Influence of Garden Green Wastes Addition and Freeze-thaw Pretreatment on Food Waste Anaerobic Digestion Efficiency

The influences of three different garden green wastes, including leaves of eucalyptus, canna lily, and weed mixture of alligator alternathera, vergate wormwood and tropic ageratum, on anaerobic digestion of food waste were investigated in a batch test. The results indicated that the treatment with weed mixture had the highest capacity to produce methane from volatile solid (VS) degraded, with the production rate of 827.0 mL/g (VS). In the treatments with leaves of eucalyptus and canna lily, the VS-methane production rates were at 307.9 mL/g(VS) and 287.3 mL/g(VS), respectively. The freeze-thaw pretreatment effectively improved methane production by 25.0% and 85.4% in the treatments with weed mixture and canna lily leaves, respectively. The energy production benefits were increased from 6 106 kW?h/t(VS) to 7 633 kW?h/t(VS) for the weed mixture treatment, and from 1 694 kW?h/t(VS) to 3 141 kW?h/t(VS) for the canna lily leaves treatment. Therefore, the addition of herbal garden waste and freeze-thaw pretreatment could enhance energy production benefit for anaerobic co-digestion of food wastes, and thus be an effective way to convert municipal solid wastes into renewable energy.