CONTROL OF ETHANOL-PRODUCTION AND MONITORING OF MEMBRANE PERFORMANCE BY MASS-SPECTROMETRIC GAS-ANALYSIS IN THE COUPLED FERMENTATION-PERVAPORATION OF WHEY PERMEATE

A coupled fermentation-pervaporation process was operated continuously with on-line mass spectrometric gas analysis monitoring of product ac cumulation on both the upstream and the downstream sides of the membra ne. Efficient coupling of the fermentation with pervaporation was atta ined when a steady state of ethanol production and removal was achieve d with whey permeate containing high concentrations of lactose (> 8%) or by controlled lactose additions that also compensated for loss of l iquid due to pervaporation. The combined system consists of a tubular membrane pervaporation module, directly connected to a stirred ferment er to form one circulation loop, kept at 38 degrees C, with both units operating under computer control. Mass spectrometric gas analysis of the CO2 gas evolved in the fermenter and the ethanol and water in the pervaporate on the downstream side of the membrane enabled us to follo w the production of ethanol and its simultaneous removal. Membrane sel ectivity was calculated on-line and served to monitor the functioning of the membrane. Batch-wise-operated fermentation-pervaporation with C andida pseudotropicalis IF-513 yielded over 120 gl(-1) of concentrated ethanol solution using supplemented whey permeate containing 16% lact ose. A steady state lasting for about 20 h was achieved with ethanol p roductivity of 20 g h(-1) (approx. 4 g l(-1) h(-1)). Membrane selectiv ity was over 8. Controlled feeding of concentrated lactose suspension in the whey permeate (350 gl(-1)) resulted in the continuous collectio n of 120-140 gl(-1) of ethanol pervaporate for 5 days, by which time s alt accumulation hampered the fermentation. Medium refreshment restore d the fermentative activity of the yeast cells and further extended th e coupled process to over 9 days (200 h), when reversible membrane fou ling occurred. The membrane module was exchanged and the combined proc ess restarted.