Promoting the ozone-liquid mass transfer through external physical fields and their applications in wastewater treatment: A review

Ozonation process is a crucial advanced oxidation process and has been commonly used for the degradation and mineralization of refractory pollutants. Ozonation water treatment process needs to transfer ozone from gas to the water phase. Although the solubility of ozone in water is higher than that of oxygen in water under the same conditions, it still belongs to the type of liquid film control in mass transfer. In the research of ozone oxidation process technology, enhancing the ozone-liquid mass transfer can improve ozone utilization efficiency and its technical economy. Therefore, numerous ozone-based process intensifications have been explored. This paper provided a summary of the application of external physical fields (ultrasonic field, hypergravity field, electric field, and magnetic/electromagnetic field) to strengthen ozone-liquid mass transfer and briefly explains the recent literature, which has applied the combination of external physical fields and ozonation to destroy organic compounds. The results show that ultrasonic can increase the mass transfer coefficient of ozone by 20–200% under optimized conditions and ultrasound can generate free radicals through its cavitation. The hypergravity field can increase the mass transfer coefficient by at least 1.5 times. The addition of electric and magnetic fields also increases the mass transfer of ozone by more than 40% or more under optimized conditions.