Effective treatment of shale oil and gas produced water by membrane distillation coupled with precipitative softening and walnut shell filtration

We developed an integrated treatment train that enables effective treatment of shale oil and gas produced water generated from the Wattenberg field in northeast Colorado. Membrane distillation (MD) was performed in tandem with simple and inexpensive pretreatment steps, namely precipitative softening (PS) and walnut shell filtration (WSF). PS removed various particulate, organic, and inorganic foulants, thereby mitigating 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 compounds. 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. Our results highlight the necessity of pretreatment prior to MD treatment of produced water and demonstrate the potential of our treatment train to achieve a cost-effective and on-site wastewater treatment system that improves the sustainability of the shale oil and gas industry.