Effect of Additives on Anaerobic Co-digestion of Rice Straw and Cattle Dung for Biogas Production: A Seasonal Performance Analysis

Abstract

Anaerobic co-digestion of agricultural residues with appropriate organic additives is an effective approach for enhancing biogas production and facilitating sustainable waste management. This study investigated the effects of poultry waste, sewage sludge and neem leaf litter as additives in the anaerobic co-digestion of rice straw and cattle dung at ambient temperatures varying in the winter (7°C-25°C) and summer (29°C-47°C). Seven different treatment combinations were tested in batch digesters to evaluate seasonal variations in biogas production, substrate degradation, microbial activity and methane content. During winter, the binary combination of cattle dung and rice straw (T3; 4:1) generated the maximum cumulative biogas (124.4 L per total volume) with a volumetric productivity of 0.423 L L-1d-1. This implies efficient lignocellulosic degradation under reduced temperatures. In contrast, the five-substrate mix of cattle dung, rice straw, poultry waste, sewage sludge and neem leaf litter (T7; 4:1:1) excelled during the summer, producing the maximum cumulative biogas (74.1 L per total volume) and methane content (61.3%). Elevated dehydrogenase activity and bacterial abundance were detected in T3 during the winter and cattle dung + paddy straw + poultry waste + sewage sludge + leaf litter of neem (T7) during the summer, demonstrating that these substrate combinations promote microbial activity. The research findings indicate that the substrate composition and seasonal temperature have an effect on anaerobic digestion performance. While the cattle dung-rice straw combination performed better in cooler temperatures, the addition of supplementary organic additives enhanced methane yield in hot weather by improving nutritional balance and microbial activity. These results provide significant insights into optimizing seasonal anaerobic co-digestion systems for agricultural waste valorization and renewable biogas production.