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. This paper demonstrates the potential of hot gas microbubbles to strip ethanol from a thermophilic fermentation process using Parageobacillus thermoglucosidasius TM333, thereby reducing product inhibition and allowing production to continue beyond the nominal toxic ethanol concentrations of ≤ 2% v/v. Using an experimental rig in which cells were grown in fed-batch cultures on sugars derived from waste bread, and the broth continuously cycled through a purpose-built microbubble stripping unit, it was shown that non/low-inhibitory dissolved ethanol concentrations could be maintained throughout, despite reaching productivities equivalent to 4.7% v/v dissolved ethanol. Ethanol recovered in the condensate was at a concentration appropriate for dewatering to be cost effective and not prohibitively energy intensive. This suggests that hot microbubble stripping could be a valuable technology for the continuous production of bioethanol from fermentation processes which suffer from product inhibition before reaching economically viable titres, which is typical of most thermophilic ethanologenic bacteria.

Electrokinetic Transport of a Charged Dye in a Freely Suspended Liquid Film: Experiments and Numerical Simulations.

Electrokinetic transport of a charged dye within a free liquid film stabilized by a cationic surfactant, trimethyl(tetradecyl)ammonium bromide, subjected to an external electric field was investigated. Confocal laser scanning microscopy was used to visualize fluorescein isothiocyanate (FITC) separation within the stabilized liquid film. Numerical simulations were performed using the finite element method to model the dynamics of charged dye separation fronts observed in the experiments. Because of the electrochemical reactions at the electrodes, significant spatial and temporal pH changes were observed within the liquid film. These local pH changes could affect the local zeta potential at the gas-liquid and solid-liquid film boundaries; hence, the flow field was found to be highly dynamic and complex. The charged dye (FITC) used in the experiments is pH-sensitive, and therefore, electrophoresis of the dye also depended on the local pH. The pH and the electroosmotic flow field predicted from the numerical simulations were useful for understanding charged dye separation near both the anode and the cathode.

Electroosmotic flow measurements in a freely suspended liquid film: Experimhents and numerical simulations.

Fluid flow profiles in free liquid films stabilised by anionic and cationic surfactants under an external electric field were investigated. Depthwise velocity fields were measured at the mid region of the free liquid film by confocal micron-resolution particle image velocimetry and corresponding numerical simulations were performed using Finite Element Method to model the system. Depthwise change in velocity profiles was observed with electroosmotic flow dominating in the vicinity of the gas-liquid and solid-liquid interfaces while backpressure drives fluid in the opposite direction at the core of the film. It was also found that the direction of the flow at various sections of the films depends on the type of surfactant used, but flow features remained the same. Numerical simulations predicted the flow profiles with reasonable accuracy; however, asymmetry of the actual film geometry caused deviations at the top half of the computational domain. Overall, electroosmotic flow profiles within a free liquid film are similar to that of the closed-end solid microchannel. However, the flow direction and features of the velocity profiles can be changed by selecting various types of surfactants. The free liquid films thickness was selected to match dimensions of foam Plateau border. Hence, these findings will be useful in developing a separation system based on foam electrokinetics.