The present invention relates to the method according to the preamble of Claim 1 for preparing microbicidic solutions.

The invention further relates to an anode solution, a cathode solution and a solution that is prepared by combining them, and a cleaning solution containing these solutions.

Microbes accumulate easily in machines that are used in the paper industry, and biofilms are formed therein during use. Attention must be paid to the prevention of biofilms in the industry. So far, the substances used for the prevention of the formation of biofilms have mainly been focused on substances, which are impeded by corrosion and ecological problems.

Sodium hypochlorite is a commonly used component in solutions that are used to prevent the growth of bacteria and other microbes. It is a highly oxidizing and effective compound that prevents the growth of bacteria, and it is commonly used, for example, in the paper industry as a microbicidic anti-slime agent. Generally, hypochlorite is delivered to the plants in either 10 or 15 % solutions in 1000-litre containers. It is a highly corrosive chemical that requires special safety precautions in use.

The hypochlorite solution contains a lot of different radicals that have a limited stability. Therefore, the quality of the hypochlorite solution may vary extensively, whereby its use is considerably more difficult. The quality variation becomes apparent especially, when the sodium hypochlorite is used jointly with, e.g. ammonium bromide, whereby the accurate concentrations of the effective agents should be known so that the amount of harmful byproducts formed would not be too high.

In the paper factory, the bromine-containing biocide used in slime control is prepared by a special device, wherein ammonium bromide is added to sodium hypochlorite and factory water. As chloramines, for example, are volatile compounds, it is realistic to prepare the combined haloamine-containing biocide "onsite", i.e. in the same factory where the use takes place.

Casini G. (Paperi ja Puu - Paper and Timber, Vol. 85, No. 7, 2003) discloses the use of the above-mentioned salts, in particular, as anti-slime agents in the paper industry. In the Casini publication, a dosing apparatus is used to mix ammonium bromide and sodium hypochlorite together and dose them afterwards into an alkaline system.

As an example of the complexity of the equipment used in the preparation of biocides, a basic drawing is shown in the publication WO 03014029. The equipment of the said publication is used to mix hypochlorite and ammonia salt and to add solutions that contain these salts into a micro-organism mixture. The solutions are used to prevent the micro-organisms from forming biofihns.

One effective agent commonly used in biocidal solutions is chlorine. It is quite unstable especially when the temperature increases, as organic impurities bind the chlorine inactivating it, while part of the chlorine vaporizes directly into the air. By combining the chlorine with ammonia, a considerably more stable compound, chloramine, is obtained. The chloramine releases hypochlorous acid for a longer time and more evenly than chlorine.

The publication US 2003/0132173 describes a method that is used to mix hypochlorite and ammonia salt together to form chlorarnines, after which the formed solution is used to destroy micro-organisms in aqueous systems.

The publication US 5,976,386 describes a method, wherein a biocide is added to a solution containing micro-organisms, the biocide being prepared by mixing an accurately dosed oxidizer, which is a sodium hypochlorite or a calcium hypochlorite, and an amine source.

On the market, there are various electrochemical reactors, wherein the electrolytic chamber is divided into two parts, for example by a membrane that keeps the anode and the cathode apart. A device of Envirolyte (Fig. 1) is an example, the use of which is based on the following publications: WO 98/23793 describes a device, wherein aqueous solutions are processed electrochemi- cally,

WO 98/25855 describes a method and a device, which are used to sterilize water, WO 98/27012 describes a method, which is used to employ electric power to clean water, and

WO 98/40536 describes a method, which is used to electrochemically process aqueous solutions and to form gases.

The Envirolyte equipment is used to activate sodium chloride solutions so that the solutions can be used to clean water.

In the known technology, microbe-containing solutions are treated with substances that are highly oxidizing and, thus, cause corrosion. When these are used to treat the parts of, e.g. a paper mill, it causes increasing wear of the parts. Furthermore, highly oxidizing agents are detrimental to the environment.

The apparatuses used have been very complex and it has not been worthwhile to place them in the vicinity of every application; therefore, some substances that are used for cleaning the solutions have been transported over long distances to the intended application. In addition to high expenses, the transportation causes a decrease in the activity of the substances in particular, as many of the agents used for treating the solutions are stable for a short period of time only.

The apparatuses placed in the vicinity of the application have been merely dosing feeders, which can be used to mix exact amounts of certain solutions with one another and to then add these to the application. These apparatuses cannot be used to prepare or activate the solutions.

