The links between the environment and energy are strong, including the potential for jeopardizing water quality due to natural gas production practices that produce vast quantities of contaminated high-saline water. In particular, an environmental concern associated with hydraulic fracturing is the management and treatment of produced waters that contain toxic metals and radionuclides. In this project, we advanced strategies for treating contaminated water to remove toxic trace elements and we examined the subsurface geochemical processes that create risks for unintended fluid migration.

Conventional treatment strategies for heavily contaminated industrial wastewaters, such as ion exchange and osmosis, can be effective but are often cost-prohibitive. Chemical precipitation is simple and cost effective, but the scientific underpinnings of this technology are not well understood when waste streams contain complex mixtures. Our research has shown that the resulting precipitated mineral phases are variable in composition, which defies conventional theoretical predictions. Our research has revealed promising findings that metal concentrations in sulfate precipitates can be much higher than expected, which points to new engineering strategies for precipitation technologies that effectively remove toxic metals from waste streams, especially for waters containing the alkaline earth metals barium, strontium, and radium.

Our work has also made significant advancements in understanding the risks of unwanted fluid migration in the subsurface. Underground fractures can enable water and other fluids to flow, which can be beneficial such as when we want to extract natural gas, or problematic such as when we want to contain wastes. This study has generated new understanding about how acids erode fracture surfaces. When calcite dissolves, it creates an opening for more acid to flow there. This creates ‘positive feedback’ because when more acid flows there, more calcite dissolves there, and so on. Channels form and act like little riverbeds along the fracture surface. This is important because we often inject acids underground. An example is the underground injection of carbon dioxide so that it doesn’t get to the atmosphere and act as a greenhouse gas. Underground, CO₂ forms carbonic acid. If it migrates, this may be a problem if fractures enlarge and fluids get away from where they are supposed to be.

This project has enabled Prof. Peters and her collaborators and students to reach out to a broad audience and communicate about the environmental implications of subsurface energy technologies. In addition to publishing scientific journal papers and organizing special issues and conference sessions, Prof. Peters made presentations at conferences, retreats and workshops that were attended by the lay public, with presentations titled “Environmental Regulation in the U.S.: From Smog to Acid Rain to Greenhouse Gases” (ACEE, 2017), “The Science and Innovation of Fossil Fuels and the Environment”  (ACEE, 2016), and “Environmental Geochemistry Perspectives on Subsurface Energy Technologies” (Pittsburgh, 2017). Prof. Peters also created new undergraduate curricular elements including a new course CEE 304 Environmental Engineering and Energy, which teaches students about a sustainable energy future in which the world’s energy needs will be met while protecting natural resources and minimizing risks to human health. At Princeton, the course is part of departmental requirements in Civil and Environmental Engineering and it is a cognate course in the certificate program in Sustainable Energy. Finally, this NSF project served to introduce undergraduate students to research and environmental sciences through summer internships and academic-year senior thesis research. Examples of undergraduate thesis topics include “Forward Osmosis Technology: Applications for Reducing Produced Wastewater Volumes in the Hydraulic Fracturing Industry” and “Optimizing the Treatment of Flowback and Produced Wastewater from Hydraulic Fracturing in the Marcellus Shale”.

Last Modified: 10/10/2018
Modified by: Catherine A Peters