Development of Anaerobic Digester for Co-Digestion of Organic Residues for Biogas Production

Abstract

The growing world demand of sustainable energy and the dire necessity of having efficient methods to manage wastes have compounded the attention of anaerobic digestion as a promising waste-to-energy approach. Although it has been conventionally employed to stabilize single feedstock, there is a common limitation to anaerobic digestion in the yield of methane and the stability of the process under heterogeneous organic wastes. To mitigate these challenges, this study focused on the design, construction and performance evaluation of a small-scale anaerobic digester suitable for co-digestion. The equipment constructed was a 220-litre cylindrical polyethylene reactor, with a L-shaped gas outlet and a dual compartment purification system to maintain high-quality gas. It was tested by co-digesting pig manure, water hyacinth (Eichhornia crassipes) and Gmelina arborea sawdust in the ratio 4:2:1. The results showed that the substrate composition (pig dung: water hyacinth: sawdust) balanced the carbon-to-nitrogen ratio and produced high quality biogas after 18 days of retention. The analysis through Gas Chromatography-Mass Spectrometry established the presence of methane and carbon-dioxide concentrations of 65.58 wt% and 28.29 wt%, respectively and trace amounts of other gases. Flammability test on the gas shows a steady bluish flame, indicating sufficient combustive power. This study has proven that co-digestion is a low cost, replicable approach to renewable energy generation and sustainable management of organic wastes in resource constrained settings.