Water treatment facility and method for operating a water treatment facility

Abstract

The invention relates to a water treatment facility (10), comprising a raw water feed (11) for providing raw water (R), a softening device (12) which has an inlet (11a) and an outlet (11b) and produces softened water (W) from the raw water (R) and provides same at the outlet (11b), a regenerating device (18) for regenerating the softening device (12) and / or a signaling device which generates a signal when the softening device (12) is depleted in order to indicate a required regeneration of the softening device (12), a controller (14) which is coupled to the regenerating device (18) and / or the signaling device in order to regenerate the softening device (12) when the softening device is depleted, and at least one measuring device (15), which is connected to the softening device (12) and to the controller (14), for detecting a hardness breakthrough in the water (W) provided at the outlet (11b) of the softening device (12). In order to determine the optimal time to regenerate the softening device during the operation of the water treatment facility in an automated process without using chemicals, the measuring device (15) comprises at least one conductivity sensor (2; 2a, 2b) and an electrolysis cell (1) with at least two electrolysis electrodes (A, K).

Description

[0001] Water treatment plant and method for operating a water treatment plant

[0002] The invention relates to a water treatment plant and a method for operating a water treatment plant.

[0003] The hardness of water is determined by the concentration of the alkaline earth metal cations dissolved in the water and, in specific applications, also by the concentration of their associated anionic partners, particularly bicarbonate. The sum of the concentrations of all dissolved alkaline earth metals (which can be present as carbonates, sulfates, chlorides, nitrites, nitrates, and phosphates) is referred to as the total hardness. The portion bound only to carbonic acid is referred to as carbonate hardness (or temporary hardness), and the difference between total hardness and carbonate hardness is referred to as non-carbonate hardness (or permanent hardness). The majority of the total hardness in drinking water is usually present as carbonate hardness. As so-called hardness formers, calcium and magnesium ions contribute primarily to the total hardness of water. The sum of the concentrations of calcium and magnesium ions therefore corresponds closely to the total water hardness.The remaining alkaline earth metals, such as strontium and barium, are usually present only as trace elements in water and therefore contribute little to water hardness. Carbonate hardness can be removed from the water by removing calcium and magnesium carbonate. The dissolved hardness-forming elements calcium and magnesium can form sparingly soluble compounds in water, particularly as carbonates, with the carbon dioxide dissolved in the water, corresponding to the lime-carbonic acid equilibrium.

[0004] The formation of compounds that are difficult to dissolve in water by the hardness formers leads to the formation of scale in household appliances, heaters and hot water heaters, particularly when the water is heated, and reduces the effectiveness of detergents and washing machines in (dish)washers and washing machines. Water hardness also influences the taste of food and drinks prepared with water. To avoid or reduce the adverse effects of hard water, i.e. water with a high concentration of alkaline earth metal ions, the calcium and magnesium ions are partially or completely removed from the water, for example in water softening systems or in demineralisation systems. This is done by replacing them with sodium ions, for example using cation exchangers, or - in demineralisation - by completely removing them from the water together with all other dissolved ions, for example.through a combination of cation and anion exchangers or through reverse osmosis.

[0005] Since the exchange capacity of ion exchangers is limited, water softening devices in which ion exchangers are used must be regenerated in good time before the ion exchanger(s) become exhausted in order to avoid a hardness breakthrough. The regeneration of an exhausted cation exchange resin takes place, for example, with a saline solution (sodium chloride solution). During regeneration, the hardness-forming substances (calcium and magnesium ions) absorbed by the ion exchanger during water softening are exchanged for sodium ions in the saline solution. The point in time at which an ion exchanger is exhausted depends on the exchange capacity of the ion exchanger material (this is usually an ion exchange resin), the hardness of the raw water and the volume flow rate of the raw water. In order to limit the consumption of regeneration material (e.g.To keep the amount of regeneration salt (e.g., regeneration salt for producing a saline solution) as low as possible and, at the same time, to prevent hardness breakthrough after the ion exchanger becomes exhausted, regeneration should be performed as shortly as possible before the ion exchanger becomes completely exhausted. Premature regeneration increases the consumption of regeneration material, and if regeneration is delayed, the ion exchangers are no longer able to completely remove the hardness-forming ions from the water, resulting in a hardness breakthrough.

[0006] DE 198 41 568 A1 discloses a method and system for determining the regeneration time of a water softening device, particularly for water-based, program-controlled household appliances. To determine the hardness of a rinsing liquid, the conductivity of the liquid, as determined by sensors, is measured before and after the softener, and a conductivity difference is determined from this. Regeneration of the softener is made dependent on a comparison with conductivity values ​​stored in a program controller memory and conductivity difference values ​​from previous measurements. Regeneration of the water softening device is initiated when the conductivity difference is zero and the conductivity is greater than a predetermined limit, or when the conductivity difference is not zero and tends toward zero.When installing the device, no hardness adjustment to the available fresh or domestic water is necessary and fluctuating mains water hardness can be automatically taken into account.

[0007] Since the electrical conductivity of water is determined by all ions dissolved in the water and not just by the hardness-forming substances dissolved in the water (particularly calcium and magnesium ions), and because the replacement of the hardness-forming substances with sodium ions during softening only leads to a slight change in conductivity, the conductivity determined using this known method is only of limited use for calculating the optimal regeneration time. Furthermore, this method cannot reliably prevent hardness breakthrough, as regeneration of the ion exchanger only occurs when the conductivity difference is zero or tending towards zero, which means that the exchange capacity of the ion exchanger is already (almost) exhausted. This known method is therefore not suitable for use in softening or desalination systems intended to permanently provide fully or partially softened water.

[0008] From WO 2009 / 071066 A2, a water softening device with an ion exchange resin is known, which splits an incoming raw water stream into two partial streams and subjects one of the two partial streams to full softening and then combines the two partial streams to a blended water stream, wherein to determine the water hardness from the electrical conductivity of the raw water, two different conversions are made from the measured electrical conductivity to the raw water hardness. For the automatic control of the regeneration of the ion exchange resin, a conversion of the measured conductivity into a water hardness is provided using a first calibration curve, which is conservatively designed and reflects the maximum water hardness occurring at different conductivities. The conversion using a second calibration curve is realistically designed and gives the average (i.e.The water hardness (i.e., with the smallest statistical error) at different conductivities is reflected, which is used to control the blending device. This allows experimentally determined variations in water composition (and thus different relationships between conductivity and water hardness) to be taken into account in order to optimally determine the regeneration time and minimize tolerances in the blending water hardness compared to a target value. The relationship between the electrical conductivity and the total hardness of the water must be recorded using characteristic curves, which must be created empirically and laboriously by titrimetrically determining the hardness of various water samples and measuring the electrical conductivity.Furthermore, the relationship between electrical conductivity and the total hardness of the water is only weak, and the replacement of hardness-forming substances with sodium ions during a softening process leads to only a minor change in conductivity. The actual water hardness at a given conductivity, which can be determined titrimetrically, can therefore deviate considerably from the hardness value determined using the characteristic curve, especially if the raw water has a relatively high non-carbonate hardness (permanent hardness).A deviation between the raw water hardness determined from the calibration curve and the actual raw water hardness may result in premature regeneration and thus increased regeneration agent consumption, or delayed regeneration with a resulting hardness breakthrough, depending on whether the raw water hardness determined from the calibration curve is greater or lesser than the actual total hardness of the raw water. For this reason, and also due to the temperature dependence of the electrical conductivity of water, this method for controlling the regeneration of a water softener is inaccurate and can only be applied to raw water qualities that exhibit a relationship between electrical conductivity and total water hardness that at least approximately corresponds to the characteristic curve used.

