Downstream processing membrane systems

The use of both hydrophilic [85, 87] and hydrophobic [84, 86] membranes has proven to be efficient in binding the enzyme. The main advantage of this system over emulsion systems lies in the ease of the downstream processing, as no enzyme-stabilized emulsion has to be broken. 

The remainder of this introductory chapter focuses on downstream processing and bioseparation relevant to the chapters presented in this book. Thus, the following topics are covered multiphase systems, membrane separation, centrifugation and adsorption techniques, electrophoresis, chromatography, and affinity separations. 

The recovery of bioactive materials from the fermentation broth is generally complicated by the fact that the bio-products are in very low concentration in these often unstable, non-newtonian systems. The downstream processing is a key area for further development of biotechnology. Membrane technologies and particularly UF,MF and RO can be considered as broad core technologies in this industrial segment (1). 

Applications of liquid emulsion membranes (LEMs) to biomedical and biochemical systems are reviewed and other potential applications identified. The LEM-mediated downstream processing of small, zwitterionic biochemicals (e.g. amino acids) is examined using chloride ion counter-transport to separate and concentrate the amino acid phenylalanine from stimulated fermentation broth. The effect of agitation rate and osmotic swelling of membranes on separation is shown to be significant. 

The versatility of LEMs is clear. From the encapsulation of living cells to the removal of toxic or inhibiting substances, and in their use as a downstream process, liquid emulsion membranes remain a powerful and, as of yet, virtually untapped resource for biochemical engineers. The ability of LEMs to separate and concentrate amino acids demonstrated here gives strength to this observation, and it is anticipated that these systems will enjoy increasing attention in the years to come. 

In membrane processes, the increase in feed impurity concentrations tend to cause a decrease in product purity, which, however, can be maintained for small feed composition changes by adjusting the feed-to-permeate pressure ratio. In most refinery membrane applications, however, the major product impurity is methane, and this can be allowed to increase slightly in the product without major downstream impact. The response time of membrane systems is essentially instantaneous, and corrective action has immediate results. The start-up time required by the process is extremely short. 

Electrokinetic trapping techniques [38-41] have been recently demonstrated as an efficient way of concentrating protein samples. Different membrane materials can be used, such as polymer monolith (Singh and coworkers), Naflon (Swerdlow and coworkers), nanochannels (Han and coworkers) and even PDMS (Kim et al.). These techniques demonstrate impressive concentration factors (up to 10 ) as well as the flexibility to be coupled to downstream analysis. These techniques are dependent on the ion depletion and concentration polarization, which as a generic process are quite common to most nanoporous membrane systems. Therefore, there is no specific buffer... 

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