Tests have been conducted to electrochemically activate the sodium chloride solution by means of the device mentioned in the WO publications, but this reaction causes one type of a biocide only, wherein the effective components are the radicals of oxygen and chlorine.

There is a demand for a method, which can be used to prepare by means of simple apparatuses, preferably in the vicinity of the application, biocides containing safe and harmless substances, which are, however, effective, to be used to destroy microbes in aqueous solu- tions or to prevent the growth or reproduction of the said microbes.

The object of the present invention is to offer an improved method for preparing biocides. The invention is based on the fact that the electrochemical apparatus can be used to prepare

biocidal salt solutions containing ions and radicals that are harmless, though effective in terms of their biocidal effect.

Another object of the invention is to offer a method that uses equipment, which is easy and inexpensive to install onsite, i.e., in the close proximity of the application.

To be more precise, the present invention is based on the fact that microbicidic solutions are prepared electrochemically by means of an apparatus known per se (Fig. 1), wherein the electrolytic chamber is divided into two parts by a membrane so that the compounds prepared on the anode and the cathode will not be brought into contact with one another. The acidic anode solution, which forms in the anode chamber, and' the alkaline cathode solution, which forms in the cathode chamber, can be kept separate or, in some cases, also be combined into a neutral solution that is electrochemically activated.

The method according to the invention preferably comprises stages, wherein: a) an aqueous solution containing sodium ions, potassium ions or ammonium ions, chloride, bromide, sulphate, nitrate, carbonate or amine or their combinations is di- rected through the chambers of the electrolytic apparatus, the chambers comprising an anode chamber, a cathode chamber and a membrane that separates the two; b) the solutions are electrochemically activated; c) optionally, the biocides that are formed in the chambers are either recovered separately or mixed with one another; and d) the thus formed activated solutions are directed out of the chambers.

More precisely, the method according to the invention is characterized by what is stated in the characterizing part of Claim 1.

The solutions according to the invention are characterized by what is stated in Claims 23, 27 and 31.

The use of the biocidal solutions according to the invention is characterized by what is stated in Claim 20, and the applications of the solutions by what is stated in Claim 21.

The cleaning solution according to the invention is characterized by what is stated in Claim 36.

The method according to the invention is used to prepare various biocides, wherein the effective ingredients preferably include different radicals of bromine and, in addition, the amines of chlorine and bromine (e.g., chloramine or bromamine), which are well-known as biocides. These substances have a different mechanism of action from that of electro- chemically activated solutions that are based on sodium chloride. They work better on biofilms, for example. Chloramines are also volatile compounds, which are less expensive to prepare onsite than to transport to the site.

One advantage of the present method is that the same apparatus can be used case- specifically to prepare various biocides for a desired application. It is easy to examine, which combination works best in that particular application.

Another advantage of the method is that it is easy to replace a biocidally active agent with another type, e.g., to shift from chlorine to bromine or chloramine. Even in the known technology, it is also sometimes necessary to replace the active biocide to prevent the formation of resistant bacterial strains in the water circulations.

Furthermore, the solutions according to the invention can be used to treat waters that are used in the paper industry in a way that neither considerably corrodes the parts of the machines nor causes considerable disadvantages to the environment. The method can be used to essentially improve the microbiological state of paper and board machines in an economic and environmental-friendly manner.

The method according to the present invention can preferably be used to prepare solutions limiting the growth of microbes from the aqueous solutions of various salts directly in one stage without storage or transportation. It is also possible to select, when necessary, the composition of the activated solution.

The other details and advantages of the invention become apparent from the following de- tailed description, which comprises several practical examples.

Figure 1 describes the principles of use of Envirolyte's "Eurostel" equipment. The equipment can be used for the electrochemical activation of solutions.

"Onsite", in connection with the invention in question means that the equipment, which is used to implement the method according to the invention, is located onsite, i.e., in the vicinity of the application of the biocide solution prepared according to the method.

According to a preferred embodiment of the invention, the aqueous solution that is directed through the chambers of the electrolytic equipment comprises sodium ions, potassium ions or ammonium ions, chloride, bromide, sulphate, nitrate, carbonate or amine or mixtures thereof.

