DE102008026546B4 - Process for the preparation of a hypohalite-containing biocide, biocide obtainable by this process and its use - Google Patents

Abstract

A process for producing a biocide comprising the steps of: a) providing water or an aqueous solution having a concentration of divalent and higher valent ions of not more than 5.0 mg / l in total, b) adding halide salt to that in step a ) and c) anodic oxidation of the mixture prepared in step b), characterized in that in step b) a mixture of a bromide salt and an iodide salt is added or an aqueous solution containing bromide ions and iodide ions is added.

Description

The present invention relates to a method for producing a hypohalite-containing biocide, a biocide obtainable by this method, and to the use thereof.

Because of their high biocidal activity, hypochlorous acid, hypobromous acid, hypochlorite and hypobromite-containing aqueous solutions have been used for some time to disinfect, for example, water such as drinking water, process water in industry, swimming pool water and the like. Because of their low stability, due to the propensity for disproportionation, hypochlorous acid and hypobromous acid are mostly prepared for this purpose at the point of use.

One way to do this is, for example, to decompose chlorine and / or bromine-containing organic substances, such as 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH), by hydrolysis to form hypochlorous and / or hypobromous acid at the site of the invention Use. However, a disadvantage of this method is that the organic precursors for hypochlorous or hypobromous acid are very expensive and the hydrolysis is not complete. In addition, uncontrolled side reactions can take place with the organic hydantoin residue and the end products pose a potential hazard.

To overcome these disadvantages, it has already been proposed to prepare hypohalite-containing aqueous solution at the site of use by anodic oxidation of halide-containing aqueous solutions. In practice, for this purpose, usually from the water to be disinfected, a partial flow, such as a partial water flow of a swimming pool removed, this partial flow a halide salt, such as sodium chloride, added and this partial water flow passed through an electrolytic cell to the halide ions contained in the partial water flow electrochemically hypohalogenations before the thus treated partial water flow is returned to the water. A disadvantage of these methods, however, is that deposit deposits in the electrolysis cell and in particular on the electrodes after a short period of operation, as a result of which the efficiency of the electrolytic cell decreases dramatically. To address this problem, in practice, the electrodes in the electrolytic cell are periodically reversed to dissolve the deposits formed. In these polarity reversals, however, a significant portion of the expensive electrode material is lost in the course of the operating time by dissolution, which is why the life of the electrode thus used is extremely short with less than 3 months. Another disadvantage of this procedure is that due to the periodic reversals, the efficiency of the electrodes over the service life is not constant. Rather, the electrodes have a higher efficiency after the removal of the coating shortly after a polarity reversal than shortly before the next polarity reversal, when deposited again on the electrodes again significant amounts of deposits. For this reason, the efficiency of the electrolytic cell varies during the operating period, so that in the electrolytic cell solutions are produced with varying over the operating time content of hypohalogenations. In order to keep the hypohalogenation concentration in the prepared solution at least reasonably constant over the service life, a very complicated and therefore expensive and fault-prone control is necessary.

From the US 2005/0263404 A1 is a method for the electrolytic production of hypobromite is known in which an aqueous solution is electrolyzed, which may contain chloride ions in addition to bromide ions. Also in the case where both bromide ions and chloride ions are used, a solution containing only hypobromite as hypohalite is prepared.

US 6,059,941 A discloses a method for producing a sterilizing solution in which water is softened by ion exchange before dissolving salt in the softened water such as sodium chloride, after which the aqueous salt-containing solution is treated in an electrolytic cell.

From the US 5,679,239 A For example, a method of preparing hypobromite solution via anodic oxidation of an aqueous halide solution is known.

In the US 4,129,493 A discloses a method for producing hypochlorite solution using deionized water.

The object of the present invention is therefore to provide a method for producing a biocide containing hypohalogenation by means of anodic oxidation of a halide ion-containing solution, in which the aforementioned disadvantages can be avoided, and which can be operated in particular without reversing the polarity of the electrodes and a constantly high over its service life Efficiency has.

