WO1998022397A1

WO1998022397A1 - Method for treating water in particular of a swimming pool and disinfectant composition

Info

Publication number: WO1998022397A1
Application number: PCT/FR1997/002036
Authority: WO
Inventors: Pierre Gaches; Louis Gaches
Original assignee: Gaches Chimie Specialites
Priority date: 1996-11-21
Filing date: 1997-11-13
Publication date: 1998-05-28
Also published as: FR2755960A1; AU5124998A; FR2755960B1; MA24404A1

Abstract

The invention concerns a method for treating water, in particular of a swimming pool, and a novel disinfectant composition. The disinfecting method consists in mixing hydrogen peroxide as bactericide with the water; it is characterised in that is also added to the water cyanuric acid or one of its salts so that the concentration is higher than about 15 ppm. The following additives can also be advantageously added: soluble silver salt, soluble copper salt, phosphoric acid. The method considerably increases the persistence of the bactericidal effect of the hydrogen peroxide.

Description

PROCESS FOR TREATING WATER, PARTICULARLY POOL AND DISINFECTANT COMPOSITION

The invention relates to a method of treating water in order to ensure its disinfection. It applies in particular to the treatment of water from individual or collective swimming pools, or other basins, but can also find application to treat industrial water or urban waste water. The invention extends to a new disinfectant composition for implementing the targeted process.

In the following, the concentrations in water will be expressed in ppm (parts per million by weight, 1 ppm being equal to 1 mg / kg). There are different types of water disinfection process in order to eliminate microorganisms (bacteria, viruses ...); this effect of destruction or inactivation of microorganisms will be called "bactericide". However, in the case of swimming pool water treatment, there is currently no disinfection process which combines all the desirable qualities: (1) effectiveness and persistence of the disinfection effect guaranteeing a duration of this effect over long periods (in order to avoid the obligation of frequent human intervention), (2) non modification of the physico-chemical characteristics of the water (pH, transparency, odorless and non-aggressive character with - human), (3) absence of decomposition products (likely to become harmful by concentrating or modifying the kinetics of the bactericidal effect), (4) safety and ease of implementation, absence of risk for the environment and non-corrosive nature vis-à-vis installations (compatibility with piping materials, coatings, etc.), (5) cost of treatment compatible with the application (in 1996, this cost in France is estimated must be less than about 1 000 F / annual for a 100 m swimming pool).

The pool water treatment process currently the most widespread consists in using the very effective bactericidal effect of chlorine by mixing with the swimming pool water a chlorinated compound, either in gaseous form (collective swimming pools), or in liquid or solid form. In addition to the well-known risks for the environment, the most serious shortcomings of resident chlorine treatments:

. for gaseous or liquid chlorine, in the risks of implementation, the absence of persistence, the corrosive nature of the treated water (which is acidified in the case of gaseous chlorine and alkalized in the case of liquid chlorine),

. for solid chlorine, in relatively low persistence (requiring frequent additions), the appearance of harmful decomposition products (calcium ions in particular), the corrosive nature of the treated water (change in pH) and, in case of excess , a modification of the physico-chemical characteristics of the water (aggressive towards the mucous membranes, olfactory, and not neutral).

In the case of a treatment with solid chlorine, a salt of chlorocyanuric acid whose molecule is stable to UV rays is frequently used, in order to increase the persistence; when it acts, this molecule decomposes, producing a release of active chlorine and a decomposition product (cyanuric acid) representing between 40 and 50% by weight of the initial product: this product concentrates over time during the treatment, causing a risk for humans and a reduction in the bactericidal effect of chlorine.

All of the aforementioned faults lead to a tendency to reduce or eliminate the use of chlorinated compounds in the treatment of swimming pool water.

Another proposed method consists in using a bromine, liquid or solid compound. However, this process is very little used because of the cost of this type of compound and its rarity.

