Chemistry for Energy - ACS Publications - American Chemical Society

9 Methane Production from Manure H. M. LAPP

Downloaded by UNIV LAVAL on October 20, 2015 | http://pubs.acs.org Publication Date: January 26, 1979 | doi: 10.1021/bk-1979-0090.ch009

Department of Agricultural Engineering, University of Manitoba, Winnipeg, Manitoba, Canada

Recent general public awareness that the reserve supply of conventional liquid and gaseous fossil fuels i s rapidly diminishing has given rise to a serious concern for securing the future energy supply for all sectors of society. This major concern was brought into sharp focus by the oil embargo imposed in 1973 by the Organization of Petroleum Exporting Countries (OPEC). This event has been of such significance that energy considerations are frequently time related as to their occurrence having taken place "Prior to" or in "Post" OPEC years. Programs in Canada to promote energy conservation and to stimulate research into potent i a l l y viable alternate sources for energy fuels have been very active during the past five "Post OPEC" years. The utilization of the anaerobic digestion process for the conversion of organic raw material into a useful energy fuel has emerged as one technology to receive serious attention. This paper will discuss the production of methane from manure. A n a e r o b i c d i g e s t i o n systems have been i n s t a l l e d i n the a g r i c u l t u r a l s e c t o r of v a r i o u s c o u n t r i e s , the m a j o r i t y of which l i e w i t h i n the t r o p i c s . Po (1) r e p o r t e d t h a t 7500 u n i t s w e r e o p e r a t i o n a l i n T a i w a n and i n a r e c e n t p e r s o n a l c o m m u n i c a t i o n he c o n f i r m e d t h a t more t h a n 8000 u n i t s w e r e c u r r e n t l y o p e r a t i o n a l . The t e c h n o l o g y has b e e n p r o m o t e d v i g o r o u s l y i n t h e P e o p l e s R e p u b l i c o f C h i n a s i n c e 1970 and S m i l (2) has r e p o r t e d t h a t t h e number o f s y s t e m s , r a n g i n g i n c a p a c i t y f r o m a few up t o 100 c u b i c m e t r e s has r e a c h e d 4.3 m i l l i o n . The I n s t i t u t e o f A g r i c u l t u r a l E n g i n e e r i n g and U t i l i z a t i o n i n K o r e a (3) r e p o r t e d t h a t 24000 u n i t s w e r e i n s t a l l e d b e t w e e n 1969 and 1973. I n d i a has p r o m o t e d the i n s t a l l a t i o n of b i o g a s p l a n t s f o l l o w i n g the i n i t i a t i o n o f exp e r i m e n t s i n 1939. A d o p t i o n o f t h e t e c h n o l o g y has expanded w i t h t h e e n c o u r a g e m e n t o f t h e K h a d i and V i l l a g e I n d u s t r i e s C o m m i s s i o n . The Gobar Gas R e s e a r c h S t a t i o n was s t a r t e d i n A j i t m a l , Etawah ( U t t a r P r a d e s h ) i n 1961 and a v a r i e t y o f d e s i g n s f o r gas p l a n t s , d e v e l o p e d by S i n g h (4_) , w e r e p u b l i s h e d b y t h i s I n s t i t u t i o n i n 1971. Many o f t h e s e p l a n t s h a v e b e e n b u i l t i n r u r a l I n d i a and i t i s e x p e c t e d t h a t upwards o f 200,000 u n i t s w i l l s o o n be o p e r a t i o n a l . 1

This chapter not subject to U.S. Copyright. Published 1979 American Chemical Society.

In Chemistry for Energy; Tomlinson, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


