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Overview

In the light of the experience gained during Stage 1 works, an International Review Panel was set up by the Government, in April 2000, to examine whether the original plans remained the most cost-effective and environmentally friendly means of treating the sewage entering Victoria Harbour.

The panel members presented their report in November 2000. In it they recommended upgrading the treatment of sewage using compact sewage treatment technology. This would then allow treated sewage to be discharged within the Harbour via an existing short outfall.

The panel also gave four options for collecting sewage from Hong Kong Island, and recommended some further trials and assessments to verify the viability of those options.

In 2004, the Government completed the trials and studies on the way forward for HATS which have confirmed that, while the four options should be technically feasible, it would be necessary to provide additional land for the construction of the biological treatment plant.

On 20 November 2004, the Government completed a 5-month public consultation programme on the way forward for the remaining stages of HATS.

Trials and Studies

(1) Environmental and Engineering Feasibility Study (EEFS)

The study was commenced in Nov 2001. The EEFS has confirmed that all the four options by the International Review Panel are environmentally acceptable and technically feasible. Besides, disinfection would also be required to remove the E.coli bacteria in order to reopen the Tsuen Wan beaches.

Among the four options, which mainly differ in the scale of decentralization, the option to centralize treatment for all sewage at Stonecutters Island is the preferred option as it performs the best overall in terms of cost, environmental and engineering aspects. The Study has also concluded that, even if the most compact sewage treatment technology is used in the biological treatment process, all the options would require extra land of at least 12 hectares outside the current boundary of the SCISTW.

(2) Compact Sewage Treatment Technology Pilot Plant Trials

Drainage Services Department awarded three trial contracts to three different technology providers in December 2001, with two employing different designs of the Biological Aerated Filter (BAF) technology and one employing the Submerged Aerated Filter (SAF) technology.

These trials were completed in 2003. The trials have demonstrated that the two BAF systems tested could perform well under local conditions (i.e. high temperature, low pH/alkalinity and high salinity) and meet the prescribed standard. On the other hand, SAF could not perform up to the prescribed standard. The trials have also revealed that the satisfactory operation of the BAF systems would depend heavily on the reliability of the on-line instrumentation and control system5 as well as the technical knowledge and experience of the operators on the respective designs of BAF technology. Therefore, competent / skilled operators would be required to ensure the reliable and stable operation of the BAF plants, in particular, during the start-up of the biological treatment process and emergency incidents.

(3) Study on Procurement Options

The Study was carried out to identify the most efficient and effective procurement arrangement for implementing the further stages of the HATS. The Study, which was administered by Drainage Services Department (DSD), commenced on 21 March 2002 and was completed in end 2006.

Under Phases I and II of the Study, all the possible procurement options for implementing HATS Stage 2 had been reviewed having regard to overseas experience. It was concluded that we should consider using the Design-Build approach to construct underground tunnels as far as possible. As regards the provision of the biological treatment facilities, the Study recommended that we should consider the use of Public Private Partnership, possibly by means of Design-Build-Operate arrangement.

The final phase of the Study, Phase III, commenced in March 2005 after the way forward for the implementation of HATS Stage 2 had been decided following the public consultation exercise held in the second half of 2004. It had developed the consultancy and contract strategies and administration structures for the phased implementation of HATS Stage 2. This last phase had also reviewed the previously recommended procurement options to take into account the fact that the upgrading of SCISTW would now be constructed in two phases. It was concluded that we should consider using enhanced Design-Build approach for both the upgrading of Stonecutters Island Sewage Treatment Works and the associated preliminary treatment works under HATS Stage 2A. Under the enhanced Design-Build approach, the Engineer will complete an outline design and a performance specification, and the contractor will carry out the detailed design and the construction works.

(4) Stage 1 Flow Reassessment Study

This study was prompted by the need to address capacity issues associated with developments in East Kowloon. To determine the capacity constraints of the deep tunnels, a hydraulic model was set up to simulate the sewage flow patterns for the various planning projections provided by the Planning Department for years 2006, 2011, 2016 and “Year X”, (i.e. the year when the projected full development scenario is reached. This envisages a population of 5.2 million in the HATS Stage 1 service area compared with 3.5 million in 2000). The results of the hydraulic model simulations indicate that the existing deep tunnels could handle all the sewage generated by the above projected ultimate population in the HATS Stage 1 catchment. There should be no overflows under dry weather conditions and the sewage overflow to the Harbour due to heavy rainstorms would be very small compared to the volume of sewage handled.

(5) SCISTW Capacity Reassessment Study

As recommended by the IRP, this study is to determine the maximum capacity of the Stage 1 Sedimentation tanks at the SCISTW and the effect of increased flow on the pollution removal efficiency of the SCISTW. The trials have concluded that the maximum flow that could be handled by the sedimentation tanks would be in line with the maximum design flow. By adjusting the flow distribution configuration of the treatment works, the sedimentation tanks were able to handle 10% more flows, but at the expense of a slight deterioration in the effluent quality, which is acceptable.

