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Highlights • Continuous removal of ethanol from dilute mixtures using hot-microbubbles. • Ethanol concentration maintained below the inhibition threshold for organism TM242. • An ethanol productivity up to 14.9 g L−1h−1 was supported by the stripping unit., 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 Parageobacillus thermoglucosidasius (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. Ethanol was continuously added to the unit to simulate microbial metabolism. The initial liquid height and the ethanol addition rate were varied from 10 to 50 mm and 2.1–21.2 g h−1 respectively. In all the experiments, ethanol concentration was maintained well below the inhibition threshold of the target organism (~2% [v/v]). This microbubble stripping unit has the potential to operate in conjunction with a 0.5–1.0 L fermenter to allow an ethanol productivity of 14.9–7.8 g L−1h−1 continuously.

Vacuum membrane distillation (VMD) is an attractive variant of the novel membrane distillation process, which is promising for various separations, including water desalination and bioethanol recovery through fermentation of agro-industrial by-products. This publication is part of an effort to develop a capillary membrane module for various applications, as well as a model that would facilitate VMD process design. Experiments were conducted in a laboratory pilot VMD unit, comprising polypropylene capillary-membrane modules. Performance data, collected at modest temperatures (37 °C to 65 °C) with deionized and brackish water, confirmed the improved system productivity with increasing feed-water temperature, excellent salt rejection was obtained. The recovery of ethanol from ethanol-water mixtures and from fermented winery by-products was also studied, in continuous, semi-continuous, and batch operating modes. At low-feed-solution temperature (27–47 °C), ethanol-solution was concentrated 4 to 6.5 times in continuous operation and 2 to 3 times in the semi-continuous mode. Taking advantage of the small property variation in the module axial-flow direction, a simple VMD process model was developed, satisfactorily describing the experimental data. This VMD model appears to be promising for practical applications, and warrants further R&amp, D work.