Membrane bioreactors support

It is expected that in the very near future, the application of closed water loops will show an intensive growth, strongly supported by the further development of separate treatment technologies such as anaerobic treatment, membrane bioreactors, advanced biofilm processes, membrane separation processes, advanced precipitation processes for recovery of nutrients, selective separation processes for recovery of heavy metals, advanced oxidation processes, selective adsorption processes, advanced processes for demineralisation, and physical/chemical processes which can be applied at elevated temperature. 

Bader et al. [35] and De Bartolo et al. [36] developed the flat membrane bioreactor which consists of a multitude of stackable flat membrane modules as shown in Fig. 5. Each module has an oxygenating surface area of 1150 cm. Up to 50 modules can presently be run in parallel mode. Isolated hepatocytes are co-cultured with non-parenchymal cells. Liver cells are located of a distance of 20 pm of extracellular matrix from a supported polytetrafluorethylene (PTFE) film. Medium and cells in the modules are oxygenated in the incubator by molecular diffusion of air across the non-porous PTFE membrane. The design of the bioreactor is also the basis for its proven potential for cryostorage with fully differentiated adult primary human liver cells. 

The possibility of having membrane systems also as tools for a better design of chemical transformation is today becoming attractive and realistic. Catalytic membranes and membrane reactors are the subject of significant research efforts at both academic and industrial levels. For biological applications, synthetic membranes provide an ideal support to catalyst immobilization due to their biomimic capacity enzymes are retained in the reaction side, do not pollute the products and can be continuously reused. The catalytic action of enzymes is extremely efficient, selective and highly stereospecific if compared with chemical catalysts moreover, immobilization procedures have been proven to enhance the enzyme stability. In addition, membrane bioreactors are particularly attractive in terms of eco-compatibility, because they do not require additives, are able to operate at moderate temperature and pressure, and reduce the formation of by-products. 

Membrane bioreactors have been reviewed previously in every detail [3,4,7,8,18], There are two main types of membrane bioreactors (i) the system consists of a traditional stirred-tank reactor combined with a membrane separation unit (Figure 14.1) (ii) the membrane contains the immobilized biocatalysts such as enzymes, micro-organisms and antibodies and thus, acts as a support and a separation unit (Figure 14.2). The biocatalyst can be immobilized in or on the membrane by entrapment, gelification, physical adsorption, ionic binding, covalent binding or crosslinking [3, 7, 18]. Our attention will be primarily focused on the second case where the membrane acts as a support for biocatalyst and as a separation unit, in this study. The momentum and mass-transport process, in principle, are the same in both cases, namely when there is... 

The obtained results demonstrated that a PEEK-WC-H F membrane bioreactor is able to support the proliferation and functions of human peripheral lymphocytes isolated from the buffy coat of healthy individuals. Therefore, the lymphocyte HF membrane bioreactor can be used as a valuable tool to maintain viable and functional lymphocytes and as an in-vitro model for pharmacological and adoptive immunotherapy. 

Bressler, E., Pines, O., Goldberg, I. and Braun, S. (2002) Conversion of fumaric add to L-malic by sol-gel immobilized Saccharomyces cerevisiae in a supported liquid membrane bioreactor. Biotechnology Progress, 18, 445. 

In particular, membrane bioreactors (MBRs) are today robust, simple to operate, and ever more affordable. They take up little space, need modest technical support, and can remove many contaminants in one step. These advantages make it practical, for the first time, to protect public health and safely reuse water for non-potable uses. Membranes can also be a component of a multi-barrier approach to supplement potable water resources. Finally, decentralization, which overcomes some of the sustainability limits of centralized systems, becomes more feasible with membrane treatment. Because membrane processes make sanitation, reuse, and decentralization possible, water sustainability can become an achievable goal for the developed and developing worlds. 

The chapter focuses on membrane bioreactors where a UF or MF membrane is employed for biomass retention and filtration. However, membrane bioreactors where the membrane provides a support for biofilms are an alternative form of membrane bioreactor for wastewater treatment application. Two processes, in particular, the membrane-aerated biofilm reactor (MABR) and the extractive membrane bioreactor (EMB), have seen significant interest in recent years. Figure 36.4 shows these two technologies schematically. The application of biofilms reactors for wastewater treatment systems is advantageous in view of... 

The modelling of enzymatic membrane reactors follows, in general, the same approach as described previously. In enzymatic membrane reactors the catalyst is a macromolecule (enzyme). It can be found either in a free form in the reactor or supported on the membrane surface, or inside the membrane porous structure by grafting it or in the form of a gel obtained by ultrafiltration. As in the case of the whole-cell membrane bioreactors discussed above, the proper calculation of the mass transfer characteristics is of great importance for the modelling of this type of reactor. One of the earliest models of enzymatic membrane bioreactors is by Salmon and Robertson [5.108]. These authors modelled an enzymatic membrane bioreactor, which was made of four coaxial compartments the enzyme is confined within one of the compartments, and one of the substrates is fed in a gaseous form. 