• a) Bereitstellen von Wasser oder einer wässrigen Lösung mit einer Konzentration an zwei- und höherwertigen Ionen von in der Summe maximal 5,0 mg/l,
• b) Zugabe von Halogenidsalz zu der in dem Schritt a) bereitgestellten Lösung und
• c) anodische Oxidation der in dem Schritt b) hergestellten Mischung,

wobei in dem Schritt b) eine Mischung aus einem Bromidsalz und einem Iodidsalz zugegeben wird oder eine Bromidionen und Iodidionen enthaltende wässrige Lösung zugegeben wird. According to the invention, this object is achieved by providing a method according to claim 1 and in particular by providing a method for producing a biocide comprising the steps:

• a) providing water or an aqueous solution having a concentration of divalent and higher valent ions of not more than 5.0 mg / l in total,
• b) adding halide salt to the solution provided in step a) and
• c) anodic oxidation of the mixture prepared in step b),

wherein in step b) a mixture of a bromide salt and an iodide salt is added or an aqueous solution containing bromide ions and iodide ions is added.

This solution is based on the finding that deposition in the electrolysis cell and in particular on the electrodes can be reliably prevented during the anodic oxidation and can be dispensed with a polarity reversal of the electrodes during anodic oxidation, if initially water or an aqueous solution with a concentration of divalent and higher valent ions of at most 5.0 mg / l is provided before halide salt is added to this solution and the mixture so produced is anodically oxidized, i. H. if, at the beginning and during the anodic oxidation, the concentration of divalent and higher valent ions in the mixture used in the anodic oxidation is a maximum of 5.0 mg / l in total. Water is never completely pure. Even drinking water contains significant amounts of impurities, such as organic compounds and especially ions. The inventors of the present invention have found that the deposits formed in anodic oxidation in the electrolytic cell and in particular on the electrodes consist predominantly of salts of divalent and higher valent cations, especially of alkaline earth metal carbonates, alkaline earth metal sulfates, alkaline earth metal phosphates and the like, whereas in the deposits salts Monovalent cations are not included. By removing these bivalent and higher valency cations prior to performing the anodic oxidation, and especially before adding the halide salt (s) to a low residual level, deposition in the electrolytic cell and particularly on the electrodes during anodic oxidation can be reliably prevented , For this reason, since polarity reversal of the electrodes during the anodic oxidation can be dispensed with, the life of the expensive electrodes is considerably increased to 50 months or more. In addition, a constant efficiency is achieved throughout the operating life of the electrolysis cell, so that the product or the biocide after the anodic oxidation contains a constant amount of Hypohalogenitionen. In addition, it has surprisingly been found within the scope of the present invention that by avoiding reversals, more active biocide is obtained. Without wishing to be bound by theory, it is believed that this is due to the fact that in the method according to the invention in the anodization in addition to Hypohalogenitverbindungen certain amounts of active oxygen compounds, such as peroxides and / or ozone, are formed which the activity increase the formed Hypohalogenitverbindungen. It is assumed that this does not occur in the processes known from the prior art, because the polarity reversal prevents the formation of these active oxygen compounds. In addition, it has been found within the scope of the present invention that a solution containing hypobromite ions and hypoiodite ions (which are formed by the anodic oxidation from the bromide ions and iodide ions) surprisingly has a much higher biocidal activity than one, one of the sum of the amount of hypobromite ions and hypoiodite ions corresponding amount of exclusively hypobromite ions or Hypoioditionen containing aqueous solution.

Providing water or an aqueous solution having a concentration of divalent and higher valent ions of not more than 5.0 mg / l in total is understood to mean the preparation of such a solution. In this case, the correspondingly pure water can be prepared immediately before carrying out process step b) or can be obtained commercially in a correspondingly pure form. The term provision should in particular also include the latter case.

