Removal of Bacterial Contamination from Bioethanol Fermentation System Using Membrane Bioreactor

Abstract

A major issue hindering efficient industrial ethanol fermentation from sugar-based feedstock is excessive unwanted bacterial contamination. In industrial scale fermentation, reaching complete sterility is costly, laborious, and difficult to sustain in long-term operation. A physical selective separation of a co-culture of Saccharomyces cerevisiae and an Enterobacter cloacae complex from a buffer solution and fermentation media at dilution rates of 0.1-1 1/h were examined using an immersed membrane bioreactor (iMBR). The effect of the presence of yeast, inoculum size, membrane pore size, and surface area, backwashing and dilution rate on bacteria removal were assessed by evaluating changes in the filtration conditions, medium turbidity, and concentration of compounds and cell biomass. The results showed that using the iMBR with dilution rate of 0.5 1/h results in successful removal of 93% of contaminating bacteria in the single culture and nearly complete bacteria decontamination in yeast-bacteria co-culture. During continuous fermentation, application of lower permeate fluxes provided a stable filtration of the mixed culture with enhanced bacteria washout. This physical selective separation of bacteria from yeast can enhance final ethanol quality and yields, process profitability, yeast metabolic activity, and decrease downstream processing costs.

Polyphenol bioactivity evolution during the spontaneous fermentation of vegetal by-products

“…GP is derived from the previous alcoholic and malolactic fermentation driven by Y and LAB (Arcena et al, 2020). The presence of both communities was confirmed by their metabolites at the beginning of the fermentation process (t=0 d); however, after that, a reduction occurred, probably due to the difficulty of both communities to adapt to the new conditions or because of the existence of LAB-Y inhibition which may have been triggered by the respective metabolites' toxicity and/or biological competition (Table 1) (Mahboubi et al, 2018). From that situation, the glucose and ethanol increased at 42 d and 56 d respectively, when the Y overcame the metabolic impasse and become predominant with respect to the LAB.…”

Anti-Contamination Strategies for Yeast Fermentations

“…Ozone treatment of substrates, such as corn mash, for ethanol production results in the reduction of lactic acid production by LAB contaminants [113]. Furthermore, bacterial contaminants can be directly removed from the bioethanol fermentation system by using membrane bioreactors [114]. This system allows physical selective separation of yeast and contaminating bacteria in an immersed membrane bioreactor and increases final ethanol yields.…”