Integrated membrane process of tubular ultrafiltration-nanofiltration-electrodialysis-reverse osmosis for treating fracturing flowback fluid

Abstract

As an underground source of natural gas, shale gas is important for ensuring national energy security and promoting the “dual carbon” target. However, shale gas extraction produces flowback fluid that requires efficient treatment to avoid negative impacts on the environment and human health. In this study, a pilot plant was constructed to implement a novel membrane-integrated process to treat fracturing flowback fluid. This process employs an aeration reaction sedimentation (ARS) tank and a tubular ultrafiltration (TUF) membrane for pretreatment, followed by three separate membranes for nanofiltration (NF), electrodialysis (ED), and reverse osmosis (RO). The pretreatment removed 99.3% of total hardness, 99.4% of total suspended solids (TSS), and 88.1% of total organic carbon (TOC). Four different types of TUF membranes were tested and compared. It was also found that physico-chemical cleaning of the TUF membrane using the ceramic particle technology resulted in a flux recovery rate of up to 98%. In addition, the NF and ED membranes can remove 99.4% of Na2SO4 and 90% of NaCl, respectively, resulting in an 85.6% decrease in TSS. Water recovery rate of the total system can reach 90%. Based on concept of sustainable green development, carbon footprint of integrated membrane process for treating fracturing flowback fluid was approximately 86.7 kgCO2 eq lower than that of traditional process. Low carbon emissions and no generation of secondary pollutants have become the keys to treat fracturing wastewater. In summary, the integrated TUF-NF-ED-RO process based on membranes is very promising for treating fracturing flowback fluid.