| A patent-pending novel dual-stage nanofiltration process developed by Long Beach Water Department is being evaluated as an alternative to reverse osmosis for seawater desalination. The primary goal of this system is to reduce energy consumption while producing potable water at an acceptable recovery rate. The UNR portion of this investigation focused on the bench-scale investigation of flux and ion rejection (including boron, bromide, and iodide), membrane surface characterization, performance modeling and flux decline.; Results from this study showed that two commercially available NF membranes can effectively desalinate seawater. The mass transfer coefficients identified in the bench-scale experiments were able to accurately model the pilot-scale performance. Although fouling was apparent---and resulted in approximately 20% flux decline over 3 days---a critical flux was not identifiable. Operation of the system at different cross-flow velocities revealed the significance of hydrodynamic conditions on concentration polarization layer thickness and hence, on membrane performance. |
