Accelerating the startup of microbial fuel cells by facile microbial acclimation

Insights on hexavalent chromium(VI) remediation strategies in abiotic and biotic dual chamber microbial fuel cells: electrochemical, physical, and metagenomics characterizations

Hexavalent chromium [Cr(VI)] is one of the most carcinogenic and mutagenic toxins, and is commonly released into the environemt from different industries, including leather tanning, pulp and paper manufacturing, and metal finishing. This study aimed to investigate the performance of dual chamber microbial fuel cells (DMFCs) equipped with a biocathode as alternative promising remediation approaches for the biological reduction of hexavalent chromium [Cr(VI)] with instantaneous power generation. A succession batch under preliminary diverse concentrations of Cr(VI) (from 5 to 60 mg L-1) was conducted to investigate the reduction mechanism of DMFCs. Compared to abiotic-cathode DMFC, biotic-cathode DMFC exhibited a much higher power density, Cr(VI) reduction, and coulombic efficiency over a wide range of Cr(VI) concentrations (i.e., 5-60 mg L-1). Furthermore, the X-ray photoelectron spectroscopy (XPS) revealed that the chemical functional groups on the surface of biotic cathode DMFC were mainly trivalent chromium (Cr(III)). Additionally, high throughput sequencing showed that the predominant anodic bacterial phyla were Firmicutes, Proteobacteria, and Deinococcota with the dominance of Clostridiumsensu strict 1, Enterobacter, Pseudomonas, Clostridiumsensu strict 11 and Lysinibacillus in the cathodic microbial community. Collectively, our results showed that the Cr(VI) removal occurred through two different mechanisms: biosorption and bioelectrochemical reduction. These findings confirmed that the DMFC could be used as a bioremediation approach for the removal of Cr(VI) commonly found in different industrial wastewater, such as tannery effluents. with simultaneous bioenergy production.

Statistical optimization of waste molasses-based exopolysaccharides and self-sustainable bioelectricity production for dual chamber microbial fuel cell by Bacillus piscis

BACKGROUND

The application of exopolysaccharide-producing bacteria (EPS) in dual chamber microbial fuel cells (DCMFC) is critical which can minimize the chemical oxygen demand (COD) of molasses with bioelectricity production. Hence, our study aimed to evaluate the EPS production by the novel strain Bacillus piscis by using molasses waste. Therefore, statistical modeling was used to optimize the EPS production. Its structure was characterized by UV, FTIR, NMR, and monosaccharides compositions. Eventually, to highlight B. piscis' adaptability in energy applications, bioelectricity production by this organism was studied in the BCMFC fed by an optimized molasses medium.

RESULTS

B. piscis OK324045 characterized by 16S rRNA is a potent EPS-forming organism and yielded a 6.42-fold increase upon supplementation of molasses (5%), MgSO4 (0.05%), and inoculum size (4%). The novel exopolysaccharide produced by Bacillus sp. (EPS-BP5M) was confirmed by the structural analysis. The findings indicated that the MFC's maximum close circuit voltage (CCV) was 265 mV. The strain enhanced the performance of DCMFC achieving maximum power density (PD) of 31.98 mW m-2, COD removal rate of 90.91%, and color removal of 27.68%. Furthermore, cyclic voltammetry (CV) revealed that anodic biofilms may directly transfer electrons to anodes without the use of external redox mediators. Additionally, CV measurements made at various sweep scan rates to evaluate the kinetic studies showed that the electron charge transfer was irreversible. The SEM images showed the biofilm growth distributed over the electrode's surface.

CONCLUSIONS

This study offers a novel B. piscis strain for EPS-BP5M production, COD removal, decolorization, and electricity generation of the optimized molasses medium in MFCs. The biosynthesis of EPS-BP5M by a Bacillus piscis strain and its electrochemical activity has never been documented before. The approach adopted will provide significant benefits to sugar industries by generating bioelectricity using molasses as fuel and providing a viable way to improve molasses wastewater treatment.

Modeling and experimental investigation of the effect of carbon source on the performance of tubular microbial fuel cell

Microbial fuel cells (MFCs) serve two main purposes: clean energy production and wastewater treatment. This study examines the impact of different carbon sources on MFC performance and develops a mathematical model to replicate the polarization curve. The biological reactor employed three types of carbon sources: glucose as a simple feed, microcrystalline cellulose (MCC), and a slurry of the organic component of municipal solid waste (SOMSW) as complex feeds. The MFCs were operated in both open and closed circuit modes. The maximum open circuit voltages achieved were 695 mV for glucose, 550 mV for MCC, and 520 mV for SOMSW as substrates. The influence of the substrate in closed circuit mode was also investigated, resulting in maximum power densities of 172 mW/m2, 55.5 mW/m2, and 47.9 mW/m2 for glucose, MCC, and SOMSW as substrates, respectively. In the second section, a mathematical model was developed to depict the polarization curve while considering voltage losses, namely activation, ohmic, and concentration loss, with an average relative error (ARE) of less than 10%. The mathematical models demonstrated that the activation loss of voltage increased with the complexity of the substrate and reached its peak value when SOMSW was used as the substrate.