Completely pure water, ie water which contains no foreign molecules or foreign ions, can not be produced in macroscopic amounts, so that water, even if it has a concentration of divalent and higher valent ions of not more than 5.0 mg / l in total, always has measurable amounts of foreign molecules and foreign ions. Thus, regardless of the degree of purity, water is always an aqueous solution in the narrower sense. This fact is taken into account by the formulation aqueous solution in process step a).

The adjustment of the concentration of divalent and higher valent ions in the water to a value of no more than 5.0 mg / l in step a) can be achieved by any method known to the person skilled in the art respectively. In particular, good results are obtained when the concentration of divalent and higher valent ions in the water is adjusted by ion exchange, osmosis or nanofiltration. Of course, it is also possible to adjust the concentration of divalent and higher valent ions in the water by a combination of various methods and, in particular, by a combination of two or more methods selected from the group consisting of ion exchange, osmosis and nanofiltration. Furthermore, deionized water produced by prior distillation can also be used.

In a further development of the concept of the invention, it is proposed to provide water or an aqueous solution having a concentration of divalent and higher valent ions of not more than 3.0 mg / l in total and preferably not more than 1.0 mg / l in process step a).

Two- and higher-valent ions, which are usually present in appreciable amounts in water and whose concentrations are reduced in the water used in the process according to the invention, for example, aluminum ions, iron ions, manganese ions and especially calcium ions and magnesium ions, and apart from silicon compounds. Preferably, the concentration of calcium ions in the water provided in step a) is less than 3.0 mg / l and preferably less than 1.0 mg / l. It is also preferred that the concentration of magnesium ions in the water provided in process step a) is less than 3.0 mg / l and preferably less than 1.0 mg / l.

According to a further preferred embodiment of the present invention, the water or the aqueous solution provided in step a) contains less than 0.001% by weight of organic compounds. This reliably prevents a possible negative influence of organic compounds on the anodic oxidation.

As already stated, in the method according to the invention in method step a), the concentration of divalent or higher valent ions is reduced as much as possible, but at least to a value of less than 5.0 mg / 1 in total, and preferably also the concentration reduced organic compounds as far as possible, whereas the content of monovalent ions need not be reduced because they do not interfere with the subsequent anodic oxidation. One parameter that reliably reflects the total ion concentration in the water is the conductivity of the water. Good results are obtained, in particular, when the water provided in process step a) before the addition of the halide salt has a conductivity measured at 25 ° C. by a standard method of less than 800 μS / cm, preferably less than 400 μS / cm and particularly preferably less than 300 μS / cm.

The halide salt, that is to say the mixture of bromide salt and iodide salt, can be added to the water provided in process step a) in process step b) in the form of solid (ie as salt in the narrower sense) or in the form of an aqueous solution. Since the addition of a solid requires weighing and salts absorb moisture from the ambient air over prolonged storage, therefore, subsequent weighing may result in a significant error due to an undefined moisture content of the salt, it has been found advantageous in practice to include the halide salt in the water in process step b) in the form of an aqueous (stock) solution having a preferably defined concentration. Preferably, the concentration of halide ions in the stock solution is 10 to 200,000 mg / l, more preferably 10,000 to 100,000 mg / l, and particularly preferably 5,000 to 50,000 mg / l

Preferably, the mixture prepared in process step b) is then mixed until homogeneous, before the anodic oxidation according to process step c) is carried out.

In order not to increase the concentration of divalent or higher valency ions in the water or in the aqueous solution prior to the anodization carried out in process step c), it is proposed in a further development of the inventive idea to use alkaline earth metal-free alkali metal halides or ammonium halides in process step b). Even in the case in which halide salts of divalent or higher valent metals are used in process step b), care should be taken that the concentration of divalent and higher valent ions in the mixture prepared in process step b) is not more than 5, 0 mg / l.

