DE202022003021U1 - Drinking water production plant - Google Patents

Abstract

Drinking water production plant (1) for producing drinking water (3) from raw water (2) by ultrafiltration and reverse osmosis, the drinking water (3) having a desired target value of a water parameter relating to its composition, at least comprising an ultrafiltration unit (14) for producing filtrate from the raw water (2), a reverse osmosis unit (20) arranged in series with the ultrafiltration unit (14) via a lockable first filtrate line (26) for producing permeate from the filtrate, which is connected to a mixing point (15), and comprising a fresh water tank for making the drinking water (3) available for withdrawal, characterized in that a lockable second filtrate line (27) connects the ultrafiltration unit (14) to the mixing point (15) by bridging the reverse osmosis unit (20), and that the drinking water production plant (1) is set up,
- to be operated in a first operating mode in which the first filtrate line (26) is open towards the mixing point (15) in order to obtain the filtrate from the raw water (2) by ultrafiltration and from this the permeate by reverse osmosis, the volume of which forms a first water volume, and
- to be operated in a second operating mode in which the second filtrate line (27) is open towards the mixing point (15) in order to obtain the filtrate from the raw water (2) by ultrafiltration, the volume of which forms a second water volume, the first and second water volumes being dimensioned such that their mixture has the desired target value and the mixture forms the drinking water (3).

Description

The present invention relates to a system for treating raw water, in particular water softening and water desalination systems and membrane filter systems. In particular, the invention relates to a system for obtaining drinking water from raw water by ultrafiltration, hereinafter abbreviated to UF, and reverse osmosis, hereinafter abbreviated to RO, wherein the drinking water has a desired target value of a water parameter relating to its composition and is provided in a fresh water tank.

The use of ultrafiltration systems to produce drinking water from raw water, which is available in the form of river water, surface water or groundwater, is well known. UF is an excellent method for removing particulate suspended matter and microorganisms from the raw water and achieving drinking water quality. Depending on its origin and the time of year, however, the raw water can also have a high salt content, which UF is unable to reduce. Salts are crystalline chemical compounds made up of positively charged and negatively charged ions that largely determine the taste of drinking water. Water with a comparatively high salt concentration is considered undrinkable by most people. Although a negative influence of a high salt content in drinking water on human health has not yet been proven by epidemiological studies, it is necessary to reduce an excessively high salt content in drinking water, i.e. to remove salts, for taste reasons. This can be achieved by reverse osmosis.

1. 1. eine reine UF-Einheit, wenn der Salzgehalt des Rohwassers unterhalb eines vorbestimmten Grenzwerts liegt,
2. 2. eine reine RO-Einheit, wenn der Salzgehalt des Rohwassers oberhalb eines vorbestimmten Grenzwerts liegt,
3. 3. eine UF-Einheit und RO-Einheit in Reihe hintereinandergeschaltet, wobei die UF als Vorbehandlung des Rohwassers für die RO dient, und
4. 4. eine UF-Einheit und RO-Einheit parallel zueinander geschaltet, wobei die UF die RO unter Bildung eines Bypasses umgeht.

Whether the salt content is unpleasantly high depends on the raw water, whereby the salt content of the raw water depends on its origin. Furthermore, the salt content is not constant over the year, but depends on the season. Depending on the salt content in the raw water or the desired salt content in the drinking water, RO may be necessary or unnecessary. The following arrangements consisting of a UF unit and/or an RO unit for drinking water production are therefore well known in drinking water treatment or drinking water preparation, depending on requirements:

1. 1. a pure UF unit if the salinity of the raw water is below a predetermined limit,
2. 2. a pure RO unit if the salinity of the raw water is above a predetermined limit,
3. 3. a UF unit and RO unit connected in series, with the UF serving as pre-treatment of the raw water for the RO, and
4. 4. a UF unit and RO unit connected in parallel, with the UF bypassing the RO to form a bypass.

The first variant, as already explained, has the disadvantage that the salt content in the drinking water cannot be reduced, so that it is only suitable if the salt content in the raw water is already low, more precisely, if it is below a limit value that is desired, for example, by the customer of the drinking water treatment plant.

The second variant has the disadvantages inherent in RO. Due to the spiral-shaped structure and the thin-film composite membrane used, it is not very effective in the long-term retention of microbiological organisms. Since RO cannot be backwashed like UF, high demands are placed on the inlet water quality of the RO. This is achieved through multi-stage pretreatment of the raw water. If substances deposit on the RO membrane over a longer period of operation (fouling), the RO membrane must be chemically cleaned. The foulants are removed using acidic and alkaline cleaners. During backwashing, as is common with the UF unit, the flow through the filter is reversed by pumping filtered water from the clean water side to the raw water side in order to loosen and rinse away the particles and microorganisms adhering to the membrane on the raw water side. This is not possible with RO filters.

RO units must also be operated with a constant volume flow during filter operation and have a high water and energy consumption. The high energy consumption is due to the small pore size, so to speak at the molecular level, of less than 0.1 nm. The high water consumption occurs because a large part of the water only flows over the filter membrane and is then discarded as a so-called concentrate. Another disadvantage of RO units is that the salt content of the permeate produced by the RO cannot be adjusted and the water quality is low because the salt content is always minimal. The water therefore has a neutral taste. Drinking drinking water with a minimal salt or mineral content can have negative health consequences. This is because the salts or minerals are needed by the human body for many functions, such as the formation of bones, teeth, cells, etc. The relevant minerals are sodium, potassium, calcium, magnesium, iodine, zinc, iron and copper. A diet exclusively with Drinking water with a low salt or mineral content can lead to deficiency symptoms if the minerals are not absorbed through other foods. Since the amount of raw water and its salt content fluctuate seasonally, it would be desirable to be able to adjust the volume flow and the target salt content in the drinking water to be produced.

