NL1038578C2 - Device and method for treating aqueous solutions. - Google Patents

Description

Device and method for treating aqueous solutions.

The invention relates to a device for the treatment of an aqueous solution by 5 means of electrolysis and ultrasound, said device comprising a flow chamber through which the aqueous solution can be guided in a certain flow direction, which chamber is provided with at least one pair of polarisable electrodes, at least one of the electrodes being attached to an ultrasound transducer, which, upon activation, causes the electrode to vibrate in a direction substantially perpendicular to the surface of the electrode. The invention also relates to a 10 method in which this device is applied.

Devices and methods of the type mentioned above are known as such, for example from the German patent application published as DE 100.15.144-A1. This document describes a method and a device for disinfection of water by treating it by means of both ultrasound and chemical electrolysis. More precisely, this document discloses a device with a 15 flow chamber comprising an ultrasound transducer. A part of the transducer is used as an electrochemical electrode. Activation of the transducer causes said electrochemical electrode part to vibrate with a certain ultrasound frequency and certain amplitude. Water guided through said chamber can be treated by both electrolysis and ultrasound. Application of the known device on an aqueous solution containing an E. coli culture resulted in a strong 20 reduction of the bacteria content in the solution.

The described device and method have the disadvantage that the combined working of both ultrasound and electrolysis in the treatment of aqueous solutions is still not optimal. This holds especially the effectiveness of the treatment of the solution as well as the construction of the ultrasound and the electrolysis parts of the device.

25 It is an object of the present invention to improve the known device and the known method for the treatment of aqueous solutions. In more detail the invention aims at enhancing the effectiveness of the disclosed method. The invention also aims at providing an improved device having a simple and reliable construction as well as at the use of such device in the treatment of certain aqueous solutions.

30 These and other objects of the invention are achieved by a device for the treatment of an aqueous solution by means of electrolysis and ultrasound, said device comprising a flow chamber through which the aqueous solution can be guided in a certain flow direction, which chamber is provided with at least one pair of polarisable electrodes, at least one of the electrodes being attached to an ultrasound transducer, which, upon activation, 1 0 38 5 78 2 causes the electrode to vibrate in a direction substantially perpendicular to the surface of the electrode, characterized in that the vibration direction of the electrode is substantially parallel to the flow direction of the aqueous solution.

The invention is inter alia based on the recognition of the inventors that the 5 effectiveness of the known device and the known method can be considerably improved by a different construction of the flow chamber. In the previously cited German patent application, the ultrasound device is connected in or to the flow chamber in such a manner that the vibration direction is substantially normal or perpendicular to the flow direction of the treated aqueous solution. The inventors now have shown that a more efficient treatment of the 10 aqueous solution is achieved when the vibration direction of the electrode(s), which is (are) attached to the transducer, is substantially parallel to the flow direction of the aqueous solution. In the course of this application, the expression ‘substantially parallel’ means that the angle between the flow direction and vibration direction is less than 30°, preferably less than 20°, and most preferably less than 10°. A smaller angle between both directions causes 15 higher treatment efficiency. Devices according to the invented design show an improvement in treatment efficiency which can be larger than 15%. In this respect it is noted that transducers usually cause unidirectional movements upon activation. Ultrasound transducer which can be applied in the device according to the present invention typically can generate vibrations with frequencies between 20 kHz and 2 MHz.

20 With the presently invented device different types of aqueous solutions can be treated. These solutions include industrially polluted water, waste water, cooling water and drinking water. Such aqueous solutions may be contaminated with micro-organisms and moreover contain organic compounds. The devices are especially suitable for treating aqueous solutions, in which the treatment is directed to the oxidative or reductive degradation of these 25 micro-organisms and compounds.

The German patent application published as DE196.18.217-A1 describes a comparable device and method for the treatment of liquids. In this device, the vibration direction caused by the transducer during operation on the movable electrode is substantially parallel to the surface of latter electrode. As a consequence, the flow direction of the aqueous 30 solution in this prior art decive is substantially parallel to the surface of the movable electrode. The known design prevents the intimate contact between the movable electrode and the solution, which is obtained with the presently invented device. The treatment efficiency of this prior art device is therefore less than the efficiency of the presently invented device.

