To solve the problem of sewage discharge in Dongtou district, Wenzhou, China, the site selection and planning of sewage outfalls into the sea is investigated in this study. The data of flow field variation and pollutant concentration diffusion from four candidate sites of the sewage outfalls, which is realised using the hydrodynamic model, are used to evaluate and select the optimal site of the sewage outfall into the sea. The results show that the optimal site of the sewage outfall into the sea is the sea area with the good hydrodynamic conditions and the pollutant concentration of the optimal sewage outfall doesn’t exceed the water quality standard.
With the rapid development of economy and society and the improvement of people's living standard in Dongtou district, Wenzhou, China, the industrial wastewater and domestic sewage are gradually increasing and the construction of sewage pipe network and sewage treatment facilities seriously lag behind the development of the city. In addition, the unreasonable layout of sewage outfalls may have adverse effects to the coastal environment and the sensitive area (Liu et al., 2007). It is therefore important to scientifically and reasonably select the sewage outfall location in the design of sewage treatment plant project (Bedri et al., 2015; Law and Tang, 2016; Li et al., 2017).
On the basis of various hydrodynamic models, coupled with water quality model, Lagrange particle tracking model and other numerical models, the optimal sewage outlet is evaluated and selected. The dilution of pollutants is taken as the main reference index for evaluation of the sewage outfalls. Specifically, Morelissen et al. (2013) dynamically coupled Delft3D in the far field with CORMIX in the near field to simulate the dilution conditions in the near and far fields of the sewage outfall. Hunt et al. (2010) studied the near and far field dispersions of pollutants through EFDC model, and the sewage outfall was performing as designed. Muhammetoglu et al. (2012) studied the far and near field dilutions and evaluated the sewage outfall using Plumes-UM3 model. Sheng and Hodgins (2004) coupled the circulating water quality model with the sewage plume model to predict the dilution near the sewage outlet.
