An innovative process for the production of bioethanol: Optimization and kinetic assessment

Abstract

Given the growing concern about the depletion of fossil fuels, global warming, and the loss of natural resources, bioethanol made from sugar cane, molasses, and corn continues to garner interest globally and is regarded as the safest and cleanest alternative to oil. Starch is a widely available renewable carbohydrate from which bioethanol is conventionally obtained through energy demanding liquefaction and saccharification processes. A significant simplification of the process and a reduction of starch processing costs would be possible by applying raw starch hydrolysis using enzymes capable of degrading starch below the gelatinization temperature. A novel strategy for highly concentrated raw corn starch (30 % w/v) hydrolysis based on a modified simultaneous saccharification and fermentation process is optimized for the production of bioethanol. Different ratios of Bacillus paralicheniformis ATCC 9945a (BliAmy) and glucoamylase (Dextrozyme® GA), glucoamylase addition time, incubation time, and pH were investigated using a Box–Behnken experimental design to ensure high process efficiency. A two-step synergistic hydrolysis and fermentation with Saccharomyces cerevisiae at 30 °C was carried out in a single bioreactor vessel at the same pH (4.5). The obtained bioethanol concentration at 129.2 g/L, with a productivity of 2.94 g/L/h and ethanol yield (YP/S) at 0.50 g EtOH/g total sugar, equivalent to 87.8 % theoretical yield indicates the viability of the proposed innovative process.