Antiscaling effect of polyaspartic acid and its derivative for RO membranes used for saline wastewater and brackish water desalination

Polyaspartic acid (PASP) and its derivative (PASP-SEA-ASP) were tested as environmentally benign scale inhibitors at lab scale for a polyamide reverse osmosis (RO) membrane in the desalination of a synthetic brackish water containing various scale-forming ions. Their performance was compared with a commercially available RO antiscalant which contains phosphonic acid. The addition of the scaling inhibitors to feedwater led to increase in water recovery and removal efficiency of inorganic matter for the RO unit operated under constant transmembrane pressure, with PASP-SEA-ASP giving greater water recovery (90%) than PASP (87%) and the commercial antiscalant (85%). PASP-SEA-ASP was superior to PASP and the commercial antiscalant in scaling inhibitor/fouling reduction due to the reduced deposition of the scale forming ions on the membrane. Examination of the used membranes with scanning electron microscopy and X-ray diffraction suggested the different effect of the antiscalants was related to the resultant crystalline morphology on the membrane surface. The PASP and its derivative appeared to be more cost effective in maintaining permeate flux and inhibiting the formation of a dense scale layer. The present study demonstrated the great potential of these non-phosphorus containing agents for scale inhibition in domestic and industrial wastewater reclamation and brackish water desalination applications.