Changi Water Reclamation Plant, Changi, Singapore
Changi Water Reclamation Plant (CWRP), located at the eastern end of Singapore, is one of the largest and most advanced reclamation facilities in the world.
It was opened by the country's Prime Minister Lee Hsien Loong in June 2009. The ground breaking ceremony for the project was held in May 2001.
The plant has a capacity to treat 176 million gallons (800,000 cubic meters) of used water a day. The plant will undergo phased expansion until its capacity reaches 528 million gallons of water a day.
The plant is spread over 32ha of land and is operated by Singapore's Public Utilities Board (PUB).
CWRP is part of the S$3.65bn (nearly $3bn) deep tunnel sewerage system (DTSS). DTSS is an important component of Singapore's water management strategy. It allows every drop of used water to be collected, treated and further purified into NEWater, Singapore's own brand of reclaimed water.
The DTSS, which is being developed in two phases, includes two large, deep tunnels, two centralised water reclamation plants, deep sea outfall pipes and a link sewer network.
Phase one of DTSS was completed in 2008. In addition to the CWRP, phase one includes a 48km tunnel from Kranji to Changi, 60km of link sewer and two 5km-long deep sea outfall pipes.
Phase two of the DTSS will consist of the south tunnel and its network of link sewers, leading to a water reclamation plant in the south-western part of Singapore and another deep sea outfall. It is expected to be developed by 2016. The existing pumping stations and reclamation plants are expected to be out of service by 2045.
Changi water reclamation plant design features
CWRP is built partially underground and stacked for maximum compactness and land use. The plant includes an influent pumping station (IPS), an effluent pumping station and a liquids processing and solids processing systems.
Used water from the DTSS is pumped to the IPS before being transferred to headworks for treatment.
The 50m-deep IPS has two pumping stations and a coarse screen shaft. Each pumping station is installed with five influent pumps with combined pumping capacity of 400,000CMD. The IPS receives used water from a sewerage tunnel.
The treated effluent is discharged into the deep sea using a twin 3m diameter outfall pipe which is about 5km long and 35m below sea level.
In February 2011, PUB decided to expand the plant to treat an additional 22 million gallons (60,000 cubic meters a day (cmd)).
Black & Veatch has been selected to provide engineering design services for the project. Phase two is proposed to include expansion of effluent pumping station, anaerobic digester and membrane plant construction. Tenders for construction and installation works were closed in July 2011 and are currently being evaluated. The expansion project is expected to be completed by 2016.
Wastewater treatment at CWRP
Captured wastewater at the CWRP is treated by removing the solids and nutrients present in the used water.
The treated water is then returned to the environment or transferred to NEWater factories for further processing. At NEWater factories, the reclaimed water is purified further and made suitable for drinking using advanced membrane technologies.
CWRP uses liquids and solids processes to treat the wastewater. The incoming used water is first fed into coarse screens for the removal of large debris.
The water is then transferred to headworks where smaller particles, grit, oil and grease are removed by using fine screens.
Heavy particles present in wastewater settle down at the bottom in the form of sludge while passing through double-deck sedimentation tanks. These solids are removed by moving scrappers.
After the removal of heavier organic particles, the wastewater is fed into bioreactors where impurities and colloidal organic matter are broken down by using micro-organisms.
The resultant used water is sent to secondary sedimentation tanks for the activated sludge or heavy micro-organisms to settle down. These are recycled to the bioreactors and some are sent for solids processing.
From the secondary sedimentation tanks, the treated used water is discharged into the Straits of Singapore through the 5km long outfall pipes.
Singapore's NEWater, central to water sustainability
NEWater is considered the pillar of Singapore's water sustainability and currently meets 30% of the total water demand in the country.
The NEWater production process uses advanced dual membrane and ultraviolet technologies to further treat the reclaimed water.
At present, there are four NEWater factories in Singapore. The Sembcorp NEWater plant, built on the rooftop of the CWRP, is the latest and the largest one. It was opened in May 2010 and has a capacity of 50mgd.
Key players involved in the CWRP
Detailed design and tendering services for the plant were provided by CH2M HILL and CPG Consultants. ABB supplied ten ACS 1000 medium voltage variable speed drives to control the pumps of the influent pumping stations.
The general contractors for the project were Lum Chang Building Contractors, Koh Brothers, Sembcorp Engineers and Constructors, Keppel Engineering, United Engineers and Voltas.
Siemens supplied two odour control trains, a dual-bed, horizontal-flow V-bank-style carbon adsorber, a 'unitary multistage' chemical scrubber system and coarse-bubble diffuser systems.
Other suppliers included BASF, Festo and Straub. BBR group was contracted to construct two non-process buildings.