PERFORMANCE EVALUATION OF CO-SUBSTRATES AND INOCULUMS IN BIOGAS PRODUCTION FROM DISTILLED CASSAVA WITH SOLUBLES

Abstract

High rate of generation with adverse environmental and pollution characteristics of distillery wastewater has continued to
worry distillery operators worldwide. This work investigated the comparative performances of cow dung versus poultry
droppings as co-substrates and sewage sludge versus ruminal fluids of cattle as inoculums, in the anaerobic treatment of
distilled cassava with solubles obtained as wastewater from a cassava-based ethanol distillery. D-optimal mixture
design was used to generate ten (10) randomly executed digestion experiments for each co-substrate and each inoculum.
Interactive effects of the proportions of the distilled cassava with solubles (50-100%) and each co-substrate (0-50 %w/w)
on methane yield were first investigated, and the experimental condition that gave maximum yield was used in the
experiments for inoculum performance evaluations within a range of 0-30 %w/w. Results showed that the distilled
cassava with solubles has a relatively high carbon-to-nitrogen ratio (43.5:1) and thus required co-substrates for its
effective anaerobic digestion. While maximum methane yields were recorded at the same co-digestion ratios of 62.5:37.5
for both co-substrates, its value for poultry dropping was higher at 11.66 ml/gVS) than for cow dung at 10.54 ml/gVS.
Furthermore, using pre-degassed ruminal fluids of cattle and sewage sludge as inoculum respectively increased methane
yield to 12.78 and 11.14 ml/gVS. The study concluded that poultry dropping had a more positive contribution to biogas
generation than cow dung while the use of inoculums enhanced biogas production, with the ruminal fluids of cattle
performing better than the sewage sludge.