110

CHEMISTRY

FOR

ENERGY

A l i m i t e d number o f d i g e s t e r s w e r e b u i l t i n E u r o p e a f t e r W o r l d War I I t o u s e manure f o r t h e p r o d u c t i o n o f methane gas f o r f a r m fuel. The use o f t h e s e u n i t s w e r e g e n e r a l l y d i s c o n t i n u e d a b o u t 1960 as low c o s t l i q u i d p e t r o l e u m f u e l a g a i n became a v a i l a b l e . F i n d l a y (j>,6) f o l l o w i n g two s u r v e y s o f 95 Gobar Gas P l a n t s i n s t a l l e d i n N e p a l i n 1975 and 1976 r e p o r t e d t h a t g o b a r gas t e c h n o l o g y was b e i n g w e l l a c c e p t e d i n N e p a l . The N e p a l A g r i c u l t u r a l B a n k , w h i c h p r o v i d e s low i n t e r e s t l o a n s f o r gas p l a n t c o n s t r u c t i o n , have f o r e c a s t t h a t many t h o u s a n d p l a n t s w i l l be b u i l t i n Nepal i n the immediate f u t u r e . I n t e r e s t i n t h e p o t e n t i a l use o f a n a e r o b i c d i g e s t e r s t o p r o d u c e methane f r o m manure i n Canada has increased i n recent years. A p r o g r a m was i n i t i a t e d i n 1971 a t t h e U n i v e r s i t y o f M a n i t o b a t o i n v e s t i g a t e t h e t e c h n i c a l and e c o n o m i c f e a s i b i l i t y o f p r o d u c i n g methane gas f r o m a n i m a l manure e m p l o y i n g t h e a n a e r obic d i g e s t i o n process. T e c h n i c a l and e c o n o m i c f e a s i b i l i t y f o r o n - f a r m o p e r a t i o n o f a n a e r o b i c d i g e s t e r s i n Canada i s c o n s t r a i n ed by t h e o c c u r r e n c e o f c o l d t e m p e r a t u r e s i n w i n t e r . However, modern c o n f i n e m e n t h o u s i n g s y s t e m s f o r l i v e s t o c k e n t e r p r i s e s r e s u l t i n r a p i d and c o n c e n t r a t e d c o l l e c t i o n o f l a r g e q u a n t i t i e s o f manure w h i c h i s f a v o r a b l e t o t h e s u c c e s s f u l o p e r a t i o n o f a n a e r o b i c d i g e s t e r s . A n i m a l manure c o n t a i n s l a r g e q u a n t i t i e s o f o r g a n i c m a t t e r w h i c h w i l l y i e l d s i g n i f i c a n t q u a n t i t i e s o f methane gas when s u b j e c t e d t o b i o c o n v e r s i o n t h r o u g h a n a e r o b i c d i g e s t i o n i n a c o n t r o l l e d e n v i r o n m e n t . The p r o g r a m a t t h e U n i v e r s i t y o f M a n i t o b a has i n v o l v e d l a b o r a t o r y i n v e s t i g a t i o n s s i n c e 1971 and t h e o p e r a t i o n o f a p i l o t p l a n t u s i n g s w i n e manure s i n c e 1973. Two f a r m s c a l e d e m o n s t r a t i o n s y s t e m s a r e u n d e r c o n s t r u c t i o n i n C a n a d a , one i n M a n i t o b a on t h e W. L a n g i l l e Farm a t S t o n e w a l l and one i n O n t a r i o on t h e J o h n F a l l i s f a r m a t P e t e r b o r o u g h . A number o f u n i v e r s i t i e s , r e s e a r c h s t a t i o n s , f a r m s and f e e d l o t s i n the U n i t e d S t a t e s have l a b o r a t o r y programs, p i l o t p l a n t s , f a r m u n i t s and c o m m e r c i a l s y s t e m s i n v a r i o u s s t a g e s o f i n v e s t i g a t i o n , d e v e l o p m e n t and o p e r a t i o n . A s e l e c t e d number o f t h e s e a c t i v i t i e s i n the Midwestern United States are d e s c r i b e d i n a 1978 t r a v e l r e p o r t by Lapp and Buchanan (7). Anaerobic

Digestion

P r o d u c t i o n o f c o m b u s t i b l e gas i s a n a t u r a l l y o c c u r r i n g b i o l o g i c a l process i n v o l v i n g the decomposition of organic matter. I t was d i s c o v e r e d i n t h e 1 7 t h C e n t u r y when s c i e n t i s t s o b s e r v e d t h e s o - c a l l e d "marsh g a s " b u r n i n g on t h e s u r f a c e o f swamps. N a t u r a l gas was o r i g i n a l l y f o r m e d by t h e d e c o m p o s i t i o n o f o r g a n i c m a t e r i a l s f r o m p r e h i s t o r i c p l a n t s and a n i m a l s t h a t had become t r a p p e d i n s e d i m e n t s . The b i o l o g i c a l p r o c e s s has become known as a n a e r o b i c d i g e s t i o n w i t h w h i c h t h e p r o d u c t i o n o f gas i s a s s o ciated. T h i s g a s , c o n s i s t i n g p r i m a r i l y o f methane (CH4) and c a r b o n d i o x i d e (CO2) i s commonly r e f e r r e d as " b i o g a s " and i t d i f f e r s o n l y f r o m "marsh g a s " and " n a t u r a l g a s " i n i t s d e g r e e o f



9.

