Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/133796
PROJECTS filtration cycle of 30 minutes followed by 5 second backwash, and an EBW with 100 mg/L free chlorine (NaOCl) after 15 filtration cycles and an EBW with 100 mg/L hydrogen peroxide (H2O2) at pH 2 after every four chlorinated EBWs. The ceramic membranes were operated during periods of variable feed water quality (ie, high particle counts), but were able to recover with continued normal operation. During these test runs, the TOC concentration in the feed water (grab samples ranging from 2.2 to 4.0 mg/L) was predominantly dissolved organic carbon (DOC; grab samples ranging from 1.8 to 2.2 mg/L). Iron and manganese concentrations in feed water were low (grab samples were less than 0.03 mg/L and 0.02 mg/L, respectively). Figure 2. CeraMac®-19 vessel (right) and backwash tank (left) being installed into an existing empty sand filter bed at CCKWW The CeraMac®-19 vessel contained 19 full-scale ceramic membrane elements from Metawater of Japan (see San Antonio Showcase, pp 42). The length of each element is 1.5 m, the diameter 18 cm and the filtration surface area 25 m2. With a 19-element vessel, a range of fluxes from 100 to 315 liters per square meter per hour (lmh) produces about 1,140 to 3,591 m3/d of treated water. The demonstration plant treated clarified water from the CCKWW without any ozone addition for the first six months. The remaining 12 months of operation were with pre-ozone to ceramic microfiltration. During the initial test runs, the optimum flux was determined, followed by trials to identify a sustainable backwash (BW) and chemically enhanced backwash (EBW) frequency. Once those parameters were determined, additional testing runs were conducted to confirm that the operating conditions were robust and sustainable. When the demonstration plant was operated with pre-ozone, the flux, which was 200 lmh at the start of the ozonated testing runs, was increased to 240 lmh, 274 lmh, and finally to 315 lmh. RESulTS The results showed that the CeraMac® system performed well as a ceramic membrane filtration system for clarified water with or without ozone. The use of pre-ozone improved the operation, with a stable transmembrane pressure (TMP) and minimal down-time for cleaning. Operating with or without pre-ozone is possible for the upgrade to CCKWW; however, PUB is interested in optimizing the available options and harnessing as much water treatment capacity as possible from the available space. The results of the demonstration study are summarized in this article, but more detailed information can be found in the referenced paper1. OPERaTiOn wiTh ClaRifiEd fEEd waTER The first six months of demonstration testing showed that the ceramic membranes could operate at a flux of 200 lmh when treating clarified water. The optimized operating parameters for treating clarified water at CCKWW are shown in Table 1. When treating clarified water, the CeraMac® system could operate with a OPERaTiOn wiTh OzOnaTEd ClaRifiEd fEEd waTER A series of test runs was performed with ozone, and the stable operation ultimately led to changing the experimental testing plan and equipment to allow operation at 315 lmh, which was higher than had been expected at the start of testing. Throughout these tests, an ozone dose of approximately 1.3 to 1.5 mg/L, which is similar to the current ozone dose at CCKWW after the existing sand filters, was applied to yield an ozone residual immediately upstream of the membrane of about 0.5 mg/L when operating at 200 lmh, >0.8 mg/L when operating at 274 lmh, and >1.0 mg/L when operating at 315 lmh. The optimized operating parameters for ozonated feed water are shown in Table 1. The recommended operation flux is 274 lmh. Table 1. Optimum CeraMac® operating conditions when treating clarified water without and with ozone Parameter Operation without Ozone Operation with Ozone Flux (lmh) 200 274 Fouling load during filtration cycle (L/m2) 100 720 Fouling load during filtration cycle (L/m2) 2 0.33 1,500 2,160 EBW frequency (1/d) 3 2.7 EBW sequence 4x NaOCl at 100 ppm Fouling load until EBW (L/m2) 1x HCl pH=2, 100 ppm H2O2 Recovery (%) CIP frequency (days) | 18 | Desalination & Water Reuse | May-June 2013 96.8 99.6 90 >360