Article pubs.acs.org/est
Current and Potential Future Bromide Loads from Coal-Fired Power Plants in the Allegheny River Basin and Their Effects on Downstream Concentrations Kelly D. Good and Jeanne M. VanBriesen* Department of Civil and Environmental Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213, United States S Supporting Information *
ABSTRACT: The presence of bromide in rivers does not affect ecosystems or present a human health risk; however, elevated concentrations of bromide in drinking water sources can lead to difficulty meeting drinking water disinfection byproduct (DBP) regulations. Recent attention has focused on oil and gas wastewater and coal-fired power plant wet flue gas desulfurization (FGD) wastewater bromide discharges. Bromide can be added to coal to enhance mercury removal, and increased use of bromide at some power plants is expected. Evaluation of potential increases in bromide concentrations from bromide addition for mercury control is lacking. The present work utilizes bromide monitoring data in the Allegheny River and a mass-balance approach to elucidate bromide contributions from anthropogenic and natural sources under current and future scenarios. For the Allegheny River, the current bromide is associated approximately 49% with oil- and gas-produced water discharges and 33% with coal-fired power plants operating wet FGD, with 18% derived from natural sources during mean flow conditions in August. Median wet FGD bromide loads could increase 3-fold from 610 to 1900 kg/day if all plants implement bromide addition for mercury control. Median bromide concentrations in the lower Allegheny River in August would rise to 410, 200, and 180 μg/L under low-, mean-, and high-flow conditions, respectively, for the bromide-addition scenario.
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saltwater intrusion into coastal aquifers or estuaries17−21 and with anthropogenic discharges to surface waters such as oil and gas (O&G) wastewater,2,22 coal-fired power plants,4,14,23 and flame retardant textile production facilities.4,24 Because bromide has relatively high human and ecotoxicity thresholds,25,26 discharges of bromide have historically been unregulated,27 and monitoring of anthropogenic sources has not been required until recently.3,4,28,29 Bromide is unreactive under typical environmental conditions, and thus, only dilution reduces its concentration in source waters. Bromide is not removed during conventional drinking water treatment processes.1,14,30 Installing new treatment processes for bromide removal at drinking water plants is not practical or cost-effective because these methods are energy intensive, expensive, of limited value in complex mixtures found in natural waters, or combinations of these.1,30,31 Thus, reducing bromide loading into source waters is the most effective option for mitigating effects at drinking water treatment plants.
INTRODUCTION Drinking water utilities and regulators are increasingly concerned about the presence of bromide in source waters.1−4 As an inorganic precursor, bromide increases the rate of disinfection byproduct (DBP) formation in conventional drinking water treatment, leading to overall increases in DBPs,5,6 and to increased bromine incorporation.7−9 Brominated DBPs are associated with higher health risk compared to their chlorinated analogs,10,11 and DBP regulatory surrogates (e.g., total trihalomethanes, TTHM) may be less useful when DBPs are brominated.6 The EPA estimates that over 260 million people are exposed to DBPs from chemically disinfected drinking water in the United States.12,13 Some inland surface water treatment plants have recently reported increasing difficulty complying with DBP regulatory limits due to changes in source -water DBP precursor characteristics (most notably, bromide concentrations).4,14 With over 80% of the U.S. population potentially affected by changes in the concentration and speciation of DBPs, even minimal changes in source water bromide can lead to significant public health concerns.10 Bromide in Drinking Water Sources. While naturally occurring source water bromide levels are typically low,15,16 elevated concentrations of bromide are associated with © 2016 American Chemical Society
Received: Revised: Accepted: Published: 9078
April 9, 2016 July 30, 2016 August 8, 2016 August 19, 2016 DOI: 10.1021/acs.est.6b01770 Environ. Sci. Technol. 2016, 50, 9078−9088
Article
Environmental Science & Technology
Figure 1. Map of the Allegheny River Basin showing coal-fired power plants and public drinking water systems. Inset map shows wet FGD power plants (blue triangles), USGS streamflow gage used in the model (black circle), sampling sites for bromide (yellow squares), and the model site at river kilometer (RKM) 12.9. Distances provided are RKM measured from the confluence in Pittsburgh, PA.
Current Anthropogenic Bromide Sources. Wet flue gas desulfurization (FGD) wastewater discharges from coal-fired power plants have been implicated in increased bromide concentrations at downstream drinking water treatment plant intakes.3,4,14,32 Bromine (Br) is naturally present in coal in trace amounts on the order of 10 ppm.33,34 The Br in the coal is primarily converted to volatile hydrogen bromide during combustion and, subsequently, to bromine gas upon cooling,35 with only a limited portion (