According to another preferred embodiment, the aqueous solution directed through the chambers of the electrolytic equipment contains at least two ions selected from a group ' comprising potassium ions, ammonium ions, chloride, bromide, sulphate, nitrate, carbonate and amine, or from a group comprising sodium ions, potassium ions, arnmoniurn ions, bromide, sulphate, nitrate, carbonate and amine.

According to another preferred embodiment, the aqueous solution directed through the chambers of the electrolytic equipment contains at least two ions selected from the group comprising potassium ions, ammonium ions, chloride, bromide and amine, or from the group comprising sodium ions, potassium ions, ammonium ions, bromide and amine, whereby the active agents formed during electrolysis include various radicals of bromine or amines of chlorine or bromine.

According to an even more preferred embodiment, the salt-containing aqueous solution comprises ammonium ions and chloride ions or sodium ions and bromide ions or ammonium ions, sodium ions, chloride ions and bromide ions. Regarding effect and reactivity, calcium ion could be used as well, but its problem in mixtures like this is its precipitation.

Before the stage of activation, the solution can also be saturated with oxygen so that electrolytic activation can be used in the anode chamber to form a larger number of reactive oxygen radicals.

Having greater reactive variation, the mixture formed by means of the activation in the electrolytic equipment provides a higher biocidal effect compared with previously known

solutions. The components of the biocidically active solution can be varied so that it also works against microbes that have developed resistance to certain compositions.

The redox potential (EH) of the activated anode solution that forms in the anode chamber is very high, i.e., over 60OmV, preferably over 90OmV, and its pH is within a range of 1.5 — 4, preferably within 1.5 - 2.5. It is acidic and contains reactive radicals that are formed from salts, oxygen and water. The activated cathode solution, which is formed in the cathode chamber, is alkaline, has a pH value of over 7, preferably over 8, and its redox potential (EH) is less than 10OmV, preferably less than -10OmV. The salt solutions, which are directed through the chambers, contain salts in concentrations of about from 0.05 to 0.20mol/l.

The activation may be carried out for example using a current that is kept within a range of 16 to 42 A, preferably 35 to 38 A. When activated, the anode solution preferably comprises metastable radicals, which are formed from at least two ions, which are selected from the group comprising the potassium ion, ammonium ion, chloride, bromide, sulphate, nitrate, carbonate and amine, or from the group comprising the sodium ion, potassium ion, ammo- mum ion, bromide, sulphate, nitrate, carbonate and amine. The said amine source can be an organic or inorganic amine or amide, such as hydrazine, isocyanurate, sulphamidic acid, ethylenediamine, ethanolamine, hexamethylene diamine, dimethylhydantoin or cyanuric acid benzotriazole or a combination thereof.

The activated anode solution may preferably also comprise metastable radicals, which are formed from at least two ions, which are selected from the group comprising potassium ions, ammonium ions, chloride, bromide and amine, or from the group comprising sodium ions, potassium ions, ammonium ions, bromide and amine, whereby the active agents in the activated solution include various radicals of bromine or amines of chlorine or bro- mine, the amine being one of the above.

The activated anode solution may preferably also comprise metastable radicals that are formed from potassium ions or ammonium ions, chloride, bromide, sulphate, nitrate, carbonate or amine or mixtures thereof, or sodium ions, chloride, bromide, sulphate, nitrate, carbonate or amine or mixtures thereof, the amine being one of the above.

When activated, the cathode solution, in turn, preferably comprises at least two ions that are selected from the group comprising the potassium ion, ammonium ion, chloride, bromide, sulphate, nitrate, carbonate and amine, or from the group comprising the sodium ion, potassium ion, ammonium ion, bromide, sulphate, nitrate, carbonate and amine, the amine being one of the above.

The activated cathode solution may also preferably comprise at least two ions selected from the group comprising potassium ions, ammonium ions, chloride, bromide and amine, or from the group comprising sodium ions, potassium ions, ammonium ions, bromide and amine, whereby the active agents in the activated solution include various radicals of bro- mine or amines of chlorine or bromine, the amine being one of the above.

The activated cathode solution may also preferably comprise potassium ions or ammonium ions, chloride, bromide, sulphate, nitrate, carbonate or amine or their mixtures, or sodium ions, chloride, bromide, sulphate, nitrate, carbonate or amine or their mixtures, the amine being one of the above.

The composite solution consists of a combination of the anode solution and the cathode solution and it can either be prepared in the apparatus itself or by first recovering the anode and the cathode solutions and then combining them outside the apparatus.

