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CONTROL OF ODORS FROM AN ANAEROBIC LAGOON TREATING MEAT PACKING WASTES
J. A. Chittenden", L. E. O r s i * * , J . L. Witherow***, and W . J . Wells, Jr.****
INTRODUCTION
The w a r m , h igh ly concent ra ted wastes from a meat packing o p e r a t i o n are uniquely s u i t e d t o t h e use of anaerobic lagoons t o provide a h igh degree of pre t rea tment p r i o r t o f i n a l ae rob ic t reatment . The advantages of anaerobic lagoons inc lude minimum design removal e f f i c i e n c i e s of BOD, g rease , and suspended s o l i d s of 80%. The anaerobic process has minimum c a p i t a l and ope ra t ing c o s t s , i s s imple t o ope ra t e , mechanical equipment i s n o t necessary , and t h e t rea tment processes can wi ths t and t h e shock loadings common i n t h e food processing indus t ry .
One major disadvantage a s soc ia t ed wi th t h e anaerobic lagoons i s t h e odors t h a t r e s u l t from such a process . companies seeking o t h e r t rea tment a l t e r n a t i v e s a t cons ide rab le p e n a l t i e s i n c a p i t a l and annual ope ra t ing cos t s .
This problem has r e s u l t e d i n many
The cause of t h e s e odors and a s u c c e s s f u l method of e l i m i n a t i n g t h e problem i s t h e s u b j e c t of t h i s paper. Also d iscussed i s a conceptua l process f o r recover ing a s i g n i f i c a n t amount of wasted energy by u t i l i z i n g t h e hea t ing va lue of t h e methane generated by t h e anaerobic process . i n c e n t i v e f o r us ing t h e anaerobic process as opposed t o a completely aerobic system f o r t h e t rea tment of meat packing wastes i n a proposed packing p l a n t i s a l s o presented .
The f i n a n c i a l
BACKGROUND
The anaerobic d i g e s t i o n process u t i l i z e s b a c t e r i a which func t ion i n t h e absence of f r e e oxygen t o break down o rgan ic waste. The waste material i s converted through a number of i n t e rmed ia t e products t o water, gases and s o l i d s of lesser molecular weight. and o b t a i n i t from o rgan ic compounds, water and oxides of n i t r o g e n and s u l f u r . odor less . However, reduct ion of su l fur -conta in ing o rgan ic matter and s u l f a t e s produce o rgan ic s u l f i d e s , occas iona l ly d i s u l f i d e s i n t h e c1-c6 range, and hydrogen s u l f i d e (1).
The b a c t e r i a u s e bound oxygen t o surv ive
The gases produced are mainly methane and carbon d ioxide which are
Hydrogen s u l f i d e (H2S) i s usua l ly t h e major cause of o b j e c t i o n a b l e odor from t h e anaerobic process . It has an odor c h a r a c t e r i s t i c of r o t t e n eggs,
* Texas Amaril lo Systems Company, Amaril lo, Texas ** Wilson & Co. , Oklahoma C i t y , Oklahoma *** U.S. Environmental P ro tec t ion Agency, C o r v a l l i s , Oregon **** B e l l , Galyard t , & Wells, Omaha, Nebraska
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They opera ted several 20 l i t e r anaerobic d i g e s t e r s t o which known amounts of s u l f a t e were added t o t h e i n f l u e n t . w a s added, t h e equi l ibr ium s o l u b l e s u l f i d e concent ra t ions w e r e 32 mg/l as S and 78 mg/l as S , r e spec t ive ly . SO4-S, a f i g u r e i n t h e Lawrence paper shows t h e s u l f i d e s i n t h e gas t o be 10 mg/l as S.
When 200 and 400 mg/l of SO4-s
For t h e d i g e s t e r r ece iv ing 400 mg/l
Lawrence, e t a l . , conclude t h a t t h e concent ra t ion of hydrogen s u l f i d e i n t h e d i g e s t e r i s r e l a t e d t o t h e concent ra t ion of hydrogen s u l f i d e and s u l f i d e pe rcu r se r s ( s u l f a t e s ) e n t e r i n g w i t h t h e waste minus t h e q u a n t i t y of hydrogen s u l f i d e s expe l l ed wi th t h e gas and t h a t t h e q u a n t i t y of s u l f i d e s i n t h e gas i s r e l a t e d t o t h e s o l u b i l i t y of hydrogen s u l f i d e , t h e pH, and t h e t o t a l amount of gases produced. They a l s o determined t h a t up t o 400 mg/l of su l - f i d e can b e p r e c i p i t a t e d by added i r o n compounds wi th no adverse e f f e c t on t h e anaerobic t rea tment process . P r e c i p i t a t i o n of t h e s u l f i d e s e l imina te s t h e hydrogen s u l f i d e odor.
Gloyna and Espino u t i l i z e d 430 l i t e r p i l o t u n i t s i n developing equat ion 2. t o c a l c u l a t e t h e s u l f i d e product ion i n lagoons.
- 2. S- = K (SO4=)
- Where S- i s 24 hour average s u l f i d e concent ra t ion i n t h e lagoon,
SO4 K w a s determined by t h e i n v e s t i g a t i o n t o be :
- - i s t h e concen t r a t ion of s u l f a t e i on i n t h e i n f l u e n t , and
K = .055 + .00012 (lb.BOD/ac) + .0016 (de ten t ion i n days)
The test d a t a i s r epor t ed i n Table 1.
TABLE 1. RESULTS FROM LABORATORY LAGOON STUDIES
Test No.
BOD l b /AC/day
136 68
136 136
68 136
so4 mg/l
23 23 23
206 200 400
T emp O C
25 23 26 23 25 26
Detent i on days
30 30 15 30 15 30
S u l f i d e mg/l
0.432 0.500 1.12 4.29 6.36 8.76
These two i n v e s t i g a t i o n s i n d i c a t e t h e concent ra t ion of hydrogen s u l f i d e i n s o l u t i o n i n an anaerobic lagoon w i l l b e between 2 and 5 pe rcen t of t h e SO4 concent ra t ion i n t h e un t r ea t ed wastewater. Using t h e e s t a b l i s h e d r a t i o of s o l u b l e s u l f i d e t o s u l f i d e i n t h e gas t h e c a l c u l a t e d hydrogen s u l f i d e concent ra t ion escaping t o t h e atmosphere w i l l be nea r ly one pe rcen t of t h e SO4 concent ra t ion i n t h e wastewater.
