Abstract

The management of highly saline wastewater released from hydraulic fracturing—also known as fracking—a hydrocarbon releasing process used in the rapidly growing shale gas industry, is a serious challenge for industry and regulators due to its adverse effects on public health and to the environment in general. As well, fracking wastewater also contains particularly concerning levels of suspended solids, mainly comprised of sand and oil. Pre-treatment of fracking wastewater through microfiltration (MF) can effectively remove these suspended solids and oily materials. Forward osmosis (FO), an emerging membrane-based technology, is a feasible method for the treatment of fracking wastewater. For the FO process to be successful, an effectively engineered draw solution, a robust FO membrane, and an efficient pre-treatment, such as MF are required. FO is particularly effective when combined with membrane distillation (MD) for the recycling of the FO draw solutions. Therefore, the goals of this research project were to a) identify an effective draw solution for FO and b) fabricate two types of advanced membrane materials: MF membranes with high water flux, high rejection, and antifouling properties, and a FO membrane for recycling fracking wastewater with high water flux, high rejection, and antifouling properties. In this research, a comprehensive study was conducted to identify novel, yet effective, organic draw solutions for the treatment of fracking wastewater by FO. A novel high water-flux polyvinyl acetate-coated electrospun nylon 6/silica (SiO2) composite MF membrane was fabricated and its performance was tested in regard to water flux, oil rejection, and antifouling properties. In the next stage of this research, a new FO membrane material with high water-flux with high rejection and antifouling properties was fabricated and characterized. Finally, real fracking wastewater was treated using MF and then FO—combined with MD as a downstream separator—using the fabricated membranes. In the pre-treatment stage, ~98.5% turbidity and ~52% of total organic carbon (TOC) were removed from the fracking wastewater via the MF process. Finally, treated water with TDS 23-44 mg/L was obtained from the pre-treated wastewater via the combined FO/MD process. This produced water can effectively be reused for hydraulic fracking.