A multichamber tower fermentor for continuous ethanol fermentation with a self-aggregating yeast mutant

Abstract

A multichamber tower fermentor, with a combined working volume of 30 L, was used to ferment sugar cane molasses to ethanol using a self-aggregating yeast mutant, Saccharomyces uvarum U4, derived from Saccharomyces uvarum ATCC 26602. The column was constructed of plexiglass tubing divided into four chambers of different depths by conical shaped dividers. Gas generated during fermentation was allowed to escape from each chamber of the column through a small tube at the top of the chamber. The rate of escape was controlled by manually-operated diaphragm valves. This design significantly reduced the turbulence caused by CO₂ evolution and made it practical to maintain a total yeast bed depth double that previously sustained with this organism in long-term, single chamber tower fermentor tests. Using the multichamber tower fermentor, a 7–8% (w/v) ethanol-containing broth was continuously produced from molasses solution, with 160 g/L fermentable sugars, for more than 460 h of operation with a maximum dilution rate of 0.18 h^-1. Less than 10³ cells/mL in the effluent was observed during most of the operation.