WO2016135571A2

WO2016135571A2 - Microbial fuel cell

Info

Publication number: WO2016135571A2
Application number: PCT/IB2016/050512
Authority: WO
Inventors: Sydney Charles DU PLESSIS
Original assignee: Du Plessis Sydney Charles
Priority date: 2015-02-25
Filing date: 2016-02-02
Publication date: 2016-09-01
Also published as: WO2016135571A3

Abstract

Wastewater is treated in a vessel (14) supported and partly submerged in the wastewater. A proton exchange membrane (PEM) (38) divides an internal cavity inside the vessel (14) into an anode chamber (32) and a cathode chamber (34) with an anode (36) supported in the anode chamber (32) and a cathode (40) supported in the cathode chamber (34). A first aperture (22) is opened in the vessel's walls (20) to allow wastewater to flow into the anode chamber (32), where organic material in the wastewater is oxidised by microbial action, forming CO₂, electrons and protons. The CO₂ formed in the anode chamber (32) is released, the protons pass through the PEM (38) to the cathode chamber (34), and the electrons are conducted from the anode (36) to the cathode (40). The electrons and protons are combined in the cathode chamber (34) with oxygen in the wastewater, to form water.

Description

MICROBIAL FUEL CELL

FIELD OF THE INVENTION

This invention relates to Microbial Fuel Cells ("MFCs") for treatment of liquids on large scale, such as wastewater.

BACKGROUND TO THE INVENTION

An MFC is a bio-chemical system in which organic matter is oxidised by microbial action in an anode chamber and water is formed in a cathode chamber. In the anode chamber, CO2 is released, electrons (e^~) are deposited on the cathode and protons (H⁺) are released. The protons pass through a proton exchange membrane (PEM) (also known as a cation specific membrane) to the cathode chamber and the electrons can flow from the anode to the cathode through external conductors. At the cathode, the electrons and protons received from the anode chamber, react with oxygen to form water. In an MFC, organic matter is thus consumed and water is formed, while an electrical current is generated that can be used as a source of electrical energy.

MFCs have been built on laboratory scales, but the present invention seeks to use MFCs to treat wastewater effectively and efficiently on a large scale.

Wastewater can include various forms of contaminated water and the present invention is suitable to treat many forms of wastewater, effluents, or the like, but the invention is described with reference to treatment of sewage, without limiting the invention to sewage.

Conventional treatment of sewage containing wastewater varies, but generally, the process includes the steps of:

Pre-treatment - mechanical removal of materials such as litter, grit, sand, as well as fats (including oils and greases);

Primary treatment - sedimentation allowing solids in the wastewater to settle and form sludge and allowing fats to float; Secondary treatment - degradation of the biological content by aeration to allow bacteria and/or protozoa to consume biodegradable soluble contaminants and to bind less soluble contaminants into floe and removing the floe (typically with secondary sedimentation); and

Tertiary treatment - removal of remaining unwanted contaminants, e.g. filtration, removal of nutrients, nitrogen, phosphorous, etc. ; disinfection and/or odour control.

The present invention is intended to supplement conventional secondary wastewater treatment, although it could potentially replace conventional secondary wastewater treatment and/or it could be used at different stages of wastewater treatment.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a method of treating wastewater, said method comprising:

supporting a vessel in wastewater, said vessel having walls that are at least partly submerged in the wastewater, preferably with the walls protruding a small distance above the surface of the wastewater;

providing a proton exchange membrane (PEM) in the vessel, that substantially divides an internal cavity inside the vessel into an anode chamber and a cathode chamber with an anode supported in the anode chamber and a cathode supported in the cathode chamber;

opening a least one first aperture in the vessel's walls to allow wastewater to flow into the anode chamber through the first aperture;

oxidising organic material in the wastewater in the anode chamber by microbial action, forming CO2, electrons and protons;

releasing the CO2 formed in the anode chamber;

allowing the protons to pass through the PEM from the anode chamber to the cathode chamber;

conducting the electrons from the anode to the cathode; and

combining the electrons and protons in the cathode chamber with oxygen in the wastewater, to form water. The method may include a preceding step of oxygenating the wastewater, typically by aerating it, e.g. through agitation. The method may include periodically closing the first aperture to stop the flow of wastewater into the anode chamber, at least substantially, but preferably completely.

