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Following is a question by the Hon Chan Hak-kan, and a written reply by the Secretary for the Environment, Mr Wong Kam-sing, in the Legislative Council today (February 26):
Question:
According to the information on the web site of the Drainage Services Department, 93 per cent of the population in Hong Kong are served by the existing sewage network. The types of sewage treatment facilities consist of preliminary treatment, primary treatment, chemically enhanced primary treatment, secondary treatment and tertiary treatment. Most of the facilities belong to the preliminary/screening or minor secondary types (the respective numbers of which are 22 and 32) and are mainly located in the old urban areas on Hong Kong Island and in Kowloon. The authorities are improving the sewage treatment facilities under a territory-wide sewage rehabilitation and improvement programme. Moreover, in an effort to explore new water resources, the Government of the previous term has launched pilot schemes of reclaimed water usage, under which wastewater is purified with a series of effective treatment processes as well as disinfection and sterilisation procedures to become reclaimed water that meets the stringent standards of effluent reuse. Regarding the proper treatment of sewage and utilisation of reclaimed water, will the Government inform this Council:
(1) of the details of the aforesaid rehabilitation and improvement programme; how the authorities intend to treat properly the sewage generated by the remaining 7 per cent of the population who are not served by the sewage network, and of the difficulties involved;
(2) given that the Ngong Ping Sewage Treatment Works is the only tertiary treatment facility at present, whether the authorities will, in addition to upgrading Shek Wu Hui Sewage Treatment Works progressively to the tertiary level, study if there is a need to provide more tertiary treatment facilities; if so, of the details; if not, the reasons for that;
(3) given that water resources in Hong Kong are very precious, whether it has assessed if the reclaimed water generated from the sewage treatment works is fully utilised at present; if so, of the outcome; whether it has any plan to expand the usage of reclaimed water; if so, of the details; if not, the reasons for that;
(4) given that Hong Kong's sewage disposal strategy was formulated in 1989 and has been in use since then, for how long the relevant sewage treatment technologies and discharge license standards (including the percentile and upper limit/monthly geometric mean) have been adopted; whether it has assessed if those technologies and standards are up to par with the latest international standards; if the assessment outcome is in the affirmative, of the details; if the assessment outcome is in the negative, whether it will conduct a review and introduce improvement;
(5) given that amendments were made only in 1990 and 1993 to the Water Pollution Control Ordinance (WPCO) (Cap. 358) since its enactment in 1980, whether the authorities have assessed if WPCO is still effective in regulating the discharge and treatment of sewage; if so, of the outcome; and
(6) as it has been reported that in addition to Shatin Sewage Treatment Works, the authorities also plan to relocate the sewage treatment works in Sai Kung and Sham Tseng to caverns, whether the authorities will take this opportunity to upgrade the treatment level of those two sewage treatment works; if so, of the details; if not, the reasons for that?
Reply:
President,
(1) For planning the public sewerage system, the whole of Hong Kong is divided into 16 catchment areas, each with a Sewerage Master Plan (SMP) produced. The SMPs provide a blueprint of the required sewerage infrastructure with the objective to collect sewage on a catchment-by-catchment basis and direct it to sewage treatment works (STWs) for processing. At present, the public sewerage system serves about 93 per cent of the population and collects about 2.8 million cubic metres of sewage every day. About 70 per cent of the collected sewage receives chemically enhanced primary treatment or a higher level of treatment before being discharged. At present, sewage treatment facilities operated by the Drainage Services Department (DSD) include 21 preliminary STWs, 4 chemically enhanced primary STWs and 40 secondary STWs.
The remaining 7 per cent of the population are mainly in unsewered rural areas. In determining the priority for implementation of new sewerage projects, we would consider various factors including the extent of the environmental problems and the benefits of the new sewerage, future development of the area, population projections, proximity to trunk sewers, cost-effectiveness, project readiness and local views and support.
(2) In determining the sewage treatment level for individual STWs to achieve optimal cost-effectiveness for protecting the environment, we would consider various factors including their geographical conditions, the relevant sensitive receivers, and the hydrology, assimilative capacity and Water Quality Objectives (WQOs) of the receiving water bodies. If the proposed STW is a designated project requiring an environmental permit, an environmental impact assessment and associated water quality modelling would need to be carried out to determine the level of sewage treatment. At present, apart from the Shek Wu Hui STWĄ@(SWH STW), we have also started the planning for upgrading the Yuen Long STW to tertiary treatment level in order to further protect the water quality of Deep Bay.
