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Biomass 17 (1988) 1-11
Anaerobic Digestion of Gliricidia Leaves for Biogas and Organic Manure
V. Nallathambi Gunaseelan
Department of Zoology, PSG College of Arts and Science, Coimbatore 641 014 India
(Received 14 September 1987; revised version received 18 May 1988; accepted 19 May 1988)
A BS TRA CT
Gliricidia maculata is a tree grown in India for green leaf manuring. The digestibility of Gliricidia leaves for biogas production was determined in 3 litre batch digesters at room temperature (32 + 3°C). Results indicate a gas yield of 165-180 ml C H 4 g- i VS added and a VS reduction of 37-39%. Determination of the N, P, K content of the digester influent and effluent slurries indicates that the anaerobically digested slurry of the Gliricidia leaves is better in quality than the fresh Gliricidia leaves as organic manure.
Key words." Gliricidia, green leaf manure, biogas, anaerobic digestion, methane, fertilizer.
INTRODUCTION
Various studies have indicated land- and water-based biomass as future sources of alternate non-conventional feedstocks for biogas produc- tion.~-3 The methane yield from biomass studied so far, varies b e t w e e n 130-300 ml g-~ volatile solids (VS) added. However, work on land- based biomass for methane production appears limited. Gliricidia rnaculata H.B.et K., a tree introduced in India from the West Indies, is grown for shade and green leaf manuring. It can be easily propagated with little energy input by planting stem cuttings on wastelands and along road sides. Cutting the twigs (lopping) for green leaf manuring from a fully grown Gliricidia tree yields green leaves at an average of 91 kg lopping-~ year-I.4 In this work, the potential of Gliricidia leaves as a substrate for biogas production and the digested slurry as organic manure has been demonstrated.
1
Biomass 0144-4565/88/S03.50 - © 1988 Elsevier Science Publishers Ltd, England. Printed in Great Britain
2 V.N. Gunaseelan
MATERIALS A N D METHODS
Substrate
The Gliricidia leaves of all age groups were collected directly from the tree. The leaves used in this study contained 26.8% total solids (TS) at the time of collection. The leaves were reduced to particles of 1 mm in a blender and made into a slurry by mixing with an equal amount of dis- tilled water (wt/vol.)
Experimental procedures
The following treatments were used to determine the digestibility of Gliricidia leaves for biogas production:
50 g Treatment (VS concentration 45 g li tre- 1); 50 g Gliricidia : 50 ml water: 1000 ml seed-inoculum 200 g Treatment (VS concentration 59 g litre-1); 200 g Gliricidia: 200 ml water: 1000 ml seed-inoculum 2 5 0 g Treatment (VS concentration 62"5 g litre-~); 250g Gliricidia: 250 ml water: 1000 ml seed-inoculum Seed-inoculum (S) (VS concentration 37.8 g litre - J); 1000 ml alone
Seed-inoculum (digested slurry) was obtained from a biogas plant operating on cattle manure at the loading rate of 4 kg TS m - 3 day - 1 and a temperature of 30 + 3°C. In the 50 g and 200 g treatments, the experi- ments were repeated three times. In the 250 g treatment the experiments were only repeated twice. The means calculated from the experiments for each treatment were used to compare different treatments.
Digesters
Three litre aspirator bottles with bottom sampling outlets were used as digesters. The digester contents were mixed throughout the period of digestion, using a magnetic stirrer and allowed to digest anaerobically at room temperature 32 _+ 3°C for 4 weeks. The gas produced was collected in rubber bladders and the volume was measured at the end of every week in a gasflow meter. The volume of gas was recorded at a tempera- ture of 32°C and a station level pressure of 723.7 mm Hg.
Analytical methods
The initial and final slurry samples in each treatment were analysed for TS, VS, pH and total volatile fatty acids (VFA) (steam distillation
Anaerobic digestion of Gliricidia leaves for biogas and manure 3
method) by standard methods? Total organic carbon was determined by the wet digestion method. 6 Total Kjeldahl nitrogen, potassium and phosphorus were determined by the methods described by Jackson. 7 Twenty millilitre samples of slurry were drawn from each digester at weekly intervals and analysed for pH and VFA. Methane content of the biogas was measured at the end of every week using an Aimil Nucon 5700 gas chromatograph (M/S Aimil Sales and Agencies Ltd, Bombay, India) with flame ionization detectors and Poropak Q 2 m column. Injector, detector and column temperatures were 100 °, 110 ° and 90°C, respectively. The nitrogen carrier gas flow was 30 ml min -
RESULTS AND DISCUSSION
Substrate
Among the physical and chemical characteristics of substrates fed to the digesters (Table 1), the C/N and C/P ratios in Gliricidia leaves were 14 and 64, respectively. Substrates with C/N ratios of less than 15 and C/P ratios of less than 75 are most suited for stable biological conversions. 8 This indicates Gliricidia leaves have potential as a substrate for biogas production in India. The N,P,K content of Gliricidia leaves accounts for their usefulness as green manure in India.