The method may include opening at least one second aperture in the vessel's walls, between the cathode chamber and the outside of the vessel, with at least some overlap between the times that the first and second apertures are open. Likewise, the method may include periodically closing the second aperture, with at least some overlap between the times that the first and second apertures are closed. Preferably, the first and second apertures are opened and closed at substantially the same time. The method may include allowing wastewater to flow from the anode chamber to the cathode chamber though at least one third aperture in the PEM.

The method may include imparting flow on the wastewater on the outside of the vessel and may include positioning the vessel relative to the flow of wastewater so that the first aperture faces at least partly upstream.

According to another aspect of the present invention there is provided apparatus for treating wastewater, said apparatus comprising:

a vessel with side walls and defining an internal cavity;

a proton exchange membrane (PEM) that substantially divides the internal cavity inside the vessel into an anode chamber and a cathode chamber;

an anode supported in the anode chamber;

a cathode supported in the cathode chamber;

a least one first aperture in the vessel's walls between the anode chamber and the outside of the vessel;

at least one electrical circuit extending between the anode and the cathode, external to the vessel; and support means for supporting the vessel in wastewater, with the walls of the vessel at least partly submerged in the wastewater preferably with the walls protruding a small distance above the surface of the wastewater. The apparatus may include at least one first closure element for selectively closing the first aperture.

The vessel's walls may define at least one second aperture between the cathode chamber and the outside of the vessel and the apparatus may include at least one second closure element for selectively closing the second aperture. The second aperture may be at a different elevation from the first aperture - preferably lower than the first aperture.

At least one third aperture may be defined in the PEM.

In preferred embodiments, the anode includes a carbon cloth and the cathode includes a stainless steel mesh.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how it may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:

Figure 1 shows an exploded front three-dimensional view of main parts of an MFC according to the present invention;

Figure 2 shows a rear three-dimensional view of the MFC of Figure 1 ;

Figure 3 shows a schematic cross-sectional view of the MFC of Figure 1 , in use;

Figure 4 shows a plan view of a bank of the MFCs of Figure 1 ;

Figure 5 shows a side view of the bank of MFCs of Figure 4; and

Figure 6 shows a schematic cross-sectional view of the MFC of Figure 1 , with an alternative embodiment of anodes. DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, a Microbial Fuel Cell ("MFC") for treating wastewater according to the present invention, is generally identified by reference number 10, whereas a bank comprising a number of the MFCs, is generally identified by reference number 12.

Referring to Figures 1 to 5, each MFC 10 includes a vessel or jug 14 that is made of stainless steel and has a flat bottom 16 and walls which include a straight rear wall 18 and a front wall 20 that curves and extends around the sides of the jug. The top of the jug 14 can be open, but is preferably closed with a lid 21 as shown in Figures 3 and 6, with a slot 23 through which an electrode sandwich can pass (see below). The lid 21 protects the MFC 10 against environmental interference such as ingress from surrounding wastewater and inhibits (preferably prevents) oxygenation of wastewater in the jug 14, but can be opened to allow access for maintenance, and the like.

In the front wall 20, three first apertures or front windows 22 are formed and each of them has a sliding door 24 that can close the window. Similarly, three second apertures or rear windows 26 are formed in the rear wall 18 and each of the rear windows has a sliding door 28. (In Figure 1 , each of the front and rear windows 22,26 are shown open, in Figure 2 the front windows 22 are shown open and the rear windows 26 are shown closed and in Figure 3, the front and rear windows are shown open.) The front windows 22 are at a relatively high elevation in the front wall 20 and the rear windows 26 are at a substantially lower elevation. Inside the inner cavity of the jug 14, a stainless steel inner support frame 30 is attached to the walls of the jug, near the rear wall 18. An electrode sandwich is attached to the inner support frame 30 and extends generally across the inner cavity of the jug 14, along the support frame 30, to divide the inner cavity of the jug into a larger anode chamber 32 between the electrode sandwich and the front wall 20, and a smaller cathode chamber 34 between the electrode sandwich and the rear wall 18.

