FR2768511A1 - Sampling and filtration system for bacteriological control of a liquid - Google Patents

Abstract

A control unit (1) controls the function of the system through a cycle including at least one filtration stage and a pause. The filtration stage is complete when a set volume of sampled liquid has been filtered. A first means of interruption stops the cycle automatically when a volume smaller that the set volume is filtered in the filtration stage by the end of a first set time period. The system comprises a sampling module (2) to sample the liquid from a source of liquid (5) and a filtration module (3) to filter the sampled liquid and retain bacteria contained therein for analysis. The cycle has a constant duration and starts at a given moment. The system includes means for determining and indicating at least the total number of cycles completed between the given moment and the end of the cycle by the first means of interruption. The system also includes a collection module (40) to collect the filtered liquid (3), and an evacuation module (41, 42) connected to the collection module. The cycle includes, in addition to the filtration stage and the pause, a stage of emptying the collection module via the evacuation module. A first probe (400) is placed in the collection module to warn the control unit of the end of the filtration stage when the set volume of filtered liquid has been collected by the collection module. The cycle is automatically stopped by the control unit if no liquid is detected by the probe at the end of the first set time period. A second means of interruption automatically stops the cycle if the collection module is not completely empty at the end of a second set time period. This comprises a second probe, connected to the control unit inside and near the bottom of the collection module. The cycle is interrupted automatically if during the emptying stage liquid is detected by the second probe after a second set time period. The collection module is open at the top and placed beneath a liquid outlet from the filtration module. The evacuation module comprises an electrovalve (41) with an inlet connected to an orifice in the bottom of the collection module and an outlet connected to an evacuation pipe to the drain. The sampling module comprises an electrovalve controlled by the control unit with an inlet connected to the source of fluid through a pipe and an outlet connected to the filtration module. The filtration module has a filtration chamber connected to the electrovalve outlet and contains inside the chamber a filtration membrane to retain the bacteria removed from the liquid as it passes through the chamber. The system also contains means of introducing a de-oxidizing solution into the filtration unit during the emptying and filtration stages. The fluid is sampled regularly (punctually).

Description

 The present invention relates to a liquid sampling and filtration system with a view in particular to bacteriological control of said liquid. The liquid is for example water produced by a treatment station.

 In the prior art, the bacteriological checks are most often carried out by punctually withdrawing fairly small volumes of liquid from a source of liquid, and by filtering an aliquot of the liquid sampled by means of a membrane. The membrane is then placed on a culture medium and the bacteria collected on the membrane are analyzed for several hours after their incubation.

 This type of bacteriological control is fairly well suited in the case of charged water. On the other hand, when the liquid to be analyzed contains few bacteria (this is particularly the case for water distributed by a distribution network to subscribers or produced at the end of the treatment process in a purification center), the spatial and temporal distribution of bacteria is very heterogeneous. A punctual sampling and a small volume of the liquid does not allow to have a good representativeness of the biological activity of the liquid.

 Certain types of membranes currently available on the market are suitable for carrying out continuous filtration of liquid. These membranes are in fact capable of withstanding the filtration of large volumes of liquid and for long periods of time. However, during such continuous filtration, the membrane gradually loses its filtration capacity due to the increase in the degree of clogging thereof, even in the case of water with a low particle content. During a continuous filtration extending for example over five hours at fixed pressure, the flow rate through the membrane may drop by a factor of four between the first and the fifth hour. The volume representativeness of the different hours is therefore totally different.

 It therefore seems interesting for a better representativeness of the number of bacteria in the liquid as a function of time to practice liquid sampling and filtration in "continuous-sequential", that is to say according to a predetermined cycle.

