EP4200063A1

EP4200063A1 - Monitoring the integrity of an ultrafiltration membrane during filter operation

Info

Publication number: EP4200063A1
Application number: EP20841704.8A
Authority: EP
Inventors: Arne Götzel; Marcel HAMMER; Michael KSOLL; Michael Reichelt; Danny RÖSLER
Original assignee: Wilo SE
Current assignee: Wilo SE
Priority date: 2020-12-21
Filing date: 2020-12-21
Publication date: 2023-06-28
Also published as: CN116457074A; WO2022135670A1

Abstract

The invention relates to a method for monitoring the integrity of an ultrafiltration membrane (6) in a filter module (3a, 3b, 3c) of an ultrafiltration plant (1) for treating drinking water while the ultrafiltration plant is in filter operation, the plant having an untreated water inlet (2) and a filtrate outlet (8) between which the filter module (3a, 3b, 3c) is located. In said method, filtered drinking water flows from the filter module (3a, 3b, 3c) via a backflow preventer (Fa, Fb, Fc) to the filtrate outlet (8) which has a known opening pressure (p_RFV) during filtrate flow, wherein the pressure difference (Δp_AN) between the pressure (P_zu) in the untreated water inlet (2) and the pressure (P_ab) in the filtrate outlet (8) is determined, and a loss of integrity is assumed if the pressure difference (Δp_AN) is below a limit value (p_RFV+ T) which is greater than the opening pressure (p_RFV).

Description

Monitoring the integrity of an ultrafiltration membrane in filter operation

The invention relates to a method for monitoring the integrity of an ultrafiltration membrane in a filter module of an ultrafiltration system for drinking water treatment during its filter operation, the system having an untreated water inlet and a filtrate outlet, between which the filter module is located. Furthermore, the invention relates to an ultrafiltration system that is set up to carry out the method.

Ultrafiltration systems for drinking water supply in buildings with filter modules working in parallel are known per se. They are used where a central supply of water of potable quality is not possible or not permanently possible. Residential and multi-family houses, hotels, hospitals, office buildings and public facilities are particularly noteworthy as buildings with such systems, which include a large number of water consumers such as washbasins, toilets, showers, bathtubs, etc. and therefore have extremely dynamic water consumption over the course of the day . A cruise ship is also to be understood as a building in the sense of a mobile hotel.

Filter modules of an ultrafiltration system have an inlet connection on the raw water side for supplying raw water and an outlet connection on the filtrate side for supplying filtered water, referred to below as filtrate. Depending on the design of the filter module, there is one or a large number of filter membranes between the inlet and outlet connections, which filter out microorganisms and dirt particles in the raw water supplied. The filter membrane(s) thus spatially separate the raw water side from the filtrate side. Regardless of the actual number of filter membranes in the module, only "one" is Filter membrane spoken in the singular, although also two or a multiplicity of

Filter membranes can/can be present.

For the proper operation of the ultrafiltration system, it is essential that the or all filter membranes are intact, otherwise dirt particles and microorganisms such as bacteria will get to the filtrate side and contaminate the system from there to the consumers. A complex cleaning and, if necessary, disinfection of the pipelines and connected hydraulic components would then be necessary. The integrity of the membrane is no longer given if there are defects such as holes or cracks that are larger than the absolute pore size of the membrane. Such defects are caused by violent pressure surges, e.g. when consumer valves are opened or closed, by external influences such as mechanical impacts due to improper transport, aging of the membrane and chemical influences on the membrane surface by e.g. impurities in the inlet water, clogging of disinfectants, etc. For this reason So-called integrity tests are carried out in ultrafiltration systems at regular intervals, usually daily.

Some of these tests are described as part of the integrity monitoring of a filtration system, for example in the American technical standard ASTM D6908-06 (year 2017) and in the US EPA's Membrane Filtration Guidance Manual (Nov. 2005). This integrity monitoring is mainly used as a pressure decay test in ultrafiltration (UF) and microfiltration (MF) systems and mostly as a vacuum decay test in reverse osmosis (RO) and nanofiltration (NF) systems.

The main integrity tests used are air based, as the wet filter membranes are impermeable to air depending on the level of pressure applied. Air can either be sucked out to create a vacuum or introduced as compressed air. This can be done locally, ie specifically for a specific filter module, or globally for all or part of the system, ie for several filter modules at the same time. Furthermore, this can be done either from the raw water side or from the filtrate side. It is then examined or measured whether and, if so, how large the pressure drop over the membrane or the filter modules over time in order to make a statement about the integrity. The level of the applied transmembrane pressure in a pressure drop test determines the minimum size of the detectable defect. A pressure of 7 bar is required to check the retention of bacteria (0.45 μm) and a test pressure of 120 bar for viruses (25 nm). These high pressures cannot be achieved with conventional filter modules with, for example, a maximum permissible transmembrane pressure of 4 bar in terms of mechanical stability. A standard transmembrane pressure of 1 bar for integrity testing is only sufficient to detect defects down to a minimum size of 3 pm. If a large number of filter modules are tested simultaneously, the natural diffusion of air through the intact membrane wall into the water medium and mini-leakage outside the membrane wall reduce the sensitivity of the pressure drop measurement.

