Stage 2A
Scope
Stage 2A works comprise the upgrading of the preliminary treatment works (PTWs) around the northern and southwestern shores of Hong Kong Island; the construction of a deep sewage conveyance system (SCS) to collect and convey the currently preliminarily treated sewage from Hong Kong Island to Stonecutters Island for chemically enhanced primary treatment (CEPT); the expansion of Stonecutters Island sewage treatment works (SCISTW) and provision of disinfection facilities.
The total length of the SCS, with a depth of up to 160 m or more, will be around 21 km and will collect the sewage discharged from the upgraded PTWs at North Point, Wan Chai East, Central, Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau.
Progress
We are now implementing HATS Stage 2A works at full speed and have made good progress. We have successfully completed all statutory procedures, including the approval of Environmental Impact Assessment report, the issuance of the Environmental Permit, and the authorization under the Sewage Tunnels (Statutory Easements) Ordinance and the Foreshore and Sea-bed (Reclamation) Ordinance. We have also consulted the relevant District Councils and the Harbour-front Enhancement Committee and have secured their support to our proposed works.
On the planning and design tasks, the investigation and design of the 21-km long deep sewage tunnels have been completed, whilst the detailed design of the various sewage and sludge treatment facilities at SCISTW and PTWs are well underway. We have investigated different options to optimize the hydraulic design of HATS Stage 2A system and have designed an adit connecting the new and existing influent pumping stations at SCISTW to allow switching of flows between pumping stations to enhance the reliability of HATS conveyance system. A number of models using computational fluid dynamics technique and site tests have also been conducted to investigate different ways to further improve the performance of CEPT process at SCISTW.
Construction of the advance disinfection facilities at SCISTW, which started in April 2008 was completed for commissioning by end 2009. This, coupled with the completion of the local sewerage improvement works in the Sham Tseng area, would facilitate the re-opening of the affected Tsuen Wan beaches at the earliest opportunity.
As for the Stage 2A main works, we have obtained funding approval from the Legislative Council. The Stage 2A works have progressively commenced in July 2009. The construction of SCS, the expansion and upgrading of SCISTW and the upgrading of PTWs at North Point, Wan Chai East and Central are progressing in full swing. The remaining upgrading works at SCISTW and the upgrading of PTWs at Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau will commence progressively in the near future. It is targeted that the whole of Stage 2A will be commissioned by 2014-15, bringing about long term improvements to the water quality of the Victoria Harbour.
Benefit of HATS Stage 2A
Stage 2A would provide chemical treatment to tackle the remaining portion of untreated sewage, amounting to around 450,000 tonnes a day, now entering into the harbour and polluting the sea from the northern and southwestern parts of Hong Kong Island. It would also provide disinfection of all the effluent. When Stage 2A is completed, based on the same performance indicators achieved in HATS Stage 1, it is expected that a further 190 to 500 tonnes of sludge would be prevented from being discharged into the harbour every day. The pollutant levels will also be further reduced. In particular, sewage pathogens (E.coli, an indicator of disease-causing organisms) will be reduced by 90% in the harbour environment after disinfection facilities are in place. Toxic ammonia will be further reduced by an average of 10%, and nutrients in terms of total inorganic nitrogen and phosphorus (which in rich supply can promote excessive algal growth) by a further 5% and 8% respectively. The dissolved oxygen level is also expected to further increase by 5%.
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