The aforementioned disadvantages of RO units are also disadvantages of the above-mentioned variant 3, i.e. the series connection of UF and RO. The salt content in the drinking water to be produced cannot be adjusted, the majority of the valuable filtrate from the UF is separated by the RO unit as retentate, and the control of the series connection of UF and RO is challenging because the filtrate volume flow must be kept constant, which, however, decreases over time as a result of the clogging of the ultrafiltration filter.

Also, the parallel connection of UF unit and RO unit is not ideal because the permeate supplied by the RO system is not free of microorganisms and is mixed with the filtrate at the outlet of the filter system.

The salt content of water can be determined in different ways. One measure for this is the so-called TDS value, for example. It indicates the mass concentration of all substances dissolved in the water (TDS, Total Dissolved Solids), without the proportion of volatile substances. The TDS value is expressed in milligrams per liter [mg/l]. Drinking water with a TDS value of 900 mg/l is considered salty and undrinkable. If the salt content of the raw water is below a TDS of 500 mg/l, a pure UF unit is sufficient for drinking water treatment. Above a TDS limit of 500 mg/l, an RO unit is usually used for drinking water treatment, which, however, reduces the salt content to a TDS of less than 20 mg/l. Since the salts in the water form ions that determine the conductivity of the water, the TDS value is also a measure of the conductivity of the water. Viewed another way, as an alternative to the total drying residue or TDS value, the conductivity of the water or its electrical resistance can be determined in order to make a quantitative statement about the salt content.

The object of the present invention is to provide a drinking water production system that uses the advantages of a combination of ultrafiltration and reverse osmosis to produce healthy and tasty drinking water, while at the same time avoiding the aforementioned disadvantages of the prior art. In particular, the salt content of the drinking water to be produced should be adjustable in the system and the drinking water should be produced with minimal water and energy consumption.

This object is achieved by a system having the features of claim 11. Advantageous further developments are specified in the subclaims and are described below.

• - ein erstes Wasservolumen erzeugt wird, indem aus dem Rohwasser durch Ultrafiltration ein Filtrat gewonnen und aus diesem durch Umkehrosmose ein Permeat gewonnen wird, dessen Volumen das erste Wasservolumen bildet,
• - ein zweites Wasservolumen erzeugt wird, indem aus dem Rohwasser durch Ultrafiltration ein Filtrat gewonnen wird, dessen Volumen das zweite Wasservolumen bildet, und
• - das erste und zweite Wasservolumen anschließend zum Erhalt des Trinkwassers gemischt werden, wobei das erste und zweite Wasservolumen derart bemessen sind, dass ihre Mischung den gewünschten Zielwert aufweist.

According to the invention, for the production of drinking water from raw water by ultrafiltration and reverse osmosis, wherein the drinking water has a desired target value of a target parameter relating to its composition, it is proposed that

• - a first volume of water is produced by obtaining a filtrate from the raw water by ultrafiltration and from this a permeate is obtained by reverse osmosis, the volume of which forms the first volume of water,
• - a second volume of water is produced by obtaining a filtrate from the raw water by ultrafiltration, the volume of which forms the second volume of water, and
• - the first and second volumes of water are subsequently mixed to obtain drinking water, the first and second volumes of water being such that their mixture has the desired target value.

To generate the first volume of water, filtrate from a UF unit can be fed via a first filtrate line to an RO unit, whose permeate is fed to a mixing point, in particular to the fresh water tank. In addition, to generate the second volume of water, filtrate from the UF unit can be fed via a second filtrate line, bypassing the RO unit, directly to the mixing point, in particular to the fresh water tank.

• - eine UF-Einheit zur Erzeugung von Filtrat aus dem Rohwasser durch Ultrafiltration,
• - eine mit der UF-Einheit über eine absperrbare erste Filtratleitung in Reihe angeordnete RO-Einheit zur Erzeugung von Permeat aus dem über die Filtratleitung zugeleiteten Filtrat durch Umkehrosmose, wobei die RO-Einheit mit einer Mischstelle, insbesondere über eine Permeatleitung, verbunden ist, und
• - einen Frischwassertank zur Bereitstellung des Trinkwassers für eine Entnahme. Zusätzlich zur ersten Filtratleitung weist die Anlage eine absperrbare zweite Filtratleitung auf, die die UF-Einheit unter Überbrückung der RO-Einheit mit der Mischstelle direkt oder indirekt verbindet. Des Weiteren ist die Trinkwassergewinnungsanlage eingerichtet, in einem ersten Betriebsmodus betrieben zu werden, in dem die erste Filtratleitung zur Erzeugung des ersten Wasservolums in Form eines Permeatvolumens zur Mischstelle hin geöffnet ist, und in einem zweiten Betriebsmodus betrieben zu werden, in dem die zweite Filtratleitung zur Erzeugung des zweiten Wasservolums in Form eines Filtratvolumens zur Mischstelle hin geöffnet ist.

To apply this method, the invention proposes a drinking water production plant for producing drinking water from raw water by ultrafiltration and reverse osmosis, the drinking water having a desired target value of a water parameter relating to its composition. The drinking water production plant has at least:

• - a UF unit for producing filtrate from the raw water by ultrafiltration,
• - an RO unit arranged in series with the UF unit via a lockable first filtrate line for producing permeate from the filtrate supplied via the filtrate line by reverse osmosis, wherein the RO unit is connected to a mixing point, in particular via a permeate line, and
• - a fresh water tank for providing drinking water for withdrawal. In addition to the first filtrate line, the system has a lockable second filtrate line that connects the UF unit to the mixing point directly or indirectly, bypassing the RO unit. Furthermore, the drinking water production system is designed to be operated in a first operating mode in which the first filtrate line is open to the mixing point to generate the first water volume in the form of a permeate volume, and to be operated in a second operating mode in which the second filtrate line is open to the mixing point to generate the second water volume in the form of a filtrate volume.

