered during a few steady-state runs. All such systems were characterized by a low F / M ratio, which also corresponds to a long SRT. It appears that filamentous growth dominated during low F / M ratios. However, bulking sludge did not necessarily affect the effluent suspended solids levels. 13. The low temperature runs encountered frequent problems with sludge settieability. 119 Due to the low temperatures, filamentous growth was inhibited, but the formation of a pinpoint floe was predominant. This was observed in the continuous-flow system, for both the 10°C and 6°C temperature runs. On the other hand, the fill-and-draw systems had low F/M ratios, which enhances filamentous growth. In these systems, at the 10° C temperature run, filamentous growth dominated and no pinpoint floe was observed; sludge bulking occurred in these fill-and-draw systems. At the lower 6°C temperature run, however, the filamentous growth appears to have been inhibited and pinpoint floe was again observed in all three systems; no sludge bulking occurred at this low temperature. It can therefore be concluded that, at lower temperatures, a low F/M ratio would result in a properly settling sludge. 5.2 RECOMMENDATIONS This experiment was carried out to study the feasibility of combined sewage: leachate treatment, and in particular, to study settling characteristics under different conditions. Certain aspects of the study which require further work are: 1. The difference in the MLSS levels of the fill-and-draw systems, at higher organic loadings, could be large enough to significantly affect effluent quality. Therefore, fill-and-draw reactors should be operated with higher MLSS values to study this effect 2. Sludge settling properties are dependent on the particular microorganisms. A study of the microorganisms speciation, for a few steady-state runs, would further enhance conclusions derived from this experiment 3. Operation of fill-and-draw systems clearly indicated that oxygen requirements vary considerably with time. This is of great practical importance, as significant cost 120 reductions could be achieved in terms of oxygen requirements. Oxygen requirements, with time, should be studied in greater detail so as to provide an efficient method of aerating fill-and-draw systems. 4. A study should be undertaken to optimize the treatment system, using parameters like organic loadings, SRT or F / M ratio, and temperature. 5. Specific Oxygen Uptake Rate (SPOUR) was used in this experiment as a measure of activity of the microrganisms. A study should be carried out using both SPOUR and ATP measurements to assess biological activity in the system. Also, measurement of factors such as UC-glucose uptake/unit ATP would provide information on the relative energetics of microorganisms at different times under different conditions. 6. The MLSS levels, in the fill-and-draw systems, at cold temperatures were found to be higher than the corresponding room temperature runs. This phenomena should be studied in greater detail and a study of the microorganisms dominating at different temperatures should also be carried out. 7. A study of the nutrient requirements for the combined sewage:leachate waste would further enhance feasibility of treatment. 8. Monitoring of effluent to look at trace metals and removal of trace organic contaminants by this process would also be useful since it helps eliminate the toxicity of the leachate prior to discharge to the environment BIBLIOGRAPHY 1. Atwater, J.W. and Mavinic, D.S., "Characterization and Treatment of Leachate from a West Coast Landfill", Environmental Engineering Group, Department of Civil Engineering, University of British Columbia, Report prepared for Environment Canada, Environmental Protection Service, January 1983. 