art Highlights  RED-RO is a promising technology for energy-efficient seawater desalination  Secondary-treated wastewater is a potential low salinity source for RED  An efficient pre-treatment of wastewater is needed before use in RED  Rapid sand filtration and 100 µm provide efficient wastewater pre-treatment  River bank filtration does not provide adequate feed water quality AbstractAlthough Reverse Electrodialysis (RED) is most commonly known as a selective separation technology used for the production of sustainable energy, it can also serve as a valuable pre-desalination tool. By coupling RED to Reverse Osmosis (RO) for seawater desalination: (1) sustainable energy is produced in the RED process and (2) seawater is partially desalinated prior to RO thus, decreasing the energy demand. In this study, secondary-treated wastewater is proposed as the low salinity source in RED and suitable pre-treatment techniques for this effluent are investigated. Although it is generally accepted that RED is less prone to fouling than typical pressure driven membrane processes, results showed that pre-treatment is a key to ensure efficient operation of the wastewater-seawater RED. Both 100 µm filtration and rapid sand filtration proved to be suitable, with an increase in pressure drop of only 0.09-0.18 bar and a permselectivity decrease of only approximately 20% during 40 days of continuous operation. Conversely, River bank filtration did not perform better than the non-pretreated sample. As such, 100 µm filtration and rapid sand filtration are considered suitable, robust, and cost efficient pretreatment options for wastewater fed RED, enabling the improvement of the hybrid process of RED-RO seawater desalination.

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