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Author ORCID Identifier
Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
Month Degree Awarded
David A. Reckhow
John E. Tobiason
Steven T. Petsch
Civil Engineering | Environmental Engineering | Other Civil and Environmental Engineering
For many years chlorination has served as a barrier to protect human health from waterborne disease outbreaks. Chlorine is viewed as a near-universal oxidant and disinfectant, that provides a stable residual preventing microbial re-growth all the way through the consumer’s tap. Upon reaction with natural organic matter (NOM) however, it forms disinfection by-products (DBPs) many of which are potent human carcinogens and therefore have been of research interest since the 1970’s (Froese et al., 1999; Krasner et al., 2006, 1989; Richardson, 2003; Rook, 1976, 1974; Singer, 1994). The trihalomethanes (THMs) and haloacetic acids (HAAs) are the most prevalent (Krasner et al., 1989) and routinely monitored and, the only ones regulated by the United States Environmental Protection Agency (USEPA) (80 ppb for THMs and 60 ppb for HAAs) (USEPA, 2006). The focus has recently shifted to the emerging DBP classes over concerns of even higher toxicity, carcinogenicity and mutagenicity (Bull, 1982; Hrudey, 2009; Plewa et al., 2004a, 2004b; Richardson et al., 2007).
Halobenzoquinones (HBQs) are emerging DBPs that are postulated drivers of bladder carcinogenicity. Prior assessments of 2,6-dichloro-1,4-benzoquinone (DCBQ) occurrence in drinking water distribution systems have revealed a gradual decline with increasing distance from points of entry. While this signals a degradation pathway, there is limited quantitative data on rate of that degradation. A systematic evaluation of DCBQ hydrolysis was performed, resulting in a rate law that is first order in both hydroxide [OH-] and [DCBQ]. The impact of temperature on that rate was characterized according to the Arrhenius relationship. Under the conditions tested (pH~7.2, T = 20 °C) chloramine did not significantly impact DCBQ concentrations. However, DCBQ was rapidly degraded in solutions containing free available chlorine (FAC). Kinetic analysis showed non-integer order with respect to FAC. Further investigation led to a model that invoked reaction with dichlorine monoxide (Cl2O) as well as FAC.
Such fast degradation of DCBQ, in the presence of free chlorine seem incompatible with the high concentrations reported for this emerging disinfection by-product in many drinking water distribution systems. In an effort to reconcile these two, a series of laboratory experiments and field tests was conducted. These eventually focused on evaluating the use of formic acid alone as a preservative without use of a conventional reducing agent. Formic acid was found to inadequately reduce free chlorine, resulting in persisting chlorine residuals during sample workup and analysis. The low pH used for sample preservation along with a free residual appeared to catalyze additional DCBQ formation provided that organic precursors were still present in the sample. This led to large errors and positive analytical bias. For future testing, the recommended protocol calls for addition of either glycine or arsenite followed by formic acid. Studies published without fully quenching chlorine residuals should be regarded with caution.
Little is known about the nature of HBQ precursors or about strategies for minimizing HBQs formation. Through a controlled laboratory study using solutions of pure natural organic matter (NOM) model compounds, phenolic structures containing activating -OH group with vacant ortho/para positions were determined to be plausible precursors to DCBQ, the most common of the HBQs. Almost all of the reactions proceeded through a 2,4,6-trichlorophenol pathway. Chlorination experiments conducted on a raw water and two relatively high DCBQ yielding p-hydroxy aromatic molecules (p-hydroxybenzoic acid and its aldehyde) revealed similar DBP trends. In each case, the rank order of resulting DBPs is: trichloroacetic acid> chloroform> dichloroacetic acid> DCBQ. The same solutions were subjected to preoxidation using ozone (O3) and chlorine dioxide (ClO2) at three different doses followed by chlorination. Both strong oxidants successfully decreased the tendency of the model compounds to produce DCBQ upon subsequent chlorination, however some increases in regulated DBPs were noted. When working with raw waters pretreatment with ClO2 resulted in about 35% less DCBQ after chlorination, whereas no impact was observed for O3. Such differences between preoxidant effectiveness in the raw water and model compound solutions can be attributed to the inhibiting effect of the raw water matrix and therefore very high doses are required for considerable DCBQ precursor removal in raw waters with high specific ultraviolet absorbance (SUVA254) values.
Mohan, Aarthi, "Analysis and Fate of 2,6-Dichloro-1,4-Benzoquinone in Real and Model Drinking Waters" (2022). Doctoral Dissertations. 2423.
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