Another process, mainly used in collective pools or to treat drinking water, consists of using gaseous ozone. This process is satisfactory with regard to the qualities (2), (3) and (4) mentioned above; on the other hand, it has the very serious defect of not exhibiting any persistence, so that bacterial pollution downstream of the treatment can develop rapidly; this process requires continuity of treatment which limits it to professional installations. Another treatment method is to use hydrogen peroxide as a bactericide; however, the serious defect of treatment with hydrogen peroxide lies in its very low persistence (4 to 5 days for the treatment of a swimming pool) and all known processes using hydrogen peroxide as a bactericide associate this compound with other compounds (biguanidine salt in particular) to increase its persistence and provide a relatively high concentration in water (100 ppm) to obtain a satisfactory bactericidal effect; however the products currently associated with hydrogen peroxide (biguanidine salt) increase this persistence in poor proportions (10 to 20 days depending on the temperature); moreover these associated products lead to inherent defects residing in the appearance of organic decomposition products (which lead to an additional consumption of peroxide) and in a total incompatibility with respect to all the other treatment products: thus to initiate a peroxide / biguanidine treatment, it is necessary beforehand to completely drain and rinse the swimming pool carefully (this draining and rinsing cost around one year of treatment). In addition, the hydrogen peroxide / biguanidine salt couple is expensive and significantly exceeds the admissible price and in particular that of a chlorine treatment (1,000 F / year for a 100 m ³ swimming pool).

Another method proposed in international application WO 93/04986 consists in treating the waters with using an iodine compound. This process is not used in France, because the product is not entered on the list of authorized products. In such a process, the iodine compound is combined with an oxidant to produce the bactericidal active iodine in situ. This application WO 93/04986 mentions as an oxidant of the iodized compound, ozone and hydrogen peroxide. The hydrogen peroxide is then combined with the iodized compound with a very low concentration, of the order of 0.12 ppm, to play the role of oxidant of the iodized compound; at this concentration, it does not have a significant specific bactericidal effect. In example 4, this application WO 93/04986 describes in particular a treatment consisting in mixing with water initially 16 ppm of an iodized salt and in mixing very low daily doses of 0.12 ppm of hydrogen peroxide for oxidize in situ a fraction of the iodized salt; it is also indicated that a percentage of cyanuric acid or derivative can be added to avoid a destabilizing effect by prolonged exposure to solar-UV radiation. Such a process is not applied in France, but its defects are easily predictable: need for daily addition of oxidant to oxidize a fraction of the iodine salt, changes in the physico-chemical characteristics of the water due the presence of iodine which causes coloring of the water, an odor and an alkalization thereof, high cost due to the cost of iodine compounds which are noble products; moreover, as for the hydrogen peroxide / biguanidine salt system, this treatment is incompatible with the chlorine treatment (which, in an already treated swimming pool, is generally the treatment which one wishes to abandon) and requires emptying and rinsing the pool.

There is therefore currently no water disinfection process which combines all of the above-mentioned qualities: (1) efficacy and persistence of the bactericidal effect, (2) non-modification of the physico-chemical characteristics of water, (3) absence of decomposition products, (4) easy and safe use for users, materials and environment, (5) price compatible with swimming pool water treatment (around 1,000 F / year for 100 m ³ in 1996).

It should be emphasized that this problem of disinfecting swimming pool water has been posed for many years and has not been satisfactorily resolved to date, despite its economic importance (given the existing pool and its development predictable). Currently, the agent generally used is chlorine despite the aforementioned serious defects and its unfavorable image for the respect of the environment.

The present invention proposes to indicate a new water disinfection process which combines the above-mentioned qualities. The method of the invention is particularly suitable for treating swimming pool water, collective or individual, but can also be applied to any other water treatment (industrial water, urban waste water, industrial basins ...).

An objective of the invention is to provide a treatment process based on hydrogen peroxide directly playing a bactericidal role, that is to say provided at a concentration suitable for exhibiting good bactericidal efficacy depending on the existing conditions ( temperature, agitation, frequentation of the swimming pool), enjoying excellent persistence (more than 40 days), and producing no decomposition product.

Another objective is to obtain the own advantages which a treatment with hydrogen peroxide gives when it is used alone: non-modification of the physico-chemical characteristics of the water, safety and ease of implementation, no corrosive character.

Another objective is to indicate a process having a cost price substantially lower than the process using chlorine (currently the cheapest) and very much lower than the aforementioned known treatment using the hydrogen peroxide / biguanidine salt system.

Another objective is to provide disinfectant composition with a residual bactericidal effect.

