Microbial Fuels Cell-Based Biosensor for Toxicity Detection: A Review
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paper_title: Twenty years of monitoring of persistent organic pollutants in Greenland biota. A review.

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The Arctic Monitoring and Assessment Programme (AMAP) is a working group under the Arctic Council with the aim to monitor and assess temporal trends of contaminants in Arctic ecosystems. The Greenland AMAP Core programme was established to contribute to this effort. The Core programme includes three main components; routine monitoring, retrospective studies and new POP screening studies. The programme is based on an adaptive approach, which has led to changes throughout the years. An overview of the temporal trends during the last two to three decades is presently given together with selected examples of different characteristic trends of POPs. The results show how tissue banked samples and retrospective studies has helped in establishing time-series of compounds of emerging concern. Lastly, the statistical power of the Greenlandic time-series is discussed. The lesson learned is that trend monitoring improves with samples over time, and only pays off after decades of data are generated.
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paper_title: Microbial fuel cells for inexpensive continuous in-situ monitoring of groundwater quality.

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Online monitoring of groundwater quality in shallow wells to detect faecal or organic pollution could dramatically improve understanding of health risks in unplanned peri-urban settlements. Microbial fuel cells (MFC) are devices able to generate electricity from the organic matter content in faecal pollution making them suitable as biosensors. In this work, we evaluate the suitability of four microbial fuel cell systems placed in different regions of a groundwater well for the low-cost monitoring of a faecal pollution event. Concepts created include the use of a sediment/bulk liquid MFC (SED/BL), a sediment/sediment MFC (SED/SED), a bulk liquid/air MFC (BL/Air), and a bulk liquid/bulk liquid MFC (BL/BL). MFC electrodes assembly aimed to use inexpensive, durable, materials, which would produce a signal after a contamination event without external energy or chemical inputs. All MFC configurations were responsive to a contamination event, however SED/SED and BL/Air MFC concepts failed to deliver a reproducible output within the tested period of time. BL/BL MFC and SED/BL MFCs presented an increase in the average current after contamination from -0.75 ± 0.35 μA to -0.66 ± 0.41 μA, and 0.07 ± 0.2 mA to 0.11 ± 0.03 mA, respectively. Currents produced by the SED/BL MFC (SMFC) were considerably higher than for the BL/BL MFCs, making them more responsive, readable and graphically visible. A factorial design of experiments (DOE) was applied to evaluate which environmental and design factors had the greatest effect on current response in a contamination event. Within the ranges of variables tested, salinity, temperature and external resistance, only temperature presented a statistically significant effect (p = 0.045). This showed that the biosensor response would be sensitive to fluctuations in temperature but not to changes in salinity, or external resistances produced from placing electrodes at different distances within a groundwater well.
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paper_title: Biosensors for clinical diagnostics industry

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There is an urgent need in the medical diagnostics laboratories for accurate, fast and inexpensive devices, which can be routinely used. The reliable and accurate information on the desired biochemical parameters is an essential prerequisite for effective healthcare. In this context, biosensors are considered to provide viable solutions to the problems posed by the contemporary healthcare industry. This is because these biosensing devices offer considerable advantages, such as specificity, small size faster response and cost. It is anticipated that these bioanalytical tools can be used for frequent measurements of metabolites, blood cations and gases, etc. In this paper, an attempt has been made to highlight some of the trends that rule the research and developments of some of the important biosensors that are likely to accelerate the growth of clinical diagnostics industry.
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paper_title: Environmental pollution of electronic waste recycling in India: A critical review.

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The rapid growth of the production of electrical and electronic products has meant an equally rapid growth in the amount of electronic waste (e-waste), much of which is illegally imported to India, for disposal presenting a serious environmental challenge. The environmental impact during e-waste recycling was investigated and metal as well as other pollutants [e.g. polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs)] were found in excessive levels in soil, water and other habitats. The most e-waste is dealt with as general or crudely often by open burning, acid baths, with recovery of only a few materials of value. As resulted of these process; dioxins, furans, and heavy metals are released and harmful to the surrounding environment, engaged workers, and also residents inhabiting near the sites. The informal e-waste sectors are growing rapidly in the developing countries over than in the developed countries because of cheapest labor cost and week legislations systems. It has been confirmed that contaminates are moving through the food chain via root plant translocation system, to the human body thereby threatening human health. We have suggested some possible solution toward in which plants and microbes combine to remediate highly contaminated sites.
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paper_title: Analytical applications of microbial fuel cells. Part II: Toxicity, microbial activity and quantification, single analyte detection and other uses.

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Microbial fuel cells were rediscovered twenty years ago and now are a very active research area. The reasons behind this new activity are the relatively recent discovery of electrogenic or electroactive bacteria and the vision of two important practical applications, as wastewater treatment coupled with clean energy production and power supply systems for isolated low-power sensor devices. Although some analytical applications of MFCs were proposed earlier (as biochemical oxygen demand sensing) only lately a myriad of new uses of this technology are being presented by research groups around the world, which combine both biological-microbiological and electroanalytical expertises. This is the second part of a review of MFC applications in the area of analytical sciences. In Part I a general introduction to biological-based analytical methods including bioassays, biosensors, MFCs design, operating principles, as well as, perhaps the main and earlier presented application, the use as a BOD sensor was reviewed. In Part II, other proposed uses are presented and discussed. As other microbially based analytical systems, MFCs are satisfactory systems to measure and integrate complex parameters that are difficult or impossible to measure otherwise, such as water toxicity (where the toxic effect to aquatic organisms needed to be integrated). We explore here the methods proposed to measure toxicity, microbial metabolism, and, being of special interest to space exploration, life sensors. Also, some methods with higher specificity, proposed to detect a single analyte, are presented. Different possibilities to increase selectivity and sensitivity, by using molecular biology or other modern techniques are also discussed here.
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paper_title: Microbial biosensors: a review.

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A microbial biosensor is an analytical device which integrates microorganism(s) with a physical transducer to generate a measurable signal proportional to the concentration of analytes. In recent years, a large number of microbial biosensors have been developed for environmental, food, and biomedical applications. Starting with the discussion of various sensing techniques commonly used in microbial biosensing, this review article concentrates on the summarization of the recent progress in the fabrication and application of microbial biosensors based on amperometry, potentiometry, conductometry, voltammetry, microbial fuel cell, fluorescence, bioluminescence, and colorimetry, respectively. Prospective strategies for the design of future microbial biosensors will also be discussed.
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paper_title: Environmental effects of heavy metals derived from the e-waste recycling activities in China: a systematic review.

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As the world's leading manufacturing country, China has become the largest dumping ground for e-waste, resulting in serious pollution of heavy metals in China. This study reviews recent studies on environmental effects of heavy metals from the e-waste recycling sites in China, especially Taizhou, Guiyu, and Longtang. The intensive uncontrolled processing of e-waste in China has resulted in the release of large amounts of heavy metals in the local environment, and caused high concentrations of metals to be present in the surrounding air, dust, soils, sediments and plants. Though the pollution of many heavy metals was investigated in the relevant researches, the four kinds of heavy metals (Cu, Pb, Cd and Cr) from e-waste recycling processes attracted more attention. The exceedance of various national and international standards imposed negative effects to the environment, which made the local residents face with the serious heavy metal exposure. In order to protect the environment and human health, there is an urgent need to control and monitor the informal e-waste recycling operations.
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paper_title: Methods for assessing biochemical oxygen demand (BOD): a review.

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The Biochemical Oxygen Demand (BOD) is one of the most widely used criteria for water quality assessment. It provides information about the ready biodegradable fraction of the organic load in water. However, this analytical method is time-consuming (generally 5 days, BOD5), and the results may vary according to the laboratory (20%), primarily due to fluctuations in the microbial diversity of the inoculum used. Work performed during the two last decades has resulted in several technologies that are less time-consuming and more reliable. This review is devoted to the analysis of the technical features of the principal methods described in the literature in order to compare their performances (measuring window, reliability, robustness) and to identify the pros and the cons of each method.
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paper_title: Pollution distribution of heavy metals in surface soil at an informal electronic-waste recycling site

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We studied distribution of heavy metals [lead (Pb), copper (Cu) and zinc (Zn)] in surface soil at an electronic-waste (e-waste) recycling workshop near Metro Manila in the Philippines to evaluate the pollution size (spot size, small area or the entire workshop), as well as to assess heavy metal transport into the surrounding soil environment. On-site length-of-stride-scale (~70 cm) measurements were performed at each surface soil point using field-portable X-ray fluorescence (FP-XRF). The surface soil at the e-waste recycling workshop was polluted with Cu, Zn and Pb, which were distributed discretely in surface soil. The site was divided into five areas based on the distance from an entrance gate (y-axis) of the e-waste recycling workshop. The three heavy metals showed similar concentration gradients in the y-axis direction. Zn, Pb and Cu concentrations were estimated to decrease to half of their maximum concentrations at ~3, 7 and 7 m from the pollution spot, respectively, inside the informal e-waste recycling workshop. Distance from an entrance may play an important role in heavy metal transport at the soil surface. Using on-site FP-XRF, we evaluated the metal ratio to characterise pollution features of the solid surface. Variability analysis of heavy metals revealed vanishing surficial autocorrelation over metre ranges. Also, the possibility of concentration prediction at unmeasured points using geostatistical kriging was evaluated, and heavy metals had a relative "small" pollution scales and remained inside the original workshop compared with toxic organohalogen compounds. Thus, exposure to heavy metals may directly influence the health of e-waste workers at the original site rather than the surrounding habitat and environmental media.
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paper_title: Increase of riboflavin biosynthesis underlies enhancement of extracellular electron transfer of Shewanella in alkaline microbial fuel cells.

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Electrolyte pH tremendously affects the electricity output of microbial fuel cells. However, its underlying molecular mechanism remains elusive, in particular for Shewanella oneidensis MR-1, one of the most widely adopted electrogenic microorganisms. Herein, we found that MFCs were able to deliver a significant (but different) electricity output in a wide range of pH (from 6 to 10), with the maximum at pH=9 (alkaline), which delivers ∼1.5times' higher power output than that at pH=7 (neutral). Furthermore, cyclic voltammetry analysis showed an enhanced electrochemical activity of riboflavin (responsible for extracellular electron transfer of Shewanella) at alkaline pH. Strikingly, the concentration of riboflavin synthesized by Shewanella in MFCs at different pH showed a good correlation with the electricity output of MFCs. Thus, our results substantiated that the increase of riboflavin biosynthesis by Shewanella at the alkaline condition underlies the improvement of the electricity output in MFCs.
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paper_title: Microbial electrolysis cells for high yield hydrogen gas production from organic matter.

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The use of electrochemically active bacteria to break down organic matter, combined with the addition of a small voltage (> 0.2 V in practice) in specially designed microbial electrolysis cells (MECs), can result in a high yield of hydrogen gas. While microbial electrolysis was invented only a few years ago, rapid developments have led to hydrogen yields approaching 100%, energy yields based on electrical energy input many times greater than that possible by water electrolysis, and increased gas production rates. MECs used to make hydrogen gas are similar in design to microbial fuel cells (MFCs) that produce electricity, but there are important differences in architecture and analytical methods used to evaluate performance. We review here the materials, architectures, performance, and energy efficiencies of these MEC systems that show promise as a method for renewable and sustainable energy production, and wastewater treatment.
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paper_title: Toxicity detection in water containing heavy metal ions with a self-powered microbial fuel cell-based biosensor.

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In this work, a self-powered microbial fuel cell (MFC)-based biosensor was developed for detecting toxicity in water containing heavy metal ions. Experimental conditions containing concentration of potassium ferricyanide, load resistor and glucose concentration were optimized. Six heavy metal ions (2mg/L, Cu2+, Hg2+, Zn2+, Cd2+, Pb2+ and Cr3+) were tested by this biosensor and the inhibition ratios obtained were 12.56%, 13.99%, 8.81%, 9.29%, 5.59% and 1.95%, respectively. The inhibition ratios of 28.13% was also obtained for detecting the laboratory wastewater containing several heavy metal ions. The experimental results exhibited the feasibility and potential of the self-powered biosensor in detecting toxicities in water containing heavy metal ions.
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paper_title: A novel biomonitoring system using microbial fuel cells.

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A novel biomonitoring system using microbial fuel cells for detecting the inflow of toxic substances into water systems has been developed for the purpose of on-site and on-line monitoring. The characteristics of electric current generation by electrochemically-active bacteria were conveniently monitored using a microbial fuel cell format and a computer-controlled potentiometer. When toxic substances (an organophosphorus compound, Pb, Hg, and PCBs) were added to the microbial fuel cell, rapid decreases in the current were observed. The inhibition ratios caused by inflow of these toxic substances (1 mg l(-1)) were 61%, 46%, 28% and 38%, respectively, when compared to the control, and generally increased in proportion to the addition time and concentration of toxic substances. When real wastewater was applied from a local wastewater treatment plant, more significant current decreases and higher inhibition ratios were observed following the introduction of toxic substances than in the laboratory tests. For example, the inhibition ratio was 76% on addition of a 1 mg l(-1) Cd and 1 mg l(-1) Pb mixture. Application of the microbial fuel cell for pollutant biomonitoring is discussed.
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paper_title: Analytical applications of microbial fuel cells. Part I: Biochemical oxygen demand.

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Microbial fuel cells (MFCs) are bio-electrochemical devices, where usually the anode (but sometimes the cathode, or both) contains microorganisms able to generate and sustain an electrochemical gradient which is used typically to generate electrical power. In the more studied set-up, the anode contains heterotrophic bacteria in anaerobic conditions, capable to oxidize organic molecules releasing protons and electrons, as well as other by-products. Released protons could reach the cathode (through a membrane or not) whereas electrons travel across an external circuit originating an easily measurable direct current flow. MFCs have been proposed fundamentally as electric power producing devices or more recently as hydrogen producing devices. Here we will review the still incipient development of analytical uses of MFCs or related devices or set-ups, in the light of a non-restrictive MFC definition, as promising tools to asset water quality or other measurable parameters. An introduction to biological based analytical methods, including bioassays and biosensors, as well as MFCs design and operating principles, will also be included. Besides, the use of MFCs as biochemical oxygen demand sensors (perhaps the main analytical application of MFCs) is discussed. In a companion review (Part 2), other new analytical applications are reviewed used for toxicity sensors, metabolic sensors, life detectors, and other proposed applications.
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paper_title: Silicon-based microfabricated microbial fuel cell toxicity sensor.

