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[A Century of Drainage Development] [Overview of Flood Mitigation and Control] [Overview of Sewage Collection, Treatment and Disposal]
Sewage collection, treatment and disposal is another core service of DSD. The majority of pollutants, toxic substances and bacteria are removed from sewage through the various sewage treatment processes and advanced technologies. We are committed to enhancing efficiency and quality of our sewage service in order to safeguard the quality of Hong Kong waters.
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Location map of STWs in 2014-15
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DSD runs various laboratories with high quality and professional testing services, and ensure that our sewage treatment processes comply with statutory requirements. Since 1999, Sha Tin Central Laboratory and Stonecutters Island Laboratory have progressively been certified under the Hong Kong Laboratory Accreditation Scheme (HOKLAS) operated by the Hong Kong Accreditation Service. In 2014-15, we initiated the application for accreditation for four testing items on trace metal. By 2015-16, the number of accredited tests is expected to be increased to 30 types.
We conduct over 14 different types of tests on a regular basis, with over 257,000 analyses completed during the year. Test results regarding the effluent quality of our major STWs are available on our website.
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Toxicity meter
While we keep appropriate maintenance and repair works to ensure effective operation of our sewage collection, treatment and disposal facilities, we continue to expand our sewerage system and upgrade the facilities in a timely manner. Our various sewerage projects proceeded smoothly during the year and the details are provided below.
The two-stage Harbour Area Treatment Scheme (HATS) aims to collect and treat sewage generated from both sides of Victoria Harbour for improving its water quality. Stage 1 was commissioned in December 2001 while the major works of Stage 2 comprises the following three components:
All the above three components were completed in early 2015 and put into operation in phases. The project cost of Stage 2A is about $17.5 billion.
As part of the upgrade, two environmentally friendly sludge vessels were built in the first quarter of 2015 and launched in the maiden voyage ceremony on 5 March 2015. The vessels, named “Clean Harbour 1” and “Clean Harbour 2”, are responsible for transferring all sludge generated from SCISTW to the sludge treatment facility in Tuen Mun. The vessels are notable in that:
During the year, the construction of an effluent tunnel (8.5 metres in diameter, some 880 metres in length), sludge holding tanks and a sludge dewatering building were completed.
Compared to regular ships, the two sludge vessels collectively reduce 130 tonnes of carbon emission each year, equivalent to the carbon load absorbed by 6,000 trees in a year.
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Maiden Voyage Ceremony for “Clean Harbour 1” on 5 March 2015
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Sludge vessel “Clean Harbour 1”
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Internal lining works of effluent tunnel
The works involve improving the eight existing PTWs at North Point, Wan Chai East, Central, Sandy Bay, Cyberport, Wah Fu, Aberdeen and Ap Lei Chau. The progress was smooth during the year, with the sewage collected by the PTWs to be diverted to the newly-built SCS in 2015.
Totaling 21 kilometres in length with a maximum depth exceeding 160 metres below sea level, the SCS is one of the deepest sewage tunnels in the world. Breakthrough of all tunnel sections was achieved in September 2014 and concrete lining works were proceeded right away.
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Upgrading works at Sandy Bay PTW
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Celebration Ceremony for Successful Breakthrough of All Sewage Tunnels on 6 October 2014
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Telescopic lining formwork inside the tunnel section from Sai Ying Pun to Stonecutters Island
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Completed tunnel section from Sai Ying Pun to Stonecutters Island
In order to accommodate population growth and new development in Tuen Mun, we commenced upgrading works to Pillar Point STW in July 2010, raising sewage treatment capacity from 215,000 cubic metres to 241,000 cubic metres while upgrading its treatment level from primary treatment to chemically enhanced primary treatment with ultraviolet disinfection.
Upgrading Works were completed and the new facilities were commissioned in May 2014 at a project cost of about $1.4 billion.
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Bird’s-eye view of Pillar Point STW
In March 2015, we completed improvement works to the sewerage systems at Sha Tin, Tai Po and North District by upgrading their capacity and expanding them to unsewered areas. The works, including the laying of 14 kilometres of sewers and rising mains as well as improving three sewage pumping stations in the district, were designed to meet the population growth and development needs in these areas.
The project commenced in 2009 and were completed and commissioned in March 2015, at a project cost is about $800 million.
