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Title:
METHOD FOR FLUIDIZED BED CAPACITIVE DEIONIZATION OF A FLUID AND DE-IONIZATION DEVICE THEREFOR
Document Type and Number:
WIPO Patent Application WO/2017/061864
Kind Code:
A1
Abstract:
The present invention relates to a method for upflow capacitive de-ionisation of a fluid and device therefor, the method comprisingthe steps of: -providing a fluidized capacitive deionization device comprisinga fluid channel,an anode channel with an anode and a cathode channel with a cathode, an anode channel inlet and outlet, and an anode channel divider, a cathode channel inlet and outlet, and acathode channel divider, wherein, in use, thechannels have a substantially vertical orientation; -providing fluid and an electrode suspension comprising the electrode particles; -applying an electrical potentialdifferencebetween the anode and the cathode; and -selecting the flow rates such that an upflowfluidized bed of anode particles in the anode channel and/or an upflowfluidized bed of cathode particles in the cathode channel are achieved.

Inventors:
DOORNBUSCH, Gijs Jan (p/a Oostergoweg 9, MA Leeuwarden, NL-8911 MA, NL)
DYKSTRA, Jouke Eabele (p/a Oostergoweg 9, MA Leeuwarden, NL-8911 MA, NL)
HAMELERS, Hubertus Victor Marie (p/a Oostergoweg 9, MA Leeuwarden, NL-8911 MA, NL)
BIESHEUVEL, Pieter Maarten (p/a Oostergoweg 9, MA Leeuwarden, NL-8911 MA, NL)
Application Number:
NL2016/050691
Publication Date:
April 13, 2017
Filing Date:
October 06, 2016
Export Citation:
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Assignee:
STICHTING WETSUS, EUROPEAN CENTRE OF EXCELLENCE FOR SUSTAINABLE WATER TECHNOLOGY (Oostergoweg 9, 8911 MA Leeuwarden, 8911 MA, NL)
International Classes:
C02F1/469; C02F1/461; C25B7/00; C25B9/16
Foreign References:
KR20150002364A2015-01-07
EP2605326A22013-06-19
KR101291768B12013-07-31
KR101318331B12013-10-16
EP2857442A12015-04-08
Other References:
SUNG-IL JEON ET AL: "Desalination via a new membrane capacitive deionization process utilizing flow-electrodes", ENERGY & ENVIRONMENTAL SCIENCE, vol. 6, no. 5, 4 March 2013 (2013-03-04), pages 1471, XP055079854, ISSN: 1754-5692, DOI: 10.1039/c3ee24443a
None
Attorney, Agent or Firm:
VERDIJCK, Gerardus Johannes Cornelis (Bezuidenhoutseweg 57, AC Den Haag, NL-2594 AC, NL)
Download PDF:
Claims:
Claims

1. Method for upflow fluidized bed capacitive deionization of a fluid, comprising the steps of:

providing a fluidized capacitive deionization device comprising:

a fluid channel for the fluid with a fluid inlet and a fluid outlet; an anode channel with an anode and a cathode channel with a cathode, with at least one of the anode and cathode comprising a current collector and an amount of electrode particles;

an anode channel inlet and an anode channel outlet, and an anode channel divider separating the anode channel from the fluid channel; and

a cathode channel inlet and a cathode channel outlet, and a cathode channel divider separating the cathode channel from the fluid channel, wherein, in use, the fluid channel, anode channel and cathode channel have a substantially vertical orientation;

providing fluid to be deionized to the fluid channel and providing an electrode suspension comprising the electrode particles to the anode channel and/or the cathode channel;

applying an electrical potential difference between the anode and the cathode such that the anode is positively charged and anions are adsorbed, and such that the cathode is negatively charged and cations are adsorbed; and

selecting the flow rates in the anode channel and/or cathode channel such that an upflow fluidized bed of anode particles in the anode channel and/or an upflow fluidized bed of cathode particles in the cathode channel are achieved.