Part of the substances contained by the solutions listed above, especially the amine sources, can also be added to the activated solutions afterwards, i.e., after the activation. Haloamines are formed from the amines and halogens in aqueous solutions also without the electrochemical activation. These haloamines are formed, among others, by mixing halide with hydantoin, chlorine or hypochlorite with sulphamidic acid, chlorine with a solution containing ammonium ions, or chlorine with isocyanurate.

The properties of both the anode solution and the cathode solution, such as the concentra- tions of the haloamines and the active chlorine or bromine, can be adjusted by adjusting the current consumption in the chambers. The pH values of the activated solutions that are directed out of the chambers can also be adjusted to the desired values by assessing the effect of the electrochemical activation on the pH value, i.e., the change in the pH during

the activation, and thus selecting the pH values of the salt solutions that are fed into the chambers of the apparatus.

When so desired, the anode and the cathode solutions can be used as such, but they can also be combined. This can either be carried out already inside the electrolytic apparatus or outside the same by mixing the solutions, which have been separately collected and directed out of the chambers, together in a separate vessel.

The invention also relates to the preparation of a cleaning solution, such as a washing fluid, preferably a disinfection solution, comprising an anode solution, a cathode solution or a composite solution and, optionally, additives that are commonly used in cleaning and dis- infection solutions. These include buffer solutions, colouring agents or aromatic substances or their mixtures.

By adjusting the flows of salt solutions in the different chambers and by thus adjusting the proportion of the anode and the cathode solutions in the composite solution, the pH of the composite solution can be adjusted to the desired range, preferably to a range of 2.5 to 10. In a paper machine, wherein the method according to the present invention can be used, the pH is usually from about 7 to 8. Thus, it is preferable to use, as a biocide or cleaning solution, a solution with the pH in the same range.

Although the electrolytically activated anode, cathode or composite solutions are prepared from the same salts, their properties may be different and, thus, they can be used for differ- ent purposes. All solutions are preferably diluted solutions, i.e., they may contain, e.g., 1% of NaCl or 2% of NaBr. The anode solution that is activated in the anode chamber is oxidizing, whereas the cathode solution that is activated in the cathode chamber is generally reducing. The composite solution obtained by combining the two, in turn, is slightly oxidizing.

The adjustment of the properties of the activated solutions is facilitated by the fact that the properties of the salt solutions that are fed into the anode and the cathode chambers, such as the concentration or the pH, can already be adjusted before the electrochemical activation. For example, if the pH of the composite solution is to be decreased, a lesser amount of salt solution can be directed to the cathode chamber in proportion to the amount of solu-

tion directed to the anode chamber, instead of directing the same amounts of salt solution to both chambers.

One of the advantages of the composite solution is its slightly oxidizing property in particular, rendering it less aggressive than ordinary biocidal solutions. The advantage of di- luted solutions, again, is that the corrosive effect of the substance decreases when the substance is diluted. Accordingly, from the point of view of the devices to be cleaned it is advantageous to use diluted solutions. The concentrations of the various salts of the diluted solution depend on the salts used and their molecular weights. For example, if sodium chloride is used, its concentration in the finished, activated work solution can be about 1%, whereas, if sodium bromide is used, its concentration in the finished, activated work solution can be about 2%.

Strong (from 10 to 15%) sodium hypochlorite solutions are particularly highly oxidizing and corrosion-causing solutions. On the other hand, electrochemically prepared solutions are relatively weak and contain, for example, active chlorine in a concentration of 500 to 700mg/l. In their working concentrations, wherein the concentrations of active chlorine (bromine) are in the order of 0.5 to 5mg/l, they should be considered weakly oxidizing solutions.

The method of the present invention is implemented at a temperature that is kept low, preferably under 40 ⁰ C, as such a low temperature is advantageous for the stability of the formed radicals. If the temperatures of the solutions rise to over about 40 to 5O ⁰ C, the stability of the formed radicals in the solutions begins to deteriorate and they start to react, forming salts and water, among others. As the electrochemical reaction is exothermal, i.e., heat is formed, the temperatures of the apparatus or the solutions should be kept low artificially. This can be carried out using any well-known methods, such as cooling the appara- tus, decreasing the concentrations of the substances contained in the solutions that are fed into the chambers, decreasing the flow velocities of the solutions running through the apparatus or reducing the consumption of current.

