Membrane distillation for treating hydraulic fracturing produced waters
March 5-10, 2017
The reuse of wastewater for beneficial uses has become increasingly important in recent years. There is an urgent need to develop innovative and more effective technologies for treatment of wastewaters. Many of these wastewaters such as hydraulic fracturing produced waters, contain very high total dissolved solids (TDS). Treatment of hydraulic fracturing produced waters can be very challenging as not only can they exhibit very high TDS, in excess of 200,000 ppm, they also contain surfactants and small organic compounds. Pressure driven membrane processes such as reverse osmosis are impractical for treating very high salinity wastewaters due to the high osmotic back pressure that must be overcome. Membrane distillation has been proposed as a new unit operation for treatment of very high TDS wastewaters. Vapor pressure is the driving force for water recovery in membrane distillation. An advantages of membrane distillation is the fact that low grade waste heat may be used.
Here we have screened a number of commercially available microporous hydrophobic membranes. We have characterized membrane surface as well as bulk properties. Using bulk membrane properties, we calculate a structural parameter that indicates membranes that display high permeate flux. Next these membranes were challenged with feed streams containing 100,000 ppm (1.7 M) NaCl. The feeds stream was concentrated until breakthrough of the feed liquid into the permeate. Breakthrough occurred when the permeate flux rose rapidly while the conductivity of the permeate increased above 50 mS cm-1. Finally, these membranes were tested with real produced waters. Membranes that enabled the greatest concentration of TDS were selected for testing.
While membrane distillation could be used to concentrate the feed to the solubility limit of the dissolved species present, leakage of feed water through the membrane pores into the distillate often occurs well before this level of water recovery. Leakage occurs due the presence of oil and suspended solids in the feed which can adsorb on the membrane surface. Thus pretreatment of the feed is essential. Here we have investigated the use of electrocoagulation as a pretreatment step for membrane distillation. Suspended solids and oil can be effectively coagulated followed by sedimentation prior to membrane distillation. A laboratory scale electrocoagulation system containing aluminum electrodes was designed, optimized and employed successfully to pretreat the feed.
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S. Ranil Wickramasinghe and Kamyar Sardari, "Membrane distillation for treating hydraulic fracturing produced waters" in "Separations Technology IX: New Frontiers in Media, Techniques, and Technologies", Kamalesh K. Sirkar, New Jersey Institute of Technology, USA Steven M. Crame, Rensselaer Polytechnic Institute, USA João G. Crespo, LAQV-Requimte, FCT-Universidade Nova de Lisboa, Caparica, Portugal Marco Mazzotti, ETH Zurich, Switzerland Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/separations_technology_ix/30