Water. desalination + reuse

May/June 2013

Water. Desalination + reuse

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Singapore trial proves ceramic-ozone synergy PROJECTS _________ Gilbert Galjaard and Holly Shorney-Darby, PWN Technologies, Netherlands; and Wui Seng Ang and Mong Hoo Lim, PUB, Singapore ___ Editor's Note: Since September 2011, PUB, Singapore's national water agency, has been testing a new ceramic membrane treatment technology as a filter for removal of suspended matter and biological pathogens. After 18 months of testing, PUB is now exploring whether ceramic membrane filtration can be included as an option in the design to upgrade Choa Chu Kang Waterworks . CHOA CHU KANG Waterworks (CCKWW), which supplies potable water to the western part of Singapore, was built in two phases. Phase 1 facilities were built in 1975 and upgraded in 2008 to include the retrofitting of sand filters with a polymeric membrane filtration system. Phase 2 facilities include a conventional water treatment plant of coagulation, flocculation, sedimentation, sand filtration and ozonation for primary disinfection. The raw water is drawn from three sources - Kranji, Pandan and the Western Catchments Reservoirs, which include the Tengeh, Poyan, Murai and Sarimbun Reservoirs. The source water has moderate organic carbon levels and low iron and manganese concentrations. There are occasional episodes of taste and odor. PUB, the national water agency, is now looking at a ceramic membrane system offered by PWN Technologies (PWNT) and referred to as CeraMac®. It was developed by the research and development department of PWN, the water supply company of North Holland in the Netherlands and is now being offered to utilities around the world. Ceramic membranes are relatively new to the drinking water industry; they have been used extensively in food processing and industrial applications, but have been historically too costly for municipal drinking water applications. As a utility, PWN wanted the durability benefits of ceramic membranes, but recognized the cost limitations. So the water company focused its research on a new configuration for ceramic membranes, which has lowered the equipment costs while offering more treatment capacity in a smaller space. PUB intereSt PUB was interested in how the CeraMac® system would perform when treating water from the existing clarifiers at CCKWW, as well as how ozonating the | 16 | Desalination & Water Reuse | May-June 2013 feed water would impact performance. The process flow diagrams that were considered are shown in Figure 1. Figure 1. Process flow diagrams of the existing CCKWW (left) and the process alternatives of adding ceramic (CeraMac®) filtration (center) and pre-ozone with ceramic filtration (right) Ozone, which is needed at CCKWW for disinfection in place of traditional chlorine to minimize formation of disinfection by-products, also for control of tastes and odors and as a pretreatment to ceramic membranes, had not been tested so extensively or on such a large scale. The results exceeded the expectations of PUB, PWNT and the drinking water industry. MetHoDoLoGy The demonstration plant consisted of an ozone generator, a side-stream venturi injection system, contactor vessels, a CeraMac®-19 vessel, a backwash supply tank, and a backwash receiving tank. The equipment was installed in an existing sand filter bed at the CCKWW during mid-2011 (Figure 2). The demonstration plant was operated from September 2011 to March 2013.

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