Water Resources Research Act Program

Details for Project ID 2013MD304B

Bromide as a Precursor of Potent Brominating Agents During Drinking Water Chlorination

Institute: Maryland
Year Established: 2013 Start Date: 2013-03-01 End Date: 2014-02-28
Total Federal Funds: $2,592 Total Non-Federal Funds: $6,532

Principal Investigators: John Sivey

Project Summary: PROBLEM: Bromide inputs into drinking water (DW) sources can stem from several natural (seawater intrusion, atmospheric deposition) and anthropogenic (wastewater discharges, pesticide applications, road salting, hydraulic fracturing) sources. Each of these sources has the potential to increase bromide levels in watersheds flowing in or through Maryland. Bromide in DW sources that are subsequently disinfected with chlorine can contribute to the formation of potentially toxic brominated disinfection byproducts (DBPs), which, once formed, are difficult to remove from DW. Accordingly, the preferred engineering option is to minimize their formation in the first place. Doing so requires a detailed understanding of bromination chemistry. Upon addition of chlorine, bromide is rapidly transformed into "free bromine" (principally HOBr and BrO-). Conventional wisdom in the environmental chemistry literature suggests that HOBr is the only kinetically-important brominating agent in chlorinated DW. In contrast to this conventional wisdom, the PI’s recent research has shown that several lower-concentration (yet highly reactive) brominating agents, including BrCl, Br2, BrOCl, and Br2O, can also influence bromination rates of the herbicide dimethenamid during simulated DW chlorination. The extent to which these often overlooked brominating agents contribute to the bromination of organic compounds other than dimethenamid is, however, poorly understood. Such information is necessary to optimize DW disinfection processes so as to comply with federal maximum contaminant levels of regulated DBPs. OBJECTIVES The objectives of this project include: 1) Elucidating the influence of the overlooked brominating agents (BrCl, Br2, BrOCl, and Br2O) on bromination rates for a series of substituted benzenes (ethylbenzene, methoxybenzene, 1,4-dimethoxybenzene). The overall bromination rates of these aromatic compounds likely span several orders of magnitude, consistent with the wide range of reactivity observed in natural organic matter. 2) Determining the changes in selectivity among brominating agents for sequential bromination reactions of methoxybenzene, noting that the selectivity of methoxybenzenes in favor of the more reactive brominating agents is anticipated to increase as the number of bromine substitutions increases. METHODS: Task 1—Bromination kinetics of substituted benzenes: Bromination rates for the three aforementioned substituted benzenes will be determined in batch reactors in which loss of parent compound and formation of product(s) will be concurrently monitored as a function of time using gas chromatography/mass spectrometry (GC/MS). Solution conditions known to influence the speciation of brominating agents (including pH, bromide concentration, chlorine dose, chloride concentration, and ionic strength) will be systematically varied and the effects on bromination rates will be evaluated. Task 2—Determination of selectivity trends for sequential bromination of anisole: Rates of the sequential bromination of methoxybenzene to its monobromo-, dibromo-, and tribromo-analogues will be determined following the method of Task 1. For both tasks, nonlinear least-squares regression analyses of kinetic data will permit an assessment of how the structure of DBP precursors (both the substituted benzenes and the brominating agents) influences rates of bromination. These results will permit the role of each brominating agent to be quantified so that more accurate models aimed at predicting bromination rates in chlorinated waters can be developed.