Toray Chemical Korea

Bench-scale testing of SW desalination using NF


A majority of Southern California municipalities, including the City of Long Beach, depend on water purchased from the Metropolitan Water District of Southern California. However, due to over-allocation of the Colorado River, this water supply could potentially be restricted in the future. Consequently, the Long Beach Water Department (LBWD) is considering the construction of a 10 million gallon per day (mgd) seawater desalination plant to augment its existing supplies.

Reverse osmosis (RO) is a proven membrane technology for seawater desalination. Although the cost of RO desalinated water has been significantly reduced, it still remains fairly high, as compared to other drinking water sources, mainly due to the high operating pressures required (typically 800-1000 psi). LBWD had recently introduced a patent-pending dual-staged nanofiltration (NF) process as a potentially lower-energy alternative to the traditional RO desalination process. The novel NF process desalts seawater by treating the permeate from the first stage with a second NF stage in order to produce finished water with salinity levels lower than drinking water standards. The primary goal of this novel desalination system is to reduce energy consumption to as low as possible while producing potable water at an acceptable recovery rate.

The Long Beach Water Department, EE&T, Inc., and the University of Nevada (UNR), Reno are engaged on an 18-month long project to better understand and optimize this technology.  The UNR focus in this research project is on the theoretical basis for the dual NF concept and includes membrane characterization and bench-scale membrane performance. The objectives of this project are to evaluate three NF membranes for their permeate water flux and ion rejection for both single salt feed water solutions as well as for synthetic seawater solutions. This data will provide the basis for a predictive model and allow the formation of a selection protocol to evaluate possible candidate NF membranes.

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