Electro-fermentation and redox mediators enhance glucose conversion into butyric acid with mixed microbial cultures

Abstract

Electro-fermentation (EF) is an emerging and promising technology consisting in the use of a polarized electrode to control the spectrum of products deriving from anaerobic bioprocesses. Here, the effect of electrode polarization on the fermentation of glucose has been studied with two mixed microbial cultures, both in the absence and in the presence of exogenous redox mediators, to verify the viability of the proposed approach under a broader and previously unexplored range of operating conditions. In unmediated experiments, EF (with the cathode polarized at −700 mV vs. SHE, Standard Hydrogen Electrode) caused an increase in the yield of butyric acid production provided that glucose was consumed along with its own fermentation products (i.e. acetic acid and ethanol). The maximum obtained yield accounted for 0.60 mol mol −1 . Mediated experiments were performed with Neutral Red or AQDS at a concentration of 500 μM both in the absence and in the presence of the electrode polarized at −700 mV or −300 mV vs. SHE, respectively. Mediators showed a high selectivity towards the generation of n-butyric acid isomer from the condensation of acetate and ethanol, hence suggesting that they provided microbial cells with the required reducing power otherwise deriving from glucose in unmediated experiments.

Bio-electrochemical production of hydrogen and electricity from organic waste

“…While such an effect could in principle be related to a pH buffering effect caused by the conversion of protons to H 2 , this was in fact found to be relatively minor (see the pH pro les in Figure 6b). The enhancement of the fermentation reactions when coupling the biological process with an electrochemical system was also reported by Paiano et al (2019), who observed an increased amount of metabolic products when exogenous redox mediators were used.…”

Biohydrogen Production Amended with Nitrogen-Doped Biochar

“…The pH impacted not only the fermentation pathway but also the microbial community structure. 17 However, the addition of BC or NDBC to the bioH 2 evolution system exerted no obvious influence on the start-up phases, indicating that the anaerobes in all the bioreactors could adapt to the pH changes during the bioH 2 generation processes. This phenomenon further confirmed that either BC or NDBC affected the bacterial concentration and community structure or promoted electron transfer during bioH 2 evolution.…”

“…In addition, electrofermentation depends on the possibility of affecting metabolic pathways by either donating electrons to microbes or changing the oxidation reduction potential of the reaction medium. 17 Nevertheless, to the best of our knowledge, there are no studies on the application of NDBC in H 2 or CH 4 production processes through anaerobic fermentation. Moreover, there is also a lack of understanding of how BC species and features ultimately influence the microbial community and functionality, subsequent H 2 and CH 4 yields, and liquid products.…”

“…Moreover, there is also a lack of understanding of how BC species and features ultimately influence the microbial community and functionality, subsequent H 2 and CH 4 yields, and liquid products. 17 Corncob is a common agricultural waste with an annual global output of 40−50 million metric tons in China, which is an inexpensive feedstock for BC production. 18 In addition, during the carbonization process, the corncob retains its natural multilayer pore structure, which has the potential to provide a high specific surface area.…”

Autotrophic Acetate Production under Hydrogenophilic and Bioelectrochemical Conditions with a Thermally Treated Mixed Culture

“…As shown in Figure 4, a lag phase of approximately 20 days was observed in terms of acetate production, with a consequent high production of hydrogen (Figure S3). Despite the possibility to convert COD in other VFA anions by an electrofermentation pathway [30], no other volatile fatty acids other than acetate have been detected in all the reported bioelectrochemical tests. The system entered a steady state condition at around the 20th day of operation, with an acetate concentration of 102 ± 14 mg/L in the cathodic chamber while, thanks to the migration of the acetate, the anodic acetate concentration reached 526 ± 95 mg/L, which resulted in a five times higher acetate concentration.…”