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-5 which can b e de t ec t ed a t very low concent ra t ions of between 1 .0 x 10 and 1.0 x 10-4 mg/l i n water (2) and 4.7 x ppm i n a i r ( 3 ) . Hydrogen s u l f i d e is a l s o a t o x i c gas , having a threshold l i m i t of 10 ppm f o r indus- t r i a l exposure w i t h concent ra t ion of 20 - 150 ppm causing eye i r r i t a t i o n . A t h i r t y minute exposure t o 500 ppm of hydrogen s u l f i d e can r e s u l t i n d i zz i - n e s s , headache, s t agge r ing , l o s s of consciousness , d i a r r h e a , b r o n c h i t i s and broncho-pneumonia. F i n a l l y , exposure t o 800 -1000 ppm can be f a t a l i n 30 minutes o r less (4) . The t o x i c i t y of t h e gas is of concern i n confined s t r u c t u r e s such as sewer o r w e t w e l l s , b u t i t s odor i s of primary importance t o t h e u t i l i z a t i o n of lagoons.
The reduct ion of s u l f a t e t o s u l f i d e under anaerobic condi t ions i s w e l l e s t a b l i s h e d . S u l f a t e is considered t o be t h e sou rce of almost a l l t h e s u l - f i d e i n t h e anaerobic lagoon. P a r t of t h e s u l f i d e produced w i l l combine w i t h metal i o n s , such as i r o n , and become inso lub le . Most of t h e s u l f i d e usua l ly remains s o l u b l e as hydrogen s u l f i d e and, a t t h e nea r n e u t r a l pH i n t h e anaerobic lagoons, p a r t i a l l y d i s s o c i a t e s i n t o hydrogen and b i s u l - f i d e ions . a i r u n t i l i t s p a r t i a l p re s su re i s i n equ i l ib r ium wi th t h e H2S i n s o l u t i o n . Thus, t h e odor of hydrogen s u l f i d e from an anaerobic lagoon is p ropor t iona l t o t h e s u l f a t e i n t h e waste water t r e a t e d . The source of s u l f a t e s i s t h e water supply. by t h e meat packing opera t ions . s ta te r egu la to ry agencies have no t u sua l ly considered us ing anaerobic lagoons when t h e s u l f a t e i n t h e water supply exceeded 200 mg/l, and some are re luc- t a n t w i th concent ra t ions over 100 mg/l.
The s u l f i d e remaining as H2S i n s o l u t i o n w i l l escape i n t o t h e
S u l f a t e concent ra t ions are no t thought t o be increased From experience, t h e meat indus t ry and
Two l abora to ry i n v e s t i g a t i o n s (5) ( 6 ) have r epor t ed on t h e theory of s u l - f i d e product ion and have developed b a s i c in format ion under c o n t r o l l e d condi- t i o n s . Lawrence, e t a l . , combine t h e d i s s o c i a t i o n and gas equi l ibr ium equat ions t o form equat ion 1. t h a t can b e used t o c a l c u l a t e t h e r a t i o of concent ra t ions of s o l u b l e s u l f i d e s i n t h e water t o hydrogen s u l f i d e i n t h e gas .
The Ha
Where TSS i s HS- + H ~ S i n water,
H S is hydrogen s u l f i d e i n gas ,
H+ i s hydrogen i o n concent ra t ion i n water,
a i s t h e absorp t ion cons t an t , and
K1 is t h e i o n i z a t i o n cons tan t .
2 g
ibook of Chemistry and Physics has va lues on a and K 1 , t va r ious Data c o l l e c t e d dur ing t h e i n v e s t i g a t i o n gave-somewhat h ighe r
From t h e experi- temperatures . r a t i o s of (TSS/H2Sg) than w a s ca l cu la t ed by t h e equat ion. mental d a t a , t h e r a t i o would be expected t o vary from 4 t o 8 a t t h e normal pH of d i g e s t e r s .
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The meatpacker had h i s own w e l l s , bu t they were i n t h e same a q u i f e r as t h e municipal w e l l s , which had s u l f a t e concent ra t ions of 1030 t o 1050 mg/l. Because of ob jec t ions by 108 l o c a l r e s i d e n t s , odor c o n t r o l w a s incorpora ted i n t h e lagoon design. packing wastewater t o s u l f a t e concent ra t ion of less than 200 mg/l by develop- ing another ground water supply. lagoon t o reduce t h e release of H2S submerged i n l e t s and o u t l e t s on t h e anaerobic lagoon t o reduce H2S release. ( 4 ) Maintaining a 7.0 pH t o reduce release of H2S by reducing t h e p a r t i a l p re s su re of t h e gas . (5) P u t t i n g t h e e f f l u e n t through a d e g a s i f i e r t o remove t h e H2S and pass ing t h e gas through an ozone chamber t o o x i d i z e t h e H2S. l i m i t s , t h e anaerobic lagoon w a s no t cons t ruc ted .
The engineered design inc luded : ( l ) Limit ing t h e meat-
(2) Maintaining a scum l a y e r on t h e (3) Using from t h e lagoon su r face .
However, because of t h e odor p o t e n t i a l and la ter imposed ammonia
Anaerobic lagoons are used by a meatpacker i n Denison, Iowa. The s u l f a t e concent ra t ion i n t h e anaerobic lagoon i n f l u e n t and e f f l u e n t averaged 332, and 39 mg/l, r e spec t ive ly . Hydrogen s u l f i d e i n t h e anaerobic lagoon e f - f l u e n t averaged 4.6 mg/l. The lagoons were covered wi th a t h i c k l a y e r of scum, bu t t h e H2S odor w a s s t r o n g a t t h e overflow w e i r and a t a s m a l l t ank i n which t h e lagoon e f f l u e n t w a s ae ra t ed . descr ibed t h e odor as a bad s i t u a t i o n and aromatic chemicals were used t o mask t h e odors.
The t rea tment p l a n t ope ra to r
I n Texas, two anaerobic lagoons t r e a t i n g meatpacking wastes are known t o have s i g n i f i c a n t odor problems (11). c i t y of Sweetwater w i th a measured s u l f a t e content of 218 mg/l. from t h e Extension Se rv ice made t h r e e odor i n t e n s i t y measurements on t h e downwind s i d e of t h e lagoon which requi red 31 (Dt) d i l u t i o n t o reach a th re sho ld odor. The o t h e r packer i n Maverick County used water from t h e Rio Grande River which had a s u l f a t e concen t r a t ion of 190 mg/l. measurements made downwind were 31 D t a longs ide t h e lagoon and 2 Dt a t 3 / 4 of a m i l e from t h e lagoon. t i o n due t o f i n a n c i a l problems and odor c o n t r o l became unnecessary. The Extension Service recommended t o t h e o t h e r packer conversion of t h e anaerobic lagoon t o an a e r a t e d lagoon.
