FR2629073A1 - Process for regulated and controlled continuous destruction of ammonia compounds in a water - Google Patents

Abstract

Process for regulated and controlled continuous destruction of ammonia compounds present in a water travelling in a water treatment plant, according to which a chlorinated active compound is injected into the water to be treated with the aid of a variable-throughput metering pump or valve, characterised in that it comprises the following stages: a) sampling of the water is performed at a point in the plant which is situated downstream of the point of injection of the active compound by the metering pump or valve, this point being situated so that the sampling takes place within a period t1 of between 10 and 60 seconds after the injection of the active compound into the water (when the latter reaches the sampling point); b) the free residual chlorine concentration present in the water flowing at the sampling point is measured and is compared with a set value Vc; c) the throughput of the metering pump or valve is adapted to this measurement so as to increase or slow down this throughput when the measured concentration is lower or higher, respectively, than the set value, in order to regulate the concentration of free residual chlorine in the treated water; the period t2 + t3 + t4 between the sampling and the injection of the chlorinated active compound resulting from this adaptation being shorter than 150 seconds and preferably than 90 seconds.

Description

METHOD OF CONTROLLED REGULATED AND CONTINUOUSLY CONTROLLED DESTRUCTION OF COMPOUNDS
AMMONIES OF A WATER
The present invention relates to a method of continuously controlled and controlled destruction of ammoniated compounds present in a water circulating in a water treatment plant.

 Most industrialized countries have, for many years, issued standards for the water distributed to communities. These standards were dictated mainly by hygiene and health criteria.

 This is the case, for example, of the standard limiting the water content in ammonium ions (NH4 +). In rural areas, the main source of ammonium ions is agricultural waste. Urea contained in this waste infiltrates the soil or is leached by rainwater. Finally, NH4 + ions accumulate in the water of rivers or groundwater, which will later be treated for distribution to communities.

 It is well known that it is essential to reduce the NH4 content of water intended for consumption. Indeed, NH4 + ions tend to oxidize to nitrite ions. These are fixed on the hemoglobin of the blood. This reduces respiratory capacity, mainly in infants.

 It has already been proposed a method - said method of chlorination of ammoniated compounds at the breaking point - which consists in treating the ammoniated compounds of water with enough chlorine to remove NH4 + ions and generate free residual chlorine.

 Industrial facilities have also been proposed to reduce and control the level of ammonium ions in raw water for consumption. Thus, there are water treatment plants using an ammonium meter. This device, very expensive, can measure the level of NH4 ions present in the water. It is coupled with a device which, when the NH4 + content is too high, injects into the water circuit, an active chlorine compound which reacts with the ammonium ions. Downstream of this set is an apparatus that can measure the residual chlorine content in the water. When this rate is abnormally high, an alarm is triggered.

 Such an installation has serious drawbacks. The first disadvantage is pecuniary. The equipment is relatively expensive so that small communities can not acquire it.

 The second drawback is due to the fact that the residual chlorine measurement which constitutes the only means of controlling the operation of the system can only be implemented via a second apparatus. This increases the heaviness and the complexity of implementation of the installation.

 The present invention aims to overcome the disadvantages mentioned above. More specifically, it aims to provide a controlled and continuously controlled destruction process of ammoniated compounds present in a water circulating in a water treatment plant, according to which is injected with the aid of a pump or a pump. metering valve with variable flow a chlorinated active compound in the water to be treated. The process in question is simple to implement, it is economical and can regulate quite satisfactorily the ammonium ion content of the treated water.

This method is essentially characterized in that it comprises the following steps
a) the water is sampled at a point in the installation located downstream of the point of injection of the active compound by the pump or the metering valve, this point being situated in such a way that the sounding takes place in a delay (t1) between 10 and 60 seconds after injection of the active compound into the water (when it reaches the sampling point)
b) the free residual chlorine concentration present in the water passing to the sampling point is measured and compared to a set value (Vc)
c) the flow rate of the pump or metering valve is adapted to this measurement so as to increase or decrease this flow rate when the measured concentration is respectively lower or higher than the set value, in order to regulate the free chlorine residual concentration of treated water
the delay (t 2 + t 3 + t 4) between the sounding and the injection of the chlorinated active compound resulting from this adaptation being less than 150 seconds, and preferably 90 seconds.

