Advancements on ozonation process for wastewater treatment: A comprehensive review

Ozonation is regarded as one of the best option for degrading the refractory organic compounds in wastewater via oxidative reactions with either direct molecular ozone (O3) or indirect hydroxyl radicals (OH•). However, ozone has a low reaction rate and does not completely mineralize the refractory organic contents due to the rise in solution toxicity. Hence, ozonation can be integrated with other water treatment techniques to enhance the production of OH• radicals, thereby improving the overall process performance. Different combinations of the ozonation process viz. ozone-electrocoagulation, ozone-hydrogen peroxide, ozone-UV radiation, ozone-sonication, catalytic ozonation and photo-catalytic ozonation are elaborately summarized and discussed in this review article. The research findings are critically analysed and recommendations are provided to enhance the efficiency of the treatment processes. The effect of operating parameters, reaction mechanism, and application of the ozone-assisted processes to degrade, mineralize, and detoxify different types of wastewater contaminants have also been demonstrated. More importantly, economic analysis of the ozonation-based processes and suggestions for their improvement are also made. Altogether, this review article successfully demonstrates the recent achievements on ozonation-based processes towards the treatment of different wastewater contaminants, which can provide new insights on the effective utilization of ozone for potential environmental applications.