 Patent FR-B-2 647 213 describes a system for sampling a biological liquid, comprising in particular a module for taking samples from a biological fluid reactor, a filtration module connected to a sampling pot and control means . The control means control a sequential taking of samples and implement a unclogging phase of the filtration module, a waiting phase, a sampling / filtration phase, and a phase of transfer of the samples collected in the jar. sampling towards analysis circuits. The sampling / filtration phase ends when a predetermined volume of biological fluid has been filtered and collected in the sampling jar. This system takes into account the problem of clogging of the filtration module. However, it requires relatively large equipment and the injection of gas to unclog the filtration module. In addition, this system is intended to allow the analysis of the biological liquid after filtration and not to collect bacteria for their analysis.

 The present invention aims to remedy the aforementioned drawbacks and to provide a simple liquid filtration system capable of taking samples and filtering liquids continuously-sequentially while controlling the clogging problem of the filtration means.

 To this end, a liquid sampling system for bacteriological control comprising a sampling module for withdrawing liquid from a source of liquid, and a filtration module for filtering the withdrawn liquid and retaining bacteria contained therein for the purpose of their analysis, is characterized in that it comprises a control means for controlling the operation of the system according to a predetermined cycle comprising at least one step of filtering said liquid withdrawn by the filtration module and a pause step, the step of filtration ends when a predetermined volume of the withdrawn liquid has been filtered by the filtration module, and in that it comprises a first interrupting means for automatically stopping said cycle when during the filtration step a volume lower than said predetermined volume of liquid has been filtered after the expiration of a first predetermined time delay.

 The liquid source is for example a water treatment center, a water distribution network, or any liquid reservoir.

 The first predetermined time delay is triggered at the start of the filtration step and corresponds to a maximum acceptable degree of clogging of the filtration module. The clogging of the filtration module is essentially due to a deposit of mineral particles present in the liquid and of sizes too large to be able to pass through the filtration module. The first means of interruption makes it possible to stop the cycle when the volumes of liquid sampled and filtered are no longer representative of the bacteriological state of the liquid due to too much clogging of the filtration module. Reliable bacteriological analysis results little influenced by clogging can thus be obtained.

 Preferably, the predetermined cycle has a duration which remains constant throughout a manipulation, a manipulation being defined as a repetitive implementation of the predetermined cycle between two given instants. In this way, it is possible to take samples and filter a constant volume of liquid at regular time intervals, for example every hour.

 Means may be provided for determining and displaying at least the total number of complete cycles carried out between a given instant at which the predetermined cycle is triggered and the cycle being stopped by the first interrupting means. Thus, even if the manipulation planned by the operator has not come to an end, the results of the bacteriological control carried out following this manipulation will be exploitable since the total volume of liquid filtered and the period during which this volume has been filtered are known to the operator. The total volume of filtered liquid is deduced from the number of complete cycles carried out displayed and from the volume of liquid filtered during the last incomplete cycle, which can be measured using an appropriate means.

 According to an embodiment of the invention, the system can further comprise a collection module for collecting the liquid filtered by the filtration module, and an evacuation module connected to the collection module. The predetermined cycle then comprises, prior to the filtration and pause steps, a step of emptying the collection module by means of the evacuation module. A first probe is arranged in the collection module to notify the control means of the end of the filtration step when said predetermined volume of filtered liquid has been collected by the collection module. The cycle is also automatically stopped by the control means when during the filtration step no presence of liquid is detected by the first probe at the expiration of the first predetermined time delay. The position of the first probe, in particular its height in the collection module, is adjustable by the system operator. This position corresponds to said predetermined volume of liquid to be filtered during each cycle.

 A second interruption means can be provided to automatically stop the cycle when during the emptying step the collection module is not completely emptied at the expiration of a second predetermined time delay. This second means of interruption makes it possible to stop the cycle when a fault occurs in the emptying, and therefore to prevent this fault from disturbing the measurements.

 Typically, the second interruption means comprises a second probe, connected to the control means, and disposed inside the collection module, near a lower part of the latter. The cycle is automatically stopped by the control means when during the emptying step a presence of liquid is detected by the second probe at the expiration of the second predetermined time delay.

 In practice, the collection module can be opened at the top and placed below a liquid outlet from the filtration module.