A core idea of the invention is therefore to achieve the desired target value of the water parameter by setting a predetermined mixing ratio of permeate from the RO unit on the one hand and filtrate from the UF unit on the other. This makes it possible to set the water parameter in question to any target value, while at the same time ensuring that the RO unit is only in operation for a minimal period of time, thus saving valuable, already ultrafiltered water and energy. The inventive design of the drinking water production system with the first and second filtrate lines ensures that the microbiological quality of the drinking water is high.

In one variant, the raw water can be fed directly to the UF unit. However, it is also possible that the raw water is first subjected to pre-treatment, e.g. pre-filtered using a pre-filter for sand or sediment, in order to obtain a pre-water, which is then fed to the UF unit. In this variant, the raw water is fed indirectly to the UF unit.

In one variant, the filtrate from the UF unit can also be fed directly to the RO unit. However, it is also possible that the filtrate is first subjected to pretreatment, e.g. a scaling inhibitor, also known as an antiscalant, is added to obtain an intermediate water, which is then fed to the RO unit. In this variant, the filtrate is fed indirectly to the RO unit.

A particularly simple structural design of the drinking water production system is achieved by mixing the first and second water volumes simply by introducing them into the fresh water tank. In this fresh water tank, the two water volumes are then mixed automatically, on the one hand as a result of the currents and turbulence when the water is introduced, and on the other hand by diffusion due to concentration differences in the two water volumes. In another design variant, however, it can also be provided that the first and second water volumes are mixed using a mixing device. Such a mixing device can be an agitator, for example. This can be located in the fresh water tank, for example, or in a mixing container that is located upstream of the fresh water tank.

In a preferred embodiment, the two water volumes can be generated in batches. This means that the first water volume is generated first, followed by the second water volume, or vice versa. The first water volume is thus generated in the first operating mode of the system, which is used for a first operating period and in which only the first filtrate line is open. In other words, the second filtrate line can be shut off to generate the first water volume. Furthermore, the second water volume is generated in the second operating mode of the system, which is used for a second operating period and in which only the second filtrate line is open. In other words, the first filtrate line is shut off to generate the second water volume. For the transition from the first operating mode to the second operating mode in batch operation, the first filtrate line is closed and the second filtrate line is opened, or for the transition from the second operating mode to the first operating mode in batch operation, the second filtrate line is closed and the first filtrate line is opened, depending on which operating mode is executed first.

In an alternative embodiment, however, it can be provided that the second water volume is generated during the generation of the first water volume. This operating case represents a temporary simultaneity of the first and second operating modes, which is considered the third operating mode. As will be explained below, the first and second filtrate lines can also be opened simultaneously at least temporarily in order to generate the second water volume at least partially during the generation of the first water volume. This reduces the total time for generating the two water volumes. The third operating mode only exists for the duration of the second operating mode because the second water volume, i.e. the only ultrafiltered drinking water, is generated more quickly than the first water volume and after the generation of the second water volume, the second filtrate line is closed. If the second water volume has not yet been completely generated at this point, only the first filtrate line remains open, so that the first operating mode is present. This means that there is a change between the first and third operating modes. The second operating mode can start at the same time as the first operating mode or end at the same time as it.

According to a preferred embodiment, the first water volume is obtained by carrying out the ultrafiltration and reverse osmosis, i.e. the first operating mode, for a predetermined first operating period. Additionally or alternatively, the second water volume can also be obtained by carrying out only the ultrafiltration, i.e. the second operating mode, for a predetermined second operating period. The deactivation of the respective operating mode is thus purely time-controlled, in particular timer-controlled, more precisely, after the operating period provided for the respective operating mode has elapsed. This has the advantage that sensors, in particular a determination of the volume of water already produced, can be dispensed with.

The time-controlled switching off of the respective operating mode can be carried out by a control unit of the drinking water system in which the corresponding operating time is stored for each of the operating modes. Accordingly, the drinking water production system can have a control unit that is set up to set the first and second operating modes for a predetermined operating time each. The control unit can be a PLC (Programmable Logic Controller), for example.

To activate the first operating mode or to open the first filtrate line, a valve in the first filtrate line can be opened at the beginning of the first operating period and closed again to deactivate the first operating mode after the first operating period has elapsed. In a similar way, to activate the second operating mode or to open the second filtrate line, a valve in the second filtrate line can be opened at the beginning of the second operating period and closed again to deactivate the second operating mode after the second operating period has elapsed. The valves are preferably controlled by the control unit mentioned.

The activation of the second operating mode can take place after the deactivation of the first operating mode, so that the two operating modes do not overlap in time, or in other words, are carried out one after the other. This enables the first and second water volumes to be produced in batches. To do this, the valve in the first filtrate line can first be opened and closed again and then the valve in the second filtrate line can be opened and closed again.

• - Die zweite Filtratleitung kann geöffnet werden, bevor die erste Filtratleitung geöffnet wurde und geschlossen werden, nachdem die erste Filtratleitung geöffnet wurde.
• - Die zweite Filtratleitung kann zeitgleich mit der ersten Filtratleitung geöffnet werden, und geschlossen werden, bevor die erste Filtratleitung geschlossen wird.
• - Die zweite Filtratleitung kann geöffnet werden, nachdem die erste Filtratleitung geöffnet wurde und geschlossen werden, bevor die erste Filtratleitung geschlossen wird.
• - Die zweite Filtratleitung kann geöffnet werden, nachdem die erste Filtratleitung geöffnet wurde und zeitgleich mit dieser geschlossen werden.
• - Die zweite Filtratleitung kann geöffnet werden, bevor die erste Filtratleitung geschlossen wird, und geschlossen werden, nachdem die erste Filtratleitung geschlossen wurde.

