Characterization and fate of effluent organic matter treated with UV/H₂O₂ and ozonation

The Advanced Oxidation Processes (AOPs) UV/H₂O₂ and ozonation are widely recognized reclamation treatments. During the oxidation processes, effluent organic matter is modified and broken down into smaller compounds, which affect the characteristics of the treated effluent. In this study, Dissolved Organic Matter (DOM) present in two secondary effluents from a Conventional Activated Sludge (CAS) and a Membrane Biological Reactor (MBR) system, was characterized and monitored during UV/H₂O₂ and ozonation reactions with the Liquid Chromatography – Organic Carbon Detector (LC-OCD) technique. The following DOM fractions were quantified: biopolymers, humic substances, building blocks, Low Molar Mass (LMM) neutrals and LMM acids. Although both technologies were efficient for nearly eliminating the entire DOM at extended oxidation conditions, some differences were observed between them. The two processes were effective in degrading biopolymers since the early stage of oxidation. In addition, ozonation, by dominant direct attack, was effective in eliminating humics and the other oxidation byproducts, with the exception of LMM acids, which were accumulated from the beginning of the reaction. For MBR effluent and high doses of oxidant, the exclusive presence of LMM acids confirmed their recalcitrance to ozonation. On the contrary, the radical non-selective oxidation mechanism of UV/H₂O₂ resulted in final CAS and MBR effluents in which the humic substances and all of the LMM compounds were present. Furthermore, monitoring of the organic matter fractions with LC-OCD demonstrated that the reduction of effluent aromaticity (decreasing in Specific UV Absorbance (SUVA)) was not strictly correlated with the complete depletion of humic substances in the effluents for both advanced treatments.