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The maximum Log Removal Value (LRV) that can be awarded to a membrane system hastraditionally been based on the primacy agency's interpretation of the Surface Water TreatmentRule for devices considered Alternative Filtration Technologies (AFTs). Granted removal creditsare influenced by the demonstrated membrane disinfection capabilities, number of microbialbarriers, and water quality. The Long Term 2 Enhanced Surface Water Treatment Rule(LT2ESWTR) will impose specific requirements and provide additional guidance for determiningthe LRV. The Proposal Draft Version of LT2ESWTR and associated Membrane FiltrationGuidance Manual (MFGM) (USEPA, 2003), detail the impact of critical operating parameters onLRVs.Carollo Engineers recently completed the design of the Eastern Municipal Water District's(EMWD) Hemet Water Filtration Plant (HWFP) (Hemet, California). The 10 million gallon perday (mgd) plant (expandable to 40 mgd), includes prefilters, coagulation, single stageflocculation, membrane filtration, chlorine contact time basin, and finished water pump station.This manuscript describes design considerations that were necessary to operate the plant at98% recovery while maintaining a membrane integrity test (MIT) sensitivity of 4 logs.Due to an increasing need for water and a persistent drought, EMWD decided to construct anew water treatment plant at Hemet with an initial capacity of 10 mgd.Based on recent experiences at its recently commissioned Perris Water Treatment Plant,EMWD selected Zenon 500d series membranes for disinfection and filtration at the HWFP.Three main bodies of regulations were considered during process selection: the proposedLT2ESWTR and its antecedents; the Stage 2 Disinfectants/Disinfection Byproducts Rule(Stage 2 D/DBPR); and, the California Department of Health Services (DHS) requirements.While the first two are Federal regulations, the specific requirements for LT2ESWTR are delegated to the State for membrane filtration. Therefore, California DHS has developedrequirements for membrane filtration, including credits for removals of pathogens such asGiardia and Cryptosporidium. DHS has done this on a system-by-system basis.The plant's source water, State Project Water (SPW), presents treatment challenges in threeareas:relatively high levels of bromide, which contribute to the formation of disinfectionbyproducts (DBPs);taste and odor episodes resulting from algae growth and production of geosmin and2-methylisoborneol (MIB); and,levels of Total Organic Carbon (TOC) and Dissolved Organic Carbon (DOC), whichcontribute to DBP formation, inhibit absorbance of ultraviolet light, and acceleratemembrane fouling.The plant is not subject to the Stage 1 Disinfection/Disinfectants Byproducts Rule (Stage 1D/DBPR) requirements for percentage TOC removal because this requirement applies only toconventional treatment processes; membrane filtration is not a conventional treatment process.In order to address these treatment challenges, the following additional processes wereselected for inclusion in the treatment train:future taste and odor control process (granular activated carbon contactors);coagulation/flocculation process (pump diffusion flash mix and single stage flocculation);future UV disinfection process (closed channel reactors);supplemental primary disinfection process (chlorination);secondary disinfection with chloramines; and,future wastewater recovery process (plate settler). Includes 2 references, table, figures.

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Edition: Vol. - No. Published: 03/01/2005 Number of Pages: 11File Size: 1 file , 780 KB