ConstructioNews
Vol 30 No 2 (11-2020)
Desalination Plant in Tseung Kwan O
Background
A reliable fresh water supply is of paramount importance in sustaining Hong Kong’s development and economic growth. However, our fresh water resources, which come from the yield collected from local gathering ground and raw water imported from Dongjiang (DJ) in Guangdong Province, are both susceptible to climate change. That aside, the reliability of fresh water supply to Hong Kong is also facing other challenges such as increasing water demand arising from population and economic growth and keen demand for DJ water resource due to the rapid economic development in the Pearl River Delta Region.
With the increasing water demand and the extreme dry weather that could be brought about by climate change, it is necessary to develop the strategic alternative water resource by seawater desalination which is not susceptible to climate change to safeguard water security in Hong Kong. Therefore, the government proposes to construct a medium-sized desalination plant on an eight-hectare site reserved in Tseung Kwan O (TKO) Area 137.
Mainlaying Works
Contract of Mainlaying in Tseung Kwan O was awarded in November 2017. It comprises the laying of a 1,200 millimetres diameter fresh water main of about 10 kilometres in length, connecting the proposed desalination plant at TKO to the existing TKO fresh water primary service reservoir, and associated works.
As the construction time required for the mainlaying works will be longer than that for the desalination plant, the mainlaying works were commenced first to match with the programme for the commissioning of the desalination plant.
Conventional method and trenchless method is being employed for laying the fresh water main. The conventional method refers to laying pipelines in trench. It involves opening up the road surface for laying of pipelines. Around 85% of the fresh water mains under this project will be laid by conventional method. The actual percentage will depend on the site conditions.
The Trenchless method (sometimes referred to as ‘minimum dig’ or ‘reduced dig’ method) refers to the use of heading, pipe jacking, micro-tunnelling or boring techniques to construct underground pipelines without opening up the road surface for laying of pipelines. This method will be employed when the conventional method is not feasible due to site constraints such as busy traffic conditions.
Design, Build and Operate First Stage of Tseung Kwan O Desalination Plant
Design, Build and Operate Contract for First Stage of Tseung Kwan O Desalination Plant was awarded in December 2019. The contract is worth about $9,018.9 million. The design and construction have commenced in December 2019.
The desalination plant using reverse osmosis will have a water production capacity at 135,000 cubic metres per day with provision for future expansion to the ultimate water production capacity up to 270,000 cubic metres per day.
Key components of the project comprise formation of the reserved site in TKO Area 137 and design and construction of the proposed desalination plant including seawater treatment components using reverse osmosis technology, intake pipes, intake pumping station and outfall pipes, administration building, laboratory, maintenance workshop, chemical building and chlorine building, sludge filter press building, fresh water pumping station and power supply facilities.
Seawater Reverse Osmosis
In order to preserve the environment in the vicinity of the project, a review of the latest development of various desalination technologies, including seawater reverse osmosis and multi-stage flash distillation, was conducted for recommendation of environmental friendly design.
According to "Feasibility Study on Development of Desalination Facilities in Hong Kong", which was completed in 2002, reverse osmosis is more suitable to be adopted as the desalination technology of the project. As no boiler is required, there will be no generation of nitrogen oxides with least energy consumption. Other advantages includes less land requirement for the treatment units, less operation complexity and less capital and operating costs.
Reverse osmosis has become a mature technology and has been used in many overseas desalination plants in recent years. According to the International Desalination Association, there are over 17,000 desalination plants worldwide with a total water production capacity of more than 80 million cubic metres per day and reverse osmosis technology accounts for approximately 60 per cent of the installed capacity.
Environmental Implications
The Project is a designated project under the Environmental Impact Assessment (EIA) Ordinance which requires an environmental permit for its construction and operation. The Director of Environmental Protection approved the EIA report in November 2015 and issued an EP for the construction and operation of the Project in December 2015.
With the implementation of the recommended mitigation measures and an environmental monitoring and audit programme, the approved EIA report concluded that the project will not cause any adverse environmental impacts. Silt curtains should be deployed during marine works. A silt curtain efficiency test for the combined use of floating silt curtain type and cage type silt curtain for dredging at seawater intake will also be completed prior to intake dredging works commencement.
Pollution control measures should be implemented during construction including frequent watering of site, provision of wheel washing facilities, covering of materials on trucks, use of silenced construction plant, temporary noise barriers and acoustic enclosures for noisy construction activities.
The waste arisings during the construction include excavated material, construction and demolition material and marine sediments from dredging works. The government requires the contractor to avoid, reduce, reuse and recycle inert construction waste. The contractor should separate the inert portion from non-inert construction waste on site for disposal at appropriate facilities.
It is noted that a majority of the desalination plant site consists of man-made habitats with very low to low ecological values. The watermain is located on existing roads which are of no particular ecological value, and the submarine facilities are located on the seabed with soft and hard bottom communities typical in other similar habitats of Hong Kong. The EIA report sets out mitigation measures to reduce ecological impacts, such as regular checks in construction site practices and boundaries. With the implementation of the proposed mitigation measures, no adverse residual impact is expected.
Conclusion
As a coastal and well-developed city with scarce freshwater resources, Hong Kong has unlimited supply of seawater from the ocean that is not affected by the acute climate changes. Thus, the desalination plant is an appropriate solution to provide potable water and to provide alternative of the freshwater resources. The planning and investigation study for the desalination plant confirmed that TKO Area 137 is a suitable location for siting the desalination plant in terms of the quality of nearby seawater. The use of the reverse osmosis technology for the desalination plant has also been proved technically feasible.
The mainlaying works will be completed by April 2022. The desalination plant is expected to commence operation in 2023 with a water production capacity of 135,000 cubic metres per day.
