Characteristics and fate of natural organic matter during UV oxidation processes

Abstract

Advanced oxidation processes (AOPs) are widely used in water treatments. During oxidation processes, natural organic matter (NOM) is modified and broken down into smaller compounds that affect the characteristics of the oxidized NOM by AOPs. In this study, NOM was characterized and monitored in the UV/hydrogen peroxide (H2O2) and UV/persulfate (PS) processes using a liquid chromatography organic carbon detector (LC-OCD) technique, and a combination of excitation emission matrices (EEM) and parallel factor analysis (PARAFAC). The percentages of mineralization of NOM in the UV/H2O2 and UV/PS processes were 20.5 and 83.3%, respectively, with a 10 mM oxidant dose and a contact time of 174 s (UV dose: approximately 30,000 mJ). Low-pressure, Hg UV lamp (254 nm) was applied in this experiment. The steady-state concentration of SO4-center dot was 38 -fold higher than that of center dot OH at an oxidant dose of 10 mM. With para-chlorobenzoic acid (pCBA) as a radical probe compound, we experimentally determined the rate constants of Suwannee River NOM (SRNOM) with center dot OH (k(oH/Nom)= 33 x 10(8) M(-1)s(-1)) and SO4-center dot (k(SO4-/) (NOM) = 4.55 x 10(8) M(-1)s(-1)). The hydroxyl radical and sulfate radical showed different mineralization pathways of NOM, which have been verified by the use of LC-OCD and EEM/PARAFAC. Consequently, higher steady-state concentrations of SO4-center dot, and different reaction preferences of center dot OH and SO4-center dot with the NOM constituent had an effect on the mineralization efficiency. (C) 2017 Elsevier Ltd. All rights reserved.