Enzymatic hollow fiber membrane bioreactor for penicilin hydrolysis

Continuous enzymatic reaction has been proven as an efficient technique for several industrial applications. In this study, a type of hollow fiber membrane bioreactor where penicillin acylase entrapped within membrane pores was applied to continuously hydrolyze Penicillin G The influences of various operating conditions on immobilization and enzymatic reaction processes were assessed. Amathematical model of the reactor behaviour at steady state condition was also developed. The immobilization results show that penicillin acylase was entrapped more than 90% (100,000 u.a m-?). Due to the much smaller size of 6-APA compared to the membrane pore, the solute diffuses freely through the membrane. However, the immobilized enzyme membrane retained around 35% of the solute. In addition, K,,, of immobilized penicillin acylase (8.04 mM) was slightly higher than that of free penicillin acylase (7.75 mM). The theoretical results indicated that convective transport was the main mechanism of mass transport even in the case where flux was very low. Low flux rate is important to avoid gel formation or enzyme release from membrane pores and to maximize the degree of conversion

Modelling the microfiltration of lactic acid fermentation broths and comparison of operating modes

clarification of fermentation broths by cross-flow microfiltration. Microfiltration experiments conducted under constant transmembrane pressure and under constant permeate fluxes (higher and lower than the critical flux) were represented by the resistance in series model in which the membrane resistance, the adsorption resistance, the bacteria cake resistance and the soluble compounds concentration polarisation resistance were taken into account. The different operating modes were compared in terms of two industrial interest criteria: the productivity and fouling rates. Higher productivities were obtained during constant transmembrane pressure runs whereas the lowest fouling rate was observed during the run conducted with a constant permeate flux lower than the critical flux. However, this fouling was mainly due to adsorption and solute components concentration polarisation. Key words

Effect of periodic backwash in the submerged membrane adsorption hybrid system

The submerged membrane adsorption hybrid system (SMAHS) is an attractive solution in treating wastewater; however it faces membrane fouling although to a less extent. In this study, different adsorbents and resins were investigated in order to find a substitute to the powdered activated carbon (PAC); The effect of new backflush was also studied in further reducing the membrane fouling. The SMAHS led to 72–86% dissolved organic carbon (DOC) removal. A detailed study on the transmembrane pressure development led to a conclusion that there is a critical flux and this value is around 16 l/h.m2 for the wastewater studied

Influence of electrostatic interactions in electrophoretic membrane contactors

In electrophoretic separators, a porous membrane is used to put into contact two flowing liquids between which an electrically driven mass transfer takes place. As far as charged solutes are concerned, the mass transfer can be affected by electrostatic interactions taking place at the membrane solution interface. The influence of these interactions on the solvent and solute transfer is investigated by associating a theoretical and an experimental work, carried out with buffered solutions of different solutes, chosen with respect to their size or electrical charge. Experimental variations of the electroosmotic flux as well as those of the solute concentrations are used to get the values of the characteristic parameters involved in the model. Results obtained with binary solutions are then compared to those obtained with single-solute solutions so as to point out the mass transfer limitation

Modified CVD of nanoscale structures in and EVD of thin layers on porous ceramic membranes

Experiments on the modified chemical vapour deposition (CVD) and the electrochemical vapour deposition (EVD) of yttria-stabilized zirconia on porous substrates are reported. It is shown that, in the CVD stage, deposition occurs in a small (<20 um) region at the edge of the substrate, very likely leading to pore narrowing. This result illustrates the feasibility of the CVD technique for the modification of ceramic membranes to the (sub)nanometer scale. Film growth in the EVD stage is shown to be controlled by the inpore diffusion of the oxygen source reactant for short (<5 h) deposition times. The yttria to zirconia ratio in the deposited film is determined by the ratio present in the vapour phase. Very thin (<2 um) films can be deposited, which have a potential application in solid oxide fuel cells

Current‐voltage curves of bipolar membranes

Bipolar membranes consist of a layered ion‐exchange structure composed of a cation selective membrane joined to an anion selective membrane. They are analogous to semiconductor p‐n devices as both of them present current‐voltage curves exhibiting similar rectification properties. In this article, we present some current‐voltage curves obtained for different bipolar membranes at several temperatures. The results can be interpreted in terms of a simple model for ion transport and field‐enhanced water dissociation previously developed. The mechanism responsible for water splitting is assumed to be a catalytic proton transfer reaction between the charged groups and the water at the membrane interface. The effects of temperature are taken into account by introducing an Arrhenius‐type relationship for the dependence of the forward rate constant of the reaction on temperature. Finally, comparison between theory and experiments provides reasonable values for the parameters introduced in the theoretical model. The analysis aims at developing a better physical understanding of a process in which chemical reactions and transport phenomena are coupled in such a way that the potential technological applications depend strongly on this [email protected]

Development and testing of a fully adaptable membrane bioreactor fouling model for a sidestream configuration system

This article is available through the Brunel Open Access Publishing Fund. Copyright © 2013 MDPI AGA dead-end filtration model that includes the three main fouling mechanisms mentioned in Hermia (i.e., cake build-up, complete pore blocking, and pore constriction) and that was based on a constant trans-membrane pressure (TMP) operation was extensively modified so it could be used for a sidestream configuration membrane bioreactor (MBR) situation. Modifications and add-ons to this basic model included: alteration so that it could be used for varying flux and varying TMP operations; inclusion of a backwash mode; it described pore constriction (i.e., irreversible fouling) in relation to the concentration of soluble microbial products (SMP) in the liquor; and, it could be used in a cross flow scenario by the addition of scouring terms in the model formulation. The additional terms in this modified model were checked against an already published model to see if they made sense, physically speaking. Next this modified model was calibrated and validated in Matlab© using data collected by carrying out flux stepping tests on both a pilot sidestream MBR plant, and then a pilot membrane filtration unit. The model fit proved good, especially for the pilot filtration unit data. In conclusion, this model formulation is of the right level of complexity to be used for most practical MBR situations

