AWWA WQTC62413

The objective of this study was to develop a testing protocol to select nanofiltration (NF) and ultra-low pressure reverse osmosis (ULPRO) membranes taking into account rejection efficiencies and operational conditions including feed pressure, specific flux, flux decline due to fouling, and total dissolved solids (TDS) removal. This comprehensive testing protocol was subsequently used to compare commonly used reverse osmosis (RO) membranes treating water of impaired quality with ULPRO and NF membranes with respect to select pharmaceutically active compounds (PhACs), personal care products (PCPs), pesticides, disinfection byproducts (DBPs), nutrients (nitrate and ammonia), and bulk organic carbon. This screening was conducted on a 2-stage laboratory-scale skid (feed flow 9 gpm) utilizing 4040 spiral wound membrane elements and resulted in a selection 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 two different types of microfiltered secondary effluents at two different full-scale facilities. At each site, 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-scale train to verify its performance. Results from this study demonstrated that new generation ULPRO and NF membranes can achieve similar removal efficiencies for the selected trace organics, nutrients and bulk parameters tested as commonly employed RO membranes at significantly lower feed pressures. Operational conditions especially the flux decline for the ULPRO membrane observed during pilot- and full-scale was accurately predicted through the laboratory testing protocol. Negatively charged PhACs were well rejected regardless of membrane characteristics while compounds characterized as hydrophilic non-ionic was dependent upon the molecular weight cut-off (MWCO) of the membrane as well as the molecular weight and molecular size of the compound of interest. Target compounds characterized as hydrophobic non-ionic were initially well rejected by almost all membranes due to adsorption onto the membrane, but decreased slightly throughout the experiments. TOC, nitrate and ammonia removal was dependent upon the MWCO of the membrane and the operating conditions of the experiment, but was generally comparable to results obtained with RO membranes. Includes 8 references, tables, figure.