3

An interesting embodiment of the device according to the present invention is characterized in that the electrode which is attached to the transducer has a substantially circular circumference and that the transducer is attached to a central area of the electrode, said transducer being mounted via a mounting frame to a wall portion of the flow chamber.

5 The use of an electrode having a substantially circular circumference has clear structural advantages. When the transducer is positioned in the centre of such electrode, its generated unidirectional vibrating forces will be directed substantially normal or perpendicular to the surface of the attached electrode, which preferably has a flat design. These forces will cause deflecting effects on the electrode, which effects propagate to its circumference. If non-10 circular electrodes - such as electrodes having a rectangular or square form - are used, uncontrolled resonances in the comer sections of such designed electrodes can be evoked. Such resonances cause undesired losses of energy in the vibrating parts.

Another interesting embodiment of the invented device has the feature that the second electrode of the pair of electrodes is designed as a circular tube, which is attached 15 to a wall portion of the flow chamber. Devices for the treatment of solutions having the electrodes designed according to this aspect of the invention can be rather small. This holds especially if the movable electrode with circular circumference is positioned inside the tubelike second electrode. Said second electrode can be attached as an additional part on the inside of a wall of the flow chamber. The second electrode can also be formed as a constructive wall 20 part of the flow chamber, thereby replacing a part of the wall of the flow chamber.

A further attractive embodiment of the device is defined by the characteristic that the mounting frame is designed as the second electrode of the pair of electrodes. A water treatment device according to this embodiment can also be small-dimensioned and therefore have a compact construction. The combination of a structural and an electrical function in one 25 element (the mounting frame) is considered to be advantageous from the point of view of costs.

Special interest is given to the embodiment of the water treatment device having the feature that another electrode is attached by means of a second transducer to the mounting frame and that both transducers are designed in such manner, that upon their 30 activation their summed force on the mounting frame is substantially zero. This embodiment has the advantage that the vibration forces of both transducers are effectively neutralized, so that effectively no forces are transmitted to the constructive parts of the flow chamber. In order to achieve this, both the frequency and the amplitude of the two transducers need to be 4 identical, whereas the direction of the movement of the moving electrodes needs to be opposed. This constructive design causes a considerably enhanced life-span of the device.

The two moveable electrodes can have an opposite polarization during treating the aqueous solution. In a device of this design, the two electrodes in principle can act as 5 counter-electrodes, when the aqueous solution is guided through the flow chamber. Under certain conditions, a device of this design may not show an optimal functioning. In that situation, each of the two movable electrodes may have its own counter-electrode. These counter-electrodes can be designed as circular tubes, which are both attached to a wall portion of the flow chamber.

10 It is however preferred to design the flow chamber in such a way that the two moveable electrodes during electrolysis have the same - preferably positive - polarity. In a device of this design under certain conditions may not function optimally. In such situation the use of at least one additional counter-electrode is preferred. Such counter-electrode(s) may have a tubular form and be attached to a wall-portion of the flow chamber, as described 15 before. It is also possible to design the mounting frame as a counter-electrode for both movable electrodes. Due to its simple construction, latter design is preferred.

A further interesting embodiment of the invented device has the feature that the device contains in the flow chamber at least two sets of mounting frames with transducers and electrodes, the transducers of the different sets being designed in such manner that, upon their 20 activation, they are working at different frequencies. This embodiment allows for treating the same aqueous solution with different ultrasound power and different type of electrolysis in a single treatment in the flow chamber. This can be advantageous in case that different elements should be removed form the solution in a single treatment.

Another attractive embodiment of the invented device is characterized in that 25 the electrode(s) attached to the transducer is (are) designed as a flat plate having a number of through holes. During the treatment of an aqueous solution in the flow chamber, the solution is guided through the holes. A skilled person can easily determine the number and dimensions of the through holes. The flow rate of the solution, the dimensions of the chamber and the material of the flat plate electrode(s) are important elements in the determinations.

30 Still another important invented embodiment has the feature that the electrode(s) attached to the transducer is (are) designed as a circular grid. This embodiment is especially advantageous in case that the flow rate of the solution to be treated is rather high. Increasing of the thickness of the grid increases also the treatment time of the solution when using the same flow rate. An increased thickness of the grid also adds to the rigidity of the electrode.

