The role of riboflavin in decolourisation of Congo red and bioelectricity production using <Emphasis Type="Italic">Shewanella oneidensis</Emphasis>-MR1 under MFC and non-MFC conditions

Dissimilatory metal reducing bacteria can exchange electrons extracellularly and hold great promise for their use in simultaneous wastewater treatment and electricity production. This study investigated the role of riboflavin, an electron carrier, in the decolourisation of Congo red in microbial fuel cells (MFCs) using Shewanella oneidensis MR-1 as a model organism. The contribution of the membrane-bound protein MtrC to the decolourisation process was also investigated. Within the range of riboflavin concentrations tested, 20 µM was found to be the best with >95% of the dye (initial concentration 200 mg/L) decolourised in MFCs within 50 h compared to 90% in the case where no riboflavin was added. The corresponding maximum power density was 45 mW/m². There was no significant difference in the overall decolourisation efficiencies of Shewanela oneidensis MR-1 ΔMtrC mutants compared to the wild type. However, in terms of power production the mutant produced more power (P_max 76 mW/m²) compared to the wild type (P_max 46 mW/m²) which was attributed to higher levels of riboflavin secreted in solution. Decolourisation efficiencies in non-MFC systems (anaerobic bottles) were similar to those under MFC systems indicating that electricity generation in MFCs does not impair dye decolourisation efficiencies. The results suggest that riboflavin enhances both decolourisation of dyes and simultaneous electricity production in MFCs.     

Increased power generation from primary sludge by a submersible microbial fuel cell and optimum operational conditions

Microbial fuel cells (MFCs) have received attention as a promising renewable energy technology for waste treatment and energy recovery. We tested a submersible MFC with an innovative design capable of generating a stable voltage of 0.250 ± 0.008 V (with a fixed 470 Ω resistor) directly from primary sludge. In a polarization test, the maximum power density was 0.18 W/m² at a current density of 0.8 A/m² with an external resistor of 300 Ω. The anodic solution of the primary sludge needs to be adjusted to a pH 7 for high power generation. The modified primary sludge with an added phosphate buffer prolonged the current generation and increased the power density by 7 and 1.5 times, respectively, in comparison with raw primary sludge. These findings suggest that energy recovery from primary sludge can be maximized using an advanced MFC system with optimum conditions.     

Power generation from cassava alcohol wastewater: effects of pretreatment and anode aeration

Cassava alcohol wastewater produced from the bioethanol production industry is carbohydrate-rich wastewater with large quantities of insoluble organic compounds. Microbial fuel cells (MFCs) were used for electricity recovery and pollutants removal from this wastewater. Different pretreatment methods (solid–liquid separation, ultrasonication, pre-fermentation) and anode-aeration modes were explored in MFCs aimed to enhance the efficiency of power generation and pollutants removal. Pre-fermentation was found to be the most effective pretreatment method. A maximum power density of 437.13 ± 15.6 mW/m² and TCOD removal of 62.5 ± 3.5 % were achieved using the pre-fermented wastewater, 150 and 20 % higher than the un-pretreated control. Aeration in anode chamber could promote the hydrolysis of organic matter and production of VFAs in the raw wastewater, and increase TCOD removal and power density. Pre-fermentation coupled with halfway anode aeration may be a feasible strategy to enhance power generation and pollutants removal from the cassava wastewater in MFCs.     

Growth of <Emphasis Type="Italic">Salinispora tropica</Emphasis> strains CNB440, CNB476, and NPS21184 in nonsaline,low-sodium media

