Mechanism and reaction kinetic of hybrid ozonation-ultrasonication treatment for intensified degradation of emerging organic contaminants in water: A critical review

The presence of recalcitrant organic compounds such as pharmaceuticals, personal care products, hormones and antibiotics in the aquatic environment is a growing concern as they are resistant to conventional treatment processes. Many of these compounds are categorized as contaminants of emerging concerns (CECs). Ozonation process is highly effective but it is usually restricted by the poor mass transfer rate of ozone into the water. Hybrid ozonation-ultrasonication system has been emerging as an efficient method for the rapid removal of these stable compounds due to the synergy between the two effects. The process is technically simple, more effective and achieves fast degradation with no addition of chemicals is necessary. Mature understanding on the hybrid system is however yet to be established. In this manuscript, a detailed review is conducted on the fundamental issues regarding ozonation-ultrasound (US/O-3) hybrid process. Phenomena towards the synergy between the two effects, the degradation potential, the optimum parameters, the possible reaction mechanism and the reaction kinetics are critically reviewed. Reported performances in the removal of some CECs are compared and analyzed. Besides, a few recommendations for future research direction with regards to the CECs reactivity, suitable system set up, operational cost etc. are also made.