One packer ob ta ins water from t h e Personnel
Odor
The packer i n Maverick County ceased opera-
I n Moerewa, New Zealand, anaerobic lagoons are used t,o treat s e t t l e d meat- packing waste (12). The main cr i t ic ism of t h e lagoon w a s r epor t ed as t h e odor of hydrogen s u l f i d e a s soc ia t ed w i t h t h e gases. t r a t i o n of t h e wastewater is n o t g iven , b u t an ana lyses of t h e evolved gas w a s : hydrogen s u l f i d e a t 0.4%, carbon d ioxide a t 7.0%, methane a t 85.0%, oxygen a t 0.6% and n i t rogen and o t h e r s a t 7.0%. A record of hydrogen s u l f i d e i n t h e a i r c l o s e t o t h e lagoons w a s kept f o r 8 months. The h i g h e s t concen- t r a t i o n w a s an i s o l a t e d occurrence of 0.99 mg/l, b u t of t h e t o t a l number of readings a t two-hour i n t e r v a l s , 1897 were n i l and 389 were p o s i t i v e wi th an average concent ra t ion of 0.02 mg/l.
The s u l f a t e concen-
The odor c o n t r o l a t Moerewa cons i s t ed of maintaining a scum cover on t h e lagoon. s u l f i d e w a s e s t a b l i s h e d by a i r samples taken f o u r inches above t h e water o r scum cover. 0.35 mg/l, compared t o t h e concent ra t ions ranging from 2.0 t o 15.0 mg/l over t h e scum f r e e areas.
The e f f e c t i v e n e s s of t h e cover i n reducing t h e escape of hydrogen
The concent ra t ion of hydrogen s u l f i d e above t h e scum averaged
Since t h e threshold odor i n a i r i s ppm f o r hydrogen s u l f i d e , t h e odor of hydrogen s u l f i d e would b e present w i t h s u l f a t e s a t 10-2 mg/l i n t h e water supply. Experience has shown t h a t a concent ra t ion of s u l f a t e s up t o 100 mg/l i n t h e water produces odors t h a t are accepted, thus d isper - s i o n of t h e hydrogen s u l f i d e i n the atmosphere is a major f a c t o r i n odor con t ro l .
Models f o r d i spe r s ion of odors were found i n t h e l i t e r a t u r e ( 7 ) (8) (9) . A s i m p l i f i e d model t o determine maximum h o r i z o n t a l d i s t a n c e of odor travel i s shown i n equat ion 3..
Where Co i s i n i t i a l odor concent ra t ion
C is odor concent ra t ion a t X
X i s h o r i z o n t a l d i s t a n c e from t h e source , and
Do i s diameter of t h e odor source.
When us ing cons tan ts (k = 1, n .- -1.5) deve loped by S h i r a z i , e t a l . (9) t h e necessary d i s t a n c e t o reach a threshold odor w a s 5 m i l e s from an an- ae rob ic lagoon r ece iv ing 388 mg/l SO4. proposed i n t h i s paper ) . An a t tempt t o v e r i f y t h e s e cons t an t s w i th odor d a t a c o l l e c t e d by Minor 2nd S t a r k (10) w a s unsuccessful . However, t h e s e f a c t s ag ree wi th exper ience t h a t odor c o n t r o l by d i spe r s ion of H2S from anaerobic lagoons t r e a t i n g h igh s u l f a t e wastewaters i s imprac t i cab le and perhaps unpredic tab le .
(The design of such a lagoon i s
CASE HISTORIES
Two of t h e f i r s t cases of hydrogen s u l f i d e odor problems wi th an anaerobic lagoon t r e a t i n g meatpacking wastes occurred a t Storm Lake and Harlan, Iowa. I n both cases, t h e odors were s u f f i c i e n t t o i n i t i a t e nuisance complaints. S u l f a t e s i n both water s u p p l i e s were q u i t e h igh; ranging from 75 t o 1560 mg/l a t Harlan and from 126 t o 690 mg/l a t Storm Lake. t h e meatpackers switched t o another source of water wi th lower s u l f a t e con- c e n t r a t i o n s t o reduce t h e odor problem.
I n both cases,
An anaerobic lagoon w a s cons t ruc ted i n 1965 t o treat packinghouse wastewater n e a r Cherokee, Iowa. of s u l f a t e . On a win te r day, minor odor w a s de t ec t ed by one of t h e au thors 20 f e e t downward from t h e lagoon. d e t e r i o r a t i o n , t y p i c a l of hydrogen s u l f i d e co r ros ion , on t h e doors of t h e c o n t r o l b u i l d i n g and on a nearby cyclone fence. de t ec t ed by l o c a l c i t i z e n s , b u t ope ra t ion o r des ign changes have n o t been necessary t o c o n t r o l odors.
The w e l l w a t e r a n a l y s i s showed an average of 90 mg/l
However, t h e r e were s i g n s of metal
Occasional odors have been
I n 1970 t h e Ci ty of Spencer, Iowa, had an anaerobic lagoon designed f o r treat- ment of municipal wastewater c o n s i s t i n g of about 90 pe rcen t meatpacking wastes.
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TABLE 2. PERCENT OF SURFACE AREA COVERED ( 1 4 ) (Cont.)
D t
Date Lagoon No. 1 Lagoon No. 3
March 9" March 8 March 3 March 2 March I* February 25* February 19* February 1 6 February 1 3 February 4 February 3* February 2 January 29* January 28 January 26
95 95 35 45 40 40 20
35 10 10 10
5 5 5
5**
100 100 100 100 100 100 100
100 100 100 100 100 100 100
60**
0 7 0
15 15 0 15 15 15 31 170
* ** Days of high winds
Odor readings by S ta te o f f i c i a l s
The o v e r a l l e f f e c t i v e n e s s of t h e scum cover i n reducing odor emissions is summarized i n F igure 1. Agency personnel are shown on t h e f i g u r e .
Only those odor measurements made by t h e State
During March 1975, a series of s u l f a t e measurements w a s made by t h e c i t y on t h e packing p l a n t e f f l u e n t and t h e i n f l u e n t t o t h e t rea tment p l a n t and are shown i n Table 3. Addi t iona l s u l f a t e measurements on t h e packing p l a n t e f f l u e n t averaged 95 and 90 mg/l i n A p r i l and May, r e s p e c t i v e l y .
