Effect Of Dissolved Organic Matter On Hydroxyl Radical-induced Oxidation Of Organic Pollutants

Dissolved organic matter (DOM) is a complex organic mixture with diverse structures, which is widespread in the environment. DOM can interact with organic pollutants (OPs) by different mechanisms, and consequently change the environmental fate of pollutants. DOM can react with different radicals in water matrix. Meanwhile, DOM can change the speciation of OPs in aqueous solution. Theoretically, There are high possibilities for DOM to affect the reaction of radicals with OPs. Hydroxyl radical (·OH) is one of widely distributed radical in natural environment with very strong oxidation potential.-OH is also widely applied in some advanced oxidation processes (AOPs) to destroy OPs in water. In this study, the photolysis of H2O2 was adopted to produce-OH. The reactions of-OH with DOM from different sources with various structures were tested. Futhermore, the influence of DOM on the reactions of ·OH with a series of environmental highly concerned OPs were examined. The findings of this study can support the clarification the influence and mechanism of DOM on the reactions of·OH with OPs, meanwhile, provide information as references in the design of AOPs.The reactions of·OH with DOM from different sources were studied firstly. TOC analyzer, ultraviolet-visible absorption spectra and fluorescence excitation-emission matrices (EEMs) were used to characterize the reactions between-OH and DOM. Terrestrial DOMs demonstrated stronger reactivity with-OH than aquatic DOMs. The reactions followed the pseudo-first-order kinetics as characterized by DOC decline. The reaction rate constants kooc related well to the ratios of aromatic carbon to aliphatic carbon (Caro/Cali) and the attenuation rate constants (kAbs ave) characterized by light absorption parameter. According to the difference of origin and variety, various DOMs demonstrated not only different EEMs before oxidation, but also various changes during the oxidation by·OH.Secondly, nine environmental concerned OPs were investigated in the effects of DOM on hydroxyl radical-induced oxidation of OPs. Generally, the pseudo-first order oxidation reaction kinetic constant (k’1OH) of OPs by·OH were significantly inhibited for all the compounds tested in the presence of DOM. The inhibition of DOM on the second-order reaction constant (k2OH) of OPs by-OH demonstrated a dependence of chemicals. The degree of inhibition of k2OH by LHA was positively correlated with logKOW of the 7 compounds tested. Since there is a good relationship between logKOW with logKDOM observed in previous studies, it is indicated that the binding of OPs with DOM affect the·OH reaction ability of OPs. It was experimently confirmed that stronger binding of OPs with DOM obviously resulted in more signicicant inhibition. Results also showed that different DOM had different effects on the reaction between HOCs and·OH. With the increasing of DOM concentration, DOM displayed correspondingly enhanced inhibitory effects on both k’1OH and k2OH of OPs with·OH. Different dosages of H2O2 applied seemed to have no significant effects on the oxidation kinetic (k’1OH) of PAHs with·OH.