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Microbial fuel cells (MFCs) have been used for several years as biosensors for measuring environmental parameters such as biochemical oxygen demand and water toxicity. The present study is focused on the detection of toxic matter using a novel silicon-based MFC. Like other existing toxicity sensors based on MFCs, this device is capable of detecting the variation on the current produced by the cell when toxic compounds are present in the medium. The MFC approach presented in this work aims to obtain a simple, compact and planar device for its further application as a biosensor in the design and fabrication of equipment for toxicity monitoring. It consists on a proton exchange membrane placed between two microfabricated silicon plates that act as current collectors. An array of square 80 μm × 80 μm vertical channels, 300 μm deep, have been defined trough the plates over an area of 6 mm × 6 mm. The final testing assembly incorporates two perspex pieces positioned onto the plates as reservoirs with a working volume of 144 μL per compartment. The operation of the microdevice as a direct electron transfer MFC has been validated by comparing its performance against a larger scale MFC, run under the same conditions. The device has been tested as a toxicity sensor by setting it at a fixed current while monitoring changes in the output power. A drop in the power production is observed when a toxic compound is added to the anode compartment. The compact design of the device makes it suitable for its incorporation into measurement equipment either as an individual device or as an array of sensors for high throughput processing.
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paper_title: Effect of different substrates on the performance, bacterial diversity, and bacterial viability in microbial fuel cells.

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Four microbial fuel cells (MFCs) were inoculated with anaerobic sludge and fed four different substrates for over one year. The Coulombic efficiency (CE) and power output varied with different substrates, while the bacterial viability was similar. Acetate fed-MFC showed the highest CE (72.3%), followed by butyrate (43.0%), propionate (36.0%) and glucose (15.0%). Glucose resulted in the lowest CE because of its fermentable nature implying its consumption by diverse non-electricity-generating bacteria. 16S rDNA sequencing results indicated phylogenetic diversity in the communities of all anode biofilms, and there was no single dominant bacterial species. A relative abundance of beta-Proteobacteria but an absence of gamma-Proteobacteria was observed in all MFCs except for propionate-fed system in which Firmicutes dominating. The glucose-fed-MFC showed the widest community diversity, resulting in the rapid generation of current without lag time when different substrates were suddenly fed. Geobacter-like species with the most representative Geobactersulfurreducens PCA(T) were integral members of the bacterial community in all MFCs except for the propionate-fed system.
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paper_title: Microbial nanowires for bioenergy applications.

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Microbial nanowires are electrically conductive filaments that facilitate long-range extracellular electron transfer. The model for electron transport along Shewanella oneidensis nanowires is electron hopping/tunneling between cytochromes adorning the filaments. Geobacter sulfurreducens nanowires are comprised of pili that have metal-like conductivity attributed to overlapping pi-pi orbitals of aromatic amino acids. The nanowires of Geobacter species have been implicated in direct interspecies electron transfer (DIET), which may be an important mode of syntrophy in the conversion of organic wastes to methane. Nanowire networks confer conductivity to Geobacter biofilms converting organic compounds to electricity in microbial fuel cells (MFCs) and increasing nanowire production is the only genetic manipulation shown to yield strains with improved current-producing capabilities. Introducing nanowires, or nanowire mimetics, might improve other bioenergy strategies that rely on extracellular electron exchange, such as microbial electrosynthesis. Similarities between microbial nanowires and synthetic conducting polymers suggest additional energy-related applications.
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paper_title: Utilization of electrically reduced neutral red by Actinobacillus succinogenes: physiological function of neutral red in membrane-driven fumarate reduction and energy conservation.

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Neutral red (NR) functioned as an electronophore or electron channel enabling either cells or membranes purified from Actinobacillus succinogenes to drive electron transfer and proton translocation by coupling fumarate reduction to succinate production. Electrically reduced NR, unlike methyl or benzyl viologen, bound to cell membranes, was not toxic, and chemically reduced NAD. The cell membrane of A. succinogenes contained high levels of benzyl viologen-linked hydrogenase (12.2 U), fumarate reductase (13.1 U), and diaphorase (109.7 U) activities. Fumarate reductase (24.5 U) displayed the highest activity with NR as the electron carrier, whereas hydrogenase (1.1 U) and diaphorase (0.8 U) did not. Proton translocation by whole cells was dependent on either electrically reduced NR or H2 as the electron donor and on the fumarate concentration. During the growth of Actinobacillus on glucose plus electrically reduced NR in an electrochemical bioreactor system versus on glucose alone, electrically reduced NR enhanced glucose consumption, growth, and succinate production by about 20% while it decreased acetate production by about 50%. The rate of fumarate reduction to succinate by purified membranes was twofold higher with electrically reduced NR than with hydrogen as the electron donor. The addition of 2-(n-heptyl)-4-hydroxyquinoline N-oxide to whole cells or purified membranes inhibited succinate production from H2 plus fumarate but not from electrically reduced NR plus fumarate. Thus, NR appears to replace the function of menaquinone in the fumarate reductase complex, and it enables A. succinogenes to utilize electricity as a significant source of metabolic reducing power.
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paper_title: Anode Biofilm Transcriptomics Reveals Outer Surface Components Essential for High Density Current Production in Geobacter sulfurreducens Fuel Cells

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The mechanisms by which Geobacter sulfurreducens transfers electrons through relatively thick (>50 µm) biofilms to electrodes acting as a sole electron acceptor were investigated. Biofilms of Geobacter sulfurreducens were grown either in flow-through systems with graphite anodes as the electron acceptor or on the same graphite surface, but with fumarate as the sole electron acceptor. Fumarate-grown biofilms were not immediately capable of significant current production, suggesting substantial physiological differences from current-producing biofilms. Microarray analysis revealed 13 genes in current-harvesting biofilms that had significantly higher transcript levels. The greatest increases were for pilA, the gene immediately downstream of pilA, and the genes for two outer c-type membrane cytochromes, OmcB and OmcZ. Down-regulated genes included the genes for the outer-membrane c-type cytochromes, OmcS and OmcT. Results of quantitative RT-PCR of gene transcript levels during biofilm growth were consistent with microarray results. OmcZ and the outer-surface c-type cytochrome, OmcE, were more abundant and OmcS was less abundant in current-harvesting cells. Strains in which pilA, the gene immediately downstream from pilA, omcB, omcS, omcE, or omcZ was deleted demonstrated that only deletion of pilA or omcZ severely inhibited current production and biofilm formation in current-harvesting mode. In contrast, these gene deletions had no impact on biofilm formation on graphite surfaces when fumarate served as the electron acceptor. These results suggest that biofilms grown harvesting current are specifically poised for electron transfer to electrodes and that, in addition to pili, OmcZ is a key component in electron transfer through differentiated G. sulfurreducens biofilms to electrodes.
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paper_title: Utility of Ochrobactrum anthropi YC152 in a Microbial Fuel Cell as an Early Warning Device for Hexavalent Chromium Determination

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Fast hexavalent chromium (Cr(VI)) determination is important for environmental risk and health-related considerations. We used a microbial fuel cell-based biosensor inoculated with a facultatively anaerobic, Cr(VI)-reducing, and exoelectrogenic Ochrobactrum anthropi YC152 to determine the Cr(VI) concentration in water. The results indicated that O. anthropi YC152 exhibited high adaptability to pH, temperature, salinity, and water quality under anaerobic conditions. The stable performance of the microbial fuel cell (MFC)-based biosensor indicated its potential as a reliable biosensor system. The MFC voltage decreased as the Cr(VI) concentration in the MFC increased. Two satisfactory linear relationships were observed between the Cr(VI) concentration and voltage output for various Cr(VI) concentration ranges (0.0125–0.3 mg/L and 0.3–5 mg/L). The MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in drinking water, groundwater, and electroplating wastewater in 45 min with low deviations (<10%). The use of the biosensor can help in preventing the violation of effluent regulations and the maximum allowable concentration of Cr(VI) in water. Thus, the developed MFC biosensor has potential as an early warning detection device for Cr(VI) determination even if O. anthropi YC152 is a possible opportunistic pathogen.
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paper_title: A novel biosensor for p-nitrophenol based on an aerobic anode microbial fuel cell.

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P-nitrophenol is one of the most common contaminants in chemical industrial wastewater, and in situ real-time monitoring of PNP cannot be achieved by conventional analytical techniques. Here, a two-chamber microbial fuel cell with an aerobic anode chamber was tested as a biosensor for in situ real-time monitoring of PNP. Pseudomonas monteilii LZU-3, which was used as the biological recognition element, can form a biofilm on the anode electrode using PNP as a sole substrate. The optimal operation parameters of the biosensor were as follows: external resistance 1000Ω, pH 7.8, temperature 30°C, and maximum PNP concentration 50mgL(-1). Under these conditions, the maximum voltages showed a linear relationship with PNP concentrations ranging from 15±5 to 44±4.5mgL(-1). Furthermore, we developed a novel portable device for in situ real-time monitoring of PNP. When the device was applied to measure PNP in wastewater containing various additional aromatic compounds and metal ions, the performance of the biosensor was not affected and the correlation between the maximum voltages and the PNP concentrations ranging from 9±4mgL(-1) to 36 ± 5mgL(-1) was conserved. The results demonstrated that the MFC biosensor provides a rapid and cost-efficient analytical method for real-time monitoring of toxic and recalcitrant pollutants in environmental samples.
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paper_title: Using electrical signals of microbial fuel cells to detect copper stress on soil microorganisms

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A method based on microbial fuel cells (MFCs) was used to evaluate the effects of copper (Cu2+) on soil microorganisms. Soil spiked with 50-400mgkg(-1) of Cu2+ as CuCl2 was incubated for 24hours before being packed into the MFC anode chambers and assayed for dehydrogenase activity (DHA), substrate-induced respiration (SIR) and microbial biomass carbon (C-mic). Soil was amended with 5% (w/w) glucose to accelerate start-up' and improve power generation, followed by 150hours of operation. Anode biofilm and soil was extracted to recover total nucleic acids and the 16S rRNA gene was subjected to PCR-DGGE, sequencing and phylogenetic analysis. Results showed that increases in soil Cu2+ concentrations reduced voltage and postponed start-up. The quantity of generated electrons within 48hours was 32.5 coulomb (C) in the without-Cu control and decreased with increasing Cu2+ concentrations (11.7, 7.7, 2.0 and 1.3C under 50, 100, 200 and 400mgkg(-1)Cu(2+), respectively). Cyclic voltammetry identified decreased soil electrochemical activity with increasing Cu2+ concentrations. The results indicate that Cu2+ reduced electrical signals by inhibiting the electrochemical activity, metabolic activity and biomass of microorganisms. The 16S sequences of recovered anodic bacteria were assigned to Firmicutes, including Bacillaceae, Acetobacteraceae, Clostridium, Bacillus and Sporolactobacillus. In general, the DGGE band intensity of anodic bacteria decreased with increasing Cu2+ concentrations, except for bands assigned to Firmicutes and Bacillus, which increased with increasing Cu2+ concentrations. We suggest that the short-term electrical signals generated from MFCs with contaminated soil can be used to assess the toxic effect of heavy metal pollutants on soil microorganisms.
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paper_title: FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin.

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A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1-1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1-100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT).
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paper_title: Microbial ecology meets electrochemistry: electricity-driven and driving communities

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Bio-electrochemical systems (BESs) have recently emerged as an exciting technology. In a BES, bacteria interact with electrodes using electrons, which are either removed or supplied through an electrical circuit. The most-described type of BES is microbial fuel cells (MFCs), in which useful power is generated from electron donors as, for example, present in wastewater. This form of charge transport, known as extracellular electron transfer, was previously extensively described with respect to metals such as iron and manganese. The importance of these interactions in global biogeochemical cycles is essentially undisputed. A wide variety of bacteria can participate in extracellular electron transfer, and this phenomenon is far more widespread than previously thought. The use of BESs in diverse research projects is helping elucidate the mechanism by which bacteria shuttle electrons externally. New forms of interactions between bacteria have been discovered demonstrating how multiple populations within microbial communities can co-operate to achieve energy generation. New environmental processes that were difficult to observe or study previously can now be simulated and improved via BESs. Whereas pure culture studies make up the majority of the studies performed thus far, even greater contributions of BESs are expected to occur in natural environments and with mixed microbial communities. Owing to their versatility, unmatched level of control and capacity to sustain novel processes, BESs might well serve as the foundation of a new environmental biotechnology. While highlighting some of the major breakthroughs and addressing only recently obtained data, this review points out that despite rapid progress, many questions remain unanswered.
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paper_title: Butler-Volmer-Monod model for describing bio-anode polarization curves.

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A kinetic model of the bio-anode was developed based on a simple representation of the underlying biochemical conversions as described by enzyme kinetics, and electron transfer reactions as described by the Butler-Volmer electron transfer kinetics. This Butler-Volmer-Monod model was well able to describe the measured bio-anode polarization curves. The Butler-Volmer-Monod model was compared to the Nernst-Monod model described the experimental data significantly better. The Butler-Volmer-Monod model has the Nernst-Monod model as its full electrochemically reversible limit. Contrary to the Nernst-Monod model, the Butler-Volmer-Monod model predicts zero current at equilibrium potential. Besides, the Butler-Volmer-Monod model predicts that the apparent Monod constant is dependent on anode potential, which was supported by experimental results.
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paper_title: Microbial fuel cells: methodology and technology.

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Microbial fuel cell (MFC) research is a rapidly evolving field that lacks established terminology and methods for the analysis of system performance. This makes it difficult for researchers to compare devices on an equivalent basis. The construction and analysis of MFCs requires knowledge of different scientific and engineering fields, ranging from microbiology and electrochemistry to materials and environmental engineering. Describing MFC systems therefore involves an understanding of these different scientific and engineering principles. In this paper, we provide a review of the different materials and methods used to construct MFCs, techniques used to analyze system performance, and recommendations on what information to include in MFC studies and the most useful ways to present results.
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paper_title: Purification and characterization of OmcZ, an outer-surface, octaheme c-type cytochrome essential for optimal current production by Geobacter sulfurreducens.