TABLE 3. SULFATE CONCENTRATIONS
Date Packing P l a n t Treatment P l a n t E f f l u e n t (mg/l) I n f l u e n t (mg/l)
March 2 March 3 March 4 March 5 March 8 March 9 March 1 5 March 16 March 19 March 22
48 110
45 110 150
121
66 160
-- --
-- 7 1 47
220 80
120 -- 120 140
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I n 1973, t h e c i t y of Greeley, Colorado, i n i t i a t e d ope ra t ion of anaerobic lagoons which rece ived 95% of t h e i r wastewater flow from a l a r g e meatpacker. The water supply a t t h e packing p l a n t contained 700 t o 800 mg/l of s u l f a t e s (13). A severe odor problem occurred a t t h e anaerobic lagoon. y e a r ' s ope ra t ion , c i t y water w a s extended t o t h e packer. The s u l f a t e con- c e n t r a t i o n i n t h e c i t y water w a s about 40 mg/l. S ix months a f t e r t h e lower s u l f a t e water w a s used, odor continued t o b e a problem. I n J u l y 1975, t h e S t a t e of Colorado A i r P o l l u t i o n Cont ro l Agency found t h e f a c i l i t y i n v io l a - t i o n of a i r q u a l i t y s tandards f o r odors and subsequent ly i s sued a cease and d e s i s t o rder . a t t h e proper ty l i n e of 15 D t .
A f t e r one
These a i r q u a l i t y s t anda rds have a maximum l i m i t f o r odor F ive o t h e r states have similar s tandards (8 ) .
Several new ope ra t ion schemes were undertaken t o c o n t r o l t h e odor. To b u i l d up a heavy scum l a y e r on t h e s u r f a c e , a l l of t h e p l a n t flow w a s rou ted t o anaerobic lagoon No. 3. The a d d i t i o n of straw and grease t o a i d i n developing a cover w a s planned as a second s t e p . Such a cover w a s expected t o reduce odor emissions from t h e lagoon. A f t e r t h e scum completely covered t h e s u r f a c e , measured odors were below t h e a i r q u a l i t y s t anda rds f o r a two month per iod .
However, due t o an excess build-up of s o l i d s i n lagoon No. 3, another lagoon (No. 1 ) w a s pu t i n t o ope ra t ion on December 17 , 1975, and odor levels i n excess of t h e a i r q u a l i t y s t anda rds reoccurred. Beginning on January 23, t h e primary t rea tment process a t t h e packing p l a n t w a s bypassed t o i n c r e a s e t h e g rease level and more r ap id ly form a cover on lagoon No. 1. t h e a d d i t i o n of 10 mg/l of c h l o r i n e t o t h e packing p l a n t e f f l u e n t w a s i n i - t i a t e d t o reduce s u l f i d e odors a t t h e lagoon i n l e t . I n t h e 30 days a f t e r t h e i n i t i a t i o n of c h l o r i n a t i o n , t h e scum l a y e r went from 35 t o 40 pe rcen t cover on lagoon No. 1 t o a 99% cover. High winds sometimes broke up t h e scum l a y e r and temporar i ly reduced t h e percent of s u r f a c e area covered. The wastewater became anaerobic i n 32,500 f e e t of f o r c e main between t h e packing p l a n t and t h e lagoons. t i o n i n t h e wastewater showed up t o a 50 mg/l decrease a t t h e i n l e t t o t h e lagoon when c h l o r i n a t i o n w a s p rac t i ced . corresponding decrease i n t h e odor d i l u t i o n s reading are shown i n Table 2 .
On March 1,
Measurement of t h e hydrogen s u l f i d e concentra-
The build-up of t h e cover and
TABLE 2. PERCENT OF SURFACE AREA COVERED (14)
Date Lagoon No. 1 Lagoon No. 3 Dt
March 30 March 29 March 26 March 25* March 24 March 22 March 19 March 18* March 1 7 March 11
-- 99 99 99 99 60** 95 98 85**
-- 100 100 100 100
100 100 loo**
60**
-- 0 7 0 0 7 7 0 7
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TABLE 3. SULFATE CONCENTRATIONS (Cont.)
Date Packing P lan t Treatment P l a n t E f f l u e n t (mg/l> I n f l u e n t (mg/l)
March 23 -- March 25 88
205 80
Average 100 120
The c i t y rechecked i ts t e s t i n g procedures and reagents f o r t h e s u l f a t e test and found no d iscrepancies . Tests on c i t y domestic water showed SO4 concent ra t ions i n t h e range of 40 - 60 mg/l. An i n c r e a s e of about 50 mg/l of s u l f a t e s by t h e meat packing process i s shown by t h i s da t a . This i n c r e a s e is cont ra ry t o t h e commonly accepted b e l i e f t h a t s u l f a t e concent ra t ions are no t increased i n t h e meat packing process .
An anaerobic lagoon w a s used t o treat meatpacking wastewater near Ada, Oklahoma. During a two-year pe r iod , one of t h e au thors inspec ted t h e lagoon over 200 t i m e s and de tec t ed s e p t i c odors w i t h i n a few f e e t of t h e lagoon, b u t t h e odor of H2S w a s no t de t ec t ed . bubbles a t t h e s u r f a c e showed cons iderable gas production. The l a c k of odor w a s a t t r i b u t e d t o the low s u l f a t e concent ra t ion i n t h e water (15).
The water supply had a s u l f a t e concent ra t ion of 4.0 mg/l.
The lagoon d id n o t have a scum cover and
DESIGN CONSIDERATIONS
A s tudy of accep tab le methods of c o n t r o l l i n g anaerobic lagoon odors w a s i n i t i a t e d i n t h e course of t h e des ign of a new m e a t packing f a c i l i t y t o be l o c a t e d i n Southwestern Arizona. I n o rde r t o enable t h e r eade r t o eva lua te t h e p o t e n t i a l of t h e concepts presented i n t h i s paper , t h e r e s u l t s of t h a t s tudy are d iscussed i n d e t a i l i n t h e remaining pages of t h i s ar t ic le .
I n t h e proposed l o c a t i o n of t h e meat packing p l a n t , ground water s u p p l i e s w e r e l i m i t e d and of such poor q u a l i t y t h a t i t w a s concluded t h a t water would have t o b e obtained elsewhere.
The only o t h e r a v a i l a b l e source of water w a s t h e i r r i g a t i o n cana l t h a t bordered t h e property. Discussions wi th t h e Bureau of Reclamation and t h e l o c a l Water and Drainage Districts i n d i c a t e d t h a t approval would b e gran ted f o r withdrawing t h e necessary water.
A t y p i c a l a n a l y s i s of t h e water is given i n Table 4 . w a s somewhat h igh i n s a l i n i t y , it would b e accep tab le f o r po tab le use a f t e r suspended s o l i d s removal and ch lo r ina t ion . Previous experience had shown, however, t h a t t h e h igh s u l f a t e s (388 mg/l) would produce unacceptably high odor emissions from t h e anaerobic lagoons.
Although t h e water
46
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cheaper a l t e r n a t i v e .
