Cross-flow Filtration Experiments Research Articles

Comparative characterisation of different commercial UF membranes for drinking water production

In this study, nine commercially available ultrafiltration membranes used in drinking water production were characterised. The aim of the study was to compare the molecular weight cut-off (MWCO) and the membrane permeability of a selection of currently available ultrafiltration membranes. Permeability and MWCO are important criteria for the selection of ultrafiltration membranes with regard to efficiency and rejection of dissolved and particulate substances. This study provides an overview of the differences in cut-off and permeability between commercial UF membranes with similar specifications. To this end, tests were conducted using eight hollow fibre membranes with effective membrane surface areas of between 0.04 and 0.26 m2 and one type of flat sheet membrane with an effective filtration area of 0.0044 m2. Cross-flow filtration experiments using a mixture of dextrane as a feed solution were performed to determine MWCO. The molecular weight of the dextrane used in the feed solution ranged from 8–2,000 kD. The concentration distribution of the dextrane in the feed and the permeate was determined by gel permeation chromatography (GPC) in the range of 10–1,000 kD. These tests showed that, from the nine UF membranes tested, four of them displayed a MWCO of below 1,000 kD with pure water permeabilities of 180–400 l/(m2 · h · bar). A further four displayed no MWCO in the range examined (10–1,000 kD) with pure water permeabilities of 130–880 l/(m2 · h · bar) and therefore their cut-offs must be in the range above 1,000 kD. One membrane, which showed no rejection for any dextrane fraction with a pure water permeability of 2,700 l/(m2 · h · bar), could be classed as a microfiltration membrane.

Crossflow filtration of chromium hydroxide suspension by ceramic membranes: fouling and its minimization by backpulsing

Crossflow filtration experiments with Cr(OH) 3 suspension as synthetic electroplating wastewater were performed in turbulent flow regime on a pilot filter unit, equipped with a backpulse device, using porous alumina ceramic membranes of various pore sizes (0.2–5.0 μm). All membranes are fouled during filtration. Except for the 5.0 μm pore membrane, the fouling process could not be described by a model considering only one of the pore blocking, pore constriction and cake formation fouling mechanisms reported in literature. However, a model considering all the three fouling mechanisms provides an improved description of the fouling process. Filtration experiments with and without backpulsing show that backpulsing is effective in reducing the fouling phenomenon resulting in up to five-fold increase in steady state permeate flux and 100% flux recovery. The permeate flux increases with increasing transmembrane pressure and crossflow velocity, both in the presence and absence of backpulsing. The membrane cleaning time during backpulse decreases with increasing backpulse amplitude and membrane pore size. However, feed concentration, pulse duration and interval do not have a significant effect. Filtration experiments with various backpulse conditions were conducted to identify the optimum forward and reverse filtration times that yield the maximum steady state permeate flux.

Use of alternating electrical fields as anti-fouling strategy in ultrafiltration of biological suspensions – Introduction of a new experimental procedure for crossflow filtration

Results of a parameter study concerning the electro-ultrafiltration with alternating electric fields of aqueous solutions of bovine serum albumin are presented. The alternating electric field diminishes membrane fouling and hence yields a higher specific filtrate flux. The effect of the electric field depends on frequency (0.5–50 Hz), field strength (0–80 V cm −1), conductivity (1–10 mS cm −1), protein concentration (0.1–5 w%), and membrane material (values in brackets are the range of each parameter examined in this work). Low frequency and high field strength yield the best result for electro-ultrafiltration with alternating fields. The effectiveness of the electric field increases with rising conductivity up to the point where a limiting electrolytic current is reached. Increasing protein concentration diminishes the effect of the electric field. A new procedure to perform crossflow filtration experiments, the so-called step-change experiment, is proposed. The results of the new procedure are compared to results of conventional experiments. The step-change experiments yielded reproducible results in good agreement with conventional experiments.

Silica-suported polyvinylpyrrolidone filtration membranes

A hybrid ceramic-polymeric membrane was developed by the growth of covalently-bonded polyvinylpyrrolidone (PVP) chains from the surface of a porous silica support membrane via a graft polymerization process. These ceramic-supported polymeric (CSP) membranes can be produced with variable surface density and length of the terminally anchored polymer chains. Hydraulic permeability measurements demonstrated the effect of the grafted chain density and length on the water permeability of the CSP membranes. The potential application of these CSP membranes for the treatment of oil-in-water emulsions, was evaluated in cross-flow filtration experiments. This preliminary evaluation indicated improved performance of a CSP membrane, relative to an unmodified support, since the CSP membrane produced a lower permeate concentration at an equivalent permeability. The improved selectivity and reduced fouling tendency is attributed to the increased hydrophilicity of the membrane surface provided by the grafted PVP chains.

Filration characteristics of charged alumina membranes for methanogenic waste.

For the purpose of selecting or developing appropriate inorganic membranes for methane fermentation membrane bioreactors, the relationship between surface charge of the inorganic membrane and filtration characteristics of methanogenic waste was examined. The zeta potential of alumina membranes with 0.5 μm pores was controlled to negative, zero and positive, respectively, in the methanogenic waste by surface treatment. Cross-flow filtration experiments showed that negatively charged alumina membranes had twice the filtration flux of positively charged membranes when waste was fed to the membrane at 3.0 m·s–1. And it was found that the influence of membrane charge on filtration flux resulted from the influence of membrane charge on the hydraulic resistance of Rp, which was attributed to the plugging of suspended particles in the feed during filtration.