A further disadvantage of this method is the not inconsiderable effort involved in carrying out the integrity test, because the filter module or modules must be emptied before the integrity test and then refilled. Some of the air also remains in the filter modules after the integrity test and reduces the filter efficiency. It must therefore be removed with an additional measure by appropriate venting. Another disadvantage of air-based testing methods is the need to shut down all or part of the operation of the filtration system during the test. As a result, it then supplies little or no drinking water, which, depending on the location of the system, e.g. for hotels, is unacceptable, or allows the process to be used only outside of the main consumption time, i.e. at night. An additional disadvantage is the technical effort required to carry out the process, since the system has to be equipped with the appropriate lines, valves and an oil-free compressed air supply, e.g. a compressor.

A very sensitive integrity monitoring method consists of injecting a defined dose of molecular or particulate markers into the raw water and checking whether and, if so, to what extent these markers appear on the filtrate side. The molecular or particulate size of a marker is larger than the nominal pore size of the filter membrane, so that the marker does not reach the filtrate side, if the membrane is intact, or only to a minimal extent. This method has the advantage that it can be used during filtration operations. However, the method requires additional equipment for dosing and injection as well as additional sensors or subsequent laboratory analysis on the filtrate side in order to detect the presence of the marker in the filtrate. Furthermore, the marker reduces the filter efficiency because it does not get through the filter membrane, but instead contributes to increased fouling of the membrane. Furthermore, such a method is not permitted for drinking water, since the suitability for drinking of the water could be restricted by the marker.

Other methods for monitoring the integrity of membranes work by analyzing the filtrate water quality. This can be done either by analyzing the particle number and particle size distribution in the filtrate or by analyzing the turbidity. However, both methods require a high level of technical effort for the optical sensors and measurement data processing.

It is also possible to make a statement about the integrity of the filter membrane(s) via the permeability or the transmembrane pressure (TMP). However, both of these are only possible if the supply water quality remains the same, which is not guaranteed for every application location and not over the entire service life of ultrafiltration systems in building technology. Furthermore, the TMP can only be used with constant volume flows, which do not exist in building technology. Due to the dynamic processes that exist there, the TMP fluctuates greatly, for example between 1 m ³ /h and 80 m ³ /h in a hotel with around 400 rooms. To determine the permeability, the flow must be determined, which is done using cost-intensive sensors according to the prior art. However, the strong fluctuations in the volume flow in building technology are only detected by many known sensors after a long response time and are therefore often subject to errors.

Against this background, it is an object of the present invention to provide a simple method for reliably monitoring the integrity of an ultrafiltration membrane in a filter module during the Filter operation and can be used without interrupting it and uses only existing pressure sensors. Furthermore, it is the object of the invention to provide a corresponding ultrafiltration system for carrying out the method.

This object is achieved by a method according to claim 1 and an ultrafiltration system according to claim 11. Advantageous developments are specified in the respective dependent claims and are explained below.

According to the invention, the method for monitoring the integrity of an ultrafiltration membrane in a filter module of an ultrafiltration system for drinking water treatment during its filter operation provides that filtered drinking water flows from the filter module via a backflow preventer to the filtrate outlet, which has a known opening pressure with a filtrate flow, the pressure difference between the pressure determined in the raw water inlet and the pressure in the filtrate outlet and a loss of integrity is assumed if the pressure difference is below a limit value that is greater than the opening pressure. A comparison is thus made between the pressure difference and the limit value and a loss of integrity is assumed if the pressure difference is less than the limit value.

The core idea of the invention is therefore to connect the filter module or modules of the ultrafiltration system via a backflow preventer to the filtrate line, which directs the filtrate to the consumers. The filter module and the backflow preventer are therefore connected in series. The backflow preventer only allows a volume flow in the direction of the filtrate line. For structural reasons, it only opens above a certain opening pressure. It then forms hydraulic resistance during the flow of filtrate, so that a pressure drop equal to said opening pressure occurs across it. This is regularly perceived as a disadvantage because attempts are always made to avoid hydraulic resistance in order to minimize hydraulic losses and maximize efficiency. However, the invention uses the opening pressure of or the pressure loss at the backflow preventer as an advantage in order to determine whether something is flowing through it or the filter module. This is usually with just one Volume flow sensor possible, but the method according to the invention can be dispensed with. According to the invention, a filtrate flow is determined via the pressure. For this purpose, the pressure drop across the system is considered, more precisely, the pressure difference between the inlet and outlet, between which the at least one filter membrane to be monitored is located. The opening pressure of the non-return valve contributes to this pressure difference in every operating state with water extraction, so that it can be evaluated as to whether the non-return valve, and thus also the filter module, is being flown through.

If no water is withdrawn, the pressure difference is zero. In this state, no membrane defect can be detected, but no unfiltered unfiltered water flows through the membrane, so that this case is insignificant in practice. In normal daily use of the ultrafiltration system, there is regularly a very dynamic but constantly high water extraction. The volume flow fluctuates strongly around a mean value and causes a pressure drop across the membrane, which, together with the opening pressure of the backflow preventer, forms the pressure drop across the system. The pressure drop across the membrane is hereinafter referred to as the transmembrane pressure (TMP). It is not constant, but increases over time, as particles and microorganisms from the raw water increasingly accumulate on the surface of the membrane. If the integrity of the filter membrane has been lost due to significant defects, such as cracks, larger pores or several severed hollow fibers, it has no hydraulic resistance or the filter module only has a negligibly low hydraulic resistance, so that the transmembrane pressure is zero. As a result, the pressure drop across the system is only in the range of the opening pressure of the non-return valve. Consequently, the finding that the pressure difference between the pressure in the raw water inlet and the pressure in the filtrate outlet is in the range of this opening pressure is an indication of a loss of integrity of the filter membrane.

