Anaerobic Membrane Bioreactor for Continuous Lactic Acid Fermentation

Abstract

Membrane bioreactor systems can enhance anaerobic lactic acid fermentation by reducing product inhibition, thus increasing productivity. In batch fermentations, the bioconversion of glucose is strongly inhibited in the presence of more than 100 g·L−1 lactic acid and is only possible when the product is simultaneously removed, which can be achieved by ceramic membrane filtration. The crossflow velocity is a more important determinant of flux than the transmembrane pressure. Therefore, to stabilize the performance of the membrane bioreactor system during continuous fermentation, the crossflow velocity was controlled by varying the biomass concentration, which was monitored in real-time using an optical sensor. Continuous fermentation under these conditions, thus, achieved a stable productivity of ~8 g·L−1·h−1 and the concentration of lactic acid was maintained at ~40 g·L−1 at a dilution rate of 0.2 h−1. No residual sugar was detected in the steady state with a feed concentration of 50 g·L−1.

Membrane Technologies for Lactic Acid Separation from Fermentation Broths Derived from Renewable Resources

“…A reduction of the permeate flux during the first 10 min of microfiltration also occurred during the processing of the sugar bread fermentation broth (from 225.6 L/h/m 2 to 136.8 L/h/m 2 ) (Figure 3C). The drop of permeate flux during microfiltration could be attributed to the concentration polarization and the formation of a cake layer from the microbial cells [16,17]. Interestingly, the flux slightly increased over the process (highest value of 194 L/h/m 2 after 48 min) and decreased again at the end of the filtration (108.3 L/h/m 2 ).…”

Removal of Small-Molecular Byproducts from Crude Fructo-Oligosaccharide Preparations by Fermentation Using the Endospore-Forming Probiotic Bacillus coagulans

“…MRS is a complex medium that is widely used to cultivate lactobacilli and B. coagulans for the production of lactic acid because it provides all necessary vitamins, amino acids, and growth factors [43,47]. This medium is therefore useful to determine the growth properties of different B. coagulans strains.…”

“…B. coagulans is a versatile bacterium, which has been used in various fields, e.g., production of lactic acid, probiotic preparations, and enzymes [47,49]. Each application has unique requirements that can be met by different strains.…”

Development and Characterization of an Enzyme Membrane Reactor for Fructo-Oligosaccharide Production

“…Recent work to investigate fouling phenomena in membrane bioreactor systems has shown that the major fouling mechanism is cake layer resistance, especially when the feed is a whole-cell suspension [25,40,41]. Various terms are used in the literature to describe cake layer formation, including gel layer formation by bacterial cells [42,43], colloids [44,45], and enzymes [46].…”