Consultation

Consultation with the Key Stakeholders and the General Public

  1. the community attaches high importance to cleaning up Victoria Harbour as a matter of priority;
  2. most people support the centralization of treatment of all the Harbour area sewage at Stonecutters Island;
  3. while some would like to see both stage 2A and 2B implemented in one go, the majority opinion is willing to accept a phased programme given the scale of HATS stage 2, the financial implications, and uncertainty surrounding the future sewage flow build-up;
  4. there are divergent views on the need for disinfection, and in particular the use of the chlorination-dechlorination process; and
  5. the community believes that it is worth paying higher sewage charges if the outcome is a cleaner harbour, though many considered it important to take into account affordability in adjusting sewage charges and to consult the public extensively beforehand.

Milestones

The following achievements and events were significant in the development of the HATS Stage 2A.

Year Achievements and events
1998
  • Commissioning of a study to investigate the feasibility of the Strategic Sewage Disposal Scheme Stage III/IV.
2000
  • Presentation of findings and recommendations by the International Review Panel on the future of the Harbour Area Treatment Scheme.
2001
  • Commencement of an intensive two-year programme of environmental and engineering feasibility studies to decide the best way forward for the remaining stages of Harbour Area Treatment Scheme.
2002
  • Commencement of the compact sewage treatment technology pilot plant trials.
  • Commencement of the study on procurement options.
2003
  • Completion of the compact sewage treatment technology pilot plant trials.
2004
  • Completion of the environmental and engineering feasibility assessment studies.
  • 5-month public consultation on the way forward for HATS.
2005
  • Announcement of the HATS Stage 2 Programme.
  • EIA Study contract for the provision of disinfection facilities at Stonecutters Island Sewage Treatment Works awarded.
  • LegCo's Finance Committee approved funding for the Harbour Area Treatment Scheme Stage 2A - Environmental impact assessment, investigations, tunnel conveyance system design.
2006
  • Contract to carry out the investigation, design and construction stage services for the sewage conveyance system of the Harbour Area Treatment Scheme (HATS) Stage 2A awarded.
  • Contract to carry out an environmental impact assessment (EIA) study for the Harbour Area Treatment Scheme (HATS) Stage 2A awarded.
  • Contract to carry out major ground investigations for the Harbour Area Treatment Scheme (HATS) Stage 2A awarded.
  • Completion of the study on procurement options.
2007
  • Harbour Area Treatment Scheme Stage 2A consultancy contract awarded.
  • Legislative Council upholds polluter-pays principle for sewage services.
2008
  • Contract for the construction of advance disinfection facilities at Stonecutters Island Sewage Treatment Works awarded in April.
  • The consultancy study, entitled “Co-use of land by the Harbour Area Treatment Scheme (HATS) Stage 2B biological treatment plant and other facilities on Stonecutters Island – Feasibility Study” commenced in May.
2009
  • In June, Finance Committee of LegCo approved the funding of the HATS 2A sewage conveyance system and advance works for upgrading of Stonecutters Island sewage treatment works.
  • Contracts awarded under HATS Stage 2A for:
    • the construction of sewage conveyance system from North Point in the east and Aberdeen in the west to SCISTW in July.
    • the construction of sewage conveyance system from Ap Lei Chau to Aberdeen in August.
    • the construction of diaphragm wall and foundation of a new main pumping station and an interconnection tunnel at SCISTW in September.
    • the provision of covers and deodourisation facilities to the existing sedimentation tanks at SCISTW in November.
2010
  • In April, the Finance Committee of LegCo approved the funding for the upgrading of Stonecutters Island sewage treatment works and eight associated preliminary treatment works on Hong Kong Island. All works items for the HATS Stage 2A project were funded.
  • Contract for the upgrading of the sludge dewatering and storage facilities and the construction of a new workshop building at Stonecutters Island Sewage Treatment Works awarded in August.
2011
  • Contract for upgrading the preliminary treatment works at North Point, Wan Chai East and Central under HATS Stage 2A awarded in January.
  • Contract for the construction of a main pumping station, sedimentation tanks and ancillary facilities for upgrading the SCISTW under HATS Stage 2A awarded in March.
  • Contract for the construction of an effluent tunnel and disinfection facilities at SCISTW under HATS Stage 2A awarded in August.
  • Contract awarded for upgrading the preliminary treatment works at Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau under HATS Stage 2A in September.
2013
  • Contract for the design, construction and operation of sludge handling and disposal facilities under HATS Stage 2A awarded in July.
2015
  • The flow turning process under HATS Stage 2A commenced in September 2015.
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