[0009] To monitor the exchange capacity of ion exchangers, hardness sensors containing a swelling or shrinking resin are also known from the state of the art. These sensors measure the degree of depletion of the ion exchanger. One such hardness sensor for water softening systems is known, for example, from DE 29 53 143 A1. However, such hardness sensors lack sufficient accuracy for many applications.

[0010] To accurately determine water hardness, complexometric titration methods can be used, e.g. using the disodium salt of ethylenediaminetetraacetic acid (EDTA) as a titrant. These can measure the concentrations of alkaline earth ions dissolved in the water and thus the total hardness of the water. To monitor the degree of depletion of ion exchangers, state-of-the-art measuring devices are known which photometrically record the color change point of a titration and trigger a signal as soon as a hardness breakthrough is detected. These measuring devices are characterized by good measuring accuracy, but are complex and expensive to manufacture, require regular maintenance and generate high consumption costs due to the use of the titrant. When detecting a hardness breakthrough using the conventional titration method, there is also a considerable time delay between the hardness breakthrough and its detection. It is usually only carried out every approximatelyA soft water sample is taken and analyzed every 5-30 minutes to minimize reagent consumption. This takes approximately another 3-5 minutes. During this time, soft water of unclear quality or already experiencing significant hardness breakthrough flows to the downstream application. Hardness breakthrough cannot be prevented, as the signal indicating the need for regeneration of the ion exchanger is only generated when the exchange capacity is already exhausted.

[0011] When determining the optimal time for the regeneration of a water softening device which is supplied with raw water from the public drinking water supply network, there is also the problem that the water supplier usually feeds a limited number of different drinking water qualities from different sources and with different compositions and hardness into the public drinking water supply network, whereby the discharge of these different drinking water qualities can change within a day or even within longer periods of time, so that the composition and hardness of the raw water supplied to a softening device can change according to the quality of the drinking water provided by the public drinking water supply.Such changes in water quality, which can occur several times throughout the day, alter the remaining exchange capacity of the softening device and thus the optimal time for regeneration. In order to be able to quickly adjust the optimal time for regeneration in the event of a change in the water quality of the incoming raw water, it is necessary to enable rapid detection of any changes in the composition or quality of the raw water during operation of a water treatment plant with a water softening device and to adjust the predicted time of depletion of the softening device accordingly.Based on this, the invention is based on the object of demonstrating a water treatment plant and a method for operating a water treatment plant with a softening device, which enable the determination of the optimal time for regenerating the softening device without the use of chemicals in an automated process during the operation of the water treatment plant and can reliably and as quickly as possible detect an incipient hardness breakthrough and prevent a complete hardness breakthrough even with changing quality or hardness of the supplied raw water.

[0012] These objects are achieved with the water treatment plant according to claim 1 and the method having the features of claim 12. Preferred embodiments of the water treatment plant and the method are set out in the dependent claims.

[0013] The water treatment plant according to the invention comprises a raw water inlet, a softening device with an inlet and an outlet and in particular with at least one regenerable or replaceable ion exchanger, a regeneration device for regenerating the softening device and / or a signaling device which, when the softening device is exhausted, generates a signal to indicate a required regeneration of the softening device and in particular a required regeneration or a required replacement of the ion exchanger, and a control device which is coupled to the regeneration device and / or the signaling device in order to regenerate the softening device in the event of exhaustion and / or to output or display the signal generated by the signaling device or to stop the operation of the softening device,and at least one measuring device connected to the softening device and the control device for detecting a hardness breakthrough in the water provided at the outlet of the softening device. According to the invention, the measuring device comprises at least one conductivity sensor and an electrolysis cell with at least two electrolysis electrodes.

[0014] In this case, raw water is supplied to the softening device at the inlet via the raw water inlet, from which the softening device produces softened water and makes it available at the outlet, wherein water which is provided at the outlet of the softening device is supplied to the measuring device in order to detect a hardness breakthrough in the water provided at the outlet of the softening device when the softening device is exhausted, and the control device then initiates a regeneration of the softening device by means of the regeneration device and / or outputs or displays a signal generated by the signaling device in order to indicate a required regeneration of the softening device and in particular a required regeneration or a required replacement of the ion exchanger, or to stop the operation of the water treatment plant or the softening device in order to preventthat non-softened water is provided at the outlet.

[0015] The measuring device can be used to conductometrically detect a hardness breakthrough via at least one conductivity sensor. The conductometric detection of a hardness breakthrough can be recorded very quickly and reliably in the measuring device by determining the conductivity difference that results in the electrolysis cell due to electrolytic precipitation of the alkaline earth ions contained in the water when a hardness breakthrough has occurred. For this purpose, the measuring device records the electrical conductivity of the water supplied to the measuring device before it enters the electrolysis cell or at an inlet of the electrolysis cell and the electrical conductivity of the water after it exits the electrolysis cell or at an outlet of the electrolysis cell, and the difference is calculated from this in order to record the change in electrical conductivity caused by the precipitation of the alkaline earth ions in the electrolysis cell.As long as the water supplied to the measuring device is fully softened and therefore contains no alkaline earth ions, assuming proper operation of the water treatment system and, in particular, when the ion exchanger is not exhausted, the conductivity of the water at the inlet and outlet of the measuring device is at least substantially the same, and the measuring device detects a conductivity difference between the inlet and outlet of the measuring device of zero or at least approximately zero. However, when a (beginning) hardness breakthrough of the softening device occurs, alkaline earth ions, particularly calcium and magnesium ions, are present in the water. These ions are precipitated in the electrolysis cell of the measuring device and lead to a reduction in the electrical conductivity at the outlet of the measuring device compared to the conductivity at the inlet.

[0016] The method according to the invention and the water treatment plant according to the invention have the advantage that the water (soft water) provided at the outlet of the softening device is continuously monitored. A time offset in the monitoring is only due to the short distance over which the analyzed water flows through the measuring device, in particular from an inlet to an outlet of the measuring device, whereby this distance and thus the time offset can be kept very short. In preferred embodiments, the electrolytically effective residence time of the water flowing through the electrolysis cell (soft water), which is decisive for the precipitation of the alkaline earth ions, is in the range of 10 to 120 seconds, preferably between 20 and 50 seconds. For the detection of a hardness breakthrough, a dead time of approximately 1 minute is also required, which is determined by the length of the supply lines.30 to 60 seconds are added so that a change in conductivity when a hardness breakthrough begins can be detected within a reaction time of 40 to 180 seconds, and in particular 50 to 110 seconds. This allows a hardness breakthrough to be detected very early on. In order to detect a hardness breakthrough, it is not necessary for all of the alkaline earth ions in the water fed to the measuring device to be precipitated. It is sufficient if only partial precipitation of the alkaline earth ions in the water fed to the measuring device occurs, because the change in conductivity caused and detected by and during the precipitation of the alkaline earth ions can indicate an exhaustion of the softening device and the resulting incipient hardness breakthrough, even if only a portion of the alkaline earth ions already in the water are precipitated.However, it is advisable for the measuring device to precipitate at least substantially all of the alkaline earth ions in the supplied water, whereby a hardness breakthrough can be delayed for a certain period of time when the softening device begins to become exhausted.

