Field study on the promotion of biogas methane production from the anaerobic co-digestion of rice straw and pig manure with composite additives

Methane production performance can depend mainly on the degradation of rice straw and pig manure during anaerobic fermentation in sustainable agriculture. In this study, a field experiment was conducted to clarify the effects of composite additives on methane production performance for anaerobic fermentation of mixed rice straw and pig manure. A field facility of anaerobic fermentation was utilized to produce the biogas. Four composite additives were selected, including HB (humic acid + biochar), TB (Tween 20 + biochar), THB (Tween 20+humic acid + biochar), SB (straw composting agent + biochar), and CK (control) treatment. The parameters were regularly measured after fermentation under each treatment, including gas production, methane concentration, and straw degradation rate. A systematic investigation was conducted to explore the effects of composite additives on the biogas production after anaerobic fermentation of rice straw and pig manure in the field. The results showed that TB treatment performed the best. 1) Temperature was dominated in methane production from anaerobic co-fermentation of mixed straw and pig manure in the field. But composite additives accelerated both the initiation and the maximum output of gas production during anaerobic fermentation. Peak gas production was significantly higher in all treatments than that in the CK; 2) Cumulative gas and biomethane production were also higher in each treatment than those in the CK. Among them, TB treatment shared the highest cumulative gas and methane production, which were 33.51% and 35.82% higher than the CK, respectively; 3) The composite additives significantly promoted the degradation of rice straw. Among all treatments, TB (Tween 20 + biochar) exhibited the highest degradation rates for cellulose, hemicellulose, and lignin, reaching 38.89%, 31.56%, and 21.23%, respectively, which were 9.24, 7.38, and 7.93 percentage points higher than those of the control group, respectively. Principal component analysis showed that four composite additives enhanced the degradation of rice straw and pig manure during anaerobic fermentation, thereby improving methane production performance.