Biogas Production From Co-Digestion of Cassava Residue and Wastewater: Effects of Substrate Ratios and Digestion System Configurations

Agricultural waste from cassava processing poses significant environmental challenges globally. This study investigated optimal anaerobic co-digestion parameters using batch experiments with six cassava residue-to-wastewater ratios (1:1, 1:2, 1:3, 1:4, 1:5, 2:1) tested in 20-liter digesters under mesophilic conditions for 20 days. The 1:3 cassava residue-to-wastewater ratio achieved maximum cumulative biogas production (6,200±450 mL) with 55% methane content, significantly outperforming other ratios (p<0.001). Increasing stirring speed from 50 to 120 rpm enhanced biogas yield by 31.2%, while hybrid configuration combining horizontal pre-digestion with vertical digestion increased production by 14.6% compared to conventional systems. The optimized process achieved 84.6% COD removal and 81.8% VS reduction, with VFA concentrations decreasing from 1,899 to 96 mg/L, indicating stable methanogenesis. Microbial analysis revealed enrichment of Methanosarcina species under 120 rpm agitation, correlating with enhanced performance. The integrated optimization of substrate ratio, mixing intensity, and reactor configuration provides a practical framework for industrial-scale cassava waste valorization, contributing to sustainable waste management and renewable energy production.