DSD has developed a sewerage network of nearly 1,700 kilometres long to collect sewage in the territory. The system is now serving 93 per cent of the total population. Through different types of treatment processes and adoption of advanced technologies, most of the pollutants, toxic materials and bacteria in the sewage can be removed to a level meeting the statutory environmental and discharge standards.
Overview of Sewage Treatment
Operation and Maintenance of Existing Sewerage Facilities
We have been properly maintaining our sewerage facilities to ensure their efficient and effective operation and we seek opportunities for continual improvement in our services.
At present, we are operating 293 sewage treatment facilities, including 68 sewage treatment works (STW) and 225 sewage pumping stations. In 2013-14, we treat about 2.8 million cubic metres of sewage every day.
|Summary of Sewage Treatment Facilities and Sewerage Network||2009-10||2010-11||2011-12||2012-13||2013-14|
|Annual sewage treatment volume (million m3)||979||979||981||1,001||1,021|
|Coverage of public sewerage (population percentage)||93%||93%||93%||93%||93%|
|Total length of sewerage network (km)||1,622||1,637||1,647||1,683||1,695|
|Total no. of sewage treatment facilities||277||284||287||292||293|
Annual Sewage Treatment Volume: 1,021 million m3
Sludge is a by-product of the sewage treatment process and we handled nearly 300,000 tonnes in 2013-14.
Sewage Services Charges
The “Sewage Services Charging Scheme” was introduced on 1 April 1995 according to the “Polluter Pays” Principle. All premises connected to public sewers are required to pay the sewage services charges, which have two components: the Sewage Charge (SC) and the Trade Effluent Surcharge (TES). At present, the number of trades that are required to pay TES is 27.
In 2013-14, we received 6,042 telephone and written enquiries. More than 98 per cent of our replies to the written enquiries were issued within one month, achieving our performance pledge.
Written Enquiries Received in 2013-14 by Types
Billing and Consumption Statistics
There are about 2.86 million water accounts, of which about 2.65 million are liable to pay SC. In the non-domestic category, about 23,000 accounts are liable to pay TES as they are operating one of the 27 designated trades. The distribution of TES accounts by trade types is shown in the following chart.
Distribution of TES Accounts by Trade Types in 2013-14
Reassessment of TES Rate and Discharge Factor
Non-domestic consumers may apply for 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 reassessment of the TES rate is three years.
Professional Laboratory Services
Ensuring the compliance of statutory environmental standards relies on the support from DSD’s own professional laboratory services. Since 1999, our Shatin Central Laboratory and Stonecutters Island Laboratory have obtained accreditations for the testing of environmental samples (water & wastewater) under the Hong Kong Laboratory Accreditation Scheme (HOKLAS) operated by the Hong Kong Accreditation Services of the Innovation & Technology Commission. Also, Stonecutters Island Laboratory has received accreditation since 2007 for the testing of chemical samples which helps assure that the procured chemicals will comply with the specifications. In 2013-14, we have applied for the accreditation of six additional tests in relation to trace metal and the number of tests accredited are expected to increase to 26 in 2014-15.
We have a comprehensive sampling scheme in place to ensure that the treated effluent meets the stipulated discharge license conditions. Extensive laboratory testing, which covers more than 14 types of analyses, has been carried out in our laboratories at Shatin, Tai Po, Sai Kung, Shek Wu Hui and Yuen Long STW. In 2013-14, we have conducted over 248,000 numbers of analyses and the analytical results of the effluent quality can be found in DSD’s website.
Planning, Design and Construction of New Sewerage Facilities
Harbour Area Treatment Scheme Stage 2A
Harbour Area Treatment Scheme (HATS) aims to improve the water quality of Victoria Harbour by collecting and treating sewage generated from both sides of the Harbour. HATS Stage 1 was commissioned in December 2001, treating about 75 per cent of the sewage from both sides of the Harbour while Stage 2A is now in progress for collecting the remaining sewage from northern and south-western Hong Kong Island. HATS Stage 2A’s main works will be commissioned progressively starting from 2015.
Upgrading of Lamma Island Sewage Treatment Works
To improve the water quality and hygiene condition at Lamma Island, we commenced the first stage of village sewerage works in 2008, comprising the construction of Yung Shue Wan STW and Sok Kwu Wan STW, as well as about 5.1 kilometres long sewers to serve eight villages. The treated effluent from the STWs will then be discharged via submarine outfalls. The village sewerage works were completed in 2011 while Yung Shue Wan STW was put into operation in November 2013. Sok Kwu Wan STW is expected to be completed by end-2014.
Upgrading of Pillar Point Sewage Treatment Works
The Pillar Point STW serves the Tuen Mun area and has been commissioned since 1980s. It was a preliminary treatment facility providing fine screening and aerated grit removal process with effluent discharge into the Urmston Road tidal stream through a two-kilometre long twin submarine outfalls. In order to provide additional treatment capacity for the sewage flows increase from anticipated population growth and developments in Tuen Mun and to reduce pollution loads to the north-western waters, we commenced the upgrading works in July 2010 to uplift the treatment capacity from 215,000 cubic metres per day to 241,000 cubic metres. We will also upgrade the treatment level to chemically enhanced primary treatment with ultraviolet disinfection. The project will be completed and commissioned by mid-2014.
