Cake-Enhanced Concentration Polarization:  A New Fouling Mechanism for Salt-Rejecting Membranes

• Published in: Environmental science & technology Vol. 37; no. 24; pp. 5581 - 5588
• Main Authors: Hoek, Eric M. V, Elimelech, Menachem
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.12.2003
• Subjects: Applied sciences; Colloids - chemistry; Drinking water and swimming-pool water. Desalination; Environmental conditions; Equipment Failure; Exact sciences and technology; Filtration; Fluid mechanics; General purification processes; Membranes; Membranes, Artificial; Models, Theoretical; Nanotechnology; Osmosis; Particle Size; Pollution; Salt; Sodium Chloride; Waste Disposal, Fluid - methods; Wastewaters; Water Movements; Water Purification - methods; Water treatment and pollution; Drinking water treatment; Fouling; Crossflow filtration; Concentration polarization; Modeling; Rejection; Membrane separation; Nanofiltration; Numerical simulation; Physicochemical purification; Reverse osmosis; Waste water purification; Performance; Colloid particle
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es0262636

Results from well-controlled colloidal fouling experiments with reverse osmosis (RO) and nanofiltration (NF) membranes suggest the existence of a new source of flux decline for salt-rejecting membranescake-enhanced osmotic pressure. The physical mechanisms leading to this enhanced osmotic pressure are a combination of hindered back-diffusion of salt ions and altered cross-flow hydrodynamics within colloidal deposit layers, which lead to an enhanced salt concentration polarization layer. A model that accounts for both hindered diffusion of salt ions and altered hydrodynamics within colloidal deposit (“cake”) layers is presented. The model successfully links permeate flux and salt rejection to cake-enhanced concentration polarization and provides new insight into the mechanisms through which salt-rejecting membranes foul. Experimental data support the model calculations and highlight the role of enhanced concentration polarization phenomena in the performance (i.e., water flux and salt rejection) of polymeric thin-film composite RO/NF membranes in environmental applications.