Methane Production from Manure

L A P P

111

p u r i t y w i t h r e s p e c t t o i t s methane c o n t e n t . The p r o d u c t i o n o f b i o g a s , o f t e n r e f e r r e d t o d i r e c t l y a s m e t h a n e , f r o m a n i m a l manure r e q u i r e s an u n d e r s t a n d i n g o f a n a e r o b i c d i g e s t i o n a s w e l l a s t h e a s s o c i a t e d manure and b i o g a s h a n d l i n g r e q u i r e m e n t s . A n a e r o b i c d i g e s t i o n means t h e b i o l o g i c a l b r e a k d o w n o f o r g a n i c m a t t e r i n the absence o f oxygen. I t i s a two-stage p r o c e s s i n w h i c h e a c h s t a g e i s p e r f o r m e d by a d i s t i n c t g r o u p o f b a c t e r i a . D u r i n g t h e f i r s t s t a g e a complex m i x t u r e o f f a t s , c a r b o h y d r a t e s and p r o t e i n s i n manure a r e d e g r a d e d and c o n v e r t e d t o s i m p l e o r g a n i c a c i d s s u c h a s a c e t i c and p r o p i o n i c . The " a c i d - f o r m i n g " b a c t e r i a r e p r o d u c e r a p i d l y and a r e n o t s e n s i t i v e t o changes i n t h e i r environment. The s e c o n d s t a g e o f t h e p r o c e s s i n v o l v e s t h e c o n v e r s i o n o f t h e o r g a n i c f a t t y a c i d s i n t o methane and c a r b o n dioxide. The " m e t h a n e - f o r m i n g " b a c t e r i a a r e r e l a t i v e l y few i n number, do n o t r e p r o d u c e r a p i d l y and a r e e x t r e m e l y s e n s i t i v e t o t h e i r e n v i r o n m e n t and p a r t i c u l a r l y t o t h e p r e s e n c e o f o x y g e n . T h i s two s t a g e p r o c e s s i s r e p r e s e n t e d c h e m i c a l l y b y (C

6

H12

0 ) 6

n

+ 3n CH3

C 0 0 H

CH3

C 0 0 H

-*· CH4

+

C0

C0

2

+ 4H

+ CH

+

2H 0

C0

2

+ H0

(C

2

-> H

2

6

H

1 2

0 ) 6

n

2

4

2

2

CO3

+ 3n H 0 2

·+·

3n CH4

+ 3n H

2

CO3

The a c i d - f o r m i n g and m e t h a n e - f o r m i n g b a c t e r i a w o r k s i m u l t a n e o u s l y i n t h e a n a e r o b i c d i g e s t i o n p r o c e s s . Oxygen i s e x c l u d ed f r o m t h e d i g e s t e r and v a r i o u s o t h e r e n v i r o n m e n t a l c o n d i t i o n s a r e c o n t r o l l e d so t h a t t h e m e t h a n e - f o r m e r s a r e m a i n t a i n e d i n b a l a n c e w i t h the a c i d - f o r m e r s . Otherwise, the methane-formers w o u l d be i n h i b i t e d and i n some c a s e s w o u l d c e a s e t o f u n c t i o n e n tirely. Technical F e a s i b i l i t y of Anaerobic D i g e s t i o n f o r Methane P r o d u c t i o n T h r e e m a j o r s y s t e m components w h i c h n e e d t o be e x a m i n e d when a s s e s s i n g t h e t e c h n i c a l f e a s i b i l i t y o f u s i n g a n a e r o b i c d i g e s t i o n t o p r o d u c e methane gas f r o m a n i m a l manure i n c l u d e i ) manure h a n d l i n g i i ) b i o l o g i c a l p r o c e s s s t a b i l i t y and i i i ) biogas handling. Manure H a n d l i n g . The p h y s i c a l c h a r a c t e r i s t i c s o f manure a r e s u c h t h a t manure h a n d l i n g s y s t e m s a r e d i f f i c u l t t o e n g i n e e r w i t h any d e g r e e o f p r e c i s i o n . Proven manure-handling systems w i l l n e e d t o be i n t e g r a t e d w i t h a n a e r o b i c d i g e s t i o n s y s t e m s i f t h e y a r e t o be a c c e p t e d b y a l i v e s t o c k e n t e r p r i s e o p e r a t o r .



