WO1994026668A1

WO1994026668A1 - Process and device for the electrochemical treatment of water

Info

Publication number: WO1994026668A1
Application number: PCT/CH1994/000088
Authority: WO
Inventors: Hans LÜBER
Original assignee: Lueber Hans
Priority date: 1993-05-18
Filing date: 1994-05-13
Publication date: 1994-11-24

Abstract

At the centre of a through-flow container (1) there is a cathode arrangement (9) around which there are preferably magnesium-containing anode rods. The area of the anode is larger than that of the cathode and the water is preferably caused to flow towards the cathode. A d.c. source (25) is connected between the anode and the cathode so that electric processes take place at the electrodes. The sodium content of the water is thereby reduced and furring is prevented at the same time.

Description

Method and device for the electrochemical treatment of water

The invention relates to a method for the electrochemical treatment of water, in particular for the reduction of the nitrate content, and a device for the electrochemical treatment of water according to the preamble of claim 4.

Such methods and devices are used for example in the water supply of residential buildings. The water is treated electrochemically in order to improve the water quality and in particular to prevent corrosion and limescale deposits in the in-house pipeline network. Such devices have been known for a long time.

A problem that has not yet been solved satisfactorily is the sometimes high nitrate content of the drinking water. Since 1985 it has been limited to 50 mg N0 ₃ / liter (guideline value even only 25 mg / l) according to the EC directive. Different treatment measures for nitrate removal are already known and eg "serschutz Gewäs¬ - _r water, waste water," in 109 (1988) pp 249-281 ben beschrie¬. However, some of these methods are quite complex and have not yet been widely used, particularly in building technology.

It is therefore an object of the invention to provide a method of the type mentioned at the outset and, in particular, to achieve a reduction in the nitrate content in the water, optimum efficiency being achievable with simple constructional means. According to the invention, this object is achieved by a method having the features of claims 1 or 2.

For the treatment, the water is passed through a continuous tank in which at least one anode arrangement and little least a cathode arrangement are held. An electrical current is generated between the anode arrangement and the cathode arrangement by means of a current source. Surprisingly, it has been shown that the nitrate content of the water is noticeably reduced if the anode arrangement has a surface which is larger than the surface of the cathode arrangement or if the flow of water essentially runs against the cathode arrangement or if both measures are combined. Particularly low nitrate values are achieved when using an anode, the surface of which is two to three times the surface of the cathode.

The known arrangements essentially consist of a flow container for the water with at least one water inlet and at least one water outlet and electrodes arranged in the container. The anode is usually made of magnesium-containing material. In operation, a direct current source is connected between the anode and the cathode. A small electrical current flows and electrochemical processes take place on the electrodes. The magnesium of the anode is slowly broken down, so the anode must be replaced from time to time. The treatment primarily decalcifies the water, so that no scale formation occurs when the treated water is used, for example in the household.

Applicant's DE-A-39-23-585 describes such an arrangement, the electrical treatment being combined with mechanical filtering. The cathode was designed as a sieve chamber, within which the magnesium-containing anode and the water outlet are located. However, in particular with high water consumption, that is to say at high flow rates, the performance of the known device is limited.

It is therefore also an object of the invention to make this known To further improve the device and in particular to increase the efficiency. This object is achieved with a device with the features of claim 1. It has surprisingly been found that particularly good results are achieved if several anode rods are arranged approximately symmetrically in the flow container around the cathode arrangement and if the flow of water essentially runs against the cathode arrangement, the cathode ¬ the arrangement has approximately the same length as the anode rods. The cathode arrangement must not necessarily be electrically connected to the line network, as was previously the case.

An arrangement in which the cathode arrangement is arranged standing in the middle of the flow container and the anode rods are arranged uniformly distributed on a circle around the cathode arrangement has proven particularly useful. With this system, a larger anode surface is achieved than if, as in the known systems, only anode rods are present in the middle. In addition, the anode rods in the uniform water flow result in a stronger mixing of the water, which also has a positive effect on the treatment of the water. This arrangement not only reduces the nitrate content but also increases the lime-reducing effect. An arrangement of at least six anode rods has proven to be particularly favorable. If the components are dimensioned appropriately, a relatively dense ring of anode rods can be built up.

The function of the arrangement can be further improved if the cathode arrangement is designed as an elongated sieve chamber made of conductive material and if the treated water is drained from the interior of the sieve chamber (pure water space). As a result, the electrical treatment is combined with a mechanical filter, as is already evident from the called DE-A-39 23 585 is known. The advantage over the already known arrangement is that the anode is arranged outside the pure water space and thus any particles separated from the anode are also filtered out. Since the water is drained from the inside of the sieve chamber, the water tends to flow towards the cathode. This flow supports the movement of the positively charged ions in the direction of the cathode and represents a further advantage of the present electrode arrangement. However, in certain cases the wall of the flow container could also be designed as an additional cathode and be effective against the anode arrangement.

