Fermentation performance of these biomass hydrolysates is limited by the lack of industrially suitable organisms to convert both glucose and xylose efficiently. To resolve this issue, several methods have been suggested, e.g., co‐cultivation of two or more species, engineering strains for enhanced substrate utilization, and use of sequential culture. Challenges of co‐culture include slower xylose fermentation due to varying affinities for oxygen, lower ethanol tolerance of xylose‐fermenters, and catabolite repression. Although successful engineering of microorganisms is demonstrated, there is limitation in understanding of the metabolic pathways regulations. Alternatively, sequential batch culture was suggested, but its productivity needs to be improved. Optimizing process conditions, e.g. process configuration, immobilization technique, cell type, enables improved yield and productivity. This paper reviews the approaches and conditions sought to improve glucose and xylose conversion from lignocellulosic hydrolysates to ethanol, with specific emphasis on microbial systems used to maximize biomass resource efficiency, ethanol yield, and productivity.

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Bioethanol fermentation kinetic studies are described with effective aspects of, but not limited to, substrate limitation, oxygen limitation, substrate inhibition, product inhibition, and cell death. The majority of these studies have used Saccharomyces cerevisiae and regular mathematical modelling in the form of unstructured unsegregated kinetic modelling. In this paper, the bioethanol fermentation kinetics of pentoses or hexoses or their combination are reviewed. The modes of culture (e.g., batch and continuous), microorganisms used, process conditions, and equations including various effective aspects are discussed. The kinetic models giving the best fit to the experimental data were proposed by the Ghaly and EL‐Taweel as well as Hjersted and Henson. The results showed better agreement between modelling and experiment on using simpler equations which consider the three important effective aspects: substrate limitation, substrate inhibition and product inhibition when grown in the standard growth medium. However, more complex equations show a better fit when the optimum temperature is unclear, co‐culturing is employed, or when growth conditions deviate from standard media and process conditions.

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