The electrode sandwich comprises an anode 36 of carbon cloth that faces the anode chamber 32, a proton exchange membrane ("PEM") 38 and a cathode 40 of stainless steel mesh that faces the cathode chamber. The anode 36, PEM 38 and cathode 40 are preferably packed closely together in the electrode sandwich, to increase the power provided by the MFC. Each of the electrodes (i.e. the anode 36 and cathode 40) is electrically insulated from the jug 14 and is connected to an external electrical load circuit (e.g. a battery or other load circuit) by electrical conductors (not shown) that are preferably of stainless steel or other suitably corrosion resistant metal.

Three third apertures 42 (only shown in Figure 3) are defined in the electrode sandwich and are generally aligned with the rear windows 26.

Each MFC 10 is supported in wastewater 44 by a support frame 46 (or other suitable support means), so that the walls 18,20 of the jug 14 are partly submerged in water. Preferably, the walls 18,20 protrude above the water to a sufficient extent to prevent excessive splashing of wastewater over upper edges of the walls, although this is less of a concern in embodiments where the jug 14 is closed with a lid 21 . In the embodiments of the invention shown in Figures 4 and 5, each bank 12 of three MFCs 10 is supported by a common support frame 46 comprising posts 48 that are anchored in the bottom of a wastewater tank in which the MFCs are supported, and diagonal braces 50 that provide stability. In different embodiments of the invention, the MFCs 10 can be arranged side-by-side and/or end-to-end in a bank and the electrodes of the MFCs can be connected together in series or in parallel - depending on preferences for the particular configuration. In use, the wastewater 44 in which the MFC's 10 are supported (and mostly submerged) is oxygenated by aerating the wastewater through agitation or other suitable means, so that there is adequate oxygen in the wastewater for conventional secondary wastewater treatment, as well as additional oxygen for operation of the MFC 10. The wastewater 40 also flows, as a result of the agitation, or other flow imparted on the wastewater and the MFC's 10 are installed so that the front windows 22 face at least partly upstream - preferably completely upstream. The front windows 22 and rear windows 26 of each MFC 10 are opened from time to time, to allow wastewater 44 to flow from upstream, outside the jug 14, through the front windows into the anode chamber 32, through the apertures 42 in the electrode sandwich into the cathode chamber 34 and out through the rear windows 26, so that the whole inside of the jug 14 is provided with a new batch of wastewater. The front and rear windows 22,26 are closed so that the flow of wastewater inside the jug 14 stops for the MFC 10 to operate.

During operation of the MFC 10, organic material in the wastewater in the anode chamber 32 is oxidised by microbial action, forming CO2, electrons and protons. The CO2 is released into the atmosphere via the open top of the jug 14, or is extracted or vented from underneath the lid 21 , or is released in any other acceptable manner. The protons pass though the PEM 38 from the anode chamber 32 to the cathode chamber 34 and the electrons are conducted from the anode to the cathode via the external load circuit. At the cathode 40, the electrons from the external load circuit, the protons that have passed through the PEM 38 and oxygen in the wastewater, are combined to form water.

Once the MFC 10 has operated to a sufficient extent, e.g. once the microbial activity in the anode chamber 32 declines (which can be detected in a drop in current between the electrodes 36,40) or once the organic contents of the water in the anode chamber has declined to a sufficient degree, the front and rear windows 22,26 are opened to allow the wastewater in the jug 14 to be replaced by a new batch of wastewater, before the process is repeated.

Referring to Figure 6, in an alternative embodiment of the invention, instead of an anode of carbon cloth in an electrode sandwich, the MFC can have one or more anodes 52 in the form of conductive wires 54 or rods (e.g. of stainless steel) with carbon bristles 56 that protrude from them to increase their contact area with the wastewater. In Figure 6, two such wire anodes 52 are shown in a horizontally spaced configuration, but the number of anodes can vary and they could be spaced apart horizontally and/or vertically.

