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The rejection coefficient of nonspherical particles from ultrafiltration and microfiltration membranes has been examined from both theoretical and experimental perspectives. Modeling efforts focused on incorporating the convective hindrance factor for a capsule shaped particle in a cylindrical pore into predictions of the rejection coefficient. First, the convective hindrance factor was approximated using previously reported results for the hydrodynamic resistances experienced by a sphere in a pore. Second, computational fluid dynamics calculations predicted the convective hindrance factor for a capsule in a cylindrical pore. Results from both approaches indicate that including hydrodynamic interactions in predictions of the rejection coefficient has a greater effect for smaller particles and particles with smaller aspect ratio (i.e., close to spherical shape). Rejections of several rod-shaped Gram negative bacteria with aspect ratio from 2 to 5 by clean track-etched membranes were in general agreement with theoretical predictions. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3863–3873, 2013

In this work, the treatment of photographic processing wastewaters (PPW) by electro-Fenton process has been investigated. The Influence of operating conditions on kinetics and efficiency of electro-Fenton process has been evaluated using carbon felt cathode and platinium (Pt) or boron-doped diamond (BDD) anode. The results of electro-Fenton treatment of PPW have shown that nearly complete removal of total phenols was obtained for all combinations with pseudo-first rate constants of 0.07, 0.012, and 0.018/min for carbon felt/Pt, carbon felt/BDD and Pt/BDD cathode/anode combinations, respectively. The combination of carbon felt cathode with BDD anode achieved the highest total organic carbon (TOC) removal of 90%, while it did not exeed 40% for carbon felt/Pt combination. Increasing current intensity and Fe2+ dose enhances the efficiency of electro-Fenton process. However, increasing pH decreases TOC removal during the treatment of PPW by electro-Fenton process. The highest efficiency of electro-Fenton process using BDD anode can be explained by the contribution of direct and indirect oxidation routes in the degradation mechanism of organics including (i) oxidation via hydroxyl radicals generated from the catalytic decomposition of H2O2 and from water discharge on BDD anode, (ii) direct oxidation of certain organic compounds on BDD anode, and (iii) mediated oxidation with inorganic oxidants electrogenerated from anodic oxidation of supporting salts.

Crossflow nanofiltration experiments were performed to investigate the factors influencing the removal of amino acids by a commercially available polymeric thin-film composite membrane. The removals of five monoprotic (Ala, Val, Leu, Gly, and Thr), one diprotic (Asp), and one dibasic (Arg) amino acids in a range of permeate fluxes, feed pH values, and ionic strengths were analyzed using a phenomenological model of membrane transport. At any given pH and ionic strength, reflection coefficients (rejection at asymptotically infinite flux) of monoprotic amino acids increased with molar radius demonstrating the role of steric interactions on their removal. Additionally, consistent with Donnan exclusion, higher reflection coefficients were obtained when the membrane and the amino acids both carried the same nature of charge (positive or negative). In other words, both co-ion repulsion and molecular size determined amino acids removal. Importantly, the removal of effectively neutral amino acids were significantly higher than neutral sugars and alcohols of similar size demonstrating that even near their isoelectric point, zwitterionic characteristics preclude them from being considered as strictly neutral. Biotechnol. Bioeng. 2007;98; 451–461. © 2007 Wiley Periodicals, Inc.

Despite greater NF fouling rates, life cycle costs for membrane facilities appear to be reduced when membranes are operated at higher permeate fluxes and feedwater recoveries.

A pilot study investigated the use of dissolved air flotation (DAF) as a pretreatment to hollow-fiber microfiltration (MF). Results showed that DAF-pretreated feedwater achieved longer MF runs than raw feedwater. MF performances with DAF-pretreated water were compared for fluxes of 70, 90, 110, and 135 gfd (120, 155, 190, and 230 L/m 2 /h). Performance results indicated that MF run lengths of more than 30 days could be achieved at flux conditions of 70 and 90 gfd (120 and 155 L/m 2 /h), with run lengths of 21 and 10 days for fluxes of 110 and gfd (190 and 230 L/m 2 /h). Experimental results fromi this pilot study were also interpreted using a mathematical model to determine MF backwash efficiency at the different flux conditions. Both the experimental and modeling results suggest that membrane fouling by the DAF-pretreated water was characterized by reduced pore blockage and lower cake compressibility as compared with treatment of raw feedwater.

An integrated membrane system pilot study compared microfiltration (MF), Ultrafiltration (UF), and conventional treatment as pretreatment strategies for surface water nanofiltration (BF) using spiral wound elements. MF and UF pretreatment resulted in lower NF fouling rates and longer cleaning intervals compared with those measured following conventional treatment. NF fouling rates evaluated under a wide range of hydrodynamic conditions following conventional treatment suggest NF fouling is more influenced by permeate flux than by feedwater recovery. NF was shownto be capable of meeting all current and anticipated trihalomethane and haloacetic acid regulations.

A theoretical description of single-phase flow through porous media having permeable boundaries is presented. The volume averaged momentum transfer equation is solved numerically by a finite difference technique after neglecting the nonlinear inertia term. The influence of fluid slip on axial velocity profiles and wall skin friction is analyzed as a function of cross-flow and the porous medium shape factor. Boundary erects on momentum transfer are quantified. The implications for the design of scale models for porous media such as filters, adsorber columns, and aeration towers are discussed. In accordance with experimental data obtained by other researchers, it is shown that in most cases, additional viscous dissipation erects due to the presence of boundaries are expected to be insignificant even in laboratory-scale models only a few packing element diameters wide

Numerical simulations and experimental work for evaluating transport mechanisms for colloidal foulants in pressure-driven membrane systems are discussed. A model for concentration polarization is used to explore the role of ionic strength in determining the distribution of dissolved humic materials near a rejecting membrane