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Title: Separation of insoluble biological material downstream from a two-liquid (organic/aqueous) phase whole cell biotransformation reactor
Author: Laurence, Mark Backhouse
ISNI:       0000 0004 2676 6135
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1994
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Literature reports of biotransformations using whole cell biocatalysts in two-liquid (organic / aqueous) phase systems show the advantages of such systems in specific circumstances. The primary problems to be resolved in the operation of these systems are the reduction in stability of the biocatalyst, and the separation of the product from the multiphase reaction. The particular problem brought about by the contact of the two liquid phases in the presence of biological material and subsequent need for their separation, was investigated. The major problem was the formation of an emulsion, stabilised by biological material. This thesis describes the development of experimental tools used to examine the relationship between stability of the biocatalyst, and the difficulty of phase separation from a two-liquid phase stirred tank reactor. The stability of the catalyst on exposure to discrete and dissolved solvent was measured by changes in the capacitance of the cell suspension. The capacitance of a suspension being proportional to the level of cells with an intact membrane. The time taken to reduce the capacitance to half the original value was described as the C1/2 value. The difficulty of phase separation was quantified using a variation of the settling test; the time taken for the emulsion volume to reach that of half the original organic phase volume was described as the E1/2 value. Thus a low E1/2 reflects a difficult separation. These tools were used to determine the affect of solvent on cells. Saccharomyces cerevisiae (yeast), Arthrobacter simplex (Gram positive). Pseudomonas putida and Pseudomonas aeruginosa (Gram negative) and the solvents toluene, nonanol, tetradecane and hexane were used for illustrative purposes. One of the uses of the tools was in the selection of a suitable cell and solvent combination for a biotransformation; as an example S. cerevisiae was shown to have a high E1/2 value and a relatively low C1/2 value; P. putida had a higher C1/2 value, but a low E1/2 value. Thus a trade off in cell/solvent selection is required. Finally this thesis reports on physical methods which can be used in the separation of an emulsion. Centrifugal methods were shown to be not always effective in emulsion separation. In these cases other methods may be used. The use of hydrophilic and hydrophobic membrane systems operated at pressures below the membrane breakthrough pressure allowed the separation of the liquid phases; the same membrane systems operated at higher pressures acted as coalescing filters and retained only biological material. An effective method for separation was found to be the removal of the bulk of the aqueous phase from the emulsion using centrifugal or membrane techniques, followed by subsequent coalescence of the organic phase by application of shear.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available