Performance and kinetic modelling of photolytic and photocatalytic ozonation for enhanced micropollutants removal in municipal wastewaters

In this work, the performances of ozonation, photolytic ozonation (UV-C/O-3), and photocatalytic ozonation (UV-A/TiO2/O-3) in degrading ozone recalcitrant micropollutants in four different real domestic wastewaters were evaluated in semi-continuous operation, together with the influence of water matrices in the ozone mass transfer and pollutant degradation rates. The (OH)-O-center dot exposure per consumed ozone ratio, defined as R-OH,R-O3, was applied for single ozonation and modified for light-assisted ozonation processes to evaluate and compare the contribution of radical pathway on micropollutants abatement for the different wastewaters studied. R-OH,R-O3 plots presented good fitting (R-2 > 0.95) in two stages, corresponding to different ozone mass transfer regimes, for all cases. Light-assisted ozonation attained higher pollutant degradation for all water matrices compared to single ozonation, although the performance of UV-assisted processes was more sensitive to matrix factors like composition and turbidity. Moreover, the improvement brought by both light-based processes on R-OHO3 values mainly took place during the second stage. Thus, photocatalytic ozonation reached R-OHO3 values higher than double for all wastewaters, compared with single ozonation (between 105% and 127% increase). These values represent a saving of almost half of the overall ozone needs (42%) for the same ozone recalcitrant micropollutant depletion, although it would require the adoption of higher ozone doses than the currently employed for ozonation in wastewater treatment plants.