Bioconversion of water-hyacinth ( Eichhornia crassipes) hemicellulose acid hydrolysate to motor fuel ethanol by xylose–fermenting yeast

Water-hyacinth ( Eichhornia crassipes) hemicellulose acid hydrolysate has been utilized as a substrate for ethanol production using Pichia stipitis NRRL Y-7124. Hydrolysate fermentability was considerable improved by boiling, and overliming up to pH 10.0 with solid Ca(OH) 2 in combination with sodium sulfite. The percent total sugar utilized and ethanol yield ( Y p/ s ) for the untreated hydrolysate were 20.15±0.17% and 0.19±0.003 g p g s −1, respectively, compared with 76.0±0.32% and 0.35 g p g s −1, respectively for the treated material. The fermentation was very effective at an aeration rate of 0.02 v/v/m, temperature 30±0.2 °C and pH 6.0±0.2. However, the volumetric productivity ( Q p ) was still considerably less than observed in a simulated synthetic hydrolysate medium with a sugar composition similar to the hemicellulose acid hydrolysate. l-Arabinose was not fermented but assimilated. The presence of acetic acid in the hydrolysate decreased the ethanol yield and productivity considerably.