Application of WASP model to assess the benefits of sewer construction on river water quality in Taoyuan City — a case study of the Dahan River, Nankan River, and Laojie River

Abstract In order to improve river water quality, the most effective approach is to control pollution sources and reduce the amount of pollution discharged into rivers. This study utilizes the Water Quality Analysis Simulation Program (WASP) model to simulate the water quality of the Dahan River, Nankan River, and Laojie River in Taoyuan City. After simulating the short, medium, and long-term effects of sewer construction (i.e., household connection rates) on water quality improvement, as well as the effects of sewer construction on greenhouse gas emissions, the analysis reveals several key findings. Under government improvement schemes aimed at increasing household connection rates to sanitary sewers, the Dahan River is expected to have continuous good water quality; after 2032, due to expected increases in household connection rates, the river pollution index at the Dakuaixi Bridge monitoring station on the Nankan River is expected to improve from severely-polluted to moderately-polluted; and on the Laojie River, ammonia nitrogen (NH3-N) and biochemical oxygen demand (BOD5) is projected to decrease at both the Zhongzheng Bridge and Xucuogang No. 1 Bridge monitoring stations. Furthermore, river water quality affects greenhouse gas emissions. Simulation results indicate that as household connection rates increase, greenhouse gas emissions along all three rivers will decrease, thereby reducing the energy demand associated with wastewater treatment facilities and benefitting long-term efforts in Taiwan geared toward achieving net zero emissions.