HATS Stage 1 works includes the construction of a 23.6 kilometres long deep tunnel conveyance system to convey sewage collected from Kowloon areas stretching from Tsuen Wan in the west to Tseung Kwan O in the east, from northeast areas of Hong Kong Island comprising Chai Wan and Shau Kei Wan to Stonecutters Island, where a treatment works adopting a chemical process using ferric chloride is built to treat sewage. The sewage treatment works, capable of handling an average flow of 1.7 million cubic metre per day, is named Stonecutters Island Sewage Treatment Works (SCISTW). After treatment, the effluent is discharged via a 1.7 kilometres long submarine outfall to the western approach of the Victoria Harbour. Stage 1 also includes the comprehensive upgrading of the seven associated preliminary treatment works (PTWs), through elevating the screening and degritting capabilities as well as the operational reliability, to cope with the requirements of the scheme.
Since the full commissioning of the HATS Stage 1, about 75% of the sewage flowing into the Victoria Harbour, which was only treated by means of screening and degritting, is now receiving chemical treatment. Such elevation of treatment level to the sewage is reducing about 600 tonnes of sludge from being discharged into the harbour each day and hence brings about significant improvement in its water quality.