According to the invention, a mixture of a bromide salt and an iodide salt is added in process step b) or an aqueous solution containing bromide ions and iodide ions is added. As stated, it has been found within the scope of the present invention that hypobromite ions and hypoiodite ions (which are formed by the anodic oxidation from the bromide ions and iodide ions) can be found Surprisingly enough, the solution has a much higher biocidal activity than an aqueous solution containing the sum of the amount of hypobromite ions and hypoiodite ions, which contains only hypobromite ions or hypoiodite ions. This effect is achieved in particular when the amount of hypobromite ions exceeds the amount of hypoiodite ions by a multiple, for example by a factor of 100.

Preferably, the mixture added in step b) as a solid or as an aqueous solution contains a salt selected from the group consisting of sodium bromide, potassium bromide, ammonium bromide and any combinations thereof and at least one of the group consisting of sodium iodide, potassium iodide, ammonium iodide and any combinations thereof selected salt.

As stated above, the very high biocidal activity of an aqueous solution containing hypobromite ions and hypoiodinates compared to an aqueous solution containing only hypobromite ions or hypoiodite ions is achieved especially when the aqueous solution contains more hypobromite ions than hypoiodite ions. Good results are obtained in this embodiment in particular when the mixture prepared in process step b) has a bromide ion concentration between 0.4 and 10,000 mg / l, preferably between 400 and 4,000 mg / l and particularly preferably between 200 and 2,000 mg / l, and an iodide ion concentration of between 0.1 and 10 mg / l, preferably between 0.5 and 5 mg / l and more preferably between 0.8 and 2.4 mg / l. The ratio between the bromide ion concentration and the iodide ion concentration is preferably between 4,000: 1 and 10: 1, more preferably between 2,000: 1 and 100: 1 and most preferably between 2,000: 1 and 800: 1.

In the anodization carried out in process step c), all electrode materials known to the person skilled in the art for this purpose can be used. For example, in the case of anodic oxidation, an electrode of ruthenium oxide and / or platinum oxide can be used as the anode, and it is preferred for reasons of cost to use an anode of ruthenium oxide and / or platinum oxide supported on an inert carrier material, for example on titanium or on a titanium alloy , Examples of suitable cathodes are titanium metal electrodes.

With respect to the current applied in the anodic oxidation, the present invention is not particularly limited. In this respect, the anodic oxidation can be carried out in current flows which are usual for anodic oxidations of halide ions. For example, it has proven to be practicable to carry out the anodic oxidation in process step c) at a current flow between 10 and 200 A, particularly preferably between 20 and 60 A and very particularly preferably between 25 and 50 A.

Preferably, the anodic oxidation in the process step c) is carried out at a temperature between 10 and 60 ° C.

Good biocidal efficacy results of the biocide produced are achieved in particular if the biocide produced in process step c) has a concentration of hypohalite ions between 10 and 1000 mg / l, preferably between 50 and 700 mg / l and particularly preferably between 100 and 700 mg / l.

A further subject of the present invention is a biocide which is obtainable by the method according to the invention described above, in which method the mixture prepared in step b) has a bromide ion concentration between 400 and 4000 mg / l and an iodide ion concentration between 0.5 and 5 mg / l.

The biocide according to the invention can be advantageously used as an additive in wastewater, as an additive in process water, as an additive in fresh water, as an additive in swimming pool water, as an additive in cooling water or as an additive in sealing water in the paper industry, in the metal industry and all other aqueous systems of numerous industries become.

• a) eine Wasserenthärtungseinrichtung,
• b) einen Mischbehälter zur Vermischung von enthärtetem Wasser mit Halogenidsalz bzw. einer wässrigen Halogenidsalzlösung sowie
• c) eine wenigstens zwei Elektroden aufweisende Elektrolysezelle zur anodischen Oxidation einer Halogenidionen enthaltenden wässrigen Lösung.

