Advisory Council on the Environment

2nd Progress Report on Trials and Studies for the Harbour Area Treatment Scheme

(ACE Paper 31/2002)
For information


This paper briefs Members on the latest progress of the various trials and studies undertaken to ascertain the feasibility of compact sewage treatment technology and options proposed by the International Review Panel (IRP) to implement the further stages of the Harbour Area Treatment Scheme (HATS).


2. In February 2002, we provided Members with an information paper, setting out the progress of various trials and studies which the Government has been conducting to ascertain the feasibility of the compact sewage treatment technology and the four IRP options. We also informed Members that a HATS Monitoring Group (MG), currently chaired by the Permanent Secretary for the Environment, Transport and Works (Environment), had been set up since June 2001 to monitor the progress of these trials and studies. This paper serves to report progress of the trials and studies made in the past eight months.


Environmental and Engineering Feasibility Studies (EEFS)

3. Camp Dresser & McKee International Inc. (CDM) was appointed in November 2001 to undertake the EEFS to verify the environmental and engineering feasibility of the IRP options for the development of the further stages of HATS. Its first major task was to formulate the Water Quality Criteria (WQC) for assessing the water quality impact of the IRP options on the receiving water bodies. After drawing up the initial WQC and seeking the advice of the MG in February, CDM conducted a consultation exercise between June and September 2002 to solicit views on its WQC proposals, including -

  • a presentation to this Council in June;
  • a view sharing workshop with stakeholders including academia, green groups, professional institutions, etc in June;
  • the issue of a public consultation document in addition to the technical details to explain the WQC in layman's language for distribution to the public through District Offices for comments. Copies of the document have also been distributed to the Environmental Affairs Panel of the Legislative Council; and
  • uploading the above document to the Internet for wider access by the public.

    4. CDM subsequently received written comments from three organizations and one individual, and where possible met with the originators of the comments to discuss them. A summary of the comments received during the consultation process and the Consultant's responses are summarized in the report at Annex I.

    5. Having reviewed all comments received including those from Members and stakeholders, CDM proposed to retain the proposed WQC except that the dissolved oxygen criteria to be applied in fish culture zones would have the same values as those specified in the existing Water Quality Objectives for fish culture zones. Following the endorsement of the finalized WQC (at Annex II MS Word Version) by the MG in October 2002, we have issued the consultation report together with the finalized WQC to all stakeholders and uploaded them to the "Clean Harbour" website - http://info.gov.hk/cleanharbour/ for public information.

    6. During the consultation, some stakeholders' expressed concerns on whether the technical compliance with numeric WQC values would be enough for the assessment. To address this issue, CDM has recommended adopting a less mechanical approach in dealing with the WQC, by engaging its science team to assess all the evidence in arriving at a view on the likely impacts of the different IRP options. In addition, to afford stakeholders an opportunity to discuss the assessment made by the CDM science team before the commencement of the extensive public consultation on the way forward in end of 2003/early 2004, EPD plans to hold one or more view-sharing workshops with stakeholders around summer of 2003.

    7. Apart from drawing up the WQC, CDM has carried out tasks such as field surveys, wastewater flow estimations and model calibration for the purpose of water quality assessment. It has also ascertained the implications for the footprint requirements of the sewage treatment works (STW) for incorporation into the future layout design work. It would soon complete its site search study for the four IRP options and develop the layout designs of the STWs for these IRP options.

    Compact Sewage Treatment Technology Pilot Plant Trials (CSTTT)

    8. These trials were recommended by the IRP to test the feasibility and effectiveness of compact technology, particularly the Biological Aerated Filter (BAF)1 technology, in treating Hong Kong's saline sewage at Stonecutters Island. Drainage Services Department (DSD) awarded three trial contracts to three different contractors in December 2001, with two employing different designs of the BAF technology and one employing the Submerged Aerated Filter (SAF)2 plus denitrification technology. DSD also appointed Professor Howard Huang of the Hong Kong University of Science and Technology as the Independent Checker to audit the trial results, and CMA Testing and Certification Laboratories, a laboratory accredited under Hong Kong Laboratory Accreditation Scheme to provide laboratory services for all the trials. The pilot plant trials, commenced in April 2002, would last for 11 months till end of February 2003. Samples of chemically enhanced primary treated (CEPT) sewage and treated effluent from the pilot plants are being collected for analysis.

    9. One BAF contractor has proposed three alternative configurations for its pilot plant. The biological process of the first configuration had stabilized by the end of April 2002 with both nitrification and denitrification achieved3 in May 2002 and has been able to operate satisfactorily at the designed average flow rate. The testing of the second configuration of the plant commenced in September and the process was satisfactorily established at low flow in the same month.

    10. The second BAF pilot plant also has two configurations. The biological process of the first one stabilized in May 2002, with both nitrification and denitrification achieved in May 2002. The pilot plant operated satisfactorily at the designed average flow rate since September 2002 after addition of methanol for denitrification. The testing of the second configuration, with less methanol addition, has commenced in early October 2002.

