Attachment of yeast to modified stainless steel wire spheres, growth of cells and ethanol production

The immobilization of yeast Saccharomyces cerevisiae, their growth and etha nol production were investigated using untreated and modified stainless ste el wire spheres (WS) as carriers. The carrier surface was modified by oxida tion, by treatment with titanium (IV) chloride (TiCl4,) or by gamma-aminopr opyltrietoxysilane (AS) in an attempt to raise the efficiency of the immobi lization of the yeast cells. The influence of the cell fixation method on c ulture growth and ethanol synthesis was investigated. The immobilization of cells to carrier surface was checked by scanning electron microscopy (SEM) . More closely attachment of yeast cells was seen on the aminated wire surf ace. It was established that during fermentation ethanol production by yeas t was stimulated using immobilized cells in oxidized WS or treated with TiC l4,. Aminated WS surface stimulated the culture growth but decreased ethano l synthesis. Free yeast cells located in the pores of WS increased the biom ass concentration and ethanol production only during the first cycle of bat ch fermentation. Stable cell growth and ethanol production was observed dur ing subsequent 4-5 repeated fermentation cycles using washing out of free c ells from WS before fermentation. The system productivity Q(eth),,, for eth anol synthesis was 0.92-1.25 g/l per h. Cell fixation in WS by lyophilizati on or convective dehydration improved cell attachment to wire surface but d id not influence positively culture growth and ethanol synthesis. The concl usion was made that stainless steel WS filled with paste-like yeast biomass can be used as inoculum for repeated batch ethanol production. The modific ation method of the stainless steel wire surface significantly influences t he immobilization efficiency of yeasts. Oxidized or modified by TiCl4, wire surface and washing out free cells from WS can be recommended for ethanol production by immobilized yeasts. (C) 2000 Elsevier Science Ltd. All rights reserved.