Enhanced desalination process using a Cu–ZnO-polyvinyl chloride-nylon nanofiltration membrane as a calcite antiscalant in reverse osmosis

Abstract

Treatment and cleaning of reverse osmosis (RO) membranes saturated with CaCO3/brine is a main issue in RO desalination processes. Herein, a Cu–ZnO-polyvinyl chloride (PVC)-nylon nanofiltration membrane was synthesized and utilized to minimize and/or eliminate CaCO3/brine during RO, along with probing the effects of Cu–ZnO antiscalant on calcite precipitation in normal aqueous and supersaturated CaCO3/brine solutions. Moreover, decreases in Ca2+ content over time were evaluated by electrical conductivity and pH measurements. Results revealed that Cu–ZnO nanocomposite substantially increases induction time and stimulates the formation of aragonite rather than calcite. A 2 mg/L dose of Cu–ZnO nanocomposite suppressed CaCO3 in both unsaturated and supersaturated solutions. In natural water sources (containing ∼500 mg/L calcium and ≈300 mg/L bicarbonate content), complete removal of CaCO3 blockage was achieved by using 2.5 mg/L of Cu–ZnO antiscalant, while in supersaturated water solutions (1000 mg/L calcium and ≈500 mg/L bicarbonate content), only 2 mg/L of Cu–ZnO antiscalant was required to fully remove the blockage. Importantly, addition of 2 mg/L of Cu–ZnO antiscalant to RO brine showed no apparent deposition on the membrane surface after 6 h, with a minimal flux decrease to 86.5%. Thus, Cu–ZnO-PVC-nylon nanofiltration membranes with low concentrations (2 mg/L) of Cu–ZnO antiscalant can play a significant role in the treatment of supersaturated CaCO3/brine water discharge.