The biocidal solutions prepared according to the method of the present invention can be used in various fields. They can be used, e.g., in the paper industry to treat solutions that are used in connection with the manufacture of various paper and board products.

The solutions can be used, for example, for disinfection, sterilization, prevention of bacterial growth, prevention of the growth of germs, cleaning, and the prevention of the formation of biofilms. In connection with the manufacture of paper products, the anode, cathode and composite solutions can be used to treat raw water or the dilution water of additives or other substances that deteriorate easily.

To fully exploit the use of the method, the apparatus can be located in the immediate vicinity of the application. Thus, the need for storage and transport is eliminated, reducing the expenses and both facilitating and quickening the implementation of the method.

The most important advantages of the biocidal solution that is manufactured electrochemi- cally onsite are:

- a highly effective biocide

- environmentally friendly

- does not form toxic organic compounds

- causes neither pathologic nor toxicological risks - economic compared with ordinary biocides

- does not require the storage of corrosive chemicals

- decomposes into completely harmless compounds after use

- no biocidal residue in the end product.

The activated biocidal solutions prepared according to the present invention can preferably be used to treat and clean the waters that are needed in the various stages of paper manufacture, and to remove biofilms from the various parts of paper mills. The potential applications of the solutions in the paper mill are:

- treatment of raw water

- dilution water of additives - spray waters

- washing waters of the machine felts

- waters of the disc filters

- waste pulps

- tail water - circulation water

The additive lines, where these biocides are used, include the spray-starch, pulp-starch, resin size, carbonate, kaolin, and retention agent and coating mix lines.

The following non-limiting examples describe the invention and its advantages.

Example 1

The aqueous solution of sodium chloride and ammonium chloride was electrochemically activated by directing the solution through a Eurostel - Demo device (http://www.envirolvte.com/) so that the anode solution and the cathode solution were mixed with one another. In the activation, the consumption of current was adjusted to a range of 19 to 2OA by diluting the salt solution or adding a stronger salt solution.

The bactericidal effect of the solution was defined by a light-producing bacterium and a cultivation test. In the photo bacterium test, the toxicity is indicated as the concentration of substance (ml/1), which reduces the light production of the bacterium by 50%. Some of the solution that had been activated in the cultivation test was added to the extremely dirty disc filtrate of a board machine that makes laminated board, the total number of aerobic bacte- ria in the disc filtrate being 1.9E+07 (CFU/ml).

Table Ia shows the properties of the activated solution.

Table Ia. The properties of the chemically activated sodium chloride/ammonium chloride solution (combined anode and cathode solutions).

The solution was highly toxic in the photo bacterium test.

Table Ib shows the biocidal effect of the activated sodium chloride/ammom ^' um chloride solution.

Table Ib. The effect of the electrochemically activated sodium chloride/ammonium chloride solution on bacteria, the addition of activated solution lOml/1 of disc filtrate.

The activated solution of sodium chloride and ammonium chloride decreased the number of live bacteria by over 95%.

Example 2

The aqueous solution of sodium bromide was electrochemically activated in a corresponding manner as the solution in Example 1.

The properties of the activated sodium bromide solution are shown in Table 2a.

Table 2a. The properties of the electrochemically activated sodium bromide solution (combined anode and cathode solutions).

Table 2b shows the biocidal effect of the activated sodium bromide solution

Table 2b. The effect of the electrochemically activated sodium bromide solution on bacteria (combined anode and cathode solutions), the addition of activated solution lOml/1 of disc filtrate.

The activated sodium bromide solution reduced the number of bacteria by over 99%.

Example 3

The aqueous solution of sodium bromide was electrochemically activated in the anode chamber. The properties of the highly acidic sodium bromide anode solution are shown in Table 3a.

Table 3a. The properties of the electrochemically activated sodium bromide anode solution.

The toxicity of the anode solution becomes obvious in the photo bacterium test, wherein less than 0.01ml of anode solution per litre completely stops the light production of the light-producing bacterium.

Table 3b shows the biocidal effect of the activated acidic sodium bromide solution (anode solution).

Table 3b. The effect of the electrochemically activated sodium bromide anode solution on bacteria, the addition of activated solution.

The anode solution of sodium bromide is a disinfectant that very effectively destroys bacteria and their germs. With a lOml/1 dose of disc filtrate, the number of bacteria was re- duced by 99.97%.

