EP2502301A2

EP2502301A2 - Bio-electrochemical device and method for upgrading a fluid

Info

Publication number: EP2502301A2
Application number: EP10787924A
Authority: EP
Inventors: Hubertus Victor Marie Hamelers; Cees Jan Nico Buisman; Tomas Hubertus Johannes Antonius Sleutels
Original assignee: Stichting Wetsus Centre for Sustainable Water Technology
Current assignee: Stichting Wetsus Centre for Sustainable Water Technology
Priority date: 2009-11-17
Filing date: 2010-11-17
Publication date: 2012-09-26
Also published as: WO2011062485A3; NL2003812C2; WO2011062485A2

Abstract

The invention relates to a device for upgrading a fluid,and a system and method therefore. The device comprises: -a housing for containing the fluid; -an anode compartment provided with an anode,and a cathode compartment provided with a cathode; and -an upgrading compartment separated from the anode compartment by a first membrane and separated from the cathode compartment by a second membrane.

Description

BIO-ELECTROCHEMICAL DEVICE AND METHOD FOR UPGRADING A FLUID

The present invention relates to a bio-electrochemical device for upgrading a fluid. More specifically, the device can be used to upgrade a liquid flow, like a waste water flow, to enable the use of the liquid flow for energy generation or the production of hydrogen, for example.

Bio-electrochemical devices are known to be able to degrade organic matter using bacteria to produce a current and thereby energy. Such system is a microbial fuel cell, for example. In a similar configuration, such as a microbial electrolysis cell, hydrogen is produced. This energy

generation or hydrogen production requires a fluid with sufficiently high alkalinity and salt concentrations. In practice alkalinity and concentrations limit scaling up the systems and/or the applicability thereof.

The object of the present invention is to improve the applicability of bio-electrochemical devices.

This object is achieved with the bio-electrochemical device according to the invention for upgrading a fluid, the device comprising:

a housing for containing the fluid;

an anode compartment provided with an anode, and a cathode compartment provided with a cathode; and

- an upgrading compartment separated from the anode

compartment by a first membrane and separated from the cathode compartment by a second membrane.

A bio-electrochemical device comprises an anode

compartment provided with an anode and a cathode compartment provided with a cathode. At the anode organic material is oxidized to electrons, protons and CO₂. At the cathode oxygen in case of a microbial fuel cell (MFC) , or protons in case of a microbial electrolysis cell (MEC) , are reduced to water and hydrogen, respectively. Electrons move from anode to cathode. To compensate this movement of negative force, cations move from anode to cathode and/or anions move from cathode to anode. The system according to the invention further comprises an upgrading compartment that is separated from the anode compartment by a first membrane and is separated from the cathode compartment by a second membrane. Because of the flow of electrons cations and anions will be transported towards this upgrading compartment. This

increases the pH and the conductivity of the fluid in the upgrading compartment. This upgrades the fluid in this compartment and enables the use thereof in a MFC for energy generation and/or a MEC for hydrogen production, for

example .

The conductivity of waste water is often in the order of 2 mS/cm. Such level of conductivity limits the applicable distance between the anode and cathode. In experiments a limit of about 1 mm was determined. This relatively small distance prevents practical application of bio- electrochemical devices using these waste water flows.

Providing these flows with additional salts is rather expensive and does not contribute to the sustainability of the system. In addition, such added salts should be removed before disposing the fluid that is used. This is especially relevant in case the fluid comprises waste water, for example .

By upgrading a fluid, such as the waste water flow mentioned above, the efficiency of operations involving a MFC and/or MEC can be improved by using the upgraded fluid.

In addition, at present flows are often not usable for use in bio-electrochemical systems. Such flows can be upgraded by incorporating the device according to the invention in the bio-electrochemical system. This incorporation in a bio-electrochemical system according to the invention increases the amount of flows that can be used. Furthermore, by improving the properties of the flows also the possibilities of scaling up the systems are

improved. This contributes to large scale energy generation or hydrogen production, for example.

By upgrading the fluid in the upgrading compartment, the pH is increased. For example, this enables treatment of waste streams with solid particles. In fact, such solid particles are made available for oxidation. Another

application is degrading the organic matter in volatile fatty acids. At present the degrading of organic matter is limited by the decreasing pH as function of the acids that are produced. The upgrading the fluid in the bio- electrochemical system according to the invention enables further acidification. This improves the efficiency of this process .

Preferably, the first membrane comprises a cation exchanging membrane, while the second membrane comprises an anion exchange membrane. The anode is separated from the cathode by a cation selective membrane on the anode side and an anion selective membrane on the cathode side of the upgrading compartment. Cations are transported from the anode compartment to the upgrading compartment and anions are transported from the cathode compartment to the

upgrading compartment. This upgrades the fluid in the upgrading compartment. Preferably, the anode and/or cathode comprise biochemical active micro-organisms. Also

preferably, the fluid in the upgrading compartment comprises waste water. This enables the use and/or re-use of a waste water flow.

