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UV Disinfection Of Seawater RO Permeate Proves Effective For A World’s First Large-scale, Dual-mode Desalination Plant

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Singapore’s fourth desalination plant is the first large-scale water treatment facility that can treat both seawater and freshwater. Officially opened in February 2021, the Keppel Marina East Desalination Plant (KMEDP), operated by Marina East Water Pte Ltd, a wholly owned subsidiary of Keppel Infrastructure, has been supplying up to 137,000 cubic metres (about 30 million gallons) per day – representing seven percent of Singapore’s water demand. This dual-source treatment facility strengthens the island’s water supply resilience as weather conditions become increasingly unpredictable.

2. Staff at UV Filter_Jolene and Nicholas_03_EK39156_web res.jpgDuring periods of heavy rainfall resulting in higher water levels in the Marina Reservoir local catchment area, the plant will treat freshwater flowing into the reservoir to produce potable water. During drought conditions, the plant will draw and treat water from the sea to produce desalinated water. This allows PUB, Singapore’s National Water Agency, to choose its water sources carefully, which will be increasingly beneficial in the future’s unpredictable but more intense weather patterns expected, due to climate change.

When planning for its Marina East Desalination Plant, PUB needed a treatment solution that could handle the disinfection of seawater reverse osmosis (RO) permeate and provide optimal operations during the treatment of both seawater and freshwater and have a smaller footprint compared to conventional full-scale chlorine disinfection system. The UV system needed to complement the plant’s RO system and provide effective post treatment to minimize secondary pollution and microbial regrowth. The UV disinfection treatment system selected for the plant would need to essentially serve the RO system and adjust itself to meet the varying conditions of the water flowing through the system.

Task

Xylem was tasked to provide a UV disinfection system that would fit the plant’s dual-flow chamber concept and adjust for the switching between the two water supplies. RO is a key procedure in the desalination process that forces seawater through a self-retaining membrane at high pressure. However, during times when fresh marina water from the reservoir is being fed, the plant needs to switch to lower energy and lower pressure RO operations. The UV system would have to adjust to the alternating RO operations. The systems were selected to meet the plant’s 4 Log Adenovirus inactivation/disinfection (99.99% removal) target of seawater RO permeate while actively monitoring real-time operational conditions.

Solution

Xylem supplied nine Wedeco Spektron® 4000e UV systems with EcoTouch 6 controls.

One of the reasons Spektron 4000e UV system was selected is because of its validated performance by state-of-6. Engineers Joan manning control panel_07_EK39551_web res.jpgthe-art bioassay in compliance with the U.S. Environmental Protection Agency’s UV Disinfection Guidance Manual (USEPA’s UVDGM). The system features low-pressure, dimmable lamps that provide relatively high UVC output. By automatically dimming and brightening based on real time conditions, the system systematically matches the UV dosage for changing water conditions. This addresses one of the major tasks of effectively meeting the conditions of the current water source being used while also saving energy and improving efficiency during major operations.

The advanced UV system’s low-pressure high-output amalgam lamps combined with advanced flow distribution technology provide uniform velocities throughout the system’s reactor chamber. With the UV system’s EcoTouch 6 controls, KMEDP can be ensured excellent UV performance through self-monitoring of UV intensity, reactor temperatures and water flow.

Results and customer benefits

7. Close up_Inserting UV Lamp_08_EK39568_web res.jpgDesalination plays a major role in Singapore’s long-term strategy for maintaining a sustainable and reliable water supply. Singapore’s Marina East Desalination plant is a world first large-scale water desalination plant able to treat both fresh water and seawater. Singapore’s fourth desalination plant was named “Desalination Plant of the Year” at the Global Water Awards 2021. A critical component of the plant is its disinfection process. The plant’s UV system - with its compact footprint - ensures optimal disinfection performance independent of the current inlet water situation.