A microbubble-sparged yeast propagation-fermentation process for bioethanol production

A 3D printed plastic frame deeply impacts yeast cell growth

Solid State Fermentation (SSF) processes have been explored for yeast growth and protein and metabolites production. However, most of these processes lack standardization. In this work, we present a polylactic acid (PLA) 3D printed matrix that dramatically enhances yeast growth when embedded in liquid media compared to equivalent static cultures, and changes yeast expression patterns at the proteome level (data are available via ProteomeXchange with identifier PXD043759). Moreover, differences in sugar assimilation and ethanol production, as the main product of alcoholic fermentation, are observed. Our results suggest that these matrixes may be useful for a vast range of biotechnological applications based on yeast fermentation.

Microbubble- and nanobubble-aeration for upgrading conventional activated sludge process: A review

The activated sludge process (ASP) is widely used for wastewater treatment, and the aeration efficiency is crucial to the operation of wastewater treatment plants. Recently, microbubble (MB)- and nanobubble (NB)-aeration has attracted much attention as there is growing evidence that it holds a great promise for upgrading the process efficiency of current ASP under conventional macro-bubble-aeration. However, a comprehensive review to elucidate the potential application of MB- and NB-aeration in ASP is still lacking. Therefore, this review will provide a systematic introduction to MB- and NB-aeration (including the unique properties and generation methods of MBs and NBs), and gain mechanistic insights on how MB- and NB-aeration improve gas-liquid mass transfer. The recent advances in MB- and NB-aeration applications to ASP and the resultant effects are also highlighted and discussed in-depth. The review concludes with a brief consideration of future research interests.

Novel Propagation Strategy of Saccharomyces cerevisiae for Enhanced Xylose Metabolism during Fermentation on Softwood Hydrolysate

An economically viable production of second-generation bioethanol by recombinant xylose-fermenting Saccharomyces cerevisiae requires higher xylose fermentation rates and improved glucose–xylose co-consumption. Moreover, xylose-fermenting S. cerevisiae recognises xylose as a non-fermentable rather than a fermentable carbon source, which might partly explain why xylose is not fermented into ethanol as efficiently as glucose. This study proposes propagating S. cerevisiae on non-fermentable carbon sources to enhance xylose metabolism during fermentation. When compared to yeast grown on sucrose, cells propagated on a mix of ethanol and glycerol in shake flasks showed up to 50% higher xylose utilisation rate (in a defined xylose medium) and a double maximum fermentation rate, together with an improved C5/C6 co-consumption (on an industrial softwood hydrolysate). Based on these results, an automated propagation protocol was developed, using a fed-batch approach and the respiratory quotient to guide the ethanol and glycerol-containing feed. This successfully produced 71.29 ± 0.91 g/L yeast with an average productivity of 1.03 ± 0.05 g/L/h. These empirical findings provide the basis for the design of a simple, yet effective yeast production strategy to be used in the second-generation bioethanol industry for increased fermentation efficiency.

Methods for Oxygenation of Continuous Cultures of Brewer’s Yeast, Saccharomyces cerevisiae

Maintaining steady-state, aerobic cultures of yeast in a bioreactor depends on the configuration of the bioreactor system as well as the growth medium used. In this paper, we compare several conventional aeration methods with newer filter methods using a novel optical sensor array to monitor dissolved oxygen, pH, and biomass. With conventional methods, only a continuously stirred tank reactor configuration gave high aeration rates for cultures in yeast extract peptone dextrose (YPD) medium. For filters technologies, only a polydimethylsiloxan filter provided sufficient aeration of yeast cultures. Further, using the polydimethylsiloxan filter, the YPD medium gave inferior oxygenation rates of yeast compared to superior results with Synthetic Complete medium. It was found that the YPD medium itself, not the yeast cells, interfered with the filter giving the low oxygen transfer rates based on the volumetric transfer coefficient (KLa). The results are discussed for implications of miniaturized bioreactors in low-gravity environments.

Microbubble intensification of bioprocessing

Microbubbles have been involved in industrial processing since the 1970s with the introduction of dissolved air flotation into common practice. The turn of the century saw microbubbles become regularly used in medical imaging. But in bioprocessing, only this decade has seen rapid advances in R&D, with some bioprocesses, particularly in wastewater treatment, adopted at full industrial scale, and others at pilot scale, such as anaerobic digestion and fermentation, which is full industrial scale for many biomanufacturing and pharmaceutical processes. This article reviews the methods of microbubble generation only briefly, as it turns out only one generation method, fluidic oscillation through microporous diffusers, has the requisite features for introduction into full scale fermentation processes. Subsequently, six fundamental physicochemical hydrodynamics mechanisms that have been exploited by microbubble innovations in bioprocessing are presented and analyzed, particularly for the roles they play in bioprocessing applications. Some examples are drawn with applications to microalgal and yeast processing, as well as usage in wastewater treatment processes. Because the smallest microbubbles can increase rates in some of these six fundamental processes by several orders of magnitude over conventional processing methods, with the optimal contacting patterns, the promise for wider exploitation in bioprocessing is substantial.