Electricity production from xylose in fed-batch and continuous-flow microbial fuel cells

Discussion on Secure Standard Network of Sensors Powered by Microbial Fuel Cells

Everyday tasks use sensors to monitor and provide information about processes in different scenarios, such as monitoring devices in manufacturing or homes. Sensors need to communicate, with or without wires, while providing secure information. Power can be derived from various energy sources, such as batteries, electrical power grids, and energy harvesting. Energy harvesting is a promising way to provide a sustainable and renewable source to power sensors by scavenging and converting energy from ambient energy sources. However, low energy is harvested through these methods. Therefore, it is becoming a challenge to design and deploy wireless sensor networks while ensuring the sensors have enough power to perform their tasks and communicate with each other through careful management and optimization, matching energy supply with demand. For this reason, data cryptography and authentication are needed to protect sensor communication. This paper studies how energy harvested with microbial fuel cells can be employed in algorithms used in data protection during sensor communication.

Platinum nanoparticles embedded into polyaniline on carbon cloth: improvement of oxygen reduction at cathode of microbial fuel cell used for conversion of medicinal plant wastes into bio-energy

A microbial fuel cell is a biological electrochemical system that extracts electrons stored in organic matter by oxidation using catalytic properties of microorganisms at bioanode. The major problem in such device, is however limited power production due to slow kinetic of oxygen reduction at cathode. It is worthwhile to develop new materials that fulfil these requirements. The polymerization of aniline onto carbon cloth for effective electrodeposition of platinum nanoparticles has been carried out by chronoamperometry and cyclic voltammetry. Three materials were thus elaborated, namely pristine carbon cloth, carbon cloth modified with platinum and carbon cloth modified by polymerization of aniline for immobilization of Pt-nanoparticles. The FTIR spectroscopy analysis revealed characteristic band located in 1720-1650 cm^-1, attributed to imine function, main component in skeleton of polymer PANI chain. The modified materials have been utilized as cathode in cell inoculated with medicinal plant wastes for improvement of oxygen reduction. Modified cathode with CC-PANI-Pt proved higher performances in all respects: increase of cell voltage from 338 to 765 mV and power density from 862 to 1510 mW/m² and abatement of COD of microbial inoculum leachate to 88%. Another feature of cell with modified cathode CC-PANI-Pt, was the enormous electric charge density harvested upon oxidation of 1 mL of acetate 7.62 C/cm² compared to that of cell with pristine CC cathode 0.54 C/cm². Nevertheless, coulombic efficiency for conversion of medicinal plant wastes into bioenergy was relatively lower 9%, making in evidence that elaborated electrochemical device was rather efficient and benificial environmentally than energetically.

A review of the operating parameters on the microbial fuel cell for wastewater treatment and electricity generation

Environmental and economic considerations suggest a more efficient and comprehensive use of biomass for bioenergy production. One of the most attractive technologies is the microbial fuel cell using the catabolic activity of microorganisms to generate electricity from organic matter. The microbial fuel cell (MFC) has operational benefits and higher performance than current technologies for producing energy from organic materials because it converts electricity from the substrate directly (at ambient temperature). However, MFCs are still not suitable for high energy demand due to practical limitations. The overall performance of an MFC depends on the electrode material, the reactor design, the operating parameters, substrates, and microorganisms. Furthermore, the optimization of the parameters will lead to the commercial development of this technology in the near future. The simultaneous effect of the parameters on each other (intensifier or attenuator) has also been investigated. The investigated parameters in this study include temperature, pH, flow rate and hydraulic retention time, mode, external resistance, and initial concentration.

