1-s2.0-096085249290117G-main

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Bioresource Technology 40 (1992) 43-48

: ' ~ ' ~ ~ i

na ero b ic D ig es t io n o f Fru it a nd Veg eta b le

Pro cess ing W a stes fo r B io g a s P ro duct io n

P r e m a V i s w a n a t h , S . S u m i t h r a D e v i K r i s h n a N a n d *

Central Food Technological Resea rch Insti tute, Myso re-570 013, Ind ia

(Received 1 Octob er 1990; revised version received 15 February 1991; accepted 22 Februa ry 1991 )

b s t r a c t

T he e f fec t o f f eed in g d i f f e ren t f r u i t a nd vege tab le

w as te s , ma ngo , p ineapp le , t oma to , jack f r u i t,

banana an d o r ange , w as s tud ied in a 60 - l i te r

d iges te r by cyc l ing each w as te ever y f i f t h d ay in

or der to oper a te the d iges te r a s and w hen ther e w as

s upp ly o f eed . T he char ac te r is t ic s o f the anaer ob ic -

a l ly d i g e st e d f l u i d a n d d i g es t er p e r f o r m a n c e i n

t e r m s o f b io g a s p r o d u c t i o n w e r e d e t e r m i n e d a t d if -

f e r en t load ing r a te s (L R) and a t d i f f e r en t hydr au l i c

r e t e n t i o n t i m e s ( H R T ) , a n d t h e m a x i m u m b i o g a s

y i e l d o f 0 6 r r d /k g V S a d d e d w a s a c h ie v e d a t a 2 0 -

d a y H R T a n d 4 0 k g T S m - 3 d a y - 1 l o a d in g r a te . T h e

hour ly gas p r od uc t io n w as obs er ve d in the d iges te r s

o p e ra t ed a t 1 6 a n d 2 4 d a y s H R T . T h e m a j o r y i e ld

(7 4 5 % ) o f g as w a s p r o d u c e d w i t h i n 1 2 h o f f e e d i n g

a t a 1 6 -d a y H R T w h e r e as a t a 24 - d a y H R T o n l y

59~ 93% o f the to ta l gas cou ld be ob ta ined a t th i s

t ime.

K e y w o r d s: A n a e r o b i c d i g e s t io n , w a s t e u t i li z a t io n ,

f ru i t and vege tab le was tes , b iogas .

I N T R O D U C T I O N

O v e r 6 0 x 1 6 t o f f ru i t s and vege tab les a re p ro-

d u c e d a n n u a l l y i n I n d i a , o f w h i c h o n l y 1 i s p r o -

c e s s e d i n t h e f r u i t a n d v e g e t a b l e p r o c e s s i n g

i n d u s t r i e s ( K r i s h n a N a n d & M a n j r e k a r , 1 9 8 8 ) .

T h e s o li d w a s t e s n o r m a l l y a c c o u n t f o r 4 0 - 5 0 o f

t h e r a w m a t e r i a l p r o c e s s e d a n d h a s a t o t a l s o l i d

c o n c e n t r a t io n o f 1 0 - 1 5 . D i s p o s a l o f t h e s e q u a n -

t i f i es o f wet , pu t r esc ib le o rgan ic r e fuse p resen t s

f o r m i d a b l e e n v i r o n m e n t a l a n d e c o n o m i c

p r o b l e m s . S i n c e a s u b s t a n t i a l q u a n t i t y o f e n e r g y i s

u s e d f o r v a r i o u s p r o c e s s i n g s t e p s, i t b e c o m e s p e r -

*To whom correspond ence should be addressed.

43

t i n e n t t o c o n v e r t t h e s e w a s t e s i n t o b i o g a s , w h i c h

c o u l d s u p p l y m u c h o f t h e e n e r g y n e e d e d f o r i n -

p l a n t o p e r a t i o n s .

T h e r e h a v e b e e n a n u m b e r o f r e p o r t s o n t h e

u t i l iz a t i o n o f fr u i t a n d v e g e t a b l e p r o c e s s i n g w a s t e s

( K n o l e ta l . , 1 9 7 8 ; L a n e , 1 9 8 4 ; S u m i t h r a D e v i a n d

K r i s h n a N a n d , 1 9 8 9 ; D N E S R e p o r t , 1 9 9 0 ) i n d i-

v i d u a l l y a s a f e e d s t o c k f o r b i o g a s p r o d u c t i o n .

