Production of a biofilm on an electrode for a biocell, electrode and biocell obtained

Abstract

A method for the production of a biofilm at the surface of an electrode in a liquid medium containing bacteria and a substrate for growth of the bacteria, in which a system of electrodes constituted of two electrodes, which are connected to a direct electric current source, is used, these two electrodes are placed in the medium and a predetermined and constant potential difference is applied between the electrodes, by virtue of which biofilms form at the surface of the electrodes. Resulting electrodes and biocells.

Claims

1. A process for producing a biofilm on the surface of an electrode in a liquid medium containing bacteria and a substrate allowing the bacteria to grow, comprising using a system of electrodes that consists of two electrodes wherein both electrodes are connected to a DC current source, placing these two electrodes in the medium and applying a predetermined constant potential difference between the electrodes, thereby forming biofilms on the surface of the electrodes, wherein the formed biofilm is rich in hi h-redox potential, wherein electron-withdrawing bacteria is produced at the anode and wherein the process does not use a membrane, and wherein the potential difference applied is between 100 mV and 700 mV.

2. The process as claimed in claim 1, in which the potential difference applied is between 300 mV and 600 mV.

3. The process as claimed in claim 1, in which the potential difference applied is between 450 mV and 550 mV.

4. The process as claimed in claim 1, in which the potential difference is applied for a length of time of between 3 and 20 days.

5. The process as claimed in claim 4, in which this length of time is between 4 and 7 days.

6. The process as claimed in claim 1, in which the electrodes are made from the same material.

7. The process as claimed in claim 6, in which the anode and/or the cathode are/is based on carbon and/or stainless steel, aluminum, nickel or on titanium alloys.

8. A process for preparing a biofuel cell comprising the preparation of an electrode according to the process as claimed in claim 1 and then the use of this electrode in a biofuel cell as either anode or cathode.

9. A process for producing electricity, in which a biofuel cell such as that obtained in claim 8 is used.

10. An electricity production facility comprising one or more biofuel cell(s) prepared according to claim 8.

11. An electrode coated with a biofilm that can be obtained by implementing the process as claimed in claim 1.

12. An anode coated with a biofilm, containing oxidizing/reducing bacteria, that can be obtained according to claim 1.

13. A biofuel cell comprising an electrode obtained by implementing the process as claimed claim 1.

14. A biofuel cell comprising an anode as claimed in claim 12.

15. A process according to claim 1 wherein the liquid medium is selected from the group consisting of industrial effluents, domestic effluents, agricultural effluents, waste water, water and sludge from wastewater treatment plants, biomass from the food processing industry, and natural water.

Description

(1) The present invention will be illustrated with the following examples, without however limiting the scope thereof, and by referring to the appended drawings.

(2) FIG. 1 shows a schematic of an electrochemical device allowing anodic and cathodic biofilms to be produced, the left-hand side of the figure showing the device at start-up and the right-hand side showing the device after a biofilm has been formed on the surface of the electrodes.

(3) FIG. 2 is a cyclic voltammogram, in a phosphate buffer (0.1M, pH=7), of a biofilm formed on the anode.

(4) FIG. 3 is a cyclic voltammogram, in a phosphate buffer (0.1M, pH=7), of a biofilm formed on the cathode.

(5) FIG. 4 is a cyclic voltammogram, in a phosphate buffer (0.1M, pH=7), of a biofilm formed on an unpolarized reference electrode.

(6) FIG. 5 shows a schematic of a biofuel cell.

(7) FIG. 6 is a graph showing the voltage of a biofuel cell according to the invention compared with a biofuel cell without anodic pretreatment, as a function of time.

EXAMPLE 1

Preparation of a Biofilm on the Anode and on the Cathode

(8) The electrochemical device shown in FIG. 1 comprises a vat 1, two similar electrodes (anode 2 and cathode 3) made of graphite and a current generator 4. The vat was filled with waste water 5 from a domestic-waste water treatment facility.

(9) Using the generator 4, a voltage of 0.5 V was applied for 4 days. The left-hand side of FIG. 1 shows the device at start-up and the right-hand side shows the device after 4 days, with a biofilm 6 formed on the anode and a biofilm 7 formed on the cathode.

(10) For comparison, a similar device was left for 4 days without applying a voltage (unpolarized electrodes).

(11) Next, the cyclic voltammograms of the biofilms formed on the anode, on the cathode and on an unpolarized electrode were determined in a phosphate buffer (0.1M, pH=7). To do this, voltammetry was carried out using a conventional device having three electrodes, one of which was a silver chloride reference electrode.

(12) Comparing the voltammograms clearly shows that biofilms having different electrochemical activities were obtained (FIGS. 2, 3 and 4). The positive potential peak of the anodic biofilm is located at about 0.46 V/Ag/AgCl and is larger than those observed for the cathode (0.31 V/Ag/AgCl) and for the unpolarized electrode (0.25 V/Ag/AgCl). The variation of the position of the anodic peaks reflects the potential-energy difference between the microbial electron donors, such as redox proteins, of each biofilm and demonstrates that, according to the invention, a positive polarization of an electrode during the formation of a biofilm allows this film to be enriched with high-redox-potential bacteria.

EXAMPLE 2

Biofuel Cell

(13) An air-cathode biofuel cell was used. It comprised a tank 8 containing an anode 9 and a cathode 10 placed level with a wall of the tank so as to have one surface turned toward the inside of the tank and one surface turned toward the outside, in contact with the air. An electrical circuit was formed connecting the electrodes and comprising a resistor 11the voltage of the biofuel cell was measured at the terminals of this resistor using a measurement device (not shown).

(14) The tank 8 and the cathode 10 defined a chamber which was filled with a minimum nutrient solution: a PBS (phosphate buffer solution), namely Na.sub.2HPO.sub.4 (4.1 g/l), NaH.sub.2PO.sub.4, H.sub.2O (2.9 g/l), NH.sub.4Cl (0.3 g/l), KCl (0.1 g/l); and an acetate substrate (>1.0 g/l).

(15) Two biofuel cells were thus prepared, one in which the anode was an anode prepared according to example 1 and covered with a biofilm 13, the other in which the anode had not been pretreated.

(16) FIG. 6 is a graph showing the voltage of these biofuel cells as a function of time. The curve showing an earlier appearance of a voltage across the terminals and a higher plateau corresponds to the biofuel cell equipped with an anode having a biofilm, obtained according to example 1. A voltage develops very quickly with the biofuel cell according to the invention. Likewise, the maximum voltage of about 470 mV is much higher than the 270 mV of the biofuel cell without the anode pretreatment. These results demonstrate that the formation of a biofilm on the anode, according to the invention, by positively polarizing the anode, clearly improves the performance of a biofuel cell by virtue of electrochemical enrichment in efficient bacteria of the biofilm.