Overview
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 2.5 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 such 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 to serve the territory's continual development and to 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 other involves meeting demands and improvement as identified by 16 Sewerage Master Plan (SMP) covering the rest of the territory.

HATS Stage I was commissioned in 2001. The centralized sewage treatment plant at Stonecutters Island treats 1.4 million cubic meters of sewage per day, bringing substantial improvement to water quality in the Victoria Harbour area.

In order to further improve the water quality in Victoria Harbour, studies and pilot trials were conducted in 2003/04. Plans are proposed to collect sewage generated in the north and northwestern parts of Hong Kong to the Stonecutters Island Sewage Treatment Works for proper treatment before discharge to the sea. Public consultation is to be launched in the latter part of 2004.

Apart from Victoria Harbour, other major environmental improvement facilities include the commissioning of the CEPT plant at Sham Tseng in end 2003. Construction of the first tertiary sewage treatment plant with effluent reuse at Ngon Ping, Lantau Island also represents a major milestone in treatment advancement in Hong Kong. Due to its close proximity to environmentally sensitive areas, very stringent discharge requirements apply. Tertiary treatment has therefore been adopted in the design. Construction started in 2003 for completion in 2005.

Prevention against SARS Infection in the Operation of
Sewage Treatment Facilities during 2003 Outbreak
On 26 February 2003, there were reports on the first case of a flu-type virus Atypical Pneumonia, now commonly known as Severe Acute Respiratory Syndrome (SARS), in Hong Kong. Thereafter, the disease spread quickly and more and more people were infected. In response to the outbreak, DSD
issued a circular memorandum on 25 March 2003 to provide guidelines to the staff, particularly those working in sewage treatment facilities, for prevention of the disease.

Shortly after the issue of the circular, individual Divisions also drew up specific guidelines for their staff to prevent against SARS infection. In the guidelines for operating sewage treatment facilities, all plant staff were reminded to maintain personal hygiene, wear suitable personal protective equipment when working in areas having high risk of contact with sewage or sewage-contaminated equipment. These guidelines were updated regularly in subsequent months. In addition, professional advices were sought from the Labour Department and the Departmental Safety Advisory Unit. Officers from the Labour Department and the Safety Advisory Unit had also made on-site inspections and offered suggestions on the safety and hygiene procedures for staff working in sewage treatment works.


In addition to the hygiene and safety guidelines, it was essential to make available sufficient suitable personal protective equipment for staff working in sewage treatment facilities. Adequate stocks of these equipment including various types of masks, goggles, protective clothes were maintained during the period of the SARS outbreak.

On 19 April 2003, a territory-wide Cleaning Day campaign was held to step up the cleansing and disinfection in the territory. On that day, we carefully monitored the operation of all sewage treatment facilities to ensure no adverse effect would be caused by the large amount of cleansing and disinfection agent flowing into the plants.

The fight against SARS had never been stopped even after the critical period of the SARS outbreak. Continuous effort has been put in the prevention of the SARS infection and a Contingency Plan has been compiled for use just in case the disease attacks Hong Kong again.



Swab Sampling in Sewage Discharge Pipe
at Amoy Garden
DSD participated in the investigation of environmental factors contributing to the outbreak of SARS in April 2003 among occupants in Block E of Amoy Garden. The main task for the Department was to conduct swab sampling at sewage discharge pipe for the examination of E Coli, an indicator of faecal contamination in water. The sampling exercise was conducted in two phases with the first phase concentrated in collecting samples from sewage discharge pipe from Block E, shortly after the building was cleaned and disinfected. The second phase included conducting similar sampling at nine other buildings of Amoy Garden.

The laboratory of Sewage Treatment Division 1 was assigned for the sampling duty. The sampling team consisted of a Chemist and two Engineering Laboratory Technicians. It was assisted by staff of the Mainland South Division who conducted a pipe work survey prior to sample collection. They were also responsible for making arrangements with other government departments and hire of contractors for the provision of lifting platform. Personal protective gears were provided to DSD's team by the Department of Health, and clean-up and disinfection were carried out on site after the sampling exercise.

Swab sampling was conducted in the light well of each block where discharge pipes from washbasin, bathtub, floor drain, and toilet bowls were opened for sample collection. More than 100 samples were collected, covering most of the targets in the sampling scheme. Some difficulties were encountered including temporary suspension of sample collection when sewage discharge was detected. Other difficulties also included opening of blocked inspection windows and answering calls in a whole set of protective gears. The DSD sampling team successfully accomplished the assignment on time, demonstrating our professionalism and commitment in combating SARS in Hong Kong.





The First Tertiary Treatment Plant with Effluent Reuse-
Ngong Ping Sewage Treatment Works (STW)
Ngong Ping is an environmentally sensitive area as it is located within the water gathering ground for Shek Pik Reservoir and surrounded by country parks. The Ngong Ping STW are designed to meet the sewage treatment and disposal needs of Ngong Ping and its surrounding area arising from the anticipated substantial increase in tourists upon the opening of the Cable Car System and associated tourist developments in Ngong Ping in late 2005.

In order to protect the water quality of the water gathering ground and other receiving water bodies, the sewage collected in Ngong Ping will be treated to tertiary level before discharge. The Ngong Ping STW is the first tertiary sewage treatment plant in Hong Kong. This plant will adopt the technologies of Sequencing Batch Reactor (SBR), dual media filter and disinfection process to reduce organic pollutants, suspended solids, nutrients and pathogenic organisms in sewage to a very low level.



The high quality of the treated effluent from the Ngong Ping STW provides a good opportunity for conducting a pilot scheme on effluent reuse. Under this scheme, the treated effluent from the sewage treatment plant will be used for flushing in the public toilets in Ngong Ping, the cable car terminal and associated tourist facilities. The scheme will provide information and useful experience for the Government to further assess the technical, administrative, cost-effectiveness and other considerations for wider use of treated effluent in the territory.

