(691f) Development of a Multi-Stage Membrane Distillation - Electrocoagulation Process for Treatment of Hydraulic Fracturing Flow Back Waters

There is an urgent need to develop innovative and more effective technologies for treatment of wastewaters. Many of these wastewaters such as hydraulic fracturing flow back waters, contain very high dissolved solids (TDS). Treatment of hydraulic fracturing flowback waters can be very challenging as they often contain TDS in excess of 200,000 ppm as well as dissolved 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. One of the advantages of membrane distillation is the fact that low grade waste heat may be used.

Here we have developed a multi-staged membrane distillation system for maximizing water recovery from actual hydraulic fracturing flowback waters. The multi-stage system has been designed to different on-site applications for wastewaters with specific TDS levels. We show that ideal membrane properties vary as the TDS of the fee increases above 300,000. At lower TDS values membranes should be selected that maximize flux. However at TDS values above 300,000, membrane surface properties such as roughness becomes important. At theses higher TDS values leakage of the feed through the membrane pores and into the permeate side is a major concern. In addition, appropriate pretreatment of the feed to remove dissolved organic compounds is essential prior to membrane distillation. Here we have developed an efficient electrocoagulation process for pretreatment of the hydraulic fracturing flow back waters.

Here different membranes have been used in the different stages and performance of the system in terms of water recovery potential and specific energy consumption has been evaluated. Significant concentration of the feed has been conducted and over 60% water recovery has been achieved for actual hydraulic fracturing flowback waters from Marcellus shale containing over 100,000 ppm TDS.