    11. The SAF plus denitrification pilot plant first achieved both nitrification and denitrification in June 2002. However, due to poor media quality, the media in the SAF required replacement in early July 2002 and the nitrification process was re-established in early August 2002. At the end of September, the pilot plant was operating at about 70% of the design flow. There were some discrete occurrences of mechanical equipment failure, which affected the effluent quality. Apart from this, both the nitrification and denitrification processes were satisfactory in the months of August and September. The biological process at the design flow-rate has yet to be established.

    12. DSD has been holding regular meetings separately with the contractors in order to closely monitor the project progress and to resolve site issues. The interim report for the trials, based on the data collected up to the end of August, is currently being reviewed by CDM for incorporation into the EEFS.

    Study on Procurement Options (SPO)

    13. This consultancy aims to review possible procurement options and to develop the most efficient and effective contractual arrangement for the implementation of further stages of HATS. The consultants selection exercise was completed in February 2002 and DSD subsequently appointed Maunsell Consultants Asia Ltd (Maunsell) to undertake the assignment in March 20024 .

    14. Maunsell has reviewed local and international practice and experience on various procurement arrangements, generic merits and demerits for various procurement options as well as potential constraints under the existing government policies and practices and interviewed stakeholders in July and August. In order to enable the project stakeholders to deliberate on the procurement options and to allow the evaluation criteria for short-listing options to be developed as well as to build consensus, a Value Management Workshop was held in October 2002. In addition, interviews with those involved with the operational and maintenance aspects of the existing HATS facilities have been carried out.

    Stage I Flow Reassessment Study

    15. This study was prompted by the need to address capacity issues associated with developments in East Kowloon. Construction of a mathematical model of the HATS Stage I sewage-tunnel system commenced in 2000. Calibration of the hydraulic model against flow data obtained from the fully commissioned HATS Stage I has been completed. The model is now being used to simulate different scenarios. The key results of the model simulations, completed in October 2002, have been made available to CDM for use in determining the sewage treatment capacity requirements at Stonecutters Island, and the need for implementation of any capacity-constraint relieving option. Further supplementary work is continuing.

    Stonecutters Island Sewage Treatment Works (SCISTW) Capacity Reassessment Study

    16. As recommended by the IRP, this study is to determine the maximum capacity of the Stage I sedimentation tanks at SCISTW and the effect of increased flow on the pollution removal efficiency of SCISTW. Trials using the full HATS Stage I flow have been completed. It was concluded that the maximum flow that can be handled by the sedimentation tanks, without changing the design settings/parameters, is in line with the maximum design flow of 39.94m3/sec.

    17. In an effort to test the performance of the sedimentation tanks for peak flows higher than the design peak flow, further trials were carried out by lowering the adjustable weirs (adjustable gates provided at the discharge end of each sedimentation tank to adjust the flow distribution between the tanks). The results indicated that the sedimentation tanks might be able to handle a maximum peak flow of up to 10% higher than the design maximum flow. The performance of the tanks suffered mainly during the duration of the enhanced peak flow. A report on these trials has been made available to CDM.

    Programme Timetable & Publicity

    18. A latest programme for the studies and trials is at Annex III. All trials and studies are generally progressing in accordance with the programme. We remain confident that we would be able to complete the trials and studies before the end of 2003 as planned.

    19. To enhance public understanding of the HATS and pave the way for the public consultation on the way forward, the Government plans to undertake more proactive publicity on the HATS project. In addition to uploading the latest development on HATS onto the website, the Government has published in October a leaflet entitled "Our Harbour: A Cleaner Tomorrow" (Annex IV) summarizing, in a simple and reader-friendly manner, the key facts about HATS and its progress and programme for distribution to public through various channels including the District Offices. The Government would also be conducting briefing sessions for the District Councils in the next few months to update them on the HATS project.


    20. Although we have taken into account the recommendations of the MG to extend the period of the pilot plant trials from an initial three months to the present eleven months; and to appoint an independent checker and a single accredited laboratory to verify and carry out the trial analysis respectively (paragraph 8 above), we anticipate that all the trials and studies could still be completed within the overall allocation of $73.6M.


    21. Members are requested to note the latest progress of the trials and studies on the further stages of HATS.

    Drainage Services Department
    Environmental Protection Department
    Environment, Transport and Works Bureau

    November 2002

    1BAF is an advance treatment process characterized by flexible operations and compact size.

    2SAF is another advance treatment process also characterized by flexible operations and compact size. It differs from BAF in that an additional downstream solid removal device is required in the treatment process.

    3Nitrification is the process of turning ammonia in sewage into nitrates and denitrification is the removal of nitrates. Ammonia is a harmful substance while excessive nitrates (a nutrient) may lead to over-abundant growth of algae, which can upset the oxygen balance resulting in fish kills. Successful achievement of nitrification and denitrification by the pilot plants would mean that the processes are suitable for treating Hong Kong sewage under Hong Kong conditions.

    4As explained in the last progress report, the study would be split into two stages. The first stage of the study on procurement arrangements for feasible options would be completed by end of April 2003. The remaining stages of this study including procuring arrangements for the selected option of HATS and the contract document preparation would proceed only after we have consulted the community on the way forward for HATS and will complete by end of November 2004.






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