Anodic microbial community analysis of microbial fuel cells based on enriched inoculum from freshwater sediment

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.

Isolation and Characterization of Bacteria with High Electroactive Potential from Poultry Wastewater

Natural resources are in short supply, and the ecosystem is being damaged as a result of the overuse of fossil fuels. The creation of novel technology is greatly desired for investigating renewable and sustainable energy sources. Microorganisms have received a lot of interest recently for their potential to transform organic waste into sustainable energy and high-value goods. New exoelectrogens that can transmit electrons to electrodes and remove specific wastewater contaminants are expected to be studied. In this study, we examined three distinct samples (as determined by chemical oxygen demand and pH) that can be used as anolytes to generate power in single-chamber and double-chamber microbial fuel cells using graphite electrodes. Wastewater from poultry farms was studied as an exoelectrogenic anolyte for microbial fuel cell power generation. The study examined 10 different bacterial strains, numbered A1 through A10. Due to their highly anticipated capacity to metabolize organic/inorganic chemicals, the diverse range of microorganisms found in poultry wastewater inspired us to investigate the viability of generating electricity using microbial fuel cells. From the investigated bacterial strains, the highest voltage outputs were produced by strains A1 (Lysinibacillus sphaericus) and A2 (Bacillus cereus), respectively, at 402 mV and 350 mV. Among the 10 different bacterial strains, strain A6 generated the least amount of electricity, measuring 35.03 mV. Furthermore, a maximum power density of 16.16 1.02 mW/m² was achieved by the microbial fuel cell using strain A1, significantly outperforming the microbial fuel cell using a sterile medium. The strain A2 showed significant current and power densities of 35 1.12 mA/m² and 12.25 1.05 mW/m², respectively. Moreover, in the two representative strains, chemical oxygen demand removal and Coulombic efficiency were noted. Samples from the effluent anode chamber were taken in order to gauge the effectiveness of chemical oxygen demand removal. Wastewater had an initial chemical oxygen demand content of 350 mg/L on average. Strains A1 and A2 decomposed 94.28% and 91.71%, respectively, of the organic substrate, according to the chemical oxygen demand removal efficiency values after 72 h. Strains A1 and A2 had electron donor oxidation efficiencies for 72 h of 54.1% and 60.67%, respectively. The Coulombic efficiency increased as the chemical oxygen demand decreased, indicating greater microbial electroactivity. With representative strains A1 and A2, Coulombic efficiencies of 10% and 3.5%, respectively, were obtained in the microbial fuel cell. The findings of this study greatly advance the field as a viable source of power technology for alternative energy in the future, which is important given the depletion of natural resources.

External resistance acclimation regulates bio-anode: new perspective from biofilm structure and its correlation with anode performance

External resistance is important for the anode and cell performance. However, little attentions were paid on the effect of external resistance on the variation of biofilm structure. Here, we used external resistance ranged from 4000 to 500 Ω for anodic acclimation to investigate the correlation between anode performance and biofilm structure. With the reduce of external resistance, the maximum current density of anode increased from 1.0 to 3.4 A/m², which was resulted from a comprehensive effect of reduced charge transfer resistance and increased diffusion resistance. Biological analysis showed that with the reduce of external resistance, biomass and extracellular polymeric substances content increased by 109 and 286%, cell viability increased by 22.7%, which contributed to the reduced charge transfer resistance. But the porosity of anodic biofilm decreased by 27.8%, which led to an increased diffusion resistance of H⁺. This work provided a clear correlation between the electrochemical performance and biofilm structure.

Sustained energy production from wastewater in microbial fuel cell: effect of inoculum sources, electrode spacing and working volume

The present study was aimed at producing enhanced and sustained bioelectricity from distillery wastewater in a double chamber microbial fuel cell (MFC) by changing inter-electrode distance, inoculum and reactor volume. Using double chamber MFC with 1 L working volume, when the distance between the electrodes was kept shorter (1 cm), it generated power density of 1.74 W/m³, which was 42.5% higher than that of MFC with electrode spacing of 10 cm (1 W/m³). Using inoculum from different sources viz. garden soil (MFC-GS), wetland sediment (MFC-WS) and sludge from wastewater treatment plant (MFC-S), the highest open circuit voltage (OCV) of 0.84 V and power density of 2.74 W/m³ were produced by MFC-WS, which also showed sustained electricity production (1.68 W/m³) from the wastewater during a 10-day experiment. Relatively lower power density was generated from MFC-S (1.42 W/m³), while that from MFC-GS was the lowest (0.94 W/m³). Bioelectricity generation and overall performance were then assessed using a smaller reactor size. Smaller working volume of MFC (250 ml) favoured greater production of power density (3.2 W/m³) than that with 1 L working volume (2.96 W/m³) with electrode distance of 1 cm. The present study was novel in selecting a suitable mixed-microbial inoculum out of the diverse sources screened and reducing resistance by sharply narrowing down inter-electrode distance and reactor volume, which led to significantly enhanced and sustained electricity generation from double chamber MFC.

Formation of electroactive biofilms derived by nanostructured anodes surfaces

Microbial fuel cells (MFCs) have significant interest in the research community due to their ability to generate electricity from biodegradable organic matters. Anode materials and their morphological structures play a crucial role in the formation of electroactive biofilms that enable the direct electron transfer. In this work, modified electrodes with nanomaterials, such as multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), Al₂O₃/rGO or MnO₂/MWCNTs nanocomposites were synthesized, characterized and utilized to support the growth of electrochemically active biofilms. The MFC's performance is optimized using anode-respiring strains isolated from biofilm-anode surface, while the adjusted operation is conducted with the consortium of (Enterobacter sp.). Besides the formation of matured biofilm on its surface, MnO₂/MWCNTs nanocomposite produced the highest electrical potential outputs (710 mV) combined with the highest power density (372 mW/m²). Thus, a correlation between the anode nanostructured materials and the progression of the electrochemically active biofilms formation is presented, allowing new thoughts for enhancing the MFC's performance for potential applications ranging from wastewater treatment to power sources.

Improving the power generation performances of Gram-positive electricigens by regulating the peptidoglycan layer with lysozyme

The power generation performance of a microbial fuel cell (MFC) greatly depends on the relative amount of electricigens in the anodic microbial community. Running the MFC multiple times can practically enrich the electricigens, and thus improve its power generation efficiency. However, Gram-positive electricigens cannot be enriched well because of their thick non-conductive peptidoglycan layer. Herein, we report a new Gram-positive electricigen enrichment method by regulating the peptidoglycan layer of the bacteria using lysozyme. Lysozyme can partially hydrolyze the peptidoglycans layer of Gram-positive Firmicutes to improve the permeability of cell wall, and thus enhance its electricity generation activity. The stimulation of Gram-positive electricigen endows MFCs a high power generation community structure, which results in the power density 42% higher than that of the control sample. Our work has provided a new and simple method for optimizing the anode community structure by regulating weak electricigens in the community with lysozyme.