The aim of this study was to evaluate the use of Maldi-Tof MS biosensor in microbial assessment of Brazilian kefir grains. Maldi-Tof MS is a new methodology for the rapid diagnosis of microorganisms. A total of microorganisms were isolated, 31 were yeasts and were bacteria divided into lactic and acetic bacteria. The microbial population identified in Brazilian kefir grains was Lactobacillus paracasei, Saccharomyces cerevisiae, Lactobacillus plantarum, Acetobacter pasteurianus , and Acetobacter syzygii.
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A microbial fuel cell MFC is a bio- electrochemical system  that drives an electric current by using bacteria and a high-energy oxidant such as O 2 ,  mimicking bacterial interactions found in nature.
MFCs can be grouped into two general categories: mediated and unmediated. The first MFCs, demonstrated in the early 20 th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Unmediated MFCs emerged in the s; in this type of MFC the bacteria typically have electrochemically active redox proteins such as cytochromes on their outer membrane that can transfer electrons directly to the anode.
The idea of using microbes to produce electricity was conceived in the early twentieth century. In , Barnett Cohen created microbial half fuel cells that, when connected in series, were capable of producing over 35 volts with only a current of 2 milliamps. A study by DelDuca et al. Though the cell functioned, it was unreliable owing to the unstable nature of hydrogen production by the micro-organisms. In the late s, little was understood about how microbial fuel cells functioned.
The concept was studied by Robin M. Allen and later by H. Peter Bennetto. People saw the fuel cell as a possible method for the generation of electricity for developing countries. Bennetto's work, starting in the early s, helped build an understanding of how fuel cells operate and he was seen by many [ who? The prototype, a 10 L design, converted brewery wastewater into carbon dioxide, clean water and electricity. The group had plans to create a pilot-scale model for an upcoming international bio-energy conference.
A microbial fuel cell MFC is a device that converts chemical energy to electrical energy by the action of microorganisms. Most MFCs contain a membrane to separate the compartments of the anode where oxidation takes place and the cathode where reduction takes place. The electrons produced during oxidation are transferred directly to an electrode or to a redox mediator species. The electron flux is moved to the cathode.
The charge balance of the system is maintained by ionic movement inside the cell, usually across an ionic membrane. Other electron donors have been reported, such as sulfur compounds or hydrogen. Other electron acceptors studied include metal recovery by reduction,  water to hydrogen,  nitrate reduction, and sulfate reduction. MFCs are attractive for power generation applications that require only low power, but where replacing batteries may be impractical, such as wireless sensor networks.
Virtually any organic material could be used to feed the fuel cell, including coupling cells to wastewater treatment plants.
Chemical process wastewater   and synthetic wastewater   have been used to produce bioelectricity in dual- and single-chamber mediatorless MFCs uncoated graphite electrodes. Higher power production was observed with a biofilm -covered graphite anode. However, MFCs can also work at a smaller scale. It provides a renewable form of energy and does not need to be recharged. Power stations can be based on aquatic plants such as algae.
If sited adjacent to an existing power system, the MFC system can share its electricity lines. Soil-based microbial fuel cells serve as educational tools, as they encompass multiple scientific disciplines microbiology, geochemistry, electrical engineering, etc.
Kits for home science projects and classrooms are available. The current generated from a microbial fuel cell is directly proportional to the organic-matter content of wastewater used as the fuel.
MFCs can measure the solute concentration of wastewater i. Wastewater is commonly assessed for its biochemical oxygen demand BOD values. Oxygen and nitrate are interfering preferred electron acceptors over the anode, reducing current generation from an MFC. This can be avoided by inhibiting aerobic and nitrate respiration in the MFC using terminal oxidase inhibitors such as cyanide and azide.
The United States Navy is considering microbial fuel cells for environmental sensors. The use of microbial fuel cells to power environmental sensors would be able to provide power for longer periods and enable the collection and retrieval of undersea data without a wired infrastructure. The energy created by these fuel cells is enough to sustain the sensors after an initial startup time.
A mixture would allow for a more complete utilization of available nutrients. Shewanella oneidensis is their primary candidate, but may include other heat- and cold-tolerant Shewanella spp. The sensor relies only on power produced by MFCs and operates continuously without maintenance.
The biosensor turns on the alarm to inform about contamination level: the increased frequency of the signal warns about a higher contamination level, while a low frequency informs about a low contamination level.
In , A. Microbial electrolysis cells have been demonstrated to produce hydrogen. MFCs are used in water treatment to harvest energy utilizing anaerobic digestion. The process can also reduce pathogens. However, it requires temperatures upwards of 30 degrees C and requires an extra step in order to convert biogas to electricity.
Spiral spacers may be used to increase electricity generation by creating a helical flow in the MFC. Scaling MFCs is a challenge because of the power output challenges of a larger surface area. Most microbial cells are electrochemically inactive. Electron transfer from microbial cells to the electrode is facilitated by mediators such as thionine , methyl viologen , methyl blue , humic acid , and neutral red.
Mediator-free microbial fuel cells use electrochemically active bacteria to transfer electrons to the electrode electrons are carried directly from the bacterial respiratory enzyme to the electrode. Among the electrochemically active bacteria are Shewanella putrefaciens ,  Aeromonas hydrophila  and others. Some bacteria are able to transfer their electron production via the pili on their external membrane.
Mediator-free MFCs are less well characterized, such as the strain of bacteria used in the system, type of ion-exchange membrane and system conditions temperature, pH, etc. Mediator-free microbial fuel cells can run on wastewater and derive energy directly from certain plants and O 2.
