Bioethanol Production by Fermentation is an Energy Balance Process

Abstract

Considerable research is aimed at determining the mechanism by which ethanol produced from food ­ waste leachate (FWL) using S. cerevisiae as inoculums when subjected to an optimized fermentation process, to be predictable and controllable. The wide range of reduced sugar concentration (RSC), from low (35 gm per liter) to very high (100 gm per liter), estimated statistically is responsible for costs increasing besides risks of FWL contamination. A mathematical model is presented that describes: the FWL growth due to lower or over or appropriate amounts of RSC accompanied by amounts of produced ethanol in each case. Simulations of the presented model showed that the FWL growth energy, RSC consumed energy, and their subsequent from produced ethanol energy are always balanced, during fermentation process according to law of conservation of energy. Furthermore, the mathematical model of energies mechanism of fermentation can predict the proper amounts of FWL and RSC that optimize fermentation process for large­scale production. The reducing sugar concentration of the food waste leachate determined by the dinitrosalicylic acid method was 75 g/L, while maximum ethanol concentration of 1.118 g/L/h was obtained at the optimum condition in the presence of 2.5 % of S. cerevisiae as inoculums. Bioethanol production by fermentation is an energy balance process, where current approach that account for variations in FWL , RSC energies should enable more accurate amount estimates and, consequently, better protection against either lower or over optimum fermentation that could lead to yeast organisms cell death, or increase risks of substrate inhibition due to osmotic stress . From an application point of view, and with agreement with prior studies, the FWL generated in the food – waste recycling facilities, if suitably sterilized prior to fermentation, can potentially serve as a promising biomass based candidate for bioethanol production. In addition, as one glucose molecule is converted into two ethanol molecules and two carbon dioxide molecules in the overall chemical reaction conducted by the yeast, the released carbon dioxide (CO2) can be used for carbonating the beverage, which shows the saving potential of this project in terms of energy consumption and CO2 emission.