# Kinetics of Hypohalous Acid Intermediates Governing Disinfection Byproduct Formation in Peracetic Acid-Treated Halide-Containing Waters

## TL;DR

This study explores how peracetic acid interacts with halides in water, forming disinfection byproducts and how adding hydrogen peroxide can reduce these harmful byproducts.

## Contribution

The study introduces a refined kinetic model and new rate constants for PAA/halide reactions, revealing mechanisms and mitigation strategies for DBP formation.

## Key findings

- Dibromoacetic acid is the dominant brominated DBP, with many unidentified byproducts indicated by TOBr analysis.
- Total organic iodine (TOI) formation is the main iodide sink in PAA/I–/NOM systems, with limited iodate formation.
- Using a PAA/H2O2 molar ratio of 1:2 reduces known DBPs by 85–90% and TOBr/TOI by 33–44%.

## Abstract

Peracetic acid (PAA)
has emerged as an alternative disinfectant
because of its lower reactivity with natural organic matter (NOM)
and minimal halogenation. However, PAA may react with halides (Br–, I–) in water to form hypohalous
acids, which can contribute to halogenated disinfection byproduct
(DBP) formation. Meanwhile, coexisting hydrogen peroxide (H2O2) can reduce HOBr/HOI back to halides. To assess and
mitigate the DBP risks of PAA in halide-containing waters, this study
investigated the oxidant change and DBP formation in PAA/halide/NOM
systems. A refined kinetic model accurately simulates PAA/Br– and PAA/Br–/NOM reactions, revealing that a small
fraction of NOM is highly reactive with HOBr and drives brominated
DBP formation. Dibromoacetic acid dominated the identified DBPs, while
total organic bromine (TOBr) analysis suggested a majority of the
unidentified byproducts. In PAA/I– and PAA/I–/NOM reactions, newly determined rate constants enabled
good model and experimental data agreement. With NOM, total organic
iodine (TOI) formation was the dominant iodide sink, with limited
iodate formation. Triiodomethane and triiodoacetic acid were the major
identified DBPs, along with more unidentified byproducts. Some unknown
iodine reactive species were observed to persist in PAA/I–/NOM systems for hours. Importantly, applying a PAA/H2O2 molar ratio of 1:2 substantially mitigated DBP formation,
decreasing known Br- or I-DBPs by 85–90% and the TOBr/TOI by
33–44%.