Boosted biodegradation of recalcitrant bisphenol S by mix-cultured microbial fuel cells under micro-aerobic condition

<i>Harvesting Energy using Biocatalysts</i>

Performance of a dual-chamber microbial fuel cell as a biosensor for in situ monitoring Bisphenol A in wastewater

Performance and biotoxicity of electro-Fenton treatment of bisphenol A: Evaluation of copper recovered from microbial fuel cell cathodes for subsequent catalytic applications

Recent advances in microbial fuel cell technology for energy generation from wastewater sources

Development of innovative materials used in electrochemical devices for the renewable production of hydrogen and electricity

The metabolic flux in microbial fuel cells (MFCs) is significantly different from conventional fermentation because the electrode in MFCs acts as a terminal electron acceptor. In this study, the difference in the carbon metabolism of Klebsiella pnuemoniae L17 (Kp L17) during growth in MFCs and conventional bioreactors was studied using glucose as the sole carbon and energy source. For metabolic flux analysis (MFA), the in silico metabolic flux model of Kp L17 was also constructed. The MFC bioreactor operated in oxidative mode, where electrons are removed by the anode electrode, generated a smaller quantity of reductive metabolites (e.g., lactate, 2,3-butanediol and ethanol) compared to the conventional fermentative bioreactor (non-MFC). Stoichiometric analysis indicated that the cellular metabolism in MFC had partially (or significantly) shifted to anaerobic respiration from fermentation, the former of which was similar to that often observed under micro-aerobic conditions. Electron balance analysis suggested that 30% of the electrons generated from glucose oxidation were extracted from the microbe and transferred to the electrode. These results highlight the potential use of MFCs in regulating the carbon metabolic flux in a bioprocess.

Due to the high cost of wastewater treatement, new and alternative low cost technologies need to be investigated. Bioelectrochemical systems and particularly microbial fuel cells (MFCs) seem to address positively this problem. In MFCs the organic waste is utilized as a fuel that is oxidised from microorganisms through their metabolism generating electricity. The main problem related with MFCs utilization is the small electricity production and high cost of the electrodes materials. These are the major reasons why MFCs are not commercialized in a large scale yet. In order to overcome the high cost, that is mainly related to the high price of the noble metals used as catalysts at the cathode, inexpensive catalysts for oxygen reduction reaction (ORR) should be explored. These catalysts belong to the group of non platinum based catalyst that are proved as very active towards ORR. This work focused on the utilization of a low cost non-PGM (Fe-Aminoantipyrine) catalyst explored in the design of oxygen reducing cathode for MFCs application. The activity of this catalyst was characterized electrochemically in a three-electrode configuration varying the pH of the electroyte. Then the cathodes were introduced in double chamber MFC (Figure 1) with the cathode completely immersed in the solution. The two compartments (125 ml) of the MFC were separated by proton-exchange membrane (Nafion 211). The anode composed of carbon brush (6x4 cm projected surface area) pre-colonized with mixed cultured bacteria. The anode chamber was filled with 50% in volume PBS (50 mM) and 50% in volume of activated sludge (pH=7.5±0.1). The non-PGM cathode (2.3 x 2.3 cm geometric area) was immersed in solution with different pHs (6, 7.5, 9 and 11) and purged with air for oxygen supply. The MFCs performance was investigated at different pHs in order to simulate possible industrial wastes with pHs different than neutral.The catalyst used in this work was synthesized by modified sacrificial support method which was developed at UNM1. In general, the metal precursor (iron nitrate) and nitrogen-containing low-molecular weight organic precursor (4-aminoantipiryne) are deposited on the surface of fumed silica (surface area ~120 m-2 g-1). the obtained composite material is heat treated in nitrogen atmosphere at T=950°C. After heat treatment fumed silica was removed by excess amount of HF.Potentiodynamic polarizations curve of the anode and the cathode separately were carried out using platinum mesh as a counter and a Ag/AgCl (3M KCl) as reference electrodes with scan rate 0.2 mV/s. MFC overall polarization curves were measured using a potentiostat with a scan rate of 1 mV/s. Power curves were determined using Ohm`s law (P= V x I).The electrochemical measurements of the cathode as a result of differences in the electrolyte pH showed highest electrocatalytic activity of the catalyst at lower pHs. This confirms our previous observation for the dependance of the Fe-AAPyr activity from the electrolyte pH2.The polarization and power curves (Figure 2) of the whole MFCs followed the same trend as the cathode polarization curves showing the dominating role of the cathode over the MFCs performance. The MFCs with low pH of the catholyte demonstrated the highest power (200 μW) and the highest open circuit voltage (OCV = 850 mV).This study demonstrated the applicability of non-PGM catalyst for the development of cathodes for MFC application. Further studies with improved MFCs design should be performed. Long-term operation test will be carried out investigating the influence of the wastewater pollutants on the cathode and subsequently the whole MFC operation and output.ReferencesA. Serov, U. Martinez, A. Falase, P. Atanassov, Electrochem. Comm. 22 (2012) 193-196.S. Brocato, A. Serov, P. Atanassov Electrochim. Acta, 87 (2013) 361-365