The reaction of wastewater treatment and power generation of single chamber microbial fuel cell against substrate concentration and anode distributions

This study demonstrated the effectiveness of single chamber up-flow membrane-less microbial fuel cell (UFML-MFC) in wastewater treatment concurrently with bioelectricity generation. The objectives of this study were to examine the effect of influent substrate concentration (0.405 g/L, 0.810 g/L, 1.215 g/L, 1.620 g/L), anode distributions (11 cm, 17 cm, 23 cm ) and surface morphologies for biofilm formation on the performance of wastewater treatment and power generation. The optimum performance was obtained with substrate concentration of 0.810 g/L. The COD removal efficiency, output voltage, internal resistance, power density and current density obtained were 84.64%, 610 mV, 200 Ω, 162.59 mW/m2 and 468.74 mA/m2, respectively. The Coulombic Efficiency (CE), Normalized Energy Recovery (NERS and NERv) were 1.03%, 789.38 kWh/kg COD and 22.56 kWh/m3, respectively. The results also indicate that the output voltage and power generation obtained in a continuous up-flow MFC were higher with A3 (23 cm), which is of larger electrodes spacing followed by A2 (17 cm) and A1 (11 cm) caused by the enrichment of anaerobic microbial population at A1.

Storing of exoelectrogenic anolyte for efficient microbial fuel cell recovery

Starting up a microbial fuel cell (MFC) requires often a long-term culture enrichment period, which is a challenge after process upsets. The purpose of this study was to develop low-cost storage for MFC enrichment culture to enable prompt process recovery after upsets. Anolyte of an operating xylose-fed MFC was stored at different temperatures and for different time periods. Storing the anolyte for 1 week or 1 month at +4°C did not significantly affect power production, but the lag time for power production was increased from 2 days to 3 or 5 days, respectively. One month storing at -20°C increased the lag time to 7 days. The average power density in these MFCs varied between 1.2 and 1.7 W/m³. The share of dead cells (measured by live/dead staining) increased with storing time. After 6-month storage, the power production was insignificant. However, xylose removal remained similar in all cultures (99-100%) while volatile fatty acids production varied. The results indicate that fermentative organisms tolerated the long storage better than the exoelectrogens. As storing at +4°C is less energy intensive compared to freezing, anolyte storage at +4°C for a maximum of 1 month is recommended as start-up seed for MFC after process failure to enable efficient process recovery.

Composition and role of the attached and planktonic microbial communities in mesophilic and thermophilic xylose-fed microbial fuel cells

A mesophilic (37 °C) and a thermophilic (55 °C) two-chamber microbial fuel cell (MFC) were studied and compared for their power production from xylose and the anode-attached, membrane-attached and planktonic microbial communities involved.

Engineering Shewanella oneidensis enables xylose-fed microbial fuel cell

BACKGROUND

The microbial fuel cell (MFC) is a green and sustainable technology for electricity energy harvest from biomass, in which exoelectrogens use metabolism and extracellular electron transfer pathways for the conversion of chemical energy into electricity. However, Shewanella oneidensis MR-1, one of the most well-known exoelectrogens, could not use xylose (a key pentose derived from hydrolysis of lignocellulosic biomass) for cell growth and power generation, which limited greatly its practical applications.

RESULTS

Herein, to enable S. oneidensis to directly utilize xylose as the sole carbon source for bioelectricity production in MFCs, we used synthetic biology strategies to successfully construct four genetically engineered S. oneidensis (namely XE, GE, XS, and GS) by assembling one of the xylose transporters (from Candida intermedia and Clostridium acetobutylicum) with one of intracellular xylose metabolic pathways (the isomerase pathway from Escherichia coli and the oxidoreductase pathway from Scheffersomyces stipites), respectively. We found that among these engineered S. oneidensis strains, the strain GS (i.e. harbouring Gxf1 gene encoding the xylose facilitator from C. intermedi, and XYL1, XYL2, and XKS1 genes encoding the xylose oxidoreductase pathway from S. stipites) was able to generate the highest power density, enabling a maximum electricity power density of 2.1 ± 0.1 mW/m².

CONCLUSION

To the best of our knowledge, this was the first report on the rationally designed Shewanella that could use xylose as the sole carbon source and electron donor to produce electricity. The synthetic biology strategies developed in this study could be further extended to rationally engineer other exoelectrogens for lignocellulosic biomass utilization to generate electricity power.