 The evacuation module may include a solenoid valve, an inlet of which is connected to an orifice made on a lower part of the collection module, and an outlet of which is connected to an evacuation pipe to the main sewer.

 The sampling module can comprise a solenoid valve controlled by the control means and an inlet of which is connected to the source of fluid by a pipe and an outlet of which is connected to the filtration module.

 The filtration module may comprise a filtration chamber of generally cylindrical shape, arranged horizontally or vertically, connected to said outlet of the solenoid valve, and comprising in its interior a filtration membrane for filtering the liquid withdrawn passing through the filtration chamber and retain the bacteria contained in it.

 According to a variant of the invention, means may be provided for introducing a deoxidizing solution into the filtration module. The deoxidizing solution makes it possible to eliminate any oxidizing agent, such as ozone or chlorine, present in the liquid, in particular when this liquid is water. The deoxidizing solution can be introduced into the filtration module during the emptying and filtration stages.

Other characteristics and advantages of the invention will emerge from the following description of particular embodiments, given by way of example with reference to the accompanying drawings, in which
- Figure 1 is a diagram of the liquid sampling system according to the present invention; and
FIG. 2 is an algorithm implemented by the automaton of the system of FIG. 1.

 Referring to Figure 1, a liquid sampling system according to the invention essentially comprises a programmable controller 1, a liquid sampling module 2, a filtration chamber 3, and a liquid collection and evacuation module 4.

 The programmable controller 1 includes a microcontroller (not shown) in which is stored an algorithm for operating the system. A display 10 and a keyboard 11 are arranged on an external face of the automaton 1 to allow the programming by an operator of parameters of the aforementioned algorithm, and the display of messages concerning the progress of the latter.

 The liquid sampling module 2 draws liquid, typically water, from a source of liquid 5 such as a water purification center. The liquid sampled by the module 2 is filtered by the filtration chamber 3 during predetermined time intervals, and collected and then discharged by the liquid collection and evacuation module 4.

 The liquid sampling module 2 comprises a three-way solenoid valve 20, controlled by the programmable controller l through an electric cable 21, and an inlet 200 of which is connected to the liquid source 5 by a liquid supply line 72, a first outlet 201 is connected to the filtration chamber 3 and a second outlet 202 is connected to a discharge pipe to the sewer 23.

 The filtration chamber 3, of generally cylindrical shape, is fixed horizontally to the first outlet 201 of the solenoid valve 20. The filtration chamber 3 comprises a central portion 30, an end portion of liquid inlet 31 and an end portion of liquid outlet 32. A filtration membrane 300 is placed vertically inside the central portion 30 so as to filter the liquid passing through the chamber 3. The pores of the membrane 300 are small enough to retain the bacteria contained in the liquid to be analyzed from source 5. The pores typically have a diameter of 0.22clam or 0.45m.

 The liquid collection and evacuation module 4 comprises a liquid collection receptacle 40, high 400 and low 401 probes arranged inside the column 40, and a two-way solenoid valve 41 of which an inlet 410 is connected to an orifice 402 made through a base 403 of the column 40 and an outlet 411 is connected to an evacuation pipe towards the sewer 42. The liquid collection receptacle 40 is in the form of an open column upper part and disposed below a liquid outlet end 320 of the filtration chamber 3 opposite the first outlet 201 of the solenoid valve 20, so that the filtered liquid leaving the filtration chamber 3 through the end 320 flows directly into column 40, as shown diagrammatically by the line LF in FIG. 1. The high 400 and low 401 probes as well as the solenoid valve 41 are connected to the programmable controller I by means of electric cables. 43, 44 and 45 respectively. The position, in particular the height, of the probes 400 and 401 is adjustable.

 Preferably, when the liquid produced by the source 5 is water containing an oxidizing agent such as ozone or chlorine, the system according to the invention further comprises a peristaltic pump 6 controlled by the automaton 1 and an inlet 60 of which is connected to a container of deoxidizing solution 7 and an outlet 61 of which is connected to a static mixer 8 inserted between the source of liquid 5 and the inlet 200 of the solenoid valve 20. The deoxidizing solution contained in the container 7 is for example sodium thiosulfate or sodium bisulfite.