The water treatment process targeted by the invention for ensuring the disinfection of water, in particular of swimming pool water, is of the type in which hydrogen peroxide is used as a bactericide at a concentration greater than 2 ppm, and preferably between 25 ppm and 75 ppm, suitable for obtaining a satisfactory bactericidal effect; according to the present invention, cyanuric acid or a salt of this acid is also mixed with water so that the concentration of cyanuric acid or salt of this acid in water is greater than a threshold substantially equal to 15 ppm .

It should be noted that the concentrations are indicated in pure compounds. According to a preferred embodiment, the quantity of cyanuric acid added, advantageously isocyanuric acid, is such that the concentration of water in cyanuric acid or salt of this acid is substantially between 25 ppm and 75 ppm. In addition, the pH is advantageously maintained at a value substantially between 7 and 7.4. It should be noted that the process has no influence on the pH and that it only needs to be adjusted in the event of changes due to external causes. In an advantageous embodiment of the invention, the compounds are added to the water so that:

. after mixing, the hydrogen peroxide concentration is substantially between 25 ppm and 75 ppm,

. the concentration of cyanuric acid or the salt of this acid is substantially between 25 ppm and 75 ppm.

Unexpectedly a priori, it was found that the process of the invention led to a remarkable persistence of the bactericidal effect (40 to 45 days, for a summer temperature of the order of 20 ° C to 30 ° C) , without adding any product during the period of effectiveness. It should be emphasized that the teaching of the international application already cited WO 93/04986 in no way suggests the system in accordance with the invention hydrogen peroxide / cyanuric acid with the above-mentioned functions and concentrations and in no way makes it possible to predict the result to which this system leads. Indeed, the indication that cyanuric acid can avoid destabilization to ultraviolet of the iodine / hydrogen peroxide system - while the peroxide is used as oxidant in very small quantity (0.12 ppm), that the percentage of cyanuric acid is not specified and the stabilization mechanism is not provided (probably stabilization of the active iodine taking into account the fact that hydrogen peroxide, is added continuously in very small quantity, its stability does not therefore not being critical) - cannot suggest to a person skilled in the art that cyanuric acid used at the above-mentioned high concentrations is capable of forming with hydrogen peroxide, itself provided in high concentration to play the role of bactericide, a binary product of stable treatment, having a remanence of the order of 3 times greater than that of the best existing systems.

It should be noted that the binary product hydrogen peroxide / cyanuric acid is mixed with water at the start of treatment and that no decomposition product is generated: the concentration of cyanuric acid (not biodegradable) is found at the end period (possibly with a slight variation due to the inflow or loss of water in the pool). The process is therefore free from the defects of the processes generating decomposition products; it allows perfect control of the amount of cyanuric acid. In this regard, the invention also results from the demonstration that it was possible to find a concentration of cyanuric acid such that this compound does not present any risk for the user, while prolonging in time remarkably l bactericidal effect of hydrogen peroxide in high concentration. In addition, the inventors' experiments have shown that cyanuric acid at the recommended concentrations (above 15 ppm) itself exhibits a certain bactericidal effect in the presence of hydrogen peroxide, and there is a cyanuric acid-peroxide synergy. of hydrogen contributing to obtaining greater bactericidal efficiency: hydrogen peroxide plays the main role in the destruction of bacteria, and cyanuric acid has a double function: prolonging the persistence of hydrogen peroxide and complementary bactericidal efficacy.

It should be emphasized that the chloro-cyanuric compounds mentioned above have a mechanism of action unrelated to the pair targeted by the invention peroxide / cyanuric acid. In fact, in the invention, two distinct compounds participate in the disinfection action, only one of these compounds (hydrogen peroxide) being consumed, whereas, in chlorocyanuric compounds, a single molecule is mixed with water and this decomposes in situ to produce chlorine and cyanuric acid, with the serious defect of a progressive increase in the concentration of cyanuric acid resulting on the one hand, a loss of bactericidal effectiveness of chlorine, on the other on the other hand, a risk for the user beyond a given concentration (of the order of 75 ppm).

In the invention, the only compound consumed is hydrogen peroxide which produces by decomposing water and oxygen. The process therefore has all the advantages of using hydrogen peroxide alone, and in particular that of avoiding a change in the physico-chemical qualities of the treated water.

