Catalytic activity of yeast extract in biofuel cell

Enriching electroactive microorganisms from ferruginous lake waters - Mind the sulfate reducers!

Electroactive microorganisms are pivotal players in mineral transformation within redox interfaces characterized by pronounced oxygen and dissolved metal gradients. Yet, their systematic cultivation from such environments remains elusive. Here, we conducted an anodic enrichment using anoxic ferruginous waters from a post-mining lake as inoculum. Weak electrogenicity (j = ∼5 µA cm-2) depended on electroactive planktonic cells rather than anodic biofilms, with a preference for formate as electron donor. Addition of yeast extract decreased the lag phase but did not increase current densities. The enriched bacterial community varied depending on the substrate composition but mainly comprised of sulfate- and nitrate-reducing bacteria (e.g., Desulfatomaculum spp. and Stenotrophomonas spp.). A secondary enrichment strategy resulted in different bacterial communities composed of iron-reducing (e.g., Klebsiella spp.) and fermentative bacteria (e.g., Paeniclostridium spp.). Secondary electron microscopy and energy-dispersive X-ray spectroscopy results indicate the precipitation of sulfur- and iron-rich organomineral aggregates at the anode surface, presumably impeding current production. Our findings indicate that (i) anoxic waters containing geogenically derived metals can be used to enrich weak electricigens, and (ii) it is necessary to specifically inhibit sulfate reducers. Otherwise, sulfate reducers tend to dominate over EAM during cultivation, which can lead to anode passivation due to biomineralization.

Overview of electroactive microorganisms and electron transfer mechanisms in microbial electrochemistry

Electroactive microorganisms acting as microbial electrocatalysts have intrinsic metabolisms that mediate a redox potential difference between solid electrodes and microbes, leading to spontaneous electron transfer to the electrode (exo-electron transfer) or electron uptake from the electrode (endo-electron transfer). These microbes biochemically convert various organic and/or inorganic compounds to electricity and/or biochemicals in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs) and microbial electrosynthesis cells (MECs). For the past two decades, intense studies have converged to clarify electron transfer mechanisms of electroactive microbes in BESs, which thereby have led to improved bioelectrochemical performance. Also, many novel exoelectrogenic eukaryotes as well as prokaryotes with electroactive properties are being continuously discovered. This review presents an overview of electroactive microorganisms (bacteria, microalgae and fungi) and their exo- and endo-electron transfer mechanisms in BESs for optimizing and advancing bioelectrochemical techniques.

Recent progress of graphene based nanomaterials in bioelectrochemical systems

The application of graphene (Gr) to microbial fuel cells (MFCs) and microbial electrolysis cell (MECs) is considered a very promising approach in terms of enhancing their performance. The superior Gr properties of high electrical and thermal conductivities, along with: superior specific surface area, high electron mobility, and mechanical strength, are the key features that endorse this. Factors impeding the advancement of a microbial fuel cell into commercialization involve primarily the cost of their components, and their production on a small scale. Gr with such outstanding characteristics can help mitigate these challenges, when used as electrode material. The application of Gr as an anode material improves the efficiency of electron transfer and bacterial attachment. When used as a cathode material, it supports the oxygen reduction reaction. This investigation, presents a thorough analysis of the feasibility of Gr as an electrode material in both MFC and MEC applications - based on experimental results from the investigation. Current technological advancements in the implementation of Gr in MFC and MEC are also highlighted in this review. To summarise, the investigation exposes critical issues impeding the advancement of microbial fuel cells, and proposes possible solutions to mitigate these challenges.

Optimization of a single chamber microbial fuel cell using Lactobacillus pentosus: Influence of design and operating parameters

Microbial fuel cells (MFCs) have been receiving an increased attention over the last years due to their potential to combat two global problems: waste pollution and energy demand. Additionally, when a wastewater is used, MFCs can perform its treatment while recovering energy, leading to the possibility of energy-producing wastewater treatment plants, offsetting their operational costs. However, to overcome their current limitations (lower power outputs and higher costs), a clear understanding of the effect of operation and design parameters on its overall performance is mandatory. Therefore, the goal of this work was to evaluate the effect of operating conditions - batch cycle and yeast extract concentration, and design parameters - anode electrode area, membrane thickness and active area, on the overall performance of a single chamber MFC. The MFC operated with a pure culture of Lactobacillus pentosus and a synthetic wastewater based on a real dairy industry effluent. The overall performance was evaluated through the power output and the COD removal rate. Additionally, the biofilm formed at the anode electrode was characterized in terms of biomass, proteins and polysaccharides content. For the conditions used in this work, a maximum power density of 5.04 ± 0.39 mW/m² was achieved with an anode electrode area of 61 cm², a batch cycle of 48 h, 50 mg/L of yeast extract and a Nafion 212 membrane with an active area of 25 cm². The different conditions tested had a clear effect on the MFC energy production and biofilm characteristics, but not on the ability of L. pentosus to treat the dairy wastewater. The COD removal rates were in the range between 42% and 58%, for all the conditions tested.