Claims

1 . A method of treating wastewater, said method comprising:

supporting a vessel (14) in wastewater, said vessel (14) and having walls (18,20) that are at least partly submerged in the wastewater; providing a proton exchange membrane (PEM) (38) in the vessel (14), that substantially divides an internal cavity inside the vessel (14) into an anode chamber (32) and a cathode chamber (34) with an anode (36) supported in the anode chamber (32) and a cathode (40) supported in the cathode chamber (34);

opening a least one first aperture (22) in the vessel's walls (20) to allow wastewater to flow into the anode chamber (32) through the first aperture (22);

oxidising organic material in the wastewater in the anode chamber (32) by microbial action, forming CO2, electrons and protons;

releasing the CO2 formed in the anode chamber (32);

allowing the protons to pass through the PEM (38) from the anode chamber (32) to the cathode chamber (34);

conducting the electrons from the anode (36) to the cathode (40); and combining the electrons and protons in the cathode chamber (34) with oxygen in the wastewater, to form water.

2. A method according to claim 1 , which includes a preceding step of oxygenating the wastewater.

3. A method according to claim 2, in which the wastewater is oxygenated by aerating it.

4. A method according to claim 3, in which the wastewater is aerated by agitating it.

5. A method according to any one of the preceding claims, which includes periodically closing the first aperture (22) to stop the flow of wastewater into the anode chamber (32), at least substantially.

6. A method according to any one of the preceding claims, which includes opening at least one second aperture (26) in the vessel's walls (18), between the cathode chamber (34) and the outside of the vessel (14), with at least some overlap between the times that the first and second apertures (22,26) are open.

7. A method according to claim 6, which includes periodically closing the second aperture (26), with at least some overlap between the times that the first and second apertures (22,26) are closed.

8. A method according to claim 7, wherein the first and second apertures (22,26) are opened and closed at substantially the same time.

9. A method according to any one of the preceding claims, which includes allowing wastewater to flow from the anode chamber (32) to the cathode chamber (34) though at least one third aperture (42) in the PEM.

10. A method according to any one of the preceding claims, which includes imparting flow on the wastewater on the outside of the vessel (14).

1 1 . A method according to claim 10, which includes positioning the vessel (14) relative to the flow of wastewater so that the first aperture (22) faces at least partly upstream.

12. Apparatus (10) for treating wastewater, said apparatus (10) comprising:

a vessel (14) with side walls (18,20) and defining an internal cavity; a proton exchange membrane (PEM) (38) that substantially divides the internal cavity inside the vessel (14) into an anode chamber (32) and a cathode chamber (34); an anode (36) supported in the anode chamber (32);

a cathode (40) supported in the cathode chamber (34);

a least one first aperture (22) in the vessel's walls (20) between the anode chamber (32) and the outside of the vessel;

at least one electrical circuit extending between the anode (36) and the cathode (40), external to the vessel (14); and

support means (46) for supporting the vessel (14) in wastewater, with the walls (18,20) of the vessel (14) at least partly submerged in the wastewater.

13. Apparatus (10) according to claim 12, which includes at least one first closure element (24) for selectively closing the first aperture (22).

14. Apparatus (10) according to claim 12 or claim 13, wherein the vessel's walls (18) define at least one second aperture (26) between the cathode chamber (34) and the outside of the vessel (14).

15. Apparatus (10) according to claim 14, which includes at least one second closure element (28) for selectively closing the second aperture (26).

16. Apparatus (10) according to claim 14 or claim 15, in which the second aperture (26) is at a different elevation from the first aperture (22).

17. Apparatus (10) according to any one of claims 12 to 16, in which at least one third aperture (42) is defined in the PEM (38).

18. Apparatus (10) according to any one of claims 12 to 17, wherein the anode (36) includes a carbon cloth.

19. Apparatus (10) according to any one of claims 12 to 18, wherein the cathode (40) includes a stainless steel mesh.