The integrity test method according to the invention requires less effort than other test methods. It is not air-based, so there is no need to perform a drain, refill and bleed of the filter module, nor does it use a marker. Furthermore, neither a special nor an additional sensor or measurement technology is required in the system. Rather, a pressure determination in the inlet line and the is sufficient to carry out the method Filtrate line, which is usually already implemented in conventional ultrafiltration systems for their control.

Another advantage of the method is that the integrity monitoring can be performed continuously and not at specific times (1-2 times a day) as in air-based methods or prior art use of markers. A significant membrane defect can thus be detected immediately and the contamination caused by it can be minimized. Finally, the method according to the invention can be carried out during filter operation, which does not have to be stopped for this purpose. This means that the supply of drinking water is not interrupted. At the same time, integrity monitoring is also uninterrupted.

The filter module can have one, two or more filter membranes, preferably a large number of hollow fiber membranes. In addition, the ultrafiltration system can have one, two or more parallel filter modules, which are each connected to the filtrate outlet or the filtrate line via a backflow preventer. The filter modules are preferably connected together to form groups. For example, two, three or more groups of two, three or more parallel filter modules can be located in parallel. The raw water inlet of the system is at the same time the raw water inlet of the groups or the filter modules. Furthermore, the filtrate outlet of the system is at the same time the filtrate outlet of the groups or the filter modules. Thus, the filter membranes, filter modules or groups are always between the raw water inlet and the filtrate outlet.

A known opening pressure is a nominal opening pressure specified by the manufacturer for the non-return valve. Insofar as a “range of the opening pressure” is spoken of within the scope of the invention, this terminology takes into account the fact that a physical quantity never exactly reaches a specific value when measured in practice. Furthermore, it must be taken into account that the actual opening pressure is not identical, even in the case of identical non-return valves, rather it varies. The temperature of the water also plays a role, or rather its temperature-dependent density and dynamic viscosity, so that the actual Opening pressure of the non-return valve fluctuates compared to the nominal value. For this reason, a limit value is used as a decision criterion according to the invention, which takes into account the scatter and temperature-related fluctuation of the opening pressure and is therefore greater than the opening pressure.

Suitably the limit is at most 20% above the known cracking pressure. For example, the limit may be 20%, 10%, or 5% above the known cracking pressure. It thus forms the upper limit of a possible fluctuation range of the opening pressure. This fluctuation range is to be understood as the "range of the opening pressure".

In order to improve the detection accuracy, provision can be made for the first-mentioned limit value to form an upper limit of a tolerance band, the lower limit of which is defined by a further limit value, with the loss of integrity being assumed only if the pressure difference lies within the tolerance band. With others, the double comparison is made as to whether the pressure difference is greater than the further limit value and smaller than the first limit value.

The further limit value is preferably at most 20% below the opening pressure. For example, the further limit value can be 20%, 10% or 5% less than the known opening pressure.

Since the TMP is flow-dependent, there is only a low TMP at very low volume flows, for example less than 1 m ³ /h, as a result of minimal water withdrawal at the consumers. In order to distinguish this case from the case of a loss of integrity, a time duration can be taken into account in addition to the pressure comparison, for which the pressure difference may be below the first-mentioned limit value. Provision can thus be made for a loss of integrity to be assumed only if the value falls below the limit value for at least a predetermined period of time. This determination can be realized, for example, with the help of a counter, which is started when the limit value is undershot and, when a counter reading corresponding to the duration of time is reached, a message about exceeding the permissible limit value outputs time duration. The counter can be an up counter (stopwatch) or a down counter (countdown).

The duration can be between 5 and 20 minutes, for example.

When using the duration as an additional decision criterion, it makes sense to differentiate between the times of day, since the characteristics of water consumption change significantly over the course of the day. So there is either no or only minimal water withdrawal at night. In contrast, water withdrawal during the day is high on average and changes very dynamically. This is the main consumption time. The fact that very low volume flows occur during the main consumption time is rather improbable, but at least more improbable than an occurrence outside the main consumption time, especially at night. Against this background, in order to quickly identify a loss of integrity, the duration of falling below the limit value used as a further decision criterion for a loss of integrity can be shorter for the main usage time than outside of the main usage time.

It can thus be provided that the loss of integrity is assumed when the limit value is not reached during a main consumption time for a first predetermined time period or outside of the main consumption time for a second predetermined time period, the second time period being longer than the first time period .

For example, the duration during the main usage time can be between 5 and 10 minutes and thus form a first duration. Outside of the main consumption time, it can be between 15 and 20 minutes and thus be a second duration.

The period between 6 a.m. and 6 p.m. can be regarded as the main consumption time. The period outside of the main consumption time, hereinafter also referred to as secondary consumption time, is then between 6 p.m. and 6 a.m. Advantageously, a warning message can be issued if the loss of integrity is accepted. This can be done with an acoustic, visual or electronic warning signal. If necessary, an electronic message can also be sent (SMS, e-mail).

The invention also relates to an ultrafiltration system for drinking water treatment, comprising at least one filter module with an ultrafiltration membrane, an untreated water inlet and a filtrate outlet, between which the filter module is located. It comprises a backflow preventer between the filter module and the filtrate outlet, a sensor system for determining the pressure difference between the pressure in the raw water inlet and the pressure in the filtrate outlet and a monitoring unit for monitoring the integrity of the ultrafiltration membrane, the monitoring unit being set up to carry out the method described above according to the invention .