This configuration is known as a plant microbial fuel cell. Possible plants include reed sweetgrass , cordgrass , rice, tomatoes, lupines and algae. While MFCs produce electric current by the bacterial decomposition of organic compounds in water, MECs partially reverse the process to generate hydrogen or methane by applying a voltage to bacteria. This supplements the voltage generated by the microbial decomposition of organics, leading to the electrolysis of water or methane production. Soil -based microbial fuel cells adhere to the basic MFC principles, whereby soil acts as the nutrient-rich anodic media, the inoculum and the proton exchange membrane PEM.
The anode is placed at a particular depth within the soil, while the cathode rests on top the soil and is exposed to air. Soils naturally teem with diverse microbes , including electrogenic bacteria needed for MFCs, and are full of complex sugars and other nutrients that have accumulated from plant and animal material decay. Moreover, the aerobic oxygen consuming microbes present in the soil act as an oxygen filter, much like the expensive PEM materials used in laboratory MFC systems, which cause the redox potential of the soil to decrease with greater depth.
Soil-based MFCs are becoming popular educational tools for science classrooms. Sediment microbial fuel cells SMFCs have been applied for wastewater treatment. Simple SMFCs can generate energy while decontaminating wastewater. Most such SMFCs contain plants to mimic constructed wetlands.
By SMFC tests had reached more than l. In researchers announced an SMFC application that extracts energy and charges a battery. Salts dissociate into positively and negatively charged ions in water and move and adhere to the respective negative and positive electrodes, charging the battery and making it possible to remove the salt effecting microbial capacitive desalination.
The microbes produce more energy than is required for the desalination process. Phototrophic biofilm MFCs ner use a phototrophic biofilm anode containing photosynthetic microorganism such as chlorophyta and candyanophyta. They carry out photosynthesis and thus produce organic metabolites and donate electrons.
The sub-category of phototrophic MFCs that use purely oxygenic photosynthetic material at the anode are sometimes called biological photovoltaic systems. The United States Naval Research Laboratory developed nanoporous membrane microbial fuel cells that use a non-PEM to generate passive diffusion within the cell. It offers comparable power densities to Nafion a well known PEM with greater durability. Porous membranes allow passive diffusion thereby reducing the necessary power supplied to the MFC in order to keep the PEM active and increasing the total energy output.
MFCs that do not use a membrane can deploy anaerobic bacteria in aerobic environments. However, membrane-less MFCs experience cathode contamination by the indigenous bacteria and the power-supplying microbe. The novel passive diffusion of nanoporous membranes can achieve the benefits of a membrane-less MFC without worry of cathode contamination.
PEM membranes can be replaced with ceramic materials. The macroporous structure of ceramic membranes allows good transport of ionic species. The materials that have been successfully employed in ceramic MFCs are earthenware , alumina , mullite , pyrophyllite , and terracotta. When microorganisms consume a substance such as sugar in aerobic conditions, they produce carbon dioxide and water. However, when oxygen is not present, they produce carbon dioxide, hydrons hydrogen ions , and electrons , as described below: .
Microbial fuel cells use inorganic mediators to tap into the electron transport chain of cells and channel electrons produced. The mediator crosses the outer cell lipid membranes and bacterial outer membrane ; then, it begins to liberate electrons from the electron transport chain that normally would be taken up by oxygen or other intermediates. The now-reduced mediator exits the cell laden with electrons that it transfers to an electrode; this electrode becomes the anode.
The release of the electrons recycles the mediator to its original oxidized state, ready to repeat the process. This can happen only under anaerobic conditions ; if oxygen is present, it will collect the electrons, as it has greater electronegativity. In MFC operation, the anode is the terminal electron acceptor recognized by bacteria in the anodic chamber.
Therefore, the microbial activity is strongly dependent on the anode's redox potential. A Michaelis—Menten curve was obtained between the anodic potential and the power output of an acetate -driven MFC.
A critical anodic potential seems to provide maximum power output. Potential mediators include natural red, methylene blue, thionine, and resorufin.
ICP Instituto de Catalisis y Petroquímica
A microbial fuel cell MFC is a bio- electrochemical system  that drives an electric current by using bacteria and a high-energy oxidant such as O 2 ,  mimicking bacterial interactions found in nature. MFCs can be grouped into two general categories: mediated and unmediated. The first MFCs, demonstrated in the early 20 th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Unmediated MFCs emerged in the s; in this type of MFC the bacteria typically have electrochemically active redox proteins such as cytochromes on their outer membrane that can transfer electrons directly to the anode. The idea of using microbes to produce electricity was conceived in the early twentieth century. In , Barnett Cohen created microbial half fuel cells that, when connected in series, were capable of producing over 35 volts with only a current of 2 milliamps. A study by DelDuca et al.
Microbial fuel cell
We'd like to understand how you use our websites in order to improve them. Register your interest. A bacterial mixed culture was immobilized in Millipore filters to construct microbial-membranes for BOD determination using an oxygen electrode. The biosensor response was best when 0.
Amperometric biosensors for phenolic compounds determination in the environmental interess samples. Phenols are widely used in many areas and commonly found as industrial by-products. A great number of agricultural and industrial activities realise phenolic compounds in the environmental. Waste phenols are produced mainly by the wood-pulp industry and during production of synthetic polymers, drugs, plastics, dyes, pesticides and others. Phenols are also released into the environmental by the degradation of pesticides with phenolic skeleton. The phenols level control is very important for the environmental protection.