The proposed p l a n t w a s t o be capable of s l a u g h t e r i n g 2880 head of beef p e r day and breaking 2000 beef carcasses pe r day i n t o boxed beef . Drawing up t h e experience of similar p l a n t s , t h e r a w and t r e a t e d wastes c h a r a c t e r i s t i c s were formulated. The i r design va lues are shown i n Table 5.
TABLE 5. WASTE CHARACTERISTICS
Raw Wastes Treated Wastes
Flow - MGD 2.88 BOD mg/l 1500 SS mg/l 1200 Grease mg/l 900 T o t a l K-N mg/l 200
2.88 60 80 10
160
A summary of t h e s tudy t o eva lua te t h e t rea tment a l t e r n a t i v e and t h e com- pa r i sons of t h e candida tes f o r a lagoon cover i s given i n t h e fol lowing paragraphs.
Completely Aerobic System
A schematic of t h e proposed completely ae rob ic system i s given i n F igure 2. The f i r s t s t a g e a e r o b i c t rea tment w a s t o b e accomplished wi th two p a r a l l e l f i x e d media towers us ing redwood media. The i n f l u e n t BOD5, es t imated a t 1500 mg/l, would b e reduced by 65% i n t h e towers. towers would main ta in an adequate we t t ing rate t o enhance t rea tment e f f i - c iency.
Rec i r cu la t ion around t h e
The second s t a g e ae rob ic t rea tment chosen w a s two p a r a l l e l a e r a t i o n bas ins each conta in ing 250 hp of e i t h e r slow speed, f i x e d p la t form a e r a t o r s , o r a d ispersed a i r system us ing s t a t i c tube d i f f u s e r s .
The f i n a l c l a r i f i e r s were used t o se t t le t h e wastes. The s e t t l e d s o l i d s were r e tu rned t o t h e i n l e t of t h e redwood towers s o t h a t t h e f ixed media towers would ope ra t e i n t h e a c t i v a t e d b i o l o g i c a l media mode. Provis ions were a l s o made t o a l low s ludge r e t u r n t o t h e extended a e r a t i o n bas in i n o rde r t o main ta in t h e MLSS a t d e s i r a b l e levels. Approximately 0.2 MGD of s ludge would b e wasted t o an a e r a t e d s ludge hold ing tank wi th two days hold ing capac i ty .
Approximately 30 acres of s t o r a g e ponds t o provide 20 days of s t o r a g e would b e provided a f t e r t h e f i n a l c l a r i f i e r s . To avoid ground water contamina- t i o n , t h e lagoons would b e sea l ed .
E f f l u e n t from t h e ponds would be u t i l i z e d f o r i r r i g a t i o n .
The a e r a t e d s ludge from t h e s ludge hold ing tanks would b e pumped d i r e c t l y t o a s e p a r a t e i r r i g a t i o n system.
48
TABLE 4. IRRIGATION WATER ANALYSIS
Cons t i tuen t Concentrat ion mg/l
S i l i ca Calcium Magnesium Sodium Pot ass ium Bicarbonate Carbonate S u l f a t e Chlor ide F luo r ide Nitrate Dissolved S o l i d s Hardners as CaC03 Non-carbonate Hardners
S p e c i f i c Conductance as CaC03
mmhos
9 91 32
126 6
172 0
388 10 7
N i l 796 360 218
0.5
1.240
The meatpacking company r e t a i n e d a consu l t ing f i r m t o s tudy t h e problem and make recommendations. I n p a r t i c u l a r , t h e consu l t an t w a s given two assignments:
1) Develop t h e c a p i t a l and ope ra t ing c o s t s of a completely a e r o b i c waste t rea tment system and compare those c o s t s w i t h t h e c a p i t a l and ope ra t ing c o s t s of an anaerobic lagoon system followed by a minimum of ae rob ic t rea tment .
2) Explore t h e va r ious t h e gases generated odor emission would cover developed f o r w a s t o b e eva lua ted lagoon.
a l t e r n a t i v e s f o r c o l l e c t i n g and t r e a t i n g by t h e anaerobic lagoon s o t h a t accep tab le r e s u l t . I n p a r t i c u l a r , t h e anaerobic lagoon t h e Wilson & Co. p l a n t a t Monmouth, I l l i n o i s as a p o t e n t i a l candida te f o r t h e Arizona
The proposed p l a n t l o c a t i o n a l s o d i c t a t e d two o t h e r s i g n i f i c a n t des ign parameters. i r r i g a t i o n . The S t a t e requi red t rea tment of t h e waste p r i o r t o i r r i g a t i o n t o a level t h a t produced a maximum BOD5 of 100 mg/l. Since t h e crops could u t i l i z e t h e n i t r o g e n i n t h e amnonical form, n i t r i f i c a t i o n w a s n o t a problem. f a c t o r d i c t a t e d by t h e proposed s i te w a s t h a t a e r o b i c lagoons f o r f i n a l t rea tment of t h e waste were precluded by t h e s o i l cond i t ions on t h e s i te . The s o i l w a s a l l sand and c o s t estimate comparisons of s e a l i n g t h e l a r g e area lagoons t o meet accep tab le e x - f i l t r a t i o n rates versus t h e c o s t of small area a e r a t i o n bas ins i n d i c a t e d t h a t extended a e r a t i o n would b e t h e
F i r s t , t h e f i n a l d i s p o s a l of t h e waste water would be cropland There w a s no stream a v a i l a b l e t o accept t r e a t e d wastes.
The second
47
I
Anaerobic/Aerobic System
I n o rde r t o u t i l i z e anaerobic lagoons i n t h i s a p p l i c a t i o n i t would be neces- s a r y t o have an e f f e c t i v e gas c o l l e c t i o n system t o prevent ob jec t ionab le odorous emissions.
A s tudy w a s made of t h e a v a i l a b l e covers t h a t could be used i n t h i s appl ica- t i o n . A c o s t summary of t h i s s tudy i s shown i n Table 6.
TABLE 6 . COMPARATIVE ANAEROBIC LAGOON COVER COSTS
TY P e Basin S ize No. Basins E s t . Cover Cost
F ibe rg la s s Arch 50' x 300' 9 $1,419,000 P r e c a s t Concrete Double Tees 50' x 300' 9 600,000 F loa t ing F ibe rg la s s 130' d i a . 5 730,000 F loa t ing F l e x i b l e Membrane 200' x 300' 2 253,000
The preceeding c o s t s are f o r t h e cover only. The c o s t of concre te , ea r th - work, p ipe , f i t t i n g s and p r o t e c t i v e coa t ings i s n o t included. Obviously, t h e f l e x i b l e membrane would b e t h e cover of choice. A flow s h e e t of t h e combination anaerobic /aerobic system i s shown on Figure 3.
