Technique on Recycle of Leachate in Biogas Production from Rice Straw with Dry Anaerobic Digestion

The rice straw can be used for production of biogas. The recycle of the leachate may enhance the rate of biogas production for rice straw with dry anaerobic digestion. The effects of different leachate recycle volumes and methods on biogas production from rice straw with dry anaerobic digestion were investigated. There was no obvious difference in the cumulated biogas production among the leachate recycle volumes (0, 0.2, 0.4, 0.6, 0.8 L·d-1) in room temperature after 43 days of anaerobic digestion. In contrast, there were marked differences in the biogas production among the different leachate recycle methods. The rates of biogas production with dry anaerobic digestion in room temperature and 20% TS after 84 days were increased by 9.53% for the recycle everyday, 23.13% for the recycle while biogas production decreasing and 12.74% for the recycle using two-phase method compared to no-recycle. The changes of COD, VAS and pH in leachate were consistent with the rates of biogas production in different leachate recycle methods. The contents of degradated cellulose, hemicelluloses and lignin in rice straw were the highest in the leachate recycle while biogas production decreasing, followed by the recycle using two-phase method, the recycle everyday and no-recycle. Hence, the recycle of leachate while the rate of biogas production decreasing could maximumly enhance the biogas production and degradation of cellulose for rice straw using dry anaerobic digestion.