Led by Mahdi Malmali, engineering professors are working on designing a modular membrane-based process to treat produced water resulting from hydraulic fracturing.
A group of professors throughout Texas Tech University's Edward E. Whitacre Jr. College of Engineering received a $1.55 million grant from the Rapid Advancement in Process Intensification Deployment (RAPID) Manufacturing Institute, a public-private partnership between the Advanced Manufacturing Office (AMO) of the U.S. Department of Energy and the American Institute of Chemical Engineers (AIChE), to develop a pathway to treat the produced water resulted from hydraulic fracturing.
With hydraulic fracturing, or "fracking," a hole is drilled into impermeable, subterranean rock formations. Then, large amounts of pressurized water are forced into the well to make the formations more porous, which allows natural gas and shale oil to flow more freely. Once that happens, the water used during the fracking process is contaminated with the shale oil, salts and other minerals at high concentrations, some of which are hazardous.
The collected wastewater returned to the surface during the well stimulation and production is collectively called "produced water," and it can't be reused or discharged into surface water unless it's treated.
Most efforts to date have been focused on developing and designing large-scale treatment processes, which make the logistics of treating produced water a major complication.
"Hydraulic fracturing is geographically distributed, so the volumes of produced water generated during this process are small," said Mahdi Malmali, an assistant professor of chemical engineering and the principal investigator (P.I.) on the project. "We as engineers should try to design processes that can address smaller scales, but for larger numbers. We have to mass-manufacture small-scale systems that can address distributed applications. Due to the high concentration of dissolved solids in the produced water, the application of conventional pressure-driven membranes is not viable. Our proposed technology is one of the few potential processes to desalinate produced water.
"We are coming up with a relatively novel, intensified membrane technology, called membrane distillation. It's a thermal-based membrane system where, unlike conventional pressure-driven membrane-based processes, the performance of the membrane is almost independent of the salinity of the produced water. It allows us to treat highly concentrated produced water streams."
From the proposed technology, the group intends to intensify membrane distillation with another technology (mechanical vapor compression) to recover the lost heat, condense water and increase the efficiency of the treatment process.
"We're going to make modular, mobile systems that are small and easily scalable, which can address different capacities," Malmali said. "That way, companies will be able to haul it to the well site, or they can scale it up and use it in their large-scale centralized treatment facilities."
By making the membrane distillation unit modular, facilities will be able to customize each unit to fit their needs, whether they need to clean 1,000 liters or 200,000 liters of water per day.
"When the produced water comes out, it can go directly to this machine, it will be treated and 50-70% of the water will be recovered," Malmali said. "The remaining produced water is highly concentrated so that, if it's cooled down, then there's a chance to crystallize some of the salts. Utilizing this technology, we are recovering a large fraction of the water. Instead of getting injected – along with numerous highly concentrated hazardous material – into the class II disposal wells, we can treat it and get a high-quality water that can at least be discharged into surface water."
Malmali said the treated water can also be used for industrial applications, agricultural use or the stimulation of the other wells in the site.
"In a water-stressed state like Texas, where 40% of fracturing is taking place, preserving water resources and managing fracturing wastewater is utterly important," Malmali said. "We believe our proposed technology offers a pathway for treatment of high total dissolved solids-produced water in locations facing water scarcity. It is small, modular and energy-efficient, thus capable of addressing the needs for highly concentrated produced-water treatment obtained from hydraulic fracturing."
Research projects like Malmali's are proof of Texas Tech's continued commitment as a Carnegie Tier One research institution and how the university works to address the growing need for energy efficiency in every capacity.
"Texas Tech is very proud of the work Dr. Malmali and his team are conducting to address the large amounts of wastewater produced in the extraction of oil and gas using enhanced recovery technologies," said Joseph Heppert, vice president for research. "This project is an outstanding example of how Texas Tech engineers and scientists are working on technologies that address the challenges faced by the energy industry in Texas, while providing collateral benefits to all the citizens of the state. Texas Tech has great expertise in preserving and improving the quality and utilization of groundwater resources, and Dr. Malmali's team is an integral contributor in this area."
Al Sacco Jr., dean of the College of Engineering, said the project is vital both domestically and internationally.
"The Edward E. Whitacre College of Engineering emphasizes energy research that is regionally, nationally and internationally important," Sacco said. "Dr. Malmali and his co-investigators' project on a modular technique to upgrade produced water for reuse is an example. Through research like this, Dr. Malmali and his fellow researchers are helping Texas, the nation and even the world to sustainably provide much-needed energy. I am very proud of our faculty who go beyond academic publications and solve real problems. Texas Tech faculty, students and staff use their expertise to build a sustainable world for us all."
Co-P.Is. on the project include:
- Denny Bullard, instructor in the Bob L. Herd Department of Petroleum Engineering
- Chau-Chyun Chen, Jack Maddox Distinguished Engineering Chair in Sustainable Energy and a professor of chemical engineering
- Fazle Hussain, President's Endowed Distinguished Chair in Engineering, Science & Medicine, senior adviser to the president and professor of mechanical engineering, chemical engineering, petroleum engineering and physics at Texas Tech and professor of internal medicine and cell physiology and molecular biophysics at Texas Tech University Health Sciences Center
- Marshall Watson, department chair, Roy Butler Chair and associate professor of petroleum engineering
Industry partners include:
- Apache Corporation
- Aspen Technology
- W.L. Gore & Associates