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Comprehensive assessment of a hybrid membrane biosystem for sustainable desalination of produced water and frac flowback wastewater, A
Riley, Stephanie Marlene
Riley, Stephanie Marlene
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2018
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Abstract
Increasing population, agricultural, and industrial growth, compounded by drought in many regions, is exacerbating the stress on existing freshwater resources. Alternative water sources must be identified to alleviate stress and enable sustainable development. The energy sector, particularly the oil and gas (O&G) industry, has the potential to make a substantial impact by reclaiming O&G wastewater and treating it for reuse. Over three million gallons of water can be used to hydraulically fracturing a single well, with up to 40% returning to the surface as wastewater (e.g., produced water (PW)). While this water is typically disposed of via deep-well injection, increasing regulations and environmental concerns are stimulating the development of sustainable and efficient strategies for treatment and reuse. Due to the high and variable total dissolved solids (TDS) in PW, and concentrations of dissolved and free phase organic chemicals and inorganic constituents, robust, multi-barrier treatment approaches are required to achieve reuse standards. Hybrid biological-physical processes could be a promising method for treatment of PW. Biological processes have proven effective at removing organic matter from a variety of waste streams including domestic waste streams, landfill leachate, and oily wastewaters; membranes are most established in desalination of seawater and brackish waters. For sustainable membrane treatment, optimizing water recovery, and reducing membrane fouling, it is critical to implement pretreatment processes that target removal of organic constituents. Several phases of this study have demonstrated high removal of organic matter from PW using biologically active filtration (BAF) with granular activated carbon (GAC) media. This serves as an effective pretreatment for subsequent membrane processes like ultrafiltration (UF) and nanofiltration (NF). Following BAF pretreatment of PW, UF has demonstrated high turbidity removal with minimal membrane fouling, producing high quality permeate. NF then exhibits low fouling propensity, maintaining high ion rejection and permeate flux, producing permeate suitable for advanced reuse applications (e.g., irrigation, streamflow augmentation). Thus, the objective of my dissertation was to assess the hybrid BAF-UF-NF treatment train as a sustainable method for reclamation and reuse of O&G wastewaters. This entailed an overall proof of concept, through evaluation of the treatment train performance (TDS and organic matter removal) with varying qualities of O&G waste streams. Multiple GAC media were compared with addition of nutrients to improve the removal of organic matter by BAF and thus, the overall sustainability of subsequent membrane treatment. The composition of organic matter following BAF, UF, and NF was also characterized to evaluate the removal of specific classes of organic constituents and develop an inexpensive monitoring technique to track organic matter. A long-term investigation of BAF provided additional insight on the feasibility and biological stability with continuous exposure to challenging PW. Evaluation of BAF as a sufficient pretreatment method for desalination of PW was explored through a comprehensive membrane fouling study, providing insight on the potential for reuse of O&G wastewater.
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