I n o rde r t o minimize t h e cover c o s t , t h e design of t h e anaerobic lagoons w a s given c a r e f u l cons idera t ion . The loadings were set on t h e high s i d e of normal design c r i te r ia - 17.5# BOD/1000 f t 3 . The water depth w a s t o be maintained a t 20 f e e t r a t h e r than t h e more convent ional 15 f e e t . F i n a l l y , t h e s lopes above water level were maintained a t 4:1, whi le t h e d ikes below water level were c u t t o 1:l s lope .
From t h e anaerobic lagoon, t h e waste w a s t o b e t r e a t e d a e r o b i c a l l y i n two a e r a t i o n bas ins ope ra t ing i n t h e completely mixed a c t i v a t e d s ludge mode. Sludge wast ing from t h e two f i n a l c l a r i f i e r s would be t o t h e anaerobic lagoons. Because of t h e h igh anaerobic lagoon BOD removal e f f i c i e n c y (80%), t h e a e r a t o r horsepower requirements would be 400 horsepower r a t h e r than t h e 500 horsepower requi red i n t h e completely ae rob ic system.
The l i n e d s t o r a g e ponds p r i o r t o i r r i g a t i o n would be i d e n t i c a l t o t h a t d i scussed i n t h e completely ae rob ic system.
Cost ComDarison
The es t imated c o s t s f o r t h e two a l t e r n a t i v e systems are shown i n Table 7.
50
LIFT STATION
I SLUDGE I
SLUDGE RECYCLE HANDLING
DIRECT- RECYCLE
I
~
I a . I 1
!N I TO IRR I GATlO 4 :,!:: 1 I l). 4 AERATION H I - 1 CTARACF
I I ' w'.Yw I CL SYSTEM TOWERS
- 1 - I- Y I R R I GATION
u I VI \nu-
.ARIFIERS n D n N n q
I
FIGURE 2. COMPLETELY AEROBIC SYSTEM SCHEMATIC.
W I
51
TABLE 7. CAPITAL COST COMPARISONS--2.88 MGD PLANT
Completely Aerobic Anaerobic/Aerobic System System
F i r s t Stage Aerat ion Anaerobic Lagoons Second Stage Aerat ion Sludge Handling F a c i l i t i e s I r r i g a t i o n S torage Ponds -
30 ac. l i n e d
$1,266,000 -0-
779,000 375 , 000 314 , 000
-0- $ 194,000
688,000 83 , 000
314,000
Sub t o t a l
Anaerobic Lagoon Cover w/Burner
T o t a l Cost
$2,734,000
-0- ~
$2,734 , 000
$1,279,000
369 , 000
$1,648,000
From t h e preceeding t a b l e i t can be seen t h a t t h e covered anaerobic lagoons followed by a mechanical ae rob ic system would r e s u l t i n an es t imated c a p i t a l c o s t sav ings of over $1,000,000 f o r a 2.88 MGD p l a n t .
I n a d d i t i o n , t h e r e would be an apprec i ab le savings i n annual ope ra t ing c o s t as shown i n Table 8.
TABLE 8. ESTIMATED ANNUAL OPERATING COST COMPARISONS
Completely Aerobic AnaerobicIAerob i c System System
Power (2.65~lKWH) $155 , 000 Labor 22,000 Maintenance 19 , 000
To t a l $196,000
$ 82,000 22 , 000
9,000
$113 , 000
Anaerobic Lagoon Cover Construct ion Details
Many a t tempts t o cons t ruc t a s u c c e s s f u l lagoon cover have been made over t h e yea r s and most of them have been no tab le f o r t h e i r l a c k of success . For one t h i n g , earl ier covers lacked t h e a b i l i t y t o wi ths tand U.V. degra- da t ion . Another weakness common t o earlier systems w a s t h e l a c k of an adequate gas removal system. This r e s u l t e d i n l a r g e pockets of gas producing bubbles under t h e f i lm . and 100 f e e t i n diameter.
Lack of permanent bonding of seams w a s a l s o a common f a i l i n g .
One system t h a t w a s inspec ted had gas bubbles 10 f e e t high
52
The system a t Monmouth, I l l i n o i s , t h a t w a s suppl ied by Globe Linings, Long Beach, C a l i f o r n i a , and designed and s p e c i f i e d by Messmair, S tan ley and Assoc ia tes of Rock I s l a n d , I l l i n o i s , appears t o have m e t and so lved these problems. The s i g n i f i c a n t design and cons t ruc t ion d e t a i l s are d iscussed below.
The cover material i s f i v e p l y , 45 m i l composite cons t ruc ted of two nylon r e i n f o r c i n g sc reens bonded t o t h r e e s h e e t s of DuPont Hypalon 45 s y n t h e t i c rubber . The es t imated c o s t of t h e anaerobic lagoon cover i s d e t a i l e d i n Table 9.
G a s removal i s of prime importance. To conduct t h e gases and t o act as a cover suppor t , f o u r inch by twelve inch Styrofoam logs were i n s e r t e d i n a fac tory-sea led envelope i n t h e l i n e r . A ske tch of t h i s concept i s shown i n F igure 4 . The logs were p laced a c r o s s t h e width of t h e lagoon on 20 f o o t c e n t e r s w i th one row down t h e l eng th of t h e lagoons.
4" I*> Styrofoam -
Factory Sealed Envelope
-*- - A *
LFactory Sealed Envelope
-*- - - -Gas Passageway --\-
FIGURE 4. CROSS SECTION OF COVER FTDAT SYSTEM
The gas generated by t h e anaerobic a c t i o n i n t h e lagoon fo l lows t h e space between t h e Styrofoam f l o a t and t h e cover o u t t o t h e edge of t h e lagoon. It w a s f ea red t h a t i n t i m e t h e s o l i d s build-up on t h e lagoon s u r f a c e would tend t o f i l l up t h e s e passageways. To d a t e , t h i s has n o t occurred. Small bubbles 6 t o 1 2 f e e t i n diameter and 6 t o 10 inches high do form, b u t when t h e cover is l i f t e d t o t h i s po in t , t h e gas leaked ou t through t h e passage- ways and t h e cover subsided back t o t h e su r face .
A ske tch of t h e edge cons t ruc t ion d e t a i l s is shown i n F igure 5 . t h e aluminum hold down p l a t e s r e s u l t s i n a p o s i t i v e seal hold ing i n t h e generated gases . The pe r fo ra t ed p i p e shown i n t h e ske tch and a 103 cfm 1 hp blower w a s used t o c o l l e c t t h e gases . t o prevent gas build-up under t h e cover.
