Thermophilic anaerobic co-digestion of garbage, screened swine and dairy cattle manure

Methane fermentation characteristics of garbage, swine manure (SM), dairy cattle manure (DCM) and mixtures of these wastes were studied. SM and DCM showed much lower volatile total solid (VTS) digestion efficiencies and methane yield than those of garbage. VTS digestion efficiency of SM was significantly increased when it was co-digested with garbage (Garbage: SM=1:1). Co-digestion of garbage, SM and DCM with respect to the relative quantity of each waste discharged in the Kikuchi (1: 16: 27) and Aso (1: 19: 12) areas indicated that co-digestion with garbage would improve the digestion characteristic of SM and DCM as far as the ratio of DCM in the wastes was maintained below a certain level. When the mixed waste (Garbage: SM: DCM=1:19:12) was treated using a thermophilic UAF reactor, methanogens responsible for the methane production were Methanoculleus and Methanosarcina species. Bacterial species in the phylum Firmicutes were dominant bacteria responsible for the digestion of these wastes. As the percentage of garbage in the mixed wastes used in this study was low (2-3%) and the digestion efficiency of DCM was obviously improved, the co-digestion of SM and DCM with limited garbage was a prospective method to treat the livestock waste effectively and was an attractive alternative technology for the construction of a sustainable environment and society in stock raising area.