AWWA WQTC65867

The Long Beach Water Department (LBWD), similar to many Southern California utilities, has been facing the issue of decreased potable water supplies. Because of its location, the City of Long Beach is ideally situated to take advantage of desalinated seawater as a source of drinking water and is interested in incorporating desalinated seawater into its potable water portfolio. However, before seawater desalination can become a reality, additional advances are needed to further reduce the cost of desalination. LBWD is currently exploring the feasibility of using nanofiltration membranes (NF) in a dual-pass configuration to evaluate the possibility of achieving additional cost reduction as well as meeting all water quality objectives. Although NF membranes have been previously tested with seawater, the application focused on using NF as pretreatment for the reverse osmosis membrane stage rather than using these membranes to produce potable water. In recent years, however, significant developments of NF membranes have been made, resulting in products that can achieve high TDS rejections (e 90%) at lower applied pressures. These advances allow a two-step, permeate-staged NF treatment process capable of producing potable water with lower overall applied pressure, and potentially lowering operating energy. To date, this concept does not appear to have been tested, as evidenced by the lack of literature in this area. To provide clear and quantifiable answers to water quality questions related to the traditional SWRO versus dual-pass nanofiltration process (NF2), LBWD has formulated an aggressive research program and constructed a 300,000 gallons per day permeate "Prototype" research facility using full-scale equipment. This paper presents LBWD's preliminary evaluation of source water quality and its removal throughout the various processes and initial water comparison of SWRO and against dual-pass nanofiltration. Includes 13 references, tables, figures.