As already mentioned, it is also possible to implement an operating mode in which the first and second operating modes overlap in time or the second operating mode is even carried out entirely during the first operating mode because the second operating period is shorter than the first operating period. The first and second filtrate lines can thus be opened at least temporarily at the same time in order to generate at least part of the second water volume during the generation of the first water volume. With regard to the operating modes, the second operating mode can be activated during the first operating mode, at the same time as or even before it, and deactivated during the first operating mode, at the same time as or after it, so that the first and second operating modes exist simultaneously at least temporarily. This makes it possible to reduce the time for generating the total volume formed from the first and second water volumes, with maximum time savings being achieved if the second water volume is generated entirely during the generation of the first water volume. The following five cases can therefore be distinguished for this temporal coexistence:

• - The second filtrate line can be opened before the first filtrate line has been opened and closed after the first filtrate line has been opened.
• - The second filtrate line can be opened at the same time as the first filtrate line and closed before the first filtrate line is closed.
• - The second filtrate line can be opened after the first filtrate line is opened and closed before the first filtrate line is closed.
• - The second filtrate line can be opened after the first filtrate line has been opened and closed at the same time.
• - The second filtrate line can be opened before the first filtrate line is closed and closed after the first filtrate line is closed.

In one embodiment, it can be provided that the first and/or second operating time is determined or calculated by the control unit. The control unit is therefore set up accordingly to determine the first and/or second operating time. Preferably, This is done based on the value of the water parameter of the raw water. In other words, in this case, the water parameter whose value is to be present as the target value in the drinking water to be produced is first determined in the raw water. The first and/or second operating periods are then determined depending on this parameter, which is done in particular by the above-mentioned control unit.

To determine the water parameters in the raw water, the drinking water production system can have a corresponding sensor, preferably a TDS sensor. The control unit is then set up accordingly to determine the first and/or second operating time depending on the water parameters measured in the raw water. This achieves a uniform system structure for the drinking water production system according to the invention, which is suitable for all installation locations. Thanks to the direct determination of the water parameters in the raw water, it is also no longer necessary to take samples from the pipe water and evaluate them to determine a suitable first and second operating time.

$$T_{OP1}=\frac{V_{RO}}{Q_{RO}}$$

und $$V_{UF}=V_X-V_{RO}$$

$$T_{OP2}=\frac{V_{UF}}{Q_{UF}}$$

wobei

• V_RO das erste Wasservolumen (Permeatvolumen),
• V_UF das zweite Wasservolumen (Filtratvolumen),
• V_X ein gewünschtes Gesamtvolumen,
• W_RT der Wert des Wasserparameters im Rohwasser,
• Z_FT der gewünschte Zielwert des Wasserparameters im Trinkwasser,
• R_RO ein prozentualer Rückhaltungswert der RO-Einheit als Dezimalwert,
• Q_RO der Volumenstrom des Permeats und
• Q_UF der Volumenstrom des Filtrats ist.

The determination of the first and second operating periods can be conveniently carried out using the following formulas: $$V_{RO}=\frac{V_X\cdot \left(W_{RT}-Z_{FT}\right)}{\left(R_{RO}\cdot W_{RT}\right)}$$

$$T_{OP1}=\frac{V_{RO}}{Q_{RO}}$$

and $$V_{UF}=V_X-V_{RO}$$

$${\mathrm{<figure-callout\; id="2"\; label="T\; O\; P"\; filenames="DE202022003021U1\_0009.png,DE202022003021U1\_0010.png"\; state="\{\{state\}\}">T</figure-callout>}}_{OP}=\frac{V_{UF}}{Q_{UF}}$$

where

• V _{RO is} the first water volume (permeate volume),
• V _UF the second water volume (filtrate volume),
• V _X a desired total volume,
• W _RT is the value of the water parameter in the raw water,
• Z _FT is the desired target value of the water parameter in drinking water,
• R _RO is a percentage retention value of the RO unit as a decimal value,
• Q _RO is the volume flow of the permeate and
• Q _UF is the volume flow of the filtrate.

Formula Eq. 1 is first used to determine the required first water volume V _RO , i.e. the volume of water that flows through both the UF unit and the RO unit. The desired total volume V _X , which is the sum of the first and second water volumes, corresponds to the tank volume of the fresh water tank when it is filled for the first time, for example between 1000l and 2000l. The value W _RT of the water parameter in the raw water is measured using a corresponding sensor. The desired target value Z _FT is specified and is therefore also known. The retention value R _RO is a specific parameter of the RO unit membrane and can be taken from the operating data of the RO unit manufacturer. It indicates the degree of retention of a certain dissolved substance or of salts in general and varies depending on the membrane and substance. The retention value R _RO is usually between 95% and 99%. Formula Eq. 2 is then used to determine the first operating time T _OP1 .

According to formula Eq. 3, the second water volume V _UF corresponds to the volume by which the first water volume or the fresh water tank must be filled in order to obtain the total volume. The second operating time T _OP2 is then determined using formula Eq. 2. The volume flow of the permeate Q _RO and the filtrate Q _UF are also operating values of the RO unit or the UF unit, which can be taken from the manufacturer's information and/or with which the drinking water production system is operated.

Using the formulas mentioned, the first and second operating times for producing the respective first and second water volumes are determined such that the mixture of the first and second water volumes has the desired target value of the water parameter in question, for example a TDS target value Z _FT between 250 mg/l and 500 mg/l.