[0017] When hardness breakthrough begins, the difference in conductivity of the water at the inlet and outlet of the measuring device can be used to determine the concentration of alkaline earth ions in the water flowing through the electrolysis cell and, consequently, the degree of depletion of the softening device. The greater the conductivity difference, the higher the degree of depletion or the lower the residual capacity of the softening device, in particular of the ion exchanger(s). When hardness breakthrough begins in the water flowing through the electrolysis cell, the concentration of alkaline earth ions is still very low, so that even with complete precipitation of the alkaline earth ions, initially only a slight change in conductivity between the inlet and outlet of the measuring device is measured.However, in the case of a hardness breakthrough, which occurs when the softening device is completely exhausted, there are so many alkaline earth ions present in the water that they can no longer be completely precipitated due to the limited residence time in the electrolysis cell, which is why the conductivity difference recorded by the measuring device asymptotically approaches a maximum when the softening device is completely exhausted, the amount of which continues to depend on the residence time of the water in the electrolysis cell and thus on the flow velocity of the water and the length of the electrolysis cell.

[0018] The electrolysis electrodes of the measuring device are expediently designed as flat electrodes arranged opposite one another in the electrolysis cell. This allows for a uniform flow of water through the electrolysis cell between the electrolysis electrodes, thus allowing sufficient residence time for the precipitation of alkaline earth ions. The electrolysis electrodes are expediently designed so that they can be connected to a direct voltage source.

[0019] To detect the electrical conductivity of the water flowing through the electrolysis cell, the measuring device preferably comprises at least two conductivity sensors. Particularly preferably, at least one conductivity sensor is integrated into the electrolysis cell. This enables a compact and cost-effective design of the measuring device. In a preferred embodiment, the measuring device comprises two conductivity sensors, wherein a first conductivity sensor is provided at an inlet of the measuring device for measuring the conductivity of the water flowing into the electrolysis cell and a second conductivity sensor is provided at an outlet of the measuring device for measuring the conductivity of the water flowing out of the electrolysis cell. The conductivity sensors can also be arranged outside the electrolysis cell. In this case, for example,a first conductivity sensor is arranged upstream or at an inlet of the electrolysis cell and a second conductivity sensor is arranged downstream or at an outlet of the electrolysis cell.

[0020] In a preferred embodiment, the measuring device comprises an inlet, at which water from the water softener is supplied to the measuring device, and an outlet, with a first conductivity sensor arranged at the inlet and a second conductivity sensor arranged at the outlet, and the electrolysis cell arranged between the inlet and the outlet. This design enables interference-free measurement of the electrical conductivity of the water flowing into the electrolysis cell at the inlet and the water flowing out of the electrolysis cell at the outlet.

[0021] Each conductivity sensor preferably comprises at least one pair of electrodes with two measuring electrodes, particularly designed as rod electrodes, which are connectable or connected to an alternating voltage source. This enables cost-effective measurement of electrical conductivity by applying an alternating electrical voltage to the measuring electrodes, while maintaining a compact design of the measuring device.

[0022] In a preferred embodiment, the measuring device comprises a first conductivity sensor and a second conductivity sensor, wherein the first conductivity sensor and the second conductivity sensor each comprise an electrode pair with two measuring electrodes, and the measuring electrodes are connectable or connected to an alternating voltage source. The two conductivity sensors can be arranged inside the electrolysis cell or outside the electrolysis cell. If the conductivity sensors are arranged inside the electrolysis cell, a first conductivity sensor is provided upstream and a second conductivity sensor is provided downstream of the opposing electrolysis electrodes. Arranging the two conductivity sensors inside the electrolysis cell enables a compact design and the use of the measuring device to determine the hardness of the water in a water sample.An arrangement outside the electrolysis cell offers metrological advantages, as the spatial decoupling of the measuring electrodes and the electrolysis electrodes prevents interference with the conductivity measurement by the measuring electrodes. When arranging the measuring electrodes inside the electrolysis cell, it may be advisable to temporally decouple the conductivity measurements using the measuring electrodes and the electrolytic precipitation of the alkaline earth ions using the electrolysis electrodes, i.e., to perform them in sequential measuring cycles and electrolysis cycles.

[0023] The control device of the water treatment plant is preferably designed to control the measuring device in such a way that the water provided at the outlet of the softening device is fed to the measuring device at the inlet of the measuring device and the conductivity (Lf a) of the water supplied at the inlet is measured with one conductivity sensor or with the first conductivity sensor and then the water is electrolyzed by applying a direct voltage to the electrolysis electrodes and finally the conductivity (Lft) of the electrolyzed water is measured at the outlet of the measuring device by means of one conductivity sensor or with the second conductivity sensor and in particular a change in conductivity caused by the electrolysis of the water (ALf = |Lfi> - Lf a|) of the water between the inlet and the outlet of the measuring device is detected. The presence of alkaline earth ions can be concluded from the detected change in conductivity (ALf), in particular if the detected change in conductivity (ALf) is above a predetermined limit. The presence of alkaline earth ions in the water supplied to the measuring device indicates an incipient hardness breakthrough in the water softening device, which is why, preferably when a change in conductivity (ALf) above the predetermined limit is detected, a regeneration process for regenerating the water softening device is initiated and / or a signal is output by the signaling device which indicates a required regeneration of the water softening device and in particular a required regeneration or a required replacement of the ion exchanger.

[0024] The control device can also control the measuring device in such a way that the original conductivity (Lf a ) of the water provided at the outlet of the softening device, in particular with a first conductivity sensor, and then the alkaline earth ions possibly contained therein in the event of a hardness breakthrough are at least partially precipitated in the measuring device by applying a direct voltage to the electrolysis electrodes and the conductivity (Lfi,) of the water during and / or after the precipitation of the alkaline earth ions is measured, in particular with a second conductivity sensor. From the difference between the measured conductivities, the control device then calculates the change in conductivity (ALf = Lfi, - Lf a ) and a hardness breakthrough is concluded if the value of ALf is above the specified limit.

[0025] If the control device detects a hardness breakthrough, it or the signaling device can output a signal and / or control the regeneration device to initiate a regeneration process to regenerate the softening device. An operator of the water treatment system is thus informed of a hardness breakthrough and, if necessary, instructed to either manually initiate a regeneration process to regenerate the softening device or to replace the replaceable ion exchanger, which can be designed, for example, as a replaceable cartridge.

[0026] The control device or the signaling device is expediently configured to output a signal when, during the precipitation of the alkaline earth ions, in particular over a predetermined period (Δt) of precipitation, a change in the measured conductivity compared to the original conductivity of the water provided at the outlet of the water softener is detected, in particular when the change in conductivity (ALf) detected over the predetermined period (Δt) exceeds a predetermined limit value. The signal can be an acoustic signal, e.g., a warning tone, and / or an optical signal, e.g., a warning light, and / or a textual and / or symbolic representation of a warning on a display of the control device.The control device or the signaling device can also be designed so that the operation of the softening device is stopped and the outlet of the softening device is closed when a hardness breakthrough is detected, for example by closing a valve at the outlet to prevent the provision of insufficiently softened water at the outlet.

[0027] Preferably, the control device is configured to directly initiate a regeneration process by means of the regeneration device depending on the detected change in conductivity (ALf), particularly when a predetermined limit is exceeded. This enables fully automatic regeneration of the softening device without the operator of the water treatment system having to intervene manually in the event of a hardness breakthrough.