112

CHEMISTRY

FOR

ENERGY

E n e r g y r e c o v e r y schemes w h i c h a r e n o t r e l i a b l e o r l a b o r - e f f i c i e n t i n a l l a s p e c t s o f manure h a n d l i n g w i l l be abandoned q u i c k l y be a l i v e s t o c k p r o d u c e r . Manure i s e x c r e t e d f r o m a n i m a l s a t n e a r optimum t e m p e r a t u r e f o r a n a e r o b i c d i g e s t i o n and optimum b i o g a s p r o d u c t i o n . L o c a t i o n of a d i g e s t e r i n s i d e the c o n f i n e s of a l i v e s t o c k b u i l d i n g t o r e c e i v e e x c r e m e n t w i t h o u t h e a t l o s s w o u l d be d e s i r e d . Unfortuna t e l y t h e e x p l o s i v e c h a r a c t e r i s t i c s of b i o g a s has p r e v e n t e d such a d e v e l o p m e n t f r o m t a k i n g p l a c e . C o n s e q u e n t l y , f r e s h manure e i t h e r p o s i t i v e l y pumped, m e c h a n i c a l l y s c r a p e d o r h y d r a u l i c a l l y f l u s h e d f r o m a c o n f i n e m e n t b u i l d i n g t o an a d j a c e n t d i g e s t e r a p p e a r s n e c e s s a r y f o r a t t a i n i n g t e c h n i c a l f e a s i b i l i t y f r o m a manure handling standpoint. H a n d l i n g does n o t end w i t h e n t r y i n t o t h e d i g e s t e r s i n c e c o n t e n t s must be m i x e d , scum f o r m a t i o n p r e v e n t e d and e f f l u e n t removed t o d i s p o s a l o r s t o r a g e . W e l s h e t a l (8) r e p o r t e d t h a t a n a e r o b i c d i g e s t i o n r e n d e r s t h e e f f l u e n t l e s s o f f e n s i v e and more pumpable w i t h f e w e r s e t t l i n g p r o b l e m s . B i o l o g i c a l Process S t a b i l i t y . The a n a e r o b i c d i g e s t i o n p r o cess i n v o l v e s a complexity of i n t e r r e l a t e d biochemical r e a c t i o n s , many o f w h i c h a r e n o t c l e a r l y u n d e r s t o o d . Anaerobic d i g e s t i o n t h e r e f o r e , has a poor r e p u t a t i o n from a p r o c e s s - s t a b i l i t y v i e w point. M u n i c i p a l d i g e s t e r s a r e f r e q u e n t l y a t t e n d e d by s k i l l e d operators with elaborate monitoring f a c i l i t i e s at their disposal. The a d o p t i o n o f o n - f a r m a n a e r o b i c d i g e s t i o n s y s t e m s f o r methane p r o d u c t i o n a r e u n l i k e l y t o o c c u r u n d e r s u c h r e q u i r e m e n t s for successful operation. Environmental factors e f f e c t i n g p r o c e s s - i n s t a b i l i t y i n c l u d e sudden changes i n t e m p e r a t u r e , l o a d i n g r a t e s , t h e n a t u r e o f t h e o r g a n i c m a t e r i a l and t h e p r e s e n c e o f t o x i c e l e m e n t s . A further complexity to the s t a b i l i t y of anaerobic d i g e s t e r s h a n d l i n g a n i m a l manure i s due t o t h e f a c t t h a t t h e s e d i g e s t e r s o p e r a t e o u t s i d e the range of c h e m i c a l parameters c o n s i d e r e d "normal" f o r municipal-sludge digestion. P a r a m e t e r s commonly u s e d t o m o n i t o r p r o c e s s s t a b i l i t y i n c l u d e pH, a l k a l i n i t y and t h e c o n c e n t r a t i o n of v o l a t i l e a c i d s . M u n i c i p a l sewage t r e a t m e n t d i g e s t e r s t y p i c a l l y o p e r a t e a t v o l a t i l e a c i d s c o n c e n t r a t i o n s l o w e r t h a n 1000 mg L"* a s a c e t i c a c i d w i t h an a l k a l i n i t y r a n g e o f 1000 t o 5000 mg L ~ l a s Ca CO3 and a pH r a n g e o f 6.6 t o 7.6. E x c e s s i v e concent r a t i o n s o f v o l a t i l e a c i d s and ammonia n i t r o g e n h a v e b e e n c o n s i d e r e d t o x i c t o methane f o r m e r s . A range o f c h e m i c a l parameters which have been r e c o r d e d d u r i n g s t e a d y - s t a t e d i g e s t i o n o f s w i n e manure d u r i n g p i l o t p l a n t s t u d i e s a t t h e U n i v e r s i t y o f M a n i t o b a a r e r e c o r d e d i n T a b l e 1. I t i s s i g n i f i c a n t t o n o t e t h a t p r o c e s s s t a b i l i t y was m a i n t a i n e d even though the c h e m i c a l parameters r e c o r d e d were w e l l o u t s i d e the normal range f o r m u n i c i p a l d i g e s t e r s . T h i s o c c u r r e n c e demo n s t r a t e s t h e u n i q u e n a t u r e o f a n i m a l - m a n u r e d i g e s t i o n a s comp a r e d t o m u n i c i p a l sewage.


9.

L A P P

Methane

Production

Table I .

