Effect of Substrate/Water Ratio on Biogas Production from the Mixture Substrate of Rice Straw and Salvinia molesta

Abstract

The substrate/water (S/W) ratio is one of the affecting parameters in anaerobic digestion (AD) since it affects the concentration of total solids (TS) in the biogas feedstocks. The appropriate S/W ratio has to be found to result in a high biogas yield. The goal of this study was to look into the influence of S/W ratio on biogas production from mixture substrate of rice straw and Salvinia molesta. Ratio of S/W was varied to be 1/7 w/v (TS 9.67%w/w), 1/10 w/v (TS 7.52%w/w), 1/13 w/v (TS 6.15%w/w), 1/16 w/v (TS 5.20%w/w). The results showed that S/W of 1/7, 1/10, 1/13, 1/16 resulted a total biogas yield of 22.86, 38.67, 42.71, 43.69 mL/g TS respectively. Decreasing TS from 9.67 %w/w (S/W of 1/7) until 6.15%w/w (S/W of 1/13) could increase the TS removal from 31.03% until 55.66%. However, at TS 5.20%w/w (S/W of 1/16), the TS removal was lower than that at TS 6.15%w/w (S/W of 1/13). The modified Gompertz (R2 = 0.94 – 0.98) can predict evolution of biogas production with higher precision than the first order kinetic (R2 = 0.91 – 0.98). The optimum TS was successfully predicted to become 5.40%w/w.