Search

The concept of a critical permeation flux for the onset of particle deposition in crossflow microfiltration (CFMF) is well-established. However, the critical flux is known to be a function of process parameters such as the particle size, bulk concentration and crossflow velocity. In the present study, the critical modified Peclet number (Pe crit ) is explored instead as a generalized criterion for the onset of particle deposition that incorporates the effects of these process parameters as well as the axial position along the membrane. A proper determination of Pe crit requires an accurate prediction of the concentration polarization boundary layer thickness δ c and shear-induced diffusion coefficient D s . The classical Lévêque model is adapted to allow for the effect of the permeation flux on the velocity profile. Moreover, the assumptions of a constant concentration at the membrane surface c w and constant D s that have been made in prior studies are relaxed in an improved numerical solution to the convective diffusion equation that is used to predict δ c and D s . The critical permeation flux is determined from particle deposition data taken for 6 and 10μm latex spheres via Direct Observation Through the Membrane (DOTM) characterization. A constant value of Pe crit =4.00±0.08 is found to characterize the effects of particle diameter, bulk concentration and crossflow velocity as well as axial position on the onset of particle deposition. [ABSTRACT FROM AUTHOR]

Abstract: The filtration behavior and energy consumption of submerged hollow fiber membranes were investigated in a dead-end mode under constant flux operation with periodic backwash. Various operating parameters such as filtration flux, feed concentration, backwash duration, backwash strength, and the aid of air scouring during backwash were investigated to optimize the filtration performance and energy consumption. Baker's yeast was used as the model foulant. The transmembrane pressure (TMP) profiles obtained with this model foulant indicated the existence of two regions: a low fouling region followed by a high fouling region. In the low fouling region, periodic backwash could effectively remove the fouling layer. The percentage of reversible fouling by backwash was significantly lower in the second region which led to a rapid increase in TMP. The Taguchi experimental design method was used to determine the critical parameters, the effect of individual parameters and the optimum conditions. Since the transition into the second region of filtration is not favorable, the fouling rate in the first 10 cycles, the net permeate volume and specific energy consumption at the end of the first region were chosen as the design method responses. The results showed that filtration flux and feed concentration have significant effects on the membrane fouling rate. In order to maximize the net permeate volume, filtration flux, backwash duration and backwash strength were found to be the most important parameters, which must be carefully selected. To minimize the specific energy consumption, filtration flux, backwash duration and aeration rate during backwash were the most important factors. [Copyright &y& Elsevier]

Abstract: Aquaporin (AQP) based biomimetic membrane has attracted increasing attention in recent years because of its potential application for water purification and seawater desalination, attributed to the exceptionally high permeability and selectivity of AQPs. Despite its superior performance, AQP based membrane faces several challenges associated with the design and preparation of such membranes for practical application. In this current study, a novel and simple method was introduced to prepare an aquaporin Z (AqpZ) based biomimetic nanofiltration (NF) membrane with a relatively large membrane area of 28.26cm2. The proteoliposome, incorporated with AqpZ, was fully encapsulated into the selective layer through crosslinking of a polyelectrolyte with the membrane substrate made by poly(amide–imde) (PAI). The water flux of the AqpZ based membrane was around 50% higher than the mutant one. At optimal preparation conditions, the AqpZ based membrane could offer a water flux of 36.6Lm−2 h−1 with a MgCl2 rejection of 95% at 0.1MPa. Results from this study showed that AqpZ could maintain its activity even under harsh environmental conditions of thermal treatment at 343K for 2h. These results and findings may provide useful insights on developing next generation of biomimetic membranes. [Copyright &y& Elsevier]

Abstract: Osmotically-driven membrane processes such as forward osmosis (FO) and pressure retarded osmosis (PRO) have interesting applications in the water and energy domains. When surface water is used as feed solution (FS) for FO and PRO, these membranes can be fouled by microalgae that are ubiquitous in rivers, lakes, and seawater. This study systematically investigates FO/PRO fouling by a model microalgae Chlorella sorokiniana. Direct microscopic observation was used to characterize FO/PRO fouling in conjunction with water flux measurements. The study demonstrated that direct microscopic observation can be highly valuable in characterizing the deposition of microalgae on FO/PRO membrane. Using a concentration stepping method, a critical flux (critical concentration) behavior was revealed. Stable flux can be achieved by operating below the critical flux (critical concentration) level. Microalgal FO/PRO fouling was more severe and less reversible when divalent Mg2+ ions were present in the FS and the draw solution (DS). The use of Mg2+-based DS can promote severe fouling due to the reverse diffusion of Mg2+ into the FS, even if Mg2+ is not present in the original FS. The use of FS spacer was beneficial in enhancing the initial flux as well as reducing the tendency of membrane fouling. [Copyright &y& Elsevier]