Separated hydrolysis and fermentation of water hyacinth leaves for ethanol production

Abstract

In this study, the acid pretreatment and enzymatic hydrolysis were used to evaluate to produce more sugar, to be fermented to ethanol. Separated hydrolysis and fermentation (SHF) studies were carried out to produce ethanol from water hyacinth leaves. The abilities of three different yeast cells, Saccharomyces cerevisiae TISTR 5048, Saccharomyces cerevisiae KM 1195 and Saccharomyces cerevisiae KM 7253, on ethanol production were compared. Dilute sulfuric acid pretreatment and enzymatic hydrolysis were conducted to select the optimum pretreatment conditions for further enzymatic hydrolysis research. The optimum dilute acid pretreatment conditions included T = 135 o C, t = 30 min, and sulfuric acid concentration = 0.1 M. The cellulosic residue was enzymatically hydrolyzed in 0.05 M citrate phosphate buffer (pH 5.0) using the mixture of enzymes cellulase, xylanase and pectinase. The maximum enzymatic saccharification of cellulosic material (76.8%) was achieved after 24 h incubation at 50 o C. SHF of water hyacinth leaves by Saccharomyces cerevisiae KM 7253 resulted lowest yield of ethanol. SHF by monoculture of Saccharomyces cerevisiae KM 1195 achieved the highest yields of ethanol. Further improvement in ethanol production was accomplished with the co-culture of S. cerevisiae TISTR 5048 and Candida tropicalis TISTR 5045 in the ratio of 1:1 which contributed to the highest increase in ethanol production. In this case, the ethanol concentration of 3.39 (g/l), percentage of the theoretical ethanol yield of 96.07%, the ethanol yield of 0.25 g/g and the volumetric productivity of 0.221 g/l-h were obtained.