Membrane-based Separation Processes for Treating High Salinity Produced Waters

摘要

Produced waters (PW) generated in the oil and gas industry within the United States often contain extreme levels of total dissolved solids (TDS). These high TDS waste streams need to be treated cost-effectively as the costs associated with the current management techniques can exceed 15 USD per barrel of discharged PW. Thermally and osmotically-driven membrane separation technologies can show promising potential for treating high TDS waste streams, as onsite low-grade waste heat may be used for their operation. In this dissertation, the application of membrane distillation (MD), forward osmosis (FO) and a hybrid FO-MD process for treating synthetic and actual high TDS PW is investigated. The aim is to maximize water recovery and minimize the high TDS sludge volume.;A number of commercially available hydrophobic membranes with varying properties have been extensively characterized and tested in a bench-scale MD system. A bulk membrane structural parameter has been defined and used to identify membranes that display the highest permeate fluxes. Then, the maximum achievable brine concentration for higher flux membranes was determined. When treating actual PW feed streams, which contain not only high TDS, but also dissolved organics, surfactants and low surface tension contaminants, pretreatment of the feed is essential to suppress the onset of membrane fouling. In this study, the feasibility of electrocoagulation (EC) followed by MD is investigated. EC was reported effective in mitigating fouling during MD.;FO is another emerging membrane-based separation technology that could find niche applications in the treatment of oil and gas PW. Here, the feasibility of treating hydraulic fracturing PW using a combined EC-FO process has been investigated. EC is shown to be effective for removing suspended solids and organic compounds which foul the membrane during FO. By accounting for internal and external concentration polarization as well as fouling, the expected FO flux may be determined. Finally, we have studied hybrid FO-MD system and shown that this process integration can combine the advantages of both processes; low fouling tendency and high quality permeate. The actual treatment used, EC-MD, EC-FO or EC-FO-MD will depend on the quality of the PW.