Polyaniline on Stainless Steel Fiber Felt as Anodes for Bioelectrodegradation of Acid Blue 29 in Microbial Fuel Cells

This study investigated the advantages of using low-cost polyaniline-fabricated stainless steel fiber felt anode-based microbial fuel cells (PANI-SSFF-MFCs) for azo dye acid blue 29 (AB29) containing wastewater treatment integrated with an aerobic bioreactor. The findings of electrochemical impedance spectroscopy (EIS) and polarization studies showed that the PANI–SSFF anode considerably decreased the MFC internal resistance. The highest power density of 103 ± 3.6 mW m−2 was achieved by PANI-SSFF-MFCs with a decolorization efficiency of 93 ± 3.1% and a start-up time of 13 days. The final chemical oxygen demand (COD) removal efficiencies for integrated PANI–SSFF–MFC–bioreactor and SSFF–MFC–bioreactor set-ups were 92.5 ± 2% and 80 ± 2%, respectively. Based on 16S rRNA gene sequencing, a substantial microbial community change was observed in MFCs. The majority of sequences were from the Proteobacteria phylum, accounting for 72% and 55% in PANI–SSFF–anodic biofilm and suspension, respectively, and 58 and 45% in SSFF–anodic biofilm and suspension, respectively. The relative abundance of the seven most abundant genera (Pseudomonas, Acinetobacter, Stenotrophomonas, Geothrix, Dysgonomonas, Shinella, and Rhizobiales) was higher in PANI–SSFF–MFCs (46.1% in biofilm and 55.4% in suspension) as compared to SSFF–MFC (43% in biofilm and 40.8% in suspension) which predominantly contributed to the decolorization of AB29 and/or electron transfer. We demonstrate in this work that microbial consortia acclimated to the MFC environment and PANI-fabricated anodes are capable of high decolorization rates with enhanced electricity production. A combined single-chamber MFC (SMFC)-aerobic bioreactor operation was also performed in this study for the efficient biodegradation of AB29.

Comparative Study of Different Production Methods of Activated Carbon Cathodic Electrodes in Single Chamber MFC Treating Municipal Landfill Leachate

The treatment of real waste extracts with simultaneous energy production is currently under research. One method of addressing this dual task is using biochemical reactors named microbial fuel cells (MFCs). MFCs consist of a bioanode and a cathode where the oxygen reduction reaction (ORR) occurs. Cathodes are currently under optimization regarding the nature of their support, their catalytic efficiency and their configurations. In this work, we present facile preparation methods for the production of activated carbon ceramic-supported cathodic electrodes produced with three different techniques (wash-coat, brush-coat, and ultrasound-assisted deposition/infiltration). The produced cathodic electrodes were tested in a single-chamber MFC, filled with the concentrated liquid residue, after the reverse osmosis (RO-CLR) treatment of leachate from a municipal waste landfill, in order to exploit their electrochemical potential for simultaneous waste treatment and energy production. The electrode produced utilizing 20 kHz ultrasounds proved to be more effective in terms of energy harvesting (10.7 mW/g·L of leachate) and wastewater treatment (COD removal 85%). Internal resistances of the ultrasound-produced electrodes are lower, as compared to the other two methods, opening new exploitation pathways in the use of ultrasound as a means in producing electrodes for microbial fuel cells.

Effect of copper ions on glucose fermentation pathways in bioelectrochemical system

Toxic metal ions were previously found to be effective removed by anodic biofilms under the coexistence of organics in bioelectrochemical system (BES). However, the effect of toxic metal ions on the organics fermentation pathways remains unclear. To investigate the pathway systematically, the glucose fermentation pathways were discussed under different Cu²⁺ concentrations. After introducing Cu²⁺, more acetate and less propionate were observed, implying that the metabolic reaction of glucose fermentation altered from mixed acid type to acetogenesis type. This pattern produced more "food" (acetate or hydrogen) for methanogens, thus, the methane content increased by 19.67%, 39.51%, and 27.71% in the presence of 0.1, 1, and 7 mg L^-1 Cu²⁺ compared to the blank, respectively. Increased Cu²⁺ concentrations resulted in the decrease of current production, which was associated with the decrease of electricigen (Geobacter). Consistent with the change of fermentation type, the fermenters (Klebsiella and norank_f__norank_o__Bacteroidales) that related to the production of acetate increased, while the dominant methanogens (Methaospirillum) didn't decrease until the Cu²⁺ concentration reached 7 mg L^-1.