TABLE 1 Physical and Chemical Characteristics" of Substrates Fed to the Digesters
Constituent Content
Seed-inoculum Gliricidia leaves
Moisture Content (%) 93.5 _+ 0.73 73.2 _+ 0.25 Volatile Solids (%) 4.09 _+ 0.03 22.4 + 0.41 Total Organic Carbon ~' 27"3 + 2-07 31'9 + 0.25 Kjeldahl Nitrogen h 1-68 -+ 0"00 2.24 + 0'(}3 Phosphorus h 0'9 + 0-07 0'5 + 0.04 Potassium h 0.4 + 0.16 1.3 _+ 0.26 pH 8.2 + 0-13 6.2 + 0.16 C/N 16.2 + 1-24 14.2 _+ 0.2 l C/P 30-3 -+ 0.31 63'8 + 5.1
"Values expressed as the mean + standard deviation of three samples. ~'Units in % dry basis.
4 V.. N. Gunaseelan
VFA and pH
The mean values of the levels of VFA in the 50 g and 200 g treatments during batch fermentation of Gliricidia leaves ranged from 1080 to 180 mg litre- ~ and 4815 to 1700 mg litre - ~ respectively whereas in the seed- inoculum it was below 300 mg litre- ~ (Fig. 1), suggesting that addition of Gliricidia leaves enhances the production of VFA. The heavy seed- inoculum of 1 litre of digested slurry with a pH of 8.2, provided buffering capacity as well as a high concentration of facultative and obligate anaerobes. The pH in the 50 g and 200 g treatments (Fig. 2) was within the desirable range of 6.6 to 8-2 and hence methane production started immediately. In the 250 g treatment, the level of VFA ranged from 7335 to 5700 mg litre - m (Fig. 1 ). Since the pH in 250 g treatment was below 6.1 till the end of the third week (Fig. 2), there was no methane produc- tion. The digestion upset occurred as a result of organic overload. However, in the fourth week the pH increased to an acceptable level of 6.8 and methane production started (Table 2). The experiment was terminated at the end of the fourth week to maintain uniform operation period for all the treatments.
P,
"T
8100
7200
6300
5400
4500
3600
2700
1800
900
1 2 3 4 TIME WEEKS
Fig. 1. Total volatile fatty acids level in different treatments during batch fermentation of Gliricidia leaves (o: 50 g treatment; o: 200 g treatment; m: 250 g treatment; x : S
treatment).
Anaerobic digestion of Gliricidia leaves for biogas and manure 5
VS reduction
The summary of digester performance data (Table 3) shows that during batch fermentation of Gliricidia there was variation in the VS reduction for the different treatments. Part of this variation was caused by the different substrate to seed ratios in each treatment. After correcting for the VS reduction of the seed-inoculum as measured in the S treatment, the VS reduction in the Gliridicia leaves alone in the 50 g and 200 g treatments showed little variability (Table 4). The VS reduction was around 37-39%. In the 250 g treatment, however, the low percentage reduction of VS was due to the digestion upset during the major part of the fermentation period.
Methane yield
The difference in total methane production in the 50 g and 200 g treat- ments (Table 2) was due to different amounts of VS present in the digesters. After correcting for the total methane production from the seed-inoculum as measured in the S treatment, the methane yield in stable digesters from Gliricidia was around 165-180 ml g- 1 VS added (Table 2). The methane concentration in the gas varied between 60-75%. Methane yield data from this work were compared with litera- ture data 9-~1 for other biomass substrates (Table 5). Work to increase the methane yield by chemical and biological pretreatments is under way.
50g
TIME WEEKS
Fig. 2. Changes in pH in different treat- ments during batch fermentation of Gliri- cidia leaves ( × : 50 g treatment; • : 200 g treatment; o: 250 g treatment; e: S treat-
ment).
TA
BL
E 2
T
otal
Met
han
e P
rod
uct
ion
Fro
m D
iffe
ren
t Tre
atm
ents
an
d M
eth
ane
Yie
ld D
ue
to G
liric
idia
Lea
ves
Trea
tmen
t E
xper
imen
t M
etha
ne p
rodu
ctio
n T
otal
N
o.
