FEASIBILITY OF ANAEROBIC BATCH CO-DIGESTION OF PEAT AND RICE STRAW FOR BIOGAS PRODUCTION

The influence of peat addition during anaerobic mesophilic digestion of rice straw was studied in this work. The work was performed in batch reactors of 1000 mL capacity, during a period of 49 days. Batch mono-digestion experiments were performed at 35 +/- 1 degrees C and the initial total solid loading (TSL) ranged from 1.2% to 8.0%. Batch co-digestion experiments were performed at 35 +/- 1 degrees C and the initial TSL of 8% with peat proportions ranged from 25% to 85% of total solid (TS). For mono-digestion of rice straw, a maximum methane yield of 231.77 mL/g TSadded was obtained at initial TSL of 3.6%, and acidification was found at initial TSL of 8.0% with the lowest pH value of 5.24 on day 3. There was nearly no biogas produced by peat digested alone. Co-digestion improved the methane yields and the biogas production rate by 5.19 %-13.29% and via improving methanegenic activity and enhancing hydrolysis rate compared with mono-digestion of rice straw. With peat addition, volatile fatty acids (VFAs) concentration, total alkalinity (TA) and pH value decreased. The maximum biogas yield of 385.75 mL/g TSadded and methane yield of 248.58 mL/g TSadded were obtained for 40% peat addition and 60% rice straw. However, over peat addition was adverse to the anaerobic process with 6.24%-19.86% biogas yield reduction. It was concluded that proper peat addition is beneficial for improving biodigestibility and methane yield from anaerobic digestion of rice straw.