 In addition, the system according to the invention comprises, according to a variant, a sampling wash bottle 9 connected, in the collection module 2, to the discharge pipe to the sewer 23. The wash bottle 9 makes it possible to carry out one-off samples of the liquid produced by the liquid source 5.

 FIG. 2 shows the operating algorithm of the liquid filtration system according to the invention, implemented by the controller 1. This algorithm is in the form of a CL cycle, which is triggered by the operator at the start of manipulation.

 The cycle CL comprises a first step, or phase, of draining El, of duration tl, a second filtration step E2, of duration t2, and a third pause step E3, of duration t3. The total duration t = tl + t2 + t3 of the CL cycle is constant, as is the duration tl of the draining step El. The duration t2 of the filtration step E2 is variable, and essentially depends on the degree of clogging of the membrane 300 as will be explained later. The duration t3 of the pause step E3 is variable and equal to t-tl-t2.

In the idle state of the system according to the invention, that is to say before the implementation of a first CL cycle, the input 200 of the solenoid valve 20 is in the open position, and the outputs 201 and 202 are respectively in the closed and open position, so that the liquid conveyed from the liquid source 5 by the supply line 22 is evacuated towards the sewer by the evacuation line 23. Also,
The inlet 410 and the outlet 411 of the solenoid valve 41 are respectively in the closed and open rest position, so as in particular to prevent the passage of liquid from the collection column 40 to the discharge pipe 42.

 During the first step E1 of the cycle CL, the liquid collection column 40 is emptied. To this end, the automaton 1 controls the opening of the inlet 410 of the solenoid valve 41 in order to put the column 40 and the evacuation pipe towards the drain 42 into communication. Under normal operating conditions of the system , the duration tl of the first step El is sufficient to completely empty the liquid collection column 40. However, at the expiration of the duration tl, if the low probe 401, placed near the base 403 of the column collection 40, again detects the presence of liquid at a step E12 of the cycle CL, an electrical signal SB is transmitted from the probe 401 to the controller 1 to warn the latter that a fault prevents the complete emptying of the column 40. L 'PLC 1 then stops the CL cycle at a step E12', and displays a message on the display 10 informing the operator that the algorithm is stopped due to a fault in the emptying.

It is left to the operator to repair the fault and restart the system to start a new manipulation.

 The second step E2 of the cycle CL begins immediately after the expiration of the abovementioned duration tl if the low probe 401 of the liquid collection column 40 does not detect the presence of water at this instant, by opening and closing of the first outlet 201 and of the second outlet 202 of the solenoid valve 20 respectively. The liquid conveyed from the source of liquid 5 by the line 22 then passes through the filtration chamber 3 where it is filtered by the membrane 300, and falls in the liquid collection column 40 to fill the latter until the level 404 identified by the high probe 400 is reached. As soon as the high probe 400 detects the presence of liquid, an electrical signal SH is transmitted from the probe 400 to the 'PLC 1 to warn the PLC of the end of the filtration phase E2.

 In response to the reception of the electrical signal SH, the automaton 1 closes the first outlet 201 of the solenoid valve 20 and opens the second outlet 202 to direct the liquid transmitted by the pipe 22 towards the evacuation pipe towards the sewer 23 .

Also, the automaton 1 measures the time t2 elapsed since the start of step E2 and triggers the pause step E3, of duration t3 = t-tl-t2, during which the system is left at rest.

 After the pause step E3, the cycle CL is restarted from the draining step El, and so on until a predetermined whole number N of cycles CL have been implemented. Once the algorithm is finished, the operator can collect the membrane 300 from the filtration chamber 3 and analyze the bacteria contained therein.