The method according to the invention can be carried out in a device for producing a biocide, which comprises:

• a) a water softening device,
• b) a mixing vessel for mixing softened water with halide salt or an aqueous halide salt solution and
• c) an electrolytic cell having at least two electrodes for the anodic oxidation of an aqueous solution containing halide ions.

Preferably, the water softening device is designed such that it reduces the concentration of divalent and higher valent ions in water to a value of not more than 5.0 mg / l in total.

The water softening device is preferably an ion exchanger, an osmosis device or a nanofiltration device.

It is proposed that the device further comprises a container containing a halide ion containing aqueous solution, wherein the container is connected to the mixing container via a line, wherein the water softening device is connected via a line to the mixing container and wherein the mixing container with the electrolytic cell via a line is connected.

The device preferably further comprises a reservoir containing at least one halide salt, wherein a solids feed line leads from the reservoir into the container and leads from the water softening device a line into the container.

Hereinafter, the present invention will be described purely by way of example with reference to advantageous embodiments and with reference to the accompanying drawings.

It shows:

1 a device suitable for carrying out the method according to the invention.

The in the 1 illustrated device 10 for the production of a biocide with the method according to the invention comprises an ion exchanger 12 , a storage container 13 for salt, a container 14 for halide stock solution, a mixing tank 16 and a two electrodes 18 . 18 ' having electrolysis cell 20 ,

The ion exchanger 12 has a supply line 22 for fresh water and a discharge pipe 24 for ion-exchanged water or softened water, of which a partial flow line 25 in the mixing container 16 leads. In addition to the partial flow line 25 flows into the mixing container 16 one out of the container 14 coming supply line 26 for halide stock solution. The container 14 itself is with one from the reservoir 13 upcoming solids supply line 28 for halide salt and with one from the discharge line 24 coming partial flow line 30 equipped for ion-exchanged water.

From the mixing container 16 leads a supply line 32 via a flow meter 34 to the electrolysis cell 20 , which further comprises a discharge line 36 for removal of in the electrolysis cell 20 produced product or biocide.

In addition, the device 10 a control device 38 which, depending on received measurement signals, the flow rates through the individual lines 22 . 24 . 25 . 26 . 28 . 30 . 32 and 36 controls.

When operating the device 10 becomes the ion exchanger 12 via the fresh water supply line 22 continuously supplied with fresh water, such as tap water, which in the ion exchanger 12 is cleaned so that the concentration of divalent and higher ions in the via the discharge line 24 from the ion exchanger 12 withdrawn water in the sum of 5.0 mg / l or less. A partial flow of the from the ion exchanger 12 via the discharge line 24 withdrawn ion-exchanged water is via the partial flow line 25 in the mixing container 16 whereas the other partial flow is via the partial flow line 30 in the container 14 is directed. The container 14 is also via the solids supply line 28 from the reservoir 13 Halide salt, for example, a mixture of sodium bromide and sodium iodide, fed in the container 14 is mixed with the ion-exchanged water via a mixing device (not shown) to a (strain) solution. Out of the container 14 is continuously adding stock solution to the mixing tank 16 passed, in which this by means of a mixing device (not shown) with the mixing container 16 via the partial flow line 25 supplied ion-exchanged water is mixed to a homogeneous solution.

About the line 32 becomes the electrolysis cell 20 from the mixing container 16 continuously fed aqueous solution containing halide ions, which in the electrolysis cell 20 anodized is oxidized. The flow rates through the individual lines 22 . 24 . 25 . 26 . 28 . 30 . 32 and 36 and the mean residence time in the electrolysis cell 20 by control device 38 so regulated that through the discharge line 36 from the electrolytic cell 20 withdrawn biocide the desired concentration of hypohalogenation, for example, hypobromite and Hypoioditionen has. The current-voltage values are chosen so that a highly active hypohalogenite is formed.

Hereinafter, the present invention will be explained with reference to an illustrative embodiment of the present invention, but not limiting, and with reference to two comparative examples.

Comparative Example 1

In one of the in the 1 As shown, a hypobromite-containing biocide was prepared.