Segregation of the Anodic Microbial Communities in a Microbial Fuel Cell Cascade

Metabolic interactions within microbial communities are essential for the efficient degradation of complex organic compounds, and underpin natural phenomena driven by microorganisms, such as the recycling of carbon-, nitrogen-, and sulfur-containing molecules. These metabolic interactions ultimately determine the function, activity and stability of the community, and therefore their understanding would be essential to steer processes where microbial communities are involved. This is exploited in the design of microbial fuel cells (MFCs), bioelectrochemical devices that convert the chemical energy present in substrates into electrical energy through the metabolic activity of microorganisms, either single species or communities. In this work, we analyzed the evolution of the microbial community structure in a cascade of MFCs inoculated with an anaerobic microbial community and continuously fed with a complex medium. The analysis of the composition of the anodic communities revealed the establishment of different communities in the anodes of the hydraulically connected MFCs, with a decrease in the abundance of fermentative taxa and a concurrent increase in respiratory taxa along the cascade. The analysis of the metabolites in the anodic suspension showed a metabolic shift between the first and last MFC, confirming the segregation of the anodic communities. Those results suggest a metabolic interaction mechanism between the predominant fermentative bacteria at the first stages of the cascade and the anaerobic respiratory electrogenic population in the latter stages, which is reflected in the observed increase in power output. We show that our experimental system represents an ideal platform for optimization of processes where the degradation of complex substrates is involved, as well as a potential tool for the study of metabolic interactions in complex microbial communities.

Highly efficient rice straw utilization for poly-(γ-glutamic acid) production by Bacillus subtilis NX-2

Lignocellulosic biomass has been identified as an economic and environmental feedstock for future biotechnological production. Here, for the first time, poly-(γ-glutamic acid) (PGA) production by Bacillus subtilis NX-2 using rice straw is investigated. Based on two-stage hydrolysis and characteristic consumption of xylose and glucose by B. subtilis NX-2, a co-fermentation strategy was designed to better accumulate PGA in a 7.5L fermentor by two feeding methods. The maximum cumulative respective PGA production and PGA productivity were 73.0 ± 0.5 g L(-1) and 0.81 g L(-1) h(-1) by the continuous feeding method, with carbon source cost was saved by 84.2% and 42.5% compared with glucose and cane molasse, respectively. These results suggest that rice straw, a type of abundant, low-cost, non-food lignocellulosic feedstock, may be feasibly and efficiently utilized for industrial-scale production of PGA.

A high performance xylose microbial fuel cell enabled by Ochrobactrum sp. 575 cells

A new bacterium, Ochrobactrum sp. 575, is applied as a high performance MFC while resolving xylose, and the formation of fumaric acid is observed during the discharging process.

Bioelectricity generation in continuously-fed microbial fuel cell: effects of anode electrode material and hydraulic retention time

The main aim of this study is to investigate the bioelectricity production in continuously-fed dual chambered microbial fuel cell (MFC). Initially, MFC was operated with different anode electrode material at constant hydraulic retention time (HRT) of 2d to evaluate the effect of electrode material on electricity production. Pt electrode yielded about 642 mW/m(2) power density, which was 4 times higher than that of the MFC with the mixed metal oxide titanium (Ti-TiO2). Further, MFC equipped with Pt electrode was operated at varying HRT (2-0.5d). The power density generation increased with decreasing HRT, corresponding to 1313 mW/m(2) which was maximum value obtained during this study. Additionally, decreasing HRT from 2 to 0.5d resulted in increasing effluent dissolved organic carbon (DOC) concentration from 1.92 g/L to 2.23 g/L, corresponding to DOC removal efficiencies of 46% and 38%, respectively.

