Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Site Selection and Planning of Sewage Outfall into the Sea
Shuqiao Fanga,b, Chong Pana, Weiyong Shia,b, Xuefeng Xua,b, Liangliang Yua

a. Key Laboratory of Nearshore Engineering Environment and Ecological Security of Zhejiang Province, Second Institute of Oceanography, Ministryof Natural Resourcesb. Key Laboratory of Ocean Space Resource Management Technology, Ministry of Natural Resources
Hangzhou, Zhejiang Province, China

ABSTRACT

dispersions of pollutants through EFDC model, and the sewage outfall
was performing as designed. Muhammetoglu et al. (2012) studied thefar and near field dilutions and evaluated the sewage outfall using
Plumes-UM3 model. Sheng and Hodgins (2004) coupled thecirculating water quality model with the sewage plume model to predictthe dilution near the sewage outlet.

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 andpollutant concentration diffusion from four candidate sites of thesewage outfalls, which is realised using the hydrodynamic model, areused 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 thepollutant concentration of the optimal sewage outfall doesn’t exceed
the water quality standard.

Pollution in coastal waters mainly comes from sewage outfalls.
Because of different ocean hydrological conditions, pollutants
discharged to different sea areas will cause different pollution to theocean. To minimize the environmental impact of the sewage outfall
into the sea, the numerical models are often adopted to investigate theeffects on coastal water quality for the different sewage outfall
locations. It can be concluded from the numerical simulation model(Liu et al., 2007; Wang et al., 2021) that the coastal hydrodynamic
factors are fully taken into consideration in the numerical method,which agrees with the actual situation of coastal pollutant diffusion.

KEY WORDS: Site selection; sewage outfall; hydrodynamic model;
pollutant concentration diffusion.

INTRODUCTION

Despite of many meaningful results of evaluating and selecting theoptimal site of the sewage outfall into the sea, it is still lack ofinvestigations of the hydrodynamic model on the site selection andplanning of sewage outfalls into the sea. In this study, based on thehydrodynamic model, we tried to determine an optimal place forconstructing a sewage outfall in Dongtou district, Wenzhou, China.

With the rapid development of economy and society and theimprovement 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. Inaddition, 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 selectthe sewage outfall location in the design of sewage treatment plant
project (Bedri et al., 2015; Law and Tang, 2016; Li et al., 2017).

HYDRODYNAMIC MODEL
According to the characteristics of the water flow in the sea area where
the sewage outfall is located, an unsteady planar two-dimensional flow
model of MIKE21 is used for the flow calculation. The twodimensional unsteady convection and diffusion model of MIKE21 isadopted for the calculation of pollutant diffusion in this project.
MIKE21 is the professional engineering software used to simulatehydrodynamics, water quality and sediment. With advanced
preprocessing and post-processing functions and friendly user interface,
MIKE21 has been widely applied in studies on estuary, coast andmarine.

On the basis of various hydrodynamic models, coupled with water
quality model, Lagrange particle tracking model and other numericalmodels, the optimal sewage outlet is evaluated and selected. The
dilution of pollutants is taken as the main reference index forevaluation of the sewage outfalls. Specifically, Morelissen et al. (2013)
dynamically coupled Delft3D in the far field with CORMIX in the nearfield to simulate the dilution conditions in the near and far fields of thesewage outfall. Hunt et al. (2010) studied the near and far field

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