H o w e v e r , t h e r e a r e n o r e p o r t s o n t h e s i m u l -

t a n e o u s u s e o f v a r i o u s f r u it w a s t e s a s f e e d s t o c k i n

a s ing le d iges te r . Mos t f ru i t s and vege tab les a re

p r o c e s s e d o n a s e a s o n a l b a s is , o n l y f o r a p e r i o d o f

2 - 3 m o n t h s , a n d t h e w a s t e s t h a t e m a n a t e d u r i n g

t h e s e p r o c e s s e s v a r y c o n s i d e r a b l y i n t h e i r

p h y s i c o - c h e m i c a l c h a r a c t e r i s t i c s . S o m e o f t h e m

a r e r i c h i n t o x i c c o n s t i t u e n t s s u c h a s l i m o n i n i n

c i t r u s w a s t e s a n d m o s t o f t h e m a r e d e f i c i e n t i n

n i t ro g e n ( s u ch a s m a n g o a n d p i n e a p p l e p r o c e s si n g

w a s te s ). S i n c e t h e o v e r a l l p o t e n t i a l f o r e n e r g y p r o -

d u c t 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 f r o m t h e s e

w a s t e s i s l a r g e , i t b e c o m e s n e c e s s a r y t o o p e r a t e

t h e d i g e s t e r s t h r o u g h o u t t h e y e a r w i t h a n y o f t h e

w a s t e s a v a il a b le . I n t h i s p a p e r o b s e r v a t i o n s m a d e

o n t h e u s e o f v a r io u s f r u i t w a s t e s i n s u c c e s s i o n o r

m i x e d a s f e e d s t o c k f o r b i o g a s p r o d u c t i o n a r e p r e -

sen ted .

M E T H O S

Substrates

T h e m a n g o , o r a n g e , p i n e a p p l e a n d t o m a t o p r o -

c e s s i n g w a s t e s w e r e c o l l e c t e d f r o m f r u i t p r o c e s s -

i n g f a c t o r i e s ( K i s s a n P r o d u c t s L t d , B a n g a l o r e ,

K a r n a t a k a ; C l e a n F o o d s , M a d a n p a l l e , A n d h r a

P r a d e s h ; G l o b e F o o d s , M y s o r e , K a r n a t a k a a n d

M y s o r e F r u i t i n , M y s o r e , K a r n a t a k a ) . J a c k f n i i t

a n d b a n a n a w a s t e s w e r e o b t a i n e d f r o m r e s t a u r -

a n t s a n d h o t e ls l o c a t e d i n M y s o r e C i ty . T h e s a m -

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4 4

P. V '~wanath, S . S . Devi , K. Nand

p le s w e re su n -d r i e d , g ro u n d a n d s to r e d a t 1 2 ° (2

a n d u se d th ro u g h o u t t h e se s tu d ie s.

D i g e s t e r s

Plas t ic d rums of 60 l i te r capac i ty , ava i lab le

loca l ly , were c onv er ted in to d iges te rs w i th in le t

a n d o u t l e t p o r t s fo r f e e d in g a n d e f f lu e n t d i s c h a rg e

a long wi th a gas ou t le t . The d iges te rs , w i th a

w o rk in g v o lu m e o f 4 5 l i te r , w e re o p e ra t e d u n d e r

th e s e m i -c o n t in u o u s m o d e o f f e e d in g a t a t e m -

p e ra tu re o f 3 0 + 2 C .

M E T H O D S

S t a r t u p p r o c e d u r e a n d i n o c u l u m

C o w d u n g d i lu t e d in t h e r a t i o o f 4 :5 w i th w a te r

w a s c h a rg e d in t h e d ig e s t e r a lo n g w i th 1 0 % o f

s t a r t e r c u l tu r e o b ta in e d f ro m th e b io g a s d ig e s t e r

(5 m 3) o f t h e E x p e r im e n ta l A n im a l P ro d u c t io n

C e n te r F a c i l i t y o f C F T R I , My so re (P re m a

V isw a n a th & K r i sh n a N a n d , 1 9 8 9 ) . I n i t i a l l y

s t a b il i z a tio n o f t h e d ig e s te r s w a s c a rd e d o u t fo r

4 - 6 w e e k s a n d t h e n t h e y w e r e o p e r a t e d o n

v a r io u s fru i t w a s t e s a d d e d in su c c e s s io n a t a c o n -

s t a n t l o a d in g r a te o f 4 0 k g T S m -3 d a y -1 a n d 2 5

Table 1.