2. Method according to claim 1, wherein the volume of electrode particles in the anode channel and/or the cathode channel is above 30% of the volume of the anode channel and/or the cathode channel.

3. Method according to claim 2, wherein the volume of electrode particles is above 40%, preferably above 50%, and preferably above 60%.

4. Method according to claim 1, 2 or 3, wherein the particle weight percentage in the anode and/or cathode channel is above 20 wt% and the particle weight percentage in the flow entering the channel or channels is below 5 wt%.

5. Method according to one of the foregoing claims, further comprising the step of collecting the electrode particles from the anode channel outlet and/or cathode channel outlet in an electrode particles reactor for discharging the electrode particles.

6. Method according to claim 5, further comprising the steps of:

returning the discharged electrode particles to the anode channel inlet and/or cathode channel inlet;

removing an outlet fluid from the electrode particles reactor; and

providing a feed flow to the electrode particles reactor.

7. Method according to claim 6, wherein the feed flow is provided at a ratio to the fluid flow below 0.5, preferably below 0.2, more preferably below 0.1, and most preferably in the range of O.01-0.075.

8. Method according to one or more of the foregoing claims, wherein providing the electrode suspension comprising the electrode particles at the channel inlet with a viscosity in the range of 0.1-10 mPa-s, preferably in the range of 0.5-5 mPa-s, and most preferably in the range of 0.8-1.2 mPa-s.

9. Deionization device for upflow fluidized bed capacitive deionization of a fluid, the device comprising:

a fluid channel for the fluid with a fluid inlet and a fluid outlet;

an anode channel with an anode and a cathode channel with a cathode, with at least one of the anode and cathode comprising a current collector and an amount of electrode particles;

an anode channel inlet and an anode channel outlet, and an anode channel divider separating the anode channel and the fluid channel; and

a cathode channel inlet and a cathode channel outlet, and a cathode channel divider separating the cathode channel and the fluid channel,

wherein the fluid channel, anode channel and cathode channel have a substantially vertical orientation.

10. Deionization device according to claim 9, wherein, in use, the anode channel and/or cathode channel comprises a fluidized bed of electrode particles.

11. Deionization device according to claim 10, further comprising a flow controller configured for controlling the flow rate of the electrode suspension in the anode channel and/or cathode channel such that the fluidized bed is achieved.

12. Deionization device according to claim 10 or 11, wherein the volume of electrode particles in the anode channel and/or cathode channel is above 30% of the volume of the anode channel and/or cathode channel, preferably above 40%, more preferably above 50%, and most preferably above 60%.

13. Deionization device according to one or more of the claims 9-12, wherein the cathode channel divider is a cation exchange membrane.

14. Deionization device according to one or more of the claims 9-13, wherein the anode channel divider is an anode exchange membrane.

15. Deionization device according to one or more of the claims 9-14, further comprising an electrode particles reactor that is connected to the anode channel outlet and/or cathode channel outlet.

16. Deionization device according to claim 15, further comprising a brine outlet, a feed inlet, and an electrode particles outlet for circulating the electrode particles over the anode channel and/or the cathode channel.

17. Deionization device according to one or more of the claims 9-16, wherein the electrode particles have a characteristic size in the range of 80-300 μπι.

18. De-ionization device according to one or more of the claims 9-17, wherein the cross- section of the anode and/or cathode channel inlet and anode and/or cathode channel outlet are smaller that the cross-section of the anode channel and/or cathode channel.

Description:
METHOD FOR FLUIDIZED BED CAPACITIVE DEIONIZATION OF A FLUID AND DE-IONIZATION

DEVICE THEREFOR

The present invention relates to a method for fluidized bed capacitive de-ionization of a fluid, specifically for desalination of salt water, such as sea water and saline ground water.

Conventional methods for performing de-ionization processes, involving the use of a fluidized bed electrode, use electrode particles involving electrochemical ion absorption for charging and ion desorption for discharge of the electrode particles. Such fluidized bed system enables a continuous flow operation, for example for desalination of sea water. Electrode particles are provided in a suspension that is pumped through the system. This requires a substantial amount of energy.

