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.....The use of disk-stack centrifuges or cell separators have been very effective in increasing cell count as described by another prior art process, the Melle-Boinot process, in which yeast is reused in fermentation at large-scale fermenters typically 500 - 1000m3 volume in the form of yeast cream. This yeast cream is recycled back either to the YAT or directly to the fermenter for another propagation and fermentation process respectively after series of labor-intensive, large-scale treatments and additional use/ cost of chemicals such as sulfuric acid for reducing bacterial contamination. It has been known that this process increases ethanol production but at the expense of a large power consumption of centrifuges, frequent cleaning of the equipment due to sludge accumulation as well as additional labor costs. ....