Periods Feedstock (wastes) used fo r

(25 days each) 5 days each in succession

Tom a to , ba na na , j a c k f ru it , o ra nge

pe e l w i th o i l , p ine a pp le

Tom a to , j a c ld ru i t , ma ngo , p ine a pp le ,

d e o i l e d o r a n g e

Pinea pple , m ango , jackf i 'u i t ,

p i n e a p p le , t o m a t o

B a na na , de o i l e d o ra nge , j a c k fru i t ,

p ine a pp le , ma ngo

Tom a to , o ra nge pe e l w i th o i l,

j a c ld ru i t, ba na na

d a ys H R T u n d e r t h e s e m i -c o n ti n u ou s m o d e ,

r e m o v in g a n d r e p l a c in g 1 . 8 l i t e r s o f s lu r ry a t a

d e f in i t e t im e o n c e a d a y . T h e p a t t e rn o f f e e d in g

was as in Table 1 .

In o rd e r t o s im u la t e n a tu ra l c o n d i t i o n s fo r a

m ix e d - f e e d s to c k a n a e ro b ic d ig e s t io n p ro c e s s , n o

re g u la r s e q u e n c e o f f e e d in g p a t t e r n w a s fo l lo w e d .

F iv e d ig e s t e rs w e re u se d in t h e se e x p e r im e n t s .

A n a ly t i c a l

m e t h o d s

D a i ly g a s p ro d u c t io n w a s r e c o rd e d b y d i s c h a rg in g

th ro u g h a g a s - f lo w m e te r (T o sh n iw a l , B a n g a lo re ,

In d ia) . G a s a n a ly s is w a s d o n e u s in g a N e te l G a s

A n a l y s e r w i th P o r a p a k Q a n d m o l e c u l a r si e ve

c o l u m n s w i th a T C D d e t e c t o r ( P r em a V i s w a n a t h

& K r i sh n a N a n d , 1 9 8 9 ) . T o ta l a n d v o la t i l e so l id s ,

f a t , a sh , t o t a l n i t ro g e n a n d p h o sp h o ru s w e re

d e t e r m i n e d a c c o r d i n g t o t h e m e t h o d s o f A O A C

(1 9 7 5) . T o ta l c a rb o n w a s a n a ly se d u s in g a C a r lo

E r b a 1 1 0 6 E l e m e n t a l A n a l ys e r . C h a r a c t er i st i c s

p e r io d ic a l ly e x a m in e d to e v a lu a t e t h e d ig e s t e rs

w e re p H , t o t a l so l id s (T S ) , t o t a l v o l a t i l e so l id s

(VS) , a lka l in i ty as C aC O 3, to ta l v o la t i le fa t ty ac ids

a s a c e t a t e , a n d N H 3 -N u s in g s t a n d a rd m e th o d s o f

t h e A m e r i c a n P u b l i c H e a l t h A s s o c i a t i o n ( 19 7 5 ).

G a s a n a ly s is w a s c a r d e d o u t f o u r t i m e s i n e a c h

r u n o f a r e t e n t i o n p e r i o d w h i l e t h e e f f l u en t

c h a ra c t e r is t i c s w e re d e t e rm in e d tw ic e d u r in g e a c h

r u n .

R E S U L T S A N D D I S C U S S I O N

T h e p r o x i m a t e c o m p o s i t i o n o f r e p r e s e n t a t i v e

samples o f d i f fe ren t was tes i s l i s ted in Table 2 .

T h e t o ta l c a rb o n c o n t e n t a p p r o a c h e d a l m o s t 4 0 %

a n d a b o v e , w h e re a s g re a t v a r i a b i l it y i n t h e

n i t ro g e n w a s o b se rv e d w h ic h r e su l t e d in a v a r i e d

c a rb o n to n i t ro g e n r a t i o o f 7 6 5 t o 2 1 . 3 2 in t h e

Table 2 . P rox ima te c ompo s i t i on o f f ru i t w a s t e s

Constituents Tomato Mango Orange Deoiled Pineapple Banana Jackfruit

( ) orang e

Mo is tu re a 70 .5 73 .6 73 .4 75 .14 87 .69 88 .14 80 .15

Tota l sof ids° 29 .5 26.4 26.6 24.86 12.31 11.86 19-85

Vola t i le so l ids b 95.73 96.4 94.2 93 61 93.7 9 95-07 92.27

As h b 4 .3 3 .6 5 .8 6-39 6 .2 4 .9 7 .7

Tota l carb on b 54-9 39.8 42.5 43.1 38 9 40-5 46-3

To ta l n i t roge nb 4.2 0.5 1.0 1.3 0.9 1-9 1-4

Phos phoru s b 0 .22 0 .56 0 00 0 .02 0 08 0 09 0 -09

C /N ra t io 13 -0 76 -5 40 .5 33 .2 42 .3 21 .3 33 .1

°On w et weight basis .

b n

dry w eight basis .

