ETHANOL-PRODUCTION BY SACCHAROMYCES-CEREVISIAE IN BIOFILM REACTORS

Biofilms are natural forms of cell immobilization in which microorgani sms attach to solid supports, At ISU, we have developed plastic compos ite-supports (PCS) (agricultural material (soybean hulls or oat hulls) , complex nutrients, and polypropylene) which stimulate biofilm format ion and which supply nutrients to the attached microorganisms, Various PCS blends were initially evaluated in repeated-batch culture-tube fe rmentation with Saccharomyces cerevisiae (ATCC 24859) in low organic n itrogen medium. The selected PCS (40% soybean hull, 5% soybean flour, 5% yeast extract-salt and 50% polypropylene) was then used in continuo us and repeated-batch fermentation in various media containing lowered nitrogen content with selected PCS. During continuous fermentation, S . cerevisiae demonstrated two to 10 times higher ethanol production in PCS bioreactors than polypropylene-alone support (PPS) control, S. ce revisiae produced 30 g L-1 ethanol on PCS with ammonium sulfate medium in repeated batch fermentation, whereas PPS-control produced 5 g L-1 ethanol, Overall, increased productivity in row cost medium can be ach ieved beyond conventional fermentations using this novel bioreactor de sign.