Development of a process model for simultaneous saccharification and fermentation (SSF) of algal starch to third-generation bioethanol

Microalgal starch was harnessed to produce ethanol, a promising alternative fuel, by simultaneous saccharification and fermentation (SSF) which combined the enzymatic hydrolysis of starch to glucose and the fermentation of glucose to ethanol bySaccharomycescerevisiaein a single step. The starch content was increased in a microalga,Chlorellasp., from 19.3% to 38.2% (w/w) by cycloheximide treatment. Crude amylase with the activity of 40 U mL(-1), produced byAspergillus niger, was used to hydrolyze the microalgal starch. An SSF process was applied for the production of bioethanol usingS.cerevisiae, and 0.116 g ethanol/g of algal biomass was produced. It was observed that the yield factor for ethanol production fromChlorellastarch was 0.305 (g g(-1)). A mathematical model was formulated to describe the kinetics of SSF based on considerations of the nature of the substrate and enzyme, and the substrate-enzyme-microorganism interactions. Critical experimentation was performed to conduct multiresponse nonlinear regression analysis to evaluate the model parameters regarding overall cell growth and ethanol production. The calculated values agreed well with experimental data, regarding the concentration of cells, starch, glucose and ethanol. This model can be used for rational SSF optimization and scale-up in future.