Switching from seawater to rainwater

A “dual mode” desalination plant completed testing and commissioning in Singapore despite “inevitable” Covid-related challenges.

The Keppel Marina East Desalination Plant (KMEDP) is said to be a world first – it can treat either seawater or freshwater from the Marina Reservoir, depending on the conditions.

KMEDP commenced operations at the end of June and was built under a Build, Own and Operate (DBOO) arrangement with National Water Agency, PUB.

Capable of producing 137,000 m3/day of drinking water the plant will be operated by Marina East Water, a wholly-owned subsidiary of Keppel Infrastructure.

A complicated set up

Dr Graeme Pearce, principal at Membrane Consultancy Associates, said the concept of “variable salinity” desalination exists, citing Thames Water’s Beckton desalination plant in London and the Tampa Bay Seawater desalination plant.

However, this is the first example of a plant that can deliberately switch water sources, as opposed to a change in feedwater that occurs naturally, for example depending on the tide.

“While the dual intake system appears simple on the surface, it’s a complicated set up.”

Speaking to Aquatech Online, he said: “While the dual intake system appears simple on the surface, it’s a complicated set up with consequences impacting the energy recovery, pumps and controls.”

This has to do with the total dissolved solids (TDS) of seawater being in the range of 40,000 mg/L, compared to lagoon water in the range of 2,000 mg/L.

“This means the plant has been designed with two completely different operation modes,” Pearce added. “Ideally, it will have been designed with two sets of membranes specifically suited to the changing feedwater.”

Energy efficient engineering design

Featuring dual intakes, in dry weather KMEDP will treat pumped seawater but in wet weather can switch to treat rainwater from to produce potable water, using less energy.

Keppel Infrastructure’s appointed engineer, Aecom, said this enables a more energy efficient process compared to a typical desalination plant.

The engineering design includes raw water intake from the sea and reservoir to a dual flow chamber, through pre-treatment using flocculation and dissolved air flotation, then ultrafiltration; a two-pass reverse osmosis system; and post-treatment using ultraviolet disinfection.

In addition to using dual water source, KMEDP also implemented other features for energy optimisation, including direct coupling and permeate split.

Technology partner, Pentair, which provided ultrafiltration membranes (UF) to the project, said KMEDP is also the first large-scale desalination plant in Singapore to use the Direct-Coupling UF-RO (reverse osmosis) approach.

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Taxonomy

• Desalination
• Sustainable Desalination
• Desalination Plant
• Desalination