Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/86284
PROJECTS Clarifier brings quality increase to UF treatment plant _________ Elisabeth Linton, Lindsay Housley, Erin Whyte, and Cory Topham, WesTech Engineering Inc, USA ___ Editor's Note: Alabama is not a US state that immediately springs to mind in connection with membrane water treatment, which is why a poster paper at the recent AWWA/AMTA conference in Arizona caught the eye of D&WR. Opened in January 2011, the High Point Water Treatment Plant has used a solids contact clarifier and ultrafiltration to improve its overall water quality by reducing turbidity, removing pathogens, and meeting secondary standards. LOW-PRESSURE ultrafiltration (UF) and microfiltration (MF) systems are attractive technologies for surface-water treatment. Highly automated, they can achieve high log removal values for pathogenic organisms and viruses, and produce a low- turbidity effluent. Membrane fouling remains a common issue, though it can be mitigated with effective pretreatment and cleaning techniques. This article discusses results from systems using solids Contact ClarifiersTM Engineering Inc of Salt Lake City, USA, as pretreatment. A UF water treatment plant in Alabama is provided as a case study. designed by WesTech SOLIDS CONTACT CLARIFIER Solids Contact Clarifier (SCC) technology combines mixing, solids recirculation, flocculation, and gravity sedimentation in one unit. Unlike conventional clarification, an SCC uses recirculation of a sludge blanket to entrap floc particles. For surface waters with high turbidity spikes and organic content, a properly operated SCC will provide a treated effluent with consistent high quality. SCCs are useful in reducing disinfection byproduct (DBP) formation through removal of organics. WesTech has supplied over 20 SCC units specifically as UF/MF pretreatment applications. Plants vary from 1 MGD (3,785 m3 Total production capacity for all systems is nearly 140 MGD (530,000 m3 /d) to 56 MGD (211,960 m3 Manufacturers whose membranes have been used with the system include GE Zenon, Pall, Aquasource and Koch, as well as WesTech with its own AltaFilterTM /d). . BENCH-SCALE MEMBRANE FILTRATION TESTS Optimisation of UF design and operation can be aided using bench-scale jar and filtration tests. Using the Filt-test, which is easily portable and operates under constant flux, membrane fibers can be potted into a small micromodule and used to evaluate a wide array of variables such as flux rates and coagulant dosing. MAINTENANCE CLEANING Maintenance cleaning (MC) is an alternative strategy to time- and labor- intensive clean-in-place (CIP) strategies. Using consistent and automated MCs can dramatically improve CIP frequency, increase flux rates, maintain higher membrane permeability and extend membrane life through minimised fouling. Filt-test Equipment Outlet launder and include a chemical soak period. MC was applied at five plants treating difficult surface waters. By performing MCs every 2-4 days, all plants reached a CIP frequency of more than 30 days, with two plants exceeding 100 days. NaOH/ NaOCl was used for cleaning at pH >10. Citric acid at pH <3.0 was also used. Preliminary estimates indicate that yearly MCs are typically 20-60 minutes long Solids contact zone Sludge line Solids Contact Clarifier | 22 | Desalination & Water Reuse | May-June 2012 Draft tube Inlet chemical costs for MCs are 1.5-4 times that of CIPs. Costs are partially offset by reduced labor, fouling and waste, as well as a higher operating flux. Under certain conditions, chemical and operating costs can be nearly identical. /d).