Using DOM fraction method to investigate the mechanism of catalytic ozonation for real wastewater

Resin fraction of dissolved organic matters (DOM) was used to investigate the mechanism of catalytic ozonation with a commercial catalyst treating petrochemical secondary effluent (PSE). The results showed hydrophilic substances (HI) and hydrophobic acids (HoA) were the dominated fractions in PSE, accounting for about 47% and 36% of the total dissolved organic carbon (DOC). HoA could be more easily oxidized by ozone than HI. It may be ascribed to the highly reactive structures of HoA with high SUVA(254). Besides, HoA could be transformed into HI during ozonation. Compared to ozonation, catalytic ozonation could enhance more removal of HI than HoA. Radical scavenger experiment verified that HoA and HI were removed by both ozone molecules and hydroxyl radical ((OH)-O-center dot). The adsorption of DOM by catalyst kept a dynamic balance process between oxidation and re-adsorption during catalytic ozonation, triggering a cyclic reaction between adsorbed DOM and adsorbed ozone as well as decomposed (OH)-O-center dot from the adsorbed ozone. In addition, DOM and ozone adsorbed onto the surface of the catalyst simultaneously could protect the quencher of (OH)-O-center dot caused by high concentration of anions (mainly Cl- and SO42-) in the bulk solution and significantly improve the catalytic performance. The fractions reaction and transformation, dynamic process between oxidation and re-adsorption, role of adsorption and (OH)-O-center dot quencher protection were clearly interpreted. For catalytic ozonation, the key point is to achieve an equilibrium for the adsorption of organics and oxidation ability. The proposed mechanism can give the direction for synthesis or modification of catalyst for real wastewater treatment.