AWWA WQTC64058

To provide clear and quantifiable answers to water quality and O&M questions related to the traditional seawater reverse osmosis (SWRO) versus dual-pass nanofiltration process, the Long Beach Water Department (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 SWRO and initial comparisons against dual-pass nanofiltration. The prototype facility was constructed with the mindset to provide unbiased aggressive process and water quality research. A process flow schematic of the prototype facility is provided in the paper. The prototype utilizes pressurized microfiltration (MF) membranes as the pretreatment process. The MF unit is operated in an outside-in configuration at a flux of approximately 35 gallons per square foot per day (gfd). To extend the operation of the MF unit between each "clean-in-place", chlorine is added in the backwash process. Sodium bisulfite is continuously added to the MF filtrate to quench any residual chlorine remaining after the backwash process. The MF effluent is collected in a main MF filtrate tank, where it is then divided equally into two trains. This ensures that the pretreatment water quality is identical for both SWRO and dual-pass NF. Currently, train 1 is set up to test LBWD's patent-pending two-pass nanofiltration (NF²) process. Dow Filmtec NF90 membranes were selected for pass 1 and the Saehan NE90 seawater membranes were selected for pass 2. Train 2 is configured to evaluate traditional single-pass SWRO, where Hydranautics SWC3+ membranes were selected as the RO membrane. Identical Energy Recovery Incorporated (ERI) pressure exchangers are used on both the SWRO and NF² trains to allow for an "apples to apples" comparison on how much these devices aid in lowering energy consumption. The permeate and brine from both trains are recombined to reconstitute raw seawater and then discharged back into the ocean. This allows for aggressive research without the risk of endangering the public water supply. Power monitors for each process (MF, SWRO, and NF²) are incorporated to accurately determine actual power costs. Includes 10 references, tables, figures.