CFD Simulation of Cross-Flow Filtration

Efficient CFD-based method for designing cross-flow nanofiltration small devices

Nanofiltration for oil-fields water injection operations: analysis of concentration polarization

This study investigates the effect of membrane properties — porosity, membrane thickness, and pore radius — on the performance of vacuum membrane distillation (VMD) process by achieving computational fluid dynamics (CFD) simulations on a three-dimensional domain of interest at fixed flow properties. The finite volume method (FVM) is adopted to solve momentum, solute mass transport, and energy equations in the feed channel. To accurately predict the rate of water vapor diffused through the membrane by Knudsen and viscous diffusion mechanism, local concentration, temperature, and flux are coupled at the membrane surfaces. In accordance with the flux, corresponding gradients for temperature and concentration are applied at the membrane boundaries. Since there is a strong coupling of flow properties at the membrane surface, the employed model is validated against an experimental study and further used to characterize the effect of PTFE membrane properties on permeate flux, temperature polarization, and concentration polarization. We found that different set of membrane design parameters substantially changes the total mass flux. The contribution of both viscous and Knudsen mechanism is comparable and, as such, prevents us neglecting neither of them. The temperature and concentration polarization are even more undesirable level for the larger pore sizes.

Evaluation of spacer-induced hydrodynamic mixing using particle image velocimetry: Impact on membrane distillation performance

A unifying model for concentration polarization, gel-layer formation and particle deposition in cross-flow membrane filtration of colloidal suspensions

In this study, a procedure for quantifying the surface deposition of proteins in crossflow ultrafiltration has been developed. The procedure consists of determining the protein adsorption behavior onto the membrane surface from a few dynamic measurements performed in a nonfiltration and a filtration mode, and evaluating the concentration polarization (CP) layer thickness based on the adsorption data. To predict the interdependence between the protein adsorption and CP, a simplified mathematical model has been formulated. The model was used to assess the protein adsorption and thus yield reduction in the ultrafiltration process at different protein concentration in the solution. As a case study, ultrafiltration of aqueous solutions of BSA and lysozyme (LYZ) was examined on a polyethersulfone membrane with the molecular weight cutoff of 10 or 100 kDa. The protein concentration in the solutions varied within a relatively low concentration range, i.e. below 10 mg mL-1, characteristic for solvent exchange between sequential operations of protein purification by chromatography and extraction. Both proteins markedly differed in the mechanism of surface deposition; for BSA hydrophobic interactions were suggested to be dominant, whereas in case of LYZ electrostatic interactions contributed the most to the deposition mechanism. The effect of additives of the protein solutions, i.e. inorganic salts, PEG, and urea depended on the adsorption mechanism and was also specific for each protein. Nevertheless, the proposed procedure performed well in the evaluation of surface deposition and yield reduction, regardless of the protein type and its solvent environment.

Quantitative evaluation of concentration polarization under different operating conditions for forward osmosis process

Computational modeling of discrete-object feed spacers attached directly onto reverse osmosis membranes for enhanced module packing capacity and improved hydrodynamics

A POM-membrane was fabricated by immobilizing a keggin type polyoxometalate (POM) H5PV2Mo10O40 onto the surface of microporous flat-sheet polymeric polyvinylidene fluoride (PVFD) membrane using a chemical deposition method. The POM-membrane was characterized by FT-IR, SEM and EDX to confirm existing of the POM onto the membrane surface. The POM-membrane was used to remove an anionic textile dye (Reactive Black 5 named as an RB5) from aqueous phases with a cross-flow membrane filtration and a batch adsorption system. The dye removal efficiency of the POM-membrane using the cross-flow membrane filtration system and the batch adsorption system was about 88% and 98%, respectively. The influence factors such as contact time, adsorbent dosage, pH, and initial dye concentration were investigated to understand the adsorption mechanism of the RB5 dye onto the POM-membrane. To find the best fitting isotherm model, Langmuir, Freundlich, BET and Harkins-Jura isotherm models were used to analyze the experimental data. The isotherm analysis showed that the Langmuir isotherm model was found to the best fit for the adsorption data (R 2=0.9982, qmax=24.87 mg/g). Also, adsorption kinetic models showed the pseudo second order kinetic model was found the best model to fit the experimental data (R2=0.9989, q=8.29 mg/g, C0=15 ppm). Moreover, after four times regeneration with HNO3 acid, the POM-membrane showed high regenerability without losing dye adsorption capacity.