The sieve chamber can be cylindrical and it can be held in the passage container by an outlet tube which extends concentrically over the entire length of the sieve chamber. The outlet tube thus also has the function of mechanically reinforcing the sieve chamber. The actual screen grid is fastened to the outlet tube with holding elements. Particularly good results are achieved if the outlet tube arranged concentrically in the sieve chamber consists of electrically conductive material and is short-circuited with the sieve chamber as part of the cathode arrangement.

The outlet pipe protruding into the pure water chamber is used as an additional cathode, i.e. electrically connected to the screen chamber. However, it would also be conceivable to manufacture the outlet pipe from electrically non-conductive material or to electrically insulate it from the sieve chamber.

In order to prevent the flow container itself from being at the potential of the cathode, the outlet tube is divided into two parts, an inner part that protrudes into the sieve chamber and an outer part that leads to the outer connection of the outlet. The inner part of the outlet pipe is connected to the outside by an electrically insulating insulating element. The inner part of the outlet pipe can also serve as a holder for the sieve chamber.

The outlet pipe has one or more outlet openings in the upper area of the sieve chamber, through which the water can flow from the sieve chamber into the outlet tube and thus to the outlet. This ensures that the water to be treated remains in the flow container for as long as possible.

To clean the sieve chamber, backwashing takes place, in which fresh water is briefly passed through the outlet pipe. However, this only under the condition that not a significant consumer is switched on.

The flow container can be cylindrical and in it a tubular partition wall open at the bottom can be held concentrically, within which the anode rods and the sieve chamber are arranged. The inlet is at the top, outside the partition. In order to achieve a cyclone-like flow, the water is introduced tangentially into the annular chamber between the flow container and the partition. This flow has proven to be particularly advantageous for the electrolytic treatment of water. The water flows down between the partition and the outer wall of the flow container and then upwards again inside the partition. The electrochemical treatment room is located inside the partition; this is where the electrochemical reaction takes place and solid particles precipitate, which sink to the lower end of the flow container. This cylindrical partition serves to introduce the incoming water as quietly as possible from below into the electrochemical treatment room. This ensures that as few as possible of the particles accumulating on the bottom of the flow container are whirled up. The tubular partition can be attached to a container lid of the flow container and it can simultaneously support the anode rods.

The device can be further improved if the metallic sieve chamber which forms the cathode arrangement is covered with a filter cloth in order to increase the filter effect.

To clean the electrodes, an alternating voltage is applied between the anode and cathode if necessary. The particles adhering to the electrodes are thereby removed and sink into the blowdown zone at the bottom of the flow tank.

The precipitated suspended particles, e.g. Lime particles accumulate in the blowdown zone. They have to be removed from time to time, e.g. a drain valve located at the bottom of the flow tank is opened and the accumulated sludge is discharged through a drain pipe.

In certain cases it would be conceivable to circulate the water through the same container several times during a certain time for more efficient treatment. In addition, a continuous container could contain several batteries of anode or cathode arrangements. Accordingly, such a container could also have several inlets and outlets.

The device according to the invention is particularly advantageous for reducing the nitrate content in drinking water. However, the device can also be used in conjunction with other treatment devices, such as according to EP-B-377 411, for wastewater disposal. The invention is explained in more detail in the following exemplary embodiments with reference to drawings. Show it:

FIG. 1 shows a sectional illustration of a device according to the invention,

Figure 2 shows an alternative embodiment with additional cathode, and

FIG. 3 shows a cross section through the device according to FIG. 1.

The device shown in Figure 1 has a flow container 1 with a cylindrical peripheral wall made of metal, e.g. stainless steel, which tapers in the lower area towards the lower end of the container. A drain line 2 is connected to this lower end, in which an electrically operable shut-off device 3 is arranged. In the flow container 1 there is a cylindrical partition 4 made of plastic, which starts from the upper end or from the container cover 5 and extends downwards over a larger part of the height of the container. The partition is sealed off from the container lid in order to prevent fresh water from flowing directly into the center. The inlet 6 for the water to be treated opens in the upper region of the flow container 1 into the annular chamber between the flow container 1 and the partition 4. At the inlet there is a water guide 7 which only moves the water sideways and in one direction (left or right) can flow into the flow tank 1. Thus, the water is introduced tangentially to the peripheral wall of the container and flows down cyclone-like until it reaches the end of the partition 4. Then the water inside the partition 4 rises again.

