EP4147289A1

EP4147289A1 - Microbial fuel cell

Info

Publication number: EP4147289A1
Application number: EP21728125.2A
Authority: EP
Inventors: Samuele FALCIANI
Original assignee: Rindi Tommaso
Current assignee: Falciani Samuele; Rindi Tommaso
Priority date: 2020-05-08
Filing date: 2021-05-06
Publication date: 2023-03-15
Also published as: IT202000010324A1; WO2021224951A1

Abstract

A microbial fuel cell, MFC, is herein described in which the anode half-cell consists of the anodes directly inserted into the feed liquid in correspondence with the respective cathode cell and batteries consisting of said cells.

Description

DESCRIPTION

Title

MICROBIAL FUEL CELL.

Technical field

The present invention relates to the field of fuel cells, particularly Microbial Fuel Cell (MFC).

Present status of the art

It is known that it is possible to produce electricity using the decomposition of organic material performed by appropri ate microbiological cells, the idea of using this capacity of some microorganisms to build generators of electricity dates back to the beginning of the last century and for many years has been the subject of studies although with minimal practical consequences.

However, in recent decades the technology has attracted con siderable interest for the useful applications that could provide, in particular the production of electricity in an environmentally friendly way together with the purification of water containing organic waste material (wastewater), therefore there has been a rapid development in research and production of batteries based on this principle.

Basically, a microbiological fuel cell allows for the pro duction of electricity through the reaction of microorgan isms with an appropriate substrate.

Like all batteries, a microbiological fuel cell is essen tially made up of a cell, isolated from the external world, including two half-cells, one containing the anode and the other one the cathode, in which said two half-cells are internally connected by a salt bridge that allows the balance of charges in the reactions of oxidation-reduction.

The anode and cathode are then connected to each other via an electrical circuit external to the cell. By connecting several cells in series (battery) a potential difference equal to the sum of the partial potential differ ences of the individual cells is obtained, however if the discontinuity between the half-cells is lost, the potential difference is no longer additive and therefore the battery becomes unusable if a stable output voltage is required, such as in a car battery.

While in normal batteries the isolation of cells from the external world is not a particular problem, in the case of cells where organic material, such as wastewater, is to be used for the production of electrons, the practical problems are considerable.

In fact, the organic material is consumed by bacteria that use it as a source of energy to survive (producing electrons as a consequence) and therefore the anodic half-cells, where this part of the process takes place, must be regularly emptied and resupplied with fresh wastewater; this involves obvious complications in the management of large plants, such as those required to have an economically interesting production of electricity.

Objects and summary of the invention

An object of the present invention is to provide a battery comprising microbial fuel cells in which the anode compart ment can be continuously supplied without requiring special operations involving opening, emptying and filling of the anode half-cell.

As mentioned, the present invention allows to overcome the above-mentioned problems thanks to a battery in which the anode half-cells are constituted by anodes directly inserted in the feeding liquid.

In fact, it was surprisingly found that the characteristics of the liquid used to supply the battery (wastewater) are such that for relatively short distances (a few millimeters) the resistance of the medium is close to 1 so that the electrodes inserted in the wastewater, even at a small dis tance between them, can be considered "approximately" iso lated from each other without the need for a confinement in a dedicated half-cell.

In this way, it is possible to create a battery in which the cathodes are isolated in the traditional manner by walls that constitute half-cells, while the anodes are isolated from each other by the resistance and/or impedance of the medium in which they are immersed, i.e., the general char acteristics of the wastewater.

Brief description of the drawings

Fig. 1 shows a schematic top view of a battery comprising microbial fuel cells according to the invention.

Detailed description of an embodiment of the invention

As shown in Figure 1, a battery according to the invention essentially comprises a tank (10) and at least two cathode half-cells (11).

The tank (10) contains the organic material that feeds the battery and at least two anodes (12); the tank has an inlet (A) and an outlet (B) for injecting and extracting the or ganic material, respectively.

According to the invention, the tank (10) may be, for exam ple, a conventional septic tank, an Imhoff-type septic tank or similar.

The half-cells (11) each contain a cathode (13) immersed in a saline solution (14) and communicate with the tank (10) through an element (15) that allows the ions to pass through. The anodes (12) are placed in sequence in proximity to the element (15) of its corresponding half-cell containing the cathode (13).

The cathode of a half-cell is connected by a current conduc tive wire (18) with the anode placed in proximity to the adjacent cell (in the series), while a conductive wire, com prising the current-user apparatus (17), connects the first anode and the last cathode to each other.

Such current-user apparatus may be, for example, an inverter, a battery, a light bulb, etc.

The tank (10) can be made of any material suitable for the application (concrete, metal, plastic, etc.) and is a closed structure (apart from the opening for injection and extrac tion) that communicates only with the cathode half-cells (11) through the element (15) which allows ions to pass through.

The tank (10), as mentioned above, contains the organic ma terial that is feeding the battery, e.g., wastewater from industrial plants, agriculture, sewerage etc.

The element (15) allowing the passage of ions may be, for example, a porous septum, a semi-permeable membrane or other similar device, among those commonly provided in the field of batteries.

