A Combined Membrane Filtration - Aeration Approach for the Treatment of Hydraulic Fracturing - Flowback and Produced Water from the Duvernay Formation

Abstract

Membrane filtration technologies have been successfully applied for the treatment of many types of wastewater. In hydraulic fracturing operations, membrane processes can be applied as a cost-effective way of removing unwanted substances from flowback and produced water (FPW) and promoting its reuse in subsequent fractured wells. High degrees of fouling has been reported when raw FPW has been passed through membranes, suggesting the need for fluid pre-treatment. In this study, aeration was used as a pre-treatment method to improve filtration flux of polymeric membranes in microfiltration (MF) and ultrafiltration (UF) processes for an FPW sample collected from the Duvernay shale play located in Alberta, Canada. The pre-treatment not only enhanced FPW flux but also increased the rejection of targeted particles (Fe, Si), and reduced some of the potentially toxic organic and inorganic compounds in the filtered fluid. Additionally, the performance of four polymeric membranes including two polyvinylidene fluoride (PVDF) MF membranes (0.2 and 0.1 µm), one polyethersulfone (PES) MF membrane (0.22 µm) and one polyethersulfone UF membrane (0.03 µm) were compared using a dead-end filtration cell. In the first test, raw FPW was used as the feed water during the experiments, and in the second stage, aeration was first applied to the raw FPW, and the aerated water was then passed through the membranes. For all membranes, severe membrane fouling was found in the first 15 min when using the untreated FPW, with a very low rejection of Fe and Si (<10%). After the aeration treatment, the filtration flux decreased by less than 20%, as compared to more than 40% in the raw FPW, while rejection of Fe and Si increased to more than 70%. No significant differences were found in the fouling mechanisms before and after filtration. The predominant fouling mechanisms were cake layer and intermediate pore blocking. Comparison of the four polymeric membranes revealed that the 0.2 PES membrane had the best flux and a similar rejection to the UF membrane. Therefore, the 0.2 PES membrane was used for further analysis such as quantification of polycyclic aromatic hydrocarbons (PAHs) and determination of the reduction of adverse effects on zebrafish embryos following aeration and filtration. This study highlights the key importance of pre-treatment when using membrane technologies to treat FPW, and further demonstrates the positive environmental implications of the two-step process developed here.