Effective wastewater treatment using microbial fuel cells (MFCs) will require a better understanding of how operational parameters and solution chemistry affect treatment efficiency, but few studies have examined power generation using actual wastewaters. The efficiency of wastewater treatment of a beer brewery wastewater was examined here in terms of maximum power densities, Coulombic efficiencies (CEs), and chemical oxygen demand (COD) removal as a function of temperature and wastewater strength. Decreasing the temperature from 30°C to 20°C reduced the maximum power density from 205 mW/m² (5.1 W/m³, 0.76 A/m²; 30°C) to 170 mW/m² (20°C). COD removals (R _COD) and CEs decreased only slightly with temperature. The buffering capacity strongly affected reactor performance. The addition of a 50-mM phosphate buffer increased power output by 136% to 438 mW/m², and 200 mM buffer increased power by 158% to 528 mW/m². In the absence of salts (NaCl), maximum power output varied linearly with wastewater strength (84 to 2,240 mg COD/L) from 29 to 205 mW/m². When NaCl was added to increase conductivity, power output followed a Monod-like relationship with wastewater strength. The maximum power (P _max) increased in proportion to the solution conductivity, but the half-saturation constant was relatively unaffected and showed no correlation to solution conductivity. These results show that brewery wastewater can be effectively treated using MFCs, but that achievable power densities will depend on wastewater strength, solution conductivity, and buffering capacity.     

Layer-by-layer construction of graphene-based microbial fuel cell for improved power generation and methyl orange removal

Development of highly efficient anode is critical for enhancing the power output of microbial fuel cells (MFCs). The aim of this work is to investigate whether modification of carbon paper (CP) anode with graphene (GR) via layer-by-layer assembly technique is an effective approach to promote the electricity generation and methyl orange removal in MFCs. Using cyclic voltammetry and electrochemical impedance spectroscopy, the GR/CP electrode exhibited better electrochemical behavior. Scanning electron microscopy results revealed that the surface roughness of GR/CP increased, which was favorable for more bacteria to attach to the anode surface. The MFCs equipped with GR/CP anode achieved a stable maximum power density of 368 mW m^?2 under 1,000 Ω external resistance and a start time for the initial maximum voltage of 180 h, which were, respectively, 51 % higher and 31 % shorter than the corresponding values of the MFCs with blank anode. The anode and cathode polarization curves revealed negligible difference in cathode potentials but obviously difference in anode potentials, indicating that the GR-modified anode other than the cathode was responsible for the performance improvement of MFC. Meanwhile, compared with MFCs with blank anode, 11 % higher decolorization efficiency and 16 % higher the chemical oxygen demand removal rate were achieved in MFC with GR-modified anode during electricity generation. This study might provide an effective way to modify the anode for enhanced electricity generation and efficient removal of azo dye in MFCs.     

Electrochemical analysis of Clostridium propionicum and its acrylic acid production in microbial fuel cells

Currently, acrylic acid is produced at a low yield by the resting cells of Clostridium propionicum with the supplement of extra electron acceptors. As an alternative way, acrylic acid production coupled with electricity generation was achieved by C. propionicum‐based microbial fuel cells (MFCs). Electricity was generated in the salt‐bridge MFCs with cysteine and resazurin in the anode chamber as mediators, and K₃Fe(CN)₆ as the cathode electron acceptor. Power generation was 21.78 mW/m² with an internal resistance of 9809 Ω. Cyclic voltammograms indicated the main mechanism of power production was the electron transfer facilitated by mediators in the system. In the salt‐bridge MFC system, 0.694 mM acrylic acid was produced together with electricity generation.     

Domestic wastewater treatment using multi-electrode continuous flow MFCs with a separator electrode assembly design

Treatment of domestic wastewater using microbial fuel cells (MFCs) will require reactors with multiple electrodes, but this presents unique challenges under continuous flow conditions due to large changes in the chemical oxygen demand (COD) concentration within the reactor. Domestic wastewater treatment was examined using a single-chamber MFC (130 mL) with multiple graphite fiber brush anodes wired together and a single air cathode (cathode specific area of 27 m²/m³). In fed-batch operation, where the COD concentration was spatially uniform in the reactor but changed over time, the maximum current density was 148?±?8 mA/m² (1,000 Ω), the maximum power density was 120 mW/m², and the overall COD removal was >90 %. However, in continuous flow operation (8 h hydraulic retention time, HRT), there was a 57 % change in the COD concentration across the reactor (influent versus effluent) and the current density was only 20?±?13 mA/m². Two approaches were used to increase performance under continuous flow conditions. First, the anodes were separately wired to the cathode, which increased the current density to 55?±?15 mA/m². Second, two MFCs were hydraulically connected in series (each with half the original HRT) to avoid large changes in COD among the anodes in the same reactor. The second approach improved current density to 73?±?13 mA/m². These results show that current generation from wastewaters in MFCs with multiple anodes, under continuous flow conditions, can be improved using multiple reactors in series, as this minimizes changes in COD in each reactor.     