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Previous studies have demonstrated that Geobacter sulfurreducens requires the c-type cytochrome OmcZ, which is present in large (OmcZL; 50-kDa) and small (OmcZS; 30-kDa) forms, for optimal current production in microbial fuel cells. This protein was further characterized to aid in understanding its role in current production. Subcellular-localization studies suggested that OmcZS was the predominant extracellular form of OmcZ. N- and C-terminal amino acid sequence analysis of purified OmcZS and molecular weight measurements indicated that OmcZS is a cleaved product of OmcZL retaining all 8 hemes, including 1 heme with the unusual c-type heme-binding motif CX14CH. The purified OmcZS was remarkably thermally stable (thermal-denaturing temperature, 94.2°C). Redox titration analysis revealed that the midpoint reduction potential of OmcZS is approximately −220 mV (versus the standard hydrogen electrode [SHE]) with nonequivalent heme groups that cover a large reduction potential range (−420 to −60 mV). OmcZS transferred electrons in vitro to a diversity of potential extracellular electron acceptors, such as Fe(III) citrate, U(VI), Cr(VI), Au(III), Mn(IV) oxide, and the humic substance analogue anthraquinone-2,6-disulfonate, but not Fe(III) oxide. The biochemical properties and extracellular localization of OmcZ suggest that it is well suited for promoting electron transfer in current-producing biofilms of G. sulfurreducens.
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paper_title: On-line detection of toxic components using a microbial fuel cell-based biosensor

paper_content:

Safe drinking water without toxic chemicals is crucial for people's health. A recently developed sensor for the detection of toxic components in water is the microbial fuel cell (MFC)-based biosensor. In this biosensor, substrate consumption rate and metabolic activity of bacteria are directly related to the electric current. A reduction in current under otherwise similar conditions is an indication of toxic inhibition. Under steady state conditions, current can be described by the Butler–Volmer–Monod (BVM) model. Knowing which parameters of this model change under toxic contamination can give an indication on the type of toxicity. The model requires that the substrate concentration is known. It is shown in this paper that is not possible to estimate both the substrate concentration as well as the BVM parameters on-line from current data at constant overpotential. However, it appears that substrate concentration and substrate consumption rate can be estimated on-line, and that after a linear reparametrization the BVM parameters can be estimated by ordinary least-squares techniques from a polarization curve that is generated as soon as a suspect change in current occurs. Analysis shows that a weighted least-squares method is necessary to secure a good fit at the overpotentials where current is most sensitive to changes in kinetic parameters. A protocol for on-line detection of toxicity and for detection of the type of kinetic inhibition is provided.
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paper_title: Concentration responses of toxicity sensor with Shewanella oneidensis MR-1 growing in bioelectrochemical systems.

paper_content:

Bioelectrochemical systems (BESs) provide an opportunity to detect biological toxicity of water samples. However, the concentration responses of toxins had not been investigated in detail. Using formaldehyde as a toxic substance, the current responses were analyzed over a concentration range from 0.01% to 0.10% in a single chambered BES with 0mV (versus saturated calomel electrode) applied on the anode. The decay percentages of currents increased in proportion with the concentration of formaldehyde after 10000s (∼2.8h), with the peak R(2) of 0.9361 observed at 35,000s (∼9.7h). Fitting results of exponential decay equation showed that the magnification factor (a) closely related with baseline currents and the toxicity factor (b) was in direct proportion to formaldehyde concentration (from 0% to 0.08%) except over the high concentration of 0.10%. These results provide preliminary information about toxin concentration responses in BESs.
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paper_title: Extracellular electron transfer via microbial nanowires

paper_content:

Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(iii) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(iii) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(iii) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(iii) reducers in many environments, must directly contact Fe(iii) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(iii) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(iii) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(iii) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials.
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paper_title: Microbial biosensors

paper_content:

A microbial biosensor is an analytical device that couples microorganisms with a transducer to enable rapid, accurate and sensitive detection of target analytes in fields as diverse as medicine, environmental monitoring, defense, food processing and safety. The earlier microbial biosensors used the respiratory and metabolic functions of the microorganisms to detect a substance that is either a substrate or an inhibitor of these processes. Recently, genetically engineered microorganisms based on fusing of the lux, gfp or lacZ gene reporters to an inducible gene promoter have been widely applied to assay toxicity and bioavailability. This paper reviews the recent trends in the development and application of microbial biosensors. Current advances and prospective future direction in developing microbial biosensor have also been discussed.
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paper_title: Microbial fuel cells for biosensor applications

paper_content:

Microbial fuel cells (MFCs) face major hurdles for real-world applications as power generators with the exception of powering small sensor devices. Despite tremendous improvements made in the last two decades, MFCs are still too expensive to build and operate and their power output is still too small. In view of this, in recently years, intensive researches have been carried out to expand the applications into other areas such as acid and alkali production, bioremediation of aquatic sediments, desalination and biosensors. Unlike power applications, MFC sensors have the immediate prospect to be practical. This review covers the latest developments in various proposed biosensor applications using MFCs including monitoring microbial activity, testing biochemical oxygen demand, detection of toxicants and detection of microbial biofilms that cause biocorrosion.
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paper_title: First international comparative study of volatile fatty acids in aqueous samples by chromatographic techniques: Evaluating sources of error

paper_content:

Abstract This first international proficiency-testing scheme evaluated the analytical performance and the state of practice in measurement of volatile fatty acids in aqueous samples. Gas chromatography and high-performance liquid chromatography were used by 25 laboratories from 15 different countries. Two reference materials were selected for analysis. The performance of each laboratory was assessed by the internationally-accepted z-score. The overall performance was rather poor. Among the causes of poor analytical performance, human errors and inadequate calibration were probably the major problems encountered.
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paper_title: Determination of Volatile Fatty Acids in Environmental Aqueous Samples

paper_content:

Volatile fatty acids (VFAs) are present in environmental waters in the range of 1 to 5,000 ppm and different methods have been reported for their determination. In this paper we have studied and compared analytical performance parameters for the distillation method followed by potentiometric titration, spec trophotometric and gas chromatographic methods. The main disadvantage of the distillation approach was quite poor absolute recovery (53-58%) from the given matrix and rather elevated limit of quantification (lOQ) at 110 mg/l. Direct potentiometric titration was characterized by acceptable accuracy (above 97%) and precision in the range 1.8%-15%. The lOQ value was 11 mg/l. The spectrophotometric method was sensitive for hydrogen carbonate alkalinity and phosphate ions; measured concentrations of acetic acid were lower than nominal. The precision and accuracy of the spectrophotometric method were in the ranges 1.3-14% and 82.1-104.2%, respectively. limit of quantification was 28 mg/l. however, if ion exchange bed is used prior to this method the lOQ can be reduced to 5 mg/l. The GC method is characterized by quite low lOQ (5 mg/l) and seems to be the best methodology to determine low VFA concentrations in environmental waters. The precision of the method ranged from 5.7 to 14.8% and accuracy was above 92%. Additionally, this method allows for determination of individual VFAs.
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paper_title: Microbial fuel-cell-based toxicity sensor for fast monitoring of acidic toxicity

paper_content:

Wastewater may contain various potential toxicants. A microbial fuel cell (MFC) is a device in which bacteria convert the chemical energy into electricity. If a toxic event occurs, microbial activity is inhibited and thus the power output of the MFC decreases. Therefore, an MFC could serve as an early toxicity warning device. A real-time biomonitoring system was developed using MFCs to detect the inflow of toxic substances into wastewater treatment systems. After the MFCs reached steady state, a toxic incident was created by adding HCl into the wastewater to alter its pH. Consequently, a rapid decrease in voltage was observed immediately, followed by a subsequent recovery. The optimal MFC design was a single-chamber air cathode MFC, where the anode and cathode were separated by a Selemion proton exchange membrane. Under an external resistance of 5 Ω, the maximum power averaged 0.23 ± 0.023 mW with domestic wastewater. The optimized MFC showed high sensitivity and fast recovery when exposed to the acidic toxic event. When the hydraulic retention time was decreased from 22 to 3.5 min, sensitivity of the MFC increased substantially. Finally, the extent of inhibition observed was found to be related to the toxicity level, suggesting that a dosage-response relationship exists.
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paper_title: Single-chamber microbial fuel cells as on-line shock-sensors for volatile fatty acids in anaerobic digesters.

paper_content:

In anaerobic digesters (AD), volatile fatty acids (VFAs) concentration is a critical operative parameter, which is usually manually monitored to prevent inhibition of microbial consortia. An on-line VFAs monitoring system as early-warning for increasing concentrations would be of great help for operators. Here, air-cathode membraneless microbial fuel cells (MFCs) were investigated as potential biosensors, whose electrical signal instantaneously moves from its steady value with the accumulation of VFAs in the anodic solution. MFCs were operated equipping four lab-scale ADs with carbon-based electrodes. Reactors were filled with the digestate from a full-scale AD and fed in batch with four kinds of feedstock (cheese whey, kitchen waste, citrus pulp and fishery waste). The MFC signal initially increased in parallel to VFAs production, then tended to a steady value for VFAs concentrations above 1000mgAcL-1. Peak concentrations of tVFAs (2500-4500mgAcL-1) and MFCs potentials were negatively correlated (r=0.916, p<0.05), regardless of the type of substrate. Inhibition of the MFC system occurred when VFAs increased fast above 4000mgAcL-1. Polarization curves of electrodes stressed that electroactive bacteria on bioanodes were strongly subjected to inhibition. The inhibition of electroactivity on bioanode trended like typical shock-sensors, opening to direct application as early-warning monitoring system in full-scale ADs.
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paper_title: Microbial Electrochemical Monitoring of Volatile Fatty Acids during Anaerobic Digestion

paper_content:

Volatile fatty acid (VFA) concentration is known as an important indicator to control and optimize anaerobic digestion (AD) process. In this study, an innovative VFA biosensor was developed based on the principle of a microbial desalination cell. The correlation between current densities and VFA concentrations was first evaluated with synthetic digestate. Two linear relationships were observed between current densities and VFA levels from 1 to 30 mM (0.04 to 8.50 mA/m(2), R(2) = 0.97) and then from 30 to 200 mM (8.50 to 10.80 mA/m(2), R(2) = 0.95). The detection range was much broader than that of other existing VFA biosensors. The biosensor had no response to protein and lipid which are frequently found along with VFAs in organic waste streams from AD, suggesting the selective detection of VFAs. The current displayed different responses to VFA levels when different ionic strengths and external resistances were applied, though linear relationships were always observed. Finally, the biosensor was further explored with real AD effluents and the results did not show significance differences with those measured by GC. The simple and efficient biosensor showed promising potential for online, inexpensive, and reliable measurement of VFA levels during AD and other anaerobic processes.
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paper_title: Microbial fuel cell type biosensor for specific volatile fatty acids using acclimated bacterial communities.

paper_content:

Volatile fatty acid (VFA) concentration is one of the most important parameters for monitoring bio-processes such as anaerobic digestion and microbial fuel cells. In this study the correlation between VFA concentration and current/voltage responses and electrochemical properties by using the MFC technology was evaluated. The discrimination between different species of VFA by using two methods i.e., coulombic efficiency and cyclic voltammetry was investigated. Columbic efficiency gave a slow response of greater than 20h, particularly at concentration levels of 20mgl(-1). By using cyclic voltammetry to measure the oxidation peak at a consistent scan rate showed linear correlation to VFA concentration and peak current produced, up to <40mgl(-1)) in a rapid response time of 1-2min. The results presented showed good correlations between the individual VFA species concentration and charge, and also current generated. A MFC based biosensor array was produced capable of measuring individual acetate, propionate and butyrate concentrations with sensitivity down to 5mgl(-1) and up to 40mgl(-1).
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paper_title: Online monitoring of concentration and dynamics of volatile fatty acids in anaerobic digestion processes with mid-infrared spectroscopy

paper_content:

An ATR-MIR-FTIR spectrometer was integrated into a laboratory scale anaerobic digestion setup. Automatically, a sludge sample from the digester was transferred to a measurement cell; an IR spectrum was recorded and evaluated by chemometric models to estimate the concentration of the individual volatile fatty acids (VFA). The calibration set included semi-artificial samples spiked with known concentrations of the VFA as well as original samples from a continuous fermentation. High-performance liquid chromatography (HPLC) was used as a reference analysis of the samples. The models were optimized for a low root mean square error of prediction (RMSEP). R 2 for acetic acid, propionic acid, isobutyric acid, butyric acid, valeric acid, and isovaleric acid were 0.94, 0.88, 0.83, 0.75, 0.59, and 0.90, respectively. The accuracy of the models was validated in a second experiment. Considering the complex and heterogeneous sludge composition and the chemical similarity of VFA, absolute concentration and dynamic (increasing and decreasing concentration of VFA) was predicted well for acetic, propionic, isobutyric, and isovaleric acid (in their respective concentration range); Butyric acid could not be detected. The installed setup was able to gather and measure native samples from the digester (every 2 h) automatically over a period of 6 months without problems of clogging or biofouling. The instant and continuous analysis of the concentration of the VFA made it possible to evaluate the current bioprocess status and adjust the organic loading rate accordingly.
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paper_title: Improvement of a microbial fuel cell performance as a BOD sensor using respiratory inhibitors.

paper_content:

Studies were made to improve the performance of a microbial fuel cell (MFC) as a biochemical oxygen demand (BOD) sensor. The signal from MFCs decreased in the presence of electron acceptors of higher redox potential such as nitrate and oxygen. The addition of azide and cyanide did not change the signal in the absence of the electron acceptors. The respiratory inhibitors eliminated the inhibitory effects of the electron acceptors on the current generation from MFCs. Similar results were obtained using oligotrophic MFCs fed with an environmental sample that contained nitrate. The use of the respiratory inhibitors is therefore recommended for the accurate BOD measurement of environmental samples containing nitrate and/or oxygen with an MFC-type BOD sensor.
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paper_title: Microbial fuel-cell-based toxicity sensor for fast monitoring of acidic toxicity

paper_content:

Wastewater may contain various potential toxicants. A microbial fuel cell (MFC) is a device in which bacteria convert the chemical energy into electricity. If a toxic event occurs, microbial activity is inhibited and thus the power output of the MFC decreases. Therefore, an MFC could serve as an early toxicity warning device. A real-time biomonitoring system was developed using MFCs to detect the inflow of toxic substances into wastewater treatment systems. After the MFCs reached steady state, a toxic incident was created by adding HCl into the wastewater to alter its pH. Consequently, a rapid decrease in voltage was observed immediately, followed by a subsequent recovery. The optimal MFC design was a single-chamber air cathode MFC, where the anode and cathode were separated by a Selemion proton exchange membrane. Under an external resistance of 5 Ω, the maximum power averaged 0.23 ± 0.023 mW with domestic wastewater. The optimized MFC showed high sensitivity and fast recovery when exposed to the acidic toxic event. When the hydraulic retention time was decreased from 22 to 3.5 min, sensitivity of the MFC increased substantially. Finally, the extent of inhibition observed was found to be related to the toxicity level, suggesting that a dosage-response relationship exists.
---
paper_title: Biochemical Oxygen Demand

paper_content:

A vast number of organisms, primarily bacteria, survives and even thrives in an environment containing no oxygen. However, most living creatures with which we commonly interact are aerobic; they need oxygen to survive. Aerobic creatures include all of the higher life forms such as fish, birds, mammals, and reptiles, as well as simpler species such as some bacteria and protozoa. The 4.7 billion year development of the earth and the evolution of species in response to this development have created many types of ecosystems; most support a balance between the demands of aerobic organisms for oxygen and the availability of oxygen. These “balanced ecosystems” are found in aquatic, terrestrial, and atmospheric biomes. ::: ::: ::: Keywords: ::: ::: biochemical oxygen demand; ::: eutrophication; ::: monod; ::: electron donor; ::: terminal electron acceptor (TEA); ::: respiration; ::: aerobic; ::: ultimate BOD; ::: BOD test
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paper_title: Single-chamber microbial fuel cells as on-line shock-sensors for volatile fatty acids in anaerobic digesters.

paper_content:

In anaerobic digesters (AD), volatile fatty acids (VFAs) concentration is a critical operative parameter, which is usually manually monitored to prevent inhibition of microbial consortia. An on-line VFAs monitoring system as early-warning for increasing concentrations would be of great help for operators. Here, air-cathode membraneless microbial fuel cells (MFCs) were investigated as potential biosensors, whose electrical signal instantaneously moves from its steady value with the accumulation of VFAs in the anodic solution. MFCs were operated equipping four lab-scale ADs with carbon-based electrodes. Reactors were filled with the digestate from a full-scale AD and fed in batch with four kinds of feedstock (cheese whey, kitchen waste, citrus pulp and fishery waste). The MFC signal initially increased in parallel to VFAs production, then tended to a steady value for VFAs concentrations above 1000mgAcL-1. Peak concentrations of tVFAs (2500-4500mgAcL-1) and MFCs potentials were negatively correlated (r=0.916, p<0.05), regardless of the type of substrate. Inhibition of the MFC system occurred when VFAs increased fast above 4000mgAcL-1. Polarization curves of electrodes stressed that electroactive bacteria on bioanodes were strongly subjected to inhibition. The inhibition of electroactivity on bioanode trended like typical shock-sensors, opening to direct application as early-warning monitoring system in full-scale ADs.
---
paper_title: Microbial electrode BOD Sensors

paper_content:

Three measurement techniques are now in use for the determination of organic pollution (1): the biochemical oxygen demand (BOD) test, the chemical oxygen demand (COD) test, and various instrumental methods most of which utilize infrared analyzers. The BOD test has remained a standard pollution monitoring tool since 1936 (2). However, the BOD test requires a 5 day incubation period at 20°C. Many papers have been published on methods for a rapid estimation of 5 day BOD (2). However, these methods are not in fact rapid or simple.
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paper_title: On-line monitoring of low biochemical oxygen demand through continuous operation of a mediator-less microbial fuel cell

paper_content:

Abstract Oligotrophic microbial fuel cells (MFCs) were tested for the continuous monitoring of low biochemical oxygen demand (BOD) by using artificial wastewater, containing glucose and glutamate, as check solution. Ten times diluted trace mineral solution was used to minimize the background current level, which is generated from the oxidation of nitrilotriacetate used as a chelating agent. The feeding rate of 0.53 ml/min could increase the sensitivity from 0.16 to 0.43 A/(mg BOD/l) at 0.15 ml/min. The dynamic linear range of the calibration curve was between 2.0 and 10.0 mg BOD/l, and the response time to the change of 2 mg BOD/l was about 60 min. The current signal from an oligotroph-type MFCs increased with the increase in salts concentration, and the salt effect could be eliminated by 50 mM phosphate buffer.
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paper_title: Novel BOD (biological oxygen demand) sensor using mediator-less microbial fuel cell

paper_content:

A microbial fuel cell type of biosensor was used to determine the biochemical oxygen demand (BOD) of wastewater. The biosensor gave a good correlation between the BOD value and the coulomb produced. The BOD sensor has been operated for over 5 years in a stable manner without any servicing. This is much longer that that of previously reported BOD biosensors.
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paper_title: Improving the dynamic response of a mediator-less microbial fuel cell as a biochemical oxygen demand (BOD) sensor

paper_content:

The dynamic behavior of a mediator-less, microbial fuel cell (MFC) was studied as a continuous biochemical oxygen demand (BOD) sensor. The response time and the sensitivity were analyzed through the step-change testing of the fuel concentration. The MFC of 25 ml had the shortest response time of 36 +/- 2 min at the fuel-feeding rate of 0.53 ml min(-1) and the resistance of 10 ohms. A smaller MFC of 5 ml had a response time of 5 +/- 1 min.
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paper_title: Enhanced response of microbial fuel cell using sulfonated poly ether ether ketone membrane as a biochemical oxygen demand sensor.

paper_content:

Abstract The present study is focused on the development of single chamber microbial fuel cell (SCMFC) using sulfonated poly ether ether ketone (SPEEK) membrane to determine the biochemical oxygen demand (BOD) matter present in artificial wastewater (AW). The biosensor produces a good linear relationship with the BOD concentration up to 650 ppm when using artificial wastewater. This sensing range was 62.5% higher than that of Nafion ® . The most serious problem in using MFC as a BOD sensor is the oxygen diffusion into the anode compartment, which consumes electrons in the anode compartment, thereby reducing the coulomb yield and reducing the electrical signal from the MFC. SPEEK exhibited one order lesser oxygen permeability than Nafion ® , resulting in low internal resistance and substrate loss, thus improving the sensing range of BOD. The system was further improved by making a double membrane electrode assembly (MEA) with an increased electrode surface area which provide high surface area for electrically active bacteria.
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paper_title: A microbial fuel cell with improved cathode reaction as a low biochemical oxygen demand sensor

paper_content:

Mediator-less microbial fuel cells (MFC) enriched with oligotrophic microbes were optimized through enhancement of cathode reaction and lowering O2 diffusion into the anode compartment as a low BOD sensor. The optimization of the MFC has greatly improved the maximum current and coulomb yield. The oligotroph-type MFC could be used as a low BOD sensor with high operational stability, good repeatability and reproducibility.
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paper_title: Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor.

paper_content:

A mediator-less microbial fuel cell (MFC) was used as a biochemical oxygen demand (BOD) sensor in an amperometric mode for real-time wastewater monitoring. At a hydraulic retention time of 1.05 h, BOD values of up to 100 mg/l were measured based on a linear relationship, while higher BOD values were measured using a lower feeding rate. About 60 min was required to reach a new steady-state current after the MFCs had been fed with different strength artificial wastewaters (Aws). The current generated from the MFCs fed with AW with a BOD of 100 mg/l was compared to determine the repeatability, and the difference was less than 10%. When the MFC was starved, the original current value was regained with a varying recovery time depending on the length of the starvation. During starvation, the MFC generated a background level current, probably due to an endogenous metabolism.
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paper_title: Microbial fuel cell-based biosensor for fast analysis of biodegradable organic matter.

paper_content:

The current study was made to develop a biosensor based on a single-chamber microbial fuel cell in which anaerobes were retained in the anode compartment separated from the cathode compartment by a proton exchange membrane. In the sensor a replaceable anaerobic consortium was used for analyzing biodegradable organic matter. The anaerobes acted as biocatalysts in oxidizing organic matter and transferring electrons to the anode. The biocatalysts were renewed for each sample analysis by replacing the old anaerobic consortium with an equal amount of fresh one. A glucose standard solution was used as the target substrate. To obtain the maximum sensor output, the MFC-based sensor system was optimized using an 800 Omega resistor as the load to the external electric circuit and 25 mM phosphate buffer with 50mM NaCl as catholyte in the aerobic compartment. The temperature of anaerobic compartment was maintained at optimal 37 degrees C. The cell potential across the electrodes increased with increasing loading of glucose. The sensor response was linear against concentration of glucose up to 25 gl(-1). The detection limit was found as 0.025 gl(-1). The microbial fuel cell with replaceable anaerobic consortium could be used as a biosensor for on-line monitoring of organic matter.
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paper_title: Submersible microbial fuel cell sensor for monitoring microbial activity and BOD in groundwater: Focusing on impact of anodic biofilm on sensor applicability

paper_content:

A sensor, based on a submersible microbial fuel cell (SUMFC), was developed for in situ monitoring of microbial activity and biochemical oxygen demand (BOD) in groundwater. Presence or absence of a biofilm on the anode was a decisive factor for the applicability of the sensor. Fresh anode was required for application of the sensor for microbial activity measurement, while biofilm-colonized anode was needed for utilizing the sensor for BOD content measurement. The current density of SUMFC sensor equipped with a biofilm-colonized anode showed linear relationship with BOD content, to up to 250 mg/L (∼233 ± 1 mA/m(2)), with a response time of <0.67 h. This sensor could, however, not measure microbial activity, as indicated by the indifferent current produced at varying active microorganisms concentration, which was expressed as microbial adenosine-triphosphate (ATP) concentration. On the contrary, the current density (0.6 ± 0.1 to 12.4 ± 0.1 mA/m(2)) of the SUMFC sensor equipped with a fresh anode showed linear relationship, with active microorganism concentrations from 0 to 6.52 nmol-ATP/L, while no correlation between the current and BOD was observed. It was found that temperature, pH, conductivity, and inorganic solid content were significantly affecting the sensitivity of the sensor. Lastly, the sensor was tested with real contaminated groundwater, where the microbial activity and BOD content could be detected in <3.1 h. The microbial activity and BOD concentration measured by SUMFC sensor fitted well with the one measured by the standard methods, with deviations ranging from 15% to 22% and 6% to 16%, respectively. The SUMFC sensor provides a new way for in situ and quantitative monitoring contaminants content and biological activity during bioremediation process in variety of anoxic aquifers.
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paper_title: A single-chamber microbial fuel cell as a biosensor for wastewaters.

paper_content:

The traditional 5-day test of the biochemical oxygen demand (BOD5 test) has many disadvantages, and principally it is unsuitable for process control and real-time monitoring. As an alternative, a single-chamber microbial fuel cell (SCMFC) with an air cathode was tested as a biosensor and the performance analysed in terms of its measurement range, its response time, its reproducibility and its operational stability. When artificial wastewater was used as fuel, the biosensor output had a linear relationship with the BOD concentration up to 350 mg BOD cm � 3 ; very high reproducibility; and stability over 7 months of operation. The system was further improved by reducing by 75% the total anolyte volume. In this way a response time close to the hydraulic retention time (HRT) of the biosensor (i.e. 40 min) was reached. When the small volume SCMFC biosensor was fed with real wastewater a good correlation between COD concentration and current output was obtained, demonstrating the applicability of this system to real effluents. The measurements obtained with the biosensor were also in accordance with values obtained with standard measurement methods. a 2009 Published by Elsevier Ltd.
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paper_title: On-line monitoring of low biochemical oxygen demand through continuous operation of a mediator-less microbial fuel cell

paper_content:

Abstract Oligotrophic microbial fuel cells (MFCs) were tested for the continuous monitoring of low biochemical oxygen demand (BOD) by using artificial wastewater, containing glucose and glutamate, as check solution. Ten times diluted trace mineral solution was used to minimize the background current level, which is generated from the oxidation of nitrilotriacetate used as a chelating agent. The feeding rate of 0.53 ml/min could increase the sensitivity from 0.16 to 0.43 A/(mg BOD/l) at 0.15 ml/min. The dynamic linear range of the calibration curve was between 2.0 and 10.0 mg BOD/l, and the response time to the change of 2 mg BOD/l was about 60 min. The current signal from an oligotroph-type MFCs increased with the increase in salts concentration, and the salt effect could be eliminated by 50 mM phosphate buffer.
---
paper_title: Improving the dynamic response of a mediator-less microbial fuel cell as a biochemical oxygen demand (BOD) sensor

paper_content:

The dynamic behavior of a mediator-less, microbial fuel cell (MFC) was studied as a continuous biochemical oxygen demand (BOD) sensor. The response time and the sensitivity were analyzed through the step-change testing of the fuel concentration. The MFC of 25 ml had the shortest response time of 36 +/- 2 min at the fuel-feeding rate of 0.53 ml min(-1) and the resistance of 10 ohms. A smaller MFC of 5 ml had a response time of 5 +/- 1 min.
---
paper_title: Enhanced response of microbial fuel cell using sulfonated poly ether ether ketone membrane as a biochemical oxygen demand sensor.

paper_content:

Abstract The present study is focused on the development of single chamber microbial fuel cell (SCMFC) using sulfonated poly ether ether ketone (SPEEK) membrane to determine the biochemical oxygen demand (BOD) matter present in artificial wastewater (AW). The biosensor produces a good linear relationship with the BOD concentration up to 650 ppm when using artificial wastewater. This sensing range was 62.5% higher than that of Nafion ® . The most serious problem in using MFC as a BOD sensor is the oxygen diffusion into the anode compartment, which consumes electrons in the anode compartment, thereby reducing the coulomb yield and reducing the electrical signal from the MFC. SPEEK exhibited one order lesser oxygen permeability than Nafion ® , resulting in low internal resistance and substrate loss, thus improving the sensing range of BOD. The system was further improved by making a double membrane electrode assembly (MEA) with an increased electrode surface area which provide high surface area for electrically active bacteria.
---
paper_title: A microbial fuel cell with improved cathode reaction as a low biochemical oxygen demand sensor

paper_content:

Mediator-less microbial fuel cells (MFC) enriched with oligotrophic microbes were optimized through enhancement of cathode reaction and lowering O2 diffusion into the anode compartment as a low BOD sensor. The optimization of the MFC has greatly improved the maximum current and coulomb yield. The oligotroph-type MFC could be used as a low BOD sensor with high operational stability, good repeatability and reproducibility.
---
paper_title: Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor.

paper_content:

A mediator-less microbial fuel cell (MFC) was used as a biochemical oxygen demand (BOD) sensor in an amperometric mode for real-time wastewater monitoring. At a hydraulic retention time of 1.05 h, BOD values of up to 100 mg/l were measured based on a linear relationship, while higher BOD values were measured using a lower feeding rate. About 60 min was required to reach a new steady-state current after the MFCs had been fed with different strength artificial wastewaters (Aws). The current generated from the MFCs fed with AW with a BOD of 100 mg/l was compared to determine the repeatability, and the difference was less than 10%. When the MFC was starved, the original current value was regained with a varying recovery time depending on the length of the starvation. During starvation, the MFC generated a background level current, probably due to an endogenous metabolism.
---
paper_title: Submersible microbial fuel cell sensor for monitoring microbial activity and BOD in groundwater: Focusing on impact of anodic biofilm on sensor applicability

paper_content:

A sensor, based on a submersible microbial fuel cell (SUMFC), was developed for in situ monitoring of microbial activity and biochemical oxygen demand (BOD) in groundwater. Presence or absence of a biofilm on the anode was a decisive factor for the applicability of the sensor. Fresh anode was required for application of the sensor for microbial activity measurement, while biofilm-colonized anode was needed for utilizing the sensor for BOD content measurement. The current density of SUMFC sensor equipped with a biofilm-colonized anode showed linear relationship with BOD content, to up to 250 mg/L (∼233 ± 1 mA/m(2)), with a response time of <0.67 h. This sensor could, however, not measure microbial activity, as indicated by the indifferent current produced at varying active microorganisms concentration, which was expressed as microbial adenosine-triphosphate (ATP) concentration. On the contrary, the current density (0.6 ± 0.1 to 12.4 ± 0.1 mA/m(2)) of the SUMFC sensor equipped with a fresh anode showed linear relationship, with active microorganism concentrations from 0 to 6.52 nmol-ATP/L, while no correlation between the current and BOD was observed. It was found that temperature, pH, conductivity, and inorganic solid content were significantly affecting the sensitivity of the sensor. Lastly, the sensor was tested with real contaminated groundwater, where the microbial activity and BOD content could be detected in <3.1 h. The microbial activity and BOD concentration measured by SUMFC sensor fitted well with the one measured by the standard methods, with deviations ranging from 15% to 22% and 6% to 16%, respectively. The SUMFC sensor provides a new way for in situ and quantitative monitoring contaminants content and biological activity during bioremediation process in variety of anoxic aquifers.
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paper_title: Renewable sustainable biocatalyzed electricity production in a photosynthetic algal microbial fuel cell (PAMFC)

paper_content:

