As demand for new energy sources grows, the wastewater co-produced alongside oil and gas (produced water) shows no signs of slowing down: The current volume of wastewater—the result of water forced underground to fracture rock and release the deposits—is estimated at 250 million barrels per day, compared to 80 million barrels per day of oil.

Engineers at the University of Pittsburgh Swanson School of Engineering are using membrane distillation technology to enable drillers to filter and reuse the produced water in the oil and gas industry, in agriculture, and other beneficial uses. The method is already being tested in Texas, North Dakota, and most recently in New Stanton, Pa.

The project is led by Radisav Vidic, professor and chair of the Department of Civil and Environmental Engineering.

Produced water contains many impurities that prevent its treatment in municipal facilities: it can be eight times saltier than seawater and harbor bacteria, sand, mud, oil and grease, as well as naturally occurring radioactive materials. Current management strategies for produced water include injections into disposal wells; processing to recover more oil from the water; and beneficial reuse after treatment.

Injection into a disposal well is the least expensive option and therefore the most common, but it leads to a permanent loss of water from the ecosystem. While drought is less of an issue in Pennsylvania than in other parts of the country where drilling is prevalent, the produced water that is not reused for hydraulic fracturing is transported to Ohio for disposal, adding to environmental concern of fuel usage and emissions in transport, as well as cost.

Membrane distillation (MD) is an emerging membrane technology with great potential for treatment of hypersaline wastewater generated by unconventional (shale) oil and gas reservoirs. However, the low energy efficiency of this technology makes the operating cost of MD systems relatively high, especially in the absence of waste heat.

The proposed solution uses waste heat to meet the technology’s thermal energy requirements, further decreasing the operation costs. Northeastern counties in the state—those farthest from disposal wells—stand to benefit the most from using this technology, saving nearly $16 million per year in disposal costs.

The project began in the lab about eight years ago and was first brought into the field for pilot-scale testing, with funding from the US Department of Energy, in Texas and North Dakota oilfields. The group has now begun implementing the same technology in Pennsylvania’s Marcellus Shale drilling on-site in New Stanton, Pa.

While implementing the technology in Marcellus Shale wells, the team encountered a problem: The operators add surfactants into their wells to enhance the well’s productivity and reduce energy consumption. The surfactants will cause wetting of the membrane, which will deteriorate the quality of the recovered water. The team is back in the lab to find a fix.

Resources

• Shamlou, Elmira & Vidic, Radisav & Khanna, Vikas. (2022). “Optimization-based modeling and economic comparison of membrane distillation configurations for application in shale gas produced water treatment.” Desalination. 526. 115513. doi: 10.1016/j.desal.2021.115513.