(litr
es w
eek
- i)
met
hane
pr
oduc
tion
1
II
111
IV
(litr
es)
Tot
al m
etha
ne
prod
ucti
on
due
to G
liri
cid
ia
(CH
4 fro
m
trea
tmen
t-
CH
4 fro
m s
eed)
(l
itres
)
Met
hane
yie
ld
from
Gli
rici
dia
(l
itre
g i
VS
adde
d)
1 0.
7 0.
7 0.
2 0.
17
1.77
1-
49
0.1
33
2
2-79
0-
41
0.2
0-08
3.
48
2.34
0"
209
50 g
3
2-44
0.
52
0.28
0.
19
3.43
2.
23
0-19
9 (l
l.2
gV
So
fGli
rici
dia
M
ea
n+
1
.98
+0
.91
0
.54
+0
"12
0
.23
+0
.04
0
.15
+0
"05
2.
9_+
0.79
2
-03
+0
-38
0
.18
1+
0"0
34
adde
d)
SD
~
1 1"
13
2"3
2"06
1'
13
6"62
6-
34
0-14
2 2
2'6
6
2"78
2.
54
1.24
9"
22
8-08
0"
180
200
g 3
2.74
2"
57
2"35
1'
34
9"00
7"
8 0"
174
(44.
8gV
SofG
liri
cidi
a M
ea
n+
2
.18
-+0
.74
2
-55
+0
'2
2.3
2+
0.2
1.
24_+
0-09
8
.29
+1
.18
7
.42
+0
-76
0
.16
5_
+0
.01
6
add
ed)
SD
"
2 0
'73
0
.00
0-
00
3.22
3"
95
2.81
0"
05
250
g 3
0"65
0-
00
0.00
2.
86
3-51
2.
31
0.04
(5
6gV
SofG
liri
cidi
a M
ean_
+
0-69
+_0
"04
0"00
0"
00
3-04
_+0'
18
3.73
_+0"
22
2'56
+_0
"25
0"05
_+0"
007
adde
d)
SD
"
See
d-i
no
culu
m (S
) 1
0.1
0-05
0.
05
0-08
0.
28
2 0-
5 0"
38
0.18
0.
08
1.14
3
0.3
0.48
0.
23
0-19
1.
2 M
ean+
_ 0.
3-+
0-16
0.
3+_0
.18
0-1
5-+
0.0
8
0.12
_+0.
05
0-87
_+0.
42
SD
.
"SD
= S
tan
dar
d D
evia
tion
.
TABL
E3
Su
mm
ary
ofD
ige
ste
r~ff
orm
an
ce
Du
rin
gB
atc
h
~rm
en
tati
on
ofG
liri
cid
iaL
ea
ve
s
7?ea
tmen
t E
xper
imen
t N
o.
Tot
al o
rgan
ic
Kje
ldah
l C
/N
carb
on (
%)
nitr
ogen
(%
) V
S V
S re
duct
ion
(%)
(O/o)
Init
ial
Fin
al
Init
ial
Fin
al
Init
ial
Fin
al
Init
ial
Fin
al
1 2 50
g
3 M
ean
_+ S
D"
1 2 2
00
g
3 M
ean
_+ S
D"
2 25
11 g
3
Mea
n _
+ SD
"
1 S
eed
-in
ocu
lum
2
(S)
3 M
ean
+ S
D"
24.4
22
.4
1.95
2.
01)
12.5
11
2
29.3
23
.11
1.68
2.
38
17-4
9.
7 28
.6
23-0
1.
80
2.66
15
,9
8-6
27
.4+
2.1
6
22-8
_+0.
28
1.81
_+11
.11
2-35
_+1/
-27
15.1
4_+
2./)
5 9.
7_+
1.1/
7
27.1
1 21
.2
1.96
2.
5 13
-8
8-4
31.4
24
.9
1.96
2.
8 16
"0
8.9
31.4
23
.0
1.96
2-
6 16
'0
88
29
.9_+
2.1/
7 23
.11_
+ 1-
51
1.96
_+[i
2.
63_+
0.12
15
.26_
+ 1
.114
8.
75_+
11"2
2
30.1
1 25
.9
1-96
2.
1 15
"3
12-3
30
.0
27.2
2.
0 2-
2 15
"0
12.4
31
1.0_
+i)
26
.6_+
11.6
5 1.
98_+
t1,1
12
2.15
_+t1
.(15
15
.15_
+0-
15
12.3
7_+
//.1t
5
24.4
21
1.5
1.68
1.
