Ethanol concentrations at 60 h using tap water, 1st
recycled permeate, 2nd recycled permeate and 3rd
recycled permeate were 8.8%, 8.4%, 7.7%, and 8.1%
respectively. Cumulative adverse effects on ethanol
yield were not observed and the ethanol concentration
even increased after the 7th recycle. This result suggests
that some large molecular weight organics
inhibiting cell growth and fermentation’2*‘3 should be
removed by the centrifuge and membrane filtration process.