An Environmental Impact Assessment (EIA) study has been conducted for the project. The EIA study, approved by the Director of Environmental Protection, has indicated that the environmental impacts are within acceptable standards.


Sham Tseng Sewage Treatment Works (STW) -
benefiting residents in the area
The Sham Tseng STW was commissioned in December 2003. It has a capacity to treat 16,500 m3 of sewage per day, adequate to serve a population of about 55,000 in the Tsing Lung Tau, Sham Tseng and Ting Kau areas.

The Sham Tseng STW adopts a chemically enhanced sedimentation plus ultraviolet disinfection process for treating sewage. Construction of the plant commenced in May 2001. The contract sum is about HK$345M. This plant uses liquid alum as coagulant and polymer to enhance the floc formation and settling. These chemicals are added proportional to the incoming flow at the optimum rates. This is achieved with a fully automated Integrated Control System.



Connection of sewers from individual residential developments and village houses in Sham Tseng to the STW for treatment are being progressively carried out. Besides, the works for extending the public sewerage system eastwards to Ting Kau and westwards to Tsing Lung Tau are under construction. Upon completion of these works in the coming years, sewage generated from Ting Kau, Sham Tseng and Tsing Lung Tau will all be collected to Sham Tseng STW for treatment and disposal. Commissioning of Sham Tseng STW will not only benefit the public with the high quality sewage treatment service, it will also help resolve the water pollution problem in the unsewered areas, thus improving the living environment of Ting Kau, Sham Tseng and Tsing Lung Tau and the water quality in local beaches.


Odour Abatement in Shatin Sewage Treatment Works


Malodourous complaints on Shatin Sewage Treatment Works had increased sharply in early 2003. Nearly 90% of these complaints were received between April and July 2003. Noting the drastic increase in odour complaints, DSD responded promptly with some improvement measures to immediately alleviate the odour impacts to the nearby sensitive receivers. From record, there was no odour complaint received from September 2003 to March 2004.

All odour control measures are derived from the principles of:
Source control;
Containment; and
Treatment.


In controlling the formation and emission of odour, mainly hydrogen sulphide, calcium nitrate was added to the incoming sewage at the inlet works as an interim measure. More effective long-term calcium nitrate dosing facilities at the pumping stations would be commissioned in 2004. Dosing of ferric chloride to reduce generation of hydrogen sulphide in the sludge treatment process has been practised for some years and the method has been proved to be effective. More dosing points were added last year to further suppress the release of hydrogen sulphide.

Efficient desludging at primary sedimentation tanks can help reduce generation of hydrogen sulphide from the settled sludge during its retention in the tanks. A modern type of continuously operated sludge scraper was used to replace most of the old, aged and less efficient travelling bridge scrapers in 2003-04.

The second step is to enclose the odour sources, such as flow channels, water chambers and screenings collection areas, that was completed in 2003. Deodouriser was installed to these enclosures to remove malodourous gases. Low cost high odour removal efficiency biofilter was used for deodourisation.

Regular monitoring of hydrogen sulphide level at ten strategic locations of the works commenced in July 2003. Monitoring results indicated that the hydrogen sulphide concentration had dropped and been maintained at very low levels since the last quarter of 2003. This finding is also in line with the odour complaints received. During an interview with a resident in the nearby Kam Tai Court on 19 June 2004, the resident greatly appreciated DSD's efforts in odour abatement and remarked that the odour level had significantly reduced in the past twelve months.

Environmental Performance Target
The effect on the environment by a sewage treatment plant is best measured by the quality of effluent it produces. The effluent quality is regulated by the Discharge License Conditions (DLC) of the Discharge License whereby limitations and standards are set by the Environmental Protection Department for a number of parameters including the total suspended solids (TSS), the 5-day biochemical oxygen demand (BOD5), ammonia nitrogen, total nitrogen and the E. Coli count for indicating the amount of faecal bacterial population in the treated effluent.

In 2003-04, a compliance record of 98% was achieved arising from 6,297 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 the DLC. This is also the performance target in the design for most sewage treatment
plants in the Department and the result should reflect the effort of the operator and the level of treatment achieved.



Difficulties in laying sewers in busy urban streets-
the traffic diversion perspective


Laying new sewers is never an easy task as roads in Hong Kong are congested with different kinds of public utilities. Though new technological development in trenchless construction method over the last 10 years or so has relieved the situation to a great extent, laying of sewers still unavoidably requires partial or even complete closure of roads for a few months or longer, and therefore causing adverse impact on the traffic particularly in busy urban streets. Closure of roads, particularly in front of shops, will never be welcome by the public and the shop owners. Laying sewers in busy urban streets therefore remains a great challenge to the Department.


In order to improve the co-ordination and control of road opening works and to reduce traffic impact, all major sewers laying projects are subject to traffic impact assessments during the design stage. Consultation with affected shop owners and residents will also be carried out. During the construction stage, all proposed works have to be discussed at Traffic Management Liaison Group with members from Police, Transport Department, Highways Department, and other stakeholders, and the proposed temporary traffic management measures and diversion schemes will be subject to trial run before the works are commenced. Consultation with concerned shop owners will be carried out again to solicit their views on the types of hoarding and other relief measures according to the prevailing site operation and condition. Appropriate conditions, such as restriction on working hours, minimum footpath width etc, would be specified in order to minimise the disturbance.

The Department always adopts a proactive public communication approach to obtain the public support for the works. Innovative design, such as fully transparent hoardings, will be adopted to enhance the construction environment. Clear and sufficient signage will be put up for both drivers and pedestrians.