Wastewater generated from all urban areas of Hong Kong and 95% of the households are connected to the public sewerage system. The quantity of sewage treated amounts to 2.6 million cubic metres a day. Our job is two-fold. Firstly, we must ensure that the existing sewerage network and sewage treatment facilities are operated and maintained properly and efficiently so that sewage is collected, treated and disposed of safely to the required standard. Secondly, we need to upgrade the existing sewerage infrastructure and build new facilities in order to serve the territory's continual development and satisfy the community's demand for a higher standard of environmental protection.
On sewerage infrastructure, our plans include the Harbour Area Treatment Scheme (HATS) which focuses on the collection and treatment of sewage generated from both sides of Victoria Harbour, and the improvement works identified by 16 Sewerage Master Plan (SMP) covering the whole territory.
HATS Stage I was commissioned in 2001. The centralized sewage treatment plant at Stonecutters Island is now treating 1.35 million cubic meters of sewage per day, bringing substantial improvement to the water quality in Victoria Harbour.
In order to further improve the water quality in Victoria Harbour, plans are proposed to collect sewage generated in the north and southwestern parts of Hong Kong Island to the Stonecutters Island Sewage Treatment Works for proper treatment before discharge to the sea, having regard to the views and comments gathered from various sectors of the community during the public consultation exercise conducted in 2004.
Apart from Victoria Harbour, other major environmental improvement facilities include the commissioning of the Shatin Sewage Treatment Works Stage 3 Phase I and the Upgrading of the Siu Ho Wan Sewage Treatment Works to CEPT process in mid 2004 and early 2005 respectively.
Sewage Treatment and Sewerage System
This Department is currently operating 239 sewage treatment facilities including 67 sewage treatment plants and 172 sewage pumping stations. Out of the 2.6 million cubic metres treated in a day, 30% receives preliminary treatment, 53% receives chemical-enhanced primary treatment and 17% receives secondary treatment. Pollutants in sewage are mainly removed as sludge for disposal in landfill sites after dewatering. The daily quantity of sludge amounts to 840 tonnes.
Drainage Services Department (DSD) is also maintaining a sewerage network of over 1,500km in length. As sewers are susceptible to blockage because of grease and solids in the sewage, DSD has implemented a preventive maintenance programme to ensure the sewers are functioning properly. In the past year, over 20,000 numbers of blocked drains were handled and a total of around 5,000 cubic metres of silt were removed from sewers.
HATS Consultations and Way Forward
|A public consultation exercise for HATS Stage 2 was conducted from June to November 2004. A series of in-depth technical briefings, discussion forums and public hearings were organized to gather views and comments from various sectors of the community. Through these outreach activities, we collected comments from 46 key stakeholders and received 81 written submissions from individuals or companies. In general, the public attach great importance to cleaning up Victoria Harbour. Most people support the centralization of treatment of all sewage from the harbour area at Stonecutters Island and accept a phased implementation programme. Also, the community generally supports the adjustment of sewage charges to support the sewage services.
||After considering the views collected, the Government decides to take forward Stage 2 in two phases, Stage 2A and Stage 2B. This will allow greater flexibility for future changes as a result of population growth and sewage flow build-up. The first phase, Stage 2A, will involve the upgrading of PTWs, construction of a conveyance system, expansion of the existing chemical treatment facilities and installation of disinfection facilities, while the second phase, Stage 2B, will involve the construction of a complex biological treatment plant. Subject to the community's acceptance of the need to increase the sewage charges in order to fully fund the recurrent costs of our sewage services, Government is aiming at completing Stage 2A by end 2013. Part of the disinfection facilities in Stage 2A will also be advanced in order to achieve early improvement of the water quality in the western harbour and at the Tsuen Wan beaches. For Stage 2B, Government will review the position in 2010-11 to finalize its implementation programme. More information on the public consultation and HATS Stage 2 is available at www.cleanharbour.gov.hk.
Environmental Performance Target
The effect of a sewage treatment plant on the environment is best measured by the quality of its effluent. The effluent quality is regulated through a discharge licensing system whereby limitations and standards are set by the Environmental Protection Department for parameters such as the total suspended solids (TSS), 5-day biochemical oxygen demand (BOD5), ammonia nitrogen, total nitrogen and E. Coli count for indicating the amount of faecal bacterial population in the treated effluent, etc.
In 2004-05, a compliance record of 99.5% was achieved arising from 12,428 tests conducted in all DSD operated plants. The environmental performance target for DSD-operated sewage treatment plants in 2004-05 is to achieve a compliance percentage of 95% in all samples tested under the self-monitoring scheme specified in discharge licence conditions. This is also the performance target in the design for most sewage treatment plants of the Department and the results reflect the effort of the operator and the level of treatment achieved.
