Hybrid process of electrocoagulation and electrooxidation system for wastewater treatment: A review

Water is one of the most essential natural resources required for all living things. Globally, due to various factors, the volume of wastewater generated and contaminant loads are increasing. Therefore, currently, there is high interest and concern in developing more effective wastewater treatment technologies. Particularly, the emerging electrochemical methods, mainly electrocoagulation (EC), electrooxidation (EO), and the hybrid of both EC and EO, have recently attracted attention as a potential method for treating wastewater due to its wide application and environmental compatibility. In the EC process, different metal hydroxide species are formed. The metal hydroxides (coagulant) aggregate the dispersed particles in the solution, which forms bigger flocs and then is removed by sedimentation. In most cases, EC is not able to reduce the stable persistent organic compounds to below the allowable discharge limits. Also, the EO process is an emerging process where contaminants are removed by oxidizing directly at the surface of the electrode or indirectly by generating oxidants in the solution. However, the main drawback of the EO method is that it is not applicable or requires a long operation time for treating water and wastewater with large amounts of suspended solids. Thus, to use the EO treatment system, the suspended solids of the wastewater have to be removed first by using other techniques. This can be achieved by a hybrid process of EC and EO. Besides, the hybrid process can enhance the removal of COD, TOC, NH4+-N, nitrates, phenol, which is not effectively achieved by using only EC or EO. Therefore, in this particular review, special emphasis was given to a hybrid of EC and EO processes, in addition to assessing electrocoagulation and electrooxidation as exceptional electrochemical methods. Even though several studies have covered EC, EO, and a hybrid process of EC and EO systems separately, to our best knowledge, there is an extremely limited number of review papers that have been done on the hybrid process of EC and EO. Therefore, this manuscript aims to review the potential of a hybrid of the EC and EO processes for treating wastewater generated from various sources.