On the increasing competitiveness of UV/Cl to UV/H2O2 advanced oxidation as the organic carbon concentration increases

Nathan Moore; Chengjin Wang; Susan Andrews; Ron Hofmann

doi:10.1016/j.watres.2023.120227

On the increasing competitiveness of UV/Cl to UV/H₂O₂ advanced oxidation as the organic carbon concentration increases

Water Res. 2023 Aug 15:242:120227. doi: 10.1016/j.watres.2023.120227. Epub 2023 Jun 13.

Authors

Nathan Moore¹, Chengjin Wang², Susan Andrews³, Ron Hofmann³

Affiliations

¹ Department of Civil and Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, ON M5S 1A4, Canada. Electronic address: nathan.moore@mail.utoronto.ca.
² Department of Civil and Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, ON M5S 1A4, Canada; Department of Civil Engineering, University of Manitoba, 15 Gillson Street, Winnipeg, Manitoba R3T 5V6, Canada.
³ Department of Civil and Mineral Engineering, University of Toronto, 35 St. George Street, Toronto, ON M5S 1A4, Canada.

PMID: 37354844
DOI: 10.1016/j.watres.2023.120227

Abstract

UV/Cl and UV/H₂O₂ are advanced oxidation processes (AOPs) used for drinking water treatment and water reuse. This work explored the hypothesis that UV/Cl becomes more competitive to UV/H₂O₂ at neutral-to-high pH as the concentration of total organic carbon (TOC) increases. Lab experiments and kinetic modelling were used to compare initial pseudo first-order contaminant decay rate coefficients between the AOPs at various pH and TOC conditions. The relative effect of increasing TOC concentrations on UV/Cl vs. UV/H₂O₂ depended on the pH, contaminant, and organic matter reactivity towards radicals. For example, while the reaction rate coefficients during both AOPs generally decreased with increasing TOC, the UV/Cl reaction rate coefficients for the solely •OH-reactive sucralose decreased 41-138% less than the UV/H₂O₂ coefficients as the TOC concentration was increased from 0 to 5 mg-C L^-1. However, UV/Cl was more affected than UV/H₂O₂ when targeting caffeine (a contaminant reactive to chlorine radicals). The data were used to define TOC-pH conditions for which either AOP would be more energy-efficient, under a set of standard conditions. The results suggest that UV/Cl may be competitive to UV/H₂O₂ under a wider range of treatment scenarios than has been conventionally thought based on tests in pure water.

Keywords: Organic matter; Scavenging; UV-based advanced oxidation; UV/chlorine; UV/hydrogen peroxide.