Modélisation du transport des solutés neutres à travers des membranes de nanofiltration

L'exclusion engendrée par la présence de membranes de nanofiltration est due à la superposition de plusieurs mécanismes. Aussi, il est important de pouvoir distinguer ces différents modes de transports afin de les comprendre et de proposer des modèles adéquats. Cette étude s'attachera uniquement à la compréhension du transport de solutés neutres à travers des membranes de ce type. Trois sucres, le glucose, le saccharose et le raffinose, ont été utilisés pour caractériser deux membranes organiques fournies par la société Osmonics. Ce travail montre qu'un modèle simple, basé sur la diffusion, tenant compte des conditions hydrodynamiques du module, est en accord avec les résultats obtenus au laboratoire mais également trouvés dans la littérature. Une bonne adéquation entre le modèle et l'expérience est ainsi obtenue, à la fois sur des modules plans et tubulaires, pour des écoulements laminaires et turbulents.Although nanofiltration appeared at the end of the 1970s under various names, it was only really recognized as a useful separation process in the 1980s. Nanofiltration membranes are porous media with a mean pore diameter around 1 nanometer. These membranes do not obey the traditional solution-diffusion model given for reverse osmosis or the convection-diffusion model used to describe ultrafiltration. Although the technique has benefited from a fast technological development, the transport mechanisms are still misunderstood and for a particular separation the choice of a nanofiltration membrane remains empirical.The main objective of this work was to understand and to model the transport of neutral solutes through nanofiltration membranes. Neutral solutes were chosen to emphasise geometrical exclusions, to avoid any electrical interactions and to identify the preponderant transport mechanisms through these materials. The experiments were carried out with a laboratory filtration apparatus. The membranes were laid out in a parallel plane osmotic cell, which makes tangential filtration possible. The geometry of the filtration cell involved the choice of two organic membranes supplied as flat sheets: a BQ01 and a MX07 membrane. The filtration area was 86 cm2. The pressure varied from 7 to 30 bars. The temperature was maintained at 20°C whereas tangential velocity in the cell was fixed at 0.45 m×s-1 (the Reynolds number was 3350). As the solutions used were slightly concentrated, the pH remained close to neutral pH. Three sugars were chosen as solutes: glucose, saccharose and raffinose. These molecules have two advantages: they are electrically neutral and they have molecular weights close to the membranes' MWCO, as provided by the manufacturer.First, saccharose was studied on the two membranes with two different concentrations. These experiments showed that the separation of neutral solutes by nanofiltration membranes is due only to a sieving effect. In subsequent experiments a single concentration was used to characterize the retentions of both glucose and raffinose. The results of the filtrations carried out on the three sugars validated the molecular weight cut-off specified by the manufacturer: the MWCO of the BQ01 membrane was estimated to be 1000 Da, and that for the MX07 membrane was 200 estimated as 200 Da.Schematically, the solute transport can be divided into three stages: in the feed, at the feed/membrane interface, and within the membrane material. In the feed, one notes an increase in solute concentration if one approaches the membrane from upstream. This phenomenon, which is general to any selective transport, is called concentration polarization and is described by film theory. This theory stipulates the creation of an antagonistic diffusive flow, from the membrane towards the feed, seeking to restore the concentration balance within the feed solution. The modification of the concentration at the feed/membrane interface leads to the definition of two retention coefficients: a measured value, the observed retention (Robs), and a calculated value, the intrinsic retention (Rm). Steric exclusion based on the size difference between the pore and the solute is set up at the interface. Uncharged solutes can be visualised as rigid spheres and the membranes can be regarded as a bundle of cylindrical, parallel, rigid and right capillaries. Since the elements are rigid and the solutes are subjected to the same geometrical constraints at the entry and at the exit of a pore, the partition coefficients are identical at those two ends. Finally, lying between reverse osmosis and ultrafiltration, transport through nanofiltration membranes is often expressed as the sum of convective and diffusive phenomena. However, the experimental results show that the observed retentions are stable or increase when pressure increases. These observations also highlight the fact that the values of infinite retention are always compatible with values close to 1. These observations corroborate the idea that diffusion is the predominant transport mechanism of neutral species through the studied materials (BQ01, MX07). The transport equation of neutral solutes can then be simplified to its diffusive component. The expression of the intrinsic retention is obtained by using Fick's law, the definition of the retention coefficients and the definition of the partition coefficients:Rm= 1-(1 / 1+Jvα)The geometrical and physicochemical characteristics of the solutes and of the membranes merge into the α parameter.The results found with the theoretical relation were confronted with experimental data derived from film theory (in order to take into account concentration polarization). The simple one-parameter model was successful in correlating the results obtained in this work. The model was also tested with data coming from Combe et al. (1997), who studied filtrations of glucose, saccharose and raffinose in a laminar flow system by ceramic nanofiltration membranes laid out in the shape of tubular module. The results obtained show that the simple model also successfully correlates with the performances of these membranes.With the data obtained in our laboratory as well with the data found in literature, this study shows that a simple one-parameter model, based on the diffusional transport of the solutes within the membrane material, predicts the rejection of neutral solutes by nanofiltration membranes. The simple one-parameter model is able to simulate any filtration carried out by these membranes for different circulation conditions, for diverse geometrical shapes and for various materials