The present invention has as one of its objectives to improve the efficiency of fluidized bed capacitive de-ionization of a fluid.

This objective is achieved with the method for upflow fluidized bed capacitive de- ionization of a fluid according to the present invention, the method comprising the steps of:

- providing a fluidized capacitive deionization device comprising:

a fluid channel for the fluid with a fluid inlet and a fluid outlet;

an anode channel with an anode and a cathode channel with a cathode, with at least one of the anode and cathode comprising a current collector and an amount of electrode particles;

an anode channel inlet and an anode channel outlet, and an anode channel divider separating the anode channel from the fluid channel; and

a cathode channel inlet and a cathode channel outlet, and a cathode channel divider separating the cathode channel from the fluid channel,

wherein, in use, the fluid channel, anode channel and cathode channel have a substantially vertical orientation;

- providing fluid to be deionized to the fluid channel and providing an electrode

suspension comprising the electrode particles to the anode channel and/or the cathode channel;

- applying an electrical potential difference between the anode and the cathode such that the anode is positively charged and anions are adsorbed, and such that the cathode is negatively charged and cations are adsorbed; and

- selecting the flow rates in the anode channel and/or cathode channel such that an upflow fluidized bed of anode particles in the anode channel and/or an upflow fluidized bed of cathode particles in the cathode channel are achieved.

By providing a device or apparatus with a fluid channel having a fluid inlet and a fluid outlet, the fluid to be treated can be provided to the apparatus or device. The anode channel is separated from the fluid channel and the cathode channel is separated from the fluid channel with channel dividers. These dividers can be provided as a filter and/or as anion exchange membranes and/or cation exchange membranes. In a presently preferred embodiment, the cathode channel divider is a cation exchange membrane and the anode channel divider is an anode exchange membrane.

At least one of the electrodes, and in a presently preferred embodiment all electrodes of the device, comprise a current collector and an amount of electrode particles. Such flow-electrodes have the advantage that they enable (continuous) steady-state operation, where the discharge of the particles preferably occurs downstream of the device, without requiring cyclical operation in the anode and/or cathode channel involving switching between charging and discharging states of the particles. As a further advantage, ions from the fluid in the fluid channel are only required to move through a divider once, preferably one membrane, and do not need to move back again during the step of cell discharge (brine formation) as in conventional operations wherein cyclical

charge/discharge is required.

In use, the fluid channel, anode channel and cathode channel have a substantially vertical orientation. By applying an up-flow fluidized bed a high loading of electrode particles in the anode and/or cathode channels, the electrode channels, can be achieved. This further reduces the electronic resistance and contributes to an effective desalination at a relatively low applied voltage between anode and cathode.

Due to the up-flow orientation, electrode particles are subjected to gravity, thereby enabling a higher residence time for the electrode particles in the electrode channels as compared to the surrounding fluid, such as water with ions. Therefore, the channels contain a relatively high density of electrode particles, while the fluid that is pumped from the electrode channel outputs contains a relatively low density of electrode particles as compared to the channels. In a presently preferred embodiment the fluid from the electrode channel outputs is pumped around in the system. The reduced density of the fluid from the outputs enables effective pumping of the electrode suspension comprising electrode particles from the electrode channel outputs, while maintaining a high packing rate in the electrode channels. The upflow configuration of the fluid bed achieves that the electrode particles have a higher (average) residence time in the anode and/or cathode channel, however, a flow of these particles through the system is maintained. This enables a high loading of electrode particles in the electrode channels that without the aforementioned residence time effect could not be pumped effectively from the channel outlets. In case of the electrode particles comprising a powder a high content of particles would result in a high viscosity.

Therefore, the present invention is capable of combining a high loading of electrode particles in the electrode channels with a fluid, such as the suspension, that is pumped from the channel outlets with a low viscosity, for example similar to water, thereby enabling effective pumping.

