A combined ultrafiltration–reverse osmosis process for external reuse of Weiyuan shale gas flowback and produced water

Abstract

The management of large volumes of flowback and produced water (FPW) generated in shale gas extraction is of great concern due to the high concentrations of total dissolved solids (TDS), scale forming constituents, and organics. The objective of this study was to evaluate the performance of a combined ultrafiltration (UF) and reverse osmosis (RO) process for treating FPW from the Weiyuan shale gas play, China. Under a constant pressure of 4.5 MPa, the RO process decreased the concentrations of TDS, chemical oxygen demand (COD) and Cl⁻ to 192, 7.5 and 97 mg L⁻¹ from 18 900, 530 and 11 000 mg L⁻¹ in the feed, respectively. The effluent of the combined process met the requirements for surface water discharge and agriculture irrigation in China. The total fouling index of the UF membrane over a range of permeate fluxes suggests a critical flux of around 19 L m⁻² h⁻¹; operation at a low flux was effective for UF fouling control. The operating pressure and recovery of the RO system significantly affected the permeate flux and quality, with both the flux and rejection increasing with increasing operating pressure but decreasing with increasing recovery. Moreover, CaCO₃ and BaCO₃ crystals were identified on the RO membrane surface at high recovery. The rejection data for TDS and COD by the RO membrane were consistent with the Spiegler–Kedem membrane transport model.