Effects of ratios of manure and straw, urea and cellulose on biogas yields at different temperatures

How to increase biogas yield and improve the utilization efficiency of crop residues and other agricultural wastes is a major problem in modern circular agricultural field. A simulation experiment using self-designed constant-temperature anaerobic fermentation equipment was conducted in indoor conditions. Effects of different ratios of chicken manure to crop residues under different temperature on the gas production were studied. The effect of adding urea and cellulose to biogas digester was also investigated. The crop residues included rice straw, wheat straw and corn straw. Results showed that the biogas production of each treatment rose with the increase of temperature in the range of 20～35℃. The highest yield was observed when the ratio of chicken manure to straw (dry matter quantity) was 2︰1 at 35℃, among which the ratio of chicken manure to corn straw at 2:1 had the maximal yield, up to 51120 mL in 50 days and the fermentation material was 2.5 kg. Both adding urea (2.5 g) and cellulose (2 g) into 2.5 kg fermentation material could significantly increase yields in the middle of fermentation, after fermentation for 28 days, the average increment was 99.8% and 40.8%, respectively. Compared with other groups, the group with the ratio of chicken manure to wheat straw at 2:1 had the highest increasing range, that is, 261.2% and 117.3%, respectively. Dynamic changes of the pH value were found at 20℃, with average pH value 6.8 at earlier fermentation stage, 6.4 at middle stage, then it slowly rose to 6.6. Therefore, suitable temperature, reasonable ratio of manure to straw as well as adding proper amount of urea and cellulose can effectively improve the biogas yield.