 According to the variant of the present invention implemented when the liquid to be analyzed supplied by the source 5 is water containing an oxidant, the peristaltic pump 6 is activated by the automaton 1 at the start of the draining step El and deactivated at the end of the filtration step E2. Thus, during the draining step El, the peristaltic pump 6 takes deoxidizing solution from the container 7 and introduces this solution into the water supplied by the source 5 through the static mixer 8. During the step of filtration E2, the deoxidizing solution supplied by the peristaltic pump 6 is mixed by the static mixer 8 with the water withdrawn from the liquid source, passing through the withdrawal module 2 and entering the filtration chamber 3, in order to remove the residual oxidant present in water.

 The volume introduced of deoxidizing solution is considered to be negligible with respect to the volume of the source of liquid sampled and filtered.

 It emerges from the above description of the filtration step E2, that the duration t2 corresponds to the duration necessary to fill a predetermined constant volume V, delimited in the collection column 40 by the base 403 and the level 404 identified by the high probe 400. Thus, during each cycle CL, exactly the predetermined volume V of liquid is filtered by the filtration chamber 3.

 In practice, before triggering the algorithm stored in the automaton 1, the operator of the system according to the invention enters on the keyboard 11 parameters of this algorithm, in particular said predetermined number of cycles to be implemented N, the duration total of a cycle t, as well as possibly the position of the high probe 400 in the collection column 40 to select the volume of liquid V to be filtered per cycle.

For example, it may be decided, when handling the system according to the invention, to filter 24 liters of liquid at a rate of 1 liter per hour. The duration t of the CL cycle is then fixed at 1 hour and the number of cycles to be implemented
N is set to 24. The position of the high probe 400 is selected so as to define a volume of 1 liter between the base 403 and the level 404 in the liquid collection column 40. The draining time tl is either calculated by the automaton 1 depending in particular on the selected position of the high probe 400 and the type of liquid to be filtered, or directly entered by the operator. In the latter case, the duration tl may be greater than the duration strictly necessary for emptying. Typically, when the liquid to be filtered is water, the duration tl is typically equal to 2 minutes.

 As previously indicated, the duration t2 of the filtration step E2 is variable. In particular, during the same manipulation, the duration t2 increases as the CL cycles unfold due to the gradual increase in clogging of the membrane 300.

 According to the invention, a time delay t2max is triggered at the start of the filtration step E2. Thus, if the timer t2max expires while the automaton 1 has not yet received any signal from the high probe 400 since the start of step E2, which means that the liquid in the collection column 40 has not still reached the level 404 identified by the probe 400, and therefore that the filtered volume is lower than the predetermined volume V, The automaton automatically stops the algorithm, as illustrated by steps E23 and E23 'in FIG. 2. The system is then put into a state of rest. The number of complete cycles carried out by the system during handling, and the duration of filtration of the liquid by the filtration chamber 3 during each of the cycles, including the last incomplete cycle, are displayed by the display 10 By measuring the volume of liquid remaining in the collection column 40, for example using a scale (not shown) engraved on the external surface thereof, the operator can deduce the total volume of filtered liquid by the filtration chamber 3 during handling.

 The aforementioned time delay t2max is for example equal to 55 minutes for a cycle time t of 1 hour. It is preferably entered by the operator on the keyboard 11 during the programming by the latter of the various parameters of the algorithm. This time delay corresponds to a maximum authorized limit of the degree of clogging of the membrane 300, beyond which the withdrawal of liquid is considered to be no longer representative.

 Also, steps E23 and E23 'make it possible to control the total volume filtered by the filtration chamber 3 during handling and to guarantee that during each cycle CL, except possibly the last cycle, a volume V of liquid is filtered by the filtration chamber 3 during the constant time interval t.

 In the embodiments of the invention described above, the detection of the end of the filtration step E2 is carried out using the liquid collection column 40 and the high probe 400. It will appear to those skilled in the art profession that these elements can be replaced by another detection means, such as a liquid meter or a device for measuring the filtered flow rate (not shown) connected to the outlet 320 of the filtration chamber 3, to the evacuation 42 and to machine 1.