(3) Reclaimed water as a new water resource is an important initiative of the water supply management measures under the Total Water Management strategy which the Government has been implementing since 2008. Reclaimed water produced from STWs is generally used for non-potable applications such as toilet flushing, irrigation or street cleansing. Currently, non-potable water demand in Hong Kong mainly comes from toilet flushing.
To save precious fresh water resources, the Water Supplies Department (WSD) has been providing seawater for toilet flushing since the 1950s. Currently, the supply network for provision of seawater for toilet flushing (the Network) covers about 80 per cent of the population in Hong Kong and save about 270 million cubic metres of fresh water each year. With the progressive completion of the seawater supply systems in Pokfulam, Yuen Long and Tin Shui Wai by next year, seawater supply for toilet flushing will be provided gradually to customers in these areas. Meanwhile, we have started planning of the seawater supply system for Tung Chung. It is anticipated that the population covered by the Network will increase to 85 per cent. Apart from saving freshwater, using seawater for toilet flushing is more cost-effective than other water resources (e.g. reclaimed water) in most areas in Hong Kong.
However, for some areas that are far from the seashore, such as Sheung Shui and Fanling, the costs for installation and operation of seawater supply systems are very high. This provides the opportunity for use of reclaimed water. The DSD is planning to expand the SWH STW and upgrade its treatment technology. Taking the opportunity, the WSD has in collaboration with the relevant departments studied the feasibility of producing reclaimed water of acceptable standard from the tertiary treated sewage effluent from the SWH STW for supplying the district for non-potable uses (including irrigation, toilet flushing, etc.). The results of the study revealed that it would be cost-effective to supply reclaimed water to the district as the additional treatment process required for producing reclaimed water from the treated effluent of the SWH STW would be simple. The WSD has already started the planning work and expects that it will take eight years from planning to commencement of the supply of reclaimed water. The WSD will continue to actively explore the opportunities and feasibility of supplying reclaimed water to those areas, which are outside seawater supply zones, for non-potable uses.
(4) The Environmental Protection Department (EPD) applies licensing control, as provided under the Water Pollution Control Ordinance (WPCO), to regulate any wastewater discharge made into the waters of Hong Kong, including treated effluent from government sewage treatment facilities. In establishing stringent standards in the WPCO licence, the EPD takes into account the need for protecting the receiving water body, and makes reference to the effluent standards stipulated in the technical memorandum issued under the WPCO and recommendations made in the relevant environmental impact assessment reports. In general, we specify more stringent effluent standards if the discharge is at a high flow rate, the receiving water body has low assimilative capacity, or the water body has sensitive uses. In summary, we establish the effluent standards in the WPCO licence according to the needs of individual cases, and our licensing criteria are in line with international practices.
(5) Following the enactment of the WPCO in 1980, the EPD progressively declared the waters of Hong Kong as Water Control Zones (WCZs), and government sewage treatment facilities located in various WCZs were also progressively put under licensing control. Since the implementation of the WPCO, the public sewerage system has already served about 93 per cent of the population and the water quality in Hong Kong has continued to improve. For example, for those rivers and streams susceptible to the impact of discharges, the compliance with the key WQOs increased from 47 per cent in 1987 to 89 per cent in 2012. The WQO compliance rate for bathing beaches increased from 65 per cent in 1987 to 100 per cent in 2010, and full compliance with the WQO has been maintained. At the same time, the occurrence of red tides in Hong Kong has decreased substantially from over 80 cases per year in 1988 to less than 20 cases per year since 2006. Overall, based on the monitoring data gathered in the past 27 years, the WPCO and our water quality management measures are effective and have successfully brought about water quality improvement in most parts of Hong Kong.
(6) As mentioned above, we would consider various factors to determine the sewage treatment level for individual STWs. The existing Sha Tin STW is a secondary STW. The treated effluent is conveyed to Kai Tak River in Wong Tai Sin for discharge to Victoria Harbour. According to the preliminary planning under the current feasibility study, the relocated Sha Tin STW could maintain the same effluent quality and export route after relocation. In the next investigation and design stage, the DSD will continue to liaise with the EPD to ensure that the future effluent quality will continue to meet the requirements for the use of the receiving water body.
The current sewage treatment levels of the existing Sai Kung STW (SK STW) and Sham Tseng STW (ST STW) have already met the WQOs of the concerned receiving waters. As the the relocation of the SK STW and ST STW would not change the environmental conditions of the concerned areas, there may not be a need for upgrading the treatment level of the two STWs after their relocation. Nevertheless, the DSD will review in the forthcoming feasibility study the effluent standards and quality of the existing SK STW and ST STW and discuss with the relevant departments, including the EPD, in detail any necessary changes or upgrading of the sewage treatment standards on relocation.
Ends/Wednesday, February 26, 2014
Issued at HKT 14:46
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