AWWA WQTC60719

A novel system developed by Long Beach Water Department to provide drinking water quality by desalting seawater through dual-staged nanofiltration is being evaluated in a Tailored Collaboration project with the American Water Works Association Research Foundation (AwwaRF). The project includes providing the theoretical basis for the system, in particular the governing equations that could predict the system performance. The solution diffusion model and thin-film theory were assessed for their worthiness in providing real-world responses to measure system performance. Equations were modified so that permeate and concentrate qualities could be determined based on measurable parameters: temperature, operating pressure, feed concentration and flow, membrane area, and the water and salt mass transfer coefficients. Comprehensive bench-scale testing of several nanofiltration membranes were conducted to determine the mass transfer coefficients and rejection level achieved for the major ions present in the seawater. The model was used to simulate performance achieved in a 15-gpm pilot plant. The model is able to provide the interplay between finished water quality, energy demand (operating pressure), and recovery and thus provide the demonstrable competitiveness of this novel seawater desalination system with conventional seawater reverse osmosis. Includes 2 references, tables, figures.