5

Attractive is also the embodiment of the invented device in which the surface of at least one of the movable electrodes comprises Ι1Ό2 and/or R.UO2. The electrode itself can 5 be made of a precious metal, preferably Titanium (Ti). The surface of this electrode comprises a metal oxide of at least one of the metals Iridium (Ir) and Ruthenium (Ru). Devices being equipped with this type of electrode can be used with great advantage in disinfection of water which contains low amounts of chloride. Due to the positive effect of the acoustic transducer, an unexpectedly efficient treatment can be performed at much lower chloride concentrations. 10 Interesting is also the embodiment of the invented device in which the surface of at least one of the movable electrodes comprises B-doped diamond material. B stands for the element Boron. Devices being equipped with this type of electrodes can be used with great advantage in disinfection of water being contaminated with organic material, like microorganisms. When using such type of electrode, radicals can be formed, which effectively 15 destructs such organic material. Due to the positive effect of the acoustic transducer, an unexpectedly efficient treatment can be performed in the cleaning of such contaminated aqueous solutions

Water treatment devices having in the flow chamber both a positively charged moveable electrode with IrC>2 and/or RuC>2 on its surface and a positively charged moveable 20 second electrode with B-doped diamond material on its surface are preferred by far. Such devices can very effectively disinfect and clean aqueous solutions containing both a low concentration of chloride as well as organic compounds (like remains of medicines in urine and/or micro-organisms). The use of ultrasound generated by means of the acoustic transducer(s) in addition to electrolysis appears to cause a positive effect on both the cleaning 25 and the disinfection of such solutions. As said before, one or more additional counterelectrodes may be applied in the flow chamber if the cleaning and disinfection process does not function optimally.

Regarding the water treatment devices designed according to the previous paragraph, the inventors have noted that the efficiency of the treating process depends on the 30 sequence of the electrodes as regards the flow direction of the aqueous solution. More precisely, it appears to be better that the solution first contacts the electrode comprising B-doped diamond and secondly the electrode comprising Ir02 and/or RuC>2. This holds especially when both electrodes are positively polarized.

6

The invention also relates to a method for the treatment of aqueous solutions by means of electrolysis and ultrasound, whereby an aqueous solution is directed through a flow chamber which chamber is provided with at least one pair of polarisable electrodes, at least one of said electrodes being attached to an ultrasound transducer, which, upon 5 activation, causes the electrode to vibrate. According to the invention, this method is characterized in that the vibration direction of the electrode is substantially parallel to the flow direction of the aqueous solution. As described above, such design enables a more intimate and therefore more effective treatment of such aqueous solution.

These and other aspects of the invention will be apparent from and elucidated 10 with reference to the embodiments described herein below.

In the drawings

Figure 1 shows in a cross-section a first embodiment of the device for treating an aqueous solution according to the present invention

Figure 2 shows a different cross-section of the device shown in Figure 1 15 Figure 3 shows in a cross-section a second embodiment of the device for treating an aqueous solution according to the present invention

Figure 4 shows a different cross-section of the device shown in Figure 3 It is stressed that the drawing is schematic and not to scale. In the different Figures, same elements are denoted with same reference numbers where possible.

20 Figure 1 shows schematically and in cross-section a first embodiment of the device for treating an aqueous solution. The device 1 comprises a flow chamber 2, which is in this embodiment designed as a circular tube 3, having a diameter of 10 cm and being made of electrically insulating material, such as polyvinylchloride (PVC). It is observed that other electrically insulating materials such as polyethylene (PE) polypropylene (PP) or ceramics 25 can be applied as well. Even non-insulating materials like stainless steel can be applied, especially when a part of the tube acts as a (counter) electrode.

Flow chamber 2 comprises a mounting frame 4, being composed in this embodiment of three mounting spikes of electrically insulating material, such as polyvinylchloride (PVC). It is observed that other electrically insulating resin materials, like 30 polyethylene (PE) or polypropylene (PP) can be used as well. It is even possible to use ceramics. Even non-insulating materials like stainless steel can be used, especially when the mounting frame acts as a (counter) electrode. Said spikes are firmly attached tot an inner wall portion of flow chamber 2 via one of their end portions. The opposite end portions meet in the centre of tube 3 and form here an attachment seat for transducer 5 (30 kHz, 1500 V, 50 Watt).