Electricity production via solar energy capturing by living higher plants and microalgae in combination with microbial fuel cells are attractive because these systems promise to generate useful energy in a renewable, sustainable, and efficient manner. This study describes the proof of principle of a photosynthetic algal microbial fuel cell (PAMFC) based on naturally selected algae and electrochemically active microorganisms in an open system and without addition of instable or toxic mediators. The developed solar-powered PAMFC produced continuously over 100 days renewable biocatalyzed electricity. The sustainable performance of the PAMFC resulted in a maximum current density of 539 mA/m2 projected anode surface area and a maximum power production of 110 mW/m2 surface area photobioreactor. The energy recovery of the PAMFC can be increased by optimization of the photobioreactor, by reducing the competition from non-electrochemically active microorganisms, by increasing the electrode surface and establishment of a further-enriched biofilm. Since the objective is to produce net renewable energy with algae, future research should also focus on the development of low energy input PAMFCs. This is because current algae production systems have energy inputs similar to the energy present in the outcoming valuable products.
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paper_title: Toxicity detection in water containing heavy metal ions with a self-powered microbial fuel cell-based biosensor.

paper_content:

In this work, a self-powered microbial fuel cell (MFC)-based biosensor was developed for detecting toxicity in water containing heavy metal ions. Experimental conditions containing concentration of potassium ferricyanide, load resistor and glucose concentration were optimized. Six heavy metal ions (2mg/L, Cu2+, Hg2+, Zn2+, Cd2+, Pb2+ and Cr3+) were tested by this biosensor and the inhibition ratios obtained were 12.56%, 13.99%, 8.81%, 9.29%, 5.59% and 1.95%, respectively. The inhibition ratios of 28.13% was also obtained for detecting the laboratory wastewater containing several heavy metal ions. The experimental results exhibited the feasibility and potential of the self-powered biosensor in detecting toxicities in water containing heavy metal ions.
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paper_title: A novel biomonitoring system using microbial fuel cells.

paper_content:

A novel biomonitoring system using microbial fuel cells for detecting the inflow of toxic substances into water systems has been developed for the purpose of on-site and on-line monitoring. The characteristics of electric current generation by electrochemically-active bacteria were conveniently monitored using a microbial fuel cell format and a computer-controlled potentiometer. When toxic substances (an organophosphorus compound, Pb, Hg, and PCBs) were added to the microbial fuel cell, rapid decreases in the current were observed. The inhibition ratios caused by inflow of these toxic substances (1 mg l(-1)) were 61%, 46%, 28% and 38%, respectively, when compared to the control, and generally increased in proportion to the addition time and concentration of toxic substances. When real wastewater was applied from a local wastewater treatment plant, more significant current decreases and higher inhibition ratios were observed following the introduction of toxic substances than in the laboratory tests. For example, the inhibition ratio was 76% on addition of a 1 mg l(-1) Cd and 1 mg l(-1) Pb mixture. Application of the microbial fuel cell for pollutant biomonitoring is discussed.
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paper_title: Microbial fuel cell as a biosensor to monitor various toxic metal substances in water

paper_content:

Toxicities of twelve kinds of metals were evaluated by using a microbial fuel cell as a monitoring sensor. Tested metals were barium(Ba), beryllium(Be), cobalt(Co), copper(Cu), iron(Fe), manganese(Mn), mercury(Hg), lead(Pb), selenium(Se), thallium(Tl), vanadium(V), and zinc(Zn). Most of the tested metals are not allowed to be present above a certain concentration in drinking water system in South Korea. To evaluate the toxicities of the metals in water, HATOX-2000, a bio-monitoring system, was utilized. Minimum concentration of response of each metal and toxicity values in certain concentration range were determined through the test. The minimum concentrations of response were less than 1.0 mg/L for all the tested metals. The lowest value was observed as 0.1 mg/L for thallium. HATOX-2000 was able to detect the tested metal substances in water system with high sensitivity.
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paper_title: Aluminum as a toxicant.

paper_content:

Although aluminum is the most abundant metal in nature, it has no known biological function. However, it is known that there is a causal role for aluminum in dialysis encephalopathy, microcytic anemia, and osteomalacia. Aluminum has also been proposed to play a role in the pathogenesis of Alzheimer's disease (AD) even though this issue is controversial. The exact mechanism of aluminum toxicity is not known but accumulating evidence suggests that the metal can potentiate oxidative and inflammatory events, eventually leading to tissue damage. This review encompasses the general toxicology of aluminum with emphasis on the potential mechanisms by which it may accelerate the progression of chronic age-related neurodegenerative disorders.
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paper_title: Demonstration of the use of a photosynthetic microbial fuel cell as an environmental biosensor

paper_content:

Microbial fuel cells (MFCs) are bioelectrochemical systems (BESs) that exploit biological catalytic processes for the generation of electrical power or the accumulation of useful compounds. Photosynthetic MFCs (pMFCs) are those that utilise photosynthetic microorganisms, such as algae and cyanobacteria, to provide reducing power at the anode. A reproducible light-dependent electrogenic effect occurs as algae or cyanobacteria convert light to electrical energy in the BES. In addition to the generation of electricity, the phenomenon may be useful in niche circumstances such as for bioelectrosynthesis or for use in environmental biosensors. In this study we measure the effect of common toxicants (copper, thallium, zinc and glyphosate) on the electrogenic activity of electrode surface-dwelling algae and cyanobacteria. We observed a decrease in the light-dependent electrical response via these photosynthetic microorganisms in our pMFC that was proportional to the concentration of toxicants. This demonstrates the utility of these BESs as potential environmental biosensors where the metabolism of photosynthetic microorganisms acts to sense signals from the environment.
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paper_title: Assessing the Solitary and Joint Biotoxicities of Heavy Metals and Acephate Using Microbial Fuel Cell

paper_content:

A microbial fuel cell (MFC)-based biosensor can be used to detect the water toxicity. In this study, the solitary and joint biotoxicities of heavy metal ions (Cu 2+ , Ni 2+ , Cd 2+ ) and acephate were investigated using single-chamber MFC. The results showed that all the contaminants could individually inhibit the electricity production of MFC, and the toxicity order of these three metals was Cd 2+ >Ni 2+ >Cu 2+ . The concentration-response curves for Cu 2+ , Ni 2+ and acephate were well fitted linearly while the curve for Cd 2+ was well fitted by an exponential function. The joint-biotoxicity results of Cd 2+ -Ni 2+ and Cu 2+ -acephate were as follows: the toxic effect of Cu 2+ and Ni 2+ was synergistic. The existence of Cu 2+ had antagonism with acephate at low concentrations, which could reduce the biotoxicity, while their toxic effect on MFC became synergistic at high concentrations. This study could provide some basic data for water quality monitoring using MFC.
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paper_title: A batch-mode cube microbial fuel cell based "shock" biosensor for wastewater quality monitoring.

paper_content:

A single chamber batch-mode cube microbial fuel cell (CMFC) was explored as a novel self-sustained biosensor for real-time monitoring the toxicity shocks (sudden change in toxins concentration) of representative toxic metals in wastewater influent. Four types of shocks, including chromium, iron, nitrate, and sodium acetate, were selected to represent the shocks of acute-toxic heavy metal, low-toxic metal, common nutrient, and organic contaminant in wastewater, respectively. Wastewater was used as the inoculum in CMFCs for anodic electrogenic bacteria that were fully acclimated within 3 days, which indicated that this self-powered sensor can be quickly adapted to wastewater. The results showed that the CMFC was able to distinguish shocks of toxins from non-toxins based on voltage signal changes. Anode open circuit potential (OCP) values were well correlated with the CMFC voltage changes, indicating that the voltage changes were mainly dependent on the activity of the electrogenic bacteria on the anode surfaces.
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paper_title: Utility of Ochrobactrum anthropi YC152 in a Microbial Fuel Cell as an Early Warning Device for Hexavalent Chromium Determination

paper_content:

Fast hexavalent chromium (Cr(VI)) determination is important for environmental risk and health-related considerations. We used a microbial fuel cell-based biosensor inoculated with a facultatively anaerobic, Cr(VI)-reducing, and exoelectrogenic Ochrobactrum anthropi YC152 to determine the Cr(VI) concentration in water. The results indicated that O. anthropi YC152 exhibited high adaptability to pH, temperature, salinity, and water quality under anaerobic conditions. The stable performance of the microbial fuel cell (MFC)-based biosensor indicated its potential as a reliable biosensor system. The MFC voltage decreased as the Cr(VI) concentration in the MFC increased. Two satisfactory linear relationships were observed between the Cr(VI) concentration and voltage output for various Cr(VI) concentration ranges (0.0125–0.3 mg/L and 0.3–5 mg/L). The MFC biosensor is a simple device that can accurately measure Cr(VI) concentrations in drinking water, groundwater, and electroplating wastewater in 45 min with low deviations (<10%). The use of the biosensor can help in preventing the violation of effluent regulations and the maximum allowable concentration of Cr(VI) in water. Thus, the developed MFC biosensor has potential as an early warning detection device for Cr(VI) determination even if O. anthropi YC152 is a possible opportunistic pathogen.
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paper_title: Using electrical signals of microbial fuel cells to detect copper stress on soil microorganisms

paper_content:

A method based on microbial fuel cells (MFCs) was used to evaluate the effects of copper (Cu2+) on soil microorganisms. Soil spiked with 50-400mgkg(-1) of Cu2+ as CuCl2 was incubated for 24hours before being packed into the MFC anode chambers and assayed for dehydrogenase activity (DHA), substrate-induced respiration (SIR) and microbial biomass carbon (C-mic). Soil was amended with 5% (w/w) glucose to accelerate start-up' and improve power generation, followed by 150hours of operation. Anode biofilm and soil was extracted to recover total nucleic acids and the 16S rRNA gene was subjected to PCR-DGGE, sequencing and phylogenetic analysis. Results showed that increases in soil Cu2+ concentrations reduced voltage and postponed start-up. The quantity of generated electrons within 48hours was 32.5 coulomb (C) in the without-Cu control and decreased with increasing Cu2+ concentrations (11.7, 7.7, 2.0 and 1.3C under 50, 100, 200 and 400mgkg(-1)Cu(2+), respectively). Cyclic voltammetry identified decreased soil electrochemical activity with increasing Cu2+ concentrations. The results indicate that Cu2+ reduced electrical signals by inhibiting the electrochemical activity, metabolic activity and biomass of microorganisms. The 16S sequences of recovered anodic bacteria were assigned to Firmicutes, including Bacillaceae, Acetobacteraceae, Clostridium, Bacillus and Sporolactobacillus. In general, the DGGE band intensity of anodic bacteria decreased with increasing Cu2+ concentrations, except for bands assigned to Firmicutes and Bacillus, which increased with increasing Cu2+ concentrations. We suggest that the short-term electrical signals generated from MFCs with contaminated soil can be used to assess the toxic effect of heavy metal pollutants on soil microorganisms.
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paper_title: Possibility of using a lithotrophic iron-oxidizing microbial fuel cell as a biosensor for detecting iron and manganese in water samples

paper_content:

Iron-oxidizing bacterial consortia can be enriched in microbial fuel cells (MFCs) operated with ferrous iron as the sole electron donor. In this study, we investigated the possibility of using such lithotrophic iron-oxidizing MFC (LIO-MFC) systems as biosensors to monitor iron and manganese in water samples. When operated with anolytes containing only ferrous iron as the sole electron donor, the experimented LIO-MFCs generated electrical currents in response to the presence of Fe(2+) in the anolytes. For the concentrations of Fe(2+) in the range of 3-20 mM, a linear correlation between the current and the concentration of Fe(2+) could be achieved (r(2) = 0.98). The LIO-MFCs also responded to the presence of Mn(2+) in the anolytes but only when the Mn(2+) concentration was less than 3 mM. The presence of other metal ions such as Ni(2+) or Pb(2+) in the anolytes reduced the Fe(2+)-associated electricity generation of the LIO-MFCs at various levels. Organic compounds, when present at a non-excessive level together with Fe(2+) in the anolytes, did not affect the generation of electricity, although the compounds might serve as alternative electron donors for the anode bacteria. The performance of the LIO-MFCs was also affected to different degrees by operational parameters, including surrounding temperature, pH of the sample, buffer strength and external resistance. The results proved the potential of LIO-MFCs as biosensors sensing Fe(2+) in water samples with a significant specificity. However, the operation of the system should be in compliance with an optimal procedure to ensure reliable performance.
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paper_title: Bioelectrochemical Sensor Using Living Biofilm To in Situ Evaluate Flocculant Toxicity

paper_content:

Flocculants have been used to clarify water for thousands of years. However, the in situ evaluation of flocculant toxicity is difficult because flocculants usually exist as growing complex flocs which is hard to monitor. With alum (KAl(SO4)2·12H2O) as the typical flocculant, a bioelectrochemical sensor is designed to in situ detect its bacterial toxicity. The attenuation ratio of current densities linearly increased with alum concentration (R2 > 0.98) with a slope of 0.0054 A m–2 drop per mg L–1 of alum, indicating a typical toxic response of alum. Turnover and nonturnover cyclic voltammetries (CVs) revealed that the alum inhibited the electrochemical activity of bacteria rather than changing the electron transfer pathways. Alum also hindered the diffusion by flocculation at a concentration larger than 100 mg L–1, which was further confirmed by the linear decrease in viability when biofilm thickness increased. It was revealed that both inactivation of biofilm and influences on diffusion by alum can be det...
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paper_title: Photosynthetic Microbial Fuel Cells.

paper_content:

This chapter presents the current state of research on bioelectrochemical systems that include phototrophic organisms. First, we describe what is known of how phototrophs transfer electrons from internal metabolism to external substrates. This includes efforts to understand both the source of electrons and transfer pathways within cells. Second, we consider technological progress toward producing bio-photovoltaic devices with phototrophs. Efforts to improve these devices by changing the species included, the electrode surfaces, and chemical mediators are described. Finally, we consider future directions for this research field.
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paper_title: A novel biomonitoring system using microbial fuel cells.

paper_content:

A novel biomonitoring system using microbial fuel cells for detecting the inflow of toxic substances into water systems has been developed for the purpose of on-site and on-line monitoring. The characteristics of electric current generation by electrochemically-active bacteria were conveniently monitored using a microbial fuel cell format and a computer-controlled potentiometer. When toxic substances (an organophosphorus compound, Pb, Hg, and PCBs) were added to the microbial fuel cell, rapid decreases in the current were observed. The inhibition ratios caused by inflow of these toxic substances (1 mg l(-1)) were 61%, 46%, 28% and 38%, respectively, when compared to the control, and generally increased in proportion to the addition time and concentration of toxic substances. When real wastewater was applied from a local wastewater treatment plant, more significant current decreases and higher inhibition ratios were observed following the introduction of toxic substances than in the laboratory tests. For example, the inhibition ratio was 76% on addition of a 1 mg l(-1) Cd and 1 mg l(-1) Pb mixture. Application of the microbial fuel cell for pollutant biomonitoring is discussed.
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paper_title: A novel p-nitrophenol degradation gene cluster from a gram-positive bacterium, Rhodococcus opacus SAO101.