It turns out that during operation of the drinking water production plant, all the variables of the above formulas are essentially constant. What is variable is, on the one hand, the value W _RT of the water parameter in the raw water, depending on where the raw water comes from (surface water, well water, river water, etc.) and, on the other hand, the desired total volume V _X , because it depends on the drinking water consumption. The latter is important if the process is repeated at a time when the fresh water tank is not yet completely empty, ie a different value for V _X is to be used than the tank content. Against this background, the first and second operating duration T _OP1 , T _OP2 can also be changed during the procedure.

In other words, for initially filling the empty fresh water tank with a first total volume, preferably equal to the nominal tank content of the fresh water tank, the first and second water volumes, the sum of which forms this first total volume, can each have an initial first value, and for later refilling the fresh water tank with a refill volume, the first and second water volumes can each have a second value, wherein the sum of the second value of the first water volume and the second value of the second water volume then form a second total volume, preferably equal to the refill volume. The method is then repeated to refill the fresh water tank, in which case the second total volume is reproduced, i.e. the first and second water volumes each have the second value. The same applies to the first and second operating periods. Thus, when initially filling the fresh water tank, the first operating time for generating the first water volume can have a first value and the second operating time for generating the second water volume can have a second value, whereas for refilling the fresh water tank, a second value can be used for the first and second operating times, each of which is smaller than the first value.

Preferably, the second total volume is adapted to the drinking water consumption. This can be achieved, for example, by determining the water level in the fresh water tank or the volume of water withdrawn from the fresh water tank and repeating the process if the water level falls below a specified limit or the volume of water withdrawn exceeds a specified limit. The level of the second total volume is known due to the determination of the corresponding limit. The process is then repeated with the second values for the first and second water volumes, or with the second values for the first and second operating periods.

The drinking water production system can therefore have a sensor for detecting the water level in the fresh water tank and/or a device for determining the volume of drinking water taken from the fresh water tank. Furthermore, the control unit can be set up to repeat the generation of the first and second water volumes if the water level falls below a specified limit or the volume of water taken exceeds a specified limit. In order to determine whether the water level falls below the specified limit, in the simplest case a binary water level sensor can be used which emits a first signal above the limit and a second signal below the limit. However, it is also possible to use a water level sensor which measures the actual water level so that the fill level of the fresh water tank is known at all times. The volume of water taken can be measured, for example, with a water meter or a water clock.

By falling below the water level limit or determining the water level in the fresh water tank, as with the direct measurement of the amount of drinking water withdrawn, it is known how much drinking water must be produced to refill the fresh water tank. If the water level limit is, for example, 50% of the maximum level or the limit for the volume of water withdrawn is, for example, 50% of the first total volume or maximum volume of the fresh water tank, the respective second value of the first and second water volumes can be 50% of the respective first value. The same applies to the first and second operating periods. In this embodiment, the volume of drinking water to be produced is always constant because the process is repeated when the water falls below the limit.

As an alternative to the limit values mentioned, additional drinking water production can be time-based and adjusted to consumption. In this case, no limit values are used. Instead, after a certain period of time, for example at intervals of between 5 and 30 minutes, the current water level is determined or the amount of drinking water taken so far is recorded. In the latter case, this amount already corresponds to the second total volume to be produced. In the case of the water level, the second total volume to be produced must first be calculated from this. In this example, the volume of drinking water to be produced is variable, as it is only determined at the end of the period mentioned.

Preferably, the target parameter used is the mass concentration of total dissolved solids (TDS), salinity, filtrate dry residue, total dried residue, electrical conductivity, electrical resistance, water hardness, the concentration of a chemical substance in the drinking water such as arsenic or fluoride, or another physical parameter of the water quality. To determine the salinity in the raw water, a TDS sensor can be used, the output signal of which is a measure of the salinity or total dried residue. Preferably, such a sensor is arranged in the raw water tank.

• 1: ein Blockschaltbild mit dem Grundaufbau einer erfindungsgemäßen Trinkwassergewinnungsanlage
• 2: ein Blockschaltbild einer detailreicheren Trinkwassergewinnungsanlage

Further features, properties and advantages of the drinking water production system according to the invention are described below using an exemplary embodiment. They show:

• 1 : a block diagram showing the basic structure of a drinking water production plant according to the invention
• 2 : a block diagram of a more detailed drinking water production plant

How 1 illustrated, a drinking water production plant 1 according to the invention comprises as core elements an ultrafiltration unit 14 for producing filtrate from raw water 2 and a reverse osmosis unit 20 for producing permeate from the filtrate. The UF unit 14 is referred to below as UF unit 14, the RO unit 20 as RO unit 20. An inlet 38 of the RO unit 20 is connected to an outlet 37 of the UF unit 14 via a lockable first filtrate line 26, so that the filtrate of the UF unit 14 can be fed to the RO unit 20 via the first filtrate line 26. The UF unit 14 and the RO unit 20 are thus connected in series. The first filtrate line 26 can be opened and closed via a first valve 34.

An outlet 39 of the RO unit 20 is connected to a mixing point 15 via a permeate line 28 in order to direct the permeate to this mixing point 15. The mixing point 15 is formed here by a fresh water tank 15, which provides the drinking water 3 for withdrawal. The concentrate 4 further produced by the RO unit 20 is discarded. The outlet 37 of the UF unit 14 is also connected to the mixing point 15 via a lockable second filtrate line 26, bypassing the RO unit 20. The second filtrate line 27 is thus parallel to the first filtrate line 26. The second filtrate line 27 can be opened and closed via a second valve 35.

The drinking water 3 should have a desired target value of a water parameter relating to its composition. In the present exemplary embodiment, the so-called TDS value (Total Dissolved Solids) is used as the water parameter, which indicates the mass of the substances dissolved in the water, i.e. the salts, in milligrams per liter. The desired target value in the drinking water is achieved by operating the drinking water production system 1 in a first operating mode in which the first filtrate line 26 is open to the mixing point 15 to produce a first water volume in the form of a permeate volume, and in a second operating mode in which the second filtrate line 27 is open to the mixing point 15 to produce a second water volume in the form of a filtrate volume. The two water volumes then mix in the mixing point 15 or the fresh water tank 15.