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Sewer laying works at Ting Kok Road, Tai Po
In 2008, we commended sewerage works on Lamma Island to improve its water quality and hygiene conditions. The project includes building new STWs in Yung Shue Wan and Sok Kwu Wan, as well as laying around 5.1 kilometres of sewers for eight villages.
Village sewerage works were completed in 2011, while Yung Shue Wan and Sok Kwu Wan STWs were put into operation in December 2014 and January 2015 respectively. The project cost is about $600 million.
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Sok Kwu Wan STW came into operation in January 2015
By relocating Sha Tin STW into caverns, 28 hectares of land can be released for other beneficial uses for the community. In September 2014, we awarded a consultancy agreement for the major works at a sum of about $640 million. The consultancy agreement covers preliminary and detailed design for the construction works, comprehensive impact assessments, site investigations, public engagement activities, tendering exercises and supervisory tasks for future construction works.
The consultancy agreement was awarded for the major works. Site investigations and design are underway and scheduled for completion in phases from 2017. Construction works will follow.
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Preliminary layout for the relocation of Sha Tin STW to caverns
To tie in with the rapid development of Northern District, we are planning to uplift the treatment capacity of Shek Wu Hui STW in phases and upgrade its treatment level to tertiary treatment to protect the ecology at Deep Bay. We will also take this opportunity to improve the environment of the STW with full-fledged odour management measures and landscaping works.
The advance works (including conversion of an existing bioreactor and two final sedimentation tanks into membrane bioreactors) and detailed design of the major works are scheduled for commencement in 2015. The cost of advance works is about $500 million.
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Shek Wu Hui STW
We are implementing improvement works at Mui Wo STW, which include upgrading the sludge treatment and deodorisation facilities as well as carrying out landscaping works, at a cost of about $300 million. Upon completion, the daily treatment capacity of Mui Wo STW will be increased from 1,190 cubic metres to 3,700 cubic metres to cope with future development needs.
Construction works commenced in 2012 and are scheduled for completion in 2017.
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Upgrading works at Mui Wo STW
Over the years, DSD strives to expand public sewerage systems to villages in a bid to improve hygienic conditions in rural areas as well as the quality of nearby water bodies. Construction works for sewerage projects are currently underway in Northern District, Tai Po, Sha Tin, Yuen Long, Kam Tin, Tuen Mun, Sai Kung and the Outlying Islands.
As of March 2015, we have laid public sewerage for over 170 villages. The works for some-80 villages are underway and the schemes for some-240 villages are under planning and design.
In accordance with the “Polluter Pays” principle, the Sewage Services Charging Scheme came into effect on 1 April 1995 for all users whose premises are connected to public sewerage. The charge is composed of Sewage Charge (SC) and Trade Effluent Surcharge (TES). There are currently 27 trades under the TES.
DSD’s services, whether they are in relation to sewage treatment or stormwater drainage, are closely related to public life. In order to provide quality services to the public, apart from enhancing the performance of our facilities, we also provide a range of routine services to cater their needs. In 2014-15, we received 7,243 written and telephone inquiries in relation to our sewage services, of which over 98% of the written inquiries were replied within a month, which is in fulfillment of our performance pledge.
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Of approximately 2.88 million water utility users in Hong Kong, about 2.66 million are liable for SC. There are around 24,200 non-domestic users operating in one of 27 trades which are liable to pay the TES. The distribution of the TES is as follows:
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Non-domestic consumers may apply for a reassessment of the TES rate or discharge factor if they consider that their effluent strength or discharge factor is lower than the corresponding values specified. The validity period for the reassessed TES rate is three years.
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DSD currently manages a total of over 4,500 kilometres of underground drains and sewers. Many of them show signs of wear and tear and we schedule regular inspection plans to monitor the conditions of these underground pipes and conduct rehabilitation works as and when necessary. In 2014-15, we rehabilitated about 23 kilometres of drains and sewers at a cost of about $85 million.
In anticipation of growing needs for rehabilitation, we are now formulating a long-term and territory-wide replacement and rehabilitation (R&R) strategy in order to better manage our underground pipes. At the same time, we also research and apply various cutting-edge R&R techniques to efficiently maintain our underground facilities so as to improve the cost-effectiveness of our works.
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