Development of Predictive Models for the Degradation of Halogenated

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Development of predictive models for the degradation of halogenated disinfection byproducts during the UV/H2O2 Advanced Oxidation Process Yi-Hsueh Chuang, Kimberly M. Parker, and William A. Mitch Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b03560 • Publication Date (Web): 15 Sep 2016 Downloaded from http://pubs.acs.org on September 20, 2016

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Environmental Science & Technology

Development of predictive models for the degradation of halogenated disinfection byproducts during the UV/H2O2 Advanced Oxidation Process

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Yi-Hsueh Chuang1, Kimberly M Parker1, and William A. Mitch1*

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Department of Civil and Environmental Engineering, Stanford University, 473 Via Ortega, Stanford, California 94305, United States

*Corresponding author: email: [email protected], Phone: 650-725-9298, Fax: 650-723-7058

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Abstract

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Previous research has demonstrated that the reverse osmosis and advanced oxidation processes

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(AOPs) used to purify municipal wastewater to potable quality have difficulty removing low

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molecular weight halogenated disinfection byproducts (DBPs) and industrial chemicals. Because of

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the wide range of chemical characteristics of these DBPs, this study developed methods to predict

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their degradation within the UV/H2O2 AOP via UV direct photolysis and hydroxyl radical (•OH)

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reaction, so that DBPs most likely to pass through the AOP could be predicted. Among 26

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trihalomethanes, haloacetonitriles, haloacetaldehydes, halonitromethanes and haloacetamides, direct

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photolysis rate constants (254 nm) varied by ~3 orders of magnitude, with rate constants increasing

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with Br and I substitution. Quantum yields varied little (0.12-0.59 mol/Einstein), such that rate

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constants were driven by the orders of magnitude variation in molar extinction coefficients. Quantum

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chemical calculations indicated a strong correlation between molar extinction coefficients and

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decreasing energy gaps between the highest occupied and lowest unoccupied orbitals (i.e., ELUMO –

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EHOMO).

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halonitromethanes, haloacetamides, and haloacetic acids with •OH measured by gamma radiolysis

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spanned 4 orders of magnitude.

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relationship model (Group Contribution Method) was developed which predicted •OH rate constants

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for 5 additional halogenated compounds within a factor of 2.

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molar extinction coefficients, quantum yields and •OH rate constants predicted experimental DBP

Rate

constants

for

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trihalomethanes,

haloacetonitriles,

haloacetaldehydes,

Based on these rate constants, a quantitative structure-reactivity

A kinetics model combining the

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loss in a lab-scale UV/H2O2 AOP well. Highlighting the difficulty associated with degrading these

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DBPs, at the 500-1000 mJ/cm2 UV fluence applied in potable reuse trains, 50% removal would be

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achieved generally only for compounds with several –Br or –I substituents, mostly due to higher

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molar extinction coefficients.

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Introduction

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Increasing numbers of utilities are considering municipal wastewater effluents as a secure and

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local supply for potable water after advanced treatment.1,2 Potable reuse facilities frequently employ

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Full Advanced Treatment (FAT) trains to remove the organic contaminants occurring in wastewater

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effluents. FAT trains consist of microfiltration (MF), reverse osmosis (RO), and the UV/hydrogen

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peroxide (H2O2) advanced oxidation process (AOP). Within the FAT train, the RO treatment

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represents a broad-screen physical barrier, and the AOP represents a broad-screen chemical barrier.

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Among organic contaminants, a report by the National Research Council on wastewater reuse2

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indicated that concentrations of disinfection byproducts (DBPs) in reuse waters are orders of

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magnitude closer to levels of potential human health concern than are pharmaceuticals and personal

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care products. While low levels of regulated and unregulated DBPs occur in secondary municipal

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effluents, ozone and/or chloramines applied upstream of microfiltration to control biofouling

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increase their concentrations by a factor of 3 or greater in the microfiltration effluent.3 Episodic

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discharges of industrial compounds to sewers (e.g., solvents such as methylene chloride), also may 3

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represent concerns.

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RO is capable of removing a broad suite of pharmaceuticals,4 perfluorinated compounds,5 and

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endocrine disrupting compounds (e.g., bisphenol A).6 Although RO exhibits efficient removal (i.e.,

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high rejection) of charged compounds, rejection rates decline with molecular weight for uncharged

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compounds with