Overview
At present, 93 per cent of the population in Hong Kong is served by public sewerage. Our sewerage collects and treats about 2.71 million m3 of sewage every day. About 70 per cent of the collected sewage receives chemical or biological treatment before being discharged. We have been properly maintaining our sewage collection, treatment and disposal facilities to ensure their efficient and effective operation. To enable the sustainable development of Hong Kong, our sewerage infrastructure would be continuously improved under a territory-wide programme for construction of new facilities and upgrade of existing ones, which includes 16 Sewerage Master Plans (SMPs) covering the whole territory and the HATS collecting screened sewage from both sides of Victoria Harbour for further treatment.

HATS is a major sewerage infrastructure in Hong Kong. The commissioning of HATS Stage 1 in December 2001, handling about 75 per cent of the sewage arising from urban areas around the Victoria Harbour, has brought significant improvement to water quality of the eastern and central part of our harbour. Disinfection facilities are being constructed since April 2008 at Stonecutters Island STW for completion in end 2009. The remaining 25 per cent of sewage from the catchment will be chemically treated with further improvement to the water quality in Victoria Harbour after the commissioning of HATS Stage 2A in 2014-15.

Apart from HATS, there are other upgrading works being carried out at major STWs. These include the Sha Tin STW Stage 3 remaining works, the Shek Wu Hui and Tai Po STW upgrading works.

 

Sewage Treatment and Sewerage System
We are currently operating 274 sewage treatment facilities including 67 sewage treatment plants and 207 sewage pumping stations. Out of the 991 million m3 sewage treated in 2008-09, 29.5 per cent receives preliminary treatment, 53 per cent receives chemically-enhanced primary treatment (CEPT) and 17.5 per cent receives secondary treatment. The daily quantity of sludge disposed of at the landfills is about 800 tonnes.

We are also maintaining a sewerage network of over 1,600 km. As sewers are susceptible to blockage by grease and solids in the sewage, we have implemented a preventive maintenance programme to ensure the sewers are functioning properly. In 2008-09, 17,095 sections of blocked drains were cleared and a total volume of 3,566 m3 of silt was removed from the sewers.
 

Progress in 2008-09
Update on HATS
The HATS Stage 2 will be implemented in two phases to further improve the water quality of Victoria Harbour. Under the first phase (HATS Stage 2A), collected sewage from the remaining parts of Hong Kong Island will be conveyed by deep tunnels to Stonecutters Island STW. Stonecutters Island STW will also be expanded to provide CEPT and disinfection for all sewage from the whole HATS catchment. The first phase will be completed in 2014-15. Under the second phase (HATS Stage 2B), biological treatment facilities will be provided, and their implementation programme will depend on the review to be carried out by Environmental Protection Department (EPD) in 2010-11.

In 2008-09, we achieved good progress in the implementation of HATS Stage 2A works. We have successfully completed all statutory procedures, including the approval of Environmental Impact Assessment report, the issuance of the Environmental Permit, and the authorization under the Sewage Tunnels (Statutory Easements) Ordinance and the Foreshore and Sea-bed (Reclamations) Ordinance. We have also consulted the relevant District Councils and the Harbour-front Enhancement Committee and secured their support to our proposed works.

On planning and design, the investigation and design of the 21-km long deep sewage tunnels have been completed whilst the detailed design of the various sewage and sludge treatment facilities at Stonecutters Island STW and Preliminary Treatment Works (PTWs) are well underway. We have investigated different options to optimize the hydraulic design of HATS Stage 2A system and have designed an adit connecting the new and existing influent pumping stations at Stonecutters Island STW to allow switching of flows between pumping stations to enhance the reliability of the system. A number of models using computational fluid dynamics technique and site tests have also been conducted to investigate different ways to further improve the performance of CEPT process at Stonecutters Island STW.

Construction of the advance disinfection facilities at Stonecutters Island STW, which started in April 2008, is progressing satisfactorily. All major civil works have been completed and the contractor is working in full swing on the electrical and mechanical installations for commissioning the disinfection facilities by end 2009 as scheduled. This, coupled with the completion of the local sewerage improvement works in the Sham Tseng area, would facilitate the re-opening of the closed Tsuen Wan beaches at the earliest opportunity.

As for the Stage 2A main works, we have awarded contracts for the three tunnels and two contracts for the Stonecutters Island STW upgrading works. We have obtained the funding approval from the Legislative Council in June 2009 for these works to start in second half of 2009. Tenders for the remaining upgrading works at Stonecutters Island STW and PTWs will be invited progressively in coming months to allow works to start in 2010. It is targeted that the whole of Stage 2A will be commissioned by 2014-15, bringing about long term improvements to the water quality of Victoria Harbour.
 

Upgrading of Pillar Point STW
DSD is now launching the first Design-Build-Operate (DBO) Contract for design, construction and operation of the proposed upgrading of Pillar Point STW. The Contractor is required to design and build the upgrading facilities and then operate and maintain the upgraded STW for a period of 10 years with an optional extension of 5 years giving a total possible term of 15 years. The Contractor is also required to take over and operate the existing Pillar Point STW at the onset of the DBO Contract.

The scope of the proposed upgrading works includes (i) upgrading of the sewage treatment level from preliminary treatment to CEPT with ultraviolet disinfection; (ii) expansion of the treatment capacity from 215,000 m3 per day to 241,000 m3 per day; and (iii) provision of new reception and treatment facilities to cater for domestic liquid waste (septic waste) of 1,200 m3 per day. On commissioning of the upgraded Pillar Point STW in 2013, pollution loads to the north-western waters will be reduced bringing about improvement to the water quality of the receiving water body.