The space inside the partition 4 is the treatment room 8, in which the electrodes are located; the electrochemical treatment of the water takes place here. The partition 4 has the advantage that the water flows into the treatment room from below and relatively calmly. At the same time it can be used to attach the electrodes. The cathode arrangement 9 is located in the middle of the container and six anode rods 10 are arranged distributed uniformly on a circle around the cathode arrangement 9 (FIG. 3). The partition 4 is used to fasten the electrodes. At the lower end of the cylindrical partition 4, a retaining ring 11 is inserted and the anode rods 10 are fixed in position by this retaining ring. At the upper end of the cylindrical partition 4, a holding cover 12 is inserted, on which both the anode rods 10 and the cathode arrangement 9 are fixed. Retaining ring 11 and retaining cover 12 are advantageously made of plastic. So that the gases arising during the electrochemical process can escape, the holding cover 12 has gas outlet holes 14 and the container cover 5 of the flow container 1 has a ventilation opening 15. With the interior closed, the degassing would take place via the outlet pipe and thus via the consumer, which is obviously not desirable. The cathode arrangement 9 and the anode rods 10 are connected to a direct current source 25.

The selected shape and arrangement of the electrodes has decisive advantages over known devices. Since several anode rods 10 are used, the anode surface is larger and because of the arrangement in the cyclonic water flow, the anode rods 10 come into greater contact with the water to be treated; the anode rods 10 are in the water flow and ensure a stronger mixing of the water. These properties have a positive effect on the electrolytic treatment of the water and in particular bring about a reduction in the nitrate content. The cathode arrangement consists of a mechanical sieve chamber 16 and, in addition to its function as an electrode, also has a mechanical filtering effect by retaining dirt particles floating in the water. The mechanical sieve chamber 16 is therefore also the cathode for the electrolytic process. In order to increase the mechanical filter effect, the filter chamber 16 can be covered with a filter cloth 17. The inner area of the sieve chamber 16 is the pure water chamber 18. From this pure water chamber, the treated water is passed through an outlet pipe 13 to the outlet 19. Since, according to the invention, the anode rods 10 are arranged outside the sieve chamber 16, any contaminants separated from the anode rods 10 do not get into the pure water chamber 18. The water tends to flow in the direction of the cathode arrangement 9, since the outlet tube 13 in the Cathode arrangement is arranged. This direction of flow supports the movement of the ions in the direction of the cathode, which brings about further improvements in lime treatment and in the reduction of the nitrate content. The electrically effective surface of the anode is nevertheless significantly (two to three times or more) larger than that of the cathode. The anode rods are sacrificial anodes made of magnesium.

The lime particles separated by the electrolytic treatment, as well as other particles floating in the incoming water, settle in the blowdown zone 29 at the bottom of the flow tank 1. Particles hanging on the filter cloth are largely removed when required by applying an alternating voltage to the electrodes and backwashing and then settle in the blowdown zone 29. If necessary, these impurities are removed by opening the shut-off device 3 and thus flushing the sludge into the drain pipe 2.

The outlet pipe 13 shown in Figure 1 extends to the lower end of the screen chamber 16 and has one at its lower end Opening 20. The sieve chamber 16 serving as the cathode consists of a cylindrically shaped sieve grid which is attached to the outlet pipe 13 by means of electrically non-conductive end elements 21 at the top and bottom and thus forms a pure water chamber 18 in its interior. One or more outlet openings 22 are provided in the outlet pipe 13, through which the water can flow from the pure water chamber 18 into the outlet pipe 13. According to the invention, these outlet openings 22 are arranged at the upper end of the pure water chamber 18 in order to ensure that the water remains in the treatment room 8 for as long as possible. In order to prevent water from reaching the outlet 19 through the opening 20 without treatment, a separating base 23 is provided in the outlet pipe 13 below the outlet openings 22. The particles separated in the outlet pipe below the partition 23 can fall down through the opening 20.

The electrical connections of the anode and the cathode are led out at connection terminals 24 which are located on the container lid 5. All elements that are related to the attachment and connection of the electrodes are attached to the container lid 5. When the container lid is lifted off, the electrodes are lifted out of the continuous container 1 and are thus easily accessible, which proves to be an advantage when the anode rods 10 are replaced.

The following table shows N0 ₃ concentrations in mg / 1. The measurements were carried out on a device according to FIG. 2. The left column shows the concentration of the fresh water to be treated, the values in the other columns correspond to the concentrations measured at the outlet of the flow container at a flow of 3, 6 and 10 liters per minute. Each of the measurements at the exit was carried out after 10 minutes of constant water flow. 3 1 / min 6 1 / min 10 1 / min

20-25 mg / 1 5-8 mg / 1 5-8 mg / 1 5 mg / 1

30-35 mg / 1 15 mg / 1 15 mg / 1 12 mg / 1

35-40 mg / 1 15 mg / 1 12-15 mg / 1 12-15 mg / 1

Figure 2 shows a further improvement of the cathode. When a voltage is applied between the anode bars 10 and the cathode, positively charged ions dissolve at the anode and migrate to the cathode.

