Revealing the performance of aerotolerant anodes for electroactive nitrification/denitrification and current production under coexistence of oxygen and nitrate conditions.

The coexistence of oxygen and/or nitrate at anode usually affects the biofilm activities of traditional anaerobic anode, thereby deteriorating wastewater treatment performance of microbial fuel cells (MFCs). Improving the aerotolerant responses of anode biofilms is a challenge for field application. In this study, we report that using the electroactive nitrifying/denitrifying inoculum and air-cathode expansion could fabricate the aerotolerant anode biofilms (AAB) under affordable nitrate stress (90 ± 5 mg/L). The highest average removal efficiencies were 99% for chemical oxygen demand (COD), NH4+-N and total nitrogen. The highest average current output of 0.69 mA and power density of 290 mW/m2 were obtained. The average current was confirmed to be reduced 10%-78% but the power density remained almost stable except the quart-air-cathodes MFC by increasing dissolved oxygen concentration with expansion of the air-cathode area. The higher oxygen concentration also contributed to oxidation of ammonium through electroactive autotrophic nitrification. The facultative anaerobic bacteria including Thauera, Microsillaceae, Shinella, Blastocatellaceae, Rhodobacter, Comamonadaceae, Caldilineaceae were enriched, which forms the AAB to remove nitrogen and produce current. Therefore, an easy-to-use method to fabricate AAB is evaluated to realize practical applications of MFCs in wastewater treatment.

The effect of anode potential on current production from complex substrates in bioelectrochemical systems: a case study with glucose.

Anode potential can affect the degradation pathway of complex substrates in bioelectrochemical systems (BESs), thereby influencing current production and coulombic efficiency. However, the intricacies behind this interplay are poorly understood. This study used glucose as a model substrate to comprehensively investigate the effect of different anode potentials (- 150 mV, 0 mV and + 200 mV) on the relationship between current production, the electrogenic pathway and the abundance of the electrogenic microorganisms involved in batch mode fed BESs. Current production in glucose-acclimatized reactors was a function of the abundance of Geobacteraceae and of the availability of acetate and formate produced by glucose degradation. Current production was increased by high anode potentials during acclimation (0 mV and + 200 mV), likely due to more Geobacteraceae developing. However, this effect was much weaker than a stimulus from an artificial high acetate supply: acetate was the rate-limiting intermediate in these systems. The supply of acetate could not be influenced by anode potential; altering the flow regime, batch time and management of the upstream fermentation processes may be a greater engineering tool in BES. However, these findings suggest that if high current production is the focus, it will be extremely difficult to achieve success with complex waste streams such as domestic wastewater.

Coupling mixotrophic denitrification and electroactive anodic nitrification by nitrate addition for promoting current generation and nitrogen removal.

Nitrate promotes anodic denitrification and fasts organic matter removal in microbial fuel cells (MFCs). However, it suffers from poor total nitrogen (TN) removal and current recovery. In this study, some novel electroactive nitrifying/denitrifying bacteria (ENDB) were introduced in a single chambered air-cathode MFC to investigate the performance of this device and the microbial community shift by adding nitrate. Results showed a similar disturbance in current output by adding nitrate during a short-term operation. However, a stable and reproducible current increase was achieved in the continuous experiment. A maximum current of 0.76 A m-3 and a maximum TN removal of >99 % were accomplished. The corresponding corrected coulombic efficiency was approximately 18 %. Under repeatable batches, a sharp decrease in chemical oxygen demand (COD) with feeding nitrate confirmed the temporary competition on electron donors through heterotrophic denitrification. The later current increase and nitrite detection occurring without metabolized COD could be considered evidence of electroactive anodic nitrification. The ENDB biofilm successfully coupled mixotrophic denitrification and electroactive anodic nitrification. It eventually promoted TN removal. In the process, genera Pseudoxanthomonas, Thauera, and Pseudomonas were enriched in the anodic ENDB biofilms. Cyclic voltammetry data confirmed the promotion of the electron transfer process by biofilms. The bacterial function predication revealed that the genes related to nitrogen removal and electron transfer were upregulated. Therefore, mixotrophic denitrification and electroactive anodic nitrification processes facilitated power recovery with the high efficiency of pollutant removal, finally ensuring water body security.

Biodegradation of petroleum wastewater for the production of bioelectricity using activated sludge biomass.

Objective: This research is based on the treatment of petroleum wastewater (PWW) with pretreated activated sludge for the production of electricity and removal of chemical oxygen demand (COD) using microbial fuel cell (MFC). Methods: The application of the MFC system which uses activated sludge biomass (ASB) as a substrate resulted in the reduction of COD by 89.5% of the original value. It generated electricity equivalent to 8.18 mA/m2 which can be reused again. This would solve the majority of environmental crises which we are facing today. Results: This study discusses the application of ASB to enhance the degradation of PWW for the production of a power density of 1012.95 mW/m2 when a voltage of 0.75 V (voltage) is applied at 30:70% of ASB when MFC is operated in a continuous mode. Microbial biomass growth was catalyzed using activated sludge biomass. The growth of microbes was observed by scanning through an electron microscope. Through oxidation in the MFC system, bioelectricity is generated which is used in the cathode chamber. Furthermore, the MFC operated using ASB in a ratio of 35 with the current density, which decreased to 494.76 mW/m2 at 10% ASB. Application: Our experiments demonstrate that the efficiency of the MFC system can generate bioelectricity and treat petroleum wastewater by using activated sludge biomass.

