Modeling Bromide River Transport and Bromide Impacts on Disinfection Byproducts

Abstract

Disinfection byproducts (DBPs) formed during potable water treatment can be affected by bromide (Br)containing discharges into receiving streams from coal-fired power plants as well as other sources that increase the bromide content of the source water. This research focused on two aspects related to bromide increases in receiving streams. First, a bromide river transport model was adapted to track bromide concentrations in the river following a point discharge. In this work, the point discharges modeled were coalfired power plants. The model tracked the bromide concentrations at river segments after the point of discharge daily and, therefore, at water intakes as a function of time. In this article, the application of the model is illustrated for two rivers: the Ohio River along the Indiana and Kentucky borders and the Dan River in Virginia and North Carolina. Second, models to predict DBP formation due to increased bromide in source waters were developed. The source waters used in the DBP models were obtained from 13 states across the United States. Good model fits were found for predicting trihalomethane as bromide varies, as well as for predicting the unregulated sum of four haloacetic acids (HAA4). A method was also developed to predict the sum of nine HAAs (HAA9) based on measured sum of five HAAs (HAA5; the currently regulated HAAs) and modeled HAA4. The DBP formation models developed using the specific criteria evaluated in this research would have applications beyond only bromide discharges from coal-fired power plants and would apply to any cause of a bromide increase in the source water.

Modeling Trihalomethane Increases Associated with Source Water Bromide Contributed by Coal-Fired Power Plants in the Monongahela River Basin

“…Figure outlines the structure of the multistep model and how data sources ,,− are incorporated; further details are discussed below.…”

“…Predicting DBP formation in drinking water is difficult due to the many factors that affect DBP chemistry, including source water conditions (e.g., temperature, pH, bromide, and total organic carbon [TOC] concentrations) and plant operational conditions (e.g., disinfectant type and dose) . Many models to predict DBPs have been developed using national full-scale operational surveys or plant-specific data. ,− Other models are based on laboratory experiments with some water characteristics and reaction conditions controlled. , Most models capture the widely observed relationship between higher source water bromide concentrations and increased bromine incorporation in THM. The net effect of elevated source water bromide is typically higher concentrations of TTHM on a molar basis, due to the increased rate of formation, and higher concentrations of TTHM on a mass basis, due to the increased rate and higher molar mass of bromine compared with chlorine. , Increased bromine incorporation in unregulated DBPs is also observed from elevated source water bromide concentrations. − While some models based on national data sets and some models based on laboratory experiments capture these observations, the predictive capacity of DBP models is generally quite limited .…”

“…Models developed by Malcolm Pirnie and Montgomery Watson incorporate data from drinking water utilities across the U.S. to predict TTHM based on various source water and operational characteristics. Ged et al identified the Malcolm Pirnie model as one of the most predictive for TTHM and identified the Montgomery Watson species-specific THM modelas the most predictive for bromodichloromethane, which is the dominant observed brominated THM for utilities on the Monongahela River. , Recently, Cornwell et al developed a laboratory-based TTHM model using only bromide and ultraviolet absorbance at 254 nm (UV 254 ), specifically for use in predicting TTHM under elevated bromide conditions, and thus, this model was also evaluated. The relevant equations for these three models are shown in Section S-D.…”

Power Plant Bromide Discharges and Potential Effects on DBP Formation

“…Since the effect of bromide on DBP formation differs depending on conditions such as temperature and natural organic matter, it may be necessary to assess how bromide discharges affect intake concentration at particular times of the year or to assess the frequency of bromide loads that exceed critical thresholds. Alternatively, if multiple sources are expected and concentration predictions are desired at multiple points along the river, a river flow model can be used (e.g., Cornwell et al 2018).…”

“…TTHM concentrations for changes in source water bromide levels, while Cornwell et al (2018) developed a model specific to elevated bromide conditions. Either of these methods can be used in conjunction with predicted bromide concentrations to predict the contribution of upstream bromide discharges to TTHM formation at downstream drinking water plants.…”