When the active compound which is injected is a liquid, a metering pump of a type known per se is used; as it's about
a gas is used a modulating valve, also of known type.

According to a particular embodiment of the invention, the sound
The step taken in the step consists of continuously sampling a water sample, the free chlorine concentration of which is then measured.

 According to another mode, the sounding of step (A) is carried out in situ by means of a sensor, for example a polarographic sensor.

 Preferably, said active compound is dispersed in water substantially at the time of its injection.

 According to another characteristic, said delay t1 is of the order of 20 to 30 seconds.

 According to an advantageous characteristic of the invention, the reference value (Vc) is between about 0.50 and about 1 mg of free chlorine per liter of water (p.p.m.).

 According to the invention, the water may be subjected, prior to step a), to a pre-clarification treatment. It is preferably a settling, flotation and / or filtration.

 According to another characteristic, said chlorinated active compound is sodium hypochlorite, calcium hypochlorite, chlorine, or mixtures thereof.

Other characteristics and advantages of the present invention will appear on reading the detailed description which follows, illustrated by the appended drawings in which
- Figure 1 shows, very schematically, the principle of operation of the method of the invention;
- Figure 2 shows, very schematically, a water treatment plant equipped with a system for the implementation of the invention ~ ion process;
FIGS. 3a and 3b relate to the results obtained during the treatment of a river water by the present process
FIGS. 4a and 4b illustrate the results obtained during the
+ treatment of river water momentarily doped with NH4 ions
- While Figures Sa and 5b illustrate the results obtained during the treatment of a water table water doped with NH4 + ions.

 As previously shown, the regulation of the destruction of ammoniated compounds by chlorine has heretofore necessitated the measurement of ammonium ions using an ammonium meter.

This technique, very expensive, did not allow to verify without another equipment the free residual chlorine content in water, which is the only way to control the proper functioning of the system.

 The Applicant has discovered a novel method of controlled and controlled destruction of ammoniated compounds of water using a chlorinated active compound which implements the theory of chlorination treatment of ammoniated compounds at the point of failure. It allows the continuous regulation of the ammonium ion content of water with simple equipment and the control downstream of the free chlorine content of the treated water.

 The current standards for drinking water limit the NH4 + ion content to about 0.5 mg.

per liter of water. As a safety measure, it is customary to treat the water until a concentration of NH4 close to 0.05 mg. per liter of water and if possible lower. This concentration is called guide level.

 The treatment of NH4 + ions with a chlorinated compound is known per se. The reaction products of chlorine and ammonium ions are progressively degraded to chloramines and then to nitrogen, which does not affect the quality of the treated water.

 It is possible to control the monitoring of the reaction by introducing into the reaction circuit a little more active chlorinated compound than is necessary to carry out the reaction. A measure of residual free chlorine accounts for the operation - good or bad - of the reaction.

 Referring to Figure 1 attached, there is shown very schematically the operating principle of the method of the invention. This method is carried out using a device 1. A water sampling is carried out continuously in the water treatment plant 10 which contains the water to be treated and a certain amount of water. proportion of active chlorinated compound. This sounding consists of taking a water sample through line 11 at point (P) -. Water flows in the direction of the arrow (F). The water sample is conveyed to a cabinet 12 which comprises a cell for measuring the free chlorine concentration contained in the water. This is a measuring cell of known type such as, for example a system of electrodes Stainless steel / Gold, Silver / Gold. The cell can be coupled with a monitor of known type which gives the value of the measurement The value of the measurement is then converted, by means of a known type, into an electrical signal, for example a current intensity, and transmitted to a regulator 15 of "proportional integral derivative" type. This regulator comprises a screen 15 'provided with a marker which can oscillate between the two extreme values of current intensities. Of course, these extreme values are proportional to extreme concentrations of chlorine. For example, a regulator is used which covers the intensities of between 4 and 20 mA, corresponding to free residual chlorine values of between 0 and 2 ppm. The regulator also comprises means for setting a set value corresponding to an intensity , (that is, a free chlorine concentration). This setpoint value is that which one wishes to maintain throughout the implementation of the process. It is for example 10 mA or 1 p.p.m. of free residual chlorine.