paper_content:

p-Nitrophenol (4-NP) is recognized as an environmental contaminant; it is used primarily for manufacturing medicines and pesticides. To date, several 4-NP-degrading bacteria have been isolated; however, the genetic information remains very limited. In this study, a novel 4-NP degradation gene cluster from a gram-positive bacterium, Rhodococcus opacus SAO101, was identified and characterized. The deduced amino acid sequences of npcB, npcA, and npcC showed identity with phenol 2-hydroxylase component B (reductase, PheA2) of Geobacillus thermoglucosidasius A7 (32%), with 2,4,6-trichlorophenol monooxygenase (TcpA) of Ralstonia eutropha JMP134 (44%), and with hydroxyquinol 1,2-dioxygenase (ORF2) of Arthrobacter sp. strain BA-5-17 (76%), respectively. The npcB, npcA, and npcC genes were cloned into pET-17b to construct the respective expression vectors pETnpcB, pETnpcA, and pETnpcC. Conversion of 4-NP was observed when a mixture of crude cell extracts of Escherichia coli containing pETnpcB and pETnpcA was used in the experiment. The mixture converted 4-NP to hydroxyquinol and also converted 4-nitrocatechol (4-NCA) to hydroxyquinol. Furthermore, the crude cell extract of E. coli containing pETnpcC converted hydroxyquinol to maleylacetate. These results suggested that npcB and npcA encode the two-component 4-NP/4-NCA monooxygenase and that npcC encodes hydroxyquinol 1,2-dioxygenase. The npcA and npcC mutant strains, SDA1 and SDC1, completely lost the ability to grow on 4-NP as the sole carbon source. These results clearly indicated that the cloned npc genes play an essential role in 4-NP mineralization in R. opacus SAO101.
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paper_title: Silicon-based microfabricated microbial fuel cell toxicity sensor.

paper_content:

Microbial fuel cells (MFCs) have been used for several years as biosensors for measuring environmental parameters such as biochemical oxygen demand and water toxicity. The present study is focused on the detection of toxic matter using a novel silicon-based MFC. Like other existing toxicity sensors based on MFCs, this device is capable of detecting the variation on the current produced by the cell when toxic compounds are present in the medium. The MFC approach presented in this work aims to obtain a simple, compact and planar device for its further application as a biosensor in the design and fabrication of equipment for toxicity monitoring. It consists on a proton exchange membrane placed between two microfabricated silicon plates that act as current collectors. An array of square 80 μm × 80 μm vertical channels, 300 μm deep, have been defined trough the plates over an area of 6 mm × 6 mm. The final testing assembly incorporates two perspex pieces positioned onto the plates as reservoirs with a working volume of 144 μL per compartment. The operation of the microdevice as a direct electron transfer MFC has been validated by comparing its performance against a larger scale MFC, run under the same conditions. The device has been tested as a toxicity sensor by setting it at a fixed current while monitoring changes in the output power. A drop in the power production is observed when a toxic compound is added to the anode compartment. The compact design of the device makes it suitable for its incorporation into measurement equipment either as an individual device or as an array of sensors for high throughput processing.
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paper_title: A mediator-less microbial fuel cell using a metal reducing bacterium, Shewanella putrefaciens

paper_content:

Abstract Direct electron transfer from different Shewanella putrefaciens strains to an electrode was examined using cyclic voltammetry and a fuel cell type electrochemical cell. Both methods determine the electrochemical activity of the bacterium without any electrochemical mediators. In the cyclic voltammetric studies, anaerobically grown cells of Shewanella putrefaciens MR-1, IR-1, and SR-21 showed electrochemical activities, but no activities were observed in aerobically grown Shewanella putrefaciens cells nor in aerobically and anaerobically grown E. coli cell suspensions. The electrochemical activities measured by the cyclic voltammetric method were closely related to the electric potential and current generation capacities in the microbial fuel cell system. Cytochromes localized to the outer membrane are believed to facilitate the direct electron transfer to the electrode from the intact bacterial cells. The concentration of the electron donor in the anode compartment determined the current generation capacity and potential development in the microbial fuel cell. When the high concentration of the bacteria (0.47 g dry cell weight/liter) and an electrode that has large surface area (apparent area: 50 cm 2 ) were used, relatively high Coulombic yield (over 3 C for 12 h) was obtained from the bacteria.
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paper_title: Analytical applications of microbial fuel cells. Part II: Toxicity, microbial activity and quantification, single analyte detection and other uses.

paper_content:

Microbial fuel cells were rediscovered twenty years ago and now are a very active research area. The reasons behind this new activity are the relatively recent discovery of electrogenic or electroactive bacteria and the vision of two important practical applications, as wastewater treatment coupled with clean energy production and power supply systems for isolated low-power sensor devices. Although some analytical applications of MFCs were proposed earlier (as biochemical oxygen demand sensing) only lately a myriad of new uses of this technology are being presented by research groups around the world, which combine both biological-microbiological and electroanalytical expertises. This is the second part of a review of MFC applications in the area of analytical sciences. In Part I a general introduction to biological-based analytical methods including bioassays, biosensors, MFCs design, operating principles, as well as, perhaps the main and earlier presented application, the use as a BOD sensor was reviewed. In Part II, other proposed uses are presented and discussed. As other microbially based analytical systems, MFCs are satisfactory systems to measure and integrate complex parameters that are difficult or impossible to measure otherwise, such as water toxicity (where the toxic effect to aquatic organisms needed to be integrated). We explore here the methods proposed to measure toxicity, microbial metabolism, and, being of special interest to space exploration, life sensors. Also, some methods with higher specificity, proposed to detect a single analyte, are presented. Different possibilities to increase selectivity and sensitivity, by using molecular biology or other modern techniques are also discussed here.
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paper_title: A novel biosensor for p-nitrophenol based on an aerobic anode microbial fuel cell.

paper_content:

P-nitrophenol is one of the most common contaminants in chemical industrial wastewater, and in situ real-time monitoring of PNP cannot be achieved by conventional analytical techniques. Here, a two-chamber microbial fuel cell with an aerobic anode chamber was tested as a biosensor for in situ real-time monitoring of PNP. Pseudomonas monteilii LZU-3, which was used as the biological recognition element, can form a biofilm on the anode electrode using PNP as a sole substrate. The optimal operation parameters of the biosensor were as follows: external resistance 1000Ω, pH 7.8, temperature 30°C, and maximum PNP concentration 50mgL(-1). Under these conditions, the maximum voltages showed a linear relationship with PNP concentrations ranging from 15±5 to 44±4.5mgL(-1). Furthermore, we developed a novel portable device for in situ real-time monitoring of PNP. When the device was applied to measure PNP in wastewater containing various additional aromatic compounds and metal ions, the performance of the biosensor was not affected and the correlation between the maximum voltages and the PNP concentrations ranging from 9±4mgL(-1) to 36 ± 5mgL(-1) was conserved. The results demonstrated that the MFC biosensor provides a rapid and cost-efficient analytical method for real-time monitoring of toxic and recalcitrant pollutants in environmental samples.
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paper_title: FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin.

paper_content:

A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1-1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1-100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT).
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paper_title: Concentration responses of toxicity sensor with Shewanella oneidensis MR-1 growing in bioelectrochemical systems.

paper_content:

Bioelectrochemical systems (BESs) provide an opportunity to detect biological toxicity of water samples. However, the concentration responses of toxins had not been investigated in detail. Using formaldehyde as a toxic substance, the current responses were analyzed over a concentration range from 0.01% to 0.10% in a single chambered BES with 0mV (versus saturated calomel electrode) applied on the anode. The decay percentages of currents increased in proportion with the concentration of formaldehyde after 10000s (∼2.8h), with the peak R(2) of 0.9361 observed at 35,000s (∼9.7h). Fitting results of exponential decay equation showed that the magnification factor (a) closely related with baseline currents and the toxicity factor (b) was in direct proportion to formaldehyde concentration (from 0% to 0.08%) except over the high concentration of 0.10%. These results provide preliminary information about toxin concentration responses in BESs.
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paper_title: Use of a site-specific recombination-based biosensor for detecting bioavailable toluene and related compounds on roots

paper_content:

We constructed and characterized a plasmid-based genetic system that reports the expression of a toluene-responsive promoter (PtbuA1) by effecting an irreversible, heritable change in the biosensor cell. Expression of the reporter gene gfp is strongly repressed in the absence of expression from the PtbuA1 promoter, and high level gfp expression in the original cell and its progeny is mediated by the site-specific recombination machinery of bacteriophage P22 to initiate removal of a repressor cassette. The reporter plasmid pTolLHB was functional in two soil saprophytes, Pseudomonas fluorescens A506 and Enterobacter cloacae JL1157, with the efficiency and sensitivity to low toluene concentrations being optimal in P. fluorescens A506. In culture, 80-100% of the A506 (pTolLHB) population expressed gfp following exposure to 0.2 micro m toluene for one to three hours. Compared to the response of A506 containing a plasmid-borne PtbuA1-gfp fusion, the recombination-based biosensor was more sensitive at detecting low toluene and trichloroethylene concentrations. An A506 (pTolLHB) inoculum, which had a background of 2.5% of the cells expressing gfp, was introduced onto barley roots in soil microcosms. If toluene was introduced into the microcosms, after 24 h, 72% of the A506 (pTolLHB) cells recovered from roots expressed gfp, indicating bioavailable toluene to rhizosphere bacteria. When toluene was not introduced, 16.5% of the A506 (pTolLHB) cells recovered from the roots expressed gfp, indicating that natural inducers of the PtbuA1 promoter were present in the barley rhizosphere. When introduced into rhizotrons containing barley plants and toluene vapours, the biosensor allowed localization of the availability of toluene along the seminal roots. In rhizotrons that were not exposed to toluene vapours, the biosensor exhibited high PtbuA1-promoter activity in distinct regions along the seminal roots, indicating spatial heterogeneity plant- or rhizosphere microbial community-derived inducers of the PtbuA1 promoter. This recombination-based toluene biosensor thus was useful in identifying bacterial exposure to transient or low levels of toluene, or related compounds, directly in the environment.
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paper_title: Functionalization of carbon buckypaper for the sensitive determination of hydrogen peroxide in human urine.

paper_content:

Abstract Here we report on a new approach for the electrochemical detection of hydrogen peroxide (H 2 O 2 ) based on the co-immobilization of horseradish peroxidase and methylene blue on the functionalized carbon buckypaper supported by a titanium substrate. Cyclic voltammetry was used to study and optimize the performance of the resulting electrochemical biosensor. The proposed biosensor exhibited high analytical performance towards the quantification of H 2 O 2 at the physiological pH 7.4. Under optimized conditions, the biosensor shows a wide linear response range from 0.1 × 10 −6 to 5 × 10 −4 M concentrations of H 2 O 2 . The detection limit was determined to be 7.5 × 10 −8 M (based on S/N = 3). Reproducibility and stability of the fabricated biosensor were examined with satisfactory results. The biological relevance of the developed electrochemical biosensor has been further studied by the determination of H 2 O 2 in human urine samples of normal volunteers prior to and following the ingestion of coffee. Increased levels of urinary H 2 O 2 concentration suggest that oxidative stress is induced by coffee drinking in humans. There is considerable interest in oxidative stress as relates to human physiology. The sensitive determination of H 2 O 2 in human urine may serve as a valuable biomarker to effectively elucidate specific levels of oxidative stress in vivo.
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paper_title: On-line monitoring of low biochemical oxygen demand through continuous operation of a mediator-less microbial fuel cell

paper_content:

Abstract Oligotrophic microbial fuel cells (MFCs) were tested for the continuous monitoring of low biochemical oxygen demand (BOD) by using artificial wastewater, containing glucose and glutamate, as check solution. Ten times diluted trace mineral solution was used to minimize the background current level, which is generated from the oxidation of nitrilotriacetate used as a chelating agent. The feeding rate of 0.53 ml/min could increase the sensitivity from 0.16 to 0.43 A/(mg BOD/l) at 0.15 ml/min. The dynamic linear range of the calibration curve was between 2.0 and 10.0 mg BOD/l, and the response time to the change of 2 mg BOD/l was about 60 min. The current signal from an oligotroph-type MFCs increased with the increase in salts concentration, and the salt effect could be eliminated by 50 mM phosphate buffer.
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paper_title: Demonstration of the use of a photosynthetic microbial fuel cell as an environmental biosensor

paper_content:

Microbial fuel cells (MFCs) are bioelectrochemical systems (BESs) that exploit biological catalytic processes for the generation of electrical power or the accumulation of useful compounds. Photosynthetic MFCs (pMFCs) are those that utilise photosynthetic microorganisms, such as algae and cyanobacteria, to provide reducing power at the anode. A reproducible light-dependent electrogenic effect occurs as algae or cyanobacteria convert light to electrical energy in the BES. In addition to the generation of electricity, the phenomenon may be useful in niche circumstances such as for bioelectrosynthesis or for use in environmental biosensors. In this study we measure the effect of common toxicants (copper, thallium, zinc and glyphosate) on the electrogenic activity of electrode surface-dwelling algae and cyanobacteria. We observed a decrease in the light-dependent electrical response via these photosynthetic microorganisms in our pMFC that was proportional to the concentration of toxicants. This demonstrates the utility of these BESs as potential environmental biosensors where the metabolism of photosynthetic microorganisms acts to sense signals from the environment.
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paper_title: Monitoring of phosphorus bioavailability in water by an immobilized luminescent cyanobacterial reporter strain.

paper_content:

Massive growth of cyanobacteria, known as "algal blooms", has become a major concern for water monitoring. It has been observed that environmental factors like temperature, light, and certain patterns of availability of nutrients such as P, N, Fe influence cyanobacterial proliferation and toxin production. In order to monitor nutrients in aquatic ecosystems, an assay for monitoring phosphorus bioavailability to cyanobacteria was developed. The test consists of an immobilized luminescent reporter strain of Synechococcus PCC 7942, designated APL. The reporter strain harbours the gene coding the reporter protein luciferase from Vibrio harveyi under control of the inducible alkaline phosphatase promoter from Synechococcus PCC 7942, and can be induced under phosphorus limitation. The resultant CyanoSensor detects PO(3-)(4)-P in a concentration range of 0.3-8 microM after a sample incubation time of 8 h under continuous illumination (50 microE m(-2) s(-1)). The sensor also responded to a variety of organic phosphorus sources and was storable for 3 weeks at 4 degrees C. It could be demonstrated that the CyanoSensor for bioavailability monitoring is an improvement to conventional phosphorus detection methods.
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paper_title: On-line monitoring of low biochemical oxygen demand through continuous operation of a mediator-less microbial fuel cell

paper_content:

Abstract Oligotrophic microbial fuel cells (MFCs) were tested for the continuous monitoring of low biochemical oxygen demand (BOD) by using artificial wastewater, containing glucose and glutamate, as check solution. Ten times diluted trace mineral solution was used to minimize the background current level, which is generated from the oxidation of nitrilotriacetate used as a chelating agent. The feeding rate of 0.53 ml/min could increase the sensitivity from 0.16 to 0.43 A/(mg BOD/l) at 0.15 ml/min. The dynamic linear range of the calibration curve was between 2.0 and 10.0 mg BOD/l, and the response time to the change of 2 mg BOD/l was about 60 min. The current signal from an oligotroph-type MFCs increased with the increase in salts concentration, and the salt effect could be eliminated by 50 mM phosphate buffer.
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paper_title: Microbial Biosensors for Environmental Monitoring and Food Analysis

paper_content:

A microbial biosensor is an elaborate analytic device that uses microorganisms as recognition elements, mainly for application in environmental monitoring, food safety, military defense, and medicine. The selection and immobilization of microorganisms are key steps that must first be addressed for microbial biosensors. Currently, genetically modified microorganisms play an increasingly significant role in improving the capacity of biosensors. Electrochemical and optical types of transducers have been widely employed in microbial biosensors, although bioluminescence and fluorescence methods have been highlighted recently. Additionally, the microbial fuel cell (MFC), which has been mainly applied in biological oxygen demand (BOD) biosensors, is a promising technology. This article reviews recent developments of microbial biosensors with respect to their applications in environmental monitoring and food analysis, including measurement of a variety of common pollutants, products in fermenting processes, antib...
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paper_title: Fast and sensitive water quality assessment: A μL-scale microbial fuel cell-based biosensor integrated with an air-bubble trap and electrochemical sensing functionality

paper_content:

Abstract This work describes the development and operation of a microliter-sized microbial fuel cell-based biosensor for monitoring toxic substances in water. The biosensor features the integration of (i) a three-electrode configuration to provide electrochemical sensing functionality for improving sensitivity and reliability in water quality testing and (ii) an air-bubble trap to prevent all unwanted bubbles from entering the sensing surface for maximizing bacterial growth and their subsequent electron transfer. The miniaturization of the biosensor produced favorable conditions for (i) reducing measurement time with high probability of cell attachment/biofilm formation in the micro-sized chamber and (ii) enhancing the reaction sensitivity with large surface area-to-volume ratio and increased reaction kinetics. When formaldehyde was introduced as a toxic component, the rapid and sensitive current responses were obtained over a concentration range from 0.001% to 0.1% in the biosensor with 0.2 V (versus solid-state thin film Ag/AgCl reference electrode) applied on the anode.
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paper_title: Increase of riboflavin biosynthesis underlies enhancement of extracellular electron transfer of Shewanella in alkaline microbial fuel cells.

paper_content:

Electrolyte pH tremendously affects the electricity output of microbial fuel cells. However, its underlying molecular mechanism remains elusive, in particular for Shewanella oneidensis MR-1, one of the most widely adopted electrogenic microorganisms. Herein, we found that MFCs were able to deliver a significant (but different) electricity output in a wide range of pH (from 6 to 10), with the maximum at pH=9 (alkaline), which delivers ∼1.5times' higher power output than that at pH=7 (neutral). Furthermore, cyclic voltammetry analysis showed an enhanced electrochemical activity of riboflavin (responsible for extracellular electron transfer of Shewanella) at alkaline pH. Strikingly, the concentration of riboflavin synthesized by Shewanella in MFCs at different pH showed a good correlation with the electricity output of MFCs. Thus, our results substantiated that the increase of riboflavin biosynthesis by Shewanella at the alkaline condition underlies the improvement of the electricity output in MFCs.
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paper_title: A three-species microbial consortium for power generation

paper_content:

Design and construction of synthetic microbial consortia is a promising strategy to enhance the performance of bioelectrochemical systems (BESs) and to facilitate practical applications in bioenergy production. According to the design principle of “division-of-labor”, we synthesized a three-species microbial consortium for power generation, consisting of engineered Escherichia coli, Bacillus subtilis and Shewanella oneidensis. In this consortium, E. coli digested glucose to produce lactate as a carbon source and an electron donor; B. subtilis produced riboflavin as an electron shuttle; and S. oneidensis served as the exoelectrogen to generate electricity. In return, S. oneidensis oxidized lactate to acetate, which fed E. coli and B. subtilis as the carbon source. Thus, the three species formed a cross-feeding microbial consortium, which performed “better together” for power generation. As a result, glucose (11 mM, total 0.28 g) was converted to electricity for more than 15 days with high energy conversion efficiency (up to 55.7%). The microbial composition and electricity output were stable throughout the operation cycle. Furthermore, the consortium exhibited highly functional robustness to fluctuations in the initial inoculation ratio of the three strains. This system provided new insight into the rational design of more efficient, stable, and robust synthetic microbial consortia applicable in bioenergy and environmental bioremediation.
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paper_title: Niobium doped lanthanum calcium ferrite perovskite as a novel electrode material for symmetrical solid oxide fuel cells

paper_content:

Abstract Development of cost-effective and efficient electrochemical catalysts for the fuel cells electrode is of prime importance to emerging renewable energy technologies. Here, we report for the first time the novel La 0.9 Ca 0.1 Fe 0.9 Nb 0.1 O 3−δ (LCFNb) perovskite with good potentiality for the electrode material of the symmetrical solid oxide fuel cells (SSOFC). The Sc 0.2 Zr 0.8 O 2−δ (SSZ) electrolyte supported symmetrical cells with impregnated LCFNb and LCFNb/SDC (Ce 0.8 Sm 0.2 O 2−δ ) electrodes achieve relatively high power outputs with maximum power densities (MPDs) reaching up to 392 and 528.6 mW cm −2 at 850 °C in dry H 2 , respectively, indicating the excellent electro-catalytic activity of LCFNb towards both hydrogen oxidation and oxygen reduction. Besides, the MPDs of the symmetrical cells with LCFNb/SDC composite electrodes in CO and syngas (CO: H 2 = 1:1) are almost identical to those in H 2 , implying that LCFNb material has similar catalytic activities to carbon monoxide compared with hydrogen. High durability in both H 2 , CO and syngas during the short term stability tests for 50 h are also obtained, showing desirable structure stability, and carbon deposition resistance of LCFNb based electrodes. The present results indicate that the LCFNb perovskite with remarkable cell performance is a promising electrode material for symmetrical SOFCs.
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paper_title: Stabilizing the baseline current of a microbial fuel cell-based biosensor through overpotential control under non-toxic conditions.

paper_content:

Abstract A MFC-based biosensor can act as online toxicity sensor. Electrical current is a direct linear measure for metabolic activity of electrochemically active microorganisms. Microorganisms gain energy from anodic overpotential and current strongly depends on anodic overpotential. Therefore control of anodic overpotential is necessary to detect toxic events and prevent false positive alarms. Anodic overpotential and thus current is influenced by anode potential, pH, substrate and bicarbonate concentrations. In terms of overpotential all factor showed a comparable effect, anode potential 1.2% change in current density per mV, pH 0.43%/mV, bicarbonate 0.75%/mV and acetate 0.8%/mV. At acetate saturation the maximum acetate conversion rate is reached and with that a constant bicarbonate concentration. Control of acetate and bicarbonate concentration can be less strict than control of anode potential and pH. Current density changes due to changing anode potential and pH are in the same order of magnitude as changes due to toxicity. Strict control of pH and anode potential in a small range is required. The importance of anodic overpotential control for detection of toxic compounds is shown. To reach a stable baseline current under nontoxic conditions a MFC-based biosensor should be operated at controlled anode potential, controlled pH and saturated substrate concentrations.
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paper_title: Influence of membrane type, current and potential on the response to chemical toxicants of a microbial fuel cell based biosensor

paper_content:

Drinking water free of chemical toxicants is important for people's health. A microbial fuel cell based biosensor can be used to detect the presence of toxic chemicals. The sensitivity of this type of biosensor for nickel was investigated. There was no delay in the response of the sensor and the sensitivity was 0.0027 A/m2/mg Ni/l at an anode potential of −0.4 V. The effect of four types of ion exchange membranes (cation exchange, anion exchange, monovalent cation exchange and bipolar membranes) on the sensitivity was not significant. ::: ::: Current density correlates with the decrease of the nickel concentration in the sensor with 16.5 mg/l/A/m2 by causing a flux of nickel towards the membrane and the catholyte. However, the sensitivity is higher at higher overpotential and thus at higher current density. Thus although nickel concentration is lower, the response is higher at high overpotentials. The sensitivity still has to be increased because even at an overpotential of −0.16 V the sensitivity is too low to be able to measure the concentrations that is maximally allowed by European directives on (drinking) water quality.
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paper_title: A novel biosensor for p-nitrophenol based on an aerobic anode microbial fuel cell.

paper_content:

P-nitrophenol is one of the most common contaminants in chemical industrial wastewater, and in situ real-time monitoring of PNP cannot be achieved by conventional analytical techniques. Here, a two-chamber microbial fuel cell with an aerobic anode chamber was tested as a biosensor for in situ real-time monitoring of PNP. Pseudomonas monteilii LZU-3, which was used as the biological recognition element, can form a biofilm on the anode electrode using PNP as a sole substrate. The optimal operation parameters of the biosensor were as follows: external resistance 1000Ω, pH 7.8, temperature 30°C, and maximum PNP concentration 50mgL(-1). Under these conditions, the maximum voltages showed a linear relationship with PNP concentrations ranging from 15±5 to 44±4.5mgL(-1). Furthermore, we developed a novel portable device for in situ real-time monitoring of PNP. When the device was applied to measure PNP in wastewater containing various additional aromatic compounds and metal ions, the performance of the biosensor was not affected and the correlation between the maximum voltages and the PNP concentrations ranging from 9±4mgL(-1) to 36 ± 5mgL(-1) was conserved. The results demonstrated that the MFC biosensor provides a rapid and cost-efficient analytical method for real-time monitoring of toxic and recalcitrant pollutants in environmental samples.
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paper_title: Carbon nanotube powders as electrode modifier to enhance the activity of anodic biofilm in microbial fuel cells.

paper_content:

Carbon nanotube (CNT) is a promising electrode material and has been used as an anode modifier in microbial fuel cells (MFCs). In this study, a new method of simultaneously adding CNT powders and Geobacter sulfurreducens into the anode chamber of a MFC was used, aiming to form a composite biofilm on the anode. The performance of MFCs such as startup time and steady-state power generation was investigated under conditions of different CNT powders dosages. Results showed that both the startup time and the anodic resistance were reduced. The optimal dosage of CNT powders pre-treated by acid was 4 mg/mL for the anode chamber with an effective volume of 25 mL. The anodic resistance and output voltage of the MFC with CNT powders addition were maintained around 180 Ω and 650 mV during 40 days operation, while those of the MFC without CNT powders addition increased from 250 Ω to 540 Ω and decreased from 630 mV to 540 mV, respectively, demonstrating that adding CNT powders helped stabilize the anodic resistance, thus the internal resistance and power generation during long-term operation. Based on cyclic voltammogram, the electrochemical activity of anodic biofilm was enhanced by adding CNT powders, though no significant increase of the biomass in anodic biofilm was detected by phospholipids analysis. There was no remarkable change of ohmic resistance with an addition of CNT powders revealed by current interrupt method, which indicated that the rate of mass transfer might be promoted by the presence of CNT powders.
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paper_title: Performance of a microbial fuel cell-based biosensor for online monitoring in an integrated system combining microbial fuel cell and upflow anaerobic sludge bed reactor

paper_content:

Abstract A hybrid system integrating a microbial fuel cell (MFC)-based biosensor with upflow anaerobic sludge blanket (UASB) was investigated for real-time online monitoring of the internal operation of the UASB reactor. The features concerned were its rapidity and steadiness with a constant operation condition. In addition, the signal feedback mechanism was examined by the relationship between voltage and time point of changed COD concentration. The sensitivity of different concentrations was explored by comparing the signal feedback time point between the voltage and pH. Results showed that the electrical signal feedback was more sensitive than pH and the thresholds of sensitivity were S = 3 × 10 −5 V/(mg/L) and S = 8 × 10 −5 V/(mg/L) in different concentration ranges, respectively. Although only 0.94% of the influent COD was translated into electricity and applied for biosensing, this integrated system indicated great potential without additional COD consumption for real-time monitoring.
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paper_title: Microbial biofuel cell operating effectively through carbon nanotube blended with gold–titania nanocomposites modified electrode

paper_content:

Abstract In this study, we have explored the possibility to fabricate microbial biofuel cell operating with carbon nanotube–gold–titania nanocomposites (CNT/Au/TiO 2 ) as anode modifier. The results demonstrate that the CNT/Au/TiO 2 electrode could be utilized as a new and effective microbial fuel cell (MFC) anode, which integrate the advantages of relevant nanocomposites such as high conductivity, high specific surface area, and easy adsorption of the microorganism. It is evident that the three-dimensional network nanostructures of CNT/Au/TiO 2 are propitious to improve the relevant anode surface area and thus the adsorption of the microorganism, which can efficiently promote the electronic transfer rate between the probe and electrode. Meanwhile, it is noted that open circuit voltage of the CNT/Au/TiO 2 nanocomposites modified carbon paper anode increased to 0.77 V, which is more than twice that of the open circuit voltage obtained with bare carbon paper anode (0.36 V). And the MFC equipped with CNT/Au/TiO 2 nanocomposites modified carbon paper anode delivers a maximum power density of 2.4 mW m −2 , which is three times larger than that obtained from the MFC with bare carbon paper. This observation illustrates that the CNT/Au/TiO 2 nanocomposites modified electrode could obviously increase the relevant electron transfer rate and promote the electron exchange at electrode surface, which could readily provide enhanced stability and relatively long life-span to facilitate the high electricity production efficiency, suggesting its promising prospect application in MFCs.
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paper_title: Effects of Operating Parameters on Measurements of Biochemical Oxygen Demand Using a Mediatorless Microbial Fuel Cell Biosensor

paper_content:

The conventional Biochemical Oxygen Demand (BOD) method takes five days to analyze samples. A microbial fuel cell (MFC) may be an alternate tool for rapid BOD determination in water. However, a MFC biosensor for continuous BOD measurements of water samples is still unavailable. In this study, a MFC biosensor inoculated with known mixed cultures was used to determine the BOD concentration. Effects of important parameters on establishing a calibration curve between the BOD concentration and output signal from the MFC were evaluated. The results indicate monosaccharides were good fuel, and methionine, phenylalanine, and ethanol were poor fuels for electricity generation by the MFC. Ions in the influent did not significantly affect the MFC performance. CN− in the influent could alleviate the effect of antagonistic electron acceptors on the MFC performance. The regression equation for BOD concentration and current density of the biosensor was y = 0.0145x + 0.3317. It was adopted to measure accurately and continuously the BOD concentration in actual water samples at an acceptable error margin. These results clearly show the developed MFC biosensor has great potential as an alternative BOD sensing device for online measurements of wastewater BOD.
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paper_title: Anode modification to improve the performance of a microbial fuel cell volatile fatty acid biosensor

paper_content:

The development of a simple and low cost sensor such as a microbial fuel cell (MFC) to measure short chain volatile fatty acids (VFAs) would enable the implementation of this important bioprocess parameter. However using microbial fuel cells (MFCs) as transducers requires consistent microbial biocatalysis at the anode. This study considers carbon/conductive polymer composite electrodes as a mechanism to ensure the sensor signal has temporal stability, repeatability and a short response time to variations in concentration of acetic, propionic and butyric acid. The immobilization of bacteria by; modifying the carbon surface with functionalized poly(pyrrole) coatings, increasing and holding the total number of negatively charged bacteria on the electrode; or by using natural polymers with mediators covering the pre-acclimated microbial community to improve catalytic action and to protect them from the sample matrix was investigated. Six different natural polymers and/or electropolymers anode configurations were compared and it was found that poly(pyrrole-alkyl ammonium) accelerates start-up of MFC based sensors and provided improved stability, repeatability and recovery shorter signal response.
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paper_title: Enhanced Performance of Micro-Electro-Mechanical-Systems (MEMS) Microbial Fuel Cells Using Electrospun Microfibrous Anode and Optimizing Operation

paper_content:

In this work, a microfabricated anode based on gold coated poly(ϵ-caprolactone) fiber was developed that outperformed gold microelectrode by a factor of 2.65-fold and even carbon paper by 1.39-fold. This is a result of its ability to three-dimensionally interface with bacterial biofilm, the metabolic “engines” of the microbial fuel cell (MFC). We also examined unavoidable issues as the MFC is significantly reduced in size (e.g. to the microscale); (1) bubble production or movement into the microchamber and (2) high sensitivity to flow rate variations. In fact, intentionally induced bubble generation in the anodic chamber reduced the MFC current density by 33% and the MFC required 4 days to recover its initial performance. Under different flow rates in the anode chamber, the current densities were almost constant, however, the current increased up to 38% with increasing flow rate in the cathode.
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paper_title: A whole-cell electrochemical biosensing system based on bacterial inward electron flow for fumarate quantification.

paper_content:

abstract Fumarate is of great importance as it is an oncometabolite as well as food spoilage indicator. However,cost-effective and fast quantiﬁcation method for fumarate is lacking although it is urgently required. Thiswork developed an electrochemical whole-cell biosensing system for fumarate quantiﬁcation. A sensitiveinwards electric output (electron ﬂow from electrode into bacteria) responded to fumarate in Shewanellaoneidensis MR-1 was characterized, and an electrochemical fumarate biosensing system was developedwithout genetic engineering. The biosensing system delivered symmetric current peak immediatelyupon fumarate addition, where the peak area increased in proportion to the increasing fumarate con-centration with a wide range of 2 μ M–10 mM (R 2 ¼0.9997). The limit of detection (LOD) and the limit ofquantiﬁcation (LOQ) are 0.83 μ M and 1.2 μ M, respectively. This biosensing system displayed remarkablespeciﬁcity to fumarate against other possible interferences. It was also successfully applied to samples ofapple juice and kidney tissue. This study added new dimension to electrochemical biosensor design, andprovide a simple, cost-effective, fast and robust tool for fumarate quantiﬁcation.& 2014 Elsevier B.V. All rights reserved.
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paper_title: Enhancing the response of microbial fuel cell based toxicity sensors to Cu(II) with the applying of flow-through electrodes and controlled anode potentials.

paper_content:

The application of microbial fuel cell (MFC)-based toxicity sensors to real-world water monitoring is partly impeded by the limited sensitivity. To address this limitation, this study optimized the flow configurations and the control modes. Results revealed that the sensitivity increased by ∼15-41times with the applying of a flow-through anode, compared to those with a flow-by anode. The sensors operated in the controlled anode potential (CP) mode delivered better sensitivity than those operated in the constant external resistance (ER) mode over a broad range of anode potentials from -0.41V to +0.1V. Electrodeposition of Cu(II) was found to bias the toxicity measurement at low anode potentials. The optimal anode potential was approximately -0.15V, at which the sensor achieved an unbiased measurement of toxicity and the highest sensitivity. This value was greater than those required for electrodeposition while smaller than those for power overshoot.
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paper_title: Effect of shear rate on the response of microbial fuel cell toxicity sensor to Cu(II)

paper_content:

Abstract A microbial fuel cell (MFC) was successfully developed as a toxicity biomonitoring system, giving a quick response to Cu(II) toxic events. The objective was to increase MFC sensitivity to Cu(II) toxicity by evaluating the impact of shear rate caused by mixing and intermittent nitrogen sparging on the biofilm structure. Low shear rate – achieved by continuously feeding the wastewater into the MFC at a low flow rate of 1.3 mL min −1 during the enrichment period – resulted in low biomass density (124 g VSS L −1 of biofilm), high porosity and reduced levels of extracellular polymeric substances (EPS). Consequently, the sensitivity was improved. Scattered nitrogen sparging also increased the sensitivity by reducing the EPS level. It suggested that MFC enriched under low flow rate with intermittent nitrogen sparging could produce an anodic biofilm that was less dense, more porous, contained less EPS and ultimately displayed higher sensitivity to Cu(II) toxicity.
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paper_title: Catalysis of oxygen reduction in PEM fuel cell by seawater biofilm

paper_content:

Abstract The catalysis of oxygen reduction on metallic materials has been widely studied in the domain of aerobic corrosion. In this framework, it has been stated that seawater biofilms are able to catalyse efficiently oxygen reduction on stainless steels. This capacity was transferred here to the catalysis of the cathodic reaction of a proton exchange membrane fuel cell. A laboratory-scale fuel cell was designed with a stainless steel cathode, a platinum anode, and two separated liquid loops. The cathodic loop was air-saturated, while the anodic loop was hydrogen saturated. Seawater biofilm was previously grown on the stainless steel cathode, which was then set up into the fuel cell. The presence of the seawater biofilm on the stainless steel surface led to efficient catalysis of oxygen reduction. The biofilm-covered cathode was able to support current density up to 1.89 A/m 2 . Power density of 0.32 W/m 2 was supplied with 1.34 A/m 2 current density.
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paper_title: FePO4 based single chamber air-cathode microbial fuel cell for online monitoring levofloxacin.

paper_content:

A bio-electrochemical strategy was developed for constructing a simple and sensitive levofloxacin (LEV) sensor based on a single chamber microbial fuel cell (SC-MFC) using FePO4 nanoparticles (NPs) as the cathode catalyst instead of traditional Pt/C. In this assembled sensor device, FePO4 NPs dramatically promoted the electrooxidation of oxygen on the cathode, which helps to accelerate the voltage output from SC-MFC and can provide a powerful guarantee for LEV detection. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to fully characterize the FePO4 NPs. Under the optimized COD condition (3mM), the LEV with a concentration range of 0.1-1000µg/L could be detected successfully, and exhibited the excellent linear interval in the concentration range of 0.1-100µg/L. During this range of concentrations of LEV, a temporary effect on the anode of exoelectrogenic bacterial in less than 10min could occur, and then came back to the normal. It exhibited a long-term stability, maintaining the stable electricity production for 14 months of continuous running. Besides, the detection mechanism was investigated by quantum chemical calculation using density functional theory (DFT).
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paper_title: A novel microbial fuel cell sensor with biocathode sensing element

paper_content:

The traditional microbial fuel cell (MFC) sensor with bioanode as sensing element delivers limited sensitivity to toxicity monitoring, restricted application to only anaerobic and organic rich water body, and increased potential fault warning to the combined shock of organic matter/toxicity. In this study, the biocathode for oxygen reduction reaction was employed for the first time as the sensing element in MFC sensor for toxicity monitoring. The results shown that the sensitivity of MFC sensor with biocathode sensing element (7.4±2.0 to 67.5±4.0mA%-1cm-2) was much greater than that showed by bioanode sensing element (3.4±1.5 to 5.5±0.7mA%-1cm-2). The biocathode sensing element achieved the lowest detection limit reported to date using MFC sensor for formaldehyde detection (0.0005%), while the bioanode was more applicable for higher concentration (>0.0025%). There was a quicker response of biocathode sensing element with the increase of conductivity and dissolved oxygen (DO). The biocathode sensing element made the MFC sensor directly applied to clean water body monitoring, e.g., drinking water and reclaimed water, without the amending of background organic matter, and it also decreased the warning failure when challenged by a combined shock of organic matter/toxicity.
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paper_title: Fast and sensitive water quality assessment: A μL-scale microbial fuel cell-based biosensor integrated with an air-bubble trap and electrochemical sensing functionality

paper_content:

Abstract This work describes the development and operation of a microliter-sized microbial fuel cell-based biosensor for monitoring toxic substances in water. The biosensor features the integration of (i) a three-electrode configuration to provide electrochemical sensing functionality for improving sensitivity and reliability in water quality testing and (ii) an air-bubble trap to prevent all unwanted bubbles from entering the sensing surface for maximizing bacterial growth and their subsequent electron transfer. The miniaturization of the biosensor produced favorable conditions for (i) reducing measurement time with high probability of cell attachment/biofilm formation in the micro-sized chamber and (ii) enhancing the reaction sensitivity with large surface area-to-volume ratio and increased reaction kinetics. When formaldehyde was introduced as a toxic component, the rapid and sensitive current responses were obtained over a concentration range from 0.001% to 0.1% in the biosensor with 0.2 V (versus solid-state thin film Ag/AgCl reference electrode) applied on the anode.
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paper_title: Kinetic models for detection of toxicity in a microbial fuel cell based biosensor

paper_content:

Currently available models describing microbial fuel cell (MFC) polarization curves, do not describe the effect of the presence of toxic components. A bioelectrochemical model combined with enzyme inhibition kinetics, that describes the polarization curve of an MFC-based biosensor, was modified to describe four types of toxicity. To get a stable and sensitive sensor, the overpotential has to be controlled. Simulations with the four modified models were performed to predict the overpotential that gives the most sensitive sensor. These simulations were based on data and parameter values from experimental results under non-toxic conditions. Given the parameter values from experimental results, controlling the overpotential at 250 mV leads to a sensor that is most sensitive to components that influence the whole bacterial metabolism or that influence the substrate affinity constant (Km). Controlling the overpotential at 105 mV is the most sensitive setting for components influencing the ratio of biochemical over electrochemical reaction rate constants (K1), while an overpotential of 76 mV gives the most sensitive setting for components that influence the ratio of the forward over backward biochemical rate constants (K2). The sensitivity of the biosensor was also analyzed for robustness against changes in the model parameters other than toxicity. As an example, the tradeoff between sensitivity and robustness for the model describing changes on K1 (IK1) is presented. The biosensor is sensitive for toxic components and robust for changes in model parameter K2 when overpotential is controlled between 118 and 140 mV under the simulated conditions.
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paper_title: Using microbial fuel cell output metrics and nonlinear modeling techniques for smart biosensing.

paper_content:

Microbial fuel cells (MFCs) are promising tools for water quality monitoring but the response peaks have not been characterized and the data processing methods require improvement. In this study MFC-based biosensing was integrated with two nonlinear programming methods, artificial neural networks (ANN) and time series analysis (TSA). During laboratory testing, the MFCs generated well-organized normally-distributed peaks when the influent chemical oxygen demand (COD) was 150 mg/L or less, and multi-peak signals when the influent COD was 200 mg/L. The area under the response peak correlated well with the influent COD concentration. During field testing, we observed normally-distributed and multi-peak profiles at low COD concentrations. The ANN predicted the COD concentration without error with just one layer of hidden neurons, and the TSA model predicted the temporal trends present in properly functioning MFCs and in a device that was gradually failing. This report is the first to integrate ANN and TSA with MFC-based biosensing.
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paper_title: Butler-Volmer-Monod model for describing bio-anode polarization curves.

paper_content:

A kinetic model of the bio-anode was developed based on a simple representation of the underlying biochemical conversions as described by enzyme kinetics, and electron transfer reactions as described by the Butler-Volmer electron transfer kinetics. This Butler-Volmer-Monod model was well able to describe the measured bio-anode polarization curves. The Butler-Volmer-Monod model was compared to the Nernst-Monod model described the experimental data significantly better. The Butler-Volmer-Monod model has the Nernst-Monod model as its full electrochemically reversible limit. Contrary to the Nernst-Monod model, the Butler-Volmer-Monod model predicts zero current at equilibrium potential. Besides, the Butler-Volmer-Monod model predicts that the apparent Monod constant is dependent on anode potential, which was supported by experimental results.
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paper_title: A three-species microbial consortium for power generation

paper_content:

Design and construction of synthetic microbial consortia is a promising strategy to enhance the performance of bioelectrochemical systems (BESs) and to facilitate practical applications in bioenergy production. According to the design principle of “division-of-labor”, we synthesized a three-species microbial consortium for power generation, consisting of engineered Escherichia coli, Bacillus subtilis and Shewanella oneidensis. In this consortium, E. coli digested glucose to produce lactate as a carbon source and an electron donor; B. subtilis produced riboflavin as an electron shuttle; and S. oneidensis served as the exoelectrogen to generate electricity. In return, S. oneidensis oxidized lactate to acetate, which fed E. coli and B. subtilis as the carbon source. Thus, the three species formed a cross-feeding microbial consortium, which performed “better together” for power generation. As a result, glucose (11 mM, total 0.28 g) was converted to electricity for more than 15 days with high energy conversion efficiency (up to 55.7%). The microbial composition and electricity output were stable throughout the operation cycle. Furthermore, the consortium exhibited highly functional robustness to fluctuations in the initial inoculation ratio of the three strains. This system provided new insight into the rational design of more efficient, stable, and robust synthetic microbial consortia applicable in bioenergy and environmental bioremediation.
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Title: Microbial Fuels Cell-Based Biosensor for Toxicity Detection: A Review
Section 1: Introduction
Description 1: Write about the impact of industrial growth on environmental pollution, traditional detection methods, and the need for MFC-based biosensors.

Section 2: The Mechanisms Governing MFCs Used as Biosensors
Description 2: Explain the electrochemical mechanisms, such as direct and mediated electron transfer, that govern the function of MFCs as biosensors.

Section 3: Analytical Applications of Microbial Fuel Cell-Based Biosensors
Description 3: Discuss the different applications of MFC-based biosensors in detecting various analytes such as VFAs, BOD, and toxicants.

Section 4: MFCs as Heavy Metal Biosensors
Description 4: Provide details on how MFCs are used to monitor heavy metal toxicity, including various studies and their findings.

Section 5: MFCs as Organic Toxin Biosensors
Description 5: Describe the use of MFCs in detecting organic toxins in wastewater, including specific studies and performance evaluations.

Section 6: Comparison of Different Biosensors
Description 6: Compare the performance and characteristics of MFC-based biosensors with other types of biosensors.

Section 7: The Performance of MFC-Based Biosensors
Description 7: Address the performance metrics of MFC-based biosensors and their applications in environmental monitoring and food analysis.

Section 8: Factors That Influence MFC-Based Biosensors
Description 8: Identify factors such as EET rate, pH, and electrode material that influence the operation and performance of MFC-based biosensors.

Section 9: Performance Improvement of MFC-Based Biosensors
Description 9: Discuss recent advancements and methods to improve the sensitivity, reliability, and sustainability of MFC-based biosensors.

Section 10: Modification of the MFC-Based Biosensors Model
Description 10: Explore the mathematical models and overpotentials affecting the accurate signal generation of MFC-based biosensors.

Section 11: Challenges and Future Prospects
Description 11: Outline the current challenges in the practical application of MFC-based biosensors and propose future directions for research and development.

Section 12: Conclusions
Description 12: Summarize the key points of the review, highlighting the potential of MFC-based biosensors as effective tools for toxic compound detection and environmental monitoring.