2. Barth, E F . , Ettinger, M.B., Salotto, B.V. and McDermott, G.N. , "Summary Report on the Effects of Heavy Metals on the Biological Treatment Processes", Journal of Water Pollution Control Federation, Vol. 37, pp. 86, January 1965. 3. Biesinger, M.G. , Stensel, H.D. and Jenkins,D.,"Brewery Wastewater Treatment without Activated Sludge Bulking Problems", Proceedings of the 35th Industrial Waste Conference, Purdue University, 1980, pp. 596-609. 4. Bisogni, J.J., Jr. and Lawrence, A.W.," Relationships Between Biological Solids Retention Time and Settling Characteristics of Activated Sludge", Water Research, Vol. 5, 1971, pp. 753-763. 5. Boyle, W.C. and Ham, R.K.," Biological Treatability of Landfill Leachate", Journal of Water Pollution Control Federation, Vol. 46, No. 5, May 1974, pp. 860-872. 6. Chian, E S . K . and DeWalle, F.B.,"Evaluation of Leachate Treatment: Biological and Physical-Chemical Processes", Office of Research and Development, U.S. EP.A. , EPA -600/2 -77 -186b, Vol II, Nov. 1977. 7. Chian, ES .K . and DeWalle, F.B.," Sanitary Landfill Leachate and their Treatment", Journal of the Environmental Engineering Division, ASCE, Vol. 102, No. EE2, April 1976, pp. 411-431. 8. Cook, E.W. and Foree, E G . , " Aerobic Biostabilization of Sanitary Landfill Leachate", Journal of Water Pollution Control Federation, Vol. 46, No. 2, Feb. 1974, pp. 380-392. 9. Daigger, G.T. and Grady, C.P.L, Jr.," Factors Affecting Effluent Quality from Fill-and-Draw Activated Sludge Reactors", Journal of Water Pollution Control Federation, Vol. 49, No. 12, Dec. 1977, pp. 2390-2396. 10. Dick, R.I.," Role of Activated Sludge Final Settling Tanks", Journal of the Sanitary Engineering Division, ASCE, Vol. 96, No. SA2, April 1970, pp. 423-436. 11. Dick, R.I. and Ewing, B.B.," Evaluation of Activated Sludge Thickening Theories", Journal of the Sanitary Engineering Division, ASCE, Vol. 93, No. SA4, pp. 9-30. 12. Dick, R . l . and Vesilind, P.A.," The Sludge Volume Index - What is it ?", Journal of Water Pollution Control Federation, Vol. 41, No. 7, July 1969, pp. 1285-1291. 13. Dick, R.I. and Young, K.W.," Analysis of Thickening Performance of Final Settling Tanks", Proceedings of the 27th Industrial Waste Conference, Purdue University, 1972, pp. 33-54. 14. Dougherty, M . H . and McNary, R.R.,"Elevated Temperature Effect on Citrus Waste Activated Sludge", Sew. and Ind. Wastes, Vol. 30, No. 10, pp. 1263, Oct 1958. 121 122 15. Edwards, C P . and Nussberger, F.E.,"The Effect of Chromate Wastes on the Activated Sludge Plant at Tallmans Island", Sew. Works Journal, Vol. 19, No. 4, pp. 598, July 1947. 16. Eikelboom, D.H.," Identification of Filamentous Organisms in Bulking Activated Sludge", Prog. WaL Tech., Vol. 8, No. 6, 1977, pp. 153-161. 17. Graham, D.W. and Mavinic, D.S.,"Biological-Chemical Treatment of Leachate", Proceedings of ASCE National Conference on Environmental Engineering, San Francisco, California, 1979, pp. 291-298. 18. Green, M . and Shelef, G.," Sludge Viability in a Biological Reactor", Water Research, V o l 15, 1981, pp. 953-959. 19. Hoepker, E C . and Schroeder, E.D.," The Effect of Loading Rate on Batch-Activated Sludge Effluent Quality", Journal of Water Pollution Control Federation, Vol. 51, No. 2, Feb. 1979, pp. 264-273. 20. Lawrence, A.W. and McCarty, P.L.," Unified Basis for Biological Treatment Design and Operation", Journal of the Sanitary Engineering Division, ASCE, Vol. 96, No. SA3, June 1970, pp. 757-778. 21. Manickam, T.S. and Gaudy, A.F., Jr.," Studies on the Relationships Between Feed COD and Effluent C O D during Treatment by Activated Sludge Processes", Proceedings of the 34th Industrial Waste Conference, Purdue University, 1979, pp. 854-867. 22. Mavinic, D.S.,"Kinetics of Carbon Utilization in Treatment of Leachate", Water Research, Vol. 18, No. 10, 1984, pp. 1279-1284. 