Three-dimensional concentration-polarization modeling of trace-ions in reverse osmosis

Concentration polarization in membrane distillation: I. Development of a laser-based spectrophotometric method for in-situ characterization

Nanofiltration (NF) is an efficient technology to produce safe and biologically stable drinking water from surface water (Cyna et al. 2002). NF can respond to the increased demand of water with higher quality due to the evolution of the legislation and of the customer’s expectation. NF treatment allows the reduction of the concentration of organic precursors to disinfection byproducts, and the reduction of the concentration of trace contaminants such as pesticides and pharmaceuticals. The introduction of NF in the drinking water production plant of Mery-sur-Oise, France, conducted to several changes in quality of the distributed water: reduction of total organic carbon (TOC) and Biodegradable dissolved organic carbon (BDOC) by a factor 3 to 5, reduction of THMs by a factor 2, reduction of viable bacteria population by a factor 10, reduction of chlorine demand of the distribution system by a factor 3, amount of pesticides below detection level. Four membrane properties are important for the efficiency of a water treatment plant: high rejection of dissolved organics, low salt rejection, low energy consumption, and stable performance after repetitive cleanings. Membrane fouling generates flux decline leading to an increase in production cost due to increased energy demand and chemical cleaning. Moreover, fouling induces reduction in membrane life. Different types of NF fouling can be defined on the basis of fouling material: inorganic fouling due to deposition on membrane surface of inorganic scales; organic fouling due to humic acids, proteins and carbohydrates (natural organic material, NOM); biofouling due to biofilm formation at the membrane surface. Flux decline associated with NOM fouling and with biofouling can be partially restored by chemical cleaning (Al-Amoudi et al. 2005, Di Martino et al. 2007, Houari et al. 2010, Roudman et al. 2000). Biofouling is distinct from NOM fouling caused by contaminated organic matter derived from biological systems (Flemming et al., 1997). Biofouling involves biologically active microorganisms which grow at the membrane surface as complex structures termed biofilms (Lappin-Scott et al. 1989). Biofilm formation precedes biofouling, which becomes an issue only when biofilms reach thickness and surface coverage that cause declined normalized flux and/or increase in normalized pressure drops during NF operation (Vrouwenvelder et al., 1998, Ridgway, et al. 1996).

A novel antifouling technique for the crossflow filtration using porous membranes: Experimental and CFD investigations of the periodic feed pressure technique

Scale formation of soluble salts is one of the major factors limiting the application of nanofiltration (NF) and reverse osmosis (RO) membranes. This article reviews the scale formation mechanisms in membrane systems, methods to retard scale formation, and a new hybrid system consisting of MF-NF/RO. Two distinct mechanisms in NF/RO fouling by scale formation including surface and bulk crystallization have been identified and investigated. The hydrodynamic operating conditions as well as module geometry determines which fouling mechanism is dominant. An increase in solute concentration at the membrane surface by concentration polarization is responsible for surface crystallization. Conventional methods for scale control only retard the rate of scale formation and their performances are unpredictable. On the other hand, using a MF-NF/RO hybrid system for continuous removal of crystal particles from the retentate stream appears to be effective at high recovery of permeate. When applying the MF-NF/RO hybrid system, substantial improvement in flux is observed in spiral wound module, whereas it is negligible in case of the tubular module. This is because the microfilter could only removes crystals formed in the retentate through the bulk crystallization that is the dominant fouling mechanism in the spiral wound module.

Treatment of cauliflower processing wastewater by nanofiltration and reverse osmosis in view of recycling