 The regulator 15 is associated with the control box 16 of a metering pump 17 of chlorinated active compound, in liquid form, at variable speed, which injects the latter into the water treatment circuit 10 at the point (Q). The chlorinated compound is intimately mixed with the water due to the permanent circulation of water within the treatment circuit, as shown by the arrows at the bridge (Q).

 Thus, when the chlorine concentration measured at a given instant and converted into a current intensity, is greater than the set point, the flow rate of the metering pump is automatically slowed down so as to lower the free residual chlorine content of the metering pump. treated water. On the contrary, when the measured intensity is smaller than the set value, it means that almost all of the chlorinated active compound has reacted with the ammonium ions. It is therefore necessary to increase the concentration. The controller acts on the control box of the pump whose flow is then increased. The free residual chlorine concentration of the treated water is thus regulated.

 It has been found that the chlorine reacts with numerous compounds present in the water to be treated according to quite variable reaction kinetics. In addition, the continuous free chlorine residual measuring devices have their error-prone results by interference with compounds such as the chloramines that form in the water after the reaction of chlorine with the ammonium ion, as well as the show JC Morris and lW Wei in "Chlorine Ammonia Breakpoint Reactions: Model Mechanisms and Computer Simulation - Am.Chem Soc., Div.Water, Dir and Waste Chem., Minneapolis, Minn., April 15, 1969" .Therefore it is necessary to perform a sufficiently selective measurement of residual free chlorine, which itself is a sufficiently specific indicator of the reaction state of the chlorinated active compound on the ammoniated compounds. Such an object is achieved according to the present invention if the sampling of the water sample is carried out within a time interval (t1) of between 10 and 60 seconds after the injection of the active compound into the water corresponding to this sample and if the time (t 2 + t 3 + t 4) between sampling and injection of the resulting chlorinated active compound is less than 150 seconds and preferably 90 seconds.

 It has also been found that it is preferable to carry out a measurement on water freed from organic matter-which could interfere with measurements and even plug some pipes. This is why it is preferred to use the method of the invention on previously clarified water. This clarification treatment consists, for example, of decantation, flotation and / or filtration or assimilated process.

Of course, if the water to be treated comes from a water table, the clarification treatment is not necessary since the organic materials are practically non-existent, but other prior treatments may be useful. This is, by
example, mineralization treatments, softening, dewatering
tion, demanganization, denitration, nitrification.

Still referring to FIG. 1, there is shown by
arrows in dashed lines, how does the duration of putting
implementation of the different steps of the method. Time t1 separates
the moment of injection of the active chlorinated compound at the point (Q) of
the moment of taking a sample of water at point (P). t2
is the time required to carry the water sample, the cir
bake treatment 10 to the measuring cell 12. t3, necessary
to perform the measurement, is related to the performance of the cabinet. The
time t4 is the time needed to transform the measurement
of the cell and act accordingly on the dosing pump.

According to one variant, the sampling line is replaced
11 by a sensor, for example polarographic placed in the vicinity
from the point (P). This sensor directly probes the concentration in situ
in residual chlorine free of water and provides an electrical signal
which is a function of this concentration. This signal is then measured
re and displayed on monitor screen 13.

 Referring to Figure 2, there is shown very schematically a water treatment plant equipped with a system for carrying out the method of the invention.

 The installation consists of four main parts: a decanter 2, a filter 3, an ozonation tank 5 and a treated water reserve 6.

 The water, as it arrives from the river, enters the treatment plant via conduit 20. The water is then treated with CaO and alumina sulphate and then discharged to the flocculator 21. so that organic matter suspended in water precipitates. The water then travels through the settling tank 22 composed of three stages 22a, 22b and 22c where the organic matter trapped by the flocculation is deposited. The water removed from most organic materials passes through the filter 3 through a pipe 23. The water 30 arrives on a sand filter 31 where are retained the last particles suspended in water. The filtered water is then discharged through line 33 to a three-compartment ozonation tank 5. Line 50 provides renewal in ozonated air. After this treatment, the water is discharged through line 60 up to a supply of treated water 6.

 The system making it possible to carry out the process of the invention is marked 4. It will be noted that the pipe 32 which makes it possible to take the water sample is connected to point (A) on the pipe 23 which ensures the junction between the decanter 2 and the filter 3.