Production of Electricity and Butanol from Microalgal Biomass in Microbial Fuel Cells

Chlorella vulgaris (a freshwater microalga) and Dunaliella tertiolecta (a marine microalga) were grown for bulk harvest, and their biomass was tested as feedstock for electricity production in cubic two-chamber microbial fuel cells (MFCs) at 37°C. The anode inoculum was anaerobic consortium from a municipal sewage sludge digester, enriched separately for the two microalgal biomass feedstocks. After repeated subculturing of the two anaerobic enrichments, the maximum power density obtained in MFCs was higher from C. vulgaris (15.0 vs. 5.3 mW m^?2) while power generation was more sustained from D. tertiolecta (13 vs. 9.8 J g^-1 volatile solids). Anolytes of algal biomass-fed MFCs also contained substantial levels of butanol (8.7–16 mM with C. vulgaris and 2.5–7.0 mM with D. tertiolecta), which represents an additional form of utilizable energy. Carryover of salts from the marine D. tertiolecta biomass slurry resulted in gradual precipitation of Ca and Mg phosphates on the cathode side of the MFC. Polymerase chain reaction-denaturing gradient gel electrophoresis profiling and sequencing of bacterial communities demonstrated the presence of Wolinella succinogenes and Bacteroides and Synergistes spp. as well as numerous unknown bacteria in both enrichments. The D. tertiolecta enriched consortium contained also Geovibrio thiophilus and Desulfovibrio spp. Thus, the results indicate potential for combining fermentation and anaerobic respiration for bioenergy production from photosynthetic biomass.     

Control of malodorous hydrogen sulfide compounds using microbial fuel cell

In this study, a microbial fuel cell (MFC) was used to control malodorous hydrogen sulfide compounds generated from domestic wastewaters. The electricity production demonstrated a distinct pattern of a two-step increase during 170 h of system run: the first maximum current density was 118.6 ± 7.2 mA m^?2 followed by a rebound of current density increase, reaching the second maximum of 176.8 ± 9.4 mA m^?2. The behaviors of the redox potential and the sulfate level in the anode compartment indicated that the microbial production of hydrogen sulfide compounds was suppressed in the first stage, and the hydrogen sulfide compounds generated from the system were removed effectively as a result of their electrochemical oxidation, which contributed to the additional electricity production in the second stage. This was also directly supported by sulfur deposits formed on the anode surface, which was confirmed by analyses on those solids using a scanning electron microscope equipped with energy dispersive X-ray spectroscopy as well as an elemental analyzer. To this end, the overall reduction efficiencies for HS^? and H₂S_(g) were as high as 67.5 and 96.4 %, respectively. The correlations among current density, redox potential, and sulfate level supported the idea that the electricity signal generated in the MFC can be utilized as a potential indicator of malodor control for the domestic wastewater system.     

Performance of microbial fuel cell in response to change in sludge loading rate at different anodic feed pH

Performance of two dual chambered mediator-less microbial fuel cells (MFCs) was evaluated at different sludge loading rate (SLR) and feed pH. Optimum performance in terms of organic matter removal and power production was obtained at the SLR of 0.75 kg COD kg VSS⁻¹ d⁻¹. Maximum power density of 158 mW/m² and 600 mW/m² was obtained in MFC-1 (feed pH 6.0) and MFC-2 (feed pH 8.0), respectively. Internal resistance of the cell decreased with increase in SLR. When operated only with biofilm on anode, the maximum power density was 109.5 mW/m² in MFC-1 and 459 mW/m² in MFC-2, which was, respectively, 30% and 23.5% less than the value obtained in MFC-1 and MFC-2 at SLR of 0.75 kg COD kg VSS⁻¹ d⁻¹. Maximum volumetric power of 15.51 W/m³ and 36.72 W/m³ was obtained in MFC-1 and MFC-2, respectively, when permanganate was added as catholyte. Higher feed pH (8.0) favoured higher power production.     

