Connecting Power Plants and Drinking Water Safety-Civil and Environmental Engineering - Carnegie Mellon University

Tuesday, January 24, 2017

Connecting Power Plants and Drinking Water Safety

When CEE professor Jeanne VanBriesen began looking for possible sources of bromide in local rivers, she was expecting to find shale gas wastewater management to be a source. But after changes made to treatment and disposal of water produced by shale gas extraction did not drop bromide levels as low as expected, she began exploring other industries.

Coal is known to contain bromide, and when coal-fired power plants use wet flue gas desulfurization to control emission of chemicals that cause acid rain, bromide can end up in the wastewater. Also, these power plants are subject to recently-finalized regulations for mercury control that may increase bromide discharges.

While bromide reduces air pollution, bromide in the wastewater can cause problems for downstream water treatment plants, which do not typically remove it from drinking water. Bromide concentrations have never been regulated and are seldom measured. VanBriesen, with PhD student Kelly Good, used many different sources of bromide information to estimate the amount of bromide entering the Allegheny River basin from coal-fired power plants, as well as oil- and gas-produced water management activities. They also examined how those bromide loads affect downstream concentrations of bromide. Their research was recently published in Environmental Science & Technology.

The Effects of Bromide

According to Good, bromide in our rivers was considered naturally occurring and harmless to humans and ecosystems until recently. However, bromide can cause changes in chemical reactions within the drinking water treatment plants that affect our water.

In short, when river water goes through a drinking water treatment plant, any bromide present combines with organic matter and chemical disinfectants (like chlorine), creating disinfection by-products (DBPs). DBPs are associated with reproductive and developmental health effects and cancer, and when bromide is present, the DBPs that form are more toxic and carcinogenic.

“What we know is that if you have bromide in your source water, it increases the rate of reaction, and you have more disinfection by-products, as well as by-products with bromide in them,” said Good, who worked as a planning engineer for a large drinking water utility before beginning her studies at CEE. “We would strongly prefer to not have bromide in our source water,” she added.

Although it is known that bromide causes DBP problems, it is not known how much of that bromide is coming from power plants. “In the absence of widespread monitoring data, we need a method to estimate how these power plants are affecting downstream drinking water plants,” said Good. “That’s the gap that this work is seeking to fill.”

The Right Place and the Right Time

The Allegheny River basin was an ideal location for this research due to the presence of multiple power plants and the availability of data on bromide concentrations. VanBriesen and Good estimated bromide loads on a mass-per-time basis, but Good emphasized that it is the concentration of bromide that is most important to the drinking water utility. “You could have a high load, but if you also have a high flow, that could dilute the bromide to a lower concentration,” she explained.

Good hopes that their research will help put the issue of bromide use into perspective for power plants, water treatment plants and regulators. She suspects there are concentrations of bromide in the Allegheny River basin at certain times of year that may be a problem to the water treatment plants.

“The point is to try to get ahead of it and affect decision making around bromide use,” she said. With the data provided by this research, drinking water treatment plants will be better able to understand their watershed. “This will help them know what’s going on in their system,” said VanBriesen. “Power plants can use this information to make more proactive decisions about meeting emissions standards.This should help them understand what the implications of those choices are on their neighbors at the drinking water treatment plant. We all want a cleaner environment, and choices we make to control one type of pollution often cause challenges for another type of pollution. It is important that we think about these issues at the watershed system level.”

Good and VanBriesen will next apply their methodology to the entire state of Pennsylvania, looking at all power plants and large, community-based drinking water treatment plants.