Thus, on the one hand, a first volume of water is produced by obtaining a filtrate from the raw water 2 by ultrafiltration and from this a permeate is obtained by reverse osmosis, the volume of which forms the first volume of water, and on the other hand, a second volume of water is produced by obtaining a filtrate from the raw water 2 by ultrafiltration, the volume of which forms the second volume of water. After each extraction, the first and second volumes of water are mixed to obtain the drinking water 3, wherein the first and second volumes of water are dimensioned such that their mixture has the desired target parameters. The dimensioning of the water volumes is carried out here based on the respective operating time for which the drinking water production system 1 is operated in the first and second operating modes. The first volume of water is obtained by carrying out the ultrafiltration and reverse osmosis for a predetermined first operating time. Furthermore, the second volume of water is obtained by carrying out only the ultrafiltration for a predetermined second operating time.

How 2 further shows that the drinking water production system 1 comprises a control unit 5, which is connected to the two valves 34, 35 via control lines shown in dashed lines in order to open or close them as desired. The first operating mode is when the first valve 34 is open. The second operating mode is when the second valve 35 is open. However, both valves 34, 35 can also be open at the same time at times, which can be considered a third operating mode. Of course, both valves 34, 35 can also be closed, which means that the drinking water production system 1 is at a standstill.

$$T_{OP1}=\frac{V_{RO}}{Q_{RO}}$$

und $$V_{UF}=V_X-V_{RO}$$

$$T_{OP2}=\frac{V_{UF}}{Q_{UF}}$$

wobei

• V_RO das erste Wasservolumen (Permeatvolumen),
• V_UF das zweite Wasservolumen (Filtratvolumen),
• V_X ein gewünschtes Gesamtvolumen,
• W_RT der Wert des Wasserparameters im Rohwasser,
• Z_FT der gewünschte Zielwert des Wasserparameters im Trinkwasser,
• R_RO ein Rückhaltungswert der RO-Einheit in Prozent,
• Q_RO der Volumenstrom des Permeats und
• Q_UF der Volumenstrom des Filtrats ist.

The first and second operating times depend on the value of the water parameter of the raw water 2, i.e. its TDS value. This value could be determined by a laboratory test, the operating times then calculated and stored in the control unit. The TDS value of the raw water 2 can, however, advantageously be measured by a TDS sensor 12 and passed from this to the control unit 5. This is illustrated by the dashed line between sensor 16 and control unit 5 in 1 The control unit 5 can then use the measured TDS value to calculate the first and second operating times. The following formulas are used: $$V_{RO}=\frac{V_X\cdot \left(W_{RT}-Z_{FT}\right)}{\left(R_{RO}-W_{RT}\right)}$$

$$T_{OP1}=\frac{V_{RO}}{Q_{RO}}$$

and $$V_{UF}=V_X-V_{RO}$$

$${\mathrm{<figure-callout\; id="2"\; label="T\; O\; P"\; filenames="DE202022003021U1\_0009.png,DE202022003021U1\_0010.png"\; state="\{\{state\}\}">T</figure-callout>}}_{OP}=\frac{V_{UF}}{Q_{UF}}$$

where

• V _{RO is} the first water volume (permeate volume),
• V _UF the second water volume (filtrate volume),
• V _X a desired total volume,
• W _RT is the value of the water parameter in the raw water,
• Z _FT is the desired target value of the water parameter in drinking water,
• R _RO is a retention value of the RO unit in percent,
• Q _RO is the volume flow of the permeate and
• Q _UF is the volume flow of the filtrate.

For example, if the TDS value in the raw water is W _RT = 800 mg/l and a TDS target value in the drinking water of Z _FT = 500 mg/l is desired, then in order to fill a fresh water tank 15 with a total volume of V _X = 1000l, and under the conservative assumption of a rejection value of the RO unit of at least R _RO = 96% and using a filtrate volume flow of Q _UF = 260 l/h and a permeate volume flow of Q _RO = 78 l/h, the first operating mode can have an operating time of T _OP1 = 5 hours and the second operating mode can have an operating time of T _OP2 = 2.4 hours. The control unit 5 then opens the first valve 34 for these 5 hours and the second valve for 2.4 hours. For example, if the TDS value in the raw water is 1200 mg/l and a target TDS value in the drinking water of 250 mg/l is desired, then, assuming the same values for V _X , R _RO , Q _UF and Q _RO as before, the first operating mode can have an operating time of 10.6 hours and the second operating mode an operating time of 0.7 hours. The control unit 5 then opens the first valve 34 for these 10.6 hours and the second valve for 0.7 hours.

It is advantageous to run the two operating modes one after the other, i.e. to produce the first and second water volumes in batches. This allows the use of a small UF unit, since filtrate for the mixing tank and the RO feed does not have to be produced at the same time.

2 shows a drinking water production plant 1 according to the invention, which, in contrast to plant 1 in 1 is supplemented by further components. The raw water 2 is provided in a raw water tank 10, which is connected to the inlet 36 of the UF unit 14 via a raw water line 25. A raw water pump 11 is arranged within the raw water line 25 to pump the raw water 2 from the tank 10 and to the UF unit 14 at a pressure p _F of, for example, 0.7 bar. A TDS sensor 12 is also connected to the raw water line 25 to determine the TDS value of the raw water 2. Furthermore, a pretreatment unit in the form of a pre-filter 13 is arranged in the raw water line 25 between the raw water pump and the raw water line 25 to filter out coarse particulate components in the raw water, such as sand.

