Full Description

The objective of this study was to develop a testingprotocol to select nanofiltration (NF) and ultra-low pressure reverse osmosis (ULPRO) membranes taking into account rejection efficiencies andoperational conditions including feed pressure, specific flux, flux decline due to fouling, andtotal dissolved solids (TDS) removal. This comprehensive testing protocol was subsequentlyused to compare commonly used reverse osmosis (RO) membranes treating water of impaired quality withULPRO and NF membranes with respect to select pharmaceutically active compounds (PhACs),personal care products (PCPs), pesticides, disinfection byproducts (DBPs), nutrients (nitrate andammonia), and bulk organic carbon. This screening was conducted on a 2-stage laboratory-scaleskid (feed flow 9 gpm) utilizing 4040 spiral wound membrane elements and resulted in aselection of one ULPRO and one NF membrane out of a list of 14 different products screened.Both candidate membranes were installed on a 23-gpm pilot-scale skid for the treatment of twodifferent types of microfiltered secondary effluents at two different full-scale facilities. At eachsite, each product was tested and monitored for target constituents for more than 2,500 hours.Seven elements of the ULPRO membrane were also installed in one vessel of a 2.5-mgd full-scaletrain to verify its performance. Results from this study demonstrated that new generationULPRO and NF membranes can achieve similar removal efficiencies for the selected traceorganics, nutrients and bulk parameters tested as commonly employed RO membranes atsignificantly lower feed pressures. Operational conditions especially the flux decline for theULPRO membrane observed during pilot- and full-scale was accurately predicted through thelaboratory testing protocol. Negatively charged PhACs were well rejected regardless ofmembrane characteristics while compounds characterized as hydrophilic non-ionic wasdependent upon the molecular weight cut-off (MWCO) of the membrane as well as themolecular weight and molecular size of the compound of interest. Target compoundscharacterized as hydrophobic non-ionic were initially well rejected by almost all membranes dueto adsorption onto the membrane, but decreased slightly throughout the experiments. TOC,nitrate and ammonia removal was dependent upon the MWCO of the membrane and theoperating conditions of the experiment, but was generally comparable to results obtained with RO membranes. Includes 8 references, tables, figure.

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Edition: Vol. - No. Published: 11/01/2005 Number of Pages: 8File Size: 1 file , 180 KB