The availability of drinking water from the current available sources is decreasing due to the high demand and population increase. Seawater is a potential source for drinking water but the current desalination technology is energy intensive, therefore energy efficient desalination technology is desired. In the past decade microbial fuel cells (MFC) were emerged for simultaneous wastewater treatment and bioelectricity generation, in the anodic chamber of MFCs, microbes work as a biocatalyst to generate electrons from the oxidation of the organic compounds (wastewater) and transfer them to the anode electrode. These electrons flow through an external circuit to the cathode electrode where they used to reduce terminal electron acceptors (e.g., oxygen). Microbial desalination cells (MDC) are new potential technique for seawater desalination, in this device energy from wastewater is extracted by using microbes and without any external energy source, water desalination is driven. To convert an MFC to an MDC, a middle chamber is inserted in between the anodic and cathodic chambers of MFC using a pair of anion and cation exchange membranes. This middle chamber works as a desalination chamber in the MDC (Fig. 1). The cations and anions from the desalination chamber moved to the anodic and the cathodic chambers, respectively, due to the cell potential difference between the anode electrode and the cathode electrode; as a result, salts are removed from the saltwater.The first MDC study was reported in 2009 and since then there have been nearly 74 papers published about various aspects of MDC design and development, indicating a strong interest and rapid development of this technology. During this short period of time, various MDC designs were developed for salt removal and wastewater treatment. The desalination chamber volumes were increased from 3 ml to 105 liters and further progress is going on for salt removal and at the same time wastewater treatment. The performance of MDC was investigated using various concentrations of saline water in desalination chamber using industrial or synthetic wastewater in the anodic chamber. Different MDC designs were reviewed here. These developed new MDC designs named as air cathode MDC, stacked MDC (SMDC), up flow MDC (UMDC), recirculated MDC (RMDC), microbial electrodialysis cell (MEDC), submerged microbial desalination- denitrification cell (SMDDC), microbial capacitive desalination cell (MCDC) and osmotic microbial desalination cell (OsMDC). Different anion and cation exchange membranes were compared for power generation and desalination efficiency. This paper also reviews different substrates that have been used in MDCs so far. The MDCs provide an energy self-sustainable system in that water desalination and wastewater treatment conducted by using microbes as catalyst in the anodic chamber. Still the available MDCs were very small in volume that can't meet today's water desalination needs. In the long term operation of MDC, the membrane fouling and electrode stability are still two major problems limiting the development of MDCs. The possibility of scale-up, possible future potentials for synchrony of the MDCs with current desalination techniques were also discussed. Case study with real wastewater in the anodic chamber and real seawater in the desalination chamber were also discussed.AcknowledgementsThis work was made possible by NPRP grant # 6-289-2-125 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.ReferenceSevda, S., Yuan, H., He, Z., Abu-Reesh, I.M., 2015. Microbial desalination cells as a versatile technology: Functions, optimization and prospective. Desalination 371, 9–17. doi:10.1016/j.desal.2015.05.021

