Covalent immobilization of enzymes and yeast: Towards a continuous simultaneous saccharification and fermentation process for cellulosic ethanol

Abstract

The immobilization of enzymes and yeast cells is a key factor for establishing a continuous process of cellulosic ethanol production, which can combine the benefits of a separated hydrolysis and fermentation process and a simultaneous saccharification and fermentation process. This paper investigates the use of cellulase enzyme and yeast cell immobilization under a flow regime of ethanol production from soluble substrates such as cellobiose and carboxymethyl cellulose. The immobilization was achieved by incubating enzymes and yeast cells on polystyrene surfaces which had been treated by nitrogen ion implantation. The saccharification by immobilized enzymes and the fermentation by immobilized yeast cells were conducted in two separate vessels connected by a pump. During the experiments, glucose concentrations were always maintained at low levels which potentially reduce product inhibition effects on the enzymes. Covalent immobilization of enzymes and yeast cells on the plasma treated polymer reduces loss by shear flow induced detachment. The potential for continuous flow production of ethanol and the influence of daughter yeast cells in the circulating flow on the immobilized enzyme activity are discussed.