Biogas and quality fertilizer production from dry anaerobic digestion of rice straw with nitrogen addition

Dry anaerobic digestion of rice straw with nitrogen additions of swine manure and/or urea at different ratios (0:0, 1:0, 4:1, 7:3, 6:4, 5:6, 4:7, 0:1) were studied through batch experiments. Biogas production, digestate composition of cellulose, hemicellulose and lignin, C/N ratio and nutrient content were evaluated. The results indicated that, the treatment of 7:3 was the optimal ratio to generate biogas efficiently, whereas the treatments of 1:0 and 0:1 caused severe inhibition. Urea could significantly promote lignin degradation, accelerate hydrolysis process and increase nitrogen contents in the digestates, and the C/N ratios were more suitable for crop fertilization than single addition of swine manure. The digestate from the treatment of 7:3 also had the highest quality of final bio-fertilizer based on the analysis of organic amendment properties, fertilization effect and innocuousness. © 2020 Elsevier Ltd