Chemical-free ion exchange and its application for desalination

In some coastal areas, the primary freshwater obtained through seawater desalination has been widely used as the feed water in high purity-water production. Due to its high conductivity, however, further lowering ionic species load is needed before the final polishing process such as the mixed bed ion exchange and electrodeionization. In this work, a new process called as chemical-free ion exchange (CFIE) was proposed to replace the conventional two-bed (cation-anion) ion exchange for the purpose above. Results demonstrated that the mixed resin regeneration was achieved mainly by electrically enhancing water split. After regeneration, the resins could resume their ability to desalinate. The conductivities of purified water were 0.8-1.5 μS/cm, and the energy consumption and water recovery were 0.29-1.04 kWh/m3 water and 81.8-94.7%, respectively. The neutral concentrate collected during regeneration could be returned to a pretreatment unit for recovery. No chemical was needed and no wastewater was produced. Repetitive experimental results showed that the CFIE system could run stably.