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AWWA MTC64632
- Using Pretreatment Processes to Evaluate Fouling Mechanisms for Reverse Osmosis Membranes
- Conference Proceeding by American Water Works Association, 03/01/2007
- Publisher: AWWA
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The Metropolitan Water District of Southern California is evaluating conventional treatmentwith and without pre-ozonation followed by biofiltration (O<sub>3</sub>/BF) as possible pretreatmentoptions for reverse osmosis (RO) salinity control of mildly brackish Colorado River water. Theuse of existing conventional treatment facilities instead of microfiltration (MF) would reduce thecost of implementing RO desalination, but this economic benefit may be offset by loweroperating RO membrane flux and increased fouling. This project evaluated the followingpretreatment processes to isolate the effect of different fouling mechanisms on membraneperformance:MF - baseline condition; MF with pre-ozonation - established the effect of organic fouling with minimalcolloidal and biological interferences;MF with pre-ozonation (MF-O<sub>3</sub>) followed by biologically active dual-media filtration(biofiltration) - established the effect of organic and biological fouling with minimalcolloidal interferences;coagulation/flocculation/sedimentation/filtration (conventional treatment) -established the effect of colloidal fouling; conventional treatment with pre-ozonation - established the effect of organics oncolloidal fouling with minimal biological interferences; and,conventional treatment with pre-ozonation followed by biofiltration - establishedthe effect of organics on colloidal and biological fouling. Silt density index and turbidity data showed MF and MF-O<sub>3</sub> to produce higher quality RO feedthan the other pretreatment processes. However, the conventional treatment processes removedhigher levels of total organic carbon and ultraviolet absorbing material, indicating organicfouling may be less problematic. RO performance data revealed potential interaction betweenaluminum chlorohydrate, the coagulant used during the conventional treatment processes, andFlocon 260 antiscalant that caused a rapid decline in specific flux. Additional RO data showed the MF processes generally performed better than the conventional processes. The addition ofpre-ozonation and biofiltration appeared to decrease the efficacy of conventional pretreatment.Analysis of autopsied membranes supported the findings observations from the RO performancedata. Includes 6 references, tables, figures.
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