For a closed circuit treatment as in the case of swimming pools, the method is advantageously implemented by initially mixing with hydrogen peroxide and cyanuric acid at appropriate concentrations, by regularly measuring the peroxide concentration. hydrogen and adding hydrogen peroxide when the concentration of this compound drops below a predetermined threshold, in particular of the order of 2 ppm. A test is preferably carried out at the start of the season to check the concentration of cyanuric acid in order to possibly compensate for the losses.

The annual cost of the process of the invention comes from the consumption of hydrogen peroxide, from the initial installation of cyanuric acid and from the compensation of the possible losses of this compound by dilution and can be evaluated at around 60%. 70% of the cost of the commonly used chlorine process.

Furthermore, it has been observed that the addition of a soluble silver salt and / or a soluble copper salt increased the bactericidal effect obtained by the peroxide / cyanuric acid system without reduction of persistence. Preferably, we will also mix with water:

- Or nitrate or sulphate of silver in an amount such that the concentration of water in silver is substantially between 0.01 ppm and 0.05 ppm. - Or copper sulphate in an amount such that the concentration of copper water is substantially between 0.05 ppm and 2.5 ppm.

- or the two aforementioned salts in combination with the concentrations indicated in order to obtain optimal residual bactericidal efficacy.

It seems that a synergistic effect occurs between these components, because we observe, when the components are combined, a bacterial reduction higher than the sum of the reductions obtained by each of the components. In view of the very low concentrations of silver and copper, the cost of the process is not appreciably increased and, in practice, the combination of all of the above-mentioned compounds is extremely advantageous. The process can in particular be carried out by mixing substantially with water:

. between 30 ppm and 40 ppm of hydrogen peroxide,

. between 30 ppm and 70 ppm of acid isocyanuric,

. between 0.01 ppm and 0.05 ppm silver in the form of a salt,

. and between 0.05 ppm and 2.5 ppm of copper in the form of a salt.

This formulation leads to an optimal efficiency / cost compromise for swimming pool or pond water while retaining the qualities of persistence mentioned above. In a manner known per se, it is also advantageous to add phosphoric acid or a salt of this acid to the water, in particular in an amount such that the concentration of water in PO4 is substantially between 0.5 ppm and 6 ppm. Generally, swimming pool water is slightly basic and phosphoric acid neutralizes it and acts as a buffer against pH (reduction of variations in the event of an external cause of variation); furthermore, phosphoric acid has a corrosion inhibiting effect, protecting the materials. In the case of a swimming pool treated in a closed circuit, the method is advantageously implemented in the following manner: initially mixed with water substantially between 30 ppm and 40 ppm of hydrogen peroxide, substantially between 30 ppm and 70 ppm of isocyanuric acid, approximately between 0.01 ppm and 0.05 ppm of silver in the form of salt, approximately between 0.05 ppm and 2.5 ppm of copper in the form of salt, and approximately between 0.5 ppm and 6 ppm of PO4 in the form of an acid or salt, and hydrogen peroxide is added when the concentration of this compound drops below a concentration of the order of 2 ppm, so as to rise the hydrogen peroxide concentration to a value close to the initial concentration. In practice, this addition of hydrogen peroxide is carried out at the end of the efficacy period after 40 to 45 days in the summer period; this addition of peroxide leads to a new period of bactericidal efficacy of the same duration.

The various compounds involved in the process of the invention can be added separately to the water to be treated. It is also possible to prepare an implementation formulation in advance, in order to reduce handling. This formulation may take the form of a liquid composition comprising a mixture of hydrogen peroxide and cyanuric acid or salt of this acid, the proportion by weight of cyanuric acid or salt of this acid relative to hydrogen peroxide being greater than 0.5. Preferably, the proportion by weight of cyanuric acid or salt of this acid relative to the hydrogen peroxide is substantially between 0.5 and 2.5. In addition, the composition can also contain silver and / or copper and / or phosphoric acid or a salt of this acid. This composition can thus be mixed with the swimming pool at the start of the treatment (first treatment or resumption of wintering).

The formulation can also take the form of a pebble called to dissolve in the water to be treated, comprising in solid form isocyanuric acid, a silver salt, a copper salt and a phosphate, linked by a binder soluble. The oxygen peroxide is then poured directly into the pool in the form of a liquid solution and the aforementioned rollers are placed in the baskets of the skimmers in an appropriate number according to the volume of the pool to lead to the indicated concentrations of the process.

