(651e) Combined Electrocoagulation and Membrane Distillation for Treatment of Hydraulic Fracturing Flow Back Waters

The reuse of wastewater has become an absolute necessity in recent years. Therefore, 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).  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.  While membrane distillation could be used to concentrate the feed water 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 often occurs due the presence of oil and suspended solids in the feed which can adsorb on the membrane surface.

Here we have investigated the use of electrocoagulation as a pretreatment step for membrane distillation.  Suspended solids and oil can be effectively coagulated by electrocoagulation followed by sedimentation prior to membrane distillation.  Electrocoagulation has the potential to eliminate the disadvantages of classical pre-treatment technologies such as filtration and sedimentation.  It is easy to operate and requires simple equipment.  A laboratory scale electrocoagulation system containing aluminium electrodes was designed and built. Different ranges of current and voltage have been tested in order to optimize the process. In addition, effect of contact time, number of electrodes, settling time in the settler and operating temperature have been studied. Total dissolved and suspend solids and chemical oxygen demand have bene determined before and after electrocoagulation.  We show that electrocoagulation can implemented as efficient and effective pretreatment step prior to membrane distillation. After pretreatment membrane distillation may be used to concentrate the dissolved specie in the feed to levels that are close to their solubility limit without leakage of water through the membrane pores.  The high conductivity of high TDS wastewaters is an important factor that results in the efficiency of electrocoagulation as a pretreatment step for membrane distillation.