Averag es of t r ip l ica te ana lyses.

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Digest ion o f ru i t and vegetable was tes 5

d e c re a s in g o rd e r : m a n g o , p in e a p p le , o r a n g e ,

d e o i l e d o ra n g e , j a c k f ru i t , t o m a to a n d b a n a n a p ro -

c e s sin g w a s te s . C / N r a t io s b e tw e e n 2 0 a n d 3 0 a r e

o p t i m u m f o r m a x i m u m b i o g a s g e n e r a t i o n

(S a n d e r s & B lo o d g o o d , 1 9 6 5 ) a n d g e n e ra t io n

fa i l e d a t 5 2 a n d a b o v e w i th p a p e r p u lp a n d

se w a g e m ix tu re s . A d ju s tm e n t o f r a t i o s w i th sy n -

th e t i c f e r ti l iz e r s su c h a s u r e a a n d a m m o n iu m su l-

p h a t e i s u n e c o n o m i c a l ( D N E S R e p o r t , 1 9 8 9) , b u t

t h e f o r m u l a t i o n o f f e e d w i t h c o m p l e m e n t a r y

w a s te s i s a n e f f e c t iv e m e th o d o f o v e rc o m in g th e se

p ro b le m s .

T h e o b se rv a t io n s r e c o rd e d d u r in g th e s t a r t -u p

s tu d ie s a r e p r e se n te d in F ig . 1 . A n in i ti a l d ro p in

p H f ro m 7 -0 to 6 . 7 w a s o b se rv e d b y th e e n d o f 5

d a y s o f t h e s tu d y, b u t t h i s g r a d u a l ly ro se t o 7 . 0 b y

th e 3 5 th d a y . B io g a s a n d m e th a n e y i e ld s v a r i e d

f rom 0 6 to 1 0

m 3

and 0 35 to 0 6

m 3

p e r k g o f

vo la t i le so l ids added respec t ive ly dur ing the f i r s t

t h r e e ru n s . D u r in g th i s p e r io d o f d r a s t ic v a r i a t i o n

in t h e b io g a s /m e th a n e y i e ld t h e re w a s , h o w e v e r ,

n e g l ig ib l e v a r i a t i o n in t h e p H . M o re o v e r , t h e c o n -

c e n t r a t i o n o f V F A (as a c e t a t e ) a n d th e a lk a l in ity

( as C a C O 3 ) d e t e rm in e d in t h e e f f lu e n t w e re o n a n

a v e ra g e 3 1 0 a n d 1 2 2 0 m g / l i t e r r e spe c t iv e ly , i n d i -

c a t in g s t a b l e a n a e ro b ic d ig e s t io n c o n d i t i o n s . A f t e r

a p e r io d o f 8 5 d a y s , t h e re w a s l i tt l e v a r i a t i o n in

th e b io g a s a n d m e th a n e y i e ld s a l t h o u g h th e f e e d -

s to c k u se d w a s c h a n g e d o n c e in 5 d a y s . A n

a v e ra g e y i e ld o f b io g a s a n d m e th a n e o f 0 -9 2 a n d

0 5 5 m 3 p e r k g V S a d d e d w a s o b ta in e d r e sp e c t -

ive ly . In a s epara te s tudy , i t has be en fo und tha t i f

so m e o f t h e se w a s t e s w e re u se d in d iv id u a l ly a s

f e e d s to c k fo r b io g a s p ro d u c t io n , t h e re w a s so u r -

in g o f t h e d ig e s t e r s l e a d in g to d ig e s t io n f a i l u r e

w h e n l o a d e d a t 4 0 k g T S m 3day i a t a H R T o f

2 5 d a y s (D N E S R e p o r t , 1 9 9 0 ) .

