Treatment of wastewater mixed with seawater in Hong Kong

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Treatment of wastewater mixed with seawater in Hong Kong


Author: Lin, Bo
Title: Treatment of wastewater mixed with seawater in Hong Kong
Degree: M.Sc.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Sewage -- Purification -- China -- Hong Kong.
Sewage sludge -- China -- Hong Kong
Department: Dept. of Civil and Structural Engineering
Pages: vi, 82 leaves : ill. ; 31 cm.
Abstract: Hong Kong has used seawater for flushing purpose more than half a century. When seawater is mixed with fresh wastewater it becomes "mixed sewage". This dissertation aims to investigate the difference between the sewage treatment works with and without mixed sewage. This project include literature review and site investigations sewage treatment works in Hong Kong. Literature review shows it is feasible for saline sewage to be treated when the salinity of the sewage is lower than 20 g/L. (Hong Kong situation is around 10g/L). The use of seawater for toilet flushing has the lowest engineering cost compared with the use of raw freshwater and reclaimed water, even though import and export pipelines are built for delivering seawater into and out of the seawater supply zone. This investigation shows the different operation data and techniques as follows: 1. Mixed sewage has a significant effect on the sewage corrosivity. 2. High buoyancy forces in saline wastewater. 3. Activated sludge survival rate and activation decline with a salinity increase. All of them would affect the performance of sewage treatment plants by deteriorating the effluent quality, increasing operation and maintenance costs. The solutions to these operational problems include: 1. Sewerage covers with coating system to protect pipes corrosion. 2. Elongate HRT (Hydraulic Retention Time) in sedimentation tanks, anoxic and oxidation tanks. 3. Extra anticorrosion materials and methods.

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