The promotions on radical formation and micropollutant degradation by the synergies between ozone and chemical reagents (synergistic ozonation): A review

The combination of ozone (O3) and chemical reagents (such as H2O2) shows synergies on the radical formation and micropollutant degradation. The promoting performance was associated with various parameters including chemical reagents, micropollutants, solution pH, and the water matrix. In this review, we summarized existing knowledge on radical formation pathways, radical yields, and radical oxidation for different synergistic ozonation processes in various water matrices (such as groundwater, surface water, and wastewater). The increase of radical yields by synergistic ozonation processes was positively related to the increase of O3-decay, with the increase being 1.1-4.4 folds than ozonation alone (0.2). Thus, synergistic ozonation can promote the degradation rate and efficiency of O3-resistant micropollutants (second order rate constant, kP,O3 200 M-1 s-1), but only slightly affects or even minorly inhibits the degradation of O3-reactive micropollutants (kP,O3 200 M-1 s-1). The water matrices, such as the dissolved organic matters, negatively suppressed the degradation of micropollutant by quenching O3-oxidation and radical oxidation (i.e. maximum promoting was decreased by 1.3 times), but may positively extend the promoting effects of synergistic ozonation to micropollutants that are more reactive to O3 (i.e. kP,O3 was extended from <200 to <2000 M-1 s-1). The formation of bromate would be increased through increasing radical oxidation by synergistic ozonation, but can be depressed by relative higher H2O2 as the reducing agent of HOBr/OBr- intermediate. The increase in bromate formation by O3/permononsulfate is a considerable concern due to permononsulfate cannot reduce the HOBr/OBr- intermediate.

Automated summary

The combination of ozone and chemical reagents such as H2O2 has synergistic effects on radical formation and micropollutant degradation. The increase in radical yields through synergistic ozonation processes positively impacts the degradation of O3-resistant micropollutants, while slightly affecting or inhibiting the degradation of O3-reactive micropollutants. Water matrices and dissolved organic matters can negatively suppress the degradation of micropollutants by quenching O3-oxidation and radical oxidation, but may extend the promoting effects of synergistic ozonation to more reactive micropollutants.