Example 4

The aqueous solution of sodium bromide was electrochemically activated in the cathode chamber. The properties of the alkaline, electrochemically activated sodium bromide solution are shown in Table 4a.

Table 4a. The properties of the electrochemically activated sodium bromide cathode solution.

In the photo bacterium test, the alkaline sodium bromide solution is highly toxic.

Table 4b shows the biocidal effect of the activated alkaline sodium bromide solution (cath- ode solution).

Table 4b. The effect of the electrochemically activated sodium bromide cathode solution on bacteria, the addition of activated solution.

The alkaline, electrochemically activated sodium bromide solution inhibits the growth of bacteria to some extent. As an alkaline solution, however, it has a strong cleaning effect that contributes to the control of the formation of biofilms in particular.

Example 5

A solution was prepared, having ammonium, sodium, bromide and chloride ions. The properties of the electrochemically activated composite solution are shown in Table 5 a.

Table 5a. The properties of the composite solution containing electrochemically activated sodium bromide and ammonium chloride.

In the photo bacterium test, the electrochemically activated composite solution containing ammonium, sodium, bromide, and chloride ions is highly toxic.

Table 5b shows the biocidal effect of the activated sodium bromide/ammonium chloride composite solution.

Table 5b. The effect of the electrochemically activated sodium bromide/ammonium chloride composite solution on bacteria, the addition of activated solution.

The electrochemically activated composite solution containing ammonium, sodium, bromide, and chloride ions effectively inhibits the growth of bacteria. With a lOml/1 dose of disc filtrate, the number of bacteria was reduced by 99.9%.

Example 6

A solution containing ammonium, sodium, bromide and chloride ions was prepared.

The properties of the electrochemically activated acidic anode solution are shown in Table 6a.

Table 6a. The properties of the anode solution containing electrochemically activated sodium bromide and ammonium chloride.

In the photo bacterium test, the electrochemically activated anode composite, which con- tains ammonium, sodium, bromide, and chloride ions, is highly toxic.

Table 6b shows the biocidal effect of the activated sodium bromide/ammonium chloride anode solution.

Table 6b. The effect of the electrochemically activated, acidic sodium bromide- ammonium chloride anode solution on bacteria, the addition of activated solution.

The electrochemically activated anode solution, which contains ammonium, sodium, bromide, and chloride ions, is highly effective in inhibiting the growth of bacteria. With a lOml/1 dose of disc filtrate, the number of bacteria was reduced by 99.98% and with a 2ml/l dose by 99.83%.

Example 7

A solution containing ammonium, sodium, bromide and chloride ions was prepared.

The properties of the electrochemically activated cathode solution are shown in Table 7a.

Table 7a. The properties of the cathode solution containing electrochemically activated sodium bromide and ammonium chloride.

In the photo bacterium test, the electrochemically activated alkaline ammonium chlo- ride/sodium bromide cathode solution is highly toxic.

Table 7b shows the biocidal effect of the activated sodium bromide/ammonium chloride cathode solution.

Table 7b. The effect of the electrochemically activated, alkaline sodium bromide/ammonium chloride cathode solution on bacteria, the addition of activated solu- tion.

The electrochemically activated, alkaline ammonium chloride/sodium bromide cathode solution inhibits the growth of bacteria to some extent.

Example 8

A solution was prepared, containing ammonium, sodium, bromide and chloride ions. The solution was activated by adjusting the charging rate. The properties of the composite solution are shown in Table 8.

Table 8. The properties of the electrochemically activated (composite) solution containing sodium, bromide, ammonium and chloride ions.

In the bacterium test, the solution that had been prepared using a low current of 18A was not toxic.

The advantages of the new method according to the invention over the known technology are that, the biocide solution (solutions) is prepared at one stage electrochemically from harmless salts of ammonium, sodium or potassium onsite, in close vicinity of the application. The salts used can be, for example, chlorides, bromides, sulphates, nitrates, carbon- ates or amines. The alkaline cathode solutions can be used for cleaning purposes, whereas the acidic anode solution or the neutral composite solution can be used for disinfection, sterilization, inhibition of the growth of bacteria, inhibition of the growth of germs, or prevention of the formation of biofilms. When so desired, the composition of the solutions can easily be varied.

In economic terms, the method is very cost-effective compared with prior art, and it is environmentally friendly.