Assisted Reverse Electrodialysis for Salinity Reduction of Produced Waters

Produced Waters (PWs) are wastewaters that come from the oil industry and are particularly salty and polluted with hydrocarbons. Recently, membrane processes have been proposed for their treatment within the framework of a circular economy approach: the treatment and reuse of these waters requires a thorough understanding of the processes, particularly regarding the fate of valuable ions. Desalinating PW can be beneficial upstream of cheap and effective biological treatment processes. With this respect, an experimental study about ions flux through the Ions Exchange Membranes (IEMs) of a laboratory scale Assisted Reverse Electrodialysis (A-RED) unit was conducted aiming at a downstream mineral recovery. The passage of several cations, such as Na+, Ca2+, Mg2+, Li+, Rb+ and B3+, was measured in a synthetic solution mimicking the real PW composition. Tests were carried out either in once-through mode or recirculating the feed solutions always applying an external voltage of 3.6 V. The solutions were sampled at regular intervals and analysed. As a result, data on the passage of each of them through the membranes was evaluated. As expected, Na+ and Li+ ions were found to exhibit the largest flux. A slight less value was found for B3+ due to its high concentration in PW. Much lower values were measured for Ca2+, Mg2+ and Rb+. The present work poses the basis for a more in-depth analysis of ion transfer in desalination membrane processes for PW, which would allow an easier design of treatment equipment while considering a possible recovery of valuable ions.