DSD is committed to providing world-class stormwater drainage and wastewater treatment services, enabling the sustainable development of Hong Kong. During the year, the largest environmental infrastructure project in Hong Kong, The Harbour Area Treatment Scheme (HATS) – Stage 2A was commissioned, which would improve the water quality of Victoria Harbour to provide better living environment and quality for the public.
Overview of Sewage Treatment in 2015-16
Sewage collection, treatment and discharge is one of the core service of DSD. Through a variety of sewage treatment processes and technological advances, we can remove most of the pollutants, toxins and bacteria from sewage. DSD strives to enhance both the efficiency and quality of our sewage treatment services, in order to safeguard the quality of Hong Kong waters.
- DSD operates 300 sewage treatment facilities
- About 1 billion cubic metres of sewage was treated over the year, i.e. on average 2.8 million cubic metres per day
- Public sewerage network runs 1,700 kilometres in length, serving around 93% of Hong Kong’s population 1
- 393,000 tonnes of sludge were processed during the year
|(1)||Based on the number of water accounts|
Location map of STWs in 2015-16
Professional Laboratory Services
DSD operates multiple laboratories which provide professional and quality laboratory services, ensuring that sewage treatment processes meet the statutory requirements. Since 1999, both Sha Tin Central Laboratory and Stonecutters Island Laboratory have been accredited under the Hong Kong Laboratory Accreditation Scheme (HOKLAS) operated by the Hong Kong Accreditation Services. As a pilot scheme to automate our laboratories, in 2015-16, an automatic Biochemical Oxygen Demand testing device was added at Shatin Central Laboratory. During the year, 26 laboratory tests were accredited.
We run more than 14 types of tests on a day-to-day basis: over 261,000 analyses were carried out in 2015-16. Analysis results for effluent quality at major STWs can be found on our website.
Managing Underground Drainage and Sewerage Networks
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 2015-16, we rehabilitated about 22 kilometres of drains and sewers at a cost of about $74 million.
In anticipation of growing needs for rehabilitation, we will take forward 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.
Full Commissioning of Harbour Area Treatment Scheme Stage 2A
The Harbour Area Treatment Scheme (HATS) is the largest environmental infrastructure project in Hong Kong, with an aim to improve the water quality of Victoria Harbour by collecting and treating sewage generated from both shores. The project has was implemented in two stages, with construction works spanning over two decades at a total cost of $25.8 billion.
With facilities for HATS Stage 2A came into full operation on 19 December 2015, all sewage from both sides of Victoria Harbour are now conveyed to a sewage treatment plant for treatment, disinfection and discharge into the western approaches of the harbour. This milestone for HATS marks the overall enhancement of water quality across the harbour.
Physical constraints were overcome by cutting-edge engineering techniques adopted in this project, enabling the construction of deep sewage tunnels totalling over 44 kilometres in length at depths up to 160 metres below sea level. HATS also involved upgrading the sewage treatment capacity of Stonecutters Island Sewage Treatment Works (SCISTW) to 900 million cubic metres per year, enabling it to serve more than five million citizens.
- commenced in 1994 and commissioned in December 2001
- treats 75% of sewage from both sides of the harbour
Major works comprise:
- construction of SCISTW;
- construction of 23.6 kilometres of deep tunnels conveying sewage collected from Kowloon and north-eastern Hong Kong Island to SCISTW for chemically enhanced primary treatment (CEPT); and
- upgrading seven Preliminary Treatment Works (PTWs) at Tsing Yi, Kwai Chung, To Kwa Wan, Kwun Tong, Tseung Kwan O, Shau Kei Wan, and Chai Wan
- commenced in 2009 and commissioned in December 2015
- treats the remaining 25% of sewage from northern and south-western parts of Hong Kong Island
Major works comprise:
- construction of 21kilometres of deep tunnels conveying sewage collected from northern and south-western Hong Kong Island to SCISTW for CEPT;
- upgrading eight PTW in northern and south-western parts of Hong Kong Island; and
- upgrading the treatment capacity of SCISTW and construction of disinfection facilities
To improve the water quality of Victoria Harbour, the Harbour Area Treatment Scheme (HATS), formerly known as Strategic Sewage Disposal Scheme, was launched in late 1980's to be implemented in stages to provide treatment for the sewage collected from the urban areas on both sides of the Harbour. Stage 1 and Stage 2A of this world-class environmental Infrastructure project are now in operation.
