Intensification of the ozone-water mass transfer in an oscillatory flow reactor with innovative design of periodic constrictions: Optimization and application in ozonation water treatment

Ozone-water mass transfer was investigated in continuous mode using a macroscale oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC). The effects of oscillation amplitude (x(0)) and frequency (f) on the mass transfer coefficient (k(L)a) were assessed through a Doehlert experimental design. Different gas and liquid flow rates were also studied. The results show that k(L)a increases with f (up to 4 Hz), x(0) (up to 15 mm), and the gas flow rate (up to 150 Ncm(3) min(-1)). No significant changes in k(L)a were observed over a wide range of liquid flow rates (up to 180 mL min(-1)) and for Re-0 < 1000. In all conditions studied, and among different reactor configurations tested, the higher k(L)a values were observed with the OFR-SPC, achieving k(L)a values up to 35 times higher than those obtained in a conventional bubble column. Moreover, the enhancement on the mass transfer efficiency (MTE) promoted by the oscillatory movement was more pronounced as the gas (ozone) flow rate decreases and liquid (water) flow rate increases, which is another advantage of this system when looking for large-scale implementation of the ozonation process in water treatment. Ozonation experiments using a mixture of fluoroquinolones in different matrices (distilled water, surface water and urban wastewater) were also performed, the results demonstrating that OFR-SPC is an interesting reactor alternative for ozone-driven water treatment.