FR2688497A1 - Process for decreasing the quantity of cyanuric acid and of chloramines present in the water of a swimming pool - Google Patents

Abstract

Process for decreasing the quantity of cyanuric acid and of chloramines present in the water of a swimming pool, in which a proportion of this water passes through an ion-exchange resin of the strongly basic anionic exchanger type.

Description

 The present invention relates to the reduction of the amount of cyanuric acid and chloramines contained in the water of a swimming pool.

 For a long time, active chlorine sources have been used, that is to say chlorine with a + 1 valency, bactericidal and algicidal, of which, for example, hypochlorous acid, or salts of the hypochlorite ion such as sodium hypochlorite, for the disinfection of pool water. However, the active chlorine, in these particular forms, had the disadvantage of being decomposed in water by ultraviolet radiation, as well as excessive sensitivity to the pH of water and heat. As a result, there was a loss of active chlorine, resulting in a decrease in the disinfecting action and the formation of algae and tear chloramines, or unpleasant haloforms, especially chloroform.

 These disadvantages have led to the development of other sources of active chlorine, mainly chloroisocyanuric or chlorocyanuric, for the disinfection of swimming pool water. These bactericidal and algicidal compounds are characterized in fact by a high stability in water vis-à-vis ultraviolet radiation, a virtually zero sensitivity to the pH of water and heat. Their implementation is accompanied by a reduction by a factor 2 to 3 of the formation of undesirable organochlorine derivatives, such as chloramines and haloforms, as well as a decrease in the content of water in corrosive chlorides.

 These chlorocyanuric are essentially selected from two compounds: sodium dichloroisocyanurate and trichloroisocyanuric acid, and are in the form of pebbles or granules extremely stable storage, and fully water soluble. These pebbles and granules are therefore perfectly compatible with long-life treatments, and do not cause fouling of the injection systems.

dichloroisocyanurate, de sodium
acide hypochloreux isocyanurate de sodium

Dissolved in water, they react according to the reactions

dichloroisocyanurate, sodium
hypochlorous acid isocyanurate sodium

<tb><SEP> and <SEP> Cl
<tb>&<SEP> g <SEP> N <SEP> \ <SEP> // <SEP> fi
<tb><SEP> H20
<tb><SEP> | <SEP> ss <SEP> + <SEP> 3 <SEP> H <SE> O <SEP><<SEP>) 3 <SEP> HOn <SEP> NH
<tb> C <SEP> C <SEP> N
<tb><SEP> ci <SEP> It
<tb><SEP> 0
<tb><SEP> 0
<tb> acid <SEP> trichloroisocyanuric acid <SEP> acid <SEP> acid <SEP> HO <SEP>> N <SEP> s
<tb><SEP> hypochlorous <SEP> isocyanuric <SEP> l <SEP> l <SEP> [
<tb><SEP> N% <SEP> N
<tb><SEP> OH
<tb><SEP> OH
<Tb>
The action of water on sodium dichlorotisocyanurate or trichloroisocyanuric acid therefore produces isocyanuric or cyanuric acid or its sodium salt. This cyanuric acid is not biologically or chemically degraded in a medium that is normally substantially free of germs and, therefore, accumulates.

However, maximum tolerable levels of cyanuric acid have been set by the Administration in some countries. In France, for example, the amount of cyanuric acid should not exceed 75 ppm. In other countries, this limit can reach 400 ppm.

 On the other hand, the concentrations of disinfectant chlorinated compounds present in the water of a swimming pool vary only very slightly from a cyanuric acid concentration of 25 ppm. In other words, this concentration of cyanuric acid is sufficient to stabilize the medium. Since such stabilization is obtained, the chlorinating disinfectant compound present in predominant amount is the monochloroisocyanurate ion.

 When cyanuric acid concentrations exceed the limits allowed by the Administration, excess cyanuric acid should be removed.

Different techniques have been considered.

 U.S. Patent 4,793,935 describes the addition of melanin to precipitate a portion of the cyanuric acid as melamine cyanurate. This method has the disadvantage of leading to a very fine precipitate, which requires the addition of flocculants and requires a closure of the pool of at least 48 hours.

 Another method consists of the absorption of cyanuric acid on activated carbon: such a process leads to implement rhédibitoires amounts of activated carbon, which makes this process unsuited to the treatment of pool water.

 To overcome these drawbacks, we can simply consider a partial or total emptying of the pool. In fact, the release of cyanuric acid into the natural environment does not cause disturbances, and cyanuric acid has no toxicity with respect to the freshwater ecosystem: it degrades under poorly controlled conditions. aerobic like the river bed.