The improvement consists in that, in addition to the screen chamber 16, the internal outlet pipe 13 is also used as the cathode and is also connected to the negative pole of the power source.

So that the flow container 1 remains insulated from the cathode, the outlet tube 13 is divided into two parts here. The inner part 26 of the outlet pipe, which is fastened to the sieve chamber, is connected to the outer part 27 of the outlet pipe via an electrically insulating insulating element 28.

If necessary, the intensity of the electrolysis could be regulated by a potentiometer which is integrated into the circuit.

The devices according to FIGS. 1 and 2 are particularly suitable for reducing the nitrate content, as the measurement results show.

Claims

1. A method for the electrochemical treatment of water, in particular for reducing the nitrate content, characterized in that the water is passed through a flow container (1) with at least one anode arrangement and with at least one cathode arrangement (9), the anode arrangement having a surface , which is larger than the surface of the cathode arrangement, and that an electrical current is generated between the anode arrangement and the cathode arrangement by means of a current source (25).

2. A method for the electrochemical treatment of water, in particular for reducing the nitrate content, characterized in that the water is passed through a pass-through container (1) with at least one anode arrangement and with at least one cathode arrangement (9), the flow of the water in the essentially runs against the cathode arrangement, and that an electrical current is generated between the anode arrangement and the cathode arrangement by means of a current source (25).

3. A method for the electrochemical treatment of water characterized by a combination of the methods according to claim 1 and claim 2.

4. Device for the electrochemical treatment of water, with a flow container (1) for the water, which is provided with at least one inlet (6) and at least one outlet (19) and in which at least one anode arrangement is held, and with an equal ¬ current source (25) for supplying electrical current to the anode arrangement, characterized in that at least one cathode arrangement is held in the same container and that the surface of the anode arrangement is larger than the surface of the cathode arrangement.

5. The device according to claim 4, characterized in that the anode surface is two to three times the cathode surface.

6. The device according to claim 4 or 5, characterized in that the anode arrangement has at least two anode rods (10) which are arranged approximately symmetrically around the cathode arrangement (9), the cathode arrangement being approximately the same length as is the anode rods (10) and the inlet (6) and the outlet (19) are arranged such that the flow essentially runs against the cathode arrangement (9).

7. The device according to claim 6, characterized in that at least six anode rods (10) are arranged around the cathode arrangement (9).

8. Device according to one of claims 6 or 7, characterized in that the cathode arrangement (9) has an elongated sieve chamber (16) made of electrically conductive material and that the outlet (19) lies within the sieve chamber (16).

9. The device according to claim 8, characterized in that the sieve chamber (16) is cylindrical and that it is held by an outlet tube (13) in the flow container (1) which extends concentrically over the entire length of the sieve chamber (16).

10. The device according to claim 9, characterized in that the outlet tube (13) consists of electrically conductive material and is short-circuited as part of the cathode arrangement (9) with the sieve chamber (16).

11. The device according to claim 9, characterized in that the outlet tube (13) consists of electrically non-conductive material or is electrically insulated from the sieve chamber (16).

12. Device according to one of claims 9 to 11, characterized in that the outlet tube (13) has at least one outlet opening (22) in the upper region of the sieve chamber (16).

13. The apparatus according to claim 12, characterized in that the flow container (1) is cylindrical, that in the flow container (1), a tubular partition wall (4) open at the bottom is held concentrically, within which the anode rods (10) and Siebkamraer (16) are arranged, and that the inlet (6) to achieve a cyclonic flow tangentially into the ring chamber (31) between the flow container (1) and the partition (4) opens.

14. The apparatus according to claim 13, characterized in that the partition (4) is attached to a container lid (5) of the flow container (1) and that the anode rods (10) are attached to the partition (4).

15. Device according to one of claims 8 to 14, characterized in that a filter cloth (17) is arranged on the outside of the sieve chamber (16).

16. Device according to one of claims 10 to 15, characterized in that the sieve chamber (16) is connected to the outlet pipe (13) at the upper and at the lower end by means of disc-shaped, electrically non-conductive end elements (21).

17. Device according to one of claims 6 to 16, characterized in that the anode rods (10) and the cathode arrangement (9) are electrically insulated from the flow container (1).

18. Device according to one of claims 4 to 17, characterized in that the anode arrangement comprises sacrificial anodes made of magnesium.