Experimental and theoretical characterization of microbial bioanodes formed in pulp and paper mill effluent in electrochemically controlled conditions

Microbial bioanodes were formed in pulp and paper effluent on graphite plate electrodes under constant polarization at -0.3 V/SCE, without any addition of nutriment or substrate. The bioanodes were characterized in 3-electrode set-ups, in continuous mode, with hydraulic retention times from 6 to 48 h and inlet COD from 500 to 5200 mg/L. Current densities around 4A/m(2) were obtained and voltammetry curves indicated that 6A/m(2) could be reached at +0.1 V/SCE. A theoretical model was designed, which allowed the effects of HRT and COD to be distinguished in the complex experimental data obtained with concomitant variations of the two parameters. COD removal due to the electrochemical process was proportional to the hydraulic retention time and obeyed a Michaelis-Menten law with respect to the COD of the outlet flow, with a Michaelis constant KCOD of 400mg/L. An inhibition effect occurred above inlet COD of around 3000 mg/L.

Lowering the applied potential during successive scratching/re-inoculation improves the performance of microbial anodes for microbial fuel cells

Microbial anodes were formed under polarisation at -0.2V/SCE on smooth graphite plate electrodes with paper mill effluents. Primary, secondary and tertiary biofilms were formed by a successive scratching and re-inoculation procedure. The secondary and tertiary biofilms formed while decreasing the polarisation potential allowed the anodes to provide current density of 6A/m(2) at -0.4V/SCE. In contrast, applying -0.4V/SCE initially to form the primary biofilms did not lead to the production of current. Consequently, the scratching/re-inoculation procedure combined with progressive lowering of the applied potential revealed an efficient new procedure that gave efficient microbial anodes able to work at low potential. The observed progressive pH drift to alkaline values above 9 explained the open circuit potentials as low as -0.6 V/SCE. The remarkable performance of the electrode at alkaline pH was attributed to the presence of Desulfuromonas acetexigens as the single dominant species in the tertiary microbial anodes.

Simultaneous water desalination and electricity generation in a microbial desalination cell with electrolyte recirculation for pH control

A recirculation microbial desalination cell (rMDC) was designed and operated to allow recirculation of solutions between the anode and cathode chambers. This recirculation avoided pH imbalances that could inhibit bacterial metabolism. The maximum power density was 931±29mW/m(2) with a 50mM phosphate buffer solution (PBS) and 776±30mW/m(2) with 25mM PBS. These power densities were higher than those obtained without recirculation of 698±10mW/m(2) (50mM PBS) and 508±11mW/m(2) (25mM PBS). The salt solution (20g/L NaCl) was reduced in salinity by 34±1% (50mM) and 37±2% (25mM) with recirculation (rMDC), and by 39±1% (50mM) and 25±3% (25mM) without recirculation (MDC). These results show that electrolyte recirculation using an rMDC is an effective method to increase power and achieve efficient desalination by eliminating pH imbalances.

Degradation of pentachlorophenol with the presence of fermentable and non-fermentable co-substrates in a microbial fuel cell

Pentachlorophenol (PCP) was more rapidly degraded in acetate and glucose-fed microbial fuel cells (MFCs) than in open circuit controls, with removal rates of 0.12 ± 0.01 mg/Lh (14.8 ± 1.0 mg/g-VSS-h) in acetate-fed, and 0.08 ± 0.01 mg/L h (6.9 ± 0.8 mg/g-VSS-h) in glucose-fed MFCs, at an initial PCP concentration of 15 mg/L. A PCP of 15 mg/L had no effect on power generation from acetate but power production was decreased with glucose. Coulombic balances indicate the predominant product was electricity (16.1 ± 0.3%) in PCP-acetate MFCs, and lactate (19.8 ± 3.3%) in PCP-glucose MFCs. Current generation accelerated the removal of PCP and co-substrates, as well as the degradation products in both PCP-acetate and PCP-glucose reactors. While 2,3,4,5-tetrachlorophenol was present in both reactors, tetrachlorohydroquinone was only found in PCP-acetate MFCs. These results demonstrate PCP degradation and power production were affected by current generation and the type of electron donor provided.

