Sewage has been leaking into the ocean after a treatment plant in Sai Kung was damaged by typhoon Mangkhut.
After the typhoon hit, the Drainage Services Department (DSD) inspected the Sai Kung Sewage Treatment Works and found that some of the pipes and secondary treatment facilities at the plant were damaged. The plant was only able to maintain its primary sewage treatment service.
The DSD said its staff conducted emergency repair immediately. “However, subsequent detailed inspections have found that the facilities were seriously damaged and it will take some time to complete the restoration works,” it said.
“As a temporary measure, an additional disinfection process has been arranged for the primary treated sewage before being bypassed for nearshore discharge, so as to minimise the impact to nearby waters.”
The facility commenced operation in 1988 and was originally designed for a flow of 15,200 cubic metres per day.
To reduce the nutrient level of the sewage, the plant was upgraded in early 1996 to include nutrient removal facilities in the aeration tanks, and the plant capacity was lowered to 8,000 cubic metres per day.
The facility has two primary sedimentation tanks, two aeration tanks, two final sedimentation tanks, an ultra-violet disinfection system and sludge treatment facilities. It can provide sewage treatment services to a population of 20,000 in Sai Kung District.
Meanwhile, three sections of rising mains in the Southern District of Hong Kong were also damaged during Typhoon Mangkhut, leading to the discharge of sewage.
They include a 450mm diameter pipe near Mills & Chung Path, a 150mm diameter pipe near Deep Water Bay Barbecue Area and a 300mm diameter pipe near Tai Tau Chau in Shek O.
The DSD has already arranged for emergency repairs and will start replacing the damaged sewers, with a view to completing the repair works within three weeks.
All beaches were closed on Monday until further notice – before the leakage was found – to clean up debris after the typhoon and repair shark prevention nets.
They include three near the Sai Kung plant – Kiu Tsui Beach, Trio Beach and Hap Mun Bay Beach – as well as Deep Water Bay Beach and Shek O Beach.
The Environmental Protection Department (EPD) collected seawater samples at the five beaches to check the water quality.
“The sewage bypass and overflow may lead to temporary deterioration of seawater quality in the vicinity,” the EPD said.
“For health reasons, the public are advised to avoid recreational activities, angling or seawater abstraction in the potentially affected sea or waterfront areas at Port Shelter near Sai Kung Sewage Treatment Works and Deep Water Bay and Shek O in Southern District of Hong Kong.”