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

The combination of ozone (O) and chemical reagents (such as HO) 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 O-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 O-resistant micropollutants (second order rate constant, k < 200 M s), but only slightly affects or even minorly inhibits the degradation of O-reactive micropollutants (k > 200 M s). The water matrices such as the dissolved organic matters, negatively suppressed the degradation of micropollutant by quenching O-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 O (i.e. k was extended from <200 to <2000 M s). The formation of bromate would be increased through increasing radical oxidation by synergistic ozonation, but can be depressed by relative higher HO as the reducing agent of HOBr/OBr intermediate. The increase in bromate formation by O/permononsulfate is a considerable concern due to permononsulfate cannot reduce the HOBr/OBr intermediate.