Similarly, the pipe 40 ensures the circulation of chlorinated active compound and opens at the beginning of the pipe 23, at the point (B) upstream of (A).

 It is also possible to implement the process of the invention with a previously filtered water. In this case, the pipe 32 'drawn in dashed lines makes it possible to take the sample.

We will now describe, again with reference to the accompanying drawings, examples of treatment implemented with water of different qualities and under different conditions.
Example 1
A control test of the ammonium ion level was carried out on a filtered river water being treated in a plant similar to that described with reference to FIG. 2. Sampling is carried out via the pipe 32 '.

 The time bed 1 + t 2 + t 3 + t 4 - necessary to implement all the steps of the process is close to 20 minutes and "such" is close to 16 minutes The chlorinated active compound used is sodium hypochlorite.

 The table below shows the results obtained.

Table I

<tb> Time <SEP> Rate <SEP> of <SEP> Chlorine <SEP> Ammonia
<tb> cumulative <SEP> chlorine <SEP> injected <SEP> free <SEP> (ppm <SEP> of <SEP> NH4 +) <SEP>
<tb><SEP> (min) <SEP> (ppm) <SEP> ppm <SEP>
<Tb>

<SEP> Before <SEP> After
<tb><SEP> Chlorination <SEP> Chlorination
<tb><SEP> û <SEP><SEP> 5.5 <SEP> û <SEP><SEP> 0.6 <SEP> 0.6
<tb><SEP> 5 <SEP> O <SEP> 0.4 <SEP> 0.6 <SEP> 0.6
<tb><SEP> 30 <SEP> 8 <SEP> 0.03 <SEP> 0.6 <SEP> 0.4
<tb><SEP> 40 <SEP><SEP> 4.5 <SEP> 0.4 <SEP> 0.6 <SEP> (0.05 <SEP>
<tb><SEP> 45 <SEP> 1 <SEP> 0.7 <SEP> 0.6 <SEP><0.05
<tb><SEP> 50 <SE> O <SEP> 0.86 <SEP> 0.65 <SE> 0.1
<tb><SEP> 52 <SEP> O <SEP> 0.88 <SEP> 0.65 <SEP> 0.15
<tb><SEP> 54 <SEP> O <SEP> 0.83 <SEP> 0.7 <SEP> 0.25
<tb><SEP> 60 <SEP> 6 <SEP> 0.15 <SEP> 0.65 <SEP> 0.4
<tb><SEP> 70 <SEP> 6 <SEP> 0.05 <SEP> 0.6 <SEP> 0.6
<Tb>
Analysis of the results in this table shows that even after a relatively long period of start-up, the ammonium ion content of the water can not be satisfactorily regulated.

 Another test was carried out on an unfiltered water (the sampling was carried out via line 32) with a time "tell less than 60 seconds and a time" t2 + t3 + t4 "close to 8 minutes, leading to comparable results.

Example 2
Referring to Figures 3a and 3b, there is shown in the form of curves, the results obtained during the treatment of an unfiltered river water by implementing the method of the invention.

 The time "t1" is equal to 20 seconds and t't1 + t2 + t3 + t4 ,, is close to 100 seconds. The chlorinated active compound is sodium hypochlorite.

 FIG. 3a shows the curves A3 and B3 representative of the level of ammonium ions per liter of water, before and after the treatment, as a function of time. These curves are listed respectively in continuous and discontinuous lines.

 At the same time, FIG. 3b shows the curves C3 and D3 which respectively represent the rate of chlorine injected per liter of water, as well as the level of free residual chlorine, as a function of time.

 It can be seen from these curves that for a period of about 10 minutes, the chlorine injected rate as well as that of residual chlorine oscillate fairly widely, but in a damped manner. This corresponds to a system balancing period (speed correction). Then the curves are balanced: the curve A3 takes a profile corresponding to that which is characteristic of the water content in ammonium ions before treatment, while the curve D3 quickly becomes flat to establish at the set point. (Vc) chosen and represented in dotted lines. It will be noted in FIG. 3a that the curve B3 representing the ammonium level is plane and close to the analytical detection threshold.

Example 3
With reference to FIGS. 4a and 4b, the results obtained during the treatment of an unfiltered river water artificially doped with ammonium ions are shown.