The effect of additional salinity on performance of a phosphate buffer saline buffered three-electrode bioelectrochemical system inoculated with wastewater.

In bioelectrochemical system (BES), phosphate buffer saline (PBS) is usually used to achieve a suitable pH condition, which also increases electrolyte salinity. A series of factors that change with salinity will affect BES performance. To simplify the scenario, a three-electrode BES is used to investigate how additional salinity affects the performance of a 50 mM PBS-buffered BES. Results demonstrated that current production decreased with increasing salinity and the dominant exoelectrogens were not inhibited with the addition of 200 mM NaCl. The distribution of system resistance was analyzed by electrochemical impedance spectroscopy. Compared to the decreased solution and biofilm resistance, the increased interfacial resistance that accounted for up to 97.8% of total resistance was the dominant reason for the decreased current production with the increasing additional salinity. The effects of additional salinity on acetate degradation and columbic efficiency were also analyzed.

Tuning Geobacter sulfurreducens biofilm with conjugated polyelectrolyte for increased performance in bioelectrochemical system.

Bioelectrochemical systems (BESs) are emerging as a platform technology with great application potentials such as wastewater remediation and power generation. Materials for electrode/microorganism modification are being examined in order to improve the current production in BESs. Herein, we report that the current production increased almost one fold in single-chamber BES reactors, by adding a conjugated polyelectrolyte (CPE-K) in the growth medium to co-form the anodic biofilm with Geobacter sulfurreducens cells. The CPE-K treated BESs had a maximum current density as high as 12.3 ±â€¯0.5 A/m2, with that of the controls being 6.2 ±â€¯0.7 A/m2. Improved current production was sustained even after CPE-K was no longer added to the medium. It was demonstrated that increased current resulted from improvement of certain biofilm properties. Analysis using electrochemical impedance spectroscopy (EIS) showed that CPE-K addition decreased the charge transfer resistance at the cell/electrode interface and the diffusion resistance through the biofilm. Protein quantification showed increased biomass growth on the electrode surface, and confocal scanning microscopy images revealed enhanced biofilm permeability. These results demonstrated for the first time that conjugated polyelectrolytes could be used for G. sulfurreducens biofilm augmentation to achieve high electricity production through tuning the anodic biofilm in BESs.

Micro-oxygen bioanode: An efficient strategy for enhancement of phenol degradation and current generation in mix-cultured MFCs.

It is controversial to introduce oxygen into anode chamber as oxygen would decrease the CE (Coulombic efficiency) while it could also enhance the degradation of aromatics in microbial fuel cell (MFCs). Therefore, it is important to balance the pros and cons of oxygen in aromatics driven MFCs. A RMO (micro-oxygen bioanode MFC) was designed to determine the effect of oxygen on electricity output and phenol degradation. The RMO showed 6-fold higher phenol removal efficiency, 4-fold higher current generation than the RAN (anaerobic bioanode MFC) at a cost of 26.9% decline in CE. The Zoogloea and Geobacter, which account for phenol degradation and current generation, respectively, were dominated in the RMO bioanode biofilm. The biomass also showed great difference between RMO and RAN (114.3 ±â€¯14.1 vs. 2.2 ±â€¯0.5 nmol/g). Therefore, different microbial community, higher biomass as well as the different degradation pathway were suggested as reasons for the better performance in RMO.

Extracellular Electron Transfer via Outer Membrane Cytochromes in a Methanotrophic Bacterium Methylococcus capsulatus (Bath).

Electron exchange reactions between microbial cells and solid materials, referred to as extracellular electron transfer (EET), have attracted attention in the fields of microbial physiology, microbial ecology, and biotechnology. Studies of model species of iron-reducing, or equivalently, current-generating bacteria such as Geobacter spp. and Shewanella spp. have revealed that redox-active proteins, especially outer membrane c-type cytochromes (OMCs), play a pivotal role in the EET process. Recent (meta)genomic analyses have revealed that diverse microorganisms that have not been demonstrated to have EET ability also harbor OMC-like proteins, indicating that EET via OMCs could be more widely preserved in microorganisms than originally thought. A methanotrophic bacterium Methylococcus capsulatus (Bath) was reported to harbor multiple OMC genes whose expression is elevated by Cu starvation. However, the physiological role of these genes is unknown. Therefore, in this study, we explored whether M. capsulatus (Bath) displays EET abilities via OMCs. In electrochemical analysis, M. capsulatus (Bath) generated anodic current only when electron donors such as formate were available, and could reduce insoluble iron oxides in the presence of electron donor compounds. Furthermore, the current-generating and iron-reducing activities of M. capsulatus (Bath) cells that were cultured in a Cu-deficient medium, which promotes high levels of OMC expression, were higher than those cultured in a Cu-supplemented medium. Anodic current production by the Cu-deficient cells was significantly suppressed by disruption of MCA0421, a highly expressed OMC gene, and by treatment with carbon monoxide (CO) gas (an inhibitor of c-type cytochromes). Our results provide evidence of EET in M. capsulatus (Bath) and demonstrate the pivotal role of OMCs in this process. This study raises the possibility that EET to solid compounds is a novel survival strategy of methanotrophic bacteria.