The UF unit 14 can be formed by one or more parallel ultrafiltration modules, for example by four such modules. Such an ultrafiltration module preferably has a large number of ultrafiltration membranes in the form of hollow fibers. The membranes are designed in such a way that particles larger than 9.5 nm are retained. The membranes separate a raw water side, to which the inlet 36 opens, from a filtrate side, from which at least one outlet 37 leads. During operation, a differential pressure, also called transmembrane pressure (TMP), of a maximum of 1.2 bar can exist between the raw water side and the filtrate side.

In order to remove the particles that accumulate on the membranes on the raw water side over time, and thus to clean the UF unit 14, the latter can be flowed through backwards, which is generally known as backwashing. Water is pumped from the filtrate side to the raw water side. For this purpose, a backwash pump 22 is provided in the drinking water production system 1, which is connected to the outlet 37 of the UF unit 14 via a backwash line 30. The backwash line 30 can be separated from the outlet 37 of the UF unit 14 via a backwash valve 40. The backwash water mixed with the accumulated particles is discharged on the raw water side through a retentate line 32 and separated in an outlet 41.

In one embodiment, the retentate line 32 can be connected to the same inlet as the raw water line 26, whereby In this case, a shut-off valve is provided between the inlet 36 and the raw water line 25 and between the inlet 36 and the retentate line 32 in order to connect either the raw water line or the retentate line to the raw water side of the UF unit 14 depending on the operating mode (filter operation, backwash operation). Alternatively, the raw water side can have two inlets 36, one inlet of which is connected to the raw water line 25 and one inlet to the retentate line 32. In this case, too, there is a shut-off valve in the raw water line 25 and the retentate line 32.

The output 37 of the UF unit 14 is also available in the version according to 2 connected to a fresh water tank 15 via two parallel lines 26, 27, through which a specific volume of water can be introduced into the tank 15. A central line section, into which the retentate line 30 also flows, connects the outlet 37 to a fork 23, at which the central line section splits into a first filtrate line 26 and a second filtrate line 27. The second filtrate line 27 flows directly into the fresh water tank 15, so that a volume of the undemineralized, ultrafiltered water from the UF unit 14 can be made available to the fresh water tank 15 via it. This can be done with a filtrate flow of, for example, Q _UF = 260 l/h. In the second filtrate line 27 there is a second valve 35 to optionally open or close it.

The first filtrate line 26 connects the fork 23 or the outlet 37 of the UF unit 14 with the inlet 38 of the RO unit 20 in order to supply the filtrate of the UF unit 14 to it. In the first filtrate line 27 there is a first valve 34 in order to open or close it as desired. Furthermore, a high-pressure pump 18 and, following this, a feed unit 19 are arranged in the second filtrate line 26. In the case of cleaning, the feed unit 19 is used for the metered addition of an antiscalant, i.e. a chemical for membrane cleaning. The feed unit 19 is thus located between the high-pressure pump 18 and the RO unit 20.

As in the case of the UF unit 14, the RO unit 20 can also be formed by one or more parallel reverse osmosis modules in order to increase the amount of permeate produced per unit of time. A reverse osmosis module has a reverse osmosis membrane which separates an inlet side from an outlet side. As a result of the permeation of the water through the membrane, a permeate, i.e. largely demineralized pure water, is produced on the outlet side, which can drain via a first outlet 39 of the RO unit 20. A permeate line 28 connects this first outlet 39 of the RO unit 20 to the fresh water tank 15, so that a volume of the water ultrafiltered and osmotically desalinated by the RO unit 20 can be made available for the fresh water tank 15 via it. The permeate can flow with a volume flow of, for example, Q _RO = 78 l/h. The transmembrane pressure across the osmosis membrane can be p _RO = 4.8 bar.

The reverse osmosis membrane is flowed over as intended, so that the inlet side has an inflow and an outflow side. Due to the permeation of the water through the membrane between the inflow and the outflow side, the salt concentration on the outflow side is higher than on the inflow side. The water flowing off on the outflow side thus forms a concentrate 4. The inflow side is connected to the inlet 38, the outflow side to a second outlet 42, to which a concentrate line 29 is connected in order to introduce the concentrate 4 into a concentrate tank 21, for example with a capacity of 150 l, to which the concentrate line 29 is connected. An overflow line 31 drains overflowing concentrate 4 in order to separate it in a drain 41. The concentrate 4 serves as backwash water, which is why the backwash line 30 is connected to the concentrate tank 21.

A level sensor 17 is arranged in the fresh water tank 15, which is at least designed to detect when a certain limit level is undershot. The level sensor 17 can preferably be designed to measure the actual level of the drinking water in the tank at any time. With the help of the level sensor 16, it can be determined whether, when and how much drinking water needs to be produced to meet the desired TDS target value. In addition, another TDS sensor is arranged in the fresh water tank 15, which measures the TDS value of the drinking water produced. This value can be used to check that the drinking water production system is working correctly.

2 also shows the central control unit 5, to which, on the one hand, the sensor data of the TDS sensor 12 for the raw water, the TDS sensor 16 for the fresh water and the water level in the fresh water tank 15 are fed via corresponding sensor lines (dash-dotted lines), and which, on the other hand, are in operative connection with the pumps 11, 18, 22 and the valves 34, 35, 40 via corresponding control lines (dashed lines) in order to control them.

When the drinking water production plant 1 starts operating, the TDS value in the raw water 2 is determined using the sensor 12 and made available to the control unit. The control unit then uses the above formulas to determine the first operating time for the first operating mode in order to determine the first water volume. lumen in the form of a permeate volume, and the second operating time for the second operating mode to generate the second water volume in the form of a filtrate volume, in such a way that the mixed total volume of the first and second volumes has the desired TDS target value. The TDS value in the raw water therefore defines the operating time of the UF unit 14 in individual operation and the combination of UF and RO unit. The advantage here is that the hydraulic structure of the drinking water production plant 1 does not need to be changed for different TDS values in the raw water. Rather, an adjustment takes place purely in terms of control technology, in that an adjustment to a changed TDS value is made simply by recalculating the first and second operating times.

