Experimental study of the effects of hypochlorite on polysulfone membrane properties

Although chemical solutions are widely employed to clean membranes, they can also be responsible for changes in membrane properties. The two major drawbacks are then either the functional properties of the membrane gradually change, so the production can no longer meet requirements in terms of volume or quality, or the membrane simply breaks up (hollow fibers), and the system has to be shut down during maintenance. The aim of this experimental study was to gain a better understanding of the effect of hypochlorite cleaning solutions in different conditions (various pHs and temperatures) on the changes observed on an ultrafiltration hollow fiber membrane made from polysulfone (PSf) and polyvinylpyrrolidone (PVP). A wide range of methods characterizing the material have been used, from the atomic scale (ESCA) up to the module scale by force measurements on fibers. Exposure to sodium hypochlorite at rather high concentration seems to lead to chain breaking in the PSf molecules (gel permeation chromatography results). The consequences are changes in the membrane texture (scanning electron microscopy images), which are closely related to changes in the mechanical properties of the membrane. Membrane permeability appears to be poorly sensitive to such changes, which can be related to the fact that the permeability relies on the skin properties mainly

Role of the cell-wall structure in the retention of bacteria by microfiltration membranes

This experimental study investigates the retention of bacteria by porous membranes. The transfer of bacteria larger than the nominal pore size of microfiltration track-etched membranes has been studied for several kinds of bacterial strains. This unexpected transfer does not correlate to the hydrophobicity,neither to the surface charge of the microorganism, as suggested in previous reports. We conclude that,in our conditions, the kind of bacteria (Gram-positive or Gram-negative) is finally the most important parameter. As the distinction between those two types of bacteria is related to the cell-wall structure, we provide an experimental evidence, via the action of an antibiotic, that the cell-wall flexibility triggers the transfer of the bacteria through artificial membranes, when the pores are smaller in size than the cell

Potable water production by membrane processes: membrane characterization using a series of bacterial strains

The aim of this study was to develop a method for characterizing membranes (ultrafiltration and microfiltration) used in drinking water production. The method accounts for the specific behaviour of microorganisms during filtration, namely their deformation under mechanical stress. The leaks of microorganisms are linked to the presence of a small number of defects or abnormally large pores in the membrane structure. Assuming that the defects are cylindrical capillaries, the range of pore diameters concerned by the method lies between 0.05 and 1.2mm

Effects of membrane alterations on bacterial retention

The study shows the respective roles of skin and support of an ultrafiltration membrane in the retention mechanisms of bacteria (Escherichia coli). For this, pinholes defects of 5–200 μm in diameter were performed through ultrafiltration polymeric membranes and their impact was assessed on bacterialretention in a stirred cell when the transmembrane pressure is set at 0.5 bars. Various techniques have been used to make the defects such as a microhardness tester or femtosecond lasers. As long as the selective skin is not altered through its whole thickness, the membrane keeps a retention efficiency equivalent to the one of an uncompromised membrane. The retention by the macroporous support is also investigated. In case of membrane with defects of cylindrical geometry, experimental results are compared to calculated data obtained with a pore flow model, and the validity of this model is discussed

Modification of membranes surfaces for blood protein separation

The main idea behind this project is to separate platelet derived growth factor (PDGF) from platelets which has a promising role to play for medical applications such as treating of diabetic ulcers and chemotherapy. The present techniques used to separate PDGF consumes large amount of energy, and the yield is also poor. Hence an alternate method of separating PDGF from platelets is by membrane separation. The main objective of this project is to modify the membrane surface with a block copolymer that can selectively capture platelets by avoiding unwanted interactions with other blood components. The present study will focus on this first step of coating the membrane and evaluation of unwanted adsorption of blood proteins. Various optimization conditions like coating time, concentration of copolymer, chain length and operating process were varied, and the coating was analyzed using FTIR mapping. Coating time of 2 hours and the copolymer concentration of 5 mg/mL following the immersion, washing, drying (IWD) process were the optimum conditions. Filtration was done over the coated membranes and the permeability was found to decrease with increase in size of the copolymer. Then filtration was done with protein solution and the concentration of protein in retentate and permeate was calculated followed by retention %. FTIR mapping was done on filtration membrane to check if there was removal of coating from the membrane surface. From the mapping it was clear that the coating was present on the membrane surface even after filtration. For future studies, it is recommended to use other blood proteins like globulin and fibrinogen on the adhesion with the copolymer. Other characterization tools like SEM and AFM can be used to analyze the morphology and surface roughness of the coated membrane, respectively. <br /