The use of
The blower must run cont inuously
Provided wi th t h e system would be an approved gas i n c i n e r a t i o n system f o r d i s p o s a l of t h e gas . A schematic of t h e gas t r a i n i s shown i n F igure 6 .
One o t h e r problem encountered wzs t h e d i s p o s a l of accumulated s torm water. A p o r t a b l e 3 inch t r a s h pump is used t o pump t h e r a i n water o u t of t h e pockets i n t h e c e n t e r of t h e lagoon.
53
r B O L T CAST IN PLACE
CHAMFERED EDGE
6" PUC PIPE W/ 3& HOLES ON i2"CTRS
4'' X 2" ALUMINUM PLATE (16" LONG)
1.6" ,
45 MIL. DUPONT HYPALON COVER f+?s r -
CONCRETE
FIGURE 5.
\---:- -
LAGOON COVER 1NSTALLATION DETAIL.
COVERED COVERED
1 A w R m i c LAGOON I- - ~ ~ - 1 ANAEROBIC LAGOON 1 L------ J L---- J
SEDIMENT & DRIP TRAP
P I - H I ? BLOWER
k C H E C K VALVE
MANOMETER I /-
TO P L A N T 4
BOILER w PRESSURE RELIEF VALVE
& FLAME TRAP
EXPLOSION RELIEF VALVE
+DRIP TRAP
FIGURE 6. GAS RECOVERY SYSTEM SCHEMATIC.
&-.WASTE GAS BURNER
ENERGY CONS ERVATI ON
I n t h e above d i scuss ion , t h e f i n a l d i s p o s a l of t h e gas w a s proposed as in- c i n e r a t i o n . With cu r ren t energy shor tages t h i s v i a b l e sou rce of energy should no t b e wasted. A s tudy w a s then made of i t s p o s s i b l e uses .
TABLE 9. ESTIMATED PROJECT COST GAS RECOVERY AND DISPOSAL
I t e m Estimated Cost
5 Ply , 4 5 m i l DuPont Hypalon Membrane (126,600 sq . f t . ) P.C. Concrete Curb-Wall S t a i n l e s s Steel Anchor Bo l t s and Nuts Aluminum Anchor P l a t e 6" Pe r fo ra t ed P.V.C. Co l l ec t ion P ipe Gas Tra in P ip ing , Valves, Blower, Meter & Appurtenances Concrete Slab and G a s Equipment S h e l t e r
T o t a l
10% Contingency
T o t a l Estimated Construct ion Cost
Engineering, Legal and F i s c a l
T o t a l Estimated P r o j e c t Cost
$253,200
3,900 4,500
10,800 9,700 1,500
12,000
$295,600
29,600
$325,200
43,600
$368,800
TABLE 10. ANAEROBIC LAGOON GAS ANALYSIS
Methane - Vol. % Carbon Dioxide - Vol. % Nitrogen Hydrogen Hydrogen S u l f i d e mg/l Estimated Heating Value BTU/ft G a s Product ion - Ant ic ipa ted Product ion f t /day
3
ft3/#V.S. Destroyed
65 - 70 30 - 35 Trace Trace
16 650
12 - 18 278,000
An expected a n a l y s i s of t h e d i g e s t o r gas i s shown i n Table 10. From t h i s t a b l e i t can be c a l c u l a t e d t h a t an average of 180 m i l l i o n BTU'S pe r day would b e generated by burning t h i s gas. I n a d d i t i o n t o d i r e c t i nc ine ra - t i o n , which would waste t h i s energy, two o t h e r methods by which t h i s energy could b e u t i l i z e d were explored.
56
A Supplement To F o s s i l Fuels Feeding Ex i s t ing Bo i l e r s
I n t h i s a l t e r n a t i v e va r ious f i r i n g schedules were examined such t h a t t h e waste gases would b e s t o r e d and used a t i n t e r v a l s t o f i r e one o r more of t h e p l a n t ' s b o i l e r s . and maintaining s t o r a g e f a c i l i t i e s , i t soon became obvious t h a t , because of t h e hydrogen s u l f i d e conten t of t h e gas , t h i s w a s n o t an accep tab le a l t e r n a t i v e . I f t h e hydrogen s u l f i d e was n o t removed from t h e gas a poten- t i a l f o r cor ros ion of t h e b o i l e r s t a c k ex i s t ed .
I n a d d i t i o n t o t h e expense involved i n cons t ruc t ing
The c a p i t a l c o s t s of t h e equipment needed t o remove t h e hydrogen s u l f i d e were es t imated t o be over $100,000.
Providing a Dedicated Bo i l e r
The next a l t e r n a t i v e w a s t o provide a s e p a r a t e b o i l e r s i z e d t o f i r e a t t h e rate of gas product ion. The b o i l e r manufacturers s t a t e t h a t i f t h e b o i l e r exhaust w a s kept above 375"C, cor ros ion would be no problem. Thus, a conven- t i o n a l carbon steel packaged b o i l e r could be used. The cos t of t h e system w a s es t imated t o t o t a l $40,000. The es t imated annual c o s t s of ope ra t ing t h e system are i n Table 11.
TABLE 11. HEAT RECOVERY ANNUAL COSTS
Labor - 0- U t i l i t i e s 4 , 000 Maintenance and Upkeep 2 , 000 Deprec ia t ion - 1 2 yea r s 3 , 000 T o t a l 9 , 000
No l a b o r f i g u r e s were as ses sed s i n c e i t w a s assumed t h e waste t rea tment ope ra to r could t ake care of t h e gas product ion and c o l l e c t i o n f a c i l i t i e s , and t h e s t a t i o n a r y engineer would handle t h e b o i l e r opera t ion .
The va lue of t h e energy thus u t i l i z e d was assumed t o b e t h e incrementa l c o s t of t h e f o s s i l f u e l n o t consumed as a r e s u l t of us ing t h e gas . These sav ings are c a l c u l a t e d below.
TABLE 1 2 . HEAT RECOVERY SAVINGS
Basis: Coal Cost = $30/ton Coal Heating Value = 9000 BTU/# Cost/lO6 BTU = $1.67/106 BTU
Gas Generat ion = 278,000 f t3 /day Heating Value = 650 BTU/// BTU Recovered @ 85% Eff . = 154 x l o 6 BTU/day
Gross Annual Savings @ 365 days/year = $94,000
57
The gross annual sav ings of $94,000 less t h e annual c o s t of $9000 g ives a n e t sav ings of $85,000 p e r year . This savings i s equ iva len t t o a p r e t a x r e t u r n i n investment of 213 pe rcen t and i t g ives a pay back of less than one year .