Here, too, the first and second water volumes are produced one after the other. The first water volume (RO batch) is produced first, followed by the second water volume (UF batch).

A further advantage of the drinking water production plant 1 is that all hydraulic lines 25, 26, 27, 28, 29, 30, 31 are formed by hoses, preferably with connectors, instead of rigid pipes with threads, which increases the compactness and simplifies the assembly of the plant.

It should be noted that the above description is given merely by way of example for the purpose of illustration and in no way limits the scope of the invention. Features of the invention which are specified as "may", "exemplary", "preferred", "optional", "ideal", "advantageous", "optionally", "suitable" or the like are to be considered purely optional and also do not limit the scope of protection, which is determined exclusively by the claims. To the extent that elements, components, process steps, values or information are mentioned in the above description which have known, obvious or foreseeable equivalents, these equivalents are included in the invention. Likewise, the invention includes any changes, variations or modifications of embodiments which involve the exchange, addition, change or omission of elements, components, process steps, values or information, as long as the basic idea of the invention is retained, regardless of whether the change, variation or modifications lead to an improvement or deterioration of an embodiment.

Although the above description of the invention mentions a large number of physical, non-physical or method-related features in relation to one or more specific embodiment(s), these features can also be used in isolation from the specific embodiment, at least as long as they do not require the mandatory presence of further features. Conversely, these features mentioned in relation to one or more specific embodiment(s) can be combined with one another as desired and with further disclosed or undisclosed features of embodiments shown or not shown, at least as long as the features do not exclude one another or lead to technical incompatibilities.

List of reference symbols

1

Drinking water production plant

2

Raw water

3

Drinking water

4

concentrate

5

Control unit

10

Raw water tank

11

Raw water pump

12

TDS sensor

13

Pretreatment unit/prefilter

14

Ultrafiltration unit/UF unit

15

Fresh water tank/mixing point

16

TDS sensor

17

Level sensor

18

high pressure pump

19

Addition unit

20

Reverse osmosis unit/RO unit

21

Concentrate tank

22

Backwash pump

23

crotch

24

Dispensing unit/ water outlet

25

Raw water pipe

26

First filtrate line

27

Second filtrate line

28

Permeate line

29

Concentrate line

30

Backwash line

31

Overflow line

32

Retentate line

33

Output line

34

first valve

35

second valve

36

Entrance of the ultrafiltration unit

37

Output of the ultrafiltration unit

38

Reverse osmosis unit input

39

First output of the reverse osmosis unit

40

Backwash valve

41

Drain

42

Second output of the reverse osmosis unit

Claims (8)

Drinking water production plant (1) for producing drinking water (3) from raw water (2) by ultrafiltration and reverse osmosis, the drinking water (3) having a desired target value of a water parameter relating to its composition, at least comprising an ultrafiltration unit (14) for producing filtrate from the raw water (2), a reverse osmosis unit (20) arranged in series with the ultrafiltration unit (14) via a lockable first filtrate line (26) for producing permeate from the filtrate, which is connected to a mixing point (15), and comprising a fresh water tank for providing the drinking water (3) for withdrawal, characterized in that a lockable second filtrate line (27) connects the ultrafiltration unit (14) to the mixing point (15) bypassing the reverse osmosis unit (20), and in that the drinking water production plant (1) is designed to be operated in a first operating mode in which the first filtrate line (26) is connected to the mixing point (15) in order to obtain the filtrate from the raw water (2) by ultrafiltration and from this the permeate by reverse osmosis, the volume of which forms a first water volume, and - to be operated in a second operating mode in which the second filtrate line (27) is open towards the mixing point (15) in order to obtain the filtrate from the raw water (2) by ultrafiltration, the volume of which forms a second water volume, the first and second water volumes being dimensioned such that their mixture has the desired target value and the mixture forms the drinking water (3). Drinking water production plant (1) according to Claim 1 , characterized in that the mixing point (15) is the fresh water tank. Drinking water production plant (1) according to one of the preceding claims, characterized in that it has a control unit (5) which is designed to set the first operating mode for a predetermined first operating period and the second operating mode for a predetermined second operating period, in particular one after the other. Drinking water production plant (1) according to Claim 3 , characterized in that it comprises a sensor (12) for determining the value of the water parameter of the raw water (2) and the control unit (5) is arranged to determine the first and second operating times as a function of this. Drinking water production plant (1) at least Claim 3 , characterized in that it comprises a sensor (17) for detecting the water level in the fresh water tank or a device for determining the volume of water withdrawn from the fresh water tank, and in that the control unit (5) is arranged to repeat the generation of the first and second water volumes when the water level falls below a predetermined limit value or the volume of water withdrawn exceeds a predetermined limit value. Drinking water production plant (1) according to Claim 1 , characterized in that it is arranged to shut off the second filtrate line (27) for the production of the first water volume, and to shut off the first filtrate line (26) for the production of the second water volume. Drinking water production plant (1) according to Claim 1 , characterized in that it is arranged to open the first and second filtrate lines (26, 27) at least temporarily simultaneously in order to produce at least part of the second water volume during the production of the first water volume. Drinking water production plant (1) according to one of the preceding claims, characterized in that the target parameter is the mass concentration of the totally dissolved solids (TDS), the salinity, the filtrate dry residue, the total drying residue, the electrical conductivity, the electrical resistance, the water hardness or the concentration of a chemical substance in the drinking water.

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