Treatment of biodiesel production wastes with simultaneous electricity generation using a single-chamber microbial fuel cell

Biodiesel production through transesterification of lipids generates large quantity of biodiesel waste (BW) containing mainly glycerin. BW can be treated in various ways including distillation to produce glycerin, use as substrate for fermentative propanediol production and discharge as wastes. This study examined microbial fuel cells (MFCs) to treat BW with simultaneous electricity generation. The maximum power density using BW was 487 ± 28 mW/m² cathode (1.5 A/m² cathode) with 50 mM phosphate buffer solution (PBS) as the electrolyte, which was comparable with 533 ± 14 mW/m² cathode obtained from MFCs fed with glycerin medium (COD 1400 mg/L). The power density increased from 778 ± 67 mW/m² cathode using carbon cloth to 1310 ± 15 mW/m² cathode using carbon brush as anode in 200 mM PBS electrolyte. The power density was further increased to 2110 ± 68 mW/m² cathode using the heat-treated carbon brush anode. Coulombic efficiencies (CEs) increased from 8.8 ± 0.6% with carbon cloth anode to 10.4 ± 0.9% and 18.7 ± 0.9% with carbon brush anode and heat-treated carbon brush anode, respectively.     

Improved performance of membrane free single-chamber air-cathode microbial fuel cells with nitric acid and ethylenediamine surface modified activated carbon fiber felt anodes

Surface modifications of anode materials are important for enhancing power generation of microbial fuel cell (MFC). Membrane free single-chamber air-cathode MFCs, MFC-A and MFC-N, were constructed using activated carbon fiber felt (ACF) anodes treated by nitric acid and ethylenediamine (EDA), respectively. Experimental results showed that the start-up time to achieve the maximum voltages for the MFC-A and MFC-N was shortened by 45% and 51%, respectively as compared to that for MFC-AT equipped with an unmodified anode. Moreover, the power output of MFCs with modified anodes was significantly improved. In comparison with MFC-AT which had a maximum power density of 1304 mW/m², the MFC-N achieved a maximum power density of 1641 mW/m². The nitric acid-treated anode in MFC-A increased the power density by 58% reaching 2066 mW/m². XPS analysis of the treated and untreated anode materials indicated that the power enhancement was attributable to the changes of surface functional groups.     

Coupling microbial fuel cells with a membrane photobioreactor for wastewater treatment and bioenergy production

Microbial fuel cells (MFCs) and membrane photobioreactors are two emerging technologies for simultaneous wastewater treatment and bioenergy production. In this study, those two technologies were coupled to form an integrated treatment system, whose performance was examined under different operating conditions. The coupled system could achieve 92–97 % removal of soluble chemical oxygen demand (SCOD) and nearly 100 % removal of ammonia. Extending the hydraulic retention time (HRT) of the membrane photobioreactor to 3.0 days improved the production of algal biomass from 44.4 ± 23.8 to 133.7 ± 12.9 mg L^?1 (based on the volume of the treated water). When the MFCs were operated in a loop mode, their effluent (which was the influent to the algal reactor) contained nitrate and had a high pH, leading to the decreased algal production in the membrane photobioreactor. Energy analysis showed that the energy consumption was mainly due to the recirculation of the anolyte and the catholyte in the MFCs and that decreasing the recirculation rates could significantly reduce energy consumption. The energy production was dominated by indirect electricity generation from algal biomass. The highest energy production of 0.205 kWh m^?3 was obtained with the highest algal biomass production, resulting in a theoretically positive energy balance of 0.033 kWh m^?3. Those results have demonstrated that the coupled system could be an alternative approach for energy-efficient wastewater treatment and using wastewater effluent for algal production.     

