A combined ion exchange–nanofiltration process for water desalination: III. Pilot scale studies

• A pilot ion-exchange –nanofiltration rig for water desalination has been built
• IX section of the hybrid system converts > 95% of chloride to sulphate ions
• 4040 NF membrane elements provides > 99% rejection of sulphate ions
• NF reject stream may be used for regeneration of the exhausted IX resins
• Feasibility of the hybrid IX-NF process of water desalination has been proved

This paper describes pilot scale studies on a novel combined ion-exchange (IX)–nanofiltration (NF) process for water desalination. Based on the preliminary results of small scale IX and NF studies, a pilot scale hybrid IX–NF system for water desalination has been designed and built for testing and evaluation. Optimization of the operability of the designed pilot system has been done and the obtained results have proved the feasibility of the hybrid IX–NF desalination process. The IX section of the pilot system filled with Purolite A500TLSO4 resin managed to treat feed waters at various salinities and composition and to convert > 95% of chloride ions to sulphate ions. The IX treated salty water was further desalinated using NF90 and NF270 spiral wound 4040 industrial membrane modules. The NF membranes were able to maintain > 99% rejection of sulphate ions. It was found that NF reject stream, which is rich in sulphate content, may be used for regeneration of the exhausted IX resins and thus no external regeneration solution is required for the hybrid IX–NF process of water desalination. An incorporation of IX stage in the hybrid process of water desalination allows membrane desalination at lower operating pressures thus reducing the energy consumption.