Resources:
TKO Desalination Plant Website
Water Supplies Department
A reliable fresh water supply is of paramount importance in sustaining Hong Kong’s development and economic growth. However, our fresh water resources, which come from the yield collected from local gathering ground and raw water imported from Dongjiang (DJ) in Guangdong Province, are both susceptible to climate change. That aside, the reliability of fresh water supply to Hong Kong is also facing other challenges such as increasing water demand arising from population and economic growth and keen demand for DJ water resource due to the rapid economic development in the Pearl River Delta Region.
With the increasing water demand and the extreme dry weather that could be brought about by climate change, it is necessary to develop the strategic alternative water resource by seawater desalination which is not susceptible to climate change to safeguard water security in Hong Kong. Therefore, the government proposes to construct a medium-sized desalination plant on an eight-hectare site reserved in Tseung Kwan O (TKO) Area 137.
Mainlaying Works
Contract of Mainlaying in Tseung Kwan O was awarded in November 2017. It comprises the laying of a 1,200 millimetres diameter fresh water main of about 10 kilometres in length, connecting the proposed desalination plant at TKO to the existing TKO fresh water primary service reservoir, and associated works.
As the construction time required for the mainlaying works will be longer than that for the desalination plant, the mainlaying works were commenced first to match with the programme for the commissioning of the desalination plant.
Conventional method and trenchless method is being employed for laying the fresh water main. The conventional method refers to laying pipelines in trench. It involves opening up the road surface for laying of pipelines. Around 85% of the fresh water mains under this project will be laid by conventional method. The actual percentage will depend on the site conditions.
The Trenchless method (sometimes referred to as ‘minimum dig’ or ‘reduced dig’ method) refers to the use of heading, pipe jacking, micro-tunnelling or boring techniques to construct underground pipelines without opening up the road surface for laying of pipelines. This method will be employed when the conventional method is not feasible due to site constraints such as busy traffic conditions.
Design, Build and Operate First Stage of Tseung Kwan O Desalination Plant
Design, Build and Operate Contract for First Stage of Tseung Kwan O Desalination Plant was awarded in December 2019. The contract is worth about $9,018.9 million. The design and construction have commenced in December 2019.
The desalination plant using reverse osmosis will have a water production capacity at 135,000 cubic metres per day with provision for future expansion to the ultimate water production capacity up to 270,000 cubic metres per day.
Key components of the project comprise formation of the reserved site in TKO Area 137 and design and construction of the proposed desalination plant including seawater treatment components using reverse osmosis technology, intake pipes, intake pumping station and outfall pipes, administration building, laboratory, maintenance workshop, chemical building and chlorine building, sludge filter press building, fresh water pumping station and power supply facilities.
Seawater Reverse Osmosis
In order to preserve the environment in the vicinity of the project, a review of the latest development of various desalination technologies, including seawater reverse osmosis and multi-stage flash distillation, was conducted for recommendation of environmental friendly design.
According to "Feasibility Study on Development of Desalination Facilities in Hong Kong", which was completed in 2002, reverse osmosis is more suitable to be adopted as the desalination technology of the project. As no boiler is required, there will be no generation of nitrogen oxides with least energy consumption. Other advantages includes less land requirement for the treatment units, less operation complexity and less capital and operating costs.
Reverse osmosis has become a mature technology and has been used in many overseas desalination plants in recent years. According to the International Desalination Association, there are over 17,000 desalination plants worldwide with a total water production capacity of more than 80 million cubic metres per day and reverse osmosis technology accounts for approximately 60 per cent of the installed capacity.
Environmental Implications
The Project is a designated project under the Environmental Impact Assessment (EIA) Ordinance which requires an environmental permit for its construction and operation. The Director of Environmental Protection approved the EIA report in November 2015 and issued an EP for the construction and operation of the Project in December 2015.
With the implementation of the recommended mitigation measures and an environmental monitoring and audit programme, the approved EIA report concluded that the project will not cause any adverse environmental impacts. Silt curtains should be deployed during marine works. A silt curtain efficiency test for the combined use of floating silt curtain type and cage type silt curtain for dredging at seawater intake will also be completed prior to intake dredging works commencement.
Pollution control measures should be implemented during construction including frequent watering of site, provision of wheel washing facilities, covering of materials on trucks, use of silenced construction plant, temporary noise barriers and acoustic enclosures for noisy construction activities.
The waste arisings during the construction include excavated material, construction and demolition material and marine sediments from dredging works. The government requires the contractor to avoid, reduce, reuse and recycle inert construction waste. The contractor should separate the inert portion from non-inert construction waste on site for disposal at appropriate facilities.
It is noted that a majority of the desalination plant site consists of man-made habitats with very low to low ecological values. The watermain is located on existing roads which are of no particular ecological value, and the submarine facilities are located on the seabed with soft and hard bottom communities typical in other similar habitats of Hong Kong. The EIA report sets out mitigation measures to reduce ecological impacts, such as regular checks in construction site practices and boundaries. With the implementation of the proposed mitigation measures, no adverse residual impact is expected.
Conclusion
As a coastal and well-developed city with scarce freshwater resources, Hong Kong has unlimited supply of seawater from the ocean that is not affected by the acute climate changes. Thus, the desalination plant is an appropriate solution to provide potable water and to provide alternative of the freshwater resources. The planning and investigation study for the desalination plant confirmed that TKO Area 137 is a suitable location for siting the desalination plant in terms of the quality of nearby seawater. The use of the reverse osmosis technology for the desalination plant has also been proved technically feasible.
The mainlaying works will be completed by April 2022. The desalination plant is expected to commence operation in 2023 with a water production capacity of 135,000 cubic metres per day.
Resources:
TKO Desalination Plant Website
Water Supplies Department