Effect of enrichment procedures on performance and microbial diversity of microbial fuel cell for Congo red decolorization and electricity generation

The purpose of this study was to determine the effect of enrichment procedure on the performance and microbial diversity of an air-cathode microbial fuel cell (MFC) which was explored for simultaneous azo dye decolorization and electricity generation. Two different enrichment procedures in which glucose and Congo red were added into the MFCs sequentially (EP1) or simultaneously (EP2) were tested by operating parallel MFCs independently for more than 6 months. The power density, electrode potential, Congo red decolorization, biofilm morphology, and bacterial diversity of the MFCs under the two enrichment procedures were compared and investigated. The results showed that the enrichment procedures have a negligible effect on the dye decolorization, but significantly affected the electricity generation. More than 90% decolorization at dye concentration of 300 mg/L was achieved within 170 h for the two tested enrichment procedures. However, the MFC with EP2 achieved a maximum power density of 192 mW/m², which was 75% higher than that of the MFC with EP1 (110 mW/m²). The depressed surfaces of the bacteria in the MFC with EP1 indicated the allergic response caused by the subsequent addition of Congo red. 16S rRNA sequencing analysis demonstrated a phylogenetic diversity in the communities of the anode biofilm and showed clear differences between the anode-attached populations in the MFCs with a different enrichment procedure. This study suggests that the enrichment procedure is important for the MFC explored for simultaneous dye decolorization and electricity generation.     

Proton exchange membrane and electrode surface areas as factors that affect power generation in microbial fuel cells

Power generation in microbial fuel cells (MFCs) is a function of the surface areas of the proton exchange membrane (PEM) and the cathode relative to that of the anode. To demonstrate this, the sizes of the anode and cathode were varied in two-chambered MFCs having PEMs with three different surface areas (A _PEM=3.5, 6.2, or 30.6 cm²). For a fixed anode and cathode surface area (A _An=A _Cat=22.5 cm²), the power density normalized to the anode surface area increased with the PEM size in the order 45 mW/m² (A _PEM=3.5 cm²), 68 mW/m² (A _PEM=6.2 cm²), and 190 mW/m² (A _PEM=30.6 cm²). PEM surface area was shown to limit power output when the surface area of the PEM was smaller than that of the electrodes due to an increase in internal resistance. When the relative cross sections of the PEM, anode, and cathode were scaled according to 2A _Cat=A_PEM=2A _An, the maximum power densities of the three different MFCs, based on the surface area of the PEM (A _PEM=3.5, 6.2, or 30.6 cm²), were the same (168±4.53 mW/m²). Increasing the ionic strength and using ferricyanide at the cathode also increased power output.     

微生物燃料电池利用乳酸产电性能与微生物群落分布特征

【目的】为探讨以乳酸为基质的微生物燃料电池(Microbial fuel cell,MFC)产电性能以及微生物群落在阳极膜、悬浮液、阳极沉淀污泥中的分布特征,【方法】试验建立了双室MFC,以乳酸为阳极主要碳源,研究了反应器的启动过程及产电效能,同时以电镜和PCR-变性梯度凝胶电泳(Denaturing gradient gelelectrophoresis,DGGE)技术解析了微生物群落的空间分布特征。【结果】结果表明,反应器启动第7天时外电压达到0.56 V,当外阻为80Ω时,电流密度为415 mA/m2,MFC的功率密度达到最大值82 mW/m2。电镜观察发现大量杆菌附着在阳极表面,结合较为紧密;DGGE图谱显示阳极膜表面微生物与种泥最为相似,与阳极悬浮液、底部沉淀污泥中的主要菌群一致,条带序列与睾丸酮丛毛单胞菌(Comamonas testosteroni)和布氏弓形菌(Arcobacter butzleri)等最为相似。【结论】本研究表明以乳酸为基质MFC可产生较高的功率密度,阳极附着的优势菌与接种污泥来源密切相关。     

