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A major problem with fermentative ethanol production is the formation of large amounts of numerous organic pollutants. In an industrial distillery, stillage, fermenter and condenser cooling water are the main sources of wastewater. However, the selection of a proper technology makes it possible to almost completely avoid emissions of such kind of wastewater to the environment. This study examines the effect of stillage recirculation on fuel ethanol production. It is based on the use of Saccharomyces cerevisiae and a granular starch hydrolyzing enzyme in a simultaneous saccharification and fermentation process using a native starch obtained from corn flour. It was shown that the yield of the ethanol production was not influenced by the recycled stillage, a mean yield being 83.38% of the theoretical value. No significant trend for change in the ethanol concentration or in the residual starch was observed during any particular run, even after the 75% of fresh water was replaced with stillage. Thus, by applying this new clean technology it is possible to significantly reduce the rate of water consumption and in this way the production of by-products such as stillage., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Background. The most important innovations in boethanol production in the last decade were: simultaneous saccharification and fermentation processes (SSF), high gravity fermentation, the use of new enzyme preparation able to hydrolyse native granular starch and construction of genetically modified strains of microorganisms able to carry out simultaneous production of hydrolytic enzymes and fermentation of C6 and C5 sugars. The aim of this study was to assess the efficiency of ethanol fermentation using new type of amylolytic enzymes able to hydrolyse native corn starch in a SSF process. Material and methods. The simultaneous saccharification and fermentation of raw corn flour by fed-batch processes using Saccharomyces cerevisiae strain Red Star Ethanol Red and Stargen 001 enzyme preparation was performed. As experimental variable were investigated: fermentation temperature (35-37-40°C), rate of mash stirring (100 and 200 rpm), fermentation time (0-92 h) and dosage of corn flour (different portion and different time). Results. It was found that optimal temperature for fed-batch SSF process was 37°C at initial pH of 5.0. However, the yeast intensively fermented the saccharides also at 40°C. The fermentation stirring rate has significant effect on starch utilization and fermentation production. The prolongation of fermentation time over 72 h has no substantiation in additional ethanol production. In all experimental fermentations the level of produced organic acids was very low, significantly below toxic concentration for the yeast. Conclusions. It was stated that the use of new method of starch raw material preparation resulted in satisfied fermentation yield and allowed to reduce energy requirements for starch liquefaction. [ABSTRACT FROM AUTHOR]