I n t h e proposed scheme, a 200 HP f i r e - tube b o i l e r w i t h i t s own exhaust s t a c k would b e provided i n t h e b o i l e r room. combination b o i l e r t o a l low h e f i r i n g of f u e l o i l of gas product ion dropped o f f . l o c a t i o n of t h e p l a n t . )
The b o i l e r would be provided wi th a
(There i s no n a t u r a l gas a v a i l a b l e f o r new i n s t a l l a t i o n i n t h e proposed
The lagoon cover i t s e l f would be used f o r gas s to rage . ra te exceeded t h e b o i l e r capac i ty , t h e gas i n c i n e r a t o r would b e f i r e d a t i n t e r v a l s t o main ta in an accep tab le balance.
I f t h e gas product ion
EMISSION CONTROL
The Enforcement Div is ion of EPA, Region I X , w a s contac ted regard ing t h e emissions from a b o i l e r o r an i n c i n e r a t o r ope ra t ing on anaerobic gas. The fol lowing comments were made:
"In t h e s o l u t i o n of any environmental problem, t h e necessary changes and usage of resources create o t h e r environmental stresses. A common case i s where a p o l l u t a n t i n one medium (water) is placed on another medium ( land) . A similar t rade- o f f occurs i n t h i s proposed s o l u t i o n f o r c o n t r o l of odors from anaerobic lagoons. gas w i l l r e s u l t i n t h e conversion of t h e h igh ly odorous compound, H2S, t o a non-odorous compound S02. However, many d ischarges of SO2 t o t h e atmosphere are l i m i t e d by r e g u l a t i o n s t o prevent a i r po l lu t ion . A t t h e proposed l o c a t i o n of t h e s e f a c i l i t i e s i n southwestern Arizona, t h e r e are regulatflons l i m i t i n g t h e emission of SO2 from e x i s t i n g b o i l e r s which use f o s s i l f u e l s . sou theas t e rn Arizona do n o t c o n s t r a i n SO2 emissions from e x i s t i n g b o i l e r s u s ing gases produced from anaerobic d iges t ion . However, any new o r modified f a c i l i t y would b e s u b j e c t t o p recons t ruc t ion review r e g u l a t i o n s of t h e S t a t e and l o c a l agencies . Such a p r o j e c t could a l s o b e s u b j e c t t o EPA new source review r e g u l a t i o n s depending on i t s s i z e and l o c a t i o n . Since c e r t a i n po r t ions of southwestern Arizona are n o t meeting t h e Nat iona l Ambient A i r Qual i ty Standards f o r S02, any major new source of SO2 l o c a t e d i n such areas would b e s u b j e c t t o s t r ic t emission l i m i t s and o f f s e t requirements descr ibed i n EPA's I n t e r p r e t i v e Ruling of December 21, 1976. Furthermore, t h e S t a t e o r l o c a l agency may impose requirements more restrictive than t h e m i n i m u m r equ i r ed by EPA."
S p e c i f i c a l l y , burning of t h e c o l l e c t e d
The SO2 r e g u l a t i o n s c u r r e n t l y i n e f f e c t f o r
From t h e above s ta tement i t can b e seen t h a t p r i o r t o a n investment dec i s ion , t h e appropr i a t e a u t h o r i t i e s should b e contac ted regard ing t h e emissions from i n c i n e r a t i n g t h e anaerobic gases . I f l o c a l cond i t ions warrant, SO2 removal may b e r equ i r ed .
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The technology f o r scrubbing f l u e gases of SO2 is w e l l e s t a b l i s h e d . h igh ly e f f e c t i v e process would be t h e use of a b i ca rbona te scrubber t o e f f e c t a 90% t o 95% removal of t h e S02. The c a l c u l a t e d SO2 emissions from burning t h e anaerobic gases a t a 16 mg/l H2S concen t r a t ion would amount t o 2.6611 SO2 pe r m i l l i o n BTU's. t h e SO2 emissions w e l l w i t h i n new source l i m i t a t i o n s r equ i r ed f o r f o s s i l f u e l b o i l e r s .
One
A 90 t o 95% SO2 removal e f f i c i e n c y would b r i n g
Discussions wi th s u p p l i e r s of sc rubbers t o remove 2.668 SO2 p e r m i l l i o n BTU's from a 200 H.P. b o i l e r i n d i c a t e d t h a t an i n s t a l l e d c a p i t a l c o s t of $70,000 and an annual ope ra t ing c o s t of $10,000 could be r o u t i n e l y achieved. Land d i s p o s a l of t h e waste l i q u o r from t h e scrubber would be an accep tab le d i s p o s a l technique.
Based on t h e economic i n c e n t i v e t h e anaerobic lagoon p r e s e n t s over a mechanical system t h e i r added c o s t s should no t change t h e management dec i s ion t o adopt anaerobic lagoons over a completely a e r o b i c mechanical system.
CONCLUSIONS
Odor problems from anaerobic lagoons t r e a t i n g m e a t packing wastes are t h e r e s u l t of hydrogen s u l f i d e emissions. The hydrogen s u l f i d e escaping t o t h e atmosphere w i l l be n e a r l y 1% of t h e s u l f a t e concen t r a t ion i n t h e wastewater.
Anaerobic lagoons which treat wastewaters conta in ing 100 mg/l o r more of s u l f a t e need s p e c i a l design and ope ra t ion f o r odor con t ro l . Design of sub- merged i n l e t s and o u t l e t s , ope ra t ion t o main ta in a complete scum cover, chlo- r i n a t i o n of t h e r a w wastewater p r i o r t o p i p e l i n e t r a n s p o r t when H2S is pro- duced, and changing t o a lower s u l f a t e water supply have been found t o reduce odor emissions.
Anaerobic lagoon t rea tment is both c o s t e f f e c t i v e and energy sav ing f o r w a r m concent ra ted wastewaters. t h e wastewater con ta ins h igh s u l f a t e concen t r a t ions , has been c o n t r o l l e d wi th a f l e x i b l e membrane cover and a p o s i t i v e gas removal system. f l o a t i n g f l e x i b l e membrane cover has been shown less expensive than r i g i d cover systems.
The major drawback of odor emission, when
The
The anaerobic lagoon has been shown economically advantageous over ae rob ic t rea tment f o r meat packing wastewater even wi th t h e added c o s t of a f l e x i b l e cover and gas removal system.
Although i n c i n e r a t i o n of odorous d i g e s t o r gas i s t h e common d i s p o s a l method, t h e s e gases can b e used economically i n a dedica ted b o i l e r f o r t h e produc- t i o n of steam f o r process uses and t o conserve our f o s s i l f u e l resources . This energy conserva t ion system has a one yea r payout.
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