Treatment of shale oil and gas produced water using membrane distillation combined with effective pretreatment
Date
2019
Authors
Zhang, Zuoyou, author
Tong, Tiezheng, advisor
Carlson, Kenneth H., committee member
Zahran, Sammy J., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Fossil energy is indispensable for society development. Shale oil and gas as unconventional energy resource plays an important role in improving the energy security of U.S. But the exploitation of shale oil and gas is accompanied by substantial freshwater consumption and wastewater generation. The wastewater generated from shale oil and gas production contains large amounts of salts, particles, and petroleum-associated pollutants, inevitably imposing harmful consequences to the ecological environment if not properly treated. Effective treatment of shale oil and gas wastewater, ideally for beneficial reuse, is essential in promoting sustainability of shale oil and gas production at the water-energy nexus. In this thesis, I am focusing on developing an integrated treatment train that enables effective treatment of shale oil and gas produced water. Membrane distillation (MD), an emerging membrane desalination technology, was performed in tandem with simple and inexpensive pretreatment steps, namely precipitative softening (PS) and walnut shell filtration (WSF). A laboratory-scale MD system was designed and built at Colorado State University, and produced water generated from the Wattenberg field in northeast Colorado was collected and treated by the PS-WSF-MD system. My results demonstrated that PS removed various particulate, organic, and inorganic foulants, and thus mitigate fouling and scaling potential of the produced water. WSF displayed exceptional efficiencies (≥95%) in eliminating volatile toxic compounds including benzene, ethylbenzene, toluene, and xylenes (BTEX) along with additional gasoline and diesel range organic contaminants. With pretreatment, the water vapor flux of MD decreased by only 10% at a total water recovery of 82.5%, with boron and total BTEX concentrations in the MD distillate meeting the regulatory requirements for irrigation and typical discharge limits, respectively. The use of pretreatment also led to robust membrane reusability within three consecutive treatment cycles, with MD water flux fully restored after physical membrane cleaning. The results of this thesis highlight the necessity of pretreatment prior to MD treatment of produced water and demonstrate the potential of the developed treatment train to achieve a cost-effective and on-site wastewater treatment system that improves the sustainability of the shale oil and gas industry. At last, an economic and technical assessment of MD-based wastewater treatment system was performed. The cost of the treatment system developed in this thesis was evaluated, and the results indicated that the cost of MD-based treatment system is around $0.29-$0.87/barrel. Further investigation is needed to validate the economic feasibility of MD-based treatment system when applied at full-scale in the oil and gas fields.