International Research Journal of Biotechnology (ISSN: 2141-5153) Vol. 2(5) pp.114-118, May, 2011
Available online http://www.interesjournals.org/IRJOB
Copyright © 2011 International Research Journals
Solar/Energy Laboratory, Department of Mechanical Engineering,Annamalai University, Annamalainagar-608 002, India
Accepted 23 May, 2011
Anaerobic digestion of rice crop residues –rice chaff, rice straw and rice husk as co-substrate with cow dung was the subject of this investigation. These wastes were treated in the digester of volume 0.90m
3
.
Each waste was mixed in different proportion (i) Rice chaff / cow dung (ii) Rice straw/ cow dung and (iii)
Rice husk / cow dung. Plastic digester was used and the digestion of residues was undertaken by batch-type anaerobic process, the digester operated at a temperature (25-35 o
C). Gas chromatography was used to quantify the different component of biogas produced. Volume and pressure of biogas stored in the cylinders were tabulated. The cumulative gas production obtained from the three substrates was 3.8m
3
, 3.4m
3
and 1.5m
3
respectively. The low performance of cow dung / rice husk was due to the high lignin content which contained unfavourable non lignin-carbon to nitrogen ratio (70:1).
Keyword: Biogas, Batch-type process, rice Crop, residues, cow dung and anaerobic process
INTRODUCTION
Biogas can be produced by anaerobic digestion of agricultural wastes like rice crop residues. Such as rice chaff, rice straw and rice husk as co-substrates with cow dung. Biogas is a clean environment friendly fuel which contains about 55-65% methane (CH dioxide (CO
2
4
) 30-45 % carbon
) traces of hydrogen sulphide (H
2
S) and fraction of water vapour [Kapdi et al., 2008]. There is a lot of potential when biogas could be made viable as a transport vehicle fuel like CNG by compressing it and filling into cylinders [Vijay 2007]. Rice chaff is the dry scaly protective casings of the paddy seeds, the ripe seed in paddy is surrounded by thin, dry scaly bracts called (Glumes, lemmas and paleas) separating the loose chaff from the grain is called winnowing. The general composition of rice chaff, rice husk and rice straw are crude protein, crude fat, crude fiber, ash pentasans, cellulose and lignin reported by [Pillaier, 1988]. The percentage of composition varies slightly between them, more percentage of cellulose, protein and fat presents, resulting in more methane production from the biogas
*Corresponding author Email: viveshanmugam@gmail.com generated. Due to higher percentage of lignin content in rice husk compared to the other residues, it has distinctive structural characteristics makes them resistant to attack by anaerobic microorganism [Yanfeng He et al.,
2009.]. The performance of rice husk reported relatively low, due to unfavorable nonlignin-carbon to nitrogen ratio
[Alexander M,1977], reported that the outstanding microbiological characteristics of lignin are resistance to enzymatic degradation. It is observed that due to synergistic effect in the co-digestion process the methane yield will be more as compared to single digestion
[Rongping Li et al., 2009]. Therefore this work was carried out to explore the potential of biogas production from co-digestion of cow dung with rice chaff, rice straw and rice husk. To study the cumulative biogas generation during fermentation, other parameters like temperature, pH, pressure and retention time.
MATERIALS AND METHODS
Experimental and analysis
The following materials were used cow dung collected, dried and crushed mechanically. Rice chaff was obtained

