Desalination, which debuted in Singapore in 2005, is one of the four national taps in the country’s long-term water strategy, the others being reservoir water, imported water and wastewater reclamation (NEWater). The city state has been securing its water resources by boosting water use from NEWater and seawater desalination.
Singapore’s water demand is expected to double by 2060, with non-domestic water demand estimated to make up 70 per cent of the overall water use. Desalination is expected to meet up to 30 per cent of the water demand by 2060, up from 25 per cent in 2017. Currently, there are three desalination plants in Singapore and a fourth one, Keppel Marina East Desalination Plant (KMEDP), is under construction. This plant is expected to be completed by 2020.
Keppel Infrastructure, through its wholly owned subsidiary, Marina East Water Private Limited, has signed a 25-year water purchase agreement with the Public Utilities Board (PUB) for KMEDP. The first-of-its-kind facility in Singapore, the plant will be a large-scale dual-mode desalination plant that can treat both seawater and freshwater to produce up to 137,000 cubic metres of drinking water daily. Depending on wet or dry weather conditions, water will be channelled either from the Marina reservoir or the sea to the plant for treatment, thus reducing plant energy usage when freshwater is abundant. This ability, to switch from treating freshwater to seawater during dry season, would ensure a more weather-resilient water supply for Singapore.
The plant will feature a sleek modern design that breaks away from that of conventional water treatment plants. Against the backdrop of Singapore’s central business district skyline, it is set along the Eastern Coastal Park Connector Network that bridges East Coast Park and Gardens by the Bay East. All of the plant’s water treatment equipment will be located underground, topped off by a gently sloping green lawn as its roof. The desalination plant will also incorporate environment friendly features such as rainwater harvesting and 20,000 square metres of open green space on the rooftop for community recreation. The rainwater collected will be used to irrigate the green roof and support the facility’s water features and landscaping needs.
The plant will have a separate dual flow chamber to enable it to treat seawater and reservoir water, with a valve that can switch between the two. The engineering design of the plant shows raw water intake from the sea and reservoir to a dual-flow chamber, through pre-treatment using flocculation and dissolved air flotation, then ultra-filtration; a two-pass reverse osmosis (RO) system and post-treatment using ultraviolet disinfection. The architectural design enables the plant to blend in with the surrounding environment, with a private viewing gallery and the rooftop park at the ground level. It will treat both seawater and freshwater by using RO and other advanced membrane technology, depending on the prevailing weather conditions.
The dual-mode desalination process took the government years of research and testing to make it practical at a large scale. Its reliability was tested on a smaller scale at a plant at Sungei Tampines that was set up in 2007. The facility, which also draws freshwater and seawater from surrounding sources, is able to produce around 1 million gallons a day (mgd).
The contract to supply RO membranes to the plant has been awarded to Nitto Denko Corporation. Nitto has been supplying its membrane technologies for Singapore’s water reclamation initiative, NEWater, since 2000. The company claims that it has contributed to the establishment of Singapore’s water supply infrastructure in collaboration with PUB. Its new product, ESPA2-LD MAX enables energy efficient high water production by maximising RO element’s membrane area. These are features that led to the selection of Nitto’s RO elements.
The Swiss engineering firm, ABB, will supply back-up power systems for the plant. The contract includes supplying complete electrical, instrumentation and automation and control systems for the plant. The scope of supply includes AC and DC uninterruptible power supply and emergency diesel generator, 66 kV gas-insulated switchgears, power and distribution transformers, medium- and low-voltage switchgears and drives, control system, remote terminal units, field instruments and analytical systems. For this plant, ABB said it will design, engineer, manufacture, install, test and commission the complete plant electrification, instrumentation and water analysers, automation and control system.
Despite the scale of the project, Keppel claims that people who walk past its future facility will hardly notice its presence. The water treatment machinery will be underground, while plants, the botanic kind, and water features on its above-ground structure will blend with the Eastern Coastal Park Connector Network that will run next to it. There will also be a viewing gallery with glass panels through which the desalination equipment can be observed, but access will be by appointment for security reasons.
However, since the plant and pipelines sit on reclaimed land, which is mostly made of clay, extra care must be taken in the building and excavation. The civil engineering component is very important in this plant because of the location, the type of soil condition, and the design of the plant. With the scheduled commissioning of this plant in 2020, Singapore will have an additional desalination capacity of 30 mgd. Also, a fifth desalination plant of similar capacity at Jurong Island is in the pipeline and is expected to be completed around the same time. Overall, this would bring the daily water production in Singapore to a total of 190 mgd of water. This will hugely supplement Singapore’s burgeoning demand for water in the years to come.