RECYCLING OF PROCESS STREAMS IN ETHANOL-PRODUCTION FROM SOFTWOODS BASED ON ENZYMATIC-HYDROLYSIS

In ethanol production from lignocellulose by enzymatic hydrolysis and fermentation, it is desirable to minimize addition of fresh-water and waste-water streams, which leads to an accumulation of substances in t he process. This study shows that the amount of fresh water used and t he amount of waste water thereby produced in the production of fuel et hanol from softwood, can be reduced to a large extent by recycling of either the stillage stream or part of the liquid stream from the ferme nter. A reduction in fresh-water demand of more than 50%, from 3 kg/kg dry raw material to 1.5 kg/kg dry raw material was obtained without a ny negative effects on either hydrolysis or fermentation. A further de crease in the amount of fresh water, to one-fourth of what was used wi thout recycling of process streams, resulted in a considerable decreas e in the ethanol productivity and a slight decrease in the ethanol yie ld.