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

Abstract

In this work, the performances of ozonation, photolytic ozonation (UV-C/O3), and photocatalytic ozonation (UV-A/TiO2/O3) 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 exposure per consumed ozone ratio, defined as ROH,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. ROH,O3 plots presented good fitting (R2 > 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 ROHO3 values mainly took place during the second stage. Thus, photocatalytic ozonation reached ROHO3 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.