Inauguration of Singapore’s third desalination plant at Tuas-

Desalination of seawater has been an important component of Singapore’s long-term strategy for water self-sufficiency. Over the years, there has been a tremendous increase in water demand in Singapore due to rapid industrial growth. At present, the city-state has three desalination plants – one at SingSpring and two at Tuaspring. Together, these plants can produce 130 million gallons per day (mgd) of desalinated water.

Before the opening of the third plant, Singapore was able to meet about 25 per cent of its drinking water needs by desalination. With the operationalisation of the third plant in June 2018, the share has increased to 30 per cent.

Singapore’s desalination expedition

The beginning of Singapore’s desalination journey can be traced back to 2005 when the first desalination plant was set up with a capacity of 30 mgd. SingSpring Pte Limited, a wholly owned subsidiary of Hyflux Limited, constructed the facility on a design-build-own-operate (DBOO) agreement. Based on the agreement, SingSpring is expected to supply 30 mgd of desalinated water to the Public Utilities Board (PUB) for a 20-year period.

The second desalination plant in Tuaspring, which was commissioned in September 2014, is one of the largest in Asia and has twice the capacity of the existing SingSpring desalination plant. This plant is also being operated and managed by Hyflux Limited. The plant has several distinguishing characteristics that make it more cost efficient in comparison to the SingSpring desalination plant. The plant’s compact design has reduced footprint (per cubic metres (cu m)) by more than 30 per cent as compared to the SingSpring desalination plant. It also holds the distinction of having one of the largest pretreatment ultrafiltration membrane facilities (318,000 cu m per day) in the world. Besides, owing to advanced technology and on-site power generation, the tariff rate of the second Tuas plant is lower than that of the SingSpring plant. In fact, the first-year price for the Tuaspring (second) plant is 0.45 cents per cu m, lower than the SingSpring’s first-year price of 0.78 cents per cu m.

Unlike the first two desalination plants that are being operated by private agencies under a public-private partnership agreement, the third plant will be owned and operated by PUB.

Even with a size as small as 3.5 hectare, it can produce 30 mgd of water. The SingSpring desalination plant, on the other hand, produces the same amount of water with the size of 6.3 hectare, nearly double that of the Tuas (third) desalination plant.

Ownership

The Tuas (third) desalination plant is the first plant to be owned as well as operated by PUB. Eight companies had bid for the project but HSL Constructor Pte Limited offered the most economical price of $217 million for the design and construction of the plant. Thus, PUB awarded the construction contract for the Tuas (third) desalination plant to HSL Constructor Pte Limited. The scope of works for the contractor included process design and engineering, civil works, mechanical, instrumentation, electrical and control works, equipment procurement and installation, testing and commissioning and maintenance for two years.

Technology at Tuas

In Singapore, the Tuas (third) desalination plant is the first to make use of an advanced pre-treatment technology. This technology brings together dissolved air flotation and ultrafiltration. The treatment process employed at this plant involves six steps.

Intake screens: Seawater is taken into the plant through a gigantic underwater pipe.

Screening: In order to remove coarse as well as fine particles, the seawater is passed through a two-stage mechanical filtration process.

Dissolved air flotation: Impurities are lumped together to form bigger particles by the addition of some chemicals. For the easy removal of impurities, fine air bubbles are pumped in to make them float.

Ultrafiltration: To remove impurities, microorganisms and bacteria of smaller sizes, the clarified seawater obtained goes through a semi-permeable membrane.

Reverse osmosis unit: To separate dissolved solids, the pretreated seawater is pumped at a high pressure through the semi-permeable membrane.

Post-treatment: To make the treated water potable, chemicals such as chlorine and fluoride are added.

To reduce the plant’s dependence on conventional energy sources, solar panels will be fitted on its roof by the end of 2018. These panels will cover more than 7,000 square metres of the roof’s total area. It is the first plant in Singapore to do this. The panels can produce 1.4 million kWh hours of energy per year. However, this amounts to only 1 per cent of the total energy needs of the plant as it takes a substantial amount of energy to run the facility. The amount of energy that will be produced can be used to run only the administrative building of the plant.

Future plans

By 2020, Singapore is planning to construct two more desalination plants. It is thus expected that by 2060, 30 per cent of the future water needs arising in Singapore will be met by desalinated water.

The consultancy tender for the fourth desalination plant to be set up at Marina East has been awarded.

Concluding remarks

Singapore’s long-term strategy aiming at a steady water supply is named PUB’s Four National Taps. Desalinated water constitutes one of those Four National Taps with the other three being water coming from local catchments, imported water from Johor and NEWater.

Accordingly, the Tuas (third) desalination plant is expected to play a key role in meeting the future drinking water demand of Singapore.

The chief executive of the water agency, Ng Joo Hee believes that the opening of this plant will prove to be a milestone in water security for Singapore. According to him, it is a test bed for the technologies that PUB has been exploring to cut energy usage for seawater desalination by half. Young Joo Chye, director (engineering development and procurement), PUB, is of the opinion that desalinated water has enhanced the resilience of water supply in Singapore. He feels that the combination of NEWater (high purity reclaimed water produced from treated used water) and desalinated water has helped Singapore combat adverse weather conditions like dry spells in recent years. Moreover, the Tuas (third) desalination plant will assist them in further expanding their water supply system to cater to growing water demands in a cost economical and dependable way.