However, the implementation of this solution leads to excessive consumption of pool water, heated and treated.

 The present invention relates to a process for reducing the amount of cyanuric acid and chloramines contained in the water of a swimming pool, wherein a portion of this water passes through a strongly basic anionic exchanger ion exchange resin. .

 Resins particularly suitable for the process of the present invention are the gel structure resins, polystyrene matrix and quaternary ammonium active groups such as benzyl-dimethyl-ethanolammoniums.

 The water having passed through resins according to the present invention, not exhausted and in good working order, no longer contains cyanuric acid or chloramines. The goal is to reduce the amount of cyanuric acid and chloramines in the pool water, while saving heated and treated water.

 Figures 1 and 2 show two possible assemblies of the resin column, bypass on the filtration circuit of a pool, in both cases.

 The bypass filtration circuit on a swimming pool shown in FIG. 1 comprises a conduit 1, a circulation pump 2, a filter 3, a conduit 4 to return to the pool. Bypassed on either side of the filter 3 is a circuit 5 which successively comprises a flow control valve 6 and a resin column 7. The water passing through the resin column 7 is the water of the pool not filtered, it is necessary to provide the column 7 with a small prefilter at its entrance.

 The water circulating in the circuit 5 passes through the resin column 7 which retains or degrades the cyanuric acid and the chloramines contained in this water.

 The bypass filtration circuit on a swimming pool shown in FIG. 2 comprises a conduit 1, a circulation pump 2, a filter 3, a conduit 4 for returning to the pool. Bypassed on either side of the pump 2 is a circuit 5 which successively comprises a flow control valve 6 and a resin column 7. In branch on either side of the filter 3 is arranged a circuit 8 which comprises successively a flow control valve 9 and a reservoir of chlorocyanuric disinfectants 10. The water passing through the resin column 7 and the chlorocyanuric reservoir 10 being the unfiltered pool water, it is necessary to provide the column 7 and the reservoir 10 of a small prefilter at their entrance.

 The function of the resin column 7 is the same as that of the resin column 7 shown in FIG. 1. On the other hand, a part of the chlorocyanuric compounds contained in the tank 10 is dissolved in the water which passes through this tank, chlorocyanuric disinfectants being thus introduced into the water of the basin.

 The following example illustrates the present invention.

EXAMPLE
Three columns, numbered from 1 to 3, are filled with 150 ml of a strongly basic anionic exchanger resin gel structure, polystyrene matrix and benzyl-dimethyl-ethanolammonium active groups, sold under the registered trademark LEWATITR M600 by the Company BAYER AG Bayerwerk.

 These columns are fed by pumps per 1000 liters of drinking water into which cyanuric acid has been added in such quantities that its concentration in water is 75 ppm.

To the water fed to column 1, bleach and ammonia were added until this water contained the equivalent of 4 ppm chlorine and 1.6 ppm nitrogen. . By reaction of bleach and ammonia, chloramines are formed: essentially
NH2Cl, but also NEC12 and NCl3.

 The feed rate of the columns is 300 ml / h for columns 1 and 2, and 3 l / h for column 3.

 At the outlet of these three columns, the concentrations of water cyanuric acid and active chlorine (so, in particular, chloramines) are zero, the cyanuric acid dosage being made by nephelometry of melamine cyanurate, and the determination of active chlorine by iodometry.

 In order to evaluate the aging of the resins, in columns 1 and 2, at the end of the tests, the nitrate index IN, the chloride number IC1 and the acid number IA are measured in each case according to the standard procedures. well known to those skilled in the art and also recommended by the manufacturer of the resin.

 We deduce the maximum capacity MK, by adding IN and IA, and the basicity indicator B by dividing ICI by IN.

 The results are recorded in the table below.

The indices o indicate a measured value before the use of the resin.