In all cases, at the end of the effectiveness period, only hydrogen peroxide is added (with in particular annual compensation for drops in concentrations of the other compounds, due to dilution).

Of course, the method of the invention which is particularly advantageous for the treatment of swimming pools because it has all the qualities sought in this application, can also be used for the treatment of water in other applications ( wastewater, industrial water, disinfection of basins ...).

The following examples with reference to diagrams of the appended drawing illustrate the process of the invention and its performance; in this drawing, the single FIGURE is a diagram illustrating the effect of remanence in the case of the method of the invention implemented in example 1 (curve A) and giving for comparison this effect in the case of a conventional treatment with hydrogen peroxide alone (curve B).

Example 1

A 100 m ³ swimming pool is treated in the sunny summer period (Toulouse region: water temperature between 19 ° C and 25 ° C) by initially mixing with water:

- 33.4 ppm of H2O2 in the form of a liquid addition of 10 liters of a 30% solution, - 40 ppm of isocyanuric acid in the form of a solid addition of 4 kg of cyanuric acid crystals 100 %,

- 0.02 ppm of silver nitrate in the form of a decinormal solution of silver nitrate (addition of 0.16 1 of this solution),

- 2 ppm of copper sulphate in the form of an addition of 0.8 kg of very fine powder of copper sulphate pentahydrate,

- 3 ppm of phosphoric acid in the form of a liquid addition of 0.35 kg of an 85% orthophosphoric acid solution.

The measured pH is 7.0, the conductivity of 320 microSiemens and the turbidity is less than 2NTU.

Remanence is assessed by regularly measuring the H2O2 concentration in the water. The results obtained during 45 days of treatment are shown in FIG. 1: curve A.

At the end of the 45-day period, the swimming pool treated according to the process of the invention is subjected to the following controls: pH measurement, conductivity measurement, turbidity measurement, cyanuric acid dosage, visual check for the presence of seaweed, bacteriological analysis; the results obtained are as follows: - pH: 7, 0 (± 0, 1 pH unit)

- conductivity: 320 microSiemens (± 20 micro Siemens)

- turbidity <2 NTU

- cyanuric acid concentration:

40 ppm

- lack of algual development

- bacteriological analysis: count of bacteria 24 h 37 ° C <100

. total compliant: <10

. thermotolerant compliant: 0 enumeration of pathogenic staphylococci: 0 No change in pH is observed without adding a pH corrector. The conductivity was not modified, which indicates the absence of formation of decomposition by-products. The turbidity shows that the transparency of the water has remained good. The cyanuric acid concentration has not changed and remains perfectly controlled, well below the danger limit for humans (75 ppm). Bacteriological analysis shows that the water complies with official French standards for public swimming pool water. The treatment in accordance with the invention is effective on the bactericidal level up to a concentration limit of approximately 2 ppm of H2O2 and the persistence of the process of the invention is approximately 45 days.

The same test was carried out on a control pool under the same conditions, by mixing 33.4 ppm of H2O2 alone with water. Curve B illustrates the results obtained: the remanence is less than 4 days in the case of H2O2 alone.

Example 2 In this example, the kinetics of disinfection are studied on a small quantity of water treated according to the method of the invention (concentration of Example 1) and seeded with an Escherichia coli strain. (pH: 7, temperature: 20 ° C).

The reduction after 24 hours is around 5.5 log. The compounds act in synergy and produce a very effective bactericidal effect, quickly destroying the strain present.

The same tests are carried out using each compound alone - in the same concentration as in Example 1- (with a simple addition of phosphoric acid to adjust the pH to neutrality). The reduction after 24 hours for H2O2 alone is 1, 2 log.

The reduction after 24 hours for cyanuric acid alone is 1 log.

The abatement after 24 hours for money alone is 1.1 log.

The reduction after 24 hours for copper alone is 1 log.

Claims

1 / - Process for treating water with a view to ensuring its disinfection, in which hydrogen peroxide is mixed with water so that the concentration of water in hydrogen peroxide is greater than 2 ppm and adapted to allow this compound to play a bactericidal role, characterized in that cyanuric acid or a salt of this acid is also mixed with water so that the concentration of water in cyanuric acid or salt of this acid is greater than a threshold substantially equal to

15 ppm.

