Enhanced bioelectricity generation by improving pyocyanin production and membrane permeability through sophorolipid addition in Pseudomonas aeruginosa-inoculated microbial fuel cells

Microbial community dynamics in a pilot-scale MFC-AA/O system treating domestic sewage

To investigate the effluent concentrations of pollutants, electricity production and microbial community structure, a pilot-scale microbial fuel cell coupled anaerobic-anoxic-oxic system for domestic sewage treatment was constructed, and continuously operated for more than 1 year under natural conditions. The results indicated that the treatment system ran well most of the whole period, but both effluent qualities and electricity production deteriorated at low temperature. The results of MiSeq sequencing showed that the microbial community structures of both anode and cathode biofilms changed extensively during long-term operation and were correlated with changes in effluent qualities. Fifteen genera of electricigens were detected in the anode biofilm, mainly including Clostridium, Paracoccus, Pseudomonas, and Arcobacter. Partial Mantel test results showed that the temperature had significant effects on the microbial community structure. The electricity production was found to have higher relevance to the variation of the anodic community than that of the cathodic community.

Alkyl Xylosides: Physico-Chemical Properties and Influence on Environmental Bacteria Cells

A group of four selected non-ionic surfactants based on carbohydrates, namely octyl d-xyloside (C8X), nonyl d-xyloside (C9X), decyl d-xyloside (C10X) and dodecyl d-xyloside (C12X), have been investigated to accomplish a better understanding of their physico-chemical properties as well as biological activities. The surface-active properties, such as critical micelle concentration (CMC), emulsion and foam stability, the impact of the compounds on cell surface hydrophobicity and cell membrane permeability together with their toxicity on the selected bacterial strains have been determined as well. The studied group of surfactants showed high surface-active properties allowing a decrease in the surface tension to values below 25 mN m-1 for dodecyl d-xyloside at the CMC. The investigated compounds did not have any toxic influence on two Pseudomonas bacterial strains at concentrations below 25 mg L-1. The studied long-chain alkyl xylosides influenced both the cell inner membrane permeability and the cell surface hydrophobicity. Furthermore, the alkyl chain length, as well as the surfactant concentration, had a significant impact on the modifications of the cell surface properties. The tested non-ionic surfactants exhibited strong surface-active properties accompanied by the significant influence on growth and properties of Pseudomonas bacteria cells.

Effects of Fe, Ni, and Fe/Ni metallic nanoparticles on power production and biosurfactant production from used vegetable oil in the anode chamber of a microbial fuel cell

In this study, metallic nanoparticles (Fe, Ni, and Fe/Ni) were used as cathode catalysts to enhance power production and to improve the anode performance of a two-chambered microbial fuel cell (MFC). The metallic nanoparticles were rod-shaped and produced by the precipitation/co-precipitation method. A biosurfactant was produced in the anode chamber of the MFC from used vegetable oil by the bacteria Serratia sp. Overall cell voltage, power density, bacterial growth, and biosurfactant production were studied by applying different types of metallic nanoparticles to the cathode electrode. The influence of various types of nanoparticles on the impedance of the MFC was also investigated by electrochemical impedance spectroscopy (EIS), including analyses of anode impedance, cathode impedance, anode solution resistance, cathode solution resistance, and membrane resistance. The nanoparticles improved MFC performance in the following order: Fe>Ni>Fe/Ni. The addition of 1.5mg/cm² Fe nanoparticles to the cathode surface enhanced power production by over 500% to 66.4mW/m³, promoted bacterial growth and biosurfactant production in the anode solution by 132.5% and 32.0%, respectively, and reduced anode impedance, cathode impedance, and membrane resistance by 26.8%, 81.6%, and 33.8% to 159.00Ω, 7.69Ω, and 261.09Ω, respectively. For the first time, biosurfacant production in the anode chamber of the MFC was promoted by using the metallic nanoparticles as cathode catalysts. By improving the cathode properties, this study showed a new way to manipulated the performance of the anode chamber of the MFC.

Bio-Electron-Fenton (BEF) process driven by microbial fuel cells for triphenyltin chloride (TPTC) degradation

The intensive use of triphenyltin chloride (TPTC) has caused serious environmental pollution. In this study, an effective method for TPTC degradation was proposed based on the Bio-Electron-Fenton process in microbial fuel cells (MFCs). The maximum voltage of the MFC with graphite felt as electrode was 278.47% higher than that of carbon cloth. The electricity generated by MFC can be used for in situ generation of H₂O₂ to a maximum of 135.96μmolL^-1 at the Fe@Fe₂O_3(*)/graphite felt composite cathode, which further reacted with leached Fe²⁺ to produce hydroxyl radicals. While 100μmolL^-1 TPTC was added to the cathodic chamber, the degradation efficiency of TPTC reached 78.32±2.07%, with a rate of 0.775±0.021μmolL^-1h^-1. This Bio-Electron-Fenton driving TPTC degradation might involve in SnC bonds breaking and the main process is probably a stepwise dephenylation until the formation of inorganic tin and CO₂. This study provides an energy saving and efficient approach for TPTC degradation.