The sensors can be a pressure sensor in the raw water inlet and in the filtrate outlet. The monitoring unit can be a PLC (programmable logic controller) or a microcomputer.

Further features, advantages, properties and effects of the invention are explained below using exemplary embodiments and the attached figures. Identical or equivalent elements, in particular elements with the same function, have the same reference symbols in the figures. The reference numbers remain valid from one figure to another.

It should be pointed out that, in the context of the present description, the terms “have”, “comprise” or “contain” in no way exclude the presence of other features. Furthermore, the use of the indefinite article with an object does not exclude its plural form.

Show it:

FIG. 1: an ultrafiltration system according to the invention

Figure 2: two diagrams to illustrate different operating cases of the ultrafiltration system FIG. 3: a flow chart of the method according to the invention

Figure 1 shows an ultrafiltration system 1 for drinking water treatment using three parallel ultrafiltration modules 3a, 3b, 3c. In another variant, only one ultrafiltration module or two or more than three parallel ultrafiltration modules can be present. Furthermore, each of these ultrafiltration modules 3a, 3b, 3c can represent a group formed from two or more parallel ultrafiltration modules. Each group can be understood as an ultrafiltration unit. In order to achieve identical filtration and backwashing behavior, all ultrafiltration units preferably have the same number of ultrafiltration modules 3a, 3b, 3c. The ultrafiltration modules of the same ultrafiltration unit can be structurally combined in a common holder, also called a rack. Depending on the filtrate requirement or consumers to be supplied at the same time, the ultrafiltration system 1 can have two, three or more ultrafiltration units or racks in one embodiment variant, which are hydraulically connected in parallel to one another. It makes sense for all ultrafiltration modules 3a, 3b, 3c to be structurally identical.

The ultrafiltration system 1 is fed from a source 20 with raw water. This source 20 may be a local water utility or a local water reservoir such as a tank or cistern. A central supply line 2, which forms the raw water inlet here, connects the ultrafiltration modules 3a, 3b, 3c to the source 20, with a pressure booster system 21 being arranged in the supply line 2 in order to provide an inlet pressure Pzu of, for example, 10 bar on the inlet side of the ultrafiltration system 1 . The latter is necessary above all in tall buildings and/or extensive drinking water distribution networks within the building, since even the supply pressure provided by any supplier alone is not sufficient to ensure sufficient flow pressure, e.g. 2 bar, at the highest or most distant tapping points or consumers to guarantee. The pressure boosting system is only symbolized by a pump 21 here.

A local supply line 2a, 2b, 2c, in each of which an inlet valve Za, Zb, Zc lies. The local supply lines 2a, 2b, 2c each end at inlet connections 4au, 4ao, which open into an untreated water side 5a of the corresponding ultrafiltration module 3a, 3b, 3c. Instead of the two inlet connections 4au, 4ao, only one inlet connection can also be present in another embodiment variant. The raw water side 5a is separated from the filtrate side 5b by at least one ultrafiltration membrane 6, from which an outlet connection 4bo leads out. The ultrafiltration modules 3a, 3b, 3c are connected via a respective local filtrate line 8a, 8b, 8c, starting from the outflow connection 4bo, to a central filtrate line 8, which leads to the consumers 40. The filtrate line 8 thus forms a filtrate outlet here. Consumers 40 can be washbasin fittings, toilets, showers, tubs, etc., for example.

In filtration operation, the ultrafiltration modules 3a, 3b, 3c produce filtrate from the raw water, in that the raw water passes through the membrane 6 and particles in the raw water remain adhering to the raw water side 5a or to the membrane 6. The water or filtrate permeated to the filtrate side 5b is conducted through the local filtrate lines 8a, 8b, 8c to the central filtrate line 8, which then forwards the filtrate to the consumers 40.

In order to loosen particles adhering to the surface of the membrane 6, each ultrafiltration module 3a, 3b, 3c can be operated independently of the other ultrafiltration modules 3a, 3b, 3c in a backwash operation, in which the filter membrane 6 is flown through backwards, ie from the filtrate side 5b to the raw water side 5a. The filtrate used for this comes from at least one of the other ultrafiltration modules 3a, 3b, 3c. In order to drain the water passing through the membrane 6 from the raw water side 5a in backwash operation, the raw water side 5a of each ultrafiltration module 3a, 3b, 3c is connected via a local retentate line 7a, 7b, 7c, in which there is a retentate valve Ra, Rb, Rc , Connected to a central retentate line 7, which leads to a free outlet 30 where the retentate is deposited. In the central retentate line 7 is a volume meter 17, also known colloquially as a water meter or water meter. The determination of which ultrafiltration module should filter at a time and which should be cleaned by backwashing is done by setting the inlet valves Za, Zb, Zc and the retentate valves Ra, Rb, Rc, these valves being related to each ultrafiltration module 3a, 3b, 3c be controlled inverted. This means that the inlet valve Za, Zb, Zc assigned to an ultrafiltration module 3a, 3b, 3c is open, while the retentate valve Ra, Rb, Rc assigned to it is closed, and vice versa. According to the snapshot of the operating states shown in FIG. 1, all three ultrafiltration modules 3a, 3b, 3c deliver filtrate. So you are in filtration mode. The arrows on the various lines and within the ultrafiltration modules 3a, 3b, 3c indicate the respective direction of flow. The valve positions are thus as follows:

As can be seen in Figure 1 and as will be used below as a convention, filled valve symbols indicate closed valves and unfilled valve symbols open valves.

