Fuzzy synthetic evaluation of disinfection by-products--a risk-based indexing system.

Disinfection by-products (DBPs) are formed when disinfectants such as chlorine, chloramine, and ozone react with organic matter in water. Chlorine being the most common disinfectant used in the drinking water industry worldwide, significant attention has been focused on chlorinated DBPs. A new indexing method using fuzzy synthetic evaluation is proposed to determine the health risk associated with the two major groups of chlorinated DBPs--trihalomethanes (THMs) and haloacetic acids (HAAs). Initially, membership functions for cancer and non-cancer risks associated with THMs and HAAs are used to establish the fuzzy evaluation matrices. Subsequently, weighted evaluation matrices for both types of risks are established by performing cross products on the weighted vectors (founded on the analytic hierarchy process) and the fuzzy evaluation matrices. In the final stage, the weighted evaluation matrices of cancer and non-cancer risks are aggregated to determine the final risk rating. Two case studies are provided to demonstrate the application of this method.