抄録
In the present study, a life inventory analysis was conducted on the input-output data for a livestock waste treatment plant (Yagi Bio-Ecology Center, Yagi Town, Kyoto), where bio-gas is recovered from the organic waste slurry of livestock's feces and urine collected from livestock farms, and bean curd refuse from food industries through an anaerobic digestion tank and then converted into electricity with a gas-engine generator. The livestock waste treatment plant successfully achieves zero-emission because the dehydrated secondary sludge from an anaerobic digestion tank is mixed with fresh livestock wastes and converted into compost. The whole process was analyzed on the basis of a life cycle inventory model using the cumulative CO2 emission unit as an index in order to evaluate the environmental impact over the long term operation for the waste treatment process. In evaluating the environmental impact of the whole system, the initial construction of the facilities, the utility inputs such as water, electricity and fuel oils for maintaining the process facilities are also taken into consideration. It is ascertained that the livestock wastes treatment plant can definitely work as an efficient CO2 sink, while generating excess electricity at a CO2 emission unit of 0.703 kg-CO2/kWh for a long term operation and achieving zero-emission without excreting any secondary wastes. It is also indicated that the use of a fuel cell generator in place of the gas engine generator would significantly increase the amount of electricity generated and the reduced CO2 amount increases by a factor of 2.16 in comparison with that for the present gas engine generation system.