2 / - A method of water treatment according to claim 1, characterized in that an amount of cyanuric acid or salt of this acid is mixed with water such as the concentration of water in cyanuric acid or salt of this acid is substantially between 25 ppm and 75 ppm.

3 / - A method of treating water according to claim 2, characterized in that:. the hydrogen peroxide is mixed with the water so that, after mixing, its concentration is substantially between 25 ppm and 75 ppm,

. Cyanuric acid or the salt of this acid is mixed with water so that its concentration is substantially between 25 ppm and 75 ppm.

4 / - A method of treating water according to one of claims 1, 2 or 3, in which the pH of the water is maintained at a value substantially between 7 and 7.4. 5 / - A method of treating water according to one of claims 1, 2, 3 or 4, characterized in that isocyanuric acid is used.

6 / - A method of treating water according to one of claims 1 to 5, characterized in that a soluble silver salt is also mixed with water.

7 / - A method of treating water according to claim 6, characterized in that silver nitrate or sulphate is mixed with water in an amount such that the silver water concentration is substantially between 0.01 ppm and 0.05 ppm.

8 / - A method of treating water according to one of claims 1 to 7, characterized in that a soluble copper salt is also mixed with water.

9 / - A method of treating water according to claim 8, characterized in that copper sulphate is mixed with water in an amount such that the concentration of copper water is substantially between 0.05 ppm and 2.5 ppm.

10 / - Water treatment method according to one of claims 1 to 9, characterized in that the water is mixed substantially:

. between 30 ppm and 40 ppm of hydrogen peroxide,

. between 30 ppm and 70 ppm isocyanuric acid,

. between 0.01 ppm and 0.05 ppm silver in the form of a salt,. and between 0.05 ppm and 2.5 ppm of copper in the form of a salt.

11 / - A method of treating water according to one of claims 1 to 10, in which phosphoric acid or a salt of this acid is also mixed with water.

12 / - A method of water treatment according to claim 11, in which the phosphoric acid or the salt of this acid is mixed in an amount such that the concentration of water in PO4 is substantially between 0, 5 ppm and 6 ppm.

13 / - Method according to one of claims 1 to 12, wherein the water treatment is carried out in a closed circuit, characterized in that initially mixed with water hydrogen peroxide, acid cyanuric and possibly the silver salt and / or the copper salt and / or the phosphoric acid, the concentration of hydrogen peroxide is regularly measured, and hydrogen peroxide is added when the concentration of this compound drops below a predetermined threshold.

14 / - Method according to claim 13 for the treatment of swimming pool water, characterized in that initially mixed with water substantially between 30 ppm and 40 ppm of hydrogen peroxide, substantially between 30 ppm and 70 ppm isocyanuric acid, approximately between 0.01 ppm and 0.05 ppm of silver in the form of salt, approximately between 0.05 ppm and 2.5 ppm of copper in the form of salt, and approximately between 0.5 ppm and 6 ppm PO4 in acid or salt form, and hydrogen peroxide is added when the concentration of this compound drops below a concentration of the order of 2 ppm, so as to raise the concentration of hydrogen peroxide to a value close to the initial concentration.

15 / - Disinfecting composition with a residual bactericidal effect, characterized in that it comprises a mixture of hydrogen peroxide and cyanuric acid or salt of this acid, the weight proportion of cyanuric acid or salt of this acid relative to the hydrogen peroxide being greater than 0.5.

16 / - Disinfectant composition according to claim 15, characterized in that it comprises a proportion by weight of cyanuric acid or salt of this acid relative to the hydrogen peroxide substantially between 0.5 and 2.5.

17 / - Disinfectant composition according to one of claims 15 or 16, characterized in that it comprises hydrogen peroxide, isocyanuric acid, silver and or copper.

18 / - Disinfecting composition according to one of claims 15, 16 or 17, comprising phosphoric acid or a salt of this acid.

19 / - Roller for the treatment of swimming pool water, characterized in that it comprises, in solid form, isocyanuric acid, a silver salt, a copper salt and a phosphate, linked by a soluble binder .