Digester

from

113

Operating C h a r a c t e r i s t i c s

D

Chemical Parameter


Manure

Total volatile acids (Mg/1 a s HAc)

850- •4680

Alkalinity (mg/1 a s CaC03>

7480-•16600

pH

7.80-•8.30

T o t a l ammonia (mg/1 a s N)

2260-•3580

l

g

e

S

t

e

r

1050- •4350

1050- •5400

1050- •4750

8000-•16850

8630-•17230

8250-•16330

8.0-•8.20

7.70-•8.30

7.70-•8.30

2240-•3530

2330-•3570

2430-•3620

Lapp e t a l ( 9 ) and K r o e k e r e t a l ( 1 0 ) d u r i n g p i l o t p l a n t and l a b o r a t o r y s t u d i e s a t t h e U n i v e r s i t y o f M a n i t o b a h a v e demons t r a t e d t h a t extreme p r o c e s s s t a b i l i t y i s p o s s i b l e i n a d i g e s t e r u s i n g s w i n e manure. D i g e s t e r - i n s t a b i l i t y r e p o r t e d f o r s w i n e and p o u l t r y manure b y A n t h o n i s e n and C a s s e l l ( 1 1 ) ; H a r t ( 1 2 ) ; Gramms e t a l (13) and Schmid and L i p p e r ( 1 4 ) need n o t o c c u r i f p r o p e r a t t e n t i o n i s given t o a c c l i m a t i n g t h e methane-forming b a c t e r i a t o t h e manure s l u r r y s u b s t r a t e . T h i s s t a b i l i t y i s due t o t h e r e l a t i v e l y h i g h c o n c e n t r a t i o n s o f ammonia n i t r o g e n i n s o l u t i o n and i s p o s s i b l e o n l y a f t e r a c c l i m a t i o n o f m e t h a n o g e n i c b a c t e r i a to the high n i t r o g e n content of the s l u r r y . S t a b l e d i g e s t e r ope r a t i o n was m a i n t a i n e d t h r o u g h o u t t h e e x p e r i m e n t s i n s p i t e o f l a r g e t e m p e r a t u r e f l u c t u a t i o n s a t h i g h and l o w o r g a n i c l o a d i n g r a t e s , and w i t h l a r g e d a i l y v a r i a t i o n s i n o r g a n i c l o a d i n g r a t e s . A l l o f t h e s e c o n d i t i o n s would be t y p i c a l o f a f u l l - s c a l e i n s t a l l a t i o n on a f a r m . 1. S e e d i n g . T h i s i s a component o f t h e s t a r t - u p p r a c t i c e a n d consists of the a d d i t i o n of a c t i v e l y d i g e s t i n g m a t e r i a l t o a newly operating d i g e s t e r . The a d d i t i o n e n s u r e s t h a t a c u l t u r e of methane-producing b a c t e r i a i s present f o r s t a r t - u p . 2. N u t r i e n t B a l a n c e . A l l b i o l o g i c a l s y s t e m s r e q u i r e a n a d e q u a t e s u p p l y o f n u t r i e n t s , p a r t i c u l a r l y n i t r o g e n , p h o s p h o r o u s , and p o tassium. A n i m a l manure n o r m a l l y c o n t a i n s a n a d e q u a t e , w e l l - b a l anced n u t r i e n t supply t o support t h e e x i s t e n c e o f a t h r i v i n g b i o l o g i c a l system. F o r good a n a e r o b i c d i g e s t i o n t h e c a r b o n t o n i t r o g e n r a t i o s h o u l d r a n g e b e t w e e n 15 t o 1 and 30 t o 1. 3. V o l a t i l e S o l i d s . V o l a t i l e s o l i d s r e p r e s e n t s t h e o r g a n i c component o f t h e t o t a l s o l i d s p r e s e n t and a p p r o x i m a t e l y 85 p e r cent o f the t o t a l s o l i d s are v o l a t i l e . A b i o l o g i c a l system a l ways c o n v e r t s a p o r t i o n o f i t s s u b s t r a t e i n t o new c e l l mass and g e n e r a l l y l e s s t h a n 50 p e r c e n t o f t h e v o l a t i l e s o l i d s a r e