As a further effect of a high packing or loading of electrode particles, the storage capacity of charge and/or salt is significantly increased, while in addition the electronic resistance for transport of electric charge from a current collector into the electrode particles is reduced. For a certain cell voltage, the salt removal can be significantly increased with the method according to the invention, for example.

As a further effect operation can be performed at a cell voltage preventing the risk of water splitting.

In use, an electric potential difference is applied between the anode and the cathode, such that the anode is positively charged and anions are adsorbed and the cathode is negatively charged and cations are adsorbed. This potential difference is called the cell voltage. According to the invention, adsorption also includes absorption of ions.

Furthermore, in use the flow rates in the anode channel and/or cathode channel are selected, such that a fluidized bed of preferably anode particles in the anode channel and/or a fluidized bed of preferably cathode particles in the cathode channel is achieved. This fluidized bed uses the electrode particles that are present in the suspension. The electrode particles can be embodied as (activated) carbon beads with a characteristic dimension, such as a diameter or length, in the range of 80-300 μπι, for example. Preferably, such beads form a fluidized bed across the entire height of the channel.

Conventional flow electrodes employ small sized carbon particles, typically about 10 μπι. These particles are entrained by the electrolyte and travel at the electrolyte's velocity. By contrast, according to a presently preferred embodiment of the invention the relatively large particles move at a significant lower (average) speed as compared to the liquid. This is the effect of the relatively large size of the particles and preferred flow against the direction of gravity, wherein the particles are subject to a significant gravitational effect. This achieves relatively densely packed particles in the electrode compartment. This difference between particles in a flow electrode and particles in a fluidized bed can be expressed in relation to the Archimedes number. For example, for a conventional flow electrode the number typically is about 0.001 and for the fluidized bed electrode about 1.

Furthermore, in preferred embodiments of the system according to the invention the carbon weight percentage in the electrode compartment can be maintained at a relatively high level, for example above 20 wt%, preferably above 30 wt%, more preferably above 35 wt%, and most preferably above 40 wt%. At the same time the weight percentage of the particles in the surrounding flow system can be maintained at a much lower level, for example below 10 wt% and preferably below 5 wt%. This prevents or at least reduces the risk of clogging in the surrounding flow system. Also, maintenance of the system can be reduced.

The flow rates can be selected manually or automatically at stationary values or can be adjusted manually or automatically when required. Preferably, a controller is provided to select the most appropriate flow rates. By controlling the flow rate the packing density of particles, such as carbon particles, in the fluidized bed can be influenced. Also, electrode particle size and composition of the flows can be selected to optimize the upflow fluid bed behaviour.

In a presently preferred embodiment according to the present invention the volume of electrode particles in the anode channel and/or cathode channel is above 30% of the volume of the anode channel and/or the cathode channel, preferably above 40%, more preferably above 50%, and most preferably above 60%. Preferably, the volume is below 70%.

Providing a substantially high loading or packing with electrode particles in the electrode channel(s) reduces electronic resistance and increases capacity of the desalination process.

According to the invention, this is achieved without requiring the pump to pump a viscous slurry of powder, for example. In fact, according to the invention, a relatively dilute suspension of particles, preferably having a viscosity not very different from that of water, is pumped through transport tubes or pipes entering the electrode channel(s) from the bottom. Due to gravity, the electrode particles are confronted with a gravitational force and the particles have a lower (average) velocity in the fluidized bed as compared to the surrounding fluid.

In a presently preferred embodiment, the channel has a larger cross-sectional area as compared to the inlet tubes and the outlet tubes, thereby reducing the velocity of the fluid and electrode particles. Due to the velocity difference between fluid and particles, a high particle loading, preferably high carbon loading, inside the electrode channel with a relatively high residence time of the electrode particles is achieved. The volume component of electrode particles in the transport piping or tubing and other components, for example a mixing reactor or vessel, is for instance about 10% and at least significant lower as compared to the packing in the electrode channel. As the electrode particle content in the transport tubing or piping is relatively small, less energy for pumping around the fluid is required. Preferably, the electrode suspension comprises electrode particles such as carbon beads, and surrounding fluids, such as salt water, and has a viscosity similar to the viscosity of water.