COLUMNS <SEP> 1 <SEP> 2
<tb> IN / INo
<tb> 0.9 <SEP> 0.99
<tb> x <SEP> 100 <SEP> = <SEP> 57.7 <SEP>% <SEP> x <SEP> 100 <SEP> = <SEP> 63.5 <SEP>%
<tb> (INo <SEP> = <SEP> 1.56eg / l) <SEP> 1.56 <SEP> 1.56
<tb> ICl / IClo
<tb> 0.826 <SEP> 0.826
<tb> x <SEP> 100 <SEP> = <SEP> 65.1 <SEP>% <SEP> x <SEP> 100 <SEP> = <SEP> 65.1 <SEP>%
<tb> (IClo <SEP> = <SEP> 1,268 <SEP> eq / l) <SEP> 1,268 <SEP> 1,268
<tb> IA <SEP> (eq / l)
<tb> (IAo <SEP> = <SEP> 0.024 <SEP> eq / l) <SEP> 0.25 <SEP> 0.17
<tb> MK / MKo
<tb> 0.9 <SEP> + <SEP> 0.25 <SEP> 0.99 <SEP> + <SEP> 0.17
<tb> x <SEP> 100 <SEP> = <SEP> 72.6 <SEP>% <SEP> x <SEP> 100 <SEP> = <SEP> 73.2 <SEP>%
<tb> MKo <SEP> = <SEP> 1.584 <SEP> eq / l) <SEP> 1.584 <SEQ> 1.584
<tb> B <SEP> 0.826 <SEP> 0.826
<tb> (Bo <SEP> = <SEP> 81.3 <SEP>%) <SEP> x <SEP> 100 <SEP> = <SEP> 91.8 <SEP>% <SEP> x <SEP> 100 <SEP> = <SEP> 83.4 <SEP>%
<tb> 0.9 <SEP> 0.99
<Tb>
The values of the various indices show a greater degradation of the resin in the presence of active chlorine (column 1), which results, in particular, in a lower maximum capacity and lower basicity (in fact, in the latter case, it is necessary to note that the ratio IC1 / IN = B is actually proportional to the reduction of the basicity of the resin).

 On the other hand, the cyanuric acid exchange capacity of the resin is measured, for each of the three columns, at the end of the test. This resin exchange capacity is initially 39.8 g of cyanuric acid per kilogram of resin.

 At the end of the test, the cyanuric acid exchange capacities of the resin, in columns 1, 2 and 3, are respectively 24.5, 23.8 and 25.6 g of cyanuric acid per kilogram of resin, that is to say, in percentages of the initial exchange capacity, 61.5%, 59.8 * and 64.4 t.

 As a result, cyanuric acid retention is little influenced by the presence of 4 ppm of active chlorine and even a slightly better capacity of column 1 than that of column 2 is observed. On the other hand, the Comparison of the exchange capacities of columns 2 and 3 shows that increasing the flow rate of the solution tends to increase the capacity. It is also observed that such an increase in flow improves the cleanliness of the resin.

 The results obtained thus show that this resin retains or degrades very well and without being destroyed cyanuric acid and chloramines in a water representative of a pool water.

 We can now consider the use of this resin to treat the water pool 350 m3 volume, and the average attendance is 250 people per day.

 For this pool, the current legislation provides for a water renewal of 7.5 m3 per day.

 On the other hand, the recommended daily consumption of sodium dichloroisocyanurate is 2 kg per day, resulting in the formation of 1.174 kg of cyanuric acid per day.

 This pool reached the cyanuric acid limit of 75 ppm on the 30th day, and a LEWATITR M600 resin reactor was started on the 31st day.

 By the daily renewal of 7.5 m3 of water, 563 g of cyanuric acid are removed, and 611 g of cyanuric acid therefore remain to be retained by the resin.

 The technical emptying of the pond taking place after 180 days of operation, the resin will be used for 150 days, at the end of which its cyanuric acid exchange capacity will be 24.5 g of cyanuric acid per kilogram of resin (value raised above on column 1). Assuming a daily regeneration of resin, the maximum amount of resin to be used will be 25 kg, or 38.2 1.

 If a column of cylindrical resin whose height is twice the diameter is used, the flow velocities will be well below the limit speeds prescribed for the resin: they are approximately 12 times lower than that chosen for column 3 above. -above. We can therefore afford to use the column only part of the day.

 On the other hand, it should be noted that the regeneration of the resin can be carried out, for example, by a 5% aqueous NaOH solution for which a dissolution tank and a metering pump can be provided.

During the period of resin depletion, 0W ions would be released and pH correction would be necessary.

Claims (3)

 A method of reducing the amount of cyanuric acid and chloramines in the water of a swimming pool, characterized in that at least a portion of said water is passed over an ion exchange resin of the type strongly basic anionic exchanger.  The method of claim 1, wherein the ion exchange resin has a gel structure, a polystyrene matrix, and quaternary ammonium active groups.  3. The process according to claim 2, wherein the quaternary ammonium active groups are benzyl-dimethyl-ethanol-ammonium groups.