The advantage of such an ultrafiltration system 1 is that backwashing of the individual ultrafiltration modules 3a, 3b, 3c can take place during operation of the ultrafiltration system 1, i.e. while filtrate is being delivered to the consumers 20, so that they experience no or at least no significant impairment. There is therefore no standstill or interruption of the filtrate delivery to the consumers 20. Furthermore, the ultrafiltration system 1 according to the invention does not require a backwash tank and a backwash pump, which reduces the complexity and costs of producing it.

A special feature of the ultrafiltration system according to the invention in Figure 1 is that each ultrafiltration module 3a, 3b, 3c not only on the local filtrate line 8a, 8b, 8c, but also via a second line 8', 8a', 8b', 8c' parallel thereto to the central filtrate line 8. The second lines each consist of a module-related, first section 8a′, 8b′, 8c′, which combine to form a common second section 8′, which then opens into the central filtrate line 8 . Viewed differently, the second lines 8', 8a', 8b', 8c' are from this common section 8' connected to the filtrate line 8 and from individual lines 8a', 8b', 8c outgoing to the individual ultrafiltration modules 3a, 3b, 3c ' educated. While the local filtrate lines 8a, 8b, 8c serve to discharge the filtrate in filtration operation, the second lines 8', 8a', 8b', 8c' are provided for a filtrate feed line in backwash operation. For example, filtrate from two of the ultrafiltration modules 3b, 3c can be fed to the third ultrafiltration module 3a via the corresponding second line 8', 8a' of the filtrate side 5b. This is done by closing the inlet valve Za to the third ultrafiltration module 3a and opening the retentate valve Ra assigned to the third ultrafiltration module 3a. The filtrate is fed to the third ultrafiltration module 3a via a further connection 4bu on the filtrate side 5b.

In order to limit the pressure above an ultrafiltration module 3a, 3b, 3c to be backwashed and thus to protect the corresponding membrane 6, there is a pressure reducing element, in particular a pressure reducer, in the common section 8' of the second lines 8', 8a', 8b', 8c' 10 arranged.

With this arrangement, it is necessary to provide a flushing valve Sa, Sb, Sc in each of the individual lines 8a', 8b', 8c' in order to separate the pressure-unreduced filtrate side 5b of the ultrafiltration modules 3b, 3c supplying the filtrate from the filtrate side 5b of the ultrafiltration module 3a to be backflushed , since the pressure reducing member 10 is otherwise bypassed. The flushing valves Sa, Sb, Sc can be designed identically to the inlet valves Za, Zb, Zc, the retentate valves Ra, Rb, Rc and/or the filtrate valves Fa, Fb, Fc. In the embodiment variant shown in FIG. 1, the flushing valves Sa, Sb, Sc are formed by non-return valves. These are arranged in the individual lines 8a', 8b', 8c' in such a way that their respective input side is connected to the common section 8' and their respective output side is connected to the corresponding ultrafiltration module 3a, 3b, 3c. In one embodiment variant, the inlet valves Za, Zb, Zc and/or retentate valves Ra, Rb, Rc can be controlled, in particular switchable (open/closed) or adjustable (0...100%) control valves which are actuated, for example, electrically, electromagnetically or pneumatically will. For example, the control valves are controllable engine valves.

According to the invention, the filtrate valves Fa, Fb, Fc are formed by non-return valves. This has the advantage that no active activation of the filtrate valves Fa, Fb, Fc is required. This design also makes use of the fact that the local filtrate lines 8a, 8b, 8c and the second lines 8a', 8b', 8c' are or may only be flowed through in one direction, depending on the operating case "filtering" or " Backwash” alternative. Because the non-return valves Fa, Fb, Fc allow flow in only one direction due to their directional nature, they are particularly suitable for the ultrafiltration system 1 according to the invention. They are arranged in the local filtrate lines 8a, 8b, 8c in such a way that their input side is connected to the corresponding ultrafiltration module 3a, 3b, 3c and their output side is connected to the central filtrate line 8.

If the pressure applied to the non-return valves Fa, Fb, Fc from the inlet side to the outlet side is above a certain opening pressure PRFV, the corresponding non-return valve Fa, Fb, Fc opens independently of the volume flow. This opening pressure PRFV is, for example, approx. 0.3 bar even for the smallest volume flows. From this property, which is perceived as disadvantageous in professional circles, the advantage arises within the scope of the present invention that the backflow preventers Fa, Fb, Fc can be used as flow indicators. While the opening pressure of normal backflow preventers is above the measuring tolerance of simple and inexpensive pressure sensors and can therefore be reliably detected, minimal volume flows can only be measured with special, expensive volume flow sensors. However, the use of backflow preventers Fa, Fb, Fc between the ultrafiltration modules 3a, 3b, 3c and the central filtrate line 8 eliminates the need for a volume flow rate detection for a flow indication. Rather, it allows the pressure difference across the series connection of ultrafiltration module 3a, 3b, 3c and associated Backflow preventer Fa, Fb, Fc a statement about an opening or non-opening of the backflow preventer Fa, Fb, Fc and thus also a statement about the flow or non-flow of filtrate even with the smallest volume flows. This in turn opens up the possibility of recognizing whether and when the ultrafiltration membrane 6 is damaged, ie has lost its integrity.