114

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FOR

E N E R G Y

destroyed i n p r a c t i c e . 4. Start-up. M e t h a n e - f o r m i n g b a c t e r i a a r e p r e s e n t i n most manure h a n d l i n g s y s t e m s b u t i t t a k e s them a l o n g t i m e t o m u l t i p l y i n t o an e f f i c i e n t m e t h a n e - p r o d u c i n g p o p u l a t i o n . The t i m e t o e s t a b l i s h a s a t i s f a c t o r y p o p u l a t i o n o f b a c t e r i a c a n be r e d u c e d b y a d d i n g an a c t i v e l y d i g e s t i n g m a t e r i a l ( s e e d ) f r o m a n o t h e r d i gester. A t l e a s t 1 5 % o f t h e v o l u m e o f t h e d i g e s t e r s h o u l d be f i l l e d w i t h seed a t s t a r t - u p . The s e e d s h o u l d b e added t o t h e d i g e s t e r w h i c h h a s a l r e a d y had t h e r e m a i n i n g v o l u m e f i l l e d w i t h w a t e r warmed t o t h e i n t e n d e d o p e r a t i n g t e m p e r a t u r e . F r e s h manure c a n t h e n be added b u t s l o w l y a t f i r s t ( a p p r o x i m a t e l y 10% o f the p l a n n e d d a i l y l o a d ) t o a l l o w t h e b a c t e r i a t i m e t o a c c l i m a t e t o t h e new e n v i r o n m e n t o f t h e f r e s h manure. A f t e r gas p r o d u c t i o n h a s r e a c h e d a b o u t 50% o f t h a t e x p e c t e d f o r t h e l o w l o a d i n g r a t e , the l o a d i n g r a t e s h o u l d be i n c r e a s e d g r a d u a l l y o v e r a t h r e e week period before reaching the desired loading r a t e . This procedure s h o u l d i n s u r e good gas p r o d u c t i o n i n a b o u t f o u r weeks f r o m s t a r t up. 5. L o a d i n g R a t e . L o a d i n g r a t e i s e x p r e s s e d i n t e r m s o f t h e mass of v o l a t i l e s o l i d s added p e r u n i t o f d i g e s t e r v o l u m e . Accepted l o a d i n g r a t e s r a n g e f r o m 0.7 t o 5.0 k g p e r c u b i c m e t r e p e r day (0.6 t o 0.31 l b / f t 3 / d a y ) . 6. R e t e n t i o n Time. The s o l i d s r e t e n t i o n t i m e r e p r e s e n t s t h e a v e r a g e t i m e t h a t m i c r o o r g a n i s m s r e m a i n i n t h e s y s t e m and i t c a n be d e t e r m i n e d b y d i v i d i n g t h e mass o f v o l a t i l e s o l i d s i n t h e d i g e s t e r b y t h e mass l e a v i n g t h e s y s t e m p e r day. The r e t e n t i o n t i m e must be g r e a t enough t o a l l o w t i m e f o r t h e m e t h a n e - f o r m e r s t o c o n v e r t t h e a c i d s t o b i o g a s . N o r m a l l y 15 t o 30 d a y s a r e a d e q u a t e f o r manure d i g e s t i o n . 7. Temperature. Two t e m p e r a t u r e r a n g e s e x i s t f o r good b i o g a s p r o d u c t i o n , m e s o p h i l i c and t h e r m o p h i l i c . Most d i g e s t e r s a r e ope r a t e d w i t h i n t h e m e s o p h i l i c r a n g e o f 20° t o 45°C (69° t o 113°F). The t h e r m o p h i l i c r a n g e i s 45 t o 55°C (113 t o 131°F). 8. A l k a l i n i t y and pH. P i l o t - p l a n t digesters at the U n i v e r s i t y of M a n i t o b a h a v e o p e r a t e d s u c c e s s f u l l y a t pH l e v e l s up t o 8.5 and a t a l k a l i n i t i e s r a n g i n g up t o 14000 mg/L. These l e v e l s a r e w e l l above t h o s e n o r m a l l y found i n m u n i c i p a l d i g e s t e r s i n w h i c h pH r a n g e s o f 7.2 t o 7.6 and a l k a l i n i t i e s o f 1000 t o 5000 mg/L normally occur. 9. Mixing. M i x i n g c a n be a c c o m p l i s h e d b y m e c h a n i c a l r e c i r c u l a t i o n , a g i t a t i o n o r b y c o n t r o l l e d gas f l o w methods. The p r a c t i c e i s d e s i r e d t o f a c i l i t a t e on i n t i m a t e c o n t a c t b e t w e e n methane f o r m i n g b a c t e r i a and t h e i r s u b s t r a t e and t o p r e v e n t t h e f o r m a t i o n o f s u r f a c e scum i n t h e d i g e s t e r . 10. Total Solids. The optimum t o t a l s o l i d s p r e s e n t i n a n a n a e r o b i c d i g e s t e r s h o u l d n o r m a l l y range from 7 t o 9 p e r c e n t . Animal manure c o n t a i n s f r o m 10 t o 25 p e r c e n t d r y s o l i d s and may r e q u i r e d i l u t i o n p r i o r t o l o a d i n g i n t o an a n a e r o b i c d i g e s t e r . Biogas Handling.

Quantitative biogas production potential


Methane

L A P P

Production

from

115

Manure


9.

Figure

1.

Pilot plant for biogas production at the Faculty of Agriculture's lea Research Station, University of Manitoba, Winnipeg, Canada


Glen-


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CHEMISTRY FOR ENERGY

Figure 2. A 16,000 poultry layer operation in a converted dairy barn with an anaerobic-digestion biogas plant in the attached shed in the foreground (W. Gibbons' farm at Ripon, Wisconsin)

Figure 3. Biogas-fired boiler installed at the Calorific Recovery Anaerobic Process Plant, Guymon, Oklahoma and operated by Thermonetics Incorporated, Oklahoma City. Manure is processed from feed lots housing 100,000 head of beef cattle.


9.