This was the reservoir 13 filled with sodium bromide. In the ion exchanger 12 was continuously over the line 22 supplied fresh water so purified that from the ion exchanger 12 over the line 24 withdrawn ion-exchanged water had a concentration of divalent and higher ions of a total of 4.3 mg / l, wherein the calcium ion concentration was 1.4 mg / l and the ion-exchanged water had a conductivity of 715 μS / cm. Furthermore, the container 14 over the wires 28 and 30 Sodium bromide and ion-exchanged water are continuously fed into the tank 14 were mixed together to form a homogeneous solution, wherein the bromide ion concentration of the prepared stock solution was 62,000 mg / l. The mixing container 16 were over the lines 26 and 25 continuously out of the container 14 Sodium bromide stock solution and from the ion exchanger 12 ion-exchanged water supplied in the container 14 were mixed together to form a homogeneous solution, wherein the bromide ion concentration of the prepared solution was 980 mg / l.

This solution was over the line 32 continuous with a flow rate of 30 l / h in the electrolytic cell 20 led, in which the solution was anodized. While the cathode was titanium, an anode of titanium metal-supported ruthenium oxide was used. Both the anode area and the cathode area was 600 cm ² . The anodic oxidation was carried out at a voltage of 10 V and at a current of 25 A, the mean residence time of the solution in the electrolysis cell 20 about 320 seconds. From the electrolytic cell 20 the biocide thus produced was continuously fed at a flow rate of 30 l / h. deducted.

The hypobromite concentration of the biocide withdrawn from the electrolysis cell was continuously measured. It was found that the hypobromite concentration in the withdrawn biocide was practically equal to 410 mg / l over an operating time of 24 hours. The deviation of the hypobromite concentration in the biocide was less than ± 2% throughout the operating time.

At the two electrodes 18 . 18 ' Even after 5 days of operation no deposits could be observed.

The biocidal activity of the biocide thus produced was determined by adding this industrial process water in an amount of 0.158 mg / l of active substance / biocide and after 10 days the total aerobic bacterial count of the process water was determined. For comparison, the total aerobic bacterial count of process water mixed with 0.168 mg / l BCDMH was also determined.

The results are shown in Table 1.

example 1

A biocide was prepared in the same manner as described in Comparative Example 1, except that in the salt reservoir 13 a mixture of sodium bromide and sodium iodide was used instead of sodium bromide. The weight ratio of sodium bromide and sodium iodide in the mixture was 100: 1.

The hypobromite concentration and hypoiodite ion concentration of the biocide withdrawn from the electrolysis cell were continuously measured. It was found that the sum of the hypobromite concentration and the hypoiodite ion concentration in the withdrawn biocide was practically equal to 423 mg / l over an operating time of 24 hours. The deviation of the hypobromite concentration or hypoiodite ion concentration in the biocide was less than ± 2% during the entire operating time.

At the two electrodes 18 . 18 ' Even after 5 days of operation, no appreciable amount of deposits could be observed.

The biocidal effect of the biocide thus prepared was determined in the same manner as in Comparative Example 1.

The results are shown in Table 1. Table 1 biocide Total aerobic number Biocide from Comparative Example 1 2.1 × 10 ⁶ Biocide from Example 1 1.15 × 10 ⁶ BCDMH 5.7 × 10 ⁶

Comparative Example 2

A biocide was prepared in the same manner as described in Comparative Example 1, except that no ion exchanger was used, but the container 14 and the mixing container 16 each non-pretreated fresh water with a concentration of divalent and higher valent ions of a total of 122 mg / l was supplied, wherein the calcium ion concentration was 108 mg / l and the fresh water had a conductivity of 0.713 mS / cm.

The hypobromite concentration of the biocide withdrawn from the electrolysis cell was continuously measured, whereby a significant decrease in the hypobromite concentration in the biocide was observed after only 15 hours of operation, which subsequently continued to decrease further. After 24 hours, it was observed that the two electrodes were completely covered with a thick layer of deposits.