Both anodes (12) and cathodes (13) are made of any material that is inert to oxidation-reduction reactions and capable of transporting electrons such as stainless steel, graphite, etc. in the form of thin plates, bars, brushes or mesh so as to ensure maximum surface exposure to the liquid contained in the tank or respectively with the saline solution con tained in the cathode half-cell (11).

According to a particular embodiment of the invention, the cathode (13) comprises a carbon brush, or plate, conformed in such a way as to increase the contact surface and thus the electrical capacity, while the potential difference re mains the same.

The distance between the anode (12) and the element (15) permeable to ions should be as small as possible to minimize the internal resistance of the battery, no more than 10 millimeters, and the distance between two anodes should be such as to ensure that small fluctuations in conductivity and impedance of the medium do not affect the discontinuity between two anodes, generally a few centimeters, preferably in a range of 1 to 10 centimeters, good results have been obtained with distances ranging from 3 to 4 centimeters.

The saline solution in the half-cell (11) containing the cathode (13) normally consists of a neutral electrolyte such as sodium chloride.

The half-cells (11) containing the cathode (13) can be open, i.e. in communication with the external world, in order to absorb the oxygen necessary for the oxidation reaction that takes place in the cathode half-cell; alternatively they can be completely closed and provided with a system of blowing air or oxygen (or other electron-acceptor element) from the outside.

The microorganisms preferably used for effluent degradation are those normally present in the effluent, normally these are yeasts, bacteria, actinomycetes that spontaneously col onize the anode.

The battery operation is based on normal oxidation-reduction processes.

The organic material coming from sewage, agricultural or industrial wastewater arrives at the collection tanks where it is attacked by fermentative organisms that obtain from it the energy necessary to live, thanks to a process that uses a single molecule as a source and as an electron acceptor with the production of waste products such as acids, alcohols and carbon dioxide.

In this process, the redox potential of the slurry is lowered due to the consumption of oxygen, albeit reduced, by these microorganisms .

When the redox potential reaches -lOOmV, a value that is reported in the literature as a real on-off switch, the activity of methanogens begins. Methanogens are able to use the matrix (usually molecular hydrogen contained in the wastewater) as electron donor and carbon dioxide as accep- tor. The methane produced in this way is already used in plants for the production of electricity from both waste and wastewater through either combustion in endothermic engines or flow in gaseous form in fuel cells with a better effi ciency, but still quite low. In the case of MFC it is thought that microorganisms directly use the electrode inserted in the wastewater as an electron acceptor (the real acceptor will be the oxidant contained in the other half-cell) and the redox potential that is gener ally measured is comparable to that of a reduced cytochrome (this is a molecule that cells use for the passage of elec trons in the respiratory chains).

According to a particular embodiment, the cathode half-cells may comprise an electrode inserted directly into a porous medium in communication with the external world, as described in CN102544562.

Claims

1. A microbial fuel cell, MFC, comprising a tank (10) for the wastewater feeding the battery, within which is accom modated an anode half-cell in which an inlet (A) and an oulet (B) are defined to allow the flow of the liquid wastewater, and a plurality of cathode half-cells (11) functionally co operating with said anode half-cell, each of which includes a respective cathode (13) immersed in a saline solution (14), characterized in that said anode half-cell accommodates a plurality of anodes (12) directly-immersed in the flow of the organic feed liquid, without any physical separation between them and whose outer surfaces are reciprocally at a distance of 2 mm or more, each of said anodes (12) being respectively connected:

- with the cathode (13) of a corresponding cathode half-cell

(11) via a flow of ions passing through a respective element (15) separating each cathode half-cell from the anode half cell, and

- with the cathode of the adjacent ionic half-cell via a flow of electrons carried by an electrical conductor (18); wherein a conductive wire (16), comprising the current user apparatus (17), connects the first anode and the last cathode to each other, and wherein the distance between each anode

(12) and the respective ion-permeable element (15) of the corresponding half-cell (11) is between 0 and 10 mm

2. The MFC cell according to the previous claim characterized in that said anode half-cell is made of any material suitable for the purpose and is a closed structure, apart from the inlet (A) for the input and outlet (B) of the wastewater, which communicates with the cathode half-cells (11) only via said element (15) which allows ions to pass through.

3. The MFC cell according to the preceding claim characterized in that said element (15) allowing ions to pass through is a porous septum, a semipermeable membrane or an other device similar to those commonly used in the batteries sector and wherein said anodes (12) and cathodes (13) are made from a conductive material inert to oxidation reduction reactions.

4. The MFC cell according to the preceding claim characterized in that said saline solution present in the half- cell (11) containing the cathode (13) consists of a neutral electrolyte.

5. The MFC cell according to any of the previous claims characterized in that the half-cells (11) containing the cathode (13) are possibly open, i.e. in communication with the external world, so as to absorb the oxygen necessary for the oxidation reaction taking place in the cathode half cell.

6. The MFC cell according to any of the previous claims from 1 to 4 characterized in that the half-cells (11) con- taining the cathode (13) are possibly completely closed and provided with a system for blowing in air, oxygen, or another electron acceptor element from the external.