7 14
.5
12-0
5 29
.1
22-4
1-
68
1 '9
17,3
11
-8
28.4
21
-6
1.68
1-
8 16
-9
12.0
27
.3_+
2-(1
7 21
.5_+
0-78
1.
68_+
0 1
.8_
+1
1./
/8
16.2
_+1.
24
11.9
_+0-
12
5"75
4"
88
15"1
,~
4"
41
3"94
10
'7
4.58
4.
05
11.6
4.
91_+
0-59
4.
29_+
0-42
1
2.6
+ 1
.9
N"
6.98
5.
32
23.8
~
- 5"
66
4"16
26
"5
~,
5.77
4.
58
20.6
6
.14
+I)
.6
4.6
9+
0-4
8
23.6
_+2.
41
5'6
4
5-01
11
"2
~ 6~
6"24
5"
67
9'1
~"
5'94
_+0.
3 5-
34_+
0"33
10
"1 -+
1"1
15
~
4" 1
2 3
'92
5"
0 4.
1 3.
87
5"6
~,
4.05
3.
82
5.7
4.1/
9-+
0.03
3.
87_+
0.11
4 5.
4-+
11"3
1
"SD
= S
tan
dar
d D
evia
tion
.
TA
BL
E
4
VS
Red
uct
ion
in
the
Gli
rici
dia
Lea
ves
Aft
er C
orre
ctin
g fo
r th
e V
S R
edu
ctio
n o
f th
e S
eed
-in
ocu
lum
Par
amet
er
VS
add
ed t
o th
e di
gest
er (
g)
VS
red
uced
(%
)"
VS
red
ucti
on (
g)
VS
red
ucti
on d
ue t
o G
liri
cidi
a le
aves
(g)
(g V
S r
educ
ed i
n tr
eatm
ent-
g
VS
red
uced
in
S)
VS
red
ucti
on d
ue t
o G
liri
cidi
a le
aves
(%
)
50 g
tre
atm
ent
200
g tr
eatm
ent
Seed
-ino
culu
m
50 g
Gli
rici
dia
200
g G
liri
cidi
a .,~
(5
0 g
Gli
rici
dia
+ S)
(2
00 g
Gli
rici
dia
+ S)
(S
)
49-0
82
.6
37"8
11
-2
44.8
12
.6
23'6
5.
4 --
--
6-
2 19
.5
2.0
--
--
,~
--
--
--
4.2
1
7-5
"
37"5
39
"1
"Tab
le 3
.
Anaerobic digestion of Gliricidia leaves for biogas and manure
TABLE 5 Yields of Methane in Anaerobic Digestion of Various Types of Biomass
Biomass Methane yield Reference (ml g- i VS added)
Gliricidia maculata 165-180 This work Grass Mixture 190 9 Laminaria saccharina 205-220 10 Lucerne 247 3 Hay 295 3 Gracilaria tikvahiae 130-200 11
Manurial value
Since Gliricidia trees are grown mainly for green manuring in India, it is essential to determine the suitability of the digested slurry of Gliricidia leaves as organic manure. The N,P,K content of the 50 g treatment digester effluent (Table 6) showed a marked increase of 30%, 4% and 29%, respectively more than the influent. The 200 g treatment showed an increase of 34%, 11% and 27% respectively for N,P,K. This indicates that the anaerobically digested slurry of the Gliricidia leaves is better in quality than the fresh Gliricidia leaves as organic manure.
CONCLUSIONS
The chemical characteristics of the Gliricidia leaves indicated that Gliricidia leaves have potential as the substrate for biogas production. Addition of the Gliricidia leaves to the batch digesters at room tempera- ture (32 _+ 3°C), enhances the production of the VFA. The VFA level in the digesters varied between 1080 to 7335 mg litre -~. The methane yield from the Gfiricidia leaves was 165-180 ml g-J VS added and the VS reduction was 37-39%. The N,P,K content in the 200 g treatment digester effluent showed a marked increase of 34%, 11% and 27%, respectively, more than the influent. This shows that the anaerobically digested slurry of the Gfiricidia leaves is better in quality than the flesh GliricMia leaves as organic manure. Thus, this work indicates Gliricidia leaves to be useful both as fuel and fertilizer.
TA
BL
E 6
E
ffec
t of
An
aero
bic
Dig
esti
on
on
the
Am
ou
nt
of F
erti
lize
r Ele
men
ts (
N,P
,K)
of G
liri
cidi
a L
eav
es
Tre
atm
ent
Exp
erim
ent
No.
