Reuse of Electroplating Wastewater: An Investigation into Factors Affecting Reliability of Reverse Osmosis

Membrane filtration processes such as ultrafiltration and reverse osmosis have great potential in significantly reducing water consumption in metal finishing industries by allowing recycling of treated electroplating effluent that is currently discharged. This research attempted to identify potential foulants in electroplating wastewaters and to study the effect of operating conditions on the performance of selected reverse osmosis membranes. Total dissolved solids of the electroplating waste from a local facility ranged from 3600 to 18,000 ppm. The primary contributors were sodium and sulfate ions which varied from 950 to 7600 ppm and 2200 to 14,200 ppm respectively. The pH of the waste varied from 8.0 to 9.3. With the Dow-FilmTec SW30 membrane, flux with model 10,000 ppm sodium sulfate was about 50 liters per square meter per hour (LMH) at a pressure of 500 psi and 30°C. It reduced to 20 LMH at 5% total solids. With the real waste stream, flux was 8-15 LMH under similar conditions. On-site trials in a continuous feed-and-bleed mode at 3X showed a 75% drop in flux over 7 days without membrane cleaning. Permeate quality was consistently excellent with less than 100 ppm total solids in the permeate.