[0028] In a preferred embodiment of the water treatment system according to the invention, the softening device is designed as a multiple or double system with a first softening device and at least one second softening device, which can be operated in oscillating mode, wherein in the oscillating mode the first softening device is alternately operated in a softening or desalination mode, while the second softening device is operated in a regeneration mode in which regeneration takes place, and vice versa. This oscillating operation of a first and a second softening device makes it possible to change the oscillating mode in the event of a hardness breakthrough detected by the measuring device during the softening or desalination mode of one softening device and, for example, to initiate the regeneration mode in the first softening device while the second softening device is switched to the softening mode.This ensures that the water treatment plant can provide partially or fully softened water at any time.

[0029] In the method according to the invention for operating a water treatment plant, which comprises a raw water inlet for providing raw water, a softening device with an inlet and an outlet, a regeneration device for regenerating the softening device and / or a signaling device which, when the softening device is exhausted, generates a signal to indicate a required regeneration of the softening device and in particular a required regeneration or a required replacement of an ion exchanger, wherein the softening device generates softened water from the raw water and provides it at the outlet and a control device is provided which is coupled to the regeneration device and / or the signaling device in order to regenerate the softening device in case of exhaustion and / or to output or display the signal generated by the signaling device,and at least one measuring device connected to the softening device and the control device is provided for detecting a hardness breakthrough in the water provided at the outlet of the softening device, and the water provided at the outlet of the softening device is fed at least temporarily or continuously to the measuring device, and an electrolytic precipitation of the alkaline earth ions in the supplied water is carried out at least temporarily in the measuring device, wherein at least before and during the electrolytic precipitation of the alkaline earth ions, the electrical conductivity of the supplied water is detected and compared, in particular by forming the difference (ALF = |Lfi> - Lf, a |) the conductivity recorded before electrolytic precipitation (Lf a ) and the conductivity (Lfb) recorded during or after precipitation.

[0030] Raw water containing alkaline earth ions, in particular calcium and / or magnesium ions, as well as hydrogen carbonate and / or carbonate ions, is fed to the inlet of the softening device via the raw water inlet.

[0031] In the method, the electrical conductivity of the water supplied to the measuring device is preferably measured at an inlet of the measuring device and an outlet of the measuring device. The measuring device preferably comprises an electrolysis cell, arranged in particular between the inlet and the outlet of the measuring device, having at least two electrolysis electrodes. The water supplied to the measuring device is electrolyzed in the electrolysis cell in order to at least partially, preferably completely, precipitate any alkaline earth ions present in the water in the event of a hardness breakthrough in the softening device. For this purpose, the electrolysis cell comprises at least two electrolysis electrodes, which are supplied with direct voltage for the electrolytic precipitation of the alkaline earth ions.The measuring device preferably contains at least one conductivity sensor with two measuring electrodes, which are supplied with alternating voltage to measure the conductivity of the water supplied to the measuring device. In order to measure the conductivity of the water supplied to the measuring device both at the inlet and at the outlet of the electrolysis cell, the measuring device preferably contains a first conductivity sensor upstream of or at the inlet and a second conductivity sensor downstream of or at the outlet of the measuring device.

[0032] This allows, on the one hand, the method according to the invention to reliably detect a hardness breakthrough when a change in conductivity (ALf = Lfi> - Lf a) of the supplied water between the inlet and the outlet of the measuring device and, on the other hand, the effects of an at least partially already occurred hardness breakthrough are at least partially neutralized by at least partially, preferably completely, precipitating the alkaline earth ions of the supplied water. From the amount of the change in conductivity caused by the precipitation of the alkaline earth ions (ALf = Lfi, - Lf a ) can be used to determine the concentration of alkaline earth ions in the water supplied to the measuring device and thus the hardness slip of the softening device, in particular the ion exchanger.

[0033] In order to detect an incipient hardness breakthrough in good time, the water provided at the outlet of the softening device is preferably passed continuously from the inlet to the outlet through the measuring device and the conductivity of the water passed through is recorded at the inlet and at the outlet. If the conductivity changes between the inlet and the outlet of the measuring device, it can be concluded that a hardness breakthrough has already occurred, at least in part, or is just beginning. A regeneration process to regenerate the softening device can be initiated via the regeneration device and / or a signal can be output by the signaling device, in particular if a predetermined difference limit of the change in conductivity recorded by the measuring device is exceeded. If a difference limit is exceeded, the water treatment plant orThe water softener must also be switched off to prevent non-softened water from being supplied to a consumer.

[0034] In the process according to the invention, the change in conductivity (ALf = Lfi - Lf) caused by the precipitation of alkaline earth ions is preferably determined as a function of the change in conductivity (ALf = Lfi - Lf a ) a regeneration process is automatically initiated to regenerate the water softener and / or a signal is issued when the difference in conductivity caused by the precipitation of alkaline earth ions (ALf = Lfi - Lf a) exceeds a predefined difference limit AG. This ensures that, if an incipient or already completed hardness breakthrough is detected, the softening device is regenerated in good time before a harmful increase in the hardness of the water supplied by the water treatment plant to a consumer occurs. In the case of an incipient hardness breakthrough, which occurs particularly with a low difference in conductivity (ALf = Lfi - Lf a ) of the water supplied to the measuring device between the inlet and the outlet of the measuring device shows that the water hardness of the water provided by the water treatment plant at the outlet of the measuring device is low and is ideally at or close to zero, due to the electrolytic precipitation of the alkaline earth ions in the electrolysis cell of the measuring device.

[0035] These and other advantages and applications as well as preferred features of the water treatment system and method according to the invention will become apparent from the exemplary embodiments of the invention described below with reference to the drawings. In the drawings:

[0036] Fig. 1: a schematic representation of a first embodiment of a water treatment plant according to the invention with a softening device and a measuring device for detecting a hardness breakthrough in the softening device;

[0037] Fig. 2: schematic representations of various embodiments of a conductometric measuring device for detecting a hardness breakthrough in a softening device, which can be used in the water treatment plant according to the invention and the method according to the invention;

[0038] Fig- 3: a diagram of the time course of the in one of the measuring devices of

[0039] Figure 2 shows the electrical conductivity of a water sample before, during and after electrolytic precipitation of alkaline earth ions;

[0040] Fig. 4: a schematic representation of a second embodiment of a water treatment plant according to the invention with a softening device and a measuring device for detecting a hardness breakthrough in the softening device;

[0041] Fig. 5: a diagram of the time course of the electrical conductivity of the water supplied to the measuring device of the water treatment plant of Figure 1, as recorded in the method according to the invention, with a hardness breakthrough in the softening device;

[0042] Fig. 6A: a schematic representation of another embodiment of a

[0043] Electrolysis cell of the measuring device for detecting a hardness breakthrough in a water softening device,

[0044] Fig. 6B: a representation of the time course of the electrical conductivity of the water supplied to the electrolysis cell of Figure 6A (soft water from the softening device) before the electrolysis cell (Lf a ) and after the electrolysis cell (Lfi,) as well as the titrimetrically determined hardness (H) of the supplied water in the event of a hardness breakthrough in the softening device (Figure 6B);

[0045] Figure 1 shows a first embodiment of a water treatment system according to the invention with a softening device 12, wherein the water treatment system 10 comprises a raw water inlet 11 connected to the softening device 12 via a distributor 24 for providing raw water R, a control device 14 and at least one conductometric measuring device 15. The measuring device

[0046] 15 is arranged downstream of the distributor 24 and is connected to the distributor 24 at an inlet 15a of the measuring device 15 via a connecting line 20. The control device 14 is coupled to the distributor 24 and the measuring device 15 in order to control them. The control device 14 controls, in particular, the volume flows of the water supplied from the raw water inlet 11 into the softening device 12 and of the water W softened therein to the connecting line 20.

