抄録
At the COP3 conference held in Kyoto in December 1997, reduction targets were set not only for carbon dioxide (CO2), but also methane (CH4) and nitrous oxide (N2O) . As processes that treat relatively large quantities of organic material and nitrogen, wastewater treatment processes are huge potential sources of these gasses. It is feared that in the years to come the quantities of CH4 and N2O produced will both rise as a result of an increase in the use of treatment that combines an anaerobic process with the conventional aerobic only treatment process to encourage nitrification and denitrification as a measure to prevent the eutrophication of closed water areas. This study, which has been carried out to clarify differences in the treated water quality and CH4 and H2O discharge properties of aerobic only treatment and a treatment method combining aerobic and anaerobic processes, was a comparative analysis of two treatment methods: the conventional activated sludge process and the A2O process that is a biological nitrogen and phosphorus removal method. The quantity of CH4 discharged by the A2O process was found to be about 1/3 of that discharged by the conventional process, presumably because CH4 was consumed as the hydrogen donor in the denitrification reaction. The quantity of N2O discharged from the A2O process was found to be about 1/8 of that discharged by the conventional process, presumably because the degree of accumulation of NO3- in the nitrification reaction has a big effect on the quantity of N2O produced. Based on these results, it was concluded that by appropriately combining anaerobic conditions with aerobic treatment, it is possible to link N2O reduction measures and eutrophication prevention measures in the sewage treatment.
