Operating condition optimization of water hyacinth and earthworm bedding wastewater for biogas production

Water hyacinth (WH) and nitrogen-rich earthworm bedding wastewater (EW) can be used to enhance biogas production as renewable energy source which would have replaced on the fossil fuels. In this study, an anaerobic digestion was conducted in batch system at laboratory scale in mesophilic condition (28-32 ºC) for 15 days. Response surface methodology (RSM) based on a central composite design was performed for the process optimization to maximize bio-methane potential (BMP). The individual and their interactive effects with three experimental factors in terms of TS of substrate (4-12%), particle size of WH (0.3-1.5 cm) and initial pH (6-8) were evaluated. It was found that the optimum conditions for maximum BMP of 35.50% with the highest specific methane yield of 0.12 m3CH4/kg CODremoved were found to be 8% TS of substrate, initial pH 7.0 and particle size of WH 0.3 cm. The linear effects of TS of substrate as well as their quadratic effects on BMP were significant (P<0.05), while the interactive effects of three parameters were insignificant. The coefficient of determination (R2) of 96.1% confirms that the model has a good fit with the experimental variables.