The bio-electrochemical system according to the

invention can be operated as a batch process by maintaining an amount of liquid in the upgrading compartment for a period of time, or as a continuous process by maintaining a continuous flow through this upgrading compartment.

Energy can be generated or hydrogen produced by

providing the upgraded flow with the system according to the invention to a MFC and/or a MEC. Other processes in the production of energy and hydrogen are also possible using the upgrading system according to the invention. For

example, the upgraded flow can be used to produce volatile fatty acids.

Preferably, upgrading the fluid comprises increasing the pH and/or the conductivity of the fluid.

The invention also relates to a bio-electrochemical system for generating energy or providing hydrogen,

comprising:

a microbial fuel cell for energy generation or a microbial electrolysis cell;

supply means for supplying a fluid to the cell; and an upgrading system including a bio-electrochemical device as described above.

Such system provides the same effects and advantages as those related to the device.

In a preferred embodiment according to the present invention the upgrading device acts as a pre-treatment system for pre-treating a fluid.

Providing the device with coupling means for coupling the device to a process device, like a MFC or a MEC, results in the bio-electrochemical device being used as a pre- treatment system in the system according to the invention. The device upgrades the fluids before processing this fluid in the system. An advantage thereof is that the processing device can be operated efficiently for upgrading the flow. Also, this configuration has the additional advantage that the pre-treatment can be performed without requiring

significant changes to the existing processing system. This improves the applicability of different types of flows, like waste water flows, for processing devices including MFC's and MEC's. Depending on the specific conditions, the entire flow, or part thereof, can be pre-treated in the device according to the invention.

In a preferred embodiment according to the present invention the bio-electrochemical device acts as

regenerating system for regenerating the fluids, the device comprising coupling means for coupling the device to a processing device.

By providing coupling means the bio-electrochemical device according to the invention can be coupled to a processing device, like a MFC and MEC. This enables a post- treatment operation in the device according to the

invention. By regenerating the fluid the (partly)

regenerated fluid can be recycled to the processing device, thereby improving the overall efficiency of the processing operation. A further advantage of regenerating the fluid in the device according to the invention is the applicability of the device in combination with existing processing equipment. Depending on the specific conditions of the processing operation the flow can be recycled in its

entirety or in part.

In addition, the device according to the invention can be used as pre-treatment and/or as post-treatment operation. This can be achieved by alternately operating the bio- electrochemical device according to the invention as pre- treatment and post-treatment device, or by providing

different devices for the different operations.

The present invention also relates to a method for upgrading a fluid comprising the steps of: providing a fluid to a bio-electrochemical device as described above; and

providing a potential difference and/or a resistance between electrodes in the device.

Such method provides the same effects and advantages as those related to the device. The method according to the invention can be applied to a batch operation or a

continuous operation like described above.

The upgrading of the fluids can be performed as a pre- treatment operation. The upgraded flow is provided to a MFC for generating energy or MEC for providing hydrogen or performing another bio-electrochemical operation. The upgraded fluid can also be provided to other alternative process operations. Furthermore, the method for upgrading a fluid can also be performed for recycling an entire fluid or a part thereof after energy is generated or hydrogen is produced, for example. Also the method can be performed as a pre-treatment and post-treatment operation.

Further advantages, features and details of the

invention are elucidated on basis of preferred embodiments therefore, wherein reference is made to the accompanying drawings, wherein:

- figure 1 illustrates a bio-electrochemical device

according to the invention;

figure 2 shows results with the device of figure 1; and

figure 3 also shows results of the device of figure 1. A bio-electrochemical device (figure 1) comprises a housing or container 4. Container 4 comprises an anode compartment 6 with an anode 8 whereon micro-organisms 10 are provided. Container 4 further comprises a cathode compartment 12 that is provided with a cathode 14. Between anode compartment 6 and cathode compartment 12 there is provided an upgrading compartment 16. Upgrading compartment 16 is separated from anode compartment 6 by a cation

exchanging membrane 16. Upgrading compartment 16 is

separated from cathode compartment 12 by anion exchanging membrane 20. Inlet 22 provides upgrading compartment 16 with a flow with a relatively low pH and a low conductivity. The upgraded fluid leaves upgrading compartment 16 through outlet 24. The influent is provided to the anode compartment 6 through inlet 26 and the effluent leaves compartment 6 through outlet 28, while hydrogen produced in the cathode compartment 12 leaves through outlet 30. A current or power source 32 is connected by circuit 34 to the electrodes 8, 14.