Preferably, the packing or loading of electrode particles in the channel(s) is above 30%, more preferably above 40%, even more preferably above 50%, and most preferably above 60%. This high packing further improves the overall efficiency of the de-ionization process. In one of the presently preferred embodiments the density of the electrode particles filled with water in a wet state is slightly higher as compared to the surrounding liquid, such as water. In a dry state of the electrode particles an electrode particles volume of 70% corresponds to a mass content of about 55 wt.%, for example.

In a presently preferred embodiment, the method according to the invention further comprises the step of collecting the electrode particles from the anode channel outlet and/or cathode channel outlet in an electrode particles reactor for discharging the electrode particles.

By providing an electrode particles reactor, a closed loop electrode system for the fluidized capacitive de-ionization process is achieved. The electrode suspension with the electrode particles is recycled over the system or device.

As a further effect, water recovery can be relatively high for example as high as 90%. Water recovery is defined as flow of product water/total feed flow, with the flow of product water being the outflow of the liquid channel, and the total feed flow being the sum of the feed water flow into the liquid channel and an additional feed flow being the diluate flow into the electrode particles reactor. The reactor preferably comprises a mixing vessel that is continuously or semi- continuously filled with fluid and electrode particles preferably coming from both the electrode channels. This makes the electrode particles reactor a mixing reactor. In the electrode particles (mixing) reactor, the two suspensions are preferably mixed, such that the different particles come into contact with each other and are discharged. As a result, cations and anions are released and salt concentrations increase.

Preferably, the discharge electrode particles are returned to the anode channel inlet and/or cathode channel inlet. An outlet fluid, such as a brine, is removed from the reactor and an additional feed flow is provided to the reactor, enabling a continuous operation. This additional feed flow is preferably provided at a ratio to the fluid flow of below 0.5, preferably below 0.2, more preferably below 0.1, and most preferably in the range of 0.01-0.075. This enables a relatively high water recovery. The outlet fluid is preferably tapped off involving the use of an overflow preventing the electrode particles to pass.

In a presently preferred embodiment the viscosity of the electrode suspension that is provided to the channel inlet is in the range of 0.01-10 mPa-s, preferably in the range of 0.5-5 mPa-s, and most preferably in the range of 0.8-1.2 mPa-s. This viscosity can be pumped between channel and particle reactor relatively easy, thereby reducing the amount of energy required for discharging/pumping while achieving a high desalination rate.

The invention further relates a de-ionization device, comprising:

- a fluid channel for the fluid with a fluid inlet and a fluid outlet;

- an anode channel with an anode and a cathode channel with a cathode, with at least one of the anode and cathode comprising a current collector and an amount of electrode particles; - an anode channel inlet and an anode channel outlet, and an anode channel divider separating the anode channel and the fluid channel; and

- a cathode channel inlet and a cathode channel outlet, and a cathode channel divider separating the cathode channel and the fluid channel,

wherein the fluid channel, anode channel and cathode channel have a substantially vertical orientation.

Such de-ionization device enables performing a capacitive de-ionization process according to the earlier described method, providing the same effects and advantages. In use, the de- ionization device achieves a fluidized bed of electrode particles in the anode channel and/or in the cathode channel. The electrode particles have a characteristic dimensional size in the range of 80- 300 μιη, in a presently preferred embodiment in the range of 100-300 μιη.

The fluidized bed is preferably achieved with the help of a flow controller that is configured for controlling a flow rate of the electrode fluid in the anode channel and/or cathode channel, such that the fluidized bed is achieved. Due to the up-flow configuration and preferred selection of flow rates in the anode channel and/or cathode channel a high packing or loading of electrode particles in the channel can be achieved, of above 30%, above 40%, above 50%, and most preferably above 60 vol.%. The dividers are preferably ion exchange membranes.

