Performance Comparison of RO and NF Systems


Courtesy of MASAR Technologies, Inc.

The nanofiltration train (NF-A) and reverse osmosis train (RO-A) at Port Hueneme Brackish Reclamation Demonstration Facility in Southern California have both suffered from biofouling since startup in November 1998 until the plant implemented a raw water chloramination scheme in June 2000 (around 13,500 hours of operation). Moreover, the nanofiltration membrane elements also suffered from a manufacturing defect that was discovered later. Plant operators monitor the membrane systems' 'health' by inputting daily average analog values for flows, pressures, and conductivities into Dow Filmtec®'s ROSA® program configuration file. They use the expected fouling factor of 1.0 and the set points for flows as published by Filmtec®. These set points are then verified against operating product flow and differential pressure trending graphs.

Recently, the plant provided operating history data from both trains for performance evaluation using MASAR®'s unique measurement of the Fouling Monitor (FM) (blue curve) against ASTM-normalized flux decline trend, using ASTM D 4516-00 standard method (red curve). Not only did MASAR® show the progress of biofouling in both trains (rising FM values) up until chloramination was instituted, but it interestingly showed a significant improvement due to more effective disinfection ONLY in the RO train! The NF train's FM performance showed a much lower degree of improvement conceivably due to biomass 'sloughing off' which could be caused by elements leak. The plant's daily monitoring procedure, just like the ASTM normalized flux decline trending, failed to pick up this important difference in Train NF-A's actual behavior as MASAR® did, and actually showed a misleading trend!

Had the plant been using MASAR®, it would have given the operators a true and early indication of the performance and fouling status of both trains. Corrective measures would have then been immediately implemented after investigating the sources of deterioration. That early determination would have had an obvious positive impact on the plant's operational efficiency and cost-effectiveness.

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