In early 2009, we invited three prequalified tenderers to submit tenders for the DBO Contract. The tender exercise is on-going with a view to commencing the DBO Contract in mid 2010. The estimated capital value of the proposed upgrading works is about $1.4 billion with an annual operational cost of about $90 million.

 
Expansion Works at Shek Wu Hui STW
Shek Wu Hui STW is a secondary treatment plant located in Sheung Shui and has a design capacity of 80,000 m3 per day. It provides treatment to the sewage generated from Fanling and Sheung Shui areas before discharging the treated effluent into Deep Bay through River Indus and Shenzhen River. The plant involves primary treatment (i.e. screening and sedimentation) plus biological process (i.e. activated sludge treatment process) to remove suspended solids, carbonaceous and nitrogenous substances. To cope with the increasing sewage flows and loads as a result of the population growth in Fanling and Sheung Shui and the extension of sewerage system to unsewered areas, expansion works to increase treatment capacity of Shek Wu Hui STW to 93,000 m3 per day commenced in September 2005. The expansion works involving modification, reconstruction and addition of sewage and sludge treatment facilities were completed and commissioned in February 2009. After expansion, Shek Wu Hui STW is now capable of serving a population of 300,000.
 
In addition to the expansion works, DSD has assisted EPD in a two-year trial completed in late 2008 on the use of reclaimed water, named as “Demonstration Scheme on Reclaimed Water Uses” in the North District. At the trial, membrane filtration, a state-of-the-art advanced treatment technology was employed to polish the secondary effluent before supplying it to schools, a home for the aged and a village house that voluntarily participated in the demonstration scheme for toilet flushing, irrigation and other non-potable uses.
 
 
At present, the treated effluent standard of Shek Wu Hui STW is among the highest in Hong Kong.

 
 

Odour Management at Siu Ho Wan STW
Siu Ho Wan STW is located about 6.5 km away from the Tung Chung new town. The catchment of the STW covers the Tung Chung new town, Chek Lap Kok Airport, Discovery Bay and the Theme Park in Penny’s Bay. The STW provided preliminary treatment initially and was upgraded to CEPT in 2005. The design capacity and the existing incoming sewage flow of the STW are 180,000 and 45,000 m3 per day respectively.

Odour comes with sewage and odour management is one of our prime concerns. Among various odourous compounds, the rotten egg smell of hydrogen sulfide (H2S) is the most common one.

After the CEPT process commenced, we noted that the odour level at the plant was higher than expected. We quickly investigated the matter and put in hand measures to address the issue. Our investigation revealed that the incoming sewage from Tung Chung was highly septic and odourous compared with the designed flow. A likely reason is the slower than expected population growth in Tung Chung leading to the relatively smaller volume of sewage flow and thus longer travelling time for sewage to reach Siu Ho Wan STW. To address the odour issue, we devised improvement measures firstly to suppress the generation of odourous gas and secondly to control the release of odourous gas from different odour sources during various stage of the treatment operation.

The following quick-fix mitigation measures were implemented gradually since 2007 and were in force in 2008-2009-

1 covering up of sewage intakes to prevent release of odourous gas from incoming sewage;
2 providing additional deodourising unit in the sludge treatment system; and
3 using ferric chloride, instead of alum, in the chemical treatment process to reduce the production of hydrogen sulphide in the sedimentation tanks.

The following additional odour abatement works are also being implemented for completion by end 2009-

1 providing further additional deodourising facilities; and
2 covering further sewage flow areas;

In addition, an automatic hydrogen sulphide monitoring system is now being installed in the STW to record the wind direction and odour levels at various points in the plant round-the-clock. We will continue to monitor the overall odour situation of the STW and will refine the odour management plan where appropriate.

 

Village Sewerage Programme
To improve the environmental and sanitary conditions of village areas and the water quality of nearby streams and waters, DSD is implementing a village sewerage programme to provide proper public sewerage for collection of sewage from unsewered village areas in the New Territories (NT).

There are about 900 villages in Hong Kong and most of them are not sewered. Under the village sewerage programme. DSD will gradually extend the public sewerage to these villages. Up to April 2009, DSD has already provided public sewerage to about 120 villages in Sai Kung, Shatin, Tai Po, NT North and Yuen Long districts, and sewerage projects for over 300 villages in various districts of NT are under various stages of planning, design or construction.

 
 
During construction, DSD endeavours to extend the public sewerage as far as possible to the lot boundary of every village house to facilitate connection by the private sewer. To achieve this, DSD has to maintain close liaison with the concerned village representatives and residents through different channels such as meetings, site inspections etc. We also consult the district councils, local interest groups and rural committees on respective village sewerage projects. We are striving to provide quality services to the NT residents through collection of views from all walks of life.
 
Environmental Performance Target
The beneficial effect of a sewage treatment plant on the environment is best measured by the amount of pollutants it removed and the quality of its treated effluent. To ensure the proper operation of a sewage treatment plant, its effluent quality is regulated through a discharge licensing system. In the discharge license, discharge conditions of the treated effluent are set by the EPD, examples of which include the limits for total suspended solids, 5-day biochemical oxygen demand, ammonia nitrogen, total nitrogen and E. coli count in the treated effluent.
 

The environmental performance target for DSD-operated sewage treatment plants is to achieve a compliance rate of 95 per cent in all samples tested under the self-monitoring scheme specified in the discharge license conditions. This is also the performance target in the design for most sewage treatment plants of the Department. In 2008-09, DSD handled 991 million m3 of sewage, 294,600 tonnes of sludge and removed 117,000 and 147,000 tones of biochemical oxygen demand and suspended solids respectively from sewage. Based on 13,505 samples taken, a compliance record of 99.8 per cent was achieved, far exceeding the compliance target of 95 per cent. The results reflect the fruitful effort of the operators and the level of treatment achieved.