Highlights of HATS
HATS Stage 2A Sewage Conveyance System
The Sewage Conveyance System (SCS) is a major component of HATS Stage 2A, comprising a network of interconnected sewage tunnels and vertical shafts. Sewage collected from the PTWs is conveyed to SCISTW via deep tunnels totalling 21 kilometres in length.
Sewage collection and treatment in HATS Stage 2A
- Collection and preliminary treatment of sewage (screening of large particles and grit removal)
- Conveyance of sewage to SCISTW via deep tunnels
- CEPT at SCISTW
- Disinfection to reduce over 99% of E. coli
- Discharge of treated sewage to the west of Victoria Harbour
Upgrading Works for SCISTW
Another core component of HATS Stage 2A is the upgrading works of SCISTW, presently the world’s largest CEPT plant, with daily treatment capacity up to 2.45 million cubic metres, equivalent to the volume of about 1,000 Olympic-size swimming pools.
When sewage arrives at SCISTW, it is pumped from the deep tunnels to the surface via Main Pumping Station, one of the world’s largest underground sewage pumping stations. With an internal diameter of 55m and a depth of 40m, the new pumping stationhouses eight sets of mega-size sewage pumps, each with a rated pumping capacity of 4 cubic metres per second (equivalent to filling up an Olympic-size swimming pool within a minute).
Sewage siphoned above ground will be pumped to the sedimentation tanks for CEPT. SCISTW adopts a double-tray sedimentation tank design to reduce the entire STW’s footprint down to 10 hectares, about half of the size of Victoria Park, despite serving up to 5.7 million people.
Sludge dewatering facilities were added to handle up to 1,200 tonnes of sludge per day, with 14 centrifuges raising the solid content of the sludge from 2% to 32%. Two special vessels were also built to deliver sludge from SCISTW to a Sludge Treatment Facility “T-Park” in Tuen Mun, minimising potential odour nuisance to nearby residents caused by land transport.
“Clean Harbour 1” and “Clean Harbour 2” are the first diesel-electric propulsion container vessels in Hong Kong They are connected to on-shore power supplies when berthed, without using diesel and thereby achieving zero emission, which improve the air quality at the shore . Compared to regular vessels, the two sludge carriers release 130 fewer tonnes of carbon dioxide into the atmosphere every year, equivalent to the amount absorbed by 6,000 trees over the same period.
Flow Turning Facilities Enter into Service (24 September 2015)
The flow turning process under HATS Stage 2A has commenced. It would progressively intercept the remaining sewage that was preliminarily treated prior to discharge into Victoria Harbour previously, and convey it to the newly expanded SCISTW for CEPT. Wan Chai East PTW was the first plant to begin the process and was followed by the remaining seven PTW at the northern and southwestern sides of Hong Kong Island. Flow turning also marks the full commissioning of the newly expanded SCISTW.
Benefits of HATS
After the full commissioning of Stage 2A, all sewage from either side of Victoria Harbour is now collected, treated and disinfected prior to discharge. As a result, over 99% of E. coli, 70% of biochemical oxygen demand and 80% of suspended solids are eliminated from the sewage, equivalent to the interception of 800-1000 tonnes of sludge from being discharged to the harbour. With the significant improvements in water quality, cross-harbour races resumed in 2011 after years of suspension at the east of the Victoria Harbour. As water quality of the beaches in Tsuen Wan district has also been improved drastically, closed beaches were reopened for public enjoyment.