Upgrading of Mui Wo Sewage Treatment Works
The existing Mui Wo STW was commissioned in 1985, providing secondary treatment to sewage collected from Chung Hau area, Ngan Wan Estate and areas near Mui Wo Ferry Pier. To cater for the forecast increase in sewage flow due to increase in population and extension of village sewerage, we started a study to investigate the feasibility of upgrading Mui Wo STW in 2007. The study recommended to increase the capacity of Mui Wo STW from 1,190 cubic metres per day to 3,700 cubic metres per day, and implement associated deodourisation facilities and greening measures. The upgrading works commenced in 2012 for completion in 2017. During the course of upgrading works, the contractor is required to maintain the operation of Mui Wo STW to ensure the proper sewage treatment service throughout.
Relocation of Shatin Sewage Treatment Works to Caverns
There is a pressing need to increase land supply for various uses by sustainable and innovative approaches to support social and economic development in Hong Kong. Rock cavern development is one of the feasible approaches to release our land resources. Relocating the Shatin STW to caverns can release about 28-hectare land of the existing site for more beneficial and compatible land uses, thereby enhancing the community and environment of Shatin as a whole.
We commenced a feasibility study on the relocation of Shatin STW in May 2012, including relevant preliminary technical and impact assessments, as well as a two-stage public engagement exercise. We completed the main tasks of the feasibility study in end 2013 and confirmed the feasibility of the relocation project. We plan to commence the investigation and design work for the project by end-2014 for completion in stages by 2022.
Further Expansion of Shek Wu Hui Sewage Treatment Works
Commissioned in 1984, the existing Shek Wu Hui STW provides secondary treatment to sewage collected from Sheung Shui, Fanling and the adjacent areas. In the coming years, Shek Wu Hui STW will reach its design capacity of 93,000 cubic metres per day. To cope with the forecast increase in sewage flow from the neighbourhoods and the extension of village sewerage, as well as the proposed new developments in Fanling North and Kwu Tung North, we plan to further increase the STW’s capacity by phases.
To minimise the impacts to Deep Bay, which is the ultimate discharge water body of the effluent from Shek Wu Hui STW, the sewage treatment level of Shek Wu Hui STW will be upgraded progressively to the tertiary level. We will also take this opportunity to improve the environmental performance of Shek Wu Hui STW by implementing comprehensive odour management measures and extensive landscaping and greening works. To promote sustainable development, we will investigate whether the effluent from the upgraded STW can be re-used for toilet flushing and other non-potable uses within Sheung Shui, Fanling and the new development areas.
We commissioned an investigation study on the expansion scheme in December 2012 and have engaged the stakeholders since September 2013 through site visits and meetings. We plan to start the detailed design and advance works of the Shek Wu Hui STW further expansion in mid-2015.
Improvement of Yuen Long Town Nullah (Town Centre Section) - Stage 1 Improvement Works
The project aims to enhance the local environment of Yuen Long Town Nullah at the town centre section (about 800 metres long) and its surroundings. The project will be implemented in two stages. Stage 1 is to construct a dry weather flow interception system, comprising about 40 interceptors, three kilometres long interception pipes and a pumping station at a capacity of 18,000 cubic metres per day.
Extension of Public Village Sewerage
Over the years, we have been making great effort to extend public sewerage to more villages for improving the sanitary conditions of village environs and the water quality of its nearby water bodies. At present, we are implementing village sewerage works at North District, Tai Po, Shatin, Yuen Long, Kam Tin, Tuen Mun, Tseung Kwan O, Sai Kung, and Outlying Islands, and as at March 2014, we have completed public sewerage for over 160 villages while sewerage works for more than 90 villages are in the pipeline. Apart from these, the schemes for some-240 villages are currently under planning and design.
Management of Underground Drainage and Sewerage Networks
DSD currently manages more than 4,000 killometres of underground conduits, comprising sewers and stormwater drains. Many of these conduits have been in service for over several decades and are suffering from aging and deterioration. We have established routine inspection programmes to monitor the conditions of the conduits and will carry out corresponding rehabilitation works as necessary. In 2013-14, approximately 26 kilometres of sewers and stormwater drains were rehabilitated at a cost of about $95 million.
To cope with the anticipated increasing demand of rehabilitation, we commissioned a study in October 2012 to develop a long-term and territory-wide replacement and rehabilitation (R&R) strategy for better management of our underground conduits. We aim at formulating a comprehensive R&R strategy with implementation plan upon completion of the study to enable timely rejuvenation of our drainage and sewerage networks. The viability and relative merits of various advanced R&R technologies are also being studied for adoption with a view to carrying out the works in the most efficient and effective manner. All these initiatives will enable us to develop a systematic and cost-effective approach in maintaining the healthiness and functioning of our networks.