Many factors affect the performance of microbial fuel cells (MFCs). Considerable attention has been given to the impact of cell configuration and materials on MFC performance. Much less work has been done on the impact of the anode microbiota, particularly in the context of using complex substrates as fuel. One strategy to improve MFC performance on complex substrates such as wastewater, is to pre-enrich the anode with known, efficient electrogens, such as Geobacter spp. The implication of this strategy is that the electrogens are the limiting factor in MFCs fed complex substrates and the organisms feeding the electrogens through hydrolysis and fermentation are not limiting. We conducted a systematic test of this strategy and the assumptions associated with it. Microbial fuel cells were enriched using three different substrates (acetate, synthetic wastewater and real domestic wastewater) and three different inocula (Activated Sludge, Tyne River sediment, effluent from an MFC). Reactors were either enriched on complex substrates from the start or were initially fed acetate to enrich for Geobacter spp. before switching to synthetic or real wastewater. Pre-enrichment on acetate increased the relative abundance of Geobacter spp. in MFCs that were switched to complex substrates compared to MFCs that had been fed the complex substrates from the beginning of the experiment (wastewater-fed MFCs - 21.9 ± 1.7% Geobacter spp.; acetate-enriched MFCs, fed wastewater - 34.9 ± 6.7% Geobacter spp.; Synthetic wastewater fed MFCs – 42.5 ± 3.7% Geobacter spp.; acetate-enriched synthetic wastewater-fed MFCs - 47.3 ± 3.9% Geobacter spp.). However, acetate pre-enrichment did not translate into significant improvements in cell voltage, maximum current density, maximum power density or substrate removal efficiency. Nevertheless, coulombic efficiency (CE) was higher in MFCs pre-enriched on acetate when complex substrates were fed following acetate enrichment (wastewater-fed MFCs – CE = 22.0 ± 6.2%; acetate-enriched MFCs, fed wastewater – CE =58.5 ± 3.5%; Synthetic wastewater fed MFCs – CE = 22.0 ± 3.2%; acetate-enriched synthetic wastewater-fed MFCs – 28.7 ± 4.2%.) The relative abundance of Geobacter ssp. and CE represents the average of the nine replicate reactors inoculated with three different inocula for each substrate. Efforts to improve the performance of anodic microbial communities in MFCs utilizing complex organic substrates should therefore focus on enhancing the activity of organisms driving hydrolysis and fermentation rather the terminal-oxidizing electrogens.

Microbes to Generate Electricity

High specific surface area graphene-like biochar for green microbial electrosynthesis of hydrogen peroxide and Bisphenol A oxidation at neutral pH.

The changes of bacterial communities and antibiotic resistance genes in microbial fuel cells during long-term oxytetracycline processing

Microbial fuel cells (MFCs) have been used to enrich microbes oxidizing formate with concomitant electricity generation. Medium containing formate was fed continuously to MFCs. MFCs showed approximately 1 mA of current after 4 months of operation. Over 90% of formate supplied was removed in MFCs, while Coulombic efficiency was only 5.3% indicating substantial electron and energy losses rather than electricity generation. Denaturing gradient gel electrophoresis (DGGE) showed that a formate-utilizing acetogenic bacterium (Acetobacterium sp.), an acetate-oxidizing metal reducer (Geobacter sp.), and another formate utilizer (Arcobacter sp.) were mainly detected on the electrode. This result indicates that some formate was consumed by acetogenic bacteria to make acetate, and acetate was used by acetate-utilizing electrochemically active bacteria (EAB) (e.g., Geobacter sp.). Additionally, formate was oxidized by nonelectrochemically active bacteria under microaerobic conditions in the anode compartment of the MFCs.

Insights into the development of microbial fuel cells for generating biohydrogen, bioelectricity, and treating wastewater

Background. The formation of an exoelectrogenic biofilm in a microbial fuel cell (MFC) is an important stage, because it affects later on current generation by the system. The fermented residue after methanogenesis as an inoculum contains not only exoelectrogenic microorganisms, but also methanogens, which reduce the productivity of MFC. The use of current allows the formation of a biofilm enriched with exoelectrogenic microorganisms. Objective. The purpose of our study was to establish the parameters of MFC under periodic application of external voltage. Methods. A two-chamber H-type MFC with a salt bridge between the chambers was used for the study. The anolyte was stirred with a magnetic stirrer for 4 h a day and a 3V voltage was simultaneously applied to create selective conditions for exoelectrogenic biofilm growth. Results. The application of external voltage stimulated the increase in the current and voltage of the MFC. With the periodic application of an external voltage, the MFC current increased to 788 ± 40 mA for the MFC with a resistor and without load. After disconnection and discharge, the MFC current dropped to 189 ± 10 mA for the MFC without load and to 154 ± 8 mA for the MFC with a resistor, respectively. Under the conditions of MFC operation without applying external voltage, the current was 960 ± 50 mA for MFC with an open circuit and 672 ± 35 mA for MFC with a closed circuit when a resistor is connected. For all MFC, the current gradually decreased over time. MFC demonstrated capacitive behaviour: after accumulating charge for 4 h, a discharge from 622 ± 30 mV to 462 ± 23 mV was observed. Microscopy showed fouling of the anode. Since the fermented residue after methanogenesis is mixed consortium, the anodic biofilm was also mixed consortium enriched with different species of exoelectrogens. Conclusions. Periodic application of external voltage allowed to increase the current by 17% and double the voltage compared to MFC without external voltage supply. However, after disconnecting the external voltage source, the MFC gradually discharged, that is, the current and voltage decreased. The maximum value of the current of the MFC with an open circuit was 22% more than the MFC with a closed circuit.