[0047] The water softening device 12 is designed as a dual system and comprises a first water softening device 12a and a second water softening device 12b, which operate in alternating mode. The first and second water softening devices 12a, 12b each contain an ion exchanger 13, each of which is arranged in an ion exchange container 8.

[0048] The ion exchange container 8 of the first and second softening devices 12a, 12b each comprises an inlet 11a and an outlet 11b, wherein the inlet 11a is connected via a supply line 7 and the outlet 11b is connected via a discharge line 7' to the distributor

[0049] 24. For the regeneration of the ion exchanger 13 of the softening devices 12a, 12b, the water treatment system further comprises a regeneration device 18, which has a regeneration tank 9 in which an aqueous regeneration solution, in particular a sodium chloride solution, is stored. When the ion exchanger 13 of one of the two softening devices 12a, 12b is exhausted, the regeneration solution is passed into and through the ion exchange tank 8 of the respective softening device 12a or 12b in a regeneration mode, whereby the calcium and magnesium ions absorbed in the ion exchanger 13 during the softening of the raw water R are replaced by sodium ions. The used regeneration solution is discharged during the regeneration mode via a discharge line connected to the distributor 24.

[0050] 25 into a channel 19. While one of the two softening devices 12a or 12b is in regeneration mode, the other softening device 12b or 12a can operate in operating mode, in which raw water R is fed into the ion exchange tank 8 via the distributor 24 and is (at least largely) completely softened therein by exchanging the hardness-forming calcium and magnesium ions for sodium ions from the ion exchanger 13. The softened water W is provided in operating mode at the outlet 11b of the respective softening device 12a, 12b and is fed via the drain line 7' to the distributor 24, which feeds the softened water W via the connecting line 20, on the one hand, to the inlet 15a of the measuring device 15 and, on the other hand, into a consumer line 21 connected to the connecting line 20.The volume flow of the softened water W, which is fed as a partial flow to the measuring device 15, is expediently substantially smaller than the total volume flow of the softened water W introduced into the connecting line 20. The majority of the total volume flow of the softened water W is introduced into the consumer line 21, which is connected to a consumer 22. The consumer 22 can be, for example, the drinking water installation of a household or a business, or a water appliance or a downstream water treatment system (e.g., a reverse osmosis system), to which the softened water W is fed directly for further treatment.

[0051] The softened water W is supplied to the measuring device 15 during operation of the water treatment system 10 continuously or intermittently in predetermined measuring cycles. The measuring cycles can be performed, in particular, for the first time upon reaching a predicted depletion level of the ion exchanger 13 of the softening device 12, e.g., after reaching a predicted depletion level of 80%, and thereafter regularly or continuously until complete depletion, in order to detect an imminent hardness breakthrough.The degree of exhaustion of the softening device 12 depends on the total (maximum) exchange capacity of the ion exchanger 13 as well as the hardness of the raw water R and the total volume of the raw water that has flowed through the softening device 12 and can therefore be predicted from the known data of the exchange capacity and the volume flow as well as the hardness H of the raw water R that can be measured by means of the measuring device 15.

[0052] After completion of a measurement in the measuring device, the water W supplied to the measuring device 15 is discharged through the outlet 15b of the measuring device into a drain line 26 which can be closed with a valve vl and which discharges the water into a channel 19.

[0053] The measuring device 15 comprises an electrolysis cell 1, which has a container 5 in which the inlet 15a and an outlet 15b are provided. The softened water W supplied from the connecting line 20 is introduced into the container 5 of the measuring device 15 via the inlet 15a and conducted through the container 5 to the outlet 15b. For complete emptying of the container 5, the container 5 has a drain 15c, preferably at the bottom. The measuring device 15 further comprises a first conductivity sensor 2a at the inlet 15a and a second conductivity sensor 2b at the outlet 15b, as well as two electrolysis electrodes A, K arranged opposite one another in the container 5, wherein the electrolysis electrodes are connected to a DC voltage source and one electrolysis electrode is designed as the anode A and the other electrolysis electrodes as the cathode K.The container 5 and the electrolysis electrodes A, K arranged therein, to which a direct voltage is applied from the direct voltage source, form the electrolysis cell 1. The electrolysis electrodes A, K are preferably designed as flat electrodes which are arranged at a distance and parallel to one another in the container 5, so that the water W conducted through the container 5 can flow between the electrolysis electrodes A, K.

[0054] The measuring device 15 is controlled by the control device 14. The control device 14 controls, in particular, the supply of direct current to the electrolysis electrodes A, K during predetermined measuring cycles or electrolysis cycles or continuously during operation of the water treatment plant. Furthermore, the detection of the electrical conductivity of the water W supplied via the connecting line 20 at the inlet 15a and at the outlet 15b of the measuring device 15 by means of the two conductivity sensors 2a, 2b is also controlled by the control device 14. Each of the two conductivity sensors 2a, 2b comprises at least one pair of electrodes 3, to which an alternating electrical voltage is applied in defined measuring cycles or continuously during operation of the water treatment plant, and the current strength is measured in order to detect the conductivity of the supplied water W. By means of a temperature sensor, which can be, for example,can be arranged in the electrolysis cell 1 or can also be integrated in at least one of the conductivity sensors 2a, 2b, the temperature of the water is expediently recorded and when determining the conductivity a temperature correction to a standard temperature of, for example, 25°C is carried out by means of a correction factor.

[0055] Figure 2 shows further embodiments of the measuring device 15 in which the two conductivity sensors 2a, 2b are integrated into the container 5 of the electrolysis cell 1, wherein the first conductivity sensor 2a is arranged upstream of the electrolysis electrodes A, K at the inlet 15a and the second conductivity sensor 2b is arranged downstream of the electrolysis electrodes A, K at the outlet 15b. As in the embodiment of the measuring device 15 of Figure 1, the two electrolysis electrodes A, K are connected to a DC voltage source, and the electrode pair 3 of the two conductivity sensors 2a, 2b is each connected to an AC voltage source, with which the measuring electrodes of the electrode pair 3 can be supplied with an AC electrical voltage of a predetermined frequency.In the examples shown in Figure 2, the two measuring electrodes of each conductivity sensor 2a, 2b are each designed as rod electrodes whose longitudinal axis runs parallel to the plane of the two electrolysis electrodes A, K designed as flat electrodes.

[0056] The embodiment of the measuring device 15 shown in Figure 2A comprises two electrolysis electrodes A, K designed as flat electrodes, which are arranged parallel and spaced apart from one another in the electrolysis cell and opposite one another. The electrolysis electrodes comprise at least one anode, preferably made of platinized titanium sheet or a platinized titanium grid or a graphite film, and at least one cathode, preferably made of steel or titanium or graphite foil. The anode and cathode are particularly preferably made of the same material, in particular each made of platinized titanium.

[0057] In the embodiment of the measuring device 15 shown in Figure 2B, several electrolysis electrodes A, K are arranged in the electrolysis cell 1. In particular, the electrolysis cell 1 of the embodiment of Figure 2B contains a cascade of electrolysis electrodes in the sequence of an outer anode A, a first cathode K, an inner anode A, a second cathode K, and a further outer anode A, as can be seen from Figure 2B. A cation exchange membrane KAT is arranged between each corresponding electrolysis electrode A, K.Due to the plurality of electrolysis electrodes A, K and the cation exchange membrane KAT arranged between corresponding electrolysis electrodes A, K, the efficiency of the electrolytic precipitation of the alkaline earth ions is increased by the precipitation in the form of alkaline earth carbonates at the cathodes K (in particular due to a larger electrode area), whereby a faster precipitation of the alkaline earth ions is achieved when flowing through the water W.