 The time '' t1 is close to 20 seconds and "t1 + t2 + t3 + t4" close to 100 seconds, the chlorinated active compound is sodium hypochlorite.

 The curve A4 is characteristic of the ammonium level of the water before treatment, as a function of time. It is noted that the water was doped so as to quickly obtain a concentration of ammonium ions close to 1.6 p.p.m.

 Curves C4 and D4 respectively represent, as a function of time, the rate of chlorine injected as well as the level of free residual chlorine.

It will be noted that the profile of the curve C4 is deeply affected by the doping of the water. On the other hand, the profile of curve D4 remains relatively close to the set point. Regulation is therefore permanent, with rapid response and a slight transient
is due to the speed and relative importance of the variation in
+ concentration of NH4 in the water treated during doping.

This example shows that even during a sudden variation in the amount of ammonium ions in the water, the quality of the treated water remains substantially the same since the curve B4, characteristic of the rate in
ammonium ions from the treated water, remains flat and at the level of the analytical detection threshold.

Example 4
With reference to FIGS. 5a and 5b, the results obtained during a treatment of a water of web containing 0.2 ppm are represented.

of ammonium ions per liter, artificially doped at 0.5 and then at 0.7 p.p.m. (curve A5).

 The profile of the curve C5, which is characteristic of the rate of chlorine injected as a function of time, echoes the two successive dopings.

 On the other hand, the profile of the D5 curve, which is characteristic of the free residual chlorine rate, undergoes only the slight inflections at the moment of doping and then returns very quickly, in less than 5 minutes at the level of the set value (Vc) equal to at 0.5 mg. free chlorine per liter of water.

 The ammonium ion content, represented on curve B5, remains constant and practically zero.

 It should be noted that for carrying out this example, a chlorinated active compound consisting of sodium hypochlorite has been used. The time "t1 is equal to 20 seconds and" t1 + t2 + t3 + t4 "is close to 90 seconds.

 All of the treatments which have been the subject of the above examples have been carried out using, as chlorinated active compound, sodium hypochlorite. Alternatively, it is quite possible to use other chlorinated compounds such as calcium hypochlorite, chlorine or mixtures of these compounds.

 As already indicated above, if this compound is gaseous, the metering pump is replaced by an equivalent device such as a modulating valve.

Claims (8)

 1. Controlled and continuously controlled destruction process of ammoniated compounds present in a water circulating in a water treatment installation, according to which a chlorinated active compound is injected with the aid of a pump or variable-dose metering valve. the water to be treated, characterized in that it comprises the following steps  a) the water is sampled at a point of the installation located downstream of the injection point of the active compound by the pump or metering valve, this point being located in such a way that the sounding takes place within a (t1) between 10 and 60 seconds after injection of the active compound into the water (when it reaches the point of probing)  b) the free residual chlorine concentration present in the water passing to the sampling point is measured and compared to a set value (Vc)  c) the flow rate of the pump or metering valve is adapted to this measurement so as to increase or decrease this flow rate when the measured concentration is respectively lower or higher than the set value, in order to regulate the free chlorine residual concentration of the treated water the delay (t2 + t3 + t4) between the sounding and the injection of the compo  4 chlorinated active resulting from this adaptation being less than 150 seconds, and preferably 90 seconds.  2. Method according to claim 1, characterized in that the sounding performed in step (a) consists in continuously taking a sample of water, which is then measured the concentration of free chlorine.  3. Method according to claim 1, characterized in that the sounding of step (a) is carried out in situ by means of a sensor, for example a polarographic sensor.  4. Method according to one of claims 1 to 3, characterized in that the chlorinated active compound is dispersed in water substantially at the time of its injection.  5. Method according to one of claims 1 to 4 characterized in that the delay (t1) is of the order of 20 to 30 seconds.  6. Method according to one of claims 1 to 5 characterized in that said set value (Vc) is between about 0.50 and about 1 mg. free chlorine per liter of water.  7. Method according to one of claims 1 to 6 characterized in that, prior to step a), the water is subjected to a clarification treatment, which preferably consists of a settling, a flotation and / or a filtration.  8. Method according to one of claims 1 to 7 characterized in that said chlorinated active compound is selected from sodium hypochlorite, calcium hypochlorite, chlorine or mixtures thereof.