Singapore implements innovative solutions to meet its water requirements-
Singapore’s Public Utilities Board (PUB) is a statutory body under the Ministry of Environment and Water Resources. It is responsible for water collection, production and distribution in Singapore, apart from collection and treatment of wastewater. In the past decade, the board has taken several initiatives to augment water supply and identify alternative sources of supply. Technological innovations such as NEWater and variable salinity have helped the country reduce its dependence on the depleting water sources. In addition, several strategies and long-term plans have been adopted to meet the growing demand for water.
The country’s current water demand stands at about 400 million gallons per day (mgd). As Singapore lacks natural aquifers, large rivers and lakes and has limited land resources to collect rainwater, PUB has adopted a long-term water supply strategy, the Four National Taps, to meet its water requirements. This policy covers local catchment water, imported water, reclaimed water (NEWater) and desalinated water. Currently, about 55 per cent of Singapore’s water demand is met through NEWater (30 per cent) and desalination (25 per cent). The remaining 45 per cent of the demand is being met through water sourced from rivers and reservoirs and imports from Malaysia under a bilateral agreement that will expire in 2061.
An important initiative that has been undertaken to augment water resources in the country involves the implementation of a large-scale water recycling programme where used water is collected and treated to produce industrial water and NEWater. While industrial water is used mainly for cooling and washing purposes, NEWater is treated to an even higher quality and is employed for process use in various water fabrication, electronics and power generation units. A small percentage of NEWater is also introduced into raw water reservoirs and employed for indirect potable purposes.
Wastewater network
PUB’s modern sanitation network provides 100 per cent coverage to households and is based on a distinctive system whereby used water is collected separately through a network of underground sewers that lead to a treatment plant. The sewerage network comprises four water reclamation plants (WRPs) – Ulu Pandan, Jurong, Kranji and Changi – over 3,400 km of gravity sewers, 220 km of pumping mains and 130 pumping installations. In 2013, around 585 billion litres of used water was treated at the four WRPs.
To centralise the collection and treatment of used water or sewage, PUB adopted the strategy of developing the deep tunnel sewerage system (DTSS), a superhighway for the collection, treatment, reclamation and disposal of used water. The overall concept of the DTSS is to use deep tunnels to intercept the flows in the existing gravity sewers, upstream of the pumping installations, and channel the flows by gravity to centralised treatment facilities. The used water is then treated and purified further into high grade reclaimed water or NEWater.
The DTSS is being developed in two phases; Phase I was completed in 2008 and involved the construction of the WRP at Changi with a capacity to treat 176 mgd of used water, a 48 km long deep tunnel and 60 km of linking sewers. The project was undertaken at a cost of $3.4 billion. Currently, used water is transported to the Changi WRP through the deep tunnel running from Kranji to Changi before it is converted to NEWater or discharged into waterbodies. About 30 decanters have been installed at the plant for the thickening and dewatering of sewage sludge. Unlike conventional sewage treatment processes, decanters offer uninterrupted operations and have low space requirements.
In June 2014, the contract for Phase II of the DTSS was awarded to a joint venture of Black & Veatch and AECOM Technology Corporation. This phase involves the extension of the DTSS to the western side of Singapore through a 30 km long tunnel, construction of 70 km of linking sewers and a WRP at Tuas with a capacity of 800 million litres per day (mld). The entire DTSS will lead to the development of three centralised collection and treatment points – the Changi WRP in the east, Kranji WRP in the north, and Tuas WRP in the west.
Water management initiative: NEWater
To meet the water requirements of a rapidly growing population, PUB conducted a study to assess the feasibility of reclaiming wastewater for domestic and industrial use. As per the study, though the process was technically feasible, the large-scale production of reclaimed water through membrane technology was economically unviable. After undertaking a two-year pilot study on membrane technology, PUB commissioned a demonstration plant with a capacity to treat 10 mld of used water in 2000. This was followed by the establishment of the first NEWater factory in 2003.
With the NEWater technology, treated used water from the WRPs undergoes a three-stage treatment process. The first stage involves microfiltration or ultrafiltration processes, which separate insoluble particles from the treated used water. At the second stage, which involves reverse osmosis, high pressure is applied to allow water molecules to pass through semi-permeable membranes. At the third stage, the ultraviolet disinfection process is used to treat all organisms. The water produced is suitable for water fabrication, petrochemical industries that require ultrapure water as well as for drinking purposes. To ensure NEWater’s compliance with water quality standards, a comprehensive water sampling and analysis programme was implemented with quality standards benchmarked against the World Health Organization’s drinking water guidelines and the United States Environmental Protection Agency’s drinking water standards.
Currently, Singapore has four operational NEWater facilities. The largest NEWater plant was operationalised in May 2010 at Changi, and has a capacity of 50 mgd. The demand for NEWater has increased from 4 mgd in 2003–04 to about 60 mgd in 2014. PUB plans to expand the NEWater production capacity to meet 55 per cent of the country’s water requirements by 2060. To this end, it is planning to integrate a NEWater factory with the Tuas WRP and is implementing the NEWater Infrastructure Plan and NIP Extension to link various NEWater factories across the country. The scope involves construction of a NEWater service reservoir and laying of pipelines across different locations.
The road ahead
Going forward, PUB plans to increase its NEWater production and desalination capacities to meet about 80 per cent of its total water requirements by 2060. The board also plans to continue to invest in research and development (R&D) to identify alternative sources of water supply. In fact, the Singapore government reportedly plans to invest about S$330 million in water R&D over the period 2014–19. These efforts will be dedicated to arriving at more cost efficient technologies to treat water.
