Bioethanol production from cellulosic materials

In the present study, pretreated sugarcane bagasse is used as the substrate for bioethanol production using cellulase and various yeast strains including thermotolerant strains by simultaneous saccharification and fermentation method at the optimized process conditions. Various pretreatment techniques namely dilute and concentrated sulphuric treatment, sodium hydroxide combined with high pressure steam treatment and steam autoclaving treatment are conducted for mechanically pretreated sugarcane bagaasse (milled ~ 100 mesh, 0.15 mm) for different time intervals (5, 10 and 15 min). The objective of the treatment step is to reduce the lignin and hemicellulose without altering the cellulose content because cellulase enzymes are highly specific in the cellulose hydrolysis reactions. From the results, the acid and alkali treatment techniques are not suitable for the enzymatic hydrolysis of pretreated sugarcane bagasse due the decreased cellulose content and also the hemicellulose and lignin content was significantly reduced. The effect of cellobiose concentration is studied by conducting batch experiments at different initial cellobiose concentrations namely 5, 10, 15, 20, and 25 g/l at the hydrolysis temperatures of 45°C with an initial enzyme loading of 15 FPU/g bagasse and with initial pH of 5.5 and with a hydrolysis period of 120h as constant. From the experimental results it is observed that the cellobiose show a strong inhibitory effect. The effect of temperature on ethanol fermentation is studied by conducting batch experiments at different incubation temperatures namely 45°C for different yeast strains. The results show the maximum ethanol concentration of 3.82 g/l is obtained at an optimum temperature of 35 °C when S.cerevisiae is used for a fermentation period of 120h. This separate hydrolysis with fermentation gives a lower yield when compared to SSF process and may be due to the inhibitory action of glucose and cellobiose in the cellulose hydrolysis.