Bioelectricity production from acidic food waste leachate using microbial fuel cells: Effect of microbial inocula

The effects of three different inocula (domestic wastewater, activated sludge, and anaerobic sludge) on the treatment of acidic food waste leachate in microbial fuel cells (MFCs) were evaluated. A food waste leachate (pH 4.76; 1000 mg chemical oxygen demand (COD)/L) was used as the substrate. The results indicate that the leachate itself can enable electricity production in an MFC, but the co-addition of different inocula significantly reduces the start-up time (approximately 7 days). High COD and volatile fatty acids removal (>87%) were obtained in all MFCs but with only low coulombic efficiencies (CEs) (14–20%). The highest power (432 mW/m³) and CE (20%) were obtained with anaerobic sludge as the co-inoculum. Microbial community analysis (PCR-DGGE) of the established biofilms suggested that the superior performance of the anaerobic sludge-MFC was associated with the enrichment of both fermentative (Clostridium sp. and Bacteroides sp.) and electrogenic bacteria (Magnetospirillum sp. and Geobacter sp.) at the anode.     

Indole oxidation enhances electricity production in an E. coli-catalyzed microbial fuel cell

Microbial fuel cells (MFCs) generate electricity from the oxidation of dissolved organic matter. A variety of Gram-positive and Gram-negative bacteria, including Escherichia coli, produce a large quantity of indole, which functions as an extracellular signal molecule. This work explored the role of indole in a mediatorless E. coli catalyzed MFC. Although the presence of indole alone did not affect power generation, indole oxidation by the indole-oxidizing enzyme toluene-o-monooxygenase (TOM) enhanced power density by 9-fold. Open circuit voltage and polarization curve showed that indole oxidation by TOM produced a maximum power density of 5.4 mW/m² at 1,000 ohm. Cyclic voltammetric results suggested that indole oxidation resulted in the production of redox compounds. This study provides a novel means of enhancing power generation in E. coli-catalyzed MFCs.     

Performance of cathodic nitrate reduction driven by electricity generated from ANAMMOX sludge in anode

In this study, ANAMMOX sludge was used as anode microbial catalysts to drive electrocatalytic reduction of nitrate in the SnCu-Pd/CFC catalytic cathode with total nitrogen (TN) removal efficiency of ANAMMOX as well as generate electricity without additional carbon and energy source. The system operation with 1.74 Kg·N/m³·d as nitrogen loading rate (NLR) exhibited a TN removal efficiency of 96.3% and obtained the highest nitrogen removal rate (NRR, 1.69 Kg·N/m³·d), increased by 14.9% and 0.30 Kg·N/m³·d compared with open circuit (control group), respectively. Maximum voltage (39.8 mV) and power density (21.20 ± 0.05 mW/m³, standardized to anode surface area) were also observed. Additionally, microbial community analysis revealed community structure of S2_anode had an obvious disparity compared with others as the predominant ANAMMOX bacteria (AnAOB) closed to anode surface was evolved from Candidatus_Kuenenia to Candidatus_Brocadia.     

Direct enrichment of perchlorate-reducing microbial community for efficient electroactive perchlorate reduction in biocathodes

Biological reduction of perchlorate (ClO₄ ^?) has emerged as a promising solution for the removal of perchlorate in contaminated water and soils. In this work, we demonstrate a simple process to enrich perchlorate-reducing microbial communities separately using acetate as electron donor and the municipal aerobic membrane bioreactor sludge as inoculum. Inoculation of cathodes in microbial fuel cells (MFCs) with these enrichments, and further electrochemical enrichment at constant resistance operation of the MFCs, led to perchlorate-reducing biocathodes with peak reduction rates of 0.095 mM/day (2 mg/m²/day). Analysis of the microbial diversity of perchlorate-reducing biocathodes using PCR-DGGE revealed unique community profiles when compared to the denitrifying biocathode communities. More importantly, the total time taken for enrichment of the electroactive communities was reduced from several months reported previously in literature to less than a month in this work.