Mathematical modelling and parametric optimization of biomethane production with response surface methodology: A case of cassava vinasse from a bioethanol distillery

Abstract

The high rate of cassava vinasse (CV) generation from distilleries and its anti-environmental characteristics threaten the sustainable production of bioethanol. In this study, the production of biomethane via anaerobic digestion (AD) of CV was modelled and optimized with response surface methodology (RSM). The D-Optimal experimental designs produced 27 digestion experiments randomly executed to investigate the effects of CV (55–100%), poultry dropping, PD (0–45%), organic loading rates, OLR (2–10 gVS/l.d), inoculum to substrate percentage, ISP (10–30%) and hydraulic residence time, HRT (20–30 days) on methane yield (MY). Experimental data were fitted to a quadratic model and its significance was assessed using the analysis of variance (ANOVA), and lack of fit test. Model efficiency was experimentally validated in the laboratory. Results showed that the CV had a high carbon-to-nitrogen ratio (C/N) of 43.5:1 and a biochemical methane potential (BMP) of 247.1 Nml/gVS demonstrates the potential for biogas production. The optimum conditions established for biomethane production were 55% CV, 10% OLR, 30% ISP and 20 days HRT with a MY of 254.4 ml/g VS. For the developed model, a coefficient of determination (R2), standard deviation (SDev.) and p-value of 0.9925, 4.91, <0.0001 respectively indicate high predictive accuracy. The study provided vital information for the bioethanol industry and the environmental agencies, on alternative treatment and utilization options for CV.