下水処理に関わる汚染の社会的費用の評価

Abstract

Recently the influence of treated wastewater on environment is not trivial. On the other hand, sewage treatment needs much electric energy generated by fossil fuel combustion, so that greenhouse effect gases are produced. Sewage treatment, therefore, can be considered to give negative impacts on the environment of water bodies and the atmosphere. The objective of this study is to estimate economic costs of pollution by sewage treatment. In this study, an economic cost estimation of pollution by sewage treatment is defined as “social cost.” Social costs of water quality deterioration with respect to COD, total-nitrogen, and total-phosphorus as well as a greenhouse effect gas, CO2, are investigated. The social cost of water quality deterioration is a total of each cost to treat wastewater by the most appropriate method, a single-stage pre-denitrification process with coagulant dose, up to each recommended water quality standard, which is considered to be a favorable water quality at present. The social cost of CO2 release is that to remove and recover CO2 by aqueous K2CO3 absorption/stripping method. By summing them up, the social cost of pollution to unit volume of treated wastewater is estimated for several sewage treatment systems. By summing social cost and treatment cost, a synthetic cost is obtained. As a result, it is shown that the relationship between social costs and wastewater treatment alternatives can be recognized with ease by use of the estimating method of social cost.