Use of potassium meta bisulfite to control bacterial contaminants during fermentation of fodder beet cubes for fuel ethanol

Abstract

Potassium meta bisulfite (PMB) was used to control bacterial contamination during batch (BDF) and sequential batch diffusion fermentation (SBDF) of fodder beets. For BDF, equal amounts of beet cubes (1·27–1·91 cm) and water were mixed with a yeast inoculum and 0–0·4% (wt/wt) PMB. At a PMB concentration of 0·25%, contamination was prevented and the ethanol yield (85% of theoretical; 4·55%, v/v) and fermentation efficiency (96%) were highest. In the SBDF process, five batches of fresh beet cubes were sequentially fermented to ethanol in the same yeast-liquid mixture. Makeup series of 0, 50, 75 and 100% were run. In the 75% (0·25% PMB in batch 1 and 0·188% in batches 2–5) and 100% (0·25% PMB throughout) series, contamination was checked or prevented while ethanol concentrations of 8·6–8·85% (v/v) were attained by the fifth batch. BDF and SBDF simulated start-up and operating conditions, respectively, in a pilot-scale, continuous diffusion fermentor which the authors are developing for commercial production of ethanol from fodder beets.