Effective Energy Saving at Plants
DSD currently operates and maintains 239 sewage treatment and pumping facilities, consuming 210M kWh/yr. We are one of the largest energy consumed Government Departments in the HKSAR. In contributing to high quality of life in Hong Kong, DSD will achieve more in coming years through further expansion in service coverage and raising treatment standards. We therefore regard energy saving as one of the top priorities, as it not only increases productivity but also fosters sustainable development. It contributes to environmental gain (less pollution), social responsibility (expanding public service without excessive demand on resources) and economic benefit (achieving savings in expenditure).
Effective energy saving measures are being lead and organized by the working committee though continuously and systematic monitoring. To coalesce staff effort to head towards a common goal, we participated in the Energy Efficiency and Conservation Best Practice Competition organized by Electrical and Mechanical Services Department (EMSD). DSD's work gained the recognition from adjudication panel of the Energy Efficiency and Conservation, which comprised Chairpersons of Energy Advisory Committee and Energy Efficiency & Conservation Subcommittee, and EMSD in 2004. In the competition, DSD won the best Practices Gold Award for having a well-organized system to achieve energy conservation and being successful in the implementation.
Great encouragement to staff was given by the Gold Award. We are looking for more effective and practical energy saving measures in the coming years to support the sustainable development in Hong Kong.
Extension of Shatin Sewage Treatment Works to Cope with The Growing Population in Shatin & Ma On Shan
|The Shatin Sewage Treatment Works (STW) is a secondary sewage treatment plant serving the Sha Tin and Ma On Shan New Towns. The Stage 3 Extension Project will increase the capacity of Shatin STW to serve an ultimate population of 830,000 and to improve the quality of the treated effluent.
Construction of the project, costing about $1,680 million, started in February 2001 and will complete in 2008.
Commissioning is being implemented in two phases. Phase I was successfully commissioned in 2004-05 and Phase II commissioning will take place in 2005-06.
Inadequate land and odour mitigation are two major challenges of the Project. By using rectangular instead of circular final clarifiers, we have reduce the foot print without lowering the quality of the treated effluent. In fact, the new rectangular final clarifiers have consistently produced an effluent in good quality. Dosing calcium nitrate into raw sewage is a newly introduced measure to mitigate odour. Results have proved that this method is effective. Other odour mitigation measures are being implemented under the project that include covers and deodorization systems in order to further reduce the odour to the adjacent areas.
The Project has also established a new laboratory building which has allowed an opportunity for the implementation of the DSD Laboratory Services Centralization Plan. The new Central Laboratory was fully accredited the status under Hong Kong Laboratory Accreditation Scheme (HOKLAS) in June 2004. The centralization has enabled our laboratory services operating more efficiently, resulting in saving of resources and achieving the benefit of close monitoring the performance of the wastewater treatment plants in Hong Kong. Siu Ho Wan - ready to serve Disneyland
|Siu Ho Wan STW, commissioned in late 1996, was only provided with preliminary treatment works. To get ready for serving the grand opening of Hong Kong Disneyland in Penny's Bay in September 2005 and coping with future flow demands in Tung Chung and other areas of North Lantau, the Siu Ho Wan STW was expanded and upgraded to chemically enhanced primary treatment (CEPT) with commissioning in March 2005.
The CEPT facilities include six sedimentation tanks, a flocculation and mixing tank, a sludge dewatering house, sludge buffer tanks, deodorization facilities and chemical dosing facilities. Siu Ho Wan STW is currently treating about 35,000 m3 of sewage per day (such amount of water is able to fill 15 standard swimming pools). These facilities allow the treatment capacity to increase to 180,000 m3 per day. The construction cost of the CEPT facilities is about $220 million.
In the CEPT process, some chemicals are added to the sewage to enhance the formation of larger suspended solids. The larger the suspended solids are, the faster they settle onto the bottom of sedimentation tanks. The settled solids will be removed at the bottom and the treated sewage will flow over the top edge of the tanks. Treated effluent will then be discharged into North Lantau waters via a submarine outfall.
We strive to serve the Disneyland and other catchments in North Lantau as well as to protect the environment. All sewage generated from tourists, hotels, restaurants, etc. in the Disneyland will be collected to three sewage pumping stations in Penny's Bay. The sewage will eventually be pumped from Sunny Bay pumping station to the Siu Ho Wan STW. We estimate that the daily sewage flow generated from the Disneyland is about 3,000 m3 in 2005 and will further increase to 6,000 m3 by 2016. To further enhance the quality of the discharged effluent, in particular to protect the Chinese White Dolphins living in North Lantau waters, an ultra-violet disinfection facility is being installed in the plant for commissioning in December 2006. By then, we witness how we can preserve the Chinese White Dolphins while we welcome the Mickey Mouse.