Enhanced Coulombic efficiency in glucose-fed microbial fuel cells by reducing metabolite electron losses using dual-anode electrodes

Glucose-fed microbial fuel cells (MFCs) have displayed low Coulombic efficiency (CE); one reason for a low CE is metabolite generation, causing significant electron loss within MFC systems. In the present study, notable electron loss (15.83%) is observed in glucose-fed MFCs due to residual propionate, a glucose metabolite. In order to enhance the low CE caused by metabolite generation, a dual-anode MFC (DAMFC) is constructed, which are separately enriched by dissimilar substrates (glucose and propionate, respectively) to effectively utilize both glucose and propionate in one-anode chamber. In the DAMFC, propionate ceases to exist as a source of electron loss, and thus the CE increased from 33 ± 6 to 59 ± 4%.

Treatment of wastewater from Dioscorea zingiberensis tubers used for producing steroid hormones in a microbial fuel cell

A two-chamber microbial fuel cell (MFC) was used to treat Dioscorea zingiberensis processing wastewater and generate electricity. The contaminant degradation process was systematically investigated with the help of UV-Vis, FTIR spectra and GC-MS. The results showed that the COD removal efficiency of the MFC reached 93.5% and the maximum power density achieved 175 mW/m(2). In the anodic chamber, low molecule weight acid, sugars and cellulose in D. zingiberensis processing wastewater were completely consumed, while complicated contaminants including some furanic and phenolic compounds were decomposed under co-metabolism process. In the cathodic chamber, fatty ester and alkene generated in the anodic chamber were removed, and aromatic compounds were further degraded. Aromatic ester and N-containing compounds were detected as the main residual contaminants by GC-MS. Compared to the effluents of anaerobic digestion and biological aerated filter, fewer and simpler aromatic pollutants existed in the effluents of MFC.

Generation of electricity and analysis of microbial communities in wheat straw biomass-powered microbial fuel cells

Electricity generation from wheat straw hydrolysate and the microbial ecology of electricity-producing microbial communities developed in two-chamber microbial fuel cells (MFCs) were investigated. The power density reached 123 mW/m(2) with an initial hydrolysate concentration of 1,000 mg chemical oxygen demand (COD)/liter, while coulombic efficiencies ranged from 37.1 to 15.5%, corresponding to the initial hydrolysate concentrations of 250 to 2,000 mg COD/liter. The suspended bacteria found were different from the bacteria immobilized in the biofilm, and they played different roles in electricity generation from the hydrolysate. The bacteria in the biofilm were consortia with sequences similar to those of Bacteroidetes (40% of sequences), Alphaproteobacteria (20%), Bacillus (20%), Deltaproteobacteria (10%), and Gammaproteobacteria (10%), while the suspended consortia were predominately Bacillus (22.2%). The results of this study can contribute to improving understanding of and optimizing electricity generation in microbial fuel cells.

Reducing organic loads in wastewater effluents from paper recycling plants using microbial fuel cells

Many industries are charged fees based on the organic loads in effluents. Therefore, it can be advantageous to reduce the wastewater strength prior to discharge. We investigated the use of microbial fuel cells (MFCs) to reduce the chemical oxygen demand (COD) of a paper-plant wastewater while at the same time producing electricity in a continuous flow system. At a hydraulic retention time (HRT) of six hours, COD removal using an unamended wastewater (506 mg/L COD) (organic loading rate, OLR = 2.0 kg COD/(m3 d)) was 26 +/- 2%, with a power density of 5.9 +/- 0.2 W/m3 (210 +/- 7 mW/m2). This amount of power was similar to the maximum power density (5.2 +/- 0.4 W/m3) produced in fed-batch tests using a slightly lower strength wastewater in the same device (405 mg/L COD). Increasing the HRT to 25 h (OLR = 0.5 kg COD/(m3 d)) increased COD removal (41 +/- 2%) but substantially decreased power (2.8 +/- 0.3 W/m3). While wastewater strength affected removal rates, the solution conductivity (0.8 mS/cm) was primarily a factor in low power production. These results demonstrate that MFCs can be used to reduce organic loads in effluents at relatively short HRTs, while at the same time generating power.