23. Metcalf, L and Eddy, H.,"Wastewater Engineering: Collection, Treatment, Disposal", McGraw-Hill Book Company (1972). 24. Monod, J.,"The Growth of Bacterial Cultures", Annual Review of Microbiology, Vol. I l l , 1949. 25. Munch, W.L. and Fitzpatrick, J.A.," Performance of Circular Final Clarifiers at an Activated Sludge Plant", Journal of Water Pollution Control Federation, Vol. 50, No. 2, Feb. 1978, pp. 265-276. 26. Neufeld, R.D. and Hermann, E.R.,"Heavy Metal Removal of Acclimated Activated Sludge", Journal of Water Pollution Control Federation, Vol. 47, No. 2, February 1975, pp. 210-279. 27. Neufeld, R.D.," Heavy Metals-Induced Deflocculation of Activated Sludge", Journal of Water Pollution Control Federation, Vol. 48, No. 8, Aug. 1976, 28. Palit T. and Qasim, S.R.," Biological Treatment Kinetics of Landfill Leachate", Journal of the Environmental Engineering Division, ASCE, Vol. 103, No. EE2, April 1977, pp. 353-366. 29. Pearse, L. and Committee,"Bulking of Sludge in the Activated Sludge Process of Sewage Treatment", American Public Health Association, Yearbook, 27, 164, 1937. 123 30. Pipes, W.O.," Actinomycete Scum Production in Activated Sludge Processes", Journal of Water Pollution Control Federation, Vol. 50, No. 4, April 1978, pp. 628-634. 31. Pipes, W.O.," Bulking, Deflocculation, and Pinpoint Floe", Journal of Water Pollution Control Federation, Vol. 51, No. 1, Jan. 1979, pp. 62-70. 32. Pipes, W.O.," Types of Activated Sludge which Separate Poorly", Journal of Water Pollution Control Federation, Vol. 41, No. 5, Part 1, May 1969, pp. 714-724. 33. Pitman, A.R.," Settling Properties of Extended Aeration Sludge", Journal of Water Pollution Control Federation, Vol. 52, No. 3, Mar. 1980, pp. 524-536. 34. Roberts, E.J.,"Thickening- Art or Science", Mining Engineering, 1, 61, 1949. 35. Sawyer, C .N. and McCarty, P.L.,"Chemistry for Environmental Engineering", 3rd Edition, 1978, McGraw-Hill Book Company. 36. Sezgin, M . , " The Role of Filamentous Microorganisms in Activated Sludge Settling", Prog. WaL Tech., Vol. 12, 1980, pp. 97-107. 37. Sezgin, M„ Jenkins, D. and Parkes, D.S.," A Unified Theory of Filamentous Activated Sludge Bulking", Journal of Water Pollution Control Federation, Vol. 50, No. 2, Feb. 1978, pp. 362-381. 38. "Standard Methods for Examination of Water and. Wastewater", American Public Health Association Inc., 14th Edition, 1980. 39. Technicon Autoanalyzer Industrial Methods No. 321-74A and No. 327-74W. 40. Temoin, E.P. and Mavinic, D.S.," Nutrient Requirements for Aerobic Biostabilization of Landfill Leachate", Proceedings of the 36th Industrial Waste Conference, Purdue University, 1981, pp. 860-866. 41. Temoin, EP.,"Nutxient Requirements for Aerobic Biostabilization of Landfill Leachate", Master of Applied Science Thesis, Department of Civil Engineering, University of British Columbia (October, 1980). 42. Uloth, V.C. and Mavinic, D.S.," Aerobic Bio-Treatment of a High-Strength Leachate", Journal of the Environmental Engineering Division, ASCE, Vol. 103, No. EE4, August 1977, pp. 647-661. 43. Wang, L.K. , Poon, C.P.C. and Wang, M.H. , " Control Tests and Kinetics of Activated Sludge Process", Water, Air, and Soil Pollution, 8, 1977, pp. 315-351. 44. Wong, P.T. and Mavinic, D.S.," Treatment of a Municipal Leachate under Multi-Variable Conditions", Water Poll. Res. Jour. Canada, Vol. 17, 1982, pp. 135-148. 45. Zapf-Gilje, R. and Mavinic, D.S.," Characteristics of Fill-and-Draw Reactor", Journal of the Environmental Engineering Division, ASCE, Vol. 108, No. EE4, August 1982, pp. 808-812. 46. Zapf-Gilje, R. and Mavinic, D.S.," Temperature Effects on Biostabilization of Leachate", Journal of the Environmental Engineering Division, ASCE, Vol. 107. No. 124 EE4, August 1981, pp. 653-663. 

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