Synergistic effect in anaerobic co-digestion of rice straw and dairy manure - a batch kinetic study

Methane yield of seven co-digestion mixture proportions (1:0, 5:1, 3:1, 1:1, 1:3, 1:5, and 0:1) of rice straw and dairy manure was investigated at a total solids (TS) loading of 8%. Methane yield was improved by 50–57% and 9–10% with co-digestion at mixture proportions of 1:1,1:3 and 1:5 compared to mono digestion of rice straw and dairy manure, respectively. The modified Gompertz model accounted well for the kinetic behavior of methane yield with an R² of 0.99 and Root Mean Square Error of 0.06–1.70. It was observed that the co-digestion caused a reduction in lag phase time and improvement in the maximum methane production rate. The positive synergistic effects are a result of nutrient balance with the co-digestion of dairy manure and rice straw.