The thickness of the lines in FIG. 1 symbolizes the pressure on the corresponding water-carrying line, the pressure being greater the thicker the line is. In contrast, the dashed lines carry no water in the operating case shown, because the corresponding valve is closed.

In this embodiment variant, the ultrafiltration modules 3a, 3b, 3c are formed from an elongate, essentially cylindrical housing. They each have a large number of hollow fiber membranes 6 between the raw water side 5a and the filtrate side 5b, with the interior of the hollow fiber membranes belonging to the raw water side 5a and the space outside the hollow fiber membranes 6 to the filtrate side 5b in this embodiment variant. Each of the two sides 5a, 5b has the two connections already mentioned, which are each arranged on opposite axial ends of the housing. In the intended vertical arrangement of the ultrafiltration modules 3a, 3b, 3c, each ultrafiltration module 3a, 3b, 3c thus has a lower inlet connection 4au and an upper inlet connection 4ao each for the raw water side 5a, as well as an upper outlet connection 4bo and a lower inlet connection 4bu each for the filtrate side 5b there.

The ultrafiltration system 1 also includes an inlet pressure sensor 11 for measuring the inlet pressure Pzu in the supply line 2 and an outlet pressure sensor 12 for measuring the outlet pressure Pab in the central filtrate line 8. In addition, another pressure sensor 14 is connected to the common section 8' of the second line 8 ', 8a, 8b, 8c connected to measure the backwash pressure PSP. The measurement signals from these pressure sensors 11 , 12 , 14 are fed to a system controller 9 . This comprises an evaluation unit 13 and a monitoring unit 16 in the form of functional units. The evaluation unit 13 uses the measured values Pzu, Pa to calculate the pressure difference APAN between the pressure Pzu in the raw water inlet 2 and the pressure Pab in the filtrate outlet 8: APAN = Pzu - Pab. This is also known as plant pressure or pressure across the plant. The pressure difference APAN is then fed to the monitoring unit 16 in order to evaluate it to determine whether there is a loss of integrity in an ultrafiltration membrane 6 of one of the ultrafiltration modules 3a, 3b, 3c. When this is the case and how this is recognized is described below with reference to FIGS.

FIG. 2 illustrates various operating cases A, B, C and D of the ultrafiltration system 1, in which the volume flow Q on the one hand and the pressure difference APAN on the other hand are considered. In operating case A, no drinking water is drawn off. In this case, the pressure Pab in the central filtrate line 8 is identical to the pressure Pzu in the central supply line 2, so that the pressure difference APAN is zero, i.e. no pressure drop across the system. Although no membrane defect can be detected in this state, no raw water then flows unfiltered through the membrane 6.

For the other operating cases B, C, D, a distinction is made between the main consumption time and the secondary consumption time. The secondary consumption time is the period outside of the main consumption time. Essentially, the main consumption time coincides with the day and the secondary consumption time with the night. For example, the main usage time is between 6 a.m. and 6 p.m., the secondary usage time is between 6 p.m. and 6 a.m.

Operating case C represents the main operating case during the day. In normal daily use of the ultrafiltration system 1, there is a very dynamic but constantly high water extraction. The resulting volume flow Q=Qnorm causes a pressure drop PTMP (the transmembrane pressure) across the membrane 6, which increases over time because particles and microorganisms from the raw water increasingly accumulate on the surface of the membrane 6. The TMP together with the opening pressure PRFV of the backflow preventer Fa, Fb, Fc forms the Pressure drop APAN across the system 1 . Since the ultrafiltration modules 3a, 3b, 3c are parallel, the pressure drop across each of the series circuits of ultrafiltration module and backflow preventer 3a + Fa, 3b + Fb, 3c + Fc is equal to the pressure drop APAN across the system 1, so that considering one of the series circuits is sufficient . Other pressure drops, for example due to pipe friction losses, are negligibly small and are not taken into account here for the sake of simplicity. The calculated pressure difference PAN is divided between the TMP PTMP and the opening pressure PRFV, so that:

APAN = Pzu - Pab = PRFV + PTMP

The pressure difference PAN is thus significantly greater than the opening pressure PRFV of the non-return valve Fa, Fb, Fc. In operating case C, the integrity is OK.

In operating case D, the integrity of the filter membrane 6 has been lost (here it is sufficient if just one of several membranes 6 in the filter module 3a, 3b, 3c is damaged). It has no hydraulic resistance, or the filter module 3a, 3b, 3c only has a negligibly small hydraulic resistance, so that the TMP PTMP is approximately equal to zero. As a result, the pressure drop APAN across system 1 is only in the range of the opening pressure PRFV of the non-return valve Fa, Fb, Fc: APAN ~ PRFV, whereby there is still a constantly high level of water withdrawal and the resulting volume flow Q = Qnorm is normal and there is no indication of one loss of integrity. Consequently, the finding that the pressure difference PAN between the pressure in the raw water inlet 2 and the pressure in the filtrate outlet 8 is in the range of the opening pressure PRFV is an indication of a loss of integrity of the filter membrane.

