A critical review on treatment of saline wastewater with emphasis on electrochemical based approaches

Increasing discharge of saline wastewater (SWW) from different industries and environmental risks asso-ciated with it has compelled researchers to search for efficient treatment methods and safe disposal techniques. Unfortunately, several industries such as agro-food, oil & gas, tannery, and pulp & paper require brine solution units to obtain a finished product that further elevates the salinity of discharged wastewater to a magnitude of 1-3% by weight of NaCl. Among the conventional treatment procedures, electrochemical technologies proved to be more efficient, robust and cost-effective. Electrocoagulation (EC), an electro-chemical based technology that produces in situ coagulant which ultimately assist in pollutant removal. It is even more suitable for the treatment of saline water as salinity increases conductivity which further en-hances the EC process efficiency. However, the elevated anodic dissolution may increase the cost which can be reduced by using scrap metals as sacrificial electrodes out of iron and aluminum. The mechanism of salt removal from SWW using EC is similar to other pollutant removal mechanisms as salt species being coa-gulated by the metal hydroxides and are further removed as sludge. However, optimization of process parameters in EC is essential to maintain a balance between anodic passivation and higher metal dis-solution so as to make the process efficient. This review paper highlights the theory of the EC technology, process parameters, potential application and recent developments of EC for the treatment of various types of SWW as well as economical assessment associated with this technology. Most of the recent research concerning EC for SWW treatment has been concentrated on the pollutant-specific evaluation without paying special attention to the process optimization, process modeling and commercial usage. This review further outlines the challenges with the recommendations for encouraging research options that can po-tentially enhance the EC performance, lower the operational costs and expand its range of applications for SWW treatment. (c) 2021 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.

Automated summary

The increasing discharge of saline wastewater and associated environmental risks have led researchers to search for efficient treatment methods, with electrochemical technologies proving to be cost-effective. Electrocoagulation is particularly effective for treating saline water, but process parameter optimization is essential for maintaining efficiency.