Optimization of Biogas and Biomethane Yield from Anaerobic Conversion of Pepper Waste Using Response Surface Methodology

Anaerobic digestion is a critical method for producing bioenergy from organic waste; however, its efficiency is highly influenced by several factors. This study aimed to enhance the AD process using the removed solid phase generated by the canning plant Amor Benamor (CAB) during the production of harissa. This research sought to identify the optimum pH conditions and inoculum/substrate ratio (I/S) for achieving the maximum biogas production while ensuring a high methane yield, using response surface methodology (RSM) and numerical optimization. The batch anaerobic digestion of pepper waste as a substrate and sewage sludge as an inoculum was conducted. The 11 experimental runs generated by Design Expert Software were conducted in reactors with a capacity of 150 mL and a working volume of 90 mL, under thermophilic conditions. The effects of pH in the range of 7 to 8 and an I/S ratio in the range of 0.167 to 0.5, and their interaction in terms of biogas and methane yield (mL/g VS), were evaluated using a central composite design (CCD). The findings highlighted that a pH of around 7.5 and an I/S ratio of 0.48 could give the highest predicted yield of 884.35 mL/g VS for biogas and 422.828 mL/g VS for methane. These predicted values were confirmed with an experimental validation run which exhibited a deviation of less than 5%. These results offer new opportunities for enhanced biogas production from accumulated waste, contributing to the growth of sustainable energy alternatives.