Evolution of molecular weight and fluorescence of effluent organic matter (EfOM) during oxidation processes revealed by advanced spectrographic and chromatographic tools

Abstract

Effluent organic matter (EfOM) is an emerging concern to receiving aquatic environment due to its refractory property. The degradation of EfOM in ozonation and other two advanced oxidation processes (AOPs), UV/H2O2 and UV/persulfate (PS), was investigated in this study. Fluorescence spectra coupled with parallel factor analysis (PARAFAC) and two-dimensional correlation gel permeation chromatography (2D-GPC) were used to track the evolution of EfOM during each oxidation process. Results showed that the degradation of EfOM indicated by dissolved organic carbon (DOC), UV254 and fluorescence components, fitted well with pseudo-first-order kinetic model during the oxidation processes. Ozonation showed higher degradation efficiency than AOPs, while UV/PS was more effective than UV/H2O2 with equimolar oxidants dosage. Ozone and SO·4− were more reactive with terrestrial humic-like substances, while hydroxyl radical preferentially reacted with protein-like substances. Organic molecules with higher molecular weight (MW) were susceptible to ozone or radicals. Ozonation could transform higher MW (MW of 3510 and 575) organic matters into lower MW organic matters (MW of 294), while reductions of all the organics were observed in both AOPs. Due to the higher reaction rates between ozone and EfOM, ozonation maybe serve as a pre-treatment for AOPs to reduce the radical and energy consumption and improve mineralization of EfOM by AOPs. The decline in DOC, UV254, fluorescence and reduction in oxidants increased with the increase of oxidants dosage, and linear correlations among them were found during the ozonation and AOPs.