Effect of Stirring on Organic Matter Conversion in Horizontal Biodigesters

This study investigated the effect of localized mechanical stirring on the performance and organic matter conversion pathways in two bench-scale horizontal flow anaerobic biodigesters treating swine wastewater (SW). Two reactors (total volume of 10.6L; working volume of 7.95 L) were operated in parallel for 150 days under identical conditions (hydraulic retention time [HRT] = 25 days; volumetric organic loading rate [VOLR] = 0.3-0.5 g V L^-1 day^-1 of TVS): one equipped with mechanical mixing (HF_w) and the other operated without mixing (HF_w/o). After system stabilization, no statistically significant differences were observed between the reactors with respect to hydrolysis and methanogenesis (%) or biogas production and composition. Mass balance analysis demonstrated that HF_w accumulated fewer solids within the reactor (5.5% of the applied chemical oxygen demand [COD]) compared with HF_w/o (13.6%). These findings indicate that mechanical stirring effectively mitigates sludge accumulation without compromising overall treatment performance or biogas generation.