Abstract
On the basis of a worldwide trend of the indirect and direct potable reuse of wastewater, methodologies of risk assessment and management for chemical and microbial risk in water were discussed. First, the definition of risk was described, and the characteristics of health risk caused by consuming drinking water were summarized. Second, the methods to set drinking water quality standards and a recent implementation of the precautious principle were explained. An example of an indirect potable reuse system proposed by the authors was shown. Only 17 chemicals, including disinfection by-products, among a tremendous number of chemicals in wastewater were selected as target chemicals. A procedure for estimating the required and sufficient removal efficiencies of the water treatment process to produce potable water, which is also the procedure for avoiding overtreatment, was described. Third, the characteristics of microbial risk were explained, and the significance of disability-adjusted life years (DALYs) , by which chemical risk and microbial risk can be compared, was highlighted. A relationship between the safety level estimated using DALYs and the required treatment level was described. Furthermore, it was pointed out that the characteristics of people’s risk perception should be taken into account when discussing acceptable risk levels.
