Abstract
Effluent organic matter (EfOM) contains a large number of substances that are harmful to both the environment and human health. To avoid the negative effects of organic matter in EfOM, advanced treatment of organic matter is an urgent task. Four typical oxidants (H2O2, PS, PMS, NaClO) and UV-combined treatments were used to treat micro-contaminants in the presence or absence of EfOM, because the active radical species produced in these UV-AOPs are highly reactive with organic contaminants. However, the removal efficiency of trace contaminants was greatly affected by the presence of EfOM. The degradation kinetics of two representative micro-contaminants (benzoic acid (BA) and para chlorobenzoic acid (pCBA)) was significantly reduced in the presence of EfOM, compared to the degradation kinetics in its absence. Using the method of competitive kinetics, with BA, pCBA, and 1,4-dimethoxybenzene (DMOB) as probes, the radicals (HO·, SO4-·, ClO·) proved to be the key to reaction species in advanced oxidation processes. UV irradiation on EfOM was not primarily responsible for the degradation of micro-contaminants. The second-order rate constants of the EfOM with radicals were determined to be (5.027 ± 0.643) × 102 (SO4-·), (3.192 ± 0.153) × 104 (HO·), and 1.35 × 106 (ClO·) (mg C/L)-1s-1. In addition, this study evaluated the production of three radicals based on the concept of Rct, which can better analyze its reaction mechanism.
Highlights
Urban sewage contains a large amount of organic matter of various and complex types
Effluent Organic Matter (EfOM).(Vigneswaran, 2006) While the concentration of emerging contaminants (ECs) in EfOM is extremely low in the environment,(Rosal et al, 2010) their high stability in wastewater makes them difficult to degrade with conventional biological treatment. (Taoufik et al, 2021) Conventional wastewater treatment processes including coagulation, sedimentation, filtration, and disinfection—can remove only a limited amount of EfOM, and sometimes highly toxic intermediate products are produced during treatment
Advanced Oxidation Process (AOPs) is a new type of highefficiency pollutant control technology developed in the 1980s.(Hisaindee et al, 2013) Because AOP has strong oxidizing ability and low selectivity to pollutants, and can remove trace amounts of harmful chemicals and refractory organics, it has been widely used in the treatment of contaminated groundwater, especially for the removal of some special trace pollutants in water
Summary
Urban sewage contains a large amount of organic matter of various and complex types. more than 90% of this organic matter can be effectively removed with conventional biological treatment, some refractory organic residue inevitably remains. An advanced oxidation process based on SO 4-· (E0 = 2.6 V) could be applied as an alternative to those based on a hydroxyl radical (HO· ) for the remediation of organic pollutants in surface water, groundwater or wastewater.(Hori et al, 2005; Yang et al, 2014) SO4-· is generated via the activation of peroxymonosulfate (HSO5-, PMS) or persulfate (S2O82-, PS) by UV, heat or transition metals.(Matta et al, 2011; Zhou et al, 2013),(Milh et al, 2021) UV/persulfate possesses several advantages, including stability of the precursors (PMS or PS), ease of storage and transportation, high water solubility, versatile activation strategies and a wide operating pH range.(And and Dionysiou, 2004; Das, 2017), (Giannakis et al., 2021). A kinetic model of UV-based AOPs was established for the degradation of micro pollutants in wastewater, and the second-order rate constants of EfOM with radicals were evaluated
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