7

The other side of transducer 5 is attached to first electrode 6. Upon its activation, transducer 5 causes electrode 6 to vibrate in a unidirectional manner. The dotted arrow indicates the vibration direction of electrode 6. For reasons of clarity, the electrical connections of the transducer 5 are not shown. These connections however can be powered by electrical wires, 5 which run via one of the hollow spikes of mounting frame 4 to the outer world, where they are connected to an electrical power source (not shown).

The device according to the present invention further comprises a second electrode 7, which is formed as a circular tube of metal. Said second electrode 7 is attached to an inner wall portion of the flow chamber 2. For reasons of compactness and efficiency, 10 movable electrode 6 is positioned inside counter-electrode 7. An electrical current (direct of alternate) can be applied on the pair of electrodes 6 and 7. For reasons of clarity, no electrical connection wires for polarization of the electrodes are shown in Figure 1.

Figure 2 shows another cross-section of the invented device as schematically depicted in Figure 1. This cross-section is made through the surface of the flat plated 15 electrode 6. This figure shows in more detail the through holes 8 which are present in electrode 6. For clarity reasons, spikes of mounting frame 4 are indicated by dotted lines.

When using the invented device for treating an aqueous solution, said solution is guided through the flow chamber in a certain direction. This direction is shown by the large (open) arrow in Figure 1. During the treatment of the solution, an effective electrical current 20 flows between the electrodes 6 and 7, which current depends on the substances which are present in the solution to be handled. Usually current flows below 100 A are used, whereas current flows in the range between 2 to 10 A are preferred. Simultaneously the transducer is electrically activated. Frequencies in the range between 20 and 500 kHz are usually applied.

In specific circumstances (with small dimensioned electrodes) frequencies up to 2 MHz can 25 be used. Due to the inventive measure to have the flow direction of the solution and the vibration direction of the movable electrode substantially parallel, a very efficient treatment of the solution can be achieved. As compared with the know design described in DE 100.15.144-A1, the efficiency can be increased with at least 15%, whereas increases between 20 and 50% are achievable.

30 Figure 3 shows a preferred embodiment of the invented device for treating an aqueous solution. In this embodiment, a first transducer 5 and a second transducer 9 are attached to mounting frame 4. Electrodes 6 and 10 are attached to transducers 5 and 9, respectively. In the present embodiment, these electrodes 6 and 10 are designed in such manner that they both have a positive polarization during the treatment of an aqueous i ί 8 solution. The surface of the positively charged moveable electrode 6 comprises B-doped diamond material. The surface of the negatively charged moveable counter-electrode 10 comprises Ι1Ό2 and/or RuC>2. Due to this design, water to be treated first contacts the electrode with B-doped material (i.e. where radicals are generated) and subsequently the electrode with 5 IrC>2 and/or R.UO2 (i.e. where chloride can be converted into hypochlorite).

For this preferred embodiment, it is essential that both transducers 5 and 9 are designed in such manner, that upon their activation their summed force on the mounting frame 4 is substantially zero. This means that at the moment on which electrode 6 moves away from mounting frame 4, electrode 10 also moves away from this mounting frame and 10 vice versa. Effectively this means that the forces exerted by these movements on the mounting frame 4 neutralize each other. So, the net force which is exerted on the mounting frame 4 during the working of the device, amount to approximately zero. In comparable devices having only a single transducer attached to the mounting frame, much larger net forces are exerted on said frame during their working, which requires rather robust designs of 15 such devices. The same holds in constructions having two transducers attached to a single mounting frame, in case that the transducers work with different frequencies and/or amplitudes. The present embodiment shows the advantage that a less robust design is needed, which makes the design of this embodiment less expensive. In such preferred device, the design of both transducers and electrodes need to be substantially identical. This also holds 20 for the used frequency and the amplitude of the movement induced by the transducers.

Figure 4 shows another cross-section of the preferred device according to the present invention, as schematically depicted in Figure 3. This cross-section is made through the surface of the flat plated electrode 6 (or 10). This figure shows in more detail that both electrodes are designed as circular grids. These grids are prepared by attaching a number of i 25 parallel plates substantially perpendicular to a second number of parallel plates. Electrodes of ! this design are especially useful in case that the flow rate of the aqueous solution guided j through the flow chamber is rather high. '

In a number of experiments, a solution of potable water containing sodium chloride (NaCl) in a concentration of 10 gr/1 (gram per liter) was treated by means of a device 30 according to the present invention. Said solution was circulated with a speed of approximately 170 liter per hour through the flow chamber 2 of the device depicted in Figure 3. A voltage of 5 V was applied between the counter-electrodes 6 and 10, which resulted in a current flow of 2,7 A. The frequency of the ultrasonic transducer was set at 30 kHz. The chloride concentration of the circulating aqueous solution was measured at regular time intervals of 5 9 minutes until 30 minutes (end of experiment) by means of a sensor to which a measuring apparatus was connected. In a comparative experiment in which the transducer was switched off, the same measurements were performed at the same time intervals.

