Optimisation of Biogas Production through Variation of PH, Detention Time and Ratio of Substrate to Water for Rural Utilization

Abstract

A response surface methodology (RSM) was utilized in this study for optimisation of biogas production process. The optimal values of process parameter capable of giving a high yield of biogas were established. A biodigester of 20 liters capacity capable of producing biogas from rural household domestic waste was designed, constructed and used in the study. Its major units are the anaerobic and gas collecting units. The process parameters investigated are the pH of the substrate, detention time and ratio of substrate to water while the yield of biogas was used as performance characteristics. The experiment was based on a central composite rotatable design (CCRD). The results revealed that the highest yield of biogas was obtained from a combination of detention time of 30 days, ratio of substrate to water of 1:1 and pH of 7, while the least yield of biogas of 11 cm3 was obtained from combination of detention time of 30 days, ratio of substrate to water of 1:3 and pH of 2. Numerical optimization carried out with the goal of maximizing the biogas yield revealed optimum values of detention time of 40 days, the ratio of substrate and water used; 1:2 and pH of 6.71 for biogas of 771.77 cm3 with the desirability of 0.9850. The detention time had the highest significant effects on the yield of biogas. The results of this study provided standard input process variables capable of yielding the optimum yield of biogas for the rural community.