Permeate Flux Performance Research Articles

Modeling water flux in forward osmosis: Implications for improved membrane design

AbstractOsmotically‐driven membrane processes, such as forward osmosis and pressure retarded osmosis, operate on the principle of osmotic transport of water across a semipermeable membrane from a dilute feed solution into a concentrated draw solution. The major hindrance to permeate water flux performance is the prevalence of concentration polarization on both sides of the membrane. This article evaluates the external and internal boundary layers, which decrease the effective osmotic driving force. By modeling permeate flux performance, the role that feed and draw concentrations, membrane orientation, and membrane structural properties play in overall permeate flux performance are elucidated and linked to prevalence of external and internal concentration polarization. External concentration polarization is found to play a significant role in the reduction of driving force, though internal concentration polarization has a far more pronounced effect for the chosen system conditions. Reduction of internal concentration polarization by way of membrane modification was found to improve the predicted flux performance significantly, suggesting that alteration of membrane design will lead to improved performance of osmotically driven membrane processes. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Effect of hydrodynamics and solution ionic strength on permeate flux in cross-flow filtration: direct experimental observation of filter cake cross-sections

The structure of membrane cakes formed in cross-flow filtration was investigated for conditions of variable particle size and solution ionic strength. In all cases, microscopic examination of membrane cake cross-sections revealed a stratified structure: a dense region of the colloidal deposit adjacent to the membrane with an abrupt transition to a much more porous layer near the membrane–suspension interface. The thickness and structure of individual layers varied as functions of particle size and solution ionic strength. Relative specific hydraulic resistances of individual layers were estimated from regressed transport coefficients in a model describing macroscopic transport and permeate flux. This work provides direct experimental confirmation of trends predicted from theory that couples hydrodynamic conditions and interparticle interactions to describe the permeate flux performance of cross-flow filtration membranes.