Mitigating combined oil-solid fouling in flowback and produced water treatment via hydrocyclone membrane filtration: The critical role of turbulent randomness.
Abstract
A novel hydrocyclone membrane module (HMM) was developed to address severe membrane fouling encountered in flowback and produced water treatment. Localized turbulent randomness, a mechanism consistently overlooked in membrane fouling studies, was also elucidated by coupling macroscopic experiments, multiphase CFD simulation, and microscopic in-situ observations. Operated in a hydrocyclone membrane filtration (HMF) mode, the HMM mitigates fouling through synergistic, size-dependent hydrodynamic mechanisms. First, HMF constructs an ultra-thin turbulent boundary layer (δf = 319 μm) enriched with micro-eddies, which boost the radial diffusion coefficient of submicron foulants to ∼10-7 m2 s-1 by coupling with turbulent ejections to kinematically prevent dense concentration polarization. Second, turbulent cascades and sweeps induce high-frequency (50.29 Hz) pulsating shear that provides the decisive transient momentum for micron-sized foulants to overcome the adhesion barriers and achieve continuous self-cleaning. Crucially, macroscopic swirl of HMF synergizes these mechanisms via spatial classification: centripetal buoyancy repels large oil droplets toward the central axis, while centrifugally enriched coarse bentonite particles capture escaped submicron oil droplets near the membrane. This size-amplification effect transforms penetrative submicron oil droplets into micron-sized aggregates, maximizing the removal benefits of pulsating shear. Consequently, the HMM exhibited exceptional resilience treating real flowback and produced waters, particularly excelling in solid-rich environments. The effluent oil concentration remained < 5 mg L-1 with flux recovery of > 97% by ultrasonic cleaning. Overall, this work significantly enriched our understanding of coupled mass transfers in multiphase turbulent filtration systems while providing a compact but robust technology for produced water treatment.