Ethanologenic fermentation by Parageobacillus thermoglucosidasius with continuous hot microbubble gas-stripping.

The increased use of biofuels in place of fossil fuels is one strategy to support the transition to net-zero carbon emissions, particularly in transport applications. However, expansion of the use of 1st generation crops as feedstocks is unsustainable due to the conflict with food use. The use of the lignocellulosic fractions from plants and/or co-products from food production including food wastes could satisfy the demand for biofuels without affecting the use of land and the availability of food, but organisms which can readily ferment all the carbohydrates present in these feedstocks often suffer from more severe bioethanol inhibition effects than yeast.

Continuous removal of ethanol from dilute ethanol-water mixtures using hot microbubbles.

Product inhibition is a barrier to many fermentation processes, including bioethanol production, and is responsible for dilute product streams which are energy intensive to purify. The main purpose of this study was to investigate whether hot microbubble stripping could be used to remove ethanol continuously from dilute ethanol-water mixtures expected in a bioreactor and maintain ethanol concentrations below the inhibitory levels for the thermophile (TM242), that can utilize a range of sugars derived from lignocellulosic biomass. A custom-made microbubble stripping unit that produces clouds of hot microbubbles (~120 °C) by fluidic oscillation was used to remove ethanol from ~2% (v/v) ethanol-water mixtures maintained at 60 °C.