Methane

L A P P

Production

from

117

Manure

f r o m manure i s r e l a t e d t o t h e b i o d e g r a d a b l e o r g a n i c m a t t e r ( v o l a t i l e s o l i d s ) p r e s e n t i n t h e manure. V o l a t i l e s o l i d s (VS) a r e e x p r e s s e d i n u n i t s o f k g o f v o l a t i l e s o l i d s p e r day p e r 1000 k g o f l i v e w e i g h t . However t h e v o l a t i l e s o l i d s f r o m one s p e c i e s , s a y p o u l t r y , i s o f t e n more b i o d e g r a d a b l e t h a n f r o m a n o t h e r s p e c i e s , say beef c a t t l e . B i o d e g r a d a b i l i t y o f manure i s a l s o a f f e c t e d by t h e l e n g t h and t y p e o f s t o r a g e w h i c h o c c u r s p r i o r t o digestion. T y p i c a l v a l u e s used to estimate p o t e n t i a l biogas p r o d u c t i o n f r o m l i v e s t o c k manure a r e c o n t a i n e d i n T a b l e I I .


Table I I .

T y p i c a l Values f o r Estimating P o t e n t i a l Biogas P r o d u c t i o n From V a r i o u s T y p e s o f L i v e s t o c k GrowingFinishing Swine

Dairy Cows

Laying Hens

Beef Feeders

U n d i l u t e d Fresh Feces p l u s U r i n e L d a y " l 1000 k g " l Liveweight

65

82

53

60

V o l a t i l e Solids Production R a t e k g VS day" 1000 k g " liveweight

4.8

8.6

9.5

5.9

F r a c t i o n of V o l a t i l e S o l i d s Converted to Biogas

0.50

0.35

0.60

0.45

3.28

6.21

2.66

1.1

1.3

1.3

1

1

Biogas Production m day-1 1000 kg-1 3

m

3

d y a

1 -3 m

0

liveweight

f digester

2.62 1.1

Methane i s f l a m m a b l e and when m i x e d w i t h a i r i n p r o p o r t i o n s r a n g i n g f r o m 5 t o 15 p e r c e n t by v o l u m e , i s e x p l o s i v e . Safety r e g u l a t i o n s c o v e r i n g b u i l d i n g s , e l e c t r i c a l and m e c h a n i c a l e q u i p ment i n s t a l l a t i o n s s h o u l d be s t r i c t l y a d h e r e d t o d u r i n g t h e p l a n n i n g , c o n s t r u c t i o n and o p e r a t i o n o f an a n a e r o b i c d i g e s t i o n s y s tem. B i o g a s i s n o r m a l l y composed o f 60 t o 70 p e r c e n t methane and f r o m 30 t o 40 p e r c e n t c a r b o n d i o x i d e w i t h s m a l l amounts o f h y d r o gen s u l f i d e and o t h e r i m p u r i t i e s . B e c a u s e i t s m a j o r c o n s t i t u e n t i s methane i t s p r o p e r t i e s c l o s e l y a p p r o x i m a t e t h o s e o f p u r e m e t h ane. The c r i t i c a l p r e s s u r e o f methane i s 4710 k P a a t -82.3°C. I t i s r e f e r r e d t o a s a permanent gas s i n c e i t c a n n o t be l i q u i f i e d by p r e s s u r e a t o r d i n a r y t e m p e r a t u r e s . This property gives r i s e t o a s t o r a g e p r o b l e m a s s o c i a t e d w i t h p r o d u c t i o n and u t i l i z a t i o n o f b i o g a s i n r e g i o n s l i k e Canada w i t h e x t r e m e c l i m a t e s . I n s u c h l o c a t i o n s t h e summer s e a s o n i s most f a v o r a b l e t o b i o g a s p r o d u c t i o n w h i l e a major need f o r space h e a t i n g o c c u r s i n w i n t e r . Biogas s t o r a g e f r o m summer t o w i n t e r s e a s o n s i s n o t p r a c t i c a l . An i d e a l farm system w o u l d i n v o l v e a p r o d u c t i o n c a p a c i t y matched t o


118

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F O R

E N E R G Y

an e n e r g y u t i l i z a t i o n r e q u i r e m e n t . Should t h e u t i l i z a t i o n r e quirement i n v o l v e t h e o p e r a t i o n o f i n t e r n a l combustion engines, w h i c h i s t e c h n i c a l l y f e a s i b l e , a d d i t i o n a l gas c l e a n i n g t e c h n o l ogy t o remove h y d r o g e n s u l f i d e i s r e q u i r e d and i f e f f i c i e n c y i s t o b e i n c r e a s e d t h e n c a r b o n d i o x i d e s h o u l d a l s o b e removed.