Vivekanandan and Kamaraj 115
Table 1. Physiochemical analysis for rice crop residues as co-digester with cow dung
Case (i) cow dung / rice chaff
Case (ii) Cow dung / Rice straw
Case (iii) Cow dung / Rice husk
Parameters influencing the Biogas Initial
Production
Nitrogen (%)
Carbon
4.35 content (%) pH
Ash (%)
6.49
6.50
0.80
Moisture (%) 89.60
Phosphorous
(%)
0.07 potassium
0.0118gm
/100gm
Case (i)
Fermented slurry
4.60
7.30
5.30
0.99
88.59
4.38mg/
100gm
13.43mg/
100gm
Volatile solid
(%)
Total Solid
(%)
93.20
97.09
91.80
72.70
Initial
0.28
5.33
5.19
1.00
93.00
2.27
100gm
86.15
89.32
Case (ii)
31.25mg/
Fermented slurry
0.91
6.62
6.62
0.50
71.75
5.17
52.89mg/
100gm
87.06
84.00
Initial
0.94
3.98
6.50
3.70
88.85
0.04
0.012gm/
100gm
64.99
87.86
Case (iii)
Fermented slurry
2.62
5.31
7.20
3.50
84.0
0.37
46.80
74.23
92.18
Table 2. Percentage of the different component of Biogas from three different rice crop residues using gas
Chromatography
Rice crop residue / cow dung
Case(i)
Case(ii)
Case (iii)
Carbon dioxide(CO
2
20.0
17.7
28.20
)(%)
Hydrogen
Sulphide H
2
0
0.2
0 as waste from rice crop, mixed with water in the ratio of weight by volume 1:2 and boiled, rice husk and rice straw also taken from rice crop. All these waste were digested
3 in 0.9m
capacity of bio digester. A gas chromatograph was used for gas analysis, AVL DIgas analyser 444, gas collecting cylinders, delivery tubes, trough of water, compression and pressure gauge, were used to store the biogas in the cylinder.
S(%)
The slurry of cow dung obtained by diluting it in the ratio of 1:2 as a co-digester for all the three cases, rice crop residues case. (i) cow dung and rice chaff 50:50 percent was mixed in the ratio of 1:2 case(ii) cow dung and rice straw 50:50 percent was mixed in the ratio of 1:5
. case (iii) cow dung and rice husk 70:30 percent was mixed in the ratio of 1:2, 600kg, 500kg and 400kg of slurry of wastes respectively were charged into the bio digester. The temperature of the digesting substrates was measured through the temperature measuring devices.
Carbon monoxide
(%)
4.2
6.5
2.8
CO
Methane other components(%)
75.8
75.5
63.30 and
The experiment setup was left and the gas volume monitored daily for 70 days 60 days and 70 days respectively. The cumulative gas production obtained from the three substrates was case (i), case (ii) and case
(iii) respectively. The curves obtained over the period of observation are presented for all the three in figures 1, 2,
3 and 4.
Both the fresh and digested slurry were analyzed for dry matter , nitrogen, carbon, phosphorous , volatile solid,
Total solid, ash, pH and moisture by standard procedures
[APHA, 1998 and Royal 1971]. It was done in
Department of Civil Engineering, Environment laboratory,
Annamalai University, the percentage content of these components mentioned above was recorded in Table1.
Gas production was measured at intervals of about 24 hours by volume displacement methods, the temperature of the gas being recorded and the volume corrected to a standard temperatures of (25-35 o
C) which is within the

116 Int. Res. J. Biotechnol.

Vivekanandan and Kamaraj 117
Figure 3 . Change in pH with respect to days
Figure 4. Cumulative gas production
RESULT AND DISCUSSION
The result of the cumulative yield in metre cube of the (i)
Cow dung / Rice chaff (ii) cow dung / rice straw and ( iii) cow dung/ rice husk are drawn in figure.4 and table.3 the result indicate that the biogas produced by case(i) became flammable on the 4 th
day while the biogas from case(ii) and case(iii) became flammable on the 20 th
and
30 th
day of digestion, as obtained from the figure-3 produces more volume of biogas ( 3.8 m
3
) for 60 days period of digestion followed by case(ii) as (3.4 m
3
) for 70 days period of digestion. While case (iii) produced the smallest volume of 1.5m
3
. Rice husk acted as a good inoculum because it increases the number of microbes in the digestion and made the biogas process faster, this microbes quicks the digestion and made the biogas generated to be combustible from the 30 th
day to the end of the digestion. [Ezekoye et al., 2006] have reported that without adding inoculum, it takes a longer day before the biogas produced will be. The analysis of biogas components produced from the three case show that case(i) 75.8% CH
4
and 20.0%, case(ii) 75.5% of CH
4
and less than 17.7% of CO
2
while case(iii) has 63.29% of CH
4 and less than 28.2% of CO
2
, this is an indication that the

118 Int. Res. J. Biotechnol.
Table 3. Total biogas production with flammable time and retention time
Rice residue cow dung
Case i
Case ii
Case iii crop
/
Flammable time
(day)
4
20
30
Retention time
(days )
60
70
70 carbon oxide produced by the three different proportion are almost the same amount.
The results of the physiochemical analysis in Table 1
Volume of biogas
Total Vol.
Biogas stored
( m
3
)
Produced
( m
3
)
0.75 3.83
0.76
0.76
3.40
1.50 show that the nitrogen, prosperous and potassium of the three cases were enhanced. After digestion this implies that the slugged from the 3rd case could serve as better fertilizers.
The rate of biogas production depends partly on the solids concentration of the microorganism [AOAC, 1980].
Total solids content is an important parameter that affects biogas production. The amount of methane to be produced depends on the solids present in the waste and their digestibility or degradability [Garba,1999].
Figure 1 shows the fluctuation of slurry temperature with retention time for the three cases. The pH values obtained during the experimental study are presented in figure-3 from figure-3 it is observed that the pH of the case (iii) sample were low and dropped below. Below pH
7.0 within the first 4 weeks. The reason for the low pH values at the beginning of digestion is attributed to the fact that initially the acid forming bacterial will be breaking down the organic matter and producing volatile fatty acids.
As a result the general acidity of the digested material will increase and the pH will fall below neutral.
Figure 2 shows the weekly pressure of the three samples case(i) has the highest pressure of 0.43 bars followed by case(ii) which has pressure of 0.3 bars and the least in case(iii) 0.17 bars.
In Figure 4 cumulative biogas production shows that as retention time increased the cumulative biogas equally increased.
The performance of the biogas plant is very satisfactory the problem of rushing or corrosion which affects the production of biogas was ruled out because of plastic
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