Setting new goals for the environmental impact of water treatment
Professor Meagan Mauter runs the Water and Energy Efficiency for the Environment (WE3Lab) program at Carnegie Mellon University and is jointly appointed in Civil and Environmental Engineering and Engineering and Public Policy. She also holds courtesy appointments in Chemical Engineering and Materials Science and Engineering. Mauter can be reached at 412.268.5688 or [email protected].
The fact that most Americans can simply open a tap and receive clean water is a marvel of human ingenuity that is too often taken for granted. Making that water potable is not without its costs, however, and learning how to more efficiently produce high-quality water is one way the industry must evolve. Professor Meagan Mauter of Carnegie Mellon University recently published research through the school’s Department of Engineering and Public Policy that illustrates the ways in which current treatment practices come up short and how they can improve. W&WD Associate Editor Michael Meyer asked Mauter what could be done to improve the efficiency of water treatment in the future.
Michael Meyer: How does some treated tap water harm people and the environment?
Meagan Mauter: Partially because of [the] tremendous successes in improving the quality of tap water and partially because of epidemiological advances in understanding the human health impacts of trace contaminant exposure, there are always debates about whether our water quality standards could be even stricter. In essence, could we deliver perfectly pure water to everyone’s tap? And the answer is yes, but the financial costs would be enormous given the way that drinking water is sourced, treated and distributed today. So the U.S. EPA is tasked with assessing the benefits of stricter standards against the financial costs to consumers. While the financial costs of water treatment are very, very important to ensuring universal access to safe drinking water, some of our recent research suggests that they are not the only costs worth considering.
After pumping water from the surface water or groundwater source, water goes through a series of unit processes that remove particulates, organics, metals and pathogens. When removing these contaminants, these unit processes consume chemicals and energy, which contribute to the financial costs of water treatment. This means that if we were to deliver perfectly pure water to your tap, the energy consumption would be many times higher than what it is for the excellent water that comes out of your tap today.
When the EPA performs a benefit-cost analysis on your perfectly pure water request, they are essentially estimating the costs of this energy and chemical consumption, along with other capital and regulatory compliance costs. What they are leaving out, though, is the fact that energy and chemical consumption also impacts human health and the environment. In the U.S., energy mostly comes from burning fossil fuels, like coal and natural gas, which emit criteria air pollutants and CO2. These pollutants carry very real risks, with some 100,000 people experiencing premature mortality from air pollution in the U.S. annually. While only a very, very small fraction of this air pollution [is] attributed to the energy consumed by water treatment processes, we believe the EPA should include those risks in their benefit-cost analyses.
Meyer: How are treatment plants and distribution systems contributing to these problems?
Mauter: In some ways, the energy and chemical consumption of water treatment plants is predetermined by the quality and availability of the water source they are drawing from. If the water originates in a well-protected aquifer with very low levels of trace organics or metals, then the energy consumption is very low and is mostly associated with disinfection processes. If, on the other hand, the treatment plant is sourcing water from an aquifer contaminated with nitrates, or has insufficient freshwater supply and needs to access saline waters using desalination processes, their energy consumption may be ten times higher. One of the easiest ways to reduce the energy consumption and air emission externalities of delivering high quality water is to focus on source water protection.
Meyer: What can water systems do to address these problems?
Mauter: In addition to focusing on source water protection, water systems and researchers can work to identify and develop efficient technologies that minimize chemical and energy consumption. There is lots of great research happening in research labs across the country on novel materials for water treatment, new processes that consume less energy, and improved sensing and automation to ensure that those processes are only operating when essential for meeting water quality targets.