F o r d ig e s te r s d e s ig n e d w i th p o l lu t io n c o n t ro l a s

t h e m a i n o b j e c t iv e , t h e o p t i m u m r e t e n t i o n p e r io d

c a n b e c o n s i d e r e d a s t h e m i n i m u m h y d r a u l i c

r e t e n t io n t im e th a t c a n b e to l e r a t e d b e fo re i n s t a -

b i l i t y o f t h e d ig e s t e r o c c u r s (H o r to n , 1 9 8 0 ) . I n

a d d i t i o n th e h ig h e r t h e l o a d in g r a t e a t w h ic h th e

d ig e s t e r c a n b e o p e ra t e d , t h e g re a t e r i s it s r o l e in

p o l lu t io n a b a t e m e n t . H e n c e , tw o e x p e r im e n t s

w e re c a r r i e d o u t o n e a f t e r a n o th e r t o o p t im iz e

t h e s e t w o i m p o r t a n t o p e r a t i o n a l p a r a m e t e r s .

S t a b i l i z e d d ig e s t e r s w e re o p e ra t e d a t r e t e n t io n

t imes of 8 , 12 , 16 , 20 and 24 days a t a cons tan t

l o a d i n g r a t e o f 4 0 k g T S m - 3 d a y - 1 . T h e p a t t e r n

o f f e e d in g fo l lo w e d w a s a s d e sc r ib e d in M e th o d s .

T h e r e su l t s a r e p r e se n te d in T a b le 3 . D ig e s t e r s

o p e r a t i n g a t 1 6 , 2 0 a n d 2 4 d a y s H R T w e r e f o u n d

to b e s t a bl e . T h e re w a s a p e r f e c t l i n k in g o f t h e

a c i d o g en i c a n d m e t h a n o g e n i c p h a s e s i nc e t h e p H

re m a in e d a t 7 -0 a n d s in c e th e re w a s n o d ra s t i c

in c re a se i n a c id i ty o r a lk a lin i ty . H o w e v e r , t h e

d ig e s t e r s o p e ra t in g a t 8 a n d 1 2 d a y s H R T w e n t

so u r b y th e e n d o f o n e ru n . I n s ta b i l i ty o f t h e

d ig e s t e r s w a s d i r e c t ly r e l a t e d to t h e d ro p in p H ,

8 0

6 .0

: o 6 1 _ A

I

I Z

. 0 -8

• o

°~ ~

~. m 0 4,

I I i t

I I I I

1 2 3 4

P e r i o d s ( 2 5 d o y s e o c h )

F i g

1 . S t a x t -u p s tu d i e s o f b i o g a s p r o d u c t i o n f r o m a m i x e d f e e d s t o c k o f v a r i o u s f r u it s a n d v e g e t a b l e s . F o r f e e d m i x t u r e s s e e

M e t h o d s .

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4 6 P. V iswanath S . S . Dev i K. N an d

increase in to ta l vo la t i le fa t ty ac ids , to ta l a lka l in i ty

a n d t o t a l a m m o n i a c o n c e n t r a t i o n as o b s e r v e d b y

o th e r w o rk e r s B ry a n t e t a L 1 9 7 7 ; H o b so n , 1 9 8 1 ;

R a n a d e e t a l . 1989; Sa les e t a l . 1989) . In the

s e c o n d e x p e r i m e n t f o u r d i g e s t e r s w e r e o p e r a t e d

a t a 1 6 d a y H R T w i th a l o a d in g r a t e o f 4 0 k g T S

m - 3 d a y -~. A f t e r t h e se r e a c h e d s t e a d y s t a te , t h e

lo a d in g r a te s o f t h r e e o f t h e m w e re r a i s e d to 6 0 ,

8 0 a n d 1 0 0 k g T S m - 3 d a y -1 . A s h a s b e e n

o b se rv e d b y o th e r w o rk e r s H a w k e s , 1 9 8 0 ;

H o r to n , 1 9 8 0 ; P y le , 1 9 8 0 ) t h e re w a s a d e f in i t e

r e l a t i o n sh ip b e tw e e n th e g a s y i e ld a n d lo a d in g

ra te Table 4 ). On ly d iges te rs ope ra t in g a t a load-

i ng r at e o f 4 0 k g T S m - a d a y - ~ w e r e f o u n d t o b e

s tab le . Sour in g of the d iges te rs op era t in g a t 60 , 80

a n d 1 0 0 k g T S m - 3 d a y -~ w a s o b s e r v e d b y t h e

e n d o f o n e ru n .