[0058] Both the embodiments of the measuring device 15 shown in Figure 1 and Figure 2 can be used in a water treatment plant 10 according to the invention for detecting a hardness breakthrough in the softening device 12, wherein the water W preferably flows continuously in flow-through operation or only in the time-defined measuring cycles continuously from the inlet 15a to the outlet 15b through the electrolysis cell 1 and the electrical conductivity of the softened water W is measured before and after the electrolysis cell 1. For this purpose, the conductivity Lf a The water flow at the inlet 15a and the conductivity Lfi> at the outlet 15b of the measuring device 15 are continuously measured in a measuring cycle using the two conductivity sensors 2a, 2b. The control device 14 calculates the difference ALf = Lfi> - Lf from the measured values ​​of the two conductivity sensors 2a, 2b. aand compares the amount of the calculated difference in electrical conductivity |ALf] with a predetermined limit value AG. If the amount of the determined difference in electrical conductivity |ALf| exceeds this limit value AG, it can be concluded that a certain amount of hardness-forming alkaline earth ions is present in the water, indicating a hardness breakthrough in the softening device 12.

[0059] Furthermore, the measuring device 15 can detect a change in the electrical conductivity of the supplied water W, which is based, for example, on a change in the water quality of the raw water R supplied to the water treatment plant 10 via the raw water inlet 11. For this purpose, untreated raw water R can be supplied to the measuring device via a bypass line (not shown in Figure 1), the conductivity of which is measured with at least one of the two conductivity sensors 2a, 2b. If the determined conductivity of the raw water R changes, a different composition and, in particular, a changed hardness of the raw water R can be inferred.

[0060] Figure 4 shows a second embodiment of a water treatment system 10 according to the invention with a softening device 12, which essentially corresponds to the first embodiment of Figure 1. In contrast to the first embodiment of Figure 1, in the second embodiment of Figure 4, an additional return line 27 is provided, which connects the drain line 26 to the consumer line 21 and opens into the consumer line 21 at a connection point 28. The water W, whose conductivity has been measured in the measuring device 15, can be introduced into the consumer line 21 through the return line 27 in order to supply the water W to the consumer 22, whereby the loss of softened water W can be reduced.A valve v2 is provided in the return line 27 for opening and closing the return line 27, and a further valve v3 is arranged upstream of the connection point 28 in the consumer line 21 for opening and closing the consumer line 21. By closing the valves v1 and v3 and opening the valve v2, it is possible to direct only the partial flow of water W that has been passed through the measuring device 15 to the consumer 22.

[0061] An embodiment of the method according to the invention that can be carried out in the water treatment plant 10 of Figure 1 is explained below:

[0062] To commission the water treatment system 10, raw water R is first fed through the raw water inlet 11 via the distributor 24 and the inlet line 7 into the ion exchange tank 8 of the first softening device 12a. In the operating mode (softening mode) of the first softening device 12a, the calcium and magnesium ions in the raw water R are exchanged for sodium ions from the ion exchanger 13, thereby producing softened water W, which is introduced at the outlet 11b of the connecting line 20 via the drain line 7' and the distributor 24. The softened water W is fed via the connecting line 20 and the connected consumer line 21 to a consumer 22, which is thus supplied with softened water W.

[0063] The second softening device 12b can be operated in regeneration mode during the operating mode of the first softening device 12a, in which the aqueous regeneration solution, in particular a sodium chloride solution, stored in the regeneration tank 9 of the regeneration device 18 is supplied to the second softening device 12b via the regeneration line 17 and the distributor 24. In the regeneration mode, the regeneration solution is passed through the ion exchanger 13 in the ion exchange tank 8 of the second softening device 12b in order to regenerate this ion exchanger 13 by exchanging the calcium and magnesium ions bound therein for sodium ions of the regeneration solution. The regeneration solution used in this process is passed via the drain line 7' and the distributor 24 into the drain line 25, which leads to a channel 19.

[0064] During operation of the first softening device 12a in operating mode, a partial flow of the softened water W provided at the outlet 11b of the first softening device 12a is conducted via the connecting line 20 to the measuring device 15. The partial flow of water W supplied to the measuring device 15 flows through the container 5 of the measuring device 15 from the inlet 15a to the outlet 15b and, with the valve vl open, is discharged into a channel 19 via the drain line 26. At least in defined measuring cycles (or continuously during operation of the water treatment system), the electrolysis electrodes A, K of the measuring device 15 are subjected to a direct electrical voltage while the water W flows through the container 5.At the same time, the electrical conductivity of the water W flowing through the container 5 is measured at the inlet 15a of the measuring device 15 by the first conductivity sensor 2a and at the outlet 15b by the second conductivity sensor 2b. The measured values ​​Lf are recorded. a of the first conductivity sensor 2a and Lfi> of the second conductivity sensor 2b are fed to the control device 14. In the control device 14, the difference between the two measured values ​​Lf a and Lfi> of the electrical conductivity of the first conductivity sensor 2a and the second conductivity sensor 2b are calculated and compared with a predetermined limit value AG. If, during this comparison, it is determined that the difference in the electrical conductivity ALf = |Lfa - Lfb| of the water W flowing through the container 5 is greater than the predetermined limit value AG, i.e., if

[0065] If ALf = |Lfa - Lfb| > AG, it is concluded that a hardness breakthrough has occurred in the first softening device 12a, and the control device 14 then initiates a regeneration process in the first softening device 12a. At the same time, a signal can be displayed via a signaling device indicating the hardness breakthrough of the first softening device 12a detected by the control device 14.In order to be able to provide softened water W with the wastewater treatment plant 10 in the consumer line 21 during the initiated regeneration mode of the first softening device 12a, the second softening device 12b is switched to the operating mode at the same time as the first softening device 12a is switched from the operating mode to the regeneration mode, in which the second softening device 12b produces softened water W from the raw water R coming from the raw water inlet 11 and feeds it via the drain line 7' and the distributor 24 into the connecting line 20 and the consumer line 21 connected thereto. While the second softening device 12a is operated in the operating mode (softening mode), the first softening device 12a is in the regeneration mode, in which the regeneration solution from the regeneration device 18 is fed into the ion exchange container 8 in order to regenerate the ion exchanger 13 located therein.During operation of the second softening device 12b in the operating mode (softening operation), a partial flow of the softened water W fed into the connecting line 20 by the second softening device 12b is again directed to the measuring device 15 to detect a hardness breakthrough in the second softening device 12b. This occurs in the same manner as in the operating mode of the first softening device 12a.

[0066] After the measuring device 15 detects a hardness breakthrough in one of the two softening devices 12a or 12b, the container 5 of the measuring device 15 is emptied by discharging the water contained therein through the outlet 15b and, with the valve vl open, through the drain line 26 and / or through the open drain 15c into the channel 19. The measuring device 15 is then ready for a subsequent measuring cycle. When the subsequent measuring cycle is initiated, the container 5 is automatically flushed by the flowing water.

