Comparison of biogas productivity of calabash waste mixed in selected ratios with sheep and donkey dungs

Abstract

Anaerobic digestion process is one of the non-thermal technologies of energy recovery to meet the ever-growing energy demand of rural areas in developing countries, particularly Ethiopia, in a green way. The aim of the present study was to investigate the effectiveness and performance characteristics of anaerobic digestion of calabash waste mixed in selected ratios with donkey and sheep dung for biogas production. Production of biogas from calabash waste, mixed with donkey and sheep dung in ratios 1:1, 2:1, 3:1, and 4:1 by mass, was investigated in a 45 L plastic container using a retention period of 20 days and within the mesophilic temperature range. The average biogas yield was significantly (P≤ 0.05) influenced by the different mixing ratios of calabash waste with dung. The composition of gas generated from each ratio ranged (from 67.41-63.81)% CH₄, (33.00-26.01)%, CO_2, (1.06-0.40)% CO, (3.00-0.07)% H₂O, (0.06-0.02)% NH₄,(0.90-0.05)% N, (0.72-0.02)% H, (0.98-0.09) % O₂, and (0.006-0.001) % H₂S. The average biogas yield was 13.5, 11.6, 10.7, and 7.8L respectively for 1:1, 2:1, 3:1, and 4:1 mixing ratios when calabash waste was mixed with sheep dung. On mixing calabash waste with donkey dung, the average biogas yield increased to 16.2, 15.5, 12.6, and 9.8L respectively for 1:1, 2:1, 3:1, and 4:1 mixing ratios. The results show that mixing both dungs with calabash waste in a ratio of 1:1 by mass-produced the highest biogas volumes, and higher in donkey dung. The reason behind this is that higher mixing ratios meant a higher quantity of waste in the mixture which also implied increased lignin content, and this made digestion activities more difficult for the microbes. Reduction in digestion activities of the methanogen bacteria resulted in lower biogas yield. The result of the present study has shown that anaerobic digestion from calabash waste, mixed with donkey and sheep dung in ratios 1:1, 2:1, 3:1, and 4:1 by mass can form a renewable energy that is comfortable and environmentally friendly. This energy production process is found to be an easy way of replacing fossil fuels.