In a n o th e r s e t o f s tu d ie s , th e h o u r ly g as p ro d u c -

t i o n in d ig e s t e rs o p e ra t in g a t 1 6 , 2 0 a n d 2 4 d a y

H R T , a t a c o n s t a n t l o a d in g r a t e o f 4 0 k g T S

m aday 1

w a s r e c o rd e d a n d i s d e p ic t e d in F ig . 2 .

I t w a s o b se rv e d th a t t h e re w a s n o u n i fo rm i ty i n

able 3 . Ef fe c t o f va ry ing the H R T

A . O pe ra t iona l pa ra me te r s

H R T ( d ay s ) 8

TS in f e e d s lu r ry (%) 4

V S in f e e d s lu r ry (%) 94 + 3

V S loa d ing ra t e 38

(kg m-3d a y - I )

B . G a s p r o d u c t i o n

D a i ly ga s p rod uc t ion ( l it e rs ) 27 .5

G a s p rodu c t ion r a t e (vo l /vo l /da y ) 0 -62

G a s y i e ld (m3/kg V S a dde d ) 0 .13

G a s y i e ld (m3/kg TS a dde d ) 0 .13

M e tha ne (%) 22 .0

Spe c i f ic me tha n e p rodu c t ion 0 -03

(m3/kg VS added )

C. Eff luent charac te r is t ics

Tota l a lka l in i ty (mg/ l i te r as Ca CO 3) 811 6

N H 3-N (mg / l it e r ) 580

Tota l v ola t i le fa t ty ac ids

as ace ta te ( rag/ l i te r) 64 30

pH 4 -6

12 16 20 24

4 4 4 4

9 4 + 3 9 4 + 3 9 4 + 3 9 4 + 3

38 38 38 38

28 5 49-0 53-5 37 0

0 63 1-09 1 2 0.82

0 20 0-49 0 63 0 .52

0 19 0-44 0 60 0-50

47-2 51.1 58-4 61.2

0 .09 0 .25 0 -37 0 .32

4 1 1 2 1 6 8 2 2 0 1 8 1 4 5 1

2 4 0 9 8 8 5 1 4 6

2 3 1 0 6 1 0 3 2 2 3 4 1

6.1 7.1 7.0 7 1

a V alue s obse rve d ju s t be fo re t he d ige s t e r w e n t sou r .

able 4 . Ef fe c t o f va ry ing the l oa d ing ra t e

A . O pe ra t iona l pa ra me te r s A a B h C h D b

TS in feed slurry (%) 4 6 8 10

VS in feed slurry (%) 94 + 2 94 + 2 94 + 2 94 + 2

VS load ing rat e (kg m - 3day - ~) 3-8 5-7 7-6 9-5

H R T (da ys) 16 16 16 16

B . G a s p r o d u c t i o n

Dai ly gas y ie ld ( l i te rs) 54 .0 88.0 71.0 32.5

Gas pro duc t ion ra te (vol /v ol /day ) 1 .2 1 .95 1-7 0-72

Gas y ie ld (m3/kg VS adde d) 0 .51 0 .46 0 .34 0 .12

G a s y i e ld (ma /kg TS a dde d ) 0 .48 0 .52 0 .32 0 .12

M e tha ne (%) 53 .1 42 .8 32 .4 30 .3

Spe c i fi c me tha ne p rodu c t ion

(m3/kg VS adde d) 0 .27 0 .19 0 .11 0-04

C. Eff lue nt charac te r is t ics

To ta l a lka lin i ty (mg / l i t e r a s 1715 3450 512 0 428 0

CaCO~)

N H a -N 2 (mg / l i te r ) 185 450 560 490

Tota l vo la t i le fa t ty ac ids as

a c e t a t e (mg / l it e r ) 710 0 5121 712 0 7450

pH 7.0 6 0 5 3 4 .3

°Values a re an av erage of three runs.

hV a lue s obse rve d ju s t be fo re t he d ige s t e r s w e n t sou r .

7/23/2019 1-s2.0-096085249290117G-main


igestion of ruit and vegetable wastes

47

5 0

t . O

o

m m

~

3 0

~

iJ

o

i

a . 2 . 0

l

/ , 8 12 16 20 2e ,

T ; m e 2 / , h o u r s )

Fig. 2. Pattern of biogas production in 24 h period while operating at various hydraulic retention times.