K
jeld
ahl
nitr
ogen
" P
hosp
horu
s"
Pot
assi
um a
Init
ial
Fin
al
Init
ial
Fin
al
Init
ial
Fin
al
1 1-
95
2.0
0.71
0.
73
0.4
0.6
2 1-
68
2'3
8
0.74
0.
7 0"
65
0"8
50 g
3
1-8
2.66
0"
8 0.
9 0.
7 0"
85
Me
an
+ S
D ~
' 1
.81
+0
.11
2
.35
+0
-27
0
-75
+0
.04
0
.78
+0
"09
0
.58
+0
.13
0
"75
+0
.11
1 1-
96
2'5
0'5
8
0.6
0'6
0"79
2
1-96
2.
8 0.
75
0.9
1.2
1.5
200
g 3
1-96
2.
6 0.
65
0.7
1.1
1.4
Me
an
+S
D t'
1
.96
+0
2
.63
+0
.12
0
.66
+0
-07
0
.73
+0
.12
0
.97
+0
.26
1
"23
+0
.31
2 1-
96
2.1
0.75
0"
78
1-3
1'45
2
50
g
3 2-
0 2-
2 0"
6 0"
58
1-2
1 '32
M
ean
+ S
D b
1
-98
+0
.02
2
-15
+0
"05
0
.68
+0
.08
0
.68
+0
.1
1.2
5+
0.0
5
1-3
9+
0.0
7
See
d in
ocu
lum
1
1.68
1.
7 0"
8 0.
9 0.
2 0.
5 (S
) 2
1"68
1.
9 0"
95
0"8
0-6
0.7
3 1.
68
1.8
0.95
0"
85
0.4
0.6
Mea
n_+
SD
b
1-68
_+0
1"8_
+0"
08
0"9_
+0-
07
0"85
_+0"
04
0-4_
+0"
16
0-6_
+0"
08
"Per
cent
age
dry
basi
s.
hSD
= S
tan
dar
d D
evia
tion
.
Anaerobic digestion of Gliricidia leaves for biogas and manure 11
A C K N O W L E D G E M E N T S
This work was supported by the Department of Science and Technology, Government of India, New Delhi, (No. 21(4)/83 STP-1). I thank the Principal, Professor D. K. P. Varadarajan and the Head of Department Dr V. S. Ramasami for providing the laboratory facilities.
R E F E R E N C E S
1. Stewart, D. J. Energy crops to methane. In: The First International Sympo- sium on Anaerobic Digestion, University Industry Centre, University College, Cardiff, Wales (1979).
2. Chynoweth, D. P. & Srivastava, V. J. Methane production from marine biomass. In: International Symposium on biogas, microalgae and livestock wastes, Taipei, Taiwan, Institute of Gas Technology, Chicago, Illinois, (1980) pp. 1-25.
3. Badger, D. M., Bogue, M. J. & Stewart, D. J. Biogas production from crops and organic wastes. New ZealandJ. Sci. 22, (1979) 11-20.
4. Kantiraj, M. Green leaf manuring and green manuring. The Madras Agricul- tural Journal, 37, (1950) 3-6.
5. American Public Heatlh Association (1980). Standard methods for the examination of water and waste water, 15th edn, Inc., New York, American Public Health Association, Washington DC, pp. 92-6,402-71.
6. Piper, C. S. Soil and plant analysis, Interscience Publishers Inc., New York (1950) pp. 223-27.
7. Jackson, M. L. Soil Chemical Analysis, Constable and Co. Ltd, London (1962) pp. 1-2.
8. Chynoweth, D. E & Srivastava, V. J. Biothermal conversion of biomass and wastes to methane. In: Fifth Symposium on biotechnology for fuels and chemicals, Gatlinburg, Tennessee, Institute of Gas Technology, Chicago, Illinois, (1983) pp. 111-92.
9. Klass, D. L., Ghosh, S. & Conrad, J. R. The conversion of grass to fuel for captive use. In: Symposium on clean fuels from biomass, sewage, urban refuse and agricultural wastes, Institute of Gas Technology, Chicago, Illinois (1976) pp. 229-52.
10. Troiano, R. A., Wise, D. L., Augenstein, D. C,, Kispert, R. G. & Cooney, C. L. Fuel gas production by anaerobic digestion of kelp. Resource recover' and conservation, 2, ( 1976) 171-6.
11. Hanisak, M. D. Methane production from the red seaweed Gracilaria tikvahiae. In: Xth International seaweed symposium proceedings, ed. by T. Levring, Walter de Gruyter, Berlin, New York, ( 1981 ) pp. 681-86.
