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Comparative study of biogas production from cow dung, cow pea and cassava peeling using 45 litres biogas digester

Ukpai, P. A. and Nnabuchi, M. N.

A 45 Litres capacity metallic prototype biogas plant constructed at the National centre for Energy Research and Development, University of Nigeria, Nsukka was used to investigate the anaerobic digestion in generating biogas from three types of wastes: Cow dung, Cowpea and Cassava peeling. The experiment was batch operated and daily gas yield from the plant was monitored for 30 days. The ambient and slurry temperature, pH, and Pressure were also monitored and presented. The digester was charged differently with these wastes in the ratio of 1:2, 1:5 and 1:5 of waste to water respectively. The mesophilic ambient temperatures range attained within the testing period were 20 - 32o C and a slurry temperature range of 22 – 360 C. The result obtained from the gas production showed that cowpea produced the highest methane content of 76.2%, followed by cow dung with 67.9% content and cassava peeling has the least methane content of 51.4%. The cow dung had the highest cumulative biogas yield of 124.3 L/total mass of slurry (TMS) while cow pea had 87.5 L/TMS and cassava peeling with lowest cumulative biogas yield of 87.1 L/TMS within this retention period. During the digestion period, the volume of biogas production and the changes in pH indicate that at neutral pH, the highest peak of gas production was attained and that at slightly acidic pH range, there was no gas production. In terms of flammability, they became flammable at different period during the digestion. Cow pea was favoured in terms of volume of flammable gas production of biogas and flamed on the 7th day. These results showed that these wastes could be a source of renewable gas if managed properly since each of the waste sluggishly continued gas production after the 30 days retention time.