Planning, Design and Construction of New Sewerage Facilities
Relocation of Sham Tseng STW to Caverns
Relocating Sham Tseng STW into caverns can release around 1.1 hectares of land for other beneficial uses for the community. We awarded a consultancy agreement for a feasibility study in December 2014 at an approximate cost of $10 million. The agreement covers research for preliminary technical and impact assessments, preparation of outline design for the engineering works, formulation of implementation strategies and schedule, and carrying out public engagement and consultation activities.
We awarded the consultancy contract of the feasibility study for completion in 2016-17. Surveys and associated studies are in progress.
Relocation of Sai Kung STW to Caverns
Approximately 2.2 hectares of land will be freed up for more suitable uses by the relocation of Sai Kung STW to caverns. In August 2014, we awarded a consultancy agreement for a study which will ascertain the feasibility of such movement and conduct preliminary technical and impact assessments, public engagement activities, and site investigations.
This project is conducted in tandem with the associated reclamation project managed by the Civil Engineering and Development Department (CEDD). Phase one of the public engagement activities and site investigations are complete. The consultancy agreement will be concluded in 2017.
Relocation of Sha Tin STW to Caverns
In addition to releasing some 28 hectares of land, the relocation of Sha Tin STW into caverns can also serve to improve living conditions across the entire district.
We have already completed the environmental impact assessment (EIA) for the project, and site investigations are well under way. We held the third stage of our public engagement exercises from December 2015 to May 2016, during which we elaborated on the results of the EIA and the preliminary construction arrangements to the public. We strive to complete the project design as soon as possible, with construction works to follow.
Expansion of Shek Wu Hui STW
To tie in with the rapid development of the North District, we will expand the treatment capacity of Shek Wu Hui STW in phases and upgrade it to a tertiary treatment plant to better protect the ecology at Deep Bay. We will also take this opportunity to revamp its exterior and promote its educational purpose on water conservation, with hopes of a makeover that will turn Shek Wu Hui STW into a landmark facility.
Advance works including partial upgrade of treatment facilities to facilitate the main works, began in July 2015. The consultancy agreement for detailed design of the main works commenced in May 2015.
Tolo Harbour Sewerage of Unsewered Areas
We are carrying out sewerage works in Sha Tin and Tai Po to improve both the water quality in Tolo Harbour and sanitation conditions for the 11 unsewered communities. The project involves building a sewaage pumping station at Kau To and laying around 12kilometres of sewers for the nine and two unsewered areas in Sha Tin and in Tai Po respectively.
Construction works commenced in 2013 and are scheduled for completion in September 2017.
Upgrading of Mui Wo STW
In view of future development, we are undertaking improvement works at Mui Wo STW to boost its daily treatment capacity from 1,190 cubic metres to 3,700 cubic metres . The project will also upgrade the sludge treatment and deodorisation facilities and the associated greening works.
Construction began in 2012 and is slated for completion in 2017.
Expansion of Village Sewerage
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, Tuen Mun, Sai Kung and the Outlying Islands.
As of March 2016, 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.
Overview of Sewage Services Charges
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 system. 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 in relation to sewage treatment or stormwater drainage, are closely intertwined with public life. In order to provide quality services for the public, we provide a range of day-to-day services to cater for their needs in addition to performance enhancements at our facilities. In 2015-16, we received 6,719 written and telephone inquiries in relation to our sewage treatment services, of which all written inquiries were replied within one month.
Written Enquiries Received in 2015-16 by Category
Billing and Water Consumption Statistics
Of approximately 2.91 million water utility users in Hong Kong, about 2.69 million are liable for SC. There are around 25,800 non-domestic users operating in the under 27 trades which are liable to pay the TES, distribution of which is as follows:
Distribution of TES Accounts in 2015-16, by Sector
Reassessment of TES Rate and Discharge Ratio
Non-domestic consumers may apply for a reassessment of the TES rate or discharge ratio if they consider that their effluent strength or discharge ratio is lower than the corresponding values stipulated by regulations. The reassessed TES rate is valid for three years.