Preferably, an electrode particles (mixing) reactor is provided, comprising a brine outlet, preferably two feed inlets and an electrode particles outlet for circulating the electrode particles over the anode channel and/or the cathode channel. Also, an additional feed flow inlet for providing a diluate flow rate into the electrode particles (mixing) reactor can be provided. This reactor enables a continuous operation with a closed loop electrode (particles) operation.

Preferably, the cross-sections of the channel inlet(s) and channel outlet(s) are smaller as compared to the cross-section of the anode channel and/or cathode channel, thereby contributing to the fluidized bed characteristics achieved with the de-ionization device according to the present invention.

Further advantages, features and details of the invention are elucidated on the basis of preferred embodiments thereof, wherein reference is made to the accompanying drawings, in which:

- Figure 1 a schematic overview of a de-ionization device with fluidized beds capable of performing a capacitive de-ionization process; and

- Figure 2 a schematic overview of a method performing a capacitive de-ionization process.

De-ionization device 2 (Figure 1) comprises fluidized bed reactor 4 comprising support 6, anode channel 8, fluid channel 10, and cathode channel 12. In the illustrated embodiment, anode channel 8 is provided with current collector 14 and separated with divider 15 from fluid channel 10. In the illustrated embodiment divider 15 is an anion exchange membrane. Cathode channel 12 is provided with current collector 16 and is separated with divider 17 from fluid channel 10. In the illustrated embodiment, divider 17 is a cation exchange membrane. In use, current collectors 14, 16 are connected to power supply 18.

At cathode channel inlet 20 an electrode suspension is provided. At fluid channel inlet 22 the fluid to be de-ionized is provided. At anode channel inlet 24 an electrode suspension is provided. In the illustrated embodiment the three fluids are leaving the respective channels at outlets 26, 28, 30, respectively.

In the illustrated embodiment anode channel 8 and cathode channel 12 are provided with a high packing or loading of electrode particles 31. Fluid channel 10 is connected with connecting tube or piping 32 to produced fresh water tank 34. Electrode channel outlets 26, 30 are connected with electrode suspension tubes or piping 36, 38 to electrode particles (mixing) reactor 40 at respective inlets 42, 44. In the illustrated embodiment, electrode particles (mixing) reactor 40 has an overflow 45 that is connected with connecting tube or piping 46 to brine tank 48. A filter (not shown) prevents electrode particles 31 to end up in brine tank 48.

Pump 78, 80, 82, 84 pump the respective fluids to and from reactors 4, 40. Controller 70 controls p ump 78, 80, 82, 84. Preferably, controller 70 uses measurement information collected by sensors and/or user input (not shown) to control flow rates, for example.

In the illustrated embodiment electrode particles reactor 40 further comprises mixer 49 making reactor 40 a mixing reactor. Mixer 49 is capable of mixing particles 31 in reactor 40. The electrode suspension is pumped through connecting tubing or piping 50, 52 to inlets 20, 24 respectively. Feed water, for example from water tank 54, is provided with supply tubing 56 to both fluid channel supply 58 that is connected fluid channel inlet 22 and feed water supply tubing or piping 60 providing water to reactor 49.

In use, de-ionization operation 62 starts with providing device 2 in initiation step 64. Anode channel 8 and cathode channel 12 are preferably supplied with beads 31 in preparation step 66. In operational phase 68 a potential is supplied over the current collectors 14, 16 and beads 31 in the electrode channels are being charged. Ions from fluid channel 10 migrate towards electrode channels 8, 12 through filters or membranes 15, 17. Anions are adsorbed by beads 31 in anion channel 8 and cations are adsorbed by beads in cation channel 12.

In the illustrated embodiment, controller 70 sends control instructions 72, 74, 76 to pumps 78, 80, 82 such that flow rates are selected that achieve the fluidized bed in anode channel 8 and cathode channel 12. Residence times of beads 31 in anode 8 and cathode channel 12 are significantly higher as compared to residence time of the surrounding fluid of the electrode suspension. In a closed loop operation, the electrode suspension is pumped to electrode particles (mixing) reactor 40 and mixed with mixer 49 such that electrode particles 31 collide with each other, thereby discharging. In step 88 the cations and anions that are released in reactor 40 are removed from device 2 as a brine 48. Feed water 54 is supplied to reactor 40.

