In Taiwan, most pollution of rivers usually comes from municipal wastewater. The treated wastewater reclamation and reuse not only increase water resource but also reduce the loading of river pollution. According to research report last year, five places were selected to draw up the water reuse system where there are potential for water reuse and four places have executed. Two of the selected places execute secondary wastewater treatment and the others execute advanced level. The additional processes were recommended to comfort the required water quality, including disinfection for microorganism removal and filtration for SS removal. The reused water qualities of BOD, SS, COD and E. coli which was treated by the additional treatments conform the related criteria (BOD＜10mg/L, SS＜10mg/L, COD＜30mg/L and E. coli: no detectable). The recommended applications of water reuse in these places include landscape irrigation, toilet flushing, landscape ponds. The average wastewater reclaimed rate in the places was 71.64% and the reclaimed water usage rate was 41.12%.Average benefit-cost ratio is 2.6 and net present value is positive. It means the enough economic benefit to execute water reuse. Recovery period for installation cost is about 4.1 years. The total benefit of reducing water pollutant loading will reach 7086.3kgBOD/yr. Twenty EIA cases which were required executing water reuse were investigated in order to understand the implementation of EIA conclusion about water reuse. These cases were required that treated wastewater quality must reach advanced criteria and set up complete wastewater reuse system. The applications of water reuse were always required for landscape irrigation and toilet flushing. Besides increasing water resources, water reclamation and reuse could promote environmental benefit such as mitigating pollutant loading on received water bodies, reducing groundwater pumped and environmental education in these cases. However, the chief managers of EIA cases always do not completely understand the related EIA guidelines. They suggested that the guidelines must be modified to clear and concrete regulations. They also need technical service for constructing the water reuse system. Chemical risk assessment for treated wastewater reuse to irrigation is not significant and is acceptable, because the secondary effluent from the Nei-Hu municipal wastewater treatment is very fine and under the related criteria. E. coli, Cryptospridium parvum and Enterovirus were selected to assess biological risk. The result of risk assessment shows risk of C. parvum is more than E. coli and Enterovirus, but its risk is still acceptable. Based on the progress of public sewerage system construction and water reuse promotion in Taiwan Water Resources Agency and Constructional Planning Agency, it is forecasted that annual water reuse in Taiwan will reach approximately 60,000 m3 by 2021. In the total environment benefit, it could reduce 375,000(kg-BOD/year) on water pollutant loading and about 75,000 equivalent of population.

wastewater reclamation and reuse；environmental impact assessment, risk and benefit