Continuous Anaerobic Digestion of Food Waste and Paper Waste under Mesophilic-Dry Condition

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With increasing concerns regarding the limited capacity of landfill, conservation of resources, and reduction of CO2 emissions, dry anaerobic digestion of organic solid waste has recently been gaining considerable attention. However, there have been few reports on continuous operation and most have involved operation under thermophilic condition. In the present study, a continuous dry anaerobic digestion system treating a mixture of food waste and paper waste was operated under mesophilic condition. For easy injection of a solid type substrate, the feed was diluted six-fold with the sludge inside the reactor, and then, fed into the reactor. During the operation, hydraulic retention time (HRT) decreased as follows: 150, 100, 60, 40, and 30 d at a fixed substrate concentration of 30% total solids (TS), corresponding to a solid loading rate (SLR) of 2.0, 3.5, 5.0, 7.5, and 10.0 kg TS/m3/d, respectively. Up to 40 d of HRT, biogas production proportionally increased as SLR increased, but at 30 d of HRT, biogas production decreased. At further operation, instead of controlling HRT, substrate concentration was increased to 40% TS, which was found to be a better option for increasing the treatability. The system could achieve a stable CH4 production yield of 0.27 m3 CH4/kg TSadded and 0.25 m3 CH4/g CODadded, and over 75% of volatile solids (VS) reduction.