Bioseparation processes

Thickeners and binders such as acacia, agar, starch, sodium alig-nate, gelatin, methyl cellulose, bentonite, and silica are used to improve product stability and enhance the convenience of the administration of a liquid formulation. Surface-active agents, colors, flavors and preservatives may also be used in the final formulation (Garcia et ah. Bioseparation Process Science, Blackwell Science, Malden, Mass., 1999, p. 374). 

Igwe, J.C. and Abia, A.A., A bioseparation process for removing heavy metals from wastewater using biosorbents, African Journal of Biotechnology, 5 (12), 1167-1179, 2006. 

Bioseparation processes make use of many separation techniques commonly used in the chemical process industries. However, bioseparations have distinct characteristics that are not common in the traditional separations of chemical processes. Some of the unique characteristics of bioseparation products can be listed as follows ... 

Unit operation Conventional bioseparation process Membrane process Membrane process feature... 

The economic feasibility of a bioreaction process clearly depends on the characteristics of the associated bioseparation process, especially in the usual case when the product is present at low concentration in a complex mixture. For example, the existence of an extremely efficient and low-cost separation process for a particular compound could significantly lower the final concentration of that compound required in the bioreactor to achieve a satisfactory overall process. After noting that special approaches and processes are needed for efficient recovery of small molecules (ethanol, amino acids, antibiotics, etc.) from the dilute aqueous product streams of current bioreactors, I shall discuss further only separations of proteins. These are the primary products of the new biotechnology industry, and their purification hinges on the special properties of these biological macromolecules. 

Examples of commonly used bioseparations include sedimentation, coagulation, and filtration. The scale of operation for such bioseparation processes is considerable, because of the volumes of effluent which are processed and the throughputs required. Proprietary aerobic digesters such as the Deep Shaft process may use centrifugation to recover biomass from the treated effluent for recycle as an inoculum for the digester or to reduce the quantity of water before sending the solid material either to incineration or land fill. 

Apart from regulations aimed at product quality, there are also issues concerned with the safe operation of certain processes, for example, where genetically modified or pathogenic microorganisms are being handled. In such cases, the bioseparation process is normally contained in other words, the potential for release of hazardous material is minimized by various methods. Many bioseparations also involve the use of solvents which must be handled in appropriately designed equipment and facilities with proper explosion protection. Again there are cost implications associated with these types of processes which must be identified at the outset of the development phase. 

Cross-flow filter performance is often characterized by a flux rate, which equates to the permeate flow rate per unit area of membrane surface. The flux rate in most biological separations is reduced by a fouling phenomenon called gel polarization, which tends to concentrate material at the surface of membrane to impose an additional resistance to transmembrane flow. The deterioration in flux rate must be well characterized for a commercial bioseparation process to ensure the correct size for the cross-flow filtration unit and avoid hold-ups at this processing stage. 

This type of centrifuge is well suited to CIP and some models can also be sterilized in place as part of a hygienic or contained bioseparation process. 

Process control structures include three major operations—measurement of a process variable, calculation of the required adjustment, and manipulation of the process to implement the correction. The measurement step may be the most routine, since almost all bioseparation systems, regardless of scale, function, or constraints are usually equipped with instruments for monitoring the process. Monitoring instrumentation is generally well understood and is documented in discussions of particular bioseparation processes and implementations. 

Finally, more such studies must be carried out on real-life examples and made available in the literature. No doubt such studies are available in the different pharmaceutical industries, but due to economic and obvious reasons, they are restricted to only in-house circulation. This is an unfortunate aspect of the economics of bioseparation of different processes. Hopefully, people in the universities, at least, will pay more attention to this aspect, and fill this critical gap in the complete analysis of bioseparation processes. 

The functionalization of the reverse micelles will create a novel application in bioseparation processes in the analytical and medical sciences. It is therefore important to reveal the recognition mechanism of proteins at the liquid-liquid interface in reversed micellar solutions. DNA is also successfully extracted in a few hours by reversed micelles formed by cationic surfactants in isooctane. The driving force of the DNA transfer is the electrostatic interaction between the cationic surfactants and the negatively charged DNA. Another important factor is the hydrophobicity of the cationic surfactants. Doublechain type cationic surfactants are found to be one of the best surfactants ensuring the efficient extraction of DNA. These results have shown that reverse micellar solutions will become a useful tool not only for protein separation, but also for DNA separation. 

Scaling up of the processes to large surface areas (i.e. to obtain asymmetric membrane systems with several layers) as is necessary for large-scale operations has been successfully demonstrated for micro/ultrafiltration and bioseparation processes, but not for other applications such as gas/vapour separation and membrane reactors, for which only small-scale laboratory equipment is available. 

---