Biogas Production from Co-digestion of Cattle Manure and Food Waste
Zeru Brhane, Dawit
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There is a growing global demand of bioenergy production from animal manures and municipal solid wastes. In this study, the potential of cattle manure, food waste and their co-digestion for biogas production was investigated. The substrates were characterized for their physic-chemical properties, total solids (TS), volatile solids (VS) and C/N ratio and they were assessed in five combinations for their suitability to biogas production in 500 ml batch digesters. The five digesters of mixing ratios R1=1:0, R2=1:1, R3=2:1, R4=1:2 and R5=0:1 were operated at three different temperature systems (35 0C, 40 0C and 45 0C) to investigate the effect of substrate level on the on biogas productivity and methane yield. Biogas production and its methane fraction was measured using airtight syringe sucking from the gas collecting plastic bags connected to the digesters, and gas analyzer regularly for 35 days. The amount of biogas obtained from the five mixing ratios R1, R2, R3, R4 and R5 respectively is 1.97 L, 6.48 L, 3.96 L, 11.22 L and 2.52 L at 35 0C; 3.16 L, 8.65 L, 5.81 L, 13.25 L and 4.01 L at 40 0C; 2.55 L, 6.90 L, 4.67 L, 9.4 L and 3.56 L at 45 0C. Highest biogas productivity and methane yield was achieved from the AD system operated at 40 0C for all the respective digesters. The highest total biogas yields were attained from R4 (33.34% food waste: cow manure 66.66%) at 40 0C as 13.25 L followed by R4 (50 % cow dung: 50 % food waste) at 35 0C as 11.22 L and the lowest was from R1 (food waste alone) at 35 0C as 1.97 L. The average values of methane yield obtained from the mixing ratios 1:0, 1:1, 2:1, 1:2 and 0:1 were 57.76%, 55.76%, 55.25%, 58.63%, and 53.3% at 35 0C; 51.62%, 60.1%, 56.84%, 62.93%, and 53.26% at 40 0C; 49.43%, 54.78%, 52.28%, 56.76% and 49.63% at 45 0C. Comparatively, slightly higher methane yield was attained from the co-digestion of FW to CM in 1:2 and 1:1 ratios at 40 0C temperature. Statistical design of the experiments and data analysis was investigated using general factorial method of DOE. Statistical test revealed that the model "F values" for the two responses i.e. biogas productivity and methane yield in the biogas were statistically significant (P<0.05). This experimental finding showed that co-digestion of CM with FW improves the stability and productivity of anaerobic digestion system than mono-substrate digestion.