LIST OF REFERENCE NUMBERS

10

Device for the production of biocide

12

ion exchanger

13

Reservoir for salt

14

Container for halide stock solution

16

mixing tank

18, 18 '

electrodes

20

electrolysis cell

22

Supply line for fresh water

24

Discharge line for ion-exchanged water

25

(first) partial flow line for ion-exchanged water

26

Feed line for halide stock solution

28

Solid supply line

30

(second) partial flow line for ion-exchanged water

32

Supply line to the electrolysis cell

34

Flowmeter

36

Discharge line for biocide

38

control device

Claims (13)

A process for preparing a biocide comprising the steps of: a) providing water or an aqueous solution having a concentration of divalent and higher valent ions of not more than 5.0 mg / l in total, b) adding halide salt to that in step a ) and c) anodic oxidation of the mixture prepared in step b), characterized in that in step b) a mixture of a bromide salt and an iodide salt is added or an aqueous solution containing bromide ions and iodide ions is added. A method according to claim 1, characterized in that in step a) water or an aqueous solution is treated by means of a method selected from the group consisting of ion exchange, osmosis, nanofiltration and any combinations thereof to increase the concentration of divalent and higher valent ions to set a maximum value of 5.0 mg / l in total. A method according to claim 1 or 2, characterized in that in step a) water or an aqueous solution having a concentration of divalent and higher valent ions of a total of at most 3.0 mg / l and preferably at most 1.0 mg / l provided. Method according to at least one of the preceding claims, characterized in that the water provided in step a) or the aqueous solution provided in step a) contains less than 0.001% by weight of organic compounds. Method according to at least one of the preceding claims, characterized in that the water provided in step a) or the aqueous solution provided in step a) has a conductivity measured at 25 ° C of less than 800 μS / cm, preferably less than 400 μS / cm, and more preferably less than 300 μS / cm. Process according to at least one of the preceding claims, characterized in that the mixture added in step b) comprises at least one compound selected from the group consisting of sodium bromide, potassium bromide, ammonium bromide and any combinations thereof and at least one of sodium iodide, potassium iodide, ammonium iodide and contains any combination thereof selected group salt. Method according to at least one of the preceding claims, characterized in that the mixture produced in step b) has a bromide ion concentration between 0.4 and 10,000 mg / l, preferably between 400 and 4,000 mg / l and particularly preferably between 200 and 2,000 mg / l , and an iodide ion concentration of between 0.1 and 10 mg / l, preferably between 0.5 and 5 mg / l and more preferably between 0.8 and 2.4 mg / l. Method according to at least one of the preceding claims, characterized in that in the anodic oxidation in step c) an anode of on an inert carrier material, preferably on titanium or on a titanium alloy, supported ruthenium oxide and / or platinum oxide and / or a cathode of titanium metal is used. Method according to at least one of the preceding claims, characterized in that the anodic oxidation in step c) at a current flow between 10 and 200 A, preferably between 20 and 60 A and more preferably between 25 and 50 A is performed. Method according to at least one of the preceding claims, characterized in that the anodic oxidation in step c) is carried out at a temperature of between 10 and 60 ° C. Method according to at least one of the preceding claims, characterized in that during the anodic oxidation in step c) in the mixture, a concentration of hypohalite ions between 10 and 1000 mg / l preferably between 50 and 700 mg / l and particularly preferably between 100 and 700 mg / l is set. Biocide obtainable by a process according to at least one of Claims 1 to 11, characterized in that the mixture prepared in step b) has a bromide ion concentration of between 400 and 4,000 mg / l and an iodide ion concentration of between 0.5 and 5 mg / l. Use of a biocide according to claim 12 as additive in sewage, in process water, in fresh water, in swimming pool water, in cooling water or in sealing water in the paper industry or in the metal industry.

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