Real-time monitoring of phenazines excretion in Pseudomonas aeruginosa microbial fuel cell anode using cavity microelectrodes

Phenazines are a kind of metabolites that can mediate extracellular Pseudomonas aeruginosa (P. aeruginosa) cells in microbial fuel cells (MFCs). However, it is still not clear that whether and how the excretion profile of phenazines is affected by the operating MFC. Here, we report a real time analysis approach based on a cavity microelectrode electrochemical sensor to investigate the phenazines excretion behavior of P. aeruginosa during MFC operation. The phenazine concentration increases at first 72 h, reaches a plateau and decreases after 120 h and also shows local dependent variation. It is dependent on the MFC current generation profile but also affect by the biofilm formation. Accordingly, a mechanism about phenazines excretion in MFC anode and the phenazines mediated extracellular electron transfer of the P. aeruginosa anode is proposed. This work provides a novel strategy for self-mediated extracellular electron transfer analysis in the operating MFCs.

Endogenously enhanced biosurfactant production promotes electricity generation from microbial fuel cells

Microbial fuel cell (MFC) is considered as a promising green energy source and energy-saving pollutants treatment technology as it integrates pollutant biodegradation with energy extraction. In this work, a facile approach to enhance endogenous biosurfactant production was developed to improve the electron transfer rate and power output of MFC. By overexpression of rhlA, the key gene responsible for rhamnolipids synthesis, over-production of self-synthesized rhamnolipids from Pseudomonas aeruginosa PAO1 was achieved. Strikingly, the increased rhamnolipids production by rhlA overexpression significantly promoted the extracellular electron transfer of P. aeruginosa by enhancing electron shuttle (pyocyanin) production and increasing bacteria attachment on the anode. As a result, the strain with endogenously enhanced rhamnolipids production delivered 2.5 times higher power density output than that of the parent strain. This work substantiated that the enhancement on endogenous biosurfactant production could be a promising approach for improvement on the electricity output of MFC.

Deciphering synergistic characteristics of microbial fuel cell-assisted dye decolorization

This study provided a novel evaluation scheme to quantitatively reveal "synergistic" stimulation of microbial fuel cell (MFC)-assisted dye decolorization for industrial practicability. This work also disclosed why dye decolorization was more electrochemically favorable during simultaneous bioelectricity generation and dye decolorization (SBG&DD). Quantitative assessment upon stimulating effects of different decolorized metabolites on BG and DD alone was also implemented for conclusive remarks. Apparently, using MFC as the method of dye decontamination could considerably increase ca. 40-70% of electron transfer capabilities for SBG&DD, thereby significantly improving the performance of dye decontamination.

Enhancement of power production with tartaric acid doped polyaniline nanowire network modified anode in microbial fuel cells

The feasibility to use tartaric acid doped PANI for MFC anode modification was determined. Uniform PANI nanowires doped with tartaric acid were synthesized and formed mesoporous networks on the carbon cloth surface. By using this tartaric acid doped PANI modified carbon cloth (PANI-TA) as the anode, the voltage output (435 ± 15 mV) and power output (490 ± 12 mW/m(2)) of MFC were enhanced by 1.6 times and 4.1 times compared to that of MFC with plain carbon cloth anode, respectively. Strikingly, the performance of PANI-TA MFC was superior to that of the MFCs with inorganic acids doped PNAI modified anode. These results substantiated that tartaric acid is a promising PANI dopant for MFC anode modification, and provided new opportunity for MFC performance improvement.

Effect of acclimatization on hexavalent chromium reduction in a biocathode microbial fuel cell

A simple acclimatization method for the reduction of hexavalent chromium (Cr(VI)) at a biocathode by first enriching an exoelectrogenic biofilm on a microbial fuel cell (MFC) anode, followed by direct inversion of the anode to function as the biocathode, has been established. This novel method significantly enhanced the Cr(VI) reduction efficiency of the MFC, which was mainly attributed to the higher microbial density and less resistive Cr(III) precipitates on the cathode when compared with a common biocathode acclimatization method (control). The biocathode acclimatization period was shortened by 19days and the Cr(VI) reduction rate was increased by a factor of 2.9. Microbial community analyses of biocathodes acclimatized using different methods further verified the feasibility of this electrode inversion method, indicating similar dominant bacteria species in biofilms, which mainly consist of Gamma-proteobacteria and Bacteria.

Bioelectrogenic role of anoxic microbial anode in the treatment of chemical wastewater: microbial dynamics with bioelectro-characterization

A membrane-less anoxic bioelectrochemical treatment (AxBET) system was evaluated to study the influence of bioelectrogenic activity during the treatment of chemical wastewater (CW). Increment in power generation was observed with increase in substrate loading (61-204 mW/m(2)) indicating the ability of anodic bacteria in BET system to utilize the complex chemicals as the sole carbon source. Derivative analysis of voltammograms depicted by positive and negative peak potentials which relate to the extracellular electron transport sites (EETs) that presumably play a significant role in electron transfer. These self-driven redox mediators varied with respect to the substrate load. The microbial population was dominated by anaerobic microorganisms which are commonly involved in effluent treatment plants during the initial phase of operation. A gradual shift in the microbial community was observed towards enrichment of electrogenically active bacteria belonging to phyla viz., Firmicutes and Proteobacteria after prolonged operation. Shannon Index and principal component analysis correlated with the microbial profile studies. The feasibility of self-driven bioremediation of chemical wastewater in an AxBET system demonstrated bioelectricity production along with multipollutant removal simultaneously.