As a rule, the nominal opening pressure PRFV is around 0.3 bar. However, production-related tolerances and temperature influences allow this to vary in practice. For example, a tolerance T of ±10% can be taken into account, which defines a tolerance band 15 around the nominal opening pressure PRFV with an upper limit of the value PRFV+T and a lower limit of the value PRFV−T. A limit value PRFV+T, which corresponds to the upper limit of the tolerance band 15, is used to determine a loss of integrity. However, a higher value between the upper limit and the sum of the nominal opening pressure PRFV and TMP with a clean membrane 6 can also be used.

Theoretically, it can happen that during the main consumption time, the water withdrawal is so low for a short time that the TMP hardly differs from zero. In order to distinguish this case from a loss of integrity, a counter (timer) is started when the limit value is not reached in order to check how long this condition lasts. If a certain period of time T1, e.g. 5 minutes, is exceeded, a loss of integrity can be assumed with certainty.

Operating case B relates to consumption outside of the main consumption time, especially at night, which is usually characterized by no or minimal water withdrawal. It is therefore more the case here that the pressure difference PAN is in the range of the opening pressure PRFV. In order to distinguish this error-free operating case B1 from an operating case B2 with a loss of integrity, a counter (timer) is also started here when the limit value is undershot in order to check how long this state lasts. If a certain period of time T2, e.g. 15 minutes, is exceeded, a loss of integrity can be assumed with certainty.

The time duration T1 is selected to be shorter than the time duration T2, because due to the usually high water withdrawal and strong dynamics in the main consumption time, a minimum volume flow or a pressure difference APAN across the system 1 in the range of the opening pressure PRFV of the backflow preventer Fa, Fb, Fc should only be available for a short time.

It should be noted that although the operating cases A, B, C, D outlined in FIG. 2 are plotted over a common time line t, the juxtaposition of the operating cases A, B, C, D in no way indicates their chronological sequence. However, in practice case D will follow case C and case B2 will follow case B1. The common timeline t is chosen here only to simplify the graphic representation. FIG. 3 illustrates the process sequence of the integrity monitoring according to the invention during filter operation of the ultrafiltration system 1. The process can even be carried out when the system 1 is backwashing one of the filter modules 3a, 3b, 3c.

The method thus begins in the filtration mode, step S1. During this operation, the pressure Pzu in the raw water inlet 2 is measured by the pressure sensor 11 and the pressure Pab in the filtrate outlet 8 by the pressure sensor 12 and the measured values are transmitted to the evaluation unit 13, which uses them to calculate the pressure difference APAN = Pzu - Pab. This takes place in step S2.

The calculated pressure difference PAN is made available to the monitoring unit 16, which checks the pressure difference APAN to see whether it lies between an upper and a lower limit value, in particular within the tolerance band 15, step S3. The upper limit here corresponds to the opening pressure PRFV of the non-return valve Fa, Fb, Fc plus a tolerance T, e.g. +10%. However, it can also be higher, as previously described. The lower limit here corresponds to the opening pressure PRFV of the non-return valve Fa, Fb, Fc minus a tolerance T, e.g. +10%. However, it can also be lower or even be zero.

In a partial step, the pressure difference APAN is compared with the upper limit value, more precisely, a check is made as to whether the pressure difference APAN is below the upper limit value. The fulfillment of this condition alone already indicates an integrity error. The comparison of the pressure difference APAN with the lower limit value that takes place in the second sub-step, more precisely the check as to whether the pressure difference APAN is above the lower limit value, serves to distinguish the integrity error from operating case A, ie the case of no water withdrawal. The second comparison can thus be viewed as a verification of the “integrity error” assumption from the first comparison. In the simplest case, the second sub-step can also consist of checking whether the pressure difference APAN is greater than zero. If the pressure difference APAN is above the upper limit value or below the lower limit value, then the integrity of the membrane 6 is OK (no branch) and the determination “no loss of integrity” is made in step S9.

If the pressure difference PAN is between the upper and lower limit values, a further check is made as to whether the main consumption time is currently present, step S4. If this is the case, the method continues with step S5 (yes branch), otherwise with step S8 (no branch). In the case differentiation in step S4, it is only decided which duration T1 is to be taken into account for the main consumption time or T2 for the secondary consumption time in the subsequent step S5, S8.

It is then monitored whether the pressure difference APAN remains below the upper limit value for a period of time. This check is carried out in step S5 for the duration T1, in step S8 for the duration T2. More precisely, in these steps S5, S8 a counter is first started and then step S2 and the test are repeated and carried out alternately as to whether the pressure difference APAN remains below the upper limit value until the corresponding duration T1, T2 is reached. If the pressure difference APAN rises above the upper limit value again within the corresponding period T1, T2 (no branch of S5, S8), the brief undershooting of the upper limit value was merely the result of minimal water removal and there is no loss of integrity, step S9. The method is then continued again at the beginning at step S1, since the integrity monitoring is continuously active in the filtration operation.

However, if the pressure difference APAN remains below the upper limit value for the corresponding period T1, T2 (yes branch of S5, S8), falling below the upper limit value is actually the result of a loss of integrity, so that such a determination is made in step S6. As a result, an error message is output in step S7.

A loss of integrity can thus be reliably detected for each of the filtration operations in a simple manner. It should be noted that the method described only establishes that or if there is a loss of integrity in any membrane 6 of an ultrafiltration module 3a, 3b, 3c. In order to find out where or in which filter module 3a, 3b, 3c this is the case, these can be taken out of operation one after the other by closing the inlet valves Za, Zb, Zc one after the other. If the inlet valves Za, Zb, Zc of that ultrafiltration module 3a, 3b, 3c that has the defective membrane 6 is closed, the pressure difference APAN rises above the upper limit value again. This means that the location of the integrity error has also been tracked down.

