This thesis investigates plasma immersion ion implantation (PIII) for immobilizing enzymes and yeast cells with the aim of developing new processes for cellulosic ethanol production.
A rapid and effective immobilization of yeast cells was demonstrated on PIII treated polymer surfaces. The immobilization does not inhibit the ability of yeast cells to produce ethanol. A model was developed to describe the different mechanisms of rehydrated yeast attachment to untreated and PIII treated surfaces. Yeast cells attach to the untreated surface by hydrophobic interactions while they attach to the PIII treated surface by covalent bonds. The immobilization of yeast cells on the PIII treated surface was found to greatly enhance their resistance to shear forces. In low ionic strength solution, pH was found to be a control factor for the immobilization through the effect of surface and molecule charges. Acidic buffers (pH 3-5) facilitate the immobilization on the PIII treated surface while alkaline buffers (pH 6-10) prevent it. Allylamine exposure was demonstrated to reduce the negative charge of the PIII treated surface in solution and thereby improve the yeast attachment.
CelB, an enzyme which has both endo- and exo-glucanase activities, was covalently immobilized on a PIII treated polymer. Immobilized celB shows the Arrhenius behaviour of the activity as a function of temperature. Approximately 70% of the immobilized celB activity was retained after 4 usage cycles. When used together with immobilized ß-glucosidase, immobilized celB activity is enhanced.
A simultaneous saccharification and fermentation process using immobilized enzymes (celB and ß-glucosidase) and immobilized yeast cells under a flow regime was demonstrated to illustrate the potential of using this immobilization technique in continuous flow processes with increased utilisation of expensive enzymes.