Development of a process for the treatment of synthetic wastewater without energy inputs using the salinity gradient of wastewaters and a reverse electrodialysis stack

Electrochemical processes are considered very effective methods for the treatment of wastewater contaminated by organics resistant to conventional biological processes and various inorganic pollutants. Large sites that treat wastewaters usually deal with a large number of waters often characterized by different salinity contents, that could be potentially used to provide the energy necessary for the electrochemical remediation. Hence, in this work a reverse electrodialysis (RED) process for the treatment of synthetic wastewaters contaminated by organics, without energy inputs, using the salinity gradient of different wastewaters, was studied, for the first time. It was found that two synthetic wastewaters with different NaCl content can be effectively used in a RED system to drive anodic and cathodic processes for the removal of their organic contents without external energy supplies. The effects of salinity gradient, external resistance and set-up of the process was evaluated. Under optimized operating conditions, a fast and high removal of TOC (about 70% every hour) in the anodic compartment and a good stability of operating conditions for all the monitored time (10 h) were achieved. In addition, about 67% of the solution with high salinity used in the stack to provide the salinity gradient was effectively treated in the anodic compartment of the stack.