Lipases used in laundry detergents and in other bulk applications do not require enzyme immobilization however, an increasing number of applications in synthesis and biotransformation demand an immobilized biocatalyst for efficient use. It has been claimed that the success of a lipase catalyzed biotransformation for the production of certain pharmaceuticals depends on immobilization. For example, in the industrial preparation of the chiral intermediate used in the synthesis of Diltiazem, the lipase from Serratia marcescens was supported in a spongy matrix, which was used in a two-phase membrane bioreactor (Cowan 1996). 

As an immobilization method, both for whole cells or enzymes, membrane bioreactors provide the advantages and drawbacks common to entrapment or adsorption methods. They nevertheless present particular assets. Mass transfer in the porous supports generally used (alginate, k-carrageenan, zeolites, silica) is a diffusion-controlled process, often becoming the overall rate-limiting step. This maybe overcome by the use of membrane modules. This equipment also avoids... 

Consequently, membrane bioreactors are an example of the combination of two unit operations in one step for example, membrane filtration with the chemical reaction. In a typical membrane bioreactor, as weU as acting as a support for the biocatalyst, the membrane can be a very effective separation system for undesirable reactions or products. The removal of a reaction product from the reaction environment can be easily achieved thanks to the membrane selective permeability, and this is of great advantage in thermodynamically unfavourable conditions, such as reversible reactions or product-inhibited enzyme reactions. A very interesting example of a membrane bioreactor is the combination of a membrane process, such as microfiltration or ultrafiltration (UF), with a suspended growth bioreactor. Such a set up is now widely used for municipal and industrial wastewater treatment, with some plants capable of treating waste from populations of up to 80 000 people (Judd, 2006). 

Steady-state flow reactors, with a constant supply of reactants and continuous removal of products, can be operated as both a continuous stirred-tank bioreactor (CSTB) and as a plug flow bioreactor (PFB). It is possible to have different configurations of the membrane bioreactor where the biocatalyst is immobilized in the fractionated membrane support (Katoh and Yoshida, 2010). In Fig. 1.6 the scheme of a CSMB in which the biocatalyst is immobilized on the surface of the membrane beads is presented. The biocatalyst immobilized in the porous structure of a fractioned membrane can also be operated in CSMB. For example, two configurations are shown in Fig. 1.7 (a) for flat-sheet and (b) for spherical porous structures, respectively. Such structures could also be adopted for PFB, where a bed of membrane support with the immobilized biocatalyst could be utilized, in either a fixed or fluid configuration. 

Key words wastewater, membrane operations, supported liquid membranes, pervaporation, membrane bioreactors, complexation... 

Membrane bioreactors and membrane reactors can be analysed as whole plants and process units, with the membranes playing the simultaneous role of catalyst support or biocatalyst and separation unit. In this case, the analysis has to be done on the system and all the costs are related to it. 

An enzyme membrane bioreactor can be created in different configurations the membrane can be used in order to confine or separate the biocatalyst from the reaction mixture furthermore, membranes can be used as a support for biocatalysts (enzymes or whole cells) immobilization. 

Fig. 7.n SEM images of the 3D macroporous functionalized macroporous zeolitic membrane zeolitic membrane used as a support for enzyme bioreactor was prepared via the LbL electrostatic immobilization by the LbL procedure. Images assembly of PEs and enzyme (catalase) on the 3D (A-D) are cross-sections of the membrane at macroporous membrane. (Reprinted from [59] different magnifications. A biomacromolecule- with permission of Wiley-VCH). 

Although several hepatocyte-based Ever support systems have been proposed, there is no current consensus on its eventual design configuration. The most devices used currently are based on conventional hollow fiber membranes, and there are many opportunities for bioengineers to design new bioreactors that will optimize device function, particularly with regard to oxygen and nutrient provision. 

Fig. 23.4 Organophilic pervaporation (PV) for in situ recovery of volatile flavour compounds from bioreactors. The principle of PV can be viewed as a vacuum distillation across a polymeric barrier (membrane) dividing the liquid feed phase from the gaseous permeate phase. A highly aroma enriched permeate is recovered by freezing the target compounds out of the gas stream. As a typical silicone membrane, an asymmetric poly(octylsiloxane) (POMS) membrane is exemplarily depicted. Here, the selective barrier is a thin POMS layer on a polypropylene (PP)/poly(ether imide) (PEI) support material. Several investigations of PV for the recovery of different microbially produced flavours, e.g. 2-phenylethanol [119], benzaldehyde [264], 6-pentyl-a-pyrone [239], acetone/buta-nol/ethanol [265] and citronellol/geraniol/short-chain esters [266], have been published...

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