Effective management of faecal sludge through co-digestion for biogas generation

Abstract

The use of fossil fuels as primary energy source has led to global climate change and human health problems. Renewable energy resources appear to be the efficient solutions to the problems resulting from the use of fossil fuels. In this study, biogas production efficiency from faecal sludge and its combination with three feed stocks was evaluated. Three feedstock materials (cow dung, cow intestinal waste and mixed organic waste) were fed into a 2 m³ capacity digester to mix with faecal sludge for biogas production. Standard methods were used to determine chemical and biological qualities of influent and effluent slurries. The biogas produced was analyzed using multi-gas analyzer to determine the concentrations of CO, CO₂, CH₄ and H₂S.Methane formed major component of the biogas produced by all the substrates (40-70%) followed by carbon dioxide (20-30%) and H₂S (8-10%). The macronutrients of the bio-slurries produced ranged from Carbon (5.3 + 0.11- 6.0 + 0.01%), Nitrogen (0.36 + 0.1 - 0.46 + 0.1%), Phosphate (0.11 + 0.02 – 0.24 + 0.11%) and Potassium (0.1 + 0.01 - 0.4 + 0.1%). The Carbon/Nitrogen ratio of the bio-slurries produced ranged from 12:1 to 15:1. The microbial contents of faecal sludge, only slurry had lowest total count of bacteria of 1.2 x 10^-2cfu/100ml. conclusively, co-digestion was effective in converting faecal sludge mixed the three feed stocks into pure biogas and nutrient rich bio-slurries as organic fertilizer.

Keywords: Cow-dung, Biogas, Escherichia coli, Faecal-sludge