[0067] Figure 5 shows, as an example, the time course of the measured values ​​of the electrical conductivity Lf recorded by the two conductivity sensors 2a and 2b aand Lfi> during operation of the water treatment device 10 of Figure 1, wherein initially the first softening device 12b is operated in the operating mode while the second softening device 12b is regenerated in the regeneration mode and a partial flow of the softened water W provided at the outlet 11b of the first softening device 12b is fed to the measuring device 15 in order to measure the electrical conductivity Lf with the first conductivity sensor 2a aof the water W at the inlet 15a and with the second conductivity sensor 2b the electrical conductivity Lfi> of the water W at the outlet 15b of the measuring device. While the electrical conductivity of the water W is being measured at the inlet 15a and at the outlet 15b of the measuring device, the electrolysis electrodes A, K are connected to a DC voltage source so that any alkaline earth ions contained in the water are precipitated as the water flows through the electrolysis cell 1 over a predetermined period of time Δt of precipitation, which depends on the flow velocity and the length of the electrolysis cell 1 in the flow direction.

[0068] At a time point of t ~ 18 minutes, a drop in the conductivity Lfi> at outlet 15b is observed in Figure 5, indicating the presence of alkaline earth ions in the softened water W and therefore a hardness breakthrough. The conductivity Lfi> at outlet 15b continues to decrease until a time point of t ~ 23 minutes and asymptotically approaches a minimum. The magnitude of the difference in electrical conductivity Lf aat the inlet 15a and the conductivity Lfi> at the outlet 15b increases accordingly and exceeds a predetermined limit value AG at t ~ 22 minutes, from which it is concluded that there has been a hardness breakthrough and that the exchange capacity of the first softening devices 12a has been exhausted. At t = 23 minutes, the second softening device 12b is switched to the operating mode, so that softened water W is now provided by the second softening device 12b and fed into the connecting line 20, which is why the measured value of the conductivity Lfi> at the outlet 15b of the measuring device 15 approaches the original measured value before the hardness breakthrough was detected and has returned to the original measured value of 730 pS / cm at t ~ 24 minutes.

[0069] Figure 6A shows a further embodiment of an electrolysis cell 1 of the measuring device 15, which was used in an experiment to detect a hardness breakthrough in a water softening device. The electrolysis cell 1 comprises a container 5 with a length L, an inlet 15a and an outlet 15b, as well as an anode A arranged centrally in the container 5 and two cathodes K arranged at a predetermined distance d therefrom and running parallel to the anode A. The length L of the container in the example is 6.7 cm and the volume of the container 5 is 8.7 ml. The distance d between the cathodes K and the anode A is 0.2 cm. The water provided by a water softening device (soft water) is passed through the container 5 at a predetermined volume flow of preferably 0.6 l / h to 1.4 l / h in a flow direction v along the length L.A direct voltage of preferably less than 12 V, in particular in the range of 6 to 10 V, is applied to the electrolysis electrodes A, K. The electrolysis current is expediently between 200 and 1000 mA, in particular between 400 and 700 mA. By means of conductivity sensors not shown in Figure 6A, the electrical conductivity of the water supplied to the electrolysis cell 1 (soft water provided by the softening device) is measured at the inlet 15a of the electrolysis cell (Lf. a ) and at the outlet 15b of the electrolytic cell (Lfi,).

[0070] Figure 6B shows the temporal progression of the electrical conductivity measured with the two conductivity sensors as well as the titrimetrically determined hardness H of the water supplied to the electrolysis cell 1 of Figure 6A during a hardness breakthrough in the water softener. The hardness (H) of the supplied water was determined titrimetrically. At time 10:50, a direct current of 700 mA was generated at the electrodes A, K ("current on"). Figure 6B shows that from time 10:55, the hardness H of the water increases from an initial 0°dH to approximately 22°dH within approximately 30 minutes due to a hardness breakthrough in the water softener. Already at the onset of the hardness breakthrough at time 10:55, a reduction in the conductivity Lfi> can be observed at the outlet 15b of the electrolysis cell 1, which drops to a conductivity minimum within approximately 30 minutes. This indicates that the hardness breakthrough has occurred.At approximately 11:38 the electrolysis current was switched off (“current off”), which is why the conductivity value at the output 15b of the electrolysis cell 1 rose again to the original value, which is approximately equal to the conductivity Lf. a at the inlet 15a of the electrolysis cell 1.

[0071] The invention is not limited to the exemplary embodiments illustrated in the drawings. For example, a desalination device, such as a reverse osmosis system or a desalination device with a cation and anion exchanger, can be used in addition to the water softening device 12.

[0072] Furthermore, in addition to or instead of the regeneration device 18, a signaling device can also be provided which, upon detected exhaustion of the water softening device, generates a signal to indicate the need for regeneration of the water softening device. For this purpose, the signaling device is expediently coupled to the control device 14 and forwards the signal to the control device 14, which then emits an acoustic warning signal, e.g., a warning tone, or displays a visual warning signal. Such a signaling device is expedient, for example, if the water softening device does not contain a regenerable ion exchanger and / or no regeneration device for regenerating the water softening device, but rather (at least) one replaceable ion exchanger, e.g., in the form of an ion exchanger cartridge arranged replaceably in the water softening device.A signal generated by the signaling device upon detection of a hardness breakthrough indicates to an operator of the wastewater treatment plant 10 that the ion exchanger is exhausted and must be replaced with a new ion exchanger, in particular with a new ion exchanger cartridge. It is also possible for the signaling device or the control device to automatically shut down the operation of the entire water treatment plant or the softening device upon detection of a hardness breakthrough, or at least to stop the supply of water at the outlet by closing the outlet of the softening device to prevent the water treatment plant from supplying non-softened water at the outlet and directing it to a consumer connected to the water treatment plant.

Claims

Claims action plan (10) comprehensive - a raw water inlet (11) for the provision of raw water (R), - a water softening device (12) with an inlet (11a) connected to the raw water inlet (11) and an outlet (11b), wherein the water softening device (12) produces softened water (W) from the raw water (R) and provides it at the outlet (11b) and in particular includes at least one regenerable or replaceable ion exchanger (13), - a regeneration device (18) for regenerating the water softening device (12), in particular the ion exchanger (13) of the water softening device (12), and / or a signaling device which, when the water softening device (12) is exhausted, generates a signal to indicate a required regeneration of the water softening device (12) and in particular a required regeneration or replacement of the ion exchanger (13), or to shut down the water treatment plant (10), - a control device (14) which is coupled to the regeneration device (18) and / or the signaling device in order to regenerate the softening device (12) in the event of exhaustion and / or to output or display the signal generated by the signaling device, and - at least one measuring device (15) connected to the softening device (12) and the control unit (14) for detecting a hardness breakthrough in the water (W) provided at the outlet (11b) of the softening device (12), characterized in that the measuring device (15) comprises at least one conductivity sensor (2; 2a, 2b) and an electrolysis cell (1) with at least two electrolysis electrodes (A, K).

2. Water treatment plant according to claim 1, characterized in that the electrolysis electrodes (A, K) are designed as flat electrodes arranged opposite each other in the electrolysis cell (1), wherein the electrolysis electrodes (A, K) can be connected to or are connected to a DC voltage source.

3. Water treatment plant according to one of claims 1 or 2, characterized in that at least one conductivity sensor (2; 2a, 2b) is integrated in the electrolysis cell (1) or that a first conductivity sensor (2a) is arranged upstream and a second conductivity sensor (2b) is arranged downstream of the electrolysis cell (1).

4. Water treatment plant according to one of the preceding claims, characterized in that at least one conductivity sensor (2) is integrated in the electrolysis cell (1), wherein the integrated conductivity sensor (2) comprises at least one electrode pair (3) with two measuring electrodes, in particular designed as rod electrodes, wherein the measuring electrodes can be connected to or are connected to an alternating voltage source.