At anode 8 micro-organisms 10 oxidize organic material to electrons, protons and CO₂. At the cathode oxygen or protons are reduced to water and hydrogen. Electrons move from anode 8 to cathode 14 through circuit 34. This provides a driving force causing cations to move from anode

compartments 6 towards cathode compartment 12 and anions to move from cathode compartment 12 towards anode compartment 6. By separating compartments 6, 12 with membranes 18, 20 cations from the anode compartment and anions from the cathode compartment 12 are transported to the upgrading compartment 16, thereby improving the pH and conductivity of the fluids in compartment 16.

In an experiment device 2 is used to upgrade a fluid. The pH (figure 2) and the conductivity (mS/cm) (figure 3) are measured of both the incoming influents (indicated with I and filled circles) and the fluid in the upgrading

compartment 16 (indicated with B and open circles) .

Measurements are performed during a time period of seven days. The results indicate a strong increase in pH and conductivity C of the fluid in the upgrading compartment 16. This illustrates the applicability of upgrading a fluid like waste water, for example. This upgraded flow can be used for energy generation or hydrogen production.

A further experiment has been performed, wherein the fluid is regenerated. The experimental setup is similar to that shown in figure 1. In this setup, the influent is provided to upgrading compartment 16 and leaves this

compartment through outlet 24. Outlet 24 is connected with outlet 28, which now acts as an inlet, and provides the anode compartment 6 with upgraded fluid. The fluid leaves the anode compartment via inlet 26, which now acts as an outlet .

Three series of measurements were performed. The influent contained 10, 5 or 0 mM phosphate buffer.

Measurements of the conductivity and pH of the influent and the fluid in all three compartments were performed after a steady state had been established. The steady state was reached when the pH and conductivity were stable in all three compartments and the current production was stable. Also the current density produced was measured. The

measurement were made for seven days .

The results obtained were similar to that described for the previous experiment. The pH and conductivity in the upgrading compartment increased. In the series with 0 mM phosphate buffer, the pH increased from 6.8 in the influent to 11.4 in the upgrading compartment and the conductivity increased from 4.4 mS/cm in the influent to 5.5 mS/cm in the upgrading compartment. Similar results were obtained for the series with 5 respectively 10 mM buffer.

The current densities measured for the 0, 5, 10 mM buffer concentration were 3.62 A/m², 3.44 A/m² and 3.46 A/m² respectively. These results show that it is possible to produce the same current when no buffer is added to the influent. This is caused by the fact that protons from the biofilm are taken up due to the higher hydroxyl

concentration resulting from upgrading the fluid in the upgrading compartment. This prevents acidification and maintains biofilm performance.

It is therefore shown that no addition of chemicals is required to control anode pH.

The present invention is by no means limited to the above described preferred embodiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.

Claims

Bio-electrochemical device for upgrading a fluid, the device comprising:

a housing for containing the fluid;

an anode compartment provided with an anode, and a cathode compartment provided with a cathode; and an upgrading compartment separated from the anode compartment by a first membrane and separated from the cathode compartment by a second membrane.

Bio-electrochemical device according to claim 1, wherein the first membrane is a cation exchanging membrane and the second membrane is an anion

exchanging membrane.

Bio-electrochemical device according to claim 1 or 2, the anode and/or cathode comprising bio-chemical active micro-organisms .

Bio-electrochemical device according to claim 1, 2 or 3, wherein the fluid comprises waste water.

Bio-electrochemical device according to any of the claims 1-4, wherein upgrading the fluid comprises increasing the pH and/or the conductivity of the fluid.

Bio-electrochemical system for generating energy or providing hydrogen, comprising:

a microbial fuel cell for energy generation or a microbial electrolysis cell;

supply means for supplying a fluid to the cell; and an upgrading system including a bio-electrochemical device according to any of the claims 1-5.

7. Bio-electrochemical system according to claim 6,

wherein the bio-electrochemical device acting as a pre- treatment system for pre-treating the fluid, the device comprising coupling means for coupling the device to the cell.

Bio-electrochemical system according to claim 6 or 7, wherein the bio-electrochemical device acting as a regenerating system for regenerating the fluid, the device comprising coupling means for coupling the device to the cell.

Method for upgrading a fluid, comprising the steps of: providing a fluid to a bio-electrochemical device according to any of the claims 1-5; and

Method according to claim 9, wherein after upgrading the fluid is provided to a microbial fuel cell for generating energy or a microbial electrolysis cell for providing hydrogen or performing another bio- electrochemical operation.

11. Method according to claim 9 or 10, wherein upgrading the fluid is performed after energy is generated or hydrogen is provided using the fluid for enabling reuse of the fluid.

12. Method according to any of the claims 9-11, wherein upgrading the fluid comprises increasing the pH and/or the conductivity of the fluid.