抄録
Objective. It is forecasted that the population of Shiga prefecture should increase until 2030. There is an apprehension that environmental load impact should also increase by population increase. In this study, we estimated future prospect of environmental load related to wastewater treatment systems in Shiga prefecture. The target year is 2003 and 2030. We proposed a new environmental efficiency indicator based on the ratio of water pollutant reduction to greenhouse gas (GHG) emission, and evaluated wastewater treatment systems by utilizing our new environmental efficiency indicator. Our estimation considers sewerage, agricultural community effluent treatment facility, combined household wastewater treatment facility and night soil treatment facility.
Results and Discussion. In 2003, 70% of the total GHG related to wastewater treatment systems in Shiga prefecture was emitted from sewerage. On the other hand, 80% to 85% of the total GHG is estimated to come from sewerage in 2030. It is estimated that the introduction of advanced treatment system accompanying water pollutant reduction (COD: 4%, T-P: 15%, T-N: 1%) should cause nearly 30% increase of GHG emission. In focusing environmental efficiency indicator based on the ratio of water pollutant reduction to GHG emission, the efficiency of sewerage is 50% to 80% higher than that of other wastewater treatment systems.
Conclusions. In this study, we estimated future prospect of environmental load and environmental efficiency related to wastewater treatment systems based on the lifecycle comparison of 8 scenarios considering future technologies and social trends such as water saving lifestyle. Our estimated results showed that the introduction of advanced treatment system for sewerage have possibilities nearly 30% increase of GHG emission. On the other hand, it was showed that water saving lifestyle should cause a definite reduction of GHG emission. We investigated a scenario in which the introduction of advanced treatment system and water saving lifestyle would spread. In comparing estimated result of this scenario with the present conduction, we could show several advantages of the environmental efficiency proposed in this study.