5. Water treatment plant according to one of the preceding claims, characterized in that a first conductivity sensor (2a) and a second conductivity sensor (2b) are integrated in the electrolysis cell (1), wherein the first conductivity sensor (2a) and the second conductivity sensor (2b) each comprise a pair of electrodes (3) with two measuring electrodes, wherein the measuring electrodes can be connected to or are connected to an alternating voltage source and are preferably arranged between the opposing electrolysis electrodes (A, K) of the electrolysis cell (1) and are preferably designed as rod electrodes. Water treatment plant according to one of the preceding claims, characterized in that the measuring device (15) comprises an inlet (15a) to which water from the water softening device (12) is supplied to the measuring device, and an outlet (15b), wherein a first conductivity sensor (2a) is arranged at the inlet (15a) and a second conductivity sensor (2b) is arranged at the outlet (15b), and the electrolysis cell (1) is arranged between the inlet (15a) and the outlet (15a). Water treatment plant according to claim 6, wherein the control device (14) controls the measuring device (15) such that water (W), which is provided at the outlet (11b) of the water softening device (12), is supplied to the measuring device (15) at the inlet (15a) and the conductivity (Lf) is measured. a) of the water (W) supplied at the inlet (15a) is detected by the first conductivity sensor (2a), and then the water (W) supplied to the measuring device (15) is electrolyzed by applying a DC voltage to the electrolysis electrodes (A, K), and finally the conductivity (Lfi) of the electrolyzed water (W) at the outlet (15b) of the measuring device (15) is measured by means of the second conductivity sensor (2b), and in particular a change in conductivity caused by the electrolysis of the water (W) (ALf = |Lfi - Lf a |) of the water (W) between the inlet (15a) and the outlet (15b) of the measuring device (15) is detected. Water treatment plant according to one of the preceding claims, wherein the control device (14) controls the measuring device (15) such that the original conductivity (Lf) is initially determined. a) of the water (W) provided at the outlet (11b) of the softening device (12) is detected and then the alkaline earth ions contained in the water (W) supplied to the measuring device (15) are at least partially precipitated in the measuring device (15) by applying a DC voltage to the electrolysis electrodes (A, K) and the conductivity (Lfi,) of the water (W) supplied to the measuring device (15) is measured during and / or after the precipitation of the alkaline earth ions. Water treatment plant according to claim 7 or 8, characterized in that the control device (14) outputs a signal and / or controls the regeneration device (18) to initiate a regeneration process for regenerating the softening device (12) when a detected difference (ALf = |Lfi>- Lf a |) between the original conductivity (Lf a) and the conductivity (Lft) of the water (W) supplied to the measuring device (15), measured after or during the precipitation of the alkaline earth ions, exceeds a predetermined limit value. Water treatment plant according to one of claims 7 to 9, characterized in that the control device (14) outputs a signal when, over a predetermined period (At) of precipitation, a change in the measured conductivity (ALf) is detected compared to the original conductivity of the water (W) supplied to the measuring device (15), in particular when the change in conductivity (ALf) detected over the predetermined period (At) exceeds a predetermined limit value (AG).A water treatment plant according to any one of claims 7 to 10, wherein the control device (14) is configured to initiate a regeneration process of the regeneration device (18) depending on the detected change in conductivity (ALf), in particular when a predetermined limit value (AG) of the detected change in conductivity (ALf) is exceeded. A method for operating a water treatment plant (10) is also included. - a raw water inlet (11) for the provision of raw water (R) containing alkaline earth ions, in particular calcium and / or magnesium ions, as well as hydrogen carbonate and / or carbonate ions, - a water softening device (12) with an inlet (11a) connected to the raw water inlet (11) and an outlet (11b), wherein the water softening device (12) produces softened water (W) from the raw water (R) and provides it at the outlet (11b) and in particular includes at least one regenerable or replaceable ion exchanger (13), - a regeneration device (18) for regenerating the water softening device (12), in particular the ion exchanger (13), and / or a signaling device which, when the water softening device (12) is exhausted, generates a signal to indicate a required regeneration of the water softening device (12) and in particular a required regeneration or replacement of the ion exchanger (13) or to stop the supply of water at the outlet (11b), - a control device (14) which is coupled to the regeneration device (18) and / or the signaling device in order to regenerate the softening device (12) in the event of exhaustion and / or to output or display the signal generated by the signaling device, - at least one measuring device (15) connected to the water softening device (12) and the control unit (14) for detecting a hardness breakthrough in the water (W) supplied at the outlet (11b) of the water softening device (12), characterized in that water (W) supplied at the outlet (11b) of the water softening device (12) is supplied to the measuring device (15) at least temporarily, preferably continuously, and an electrolytic precipitation of the alkaline earth ions in the supplied water (W) is carried out in the measuring device (15), wherein the electrical conductivity of the supplied water (W) is detected and compared at least before and during the electrolytic precipitation of the alkaline earth ions, in particular by calculating the difference (ALF = |Lfi> - Lfi>). a |) the conductivity measured before electrolytic precipitation (Lf a ) and the conductivity (Lfb) measured during or after the felling.

13. Method according to claim 12, characterized in that the electrical conductivity of the water (W) supplied to the measuring device (15) is detected at an inlet (15a) of the measuring device (15) and an outlet (15b) of the measuring device (15).

14. Method according to one of claims 12 to 13, characterized in that the measuring device (15) comprises an electrolysis cell (1) with at least two electrolysis electrodes (A, K) arranged in particular between the inlet (15a) and the outlet (15b) of the measuring device (15), wherein the water (W) supplied to the measuring device (15) is electrolyzed in the electrolysis cell (1) in order to at least partially precipitate the alkaline earth ions in the supplied water (W).

15. Method according to one of claims 12 to 14, characterized in that in the measuring device (15) a partial or at least substantially complete precipitation of the alkaline earth ions in the supplied water (W) takes place and that the change in conductivity (ALf = Lfi> - Lf) caused by the precipitation of the alkaline earth ions a ) of the supplied water (W) is recorded.

16. Method according to one of claims 12 to 15, characterized in that the measuring device (15) comprises an electrolysis cell (1) which contains at least two electrolysis electrodes (A, K) which are subjected to a direct voltage for the electrolytic precipitation of the alkaline earth ions in the water supplied to the measuring device (15).

17. Method according to claim 16, characterized in that the measuring device (15) includes at least one conductivity sensor (2) with two measuring electrodes, which are subjected to alternating voltage to detect the conductivity of the water supplied to the measuring device (15), wherein the measuring device (15) preferably includes a first conductivity sensor (2a) and a second conductivity sensor (2b) each with two measuring electrodes. A method according to any one of claims 12 to 17, characterized in that water (W) which is provided at the outlet (11b) of the softening device (12) is continuously passed from an inlet (15a) to an outlet (15b) through the measuring device (15) and the conductivity of the water passed through is recorded at the inlet (15a) and at the outlet (15b) and, in the event of a change in conductivity (ALf = Lfi - Lf a) between the inlet (15a) and the outlet (15b) a regeneration process for regenerating the softening device (12) is initiated and / or a signal is output or the water treatment system is switched off. Method according to claim 18, characterized in that, depending on the detected change in conductivity (ALf = Lfi, - Lf a ) the regeneration process for regenerating the softening device (12) is initiated and / or the signal is issued or the water treatment plant is switched off when the difference in conductivity (ALf = Lfi - Lf) caused by the precipitation of the alkaline earth ions a ) exceeds a specified difference limit (AG).

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