Claims (14)

 1. Liquid sampling and filtration system for bacteriological control comprising a sampling module (2) for withdrawing liquid from a source of liquid (5), and a filtration module (3) for filtering the collected liquid and retaining bacteria contained therein for analysis, characterized in that it comprises control means (1) for controlling the operation of the system according to a predetermined cycle (CL) comprising at least one filtration step (E2) of said liquid sampled by the filtration module (3) and a pause step (E3), The filtration step (E2) ends when a predetermined volume (V) of the sampled liquid has been filtered by the filtration module (3 ), and in that it comprises a first interrupting means (1, 40, 400) for automatically stopping said cycle (CL) when during the filtration step (E2) a volume lower than said predetermined volume ( V) liquid has been filtered at expi ration of a first predetermined time delay (t2max).  2. A liquid sampling and filtration system according to claim 1, in which said predetermined cycle (CL) has a constant duration.  3. A liquid sampling and filtration system according to claim 1 or 2, wherein said predetermined cycle (CL) is triggered at a given time, the system comprising means (1, 10) for determining and displaying at least the number total of complete cycles (CL) carried out between the given instant and the stopping of said cycle by said first interruption means (1, 40, 400).  4. liquid sampling and filtration system according to any one of claims 1 to 3, characterized in that it comprises a collection module (40) for collecting the liquid filtered by the filtration module (3), and an evacuation module (41, 42) connected to the collection module (40), in that said predetermined cycle (CL) comprises, prior to the filtration (E2) and pause (E3) steps, an emptying step ( E1) of the collection module (40) by means of the evacuation module (41, 42), and in that a first probe (400) is arranged in the collection module (40) to warn the control means ( 1) from the end of the filtration step (E2) when said predetermined volume (V) of filtered liquid has been collected by the collection module (40).  5. liquid sampling and filtration system according to claim 4, wherein said cycle (CL) is automatically stopped by said control means (1) when during the filtration step (E2) no presence of liquid is not detected by said first probe (400) at the expiration of said first predetermined time delay (t2max).  6. liquid sampling and filtration system according to claim 4 or 5, comprising a second interrupting means (1, 40, 401) for automatically stopping said cycle (CL) when during said draining step (El ) said collection module (40) is not completely emptied at the expiration of a second predetermined time delay (tl).  7. A liquid sampling and filtration system according to claim 6, in which said second interruption means comprises a second probe (401), connected to said control means (1), and disposed inside said collection module. (40), near a lower part (403) thereof, said cycle being stopped automatically by said control means (1) when during the draining step (El) a presence of liquid is detected by said second probe (401) at the expiration of said second predetermined time delay (tl).  8. liquid sampling and filtration system according to any one of claims 4 to 7, in which said collection module (40) is open in the upper part and disposed below a liquid outlet (320) of said filtration module (3).  9. Liquid sampling and filtration system according to any one of claims 4 to 8, in which said evacuation module comprises a solenoid valve (41), an inlet of which is connected to an orifice (402) formed on a lower part. (403) of said collection module (40), and an outlet (411) is connected to a discharge pipe to the sewer (42).  10. Liquid sampling and filtration system according to any one of claims 1 to 9, in which said sampling module (2) comprises a solenoid valve (20) controlled by said control means (1) and including an inlet ( 200) is connected to said fluid source (5) by a pipe (22) and an outlet (201) is connected to said filtration module (3).  11. filtration system and liquid filtration according to claim 10, wherein said filtration module (3) comprises a filtration chamber (3), connected to said outlet (201) of the solenoid valve (20), and comprising in its inner part a filtration membrane (300) for retaining the bacteria contained in said sampled liquid passing through the filtration chamber (3).  12. System according to any one of claims 1 to 11, comprising means (6, 7, 8) for introducing a deoxidizing solution into said filtration module (3).  13. System according to claims 4 and 12, wherein said deoxidizing solution is introduced into said filtration module (3) during said emptying (El) and filtration (E2) steps.  14. System according to any one of claims 1 to 13, comprising means (22, 20, 23, 9) for punctually withdrawing liquid from said liquid source (5).