Treatment of Industrial Reverse Osmosis Brine using Nanofiltration

Membrane processes may be used to further concentrate reverse osmosis brine for a cost-effective zero liquid discharge (ZLD) approach. In this study, three types of nanofiltration (NF) membranes were evaluated, namely NF270 (Dow Filmtec), NF90 (Dow Filmtec) and DL (GE Osmonics). Feed representing moderate and high strength industrial brine were used. Results showed crossflow velocity had varying impact on the permeate quality of different NF membranes. NF90 had the highest ion and organic rejection due to its small pore size. The results also demonstrated pH had significant impact on organic fouling. Under acidic conditions, humic acid substances in the feed has partial negative charge, which could lead to greater attraction towards the NF90 surface at pH close to its isoelectric point (pH 3-4). This could have caused higher flux decline observed in the study when operating at feed pH 4-5 as compared to operating at pH 6.