In order to investigate the effect of feedstock ratios in biogas production, anaerobic co-digestions of rice
straw with kitchen waste and pig manure were carried out. A series of single-stage batch mesophilic
(37 ± 1 C) anaerobic digestions were performed at a substrate concentration of 54 g/L based on volatile
solids (VS). The results showed that the optimal ratio of kitchen waste, pig manure, and rice straw was 0.4:1.6:1, for which the C/N ratio was 21.7. The methane content was 45.9–70.0% and rate of VS reduction was 55.8%. The biogas yield of 674.4 L/kg VS was higher than that of the digestion of rice straw or pig manure alone by 71.67% and 10.41%, respectively. Inhibition of biogas production by volatile fatty acids(VFA) occurred when the addition of kitchen waste was greater than 26%. The VFA analysis showed that,in the reactors that successfully produced biogas, the dominant intermediate metabolites were propionate and acetate, while they were lactic acid, acetate, and propionate in the others.