Furthermore, in the illustrated embodiment, controller 70 controls pump 84 with control instructions 86 to control feed water supply. According to the invention, the feed water supply rate is below 10% of the fluid rate in fluid channel 10.

Experiments were performed with a (small-scale) experimental setup as shown in figure 1. A recess with dimensions of about 11 mm deep and about 20 mm wide is milled in plate of about 15 mm PMMA with dimensions 66 x 155 mm. A 10 mm Melange compound graphite (Eisenhuth, Germany) current collector with an effective area of 22 cm 2 is provided leaving a cavity of 1 mm in the acrylic above the current collector. A 1.5 mm silicon gasket is placed on top. This forms the electrode compartment, having a thickness after compression of about 2.4 mm. Two ion exchange membranes, one IEM (Neoseopta CMX, membrane thickness= 170 μπι), and the other AMX (membrane thickness= 140 μπι, Tokuyama, Japan) is provided. After compression the flow channel or spacer compartment is 200 μπι. The stacked layers that form the cell are fixated using lOx M6x50 mm SS bolts. An electrical connection with the current collector is made using a M6x40 mm titanium bolt. The system used for the desalination experiments is schematically exhibited in Figure 1. The feed water is pumped through the fluid channel or spacer compartment (between the two membranes) by a peristaltic pump (Masterflex) at 0.5 or 1.5 ml/min flowrate. The

concentration of sodium chloride in the feed water is 20 mM. The effluent concentration of the spacer compartment is measured using a 5-ring PtlOOO conductivity meter (Metrohm 856, K=0.7 cm-1). A defined constant cell voltage of 1.6 V is applied to the system using a Keithley 2400 power supply, which also measures the electric current.

The particle volume fraction of electrode particles in the reactor is about 10%. The flowrate is 2.5 ml/min using a 1.6 mm inner diameter Norprene tubing (Saint Gobain). The electrode suspension flows through the electrode channel. The conductivity in the mixing reactor is measured using a second conductivity sensor placed in the reactor. The conductivity measurements were taken by stopping the mixer for about 60 seconds allowing the beads to temporarily settle away from the sensor. To control the salt concentration in the mixing reactor, a flow of 0.15 ml/min feed water is continuously pumped into the reactor using a peristaltic pump. The brine is separated from the mixing reactor. It will be understood that flows depend on dimensions of the equipment.

Results showed an effluent concentration of about 11 mM. Water recovery was about 91%. The brine concentration was about 49 mM. The current efficiency was calculated with Current efficiency=(Cin-Cout)®voi,spacer F Imeasured (eqA), wherein, c in is the salt concentration flowing in the cell [mol/m 3 ], c out is the salt concentration flowing out the cell [mol/m 3 ], vo i,s P acer is the volumetric flowrate through the spacer [m /s], F is the Faraday constant [C/mol], and I measU red is the measured current [A] . In the experiment, a current efficiency was calculated of about 84%. Other process conditions resulted in even higher current efficiencies.

Experiments showed that it was possible to establish the fluid bed in the compartment. In fact, in the experiments in the compartment a carbon weight percentage of 35 wt% was achieved, while the incoming flow had a carbon weight percentage of about 2.5 wt%. Therefore, an effective electric charge percolation through the electrode is achieved with a high carbon weight percentage, while a low carbon weight percentage was maintained in the surrounding flow system, thereby minimizing pump requirements and preventing clogging in this surrounding flow system.

It will be understood that the aforementioned experiment illustrates the operation of system 2. Other embodiments, including large scale reactors, can be operated similarly.

The present invention is by no means limited to the above described and preferred embodiments thereof. The rights sought are defined in the following claims, within the scope of which many modifications can be envisaged. For example, a number of reactors 40 can be provided in series of in parallel. Similarly, a number of electrode mixing reactors can be provided.