The experiments showed that application of ultrasound causes a positive effect 5 on the reduction of the Cl-concentration. Compared with the series in which the ultrasound transducer was switched off, the increase of the efficiency was determined to be between 30% and 70%. These values were measured in the case that the flow direction of the aqueous solution was substantially parallel to the vibration direction of the electrodes.

An additional comparative experiment (not according to the invention) was 10 performed. In this experiment, the vibration direction of the electrodes was substantially perpendicular to the flow direction of the aqueous solution. Compared with a series in which the ultrasound transducer was switched off, this experiment showed an increase in efficiency on the Cl-reduction of approximately 10%. As shown in the previous paragraph, a much higher increase of efficiency can be obtained in case that the flow direction of the solution is 15 almost parallel to the vibration direction of the electrodes. So, this series of experiments show the advantage of having the flow direction and the vibrating direction substantially parallel.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

20 Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain 25 measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

1038578 30

Claims (12)

Device for treating an aqueous solution by means of electrolysis and ultrasound, wherein the device (1) contains a through-flow chamber (2) through which the aqueous solution can be guided in a certain flow direction, wherein the chamber (2) is provided with at least one pair of polarizable electrodes (6,7) such that at least one of the electrodes (6) is attached to an ultrasound transducer (5) which, after activation, causes the electrode (6) to vibrate in a direction which is substantially perpendicular to the surface of the electrode, characterized in that the direction of vibration of the electrode (6) is substantially parallel to the direction of flow of the aqueous solution. 2. Device as claimed in claim 1, characterized in that the electrode (6) attached to the transducer (5) has a substantially circular circumference, and that the transducer (5) is attached to a central region of the electrode (6). ), wherein the transducer (5) is attached to a wall portion of the flow chamber (2) via a mounting frame (4). 3. Device as claimed in claim 3, characterized in that the second electrode (7) of the pair of electrodes (6,7) is formed as a circular tube which is attached to a wall portion of the flow-through chamber (2). Device according to claim 2, characterized in that the mounting frame (4) is formed as the second electrode (7) of the pair of electrodes (6,7). Device according to claim 2, characterized in that a further electrode (10) is attached to the mounting frame (4) by means of a second converter (9), and that both transducers (5, 9) are designed such that, after their activation, the added force that they exert on the mounting frame (4) is virtually zero. Device according to claim 5, characterized in that the two movable electrodes (6, 10) have the same polarity during electrolysis. Device according to one of the preceding claims, characterized in that the device (1) in the flow-through chamber (2) has at least two sets of mounting frames (4) with transducers (5.9) and electrodes (6.10) ), wherein the converter (5) of the different systems are designed such that, after activation, they operate at a mutually different frequency. Device according to one of the preceding claims, characterized in that the electrode (s) (6, 10) attached to the transducer (s) (5, 9) are formed as a flat plate in which a number of through-going openings ( 8). 9. Device as claimed in any of the claims 1-7, characterized in that the electrode (s) attached to the transducer (5, 9) are formed as a circular grid. Device according to one of the preceding claims, characterized in that the surface of at least one of the movable electrodes (6, 10) contains IrC> 2 and / or RuCh. 15 Device according to one of the preceding claims, characterized in that the surface of at least one of the movable electrodes (6, 10) contains B-doped diamond material. A method for treating an aqueous solution by electrolysis and ultrasound, wherein an aqueous solution is passed through the flow chamber (2) of a device (1), the chamber (2) being provided with at least one pair of polarizable electrodes (6,7) such that at least one of the electrodes (6) is attached to an ultrasound transducer (5) which, after activation, causes the electrode (6) to vibrate, characterized in that the direction of vibration of the electrode (6) is substantially parallel to the flow direction of the aqueous solution. \ 10 385 78