Summary The p r o d u c t i o n o f methane f r o m a n i m a l manure i s t e c h n i c a l l y f e a s i b l e u n d e r t h e management o f a l i v e s t o c k e n t e r p r i s e o p e r a t o r . Many s m a l l f a r m e r s a r e s u c c e s s f u l l y o p e r a t i n g s m a l l s c a l e d i g e s ters i n tropical countries. The d e c i s i o n t o b u i l d a n a n a e r o b i c d i g e s t e r o n a C a n a d i a n l i v e s t o c k f a r m s h o u l d b e b a s e d on a d v a n t a g e s t o b e d e r i v e d f r o m t h e d i g e s t e r a s a component o f t h e t o t a l manure h a n d l i n g s y s t e m . Economic j u s t i f i c a t i o n c a n o n l y be s u p p o r t e d a t p r e s e n t i f c r e d i t s a r e g i v e n t o m a t e r i a l s h a n d l i n g , e n v i r o n m e n t a l improvement, f e r t i l i z e r n u t r i e n t r e t e n t i o n , p o l l u t i o n r e d u c t i o n and b i o g a s (methane) p r o d u c t i o n . Economic f e a s i b i l i t y f o r l a r g e s c a l e conf i n e m e n t h o u s i n g s y s t e m s t o employ a n a e r o b i c d i g e s t i o n f o r b i o gas p r o d u c t i o n i s n e a r a t h a n d i n t h e c o l d c l i m a t e a r e a s o f North America. This v i a b i l i t y i s being accelerated as p r i c e s f o r c o n v e n t i o n a l l i q u i d p e t r o l e u m f u e l s c o n t i n u e t o e s c a l a t e and as u r b a n e n v i r o n m e n t a l c o n c e r n s c o n t i n u e t o grow.

LITERATURE CITED 1.

Po, C. Proc. the Biomass duction and Pp. XVI - 1

of Int. Biomass Energy Conf. (1973). Pub. by Energy Institute Inc., Winnipeg, Canada. ProUse of Methane From Animal Wastes in Taiwan. to XVI - 8.

2.

Smil, V. Environment China. Pp. 27:31.

3.

Institute of Agricultural Engineering and Utilization (1973). Present Status of Methane Gas Utilization as a Rural Fuel in Korea.

4.

Singh, R. B. Gobar Gas Research Station, Ajitmal, Etawah (U.P.), India (1971). Biogas Plant, Generating Methane from Organic Wastes.

5.

Findlay, J . H. Development and Consulting Services, Butwal, Nepal (1976). Report on First Inspection Visit to 95 Gobar Gas Plants Constructed in Nepal.

6.

Findlay, J . H. Development and Consulting Services, Butwal, Nepal (1977). Report on Second Inspection Visit to 95 Gobar Gas Plants Constructed in Nepal.

(1977).

19

(7).

Energy Solution in



9.

LAPP

Methane Production from Manure

119

7.

Lapp, H. M. and L. C. Buchanan. Agriculture Canada, Ottawa (1978). A Travel Report on a Study of Methane Production From Animal Manure in the Midwestern United States. 44 p.

8.

Welsh, F. W., D. D. Schulte, E. J . Kroeker and H. M. Lapp. Can. Agric. Eng. (1977). 19 (2). The Effect of Anaerobic Digestion Upon Swine Manure Odours. Pp. 122 126.

9.

Lapp, H. M., D. D. Schulte, E. J . Kroeker, A. B. Sparling and Β. H. Topnik. "Managing Livestock Wastes". Amer. Soc. Agric. Engrs. St. Joseph, Mich. (1975). Start-up of Pilot Scale Swine Manure Digesters for Methane Production. Pp. 234 - 238, 243.

10. Kroeker, E. J., H. M. Lapp, D. D. Schulte, J . D. Haliburton and A. B. Sparling. Can. Soc. Agric. Eng., Annual Meet ing, Halifax. 1976. Unpublished Paper No. 76-208, Methane Production From Animal Wastes II - Process Stability. 11.

Anthonisen, A. and E. A. Cassell. New York State Department of Health, Albany, N.Y. (1966). Studies on Chicken Manure Disposal. II Anaerobic Digestion, Research Report No. 12. Pp. 65 - 112.

12. Hart, S. A. Jour. Water Poll. Control Fed. (1963). 35. Digestion Tests of Livestock Wastes. Pp. 748 - 757. 13.

Gramms, L. C., L. B. Polkowski and S. A. Witzel. Trans. Amer. Soc. Agric. Engrs. (1971). 14. Anaerobic Digestion of Farm Waste (dairy b u l l , swine and poultry). Pp. 7 - 11, 13.

14.

Schmid, L. A. and R. I. Lipper. Proc. Conf. on Agric. Waste Management, Cornell Univ., Ithaca, N.Y. (1969). Swine Wastes, Characterization and Anaerobic Digestion. Pp. 5057.

RECEIVED September 25, 1978.


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