Issue 4, 2016

Emerging investigators series: the efficacy of chlorine photolysis as an advanced oxidation process for drinking water treatment

Abstract

The photolysis of hypochlorous acid (HOCl) and hypochlorite (OCl) produces a suite of reactive oxidants, including hydroxyl radical (˙OH), chlorine radical (Cl˙), and ozone (O3). Therefore, the addition of light to chlorine disinfection units could effectively convert existing drinking water treatment systems into advanced oxidation processes. This review critically examines existing studies on chlorine photolysis as a water treatment process. After describing the fundamental chemistry of chlorine photolysis, we evaluate the ability of chlorine photolysis to transform model probe compounds, target organic contaminants, and chlorine-resistant microorganisms. The efficacy of chlorine photolysis to produce reactive oxidants is dependent on solution and irradiation conditions (e.g., pH and irradiation wavelengths). For example, lower pH values result in higher steady-state concentrations of ˙OH and Cl˙, resulting in enhanced contaminant removal. We also present the current state of knowledge on the alteration of dissolved organic matter and subsequent formation of disinfection by-products (DBPs) during chlorine photolysis. Although the relative yields of DBPs during chlorine photolysis are also dependent on solution conditions (e.g., higher organic DBP yields at low pH values), there is conflicting evidence on whether chlorine photolysis increases or decreases DBP production compared to thermal reactions between chlorine and dissolved organic matter in the dark. We conclude the review by identifying knowledge gaps in the current body of literature.

Graphical abstract: Emerging investigators series: the efficacy of chlorine photolysis as an advanced oxidation process for drinking water treatment

Supplementary files

Article information

Article type
Critical Review
Submitted
28 Jän 2016
Accepted
17 Mai 2016
First published
17 Mai 2016

Environ. Sci.: Water Res. Technol., 2016,2, 565-579

Emerging investigators series: the efficacy of chlorine photolysis as an advanced oxidation process for drinking water treatment

C. K. Remucal and D. Manley, Environ. Sci.: Water Res. Technol., 2016, 2, 565 DOI: 10.1039/C6EW00029K

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