A life cycle solution to the impacts of fossil fuels

PITTSBURGH (November 27, 2018) … The energy history of Pennsylvania is rich in the amount of fossil fuels that it has produced, but it is also imbued with the environmental legacy of the city. coal mining and, more recently, hydrofracturing. Water flowing into abandoned coal mines throughout the Commonwealth resurfaced as acid mine drainage (AMD), while freshwater fractured or "fractured" oil and gas deposits. Natural gas reemerged in the form of "produced" water contaminated with salts, metals and radioactive material.

The clearance of AMD and production water is an expensive process and the federal law prohibits the elimination of production water in municipal wastewater treatment plants. However, a research from the University of Pittsburgh Swanson School of Engineering, recently published in Science and technology of the environment, found that co-treatment of both fluids can not only solve two environmental problems at once, but also reduce the environmental impact of the two existing wastes.

Leanne Gilbertson, Assistant Professor in Civil and Environmental Engineering, is the principal investigator of the research entitled "Impact of the Life Cycle and Tradeoff Between the Benefits of a Simultaneous Process of Production Water Treatment". and abandoned mine drainage "(DOI: 10.1021 / acs.is.8b03773). The article, written by Yan Wang, a graduate student, integrates related research conducted by his colleagues at Swanson School, Radisav Vidic, Professor William Kepler Whiteford, and director of civil engineering department. and environmental and associate professor Vikas Khanna.

"This study is a fortuitous result of three different researchers who found a common theme to unite their collaboration.The Radisav group has developed the method of co-treatment of AMD and water production. a leading researcher in the field of water treatment by membrane distillation, while the Vikas group focuses on the analysis of complex systems, "explained Dr. Gilbertson. "My expertise in life cycle analysis brings a new perspective to these industries and a way to quantify the trade-offs of environmental and human health impacts of alternative approaches to the use of these two. waste."

Dr. Gilbertson and her group have focused on an area of ​​five counties in southwestern Pennsylvania affected by both AMD and hydrofracturing: Allegheny, Fayette, Greene, Washington and Westmoreland counties. . The research focused on three essential mutual aspects of remediation: co-processing of production water and AMD, transporting water to and from the drilling and mine sites, and the 39 avoid releases of AMD into the environment. Dr. Gilbertson's ACV revealed that co-treatment of AMD and produced water is beneficial because, although the chemical composition of each fluid varies from site to site, both by-products share opposite amounts of barium and sulphates which can be removed by precipitation. . The resulting fluid can then be used to replace fresh water in future fracturing operations, while the barite produced by this process can be used in drilling operations.

Dr. Gilbertson emphasized that this result is important because it creates value for two important wastes and prevents the environmental impacts of AMD. "While the combined water volume from fracking is 4,450 cubic meters per day, there are 281,000 cubic meters of orphan AMD produced daily in the region." treatment would result in a reduction in the use of fresh water benefit. "

But even with the potential positive impact of co-treatment, transporting fluids between the operating and drilling sites could create a significant negative trade-off. It will be a balance between the proposed and current treatment of produced water, which he has often traveled considerable distances to treat, or out of state to be evacuated via large trucks recording several hundreds of thousands of kilometers per year.

In order to minimize these significant impacts, which include not only fuel consumption, but also the wear and tear of trucks' roads and exhaust, Dr. Khanna and his PhD student, Sakineh Tavakoli, have developed a model to identify the optimal locations for co-treatment sites between AMD and gas wells in the five county area. Although the costs associated with optimized co-treatment may be higher than those associated with freshwater use, the environmental benefits could be considerable. Another potential option currently being tested by Drs. Vidic and Khanna is a mobile membrane distillation system that would be powered by waste heat generated during drilling to treat the water produced at the site.

And while the optimization model was developed using mining sites and gas wells in the five county area, researchers point out that this approach can be applied to other regions. from Pennsylvania and the United States using similar data.
Ms. Wang added that what is innovative in this research is that the group has attempted to quantify the benefits of not releasing AMD in ecosystems and the environment.

"These are" credits "of the system that you would not necessarily think of – for example, using AMD as a fracturing fluid, we are dramatically reducing the amount of fresh water that would be wasted. transport and developing mobile processing sites, we are dramatically reducing the environmental impact of long-haul trucking, "said Ms. Wang. "More importantly, by using AMD as a resource, we are helping to mitigate legacy environmental waste that then improves restoration efforts. In summary, the cascading effect of joint treatment of these two wastes may represent a net benefit to Pennsylvania. "

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