/ x - - , 20 day; [] ,24 day HRT.

o ,1 6 day;

t h e g as p r o d u c t i o n i n a 2 4 h p e r i o d . M a x i m u m g a s

w a s p r o d u c e d a t t h e f o u r t h h o u r a f t e r a d d i t i o n o f

f e e d a n d t h e r e w a s a s p u r t i n g a s p r o d u c t i o n a t

m o r e o r l e ss r e g u l a r i n t e r v a l s. M o r e o v e r , m o r e

t h a n 6 0 o f t h e g a s w a s p r o d u c e d w i t h i n t h e f i rs t

1 2 h o f a n a e r o b i c d i g e s t i o n . F u r t h e r m o r e , c o m -

p a r i s o n s o f th e p e r c e n t a g e o f g a s p r o d u c e d a t

r e g u l a r i n t e rv a l s o f t i m e i n d i g e s t e r s o p e r a t i n g a t

v a r i o u s H R T s i n d i c a t e d t h a t d u r i n g t h e f i r s t 1 2 h

w h i l e 7 4 - 5 o f t h e t o t a l b i o g a s i s p r o d u c e d i n

d i g e s t e r s o p e r a t i n g a t s h o r t e r h y d r a u l i c r e t e n t i o n

t imes o f 16 days , on ly 59-03 of the to ta l gas i s

p r o d u c e d i n di g es te r s o p e r a t in g a t a 2 4 d a y s H R T

b y t h e s a m e p e r i o d . T h i s m a y b e d u e t o v a r i a t i o n

i n t h e m i c r o f l o r a d o m i n a t i n g i n d i g e s t e r s o p e r a t -

i n g a t d if f e re n t r e t e n t i o n t i m e s . C h a r t r a i n & Z e i -

k u s ( 1 9 8 6 ) h a v e o b s e r v e d t h a t

Methanosarc ina

b a r k e d

d o m i n a t e u n d e r c o n d i t io n s w h e n t h e d i lu -

t ion r a t e i s h igh whi l e

Methanothr ix soehgeni i

p r e -

d o m i n a t e u n d e r c o n d i t i o n s o f l o w d i l u t i o n ra t e s .

B a s e d o n t h e s e o b s e r v a t i o n s i t is fe l t t h a t i n o r d e r

to increa se the e f f i c i ency of d iges t ion , the da i ly

v o l u m e o f f ee d s l u r r y c o u l d b e i n t r o d u c e d i n t o t h e

d i g e s te r s t w i c e a d a y , w h e n o p e r a t i n g d i g e s t e rs a t

s h o r t h y d r a u l i c r e t e n t i o n t i m e .

C O N C L U S I O N

T h u s i n t h e s e s t u d i e s , i t c a n b e s e e n t h a t f r u i t

w a s t e s s u c h a s m a n g o , p i n e a p p l e , o r a n g e , b a n a n a ,

j a c k f r u i t a n d t o m a t o c a n b e u s e d a s f e e d s t o c k f o r

b i o g a s p r o d u c t i o n b y u s i n g t h e m i n s u c c e s s i o n f o r

s h o r t p e r i o d s o f t i m e ( 5 d a y s ) w i t h o u t a n y s u p p l e -

m e n t a t i o n w i th n i t ro g e n u n d e r m e s o p h i li c c o n d i -

t io n s . T h e d i g e st e r o p e r a t i n g a t a 1 6 d a y H R T a n d

a t a l o a d in g r a t e o f 4 0 k g T S m - 3 d a y -1 h a s b e e n

o p e r a t e d f o r 1½ y e a r s a n d h a s s h o w n n o s i gn s o f

f a il u re . A n a v e r a g e y i e l d o f 0 . 5 - 0 . 6 m 3 o f b i o g a s

p e r k g V S a d d e d w a s r e c o r d e d w i t h a m e t h a n e

c o n t e n t o f 5 1 - 5 3 . B a s e d o n t h e s e o b s e rv a t io n s ,

f u r t h e r s t u d i e s a r e i n p r o g r e s s t o c a r r y o u t l a r g e

sca le t r i a ls in 1 .5 an d 25 m 3 d iges te r s .

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• s p o n s o r e d b y t h e D e p a r t m e n t o f N o n - C o n v e n t i o n a l

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Digestion ed . D. A. S ta f fo rd , B . I . W hea t ley D. E .

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Production from Agricultural and Domestic Wastes.

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produc t ion by anae rob ic d iges t ion o f f ru i t and vege tab le

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and chem ica l s . Proceedings of the Second International

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