Bakers' yeast cultivation on by-products and wastes of potato and wheat starch production on a laboratory and pilot-plant scale

Saccharomyces cerevisiae was cultivated in a 10 litre laboratory stirred tank, an 80 litre laboratory airlift tower loop and a 4 m³ pilot-plant airlift tower loop reactor using by-products and wastes of potato and wheat starch production in batch and continuous cultures. Potato protein liquor, potato liquor retentate, potato liquor residue, and wheat process water were used as nutrients and glucose from the enzymatic conversion of potato starch as energy source. Besides the performance of the cultivation (cell concentrations, specific growth rates in the first (glucose) and second (ethanol) growth phases, productivities, yield coefficients), the qualities of the effluents (concentrations of phosphate, dissolved organic carbon, dissolved organic nitrogen, and chemical oxygen demand) were also determined in the different reactors as functions of the operational parameters. The optimal conditions were evaluated with regard to cultivation performance and effluent quality. These performances do not vary with the scale of the reactors. The performance of continuous cultures is considerably better than that of batch cultures.