Comparative study of various pretreatment techniques for ethanol production from water hyacinth

Alkali, acid and oxidative pretreatments were compared for their effect on lignin removal from water hyacinth and among them alkali pretreatment gave good results as compared to others. Alkali pretreatment conditions were further optimized by central composite design with two variables sodium hydroxide concentration and pretreatment time. Highest delignification observed at 90 min with 5.0% NaOH concentration but depending upon severity analysis 2.75% NaOH and 60 min pretreatment time was selected for further study. Pretreated water hyacinth was used as substrate for enzyme production by Aspergillus niger and onsite produced enzymes were used for saccharification. The enzymatic hydrolysate was concentrated and fermented by Saccharomyces cerevisiae, Scheffersomyces stipitis and by co-culture of both, with ethanol concentrations 4.3 g/L, 6.2 g/L and 9.8 g/L, respectively. Co-culture of S. cerevisiae, S. stipitis gave better results as compared to monocultures of S. cerevisiae and S. stipitis. (C)2012 Elsevier B.V. All rights reserved.