Adsorption of MS2 bacteriophage on ultrafiltration membrane laboratory equipments

Virus adsorption has been quantified (i) on different materials including various containers made of glass, plastic or stainless steel and hollow fiber membranes made of polyethersulfone, polysulfone, PVDF or cellulose acetate (with two configurations: in/out and out/in and various molecular weight cut-offs); and (ii) on the filtration equipment. The selected virus is MS2 bacteriophage used as a model to estimate viral survival in water or to quantify virus elimination by membrane filtration. A series of experiments have been conducted with suspensions of MS2 at different concentrations prepared in a sterilized saline solution (8 g/L of KCl) or in sterilized distilled water. This study has shown that the most appropriate material to be used as a filtration test tank is Pyrex glass. We show that an addition of a virus solution 15 min after the beginning of the experiment allows keeping the virus concentration at a high level in the system (including tank, tubing,and pump). No adsorption was observed on membrane materials tested during soaking

Improvement of a method for the characterization of ultrafiltration membranes by measurements of tracers retention

The aim of this study is to improve protocols for assessing accurate characteristic retention curve and cut-off of membranes, thus enabling the manufacture and performance of the membrane to be monitored. Different data treatments are considered in order to determine membrane retention for fractions of tracer filtered (PEGs in the molar mass range of 1–100 kg mol−1). In the most advanced method of treatment, the observed retention is expressed as a combination of solute transfer coefficients in the boundary layer (kBL) and porous structure (kpore), and the asymptotic retention (Rinf ), which is an intrinsic characteristic of the membrane to solute as it is independent of operating conditions. The developed method has proved to be accurate and reproducible in two cases: (i) monitoring of UF membrane integrity during accelerated aging; (ii) for quantification of cut-off change due to UF membrane modification by UV grafting. We propose a simplified procedure that allows a reduction in experimental workload, without loss of sensitivity, for the most advanced method

Formation of bacterial streamers during filtration in microfluidic systems

Bacterial behavior during filtration is complex and is influenced by numerous factors. The aim of this paper is to report on experiments designed to make progress in the understanding of bacterial transfer in filters and membranes. Polydimethylsiloxane (PDMS) microsystems were built to allow direct dynamic observation of bacterial transfer across different microchannel geometries mimicking filtration processes. When filtering Escherichia coli suspensions in such devices, the bacteria accumulated in the downstream zone of the filter forming long streamers undulating in the flow. Confocal microscopy and 3D reconstruction of streamers showed how the streamers are connected to the filter and how they form in the stream. Streamer development was found to be influenced by the flow configuration and the presence of connections or tortuosity between channels. Experiments showed that streamer formation was greatest in a filtration system composed of staggered arrays of squares 10 μm apart

Dichloroaniline retention by nanofiltration membranes

This study evaluates the performance of two nanofiltration membranes in removing a herbicide: dichloroaniline. The membranes, one polyamide and one cellulose acetate, have a cut-off in the range 150–300 g/mol (manufacturers’ data). The experiments were carried out with solutions of dichloroaniline in demineralized water, with concentrations from 1 to 10 ppb. For each membrane, the amount of herbicide retained and adsorbed by the membrane was determined as a function of feed concentration and transmembrane pressure. The two membranes, made of different materials but having the same nominal cut-off, retained dichloroaniline to very different extents and by different mechanisms

Ageing of polysulfone membranes in contact with bleach solution: Role of radical oxidation and of some dissolved metal ions

In water production plants using membrane processes, contact with chemicals such as chlorine plays an important role in membrane ageing. This experimental study was aimed at gaining a better understanding of the effect of hypochlorite cleaning solutions on the properties of a polysulfone ultrafiltration membrane. Accelerated ageing of the membrane was simulated by soaking it in chlorine solutions and the mechanical properties of the membrane were monitored versus soaking time. An oxidation mechanism is validated which involves the catalytic effect of dissolved metal ions and the inhibitor effect of an antioxidant when these are present in soaking solutions