It should be understood that the foregoing description is given by way of example for purposes of illustration and does not limit the scope of the invention in any way. Features of the invention that are indicated as "may", "exemplary", "preferred", "optional", "ideal", "advantageous", "optional" or "suitable" are to be considered purely optional and also limit the does not include a scope of protection, which is defined solely by the claims. Insofar as elements, components, process steps, values or information are mentioned in the above description which have known, obvious or foreseeable equivalents, these equivalents are also included in the invention. The invention also includes any changes, alterations or modifications of exemplary embodiments which have the exchange, addition, alteration or omission of elements, components, method steps, values or information as their subject matter, as long as the basic idea according to the invention is retained, regardless of whether the change, alteration, or modifications improves or degrades an embodiment.

Although the above description of the invention mentions a large number of physical, non-physical or procedural features in relation to one or more specific exemplary embodiments, these features can also be used in isolation from the specific exemplary embodiment, at least insofar as they do not necessarily require the presence of further features. Conversely, these features mentioned in relation to one or more specific exemplary embodiment(s) may or may not be disclosed in any way with one another and with others disclosed features of shown or not shown embodiments can be combined, at least insofar as the features are not mutually exclusive or lead to technical incompatibilities.

Reference List

1 ultrafiltration plant

2 pipe water inlet, central supply line

2a, 2b, 2c local supply line

3 ultrafiltration unit

3a, 3b, 3c ultrafiltration module

4ao upper inlet connection

4au lower inlet connection

4bo top drain connection

4bu lower inlet connection

5a raw water side

5b filtrate side

6 filtration membrane

7 central retentate line

7a, 7b, 7c local retentate lines

8 Filtrate drain, central filtrate line

8a, 8b, 8c local first filtrate line, first line for filtrate discharge

8a', 8b', 8c' local second filtrate line, second line to filtrate feed line

8' common section of the second filtrate line

9 plant control

10 pressure reducing element

11 inlet pressure sensor

12 outlet pressure sensor

13 evaluation unit

14 backwash pressure sensor

15 tolerance band

16 surveillance unit

17 volume counters 20 Raw Water Source

30 consumers

40 free drain

Za, Zb, Zc inlet valves

Ra, Rb, Rc retentate valves

Fa, Fb, Fc filtrate valves

Sa, Sb, Sc backwash valves

Claims

25

Claims Method for monitoring the integrity of an ultrafiltration membrane (6) in a filter module (3a, 3b, 3c) of an ultrafiltration system (1) for drinking water treatment during its filter operation, the system having a raw water inlet (2) and a filtrate outlet (8) between which the filter module (3a, 3b, 3c) is located, characterized in that filtered drinking water flows from the filter module (3a, 3b, 3c) via a backflow preventer (Fa, Fb, Fc) to the filtrate outlet (8), which has a known opening pressure when the filtrate flows (PRFV), wherein the pressure difference (APAN) between the pressure (Pzu) in the raw water inlet (2) and the pressure (Pab) in the filtrate outlet (8) is determined and a loss of integrity is assumed if the pressure difference (APAN) is below a limit value ( PRFV + T) that is greater than the cracking pressure (PRFV). Method according to claim 1, characterized in that the limit value (PRFV + T) is a maximum of 20% above the known opening pressure (PRFV), preferably 10% or 5% above the known opening pressure (PRFV). Method according to Claim 1 or 2, characterized in that the limit value (PRFV + T) forms an upper limit of a tolerance band (15), the lower limit of which is defined by a further limit value (PRFV - T), and that the loss of integrity is only accepted when the pressure difference (APAN) is within the tolerance band (15). Method according to Claim 3, characterized in that the further limit value (PRFV - T) is at most 20% below the known opening pressure (PRFV). Method according to one of the preceding claims, characterized in that the loss of integrity is only assumed if the limit value is not reached for at least a predetermined period of time (T1, T2). Method according to Claim 5, characterized in that the duration (T1, T2) is between 5 and 20 minutes. Method according to one of the preceding claims, characterized in that the loss of integrity is assumed when the limit value is not reached during a main consumption time for a first predetermined time period (T1) or outside the main consumption time for a second predetermined time period (T2), the second duration (T2) is longer than the first duration (T1). Method according to Claim 7, characterized in that the first duration (T1) is between 5 and 10 minutes and the second duration is between 15 and 20 minutes. Method according to Claim 7 or 8, characterized in that the main usage time is between 6 a.m. and 6 p.m. Method according to one of the preceding claims, characterized in that a warning message is issued if the loss of integrity is accepted. Ultrafiltration system (1) for drinking water treatment comprising at least one filter module (3a, 3b, 3c) with an ultrafiltration membrane (6), an untreated water inlet (2) and a filtrate outlet (7), between which the filter module (3a, 3b, 3c) is located by a backflow preventer (Fa, Fb, Fc) between the filter module (3a, 3b, 3c) and the filtrate outlet (7), a sensor system (11, 12, 13) for determining the pressure difference (APAN) between the pressure (Pzu) im raw water inlet (2) and the pressure (Pab) in the filtrate outlet (7) and a monitoring unit (16) for monitoring the integrity of the ultrafiltration membrane (6), the monitoring unit (16) being set up to carry out the method according to one of Claims 1 to 10 .