PROCESS ENGINEERING STUDIES ON CONTINUOUS ETHANOL-PRODUCTION BY IMMOBILIZED SACCHAROMYCES-CEREVISIAE

Saccharomyces cerevisiae cells were immobilized on three supports-calcium alginate beads, raw and hexamethylene diamine treated bagasse-for their comparative assessment in terms of cell retention on to the carrier and metabolic and physiological activities of the immobilized cells. The chosen carrier-activated bagasse adsorbed 0.41 g of cells per g of carrier (on a dry weight basis). The Gibbs free energy and activation energy for immobilization for the first and second stages was computed to be 3273.45, 14621.27 and 6336.34 J g mol-1, respectively. The immobilized cells were used in a packed bed reactor for the continuous bioconversion of sucrose to ethanol and the packing density of the carrier and the height to diameter ratio of the packed bed bioreactor were optimized to be 50 g l-1 and 2.5, respectively. The maximum productivity obtained was 31.8 g l-1 h-1 at a feed sugar concentration of 200 g l-1 and space velocity of 0.53 h-1. The system was operationally stable in terms of productivity for 76 days. The system then could be reactivated by intermittent air sparging for further operation.