Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/133796
PROJECTS The specific flux (Figure 3), which is the flux normalized to 25oC and divided by the TMP, when operating with ozonated feed water was more than double that when operating without ozone. This means that with ozone, over twice as much water can be treated through the ceramic membrane at equal operating pressures, and this translates to substantial operating cost savings. Another operating parameter of interest is the frequency of cleaning the ceramic membranes (ie, clean-in-place; CIP). A CIP requires that the ceramic membrane vessel be removed from service for 6 -10 hours while chemical solutions are circulated through the vessel to remove deposits (foulants) which block the filtration pores and cause higher operating pressures, and thus higher operating cost. A longer CIP interval is desirable because more frequent CIPs means more operator man-hours, chemical use, and operational downtime. The CIP frequency for the ozonated feed water was estimated from the fouling rate, which was calculated as the TMP increase rate over time (kPa/h at 25oC; Figure 4). Figure 5. The preliminary design for ozone contacting (foreground) and CeraMac® microfiltration is compact, and fits within four existing sand filter beds at CCKWW When operating without ozone, the CIP frequency was estimated to be every 92 days, and when operating with ozone, it would be every 920 days, based on the theoretical TMP increase rate calculations. In practice, it would be recommended to consider a CIP once per year. The operational synergy between ozone and ceramic membranes appears to not only solve fouling issues, which have been problematic for membrane systems, but also achieves a steady state of filtration that has never been shown Figure 3. The average specific flux when operating with pre-ozone is twice as before. The data of high as when operating without pre-ozone. this demonstrationscale study at the CCKWW bring light to a long quest for better stability of membrane filtration. Figure 4. The average fouling rate (as TMP increase rate of kPa/hr at 25ºC) when operating with ozone indicates that infrequent CIPs would be needed. PREliminaRy DESign The results of the demonstration plant tests have led PUB to explore if ceramic membrane filtration can be included as an option in the upgrading of CCKWW. A preliminary design for a 180,000 m3/d upgrade to the existing CCKWW has been based on an operating flux of 274 lmh (Table 1), but with the possibility of operating at 315 lmh when one vessel is out of service for maintenance. The CeraMac® vessels that may be included as an option for filtration at CCKWW contain 192 membrane elements. Six ceramic membrane vessels, including six backwash vessels would be used (Figure 5). Ozone, which is generated from the existing CCKWW ozone system, would be fed upstream of the membranes and allowed contact for 3-5 minutes. References 1. G Galjaard, J Clement, WS Ang and MH Lim (2013). CeraMac®-19 Demonstration Plant Ceramic Microfiltration at Choa Chu Kang Waterworks, Proceedings of the American Membrane Technology Association and American Water Works Association Membrane Technology Conference and Exposition, San Antonio, TX, 25-28 February. ViSiT OnlinE desalination.biz May-June 2013 | Desalination & Water Reuse | 19 |