1. Technical field

The present disclosure relates to a method for treating feed water and a system for treating feed water.

2. Prior art

Climatic changes and population growth are causing an increasing water scarcity and an increasingly growing demand for water. As a result, improved water treatment is becoming increasingly important.

For treating water, it is known to use ceramic filtration based on ceramic filtration membranes. Especially for operating reverse osmosis systems which are often used to provide potable water it is known to treat feed water by means of ceramic filtration prior to a reverse osmosis process. Thereby reverse osmosis systems based on the reverse osmosis technology can remove various types of dissolved and/or suspended chemical species as well as biological species, such as bacteria, from water. However, there are several contaminants, such as suspended solids, Extracellular Polymeric Substances (EPSs), bacteria, microorganisms, planktonic substances, calcium/magnesium carbonates, sulfides, etc., which must be removed and/or inactivated before the reverse osmosis process, as reverse osmosis membranes are very sensitive. Hence, it is very important to deliver sufficiently treated water into the reverse osmosis system. Therefore, often a treatment with ceramic filtration membranes is chosen.

However, in existing systems for treating feed water, particularly for reverse osmosis processes, the ceramic filtration membranes regularly require maintenance, backwashing and/or chemical cleaning due to biological fouling and/or the buildup of sediment layers. During maintenance, backwashing and/or chemical cleaning the supply with treated, i.e. filtered water, is interrupted or at least decreased. This is particularly problematic in dry regions which require a constant supply with clean or even potable water. Nevertheless, maintenance, backwashing and/or chemical cleaning are vital as biological fouling and the buildup of sediment layers may cause downtimes or at least negatively affect the efficiency and/ or the quality of a water treatment plant. Thereby water treatment plants are often located in less developed and/or less populated regions of the world, where technical support is not permanently available and/ or requires significant time. As a result, downtimes and/or delayed maintenance could not only have an economic impact but could particularly cause a shortage of drinking water and/or make it impossible to irrigate fields.

Even further, although ceramic filtration is regularly used prior to the reverse osmosis process with sufficient maintenance, backwashing and/or chemical cleaning, the reverse osmosis membranes get damaged and/or contaminated. One reason is that the filtering performance of the ceramic filtration membranes is regularly not sufficient. This is as reverse osmosis membranes, which have a very low porosity, are veiy sensitive to any particles, salts, and/ or microorganisms as they quickly cover the membrane's surface and/or form fouling and/or scaling layers, which slowly destroys the membranes and/or decreases their performance.

Thus, it is an object of the present disclosure to provide a method and a system for treating feed water that overcome the aforementioned drawbacks at least partially.

3. Summary of the invention

This object is achieved, at least partly, by a method for treating feed water and a system for treating feed water, as defined in the independent claims. Further aspects of the present disclosure are defined in the dependent claims. Since the method and the system both relate to treating feed water, it will be understood that advantages and/or features of the method may also apply to the system and vice versa.

In particular, the object is achieved by a method for treating feed water, in particular for use in a reverse osmosis process. Hence, the method may serve to treat a feed water prior to entering the reverse osmosis process.

The method comprises the step a. of providing feed water. Thereby the feed water may be provided as a flow or within a reservoir. Further, the feed water may be wastewater, seawater, groundwater and/ or brackish water. Moreover, the feed water may comprise at least one of the following: suspended solids, Extracellular Polymeric Substances (EPSs), bacteria, microorganisms, planktonic substances, calcium carbonates, magnesium carbonates and/or sulfides etc.

Further, the method comprises the step b. of generating ozonated water, wherein ozone gas is provided in water at least partially as ultra-fine ozone bubbles, wherein ultra-fine bubbles are defined as having a diameter from io nm to 900 nm.

It is understood that ozone gas may not exclusively be provided as ultra-fine ozone bubbles but also in other bubble sizes. Moreover, providing ozone gas in water as ultrafine ozone bubbles may comprise providing the ozone gas in any bubble size in the water and subsequently transforming these bubbles at least partially into ultra-fine ozone bubbles. Said transformation maybe conducted by means of a hydrodynamic cavitation device and preferably by means of a multi-stage hydrodynamic cavitation device. Particularly, the transformation maybe based on a hydrodynamic cavitation phenomenon. In detail, kinetic energy delivered by a centrifugal pump may be utilized to create a vortex flow with a high turbulence. Thereby in a core of the vortex flow a vacuum region is generated and outside the core a high-pressure region is generated and centrifugal forces in the vortex flow throw out gas bubbles from the vacuum region into the high-pressure region. This leads to cavitation and the generation of ultra-fine bubbles. Further, the ultra-fine ozone bubbles maybe provided in the water by means of a pressurized dissolution method, a shear force method and/ or porous film permeation method. Furthermore, the ozone gas may be provided in the water together with other gases such as oxygen and/or carbon dioxide. Particularly preferred a mixture of oxygen and ozone gas is provided in the water, wherein the mixture comprises between 1 wt.% and 20 wt.% of ozone gas. Said mixture ensures stability of the ozone gas and therefore enhances safety.

The ultra-fine ozone bubbles may be differentiated from ozone bubbles with a larger diameter therein that they do not rise in water but stably float. That the ultra-fine ozone bubbles do not rise in water may allow for a more homogeneous bubble distribution. Thereby, with a more homogeneous bubble distribution in the feed water, the filtering can be improved.

Moreover, the method comprises the step c. of mixing the ozonated water with the feed water, and after that the step d. of filtering the mixture by means of a ceramic filtration means. Mixing may be understood as introducing the ozonated water into the feed water. Moreover, mixing may be understood as merging a flow of the ozonated water and a flow of the feed water. An active mixing may take place, however, it is not strictly required. For example, the mixing may be done by means of a static mixer.

Filtering the mixture by means of the ceramic filtration means may include transferring the mixture through the ceramic filtration means. The ceramic filtration means may comprise a material with macropores. Further, a pore size of the ceramic filtration means may range from 0.09 pm to 1.2 pm, preferably from 0.092 pm to 1.1 pm, more preferably from 0.095 pm to 1.0 pm, even more preferably from 0.097 pm to 0.9 pm, and most preferably from 0.1 pm to 0.2 pm. These pore sizes allow an enhanced filtering performance and a sufficient flow rate. This is as these pore sizes exhibit an improved interaction with ultra-fine ozone bubbles.

The ceramic filtration means may comprise at least one ceramic filtration membrane. Further, the ceramic filtration means may comprise at least one flat sheet ceramic filtration membrane. The ceramic filtration means is preferably installed in a low- pressure filtration tank. The ceramic filtration means may comprise at least one silicon carbide-based membrane and/ or at least one AI2O3 based ceramic membrane.

Mixing the ozonated water with the feed water before filtering with the ceramic filtration means improves the filtering performance and/ or at least partially reduces the need for maintenance, backwashing and/ or chemical cleaning. First, mixing the ozonated water with the feed water before filtering with the ceramic filtration means allows for a continuous oxidation of organic material by means of oxidation processes. This already leads to an at least partial purification of the feed water. Further, a biological fouling and/ or a buildup of sediment layers at the ceramic filtration means can be at least partially avoided. Thus, a decrease of the permeability of the ceramic filtration means may be at least partially avoided and/ or slowed down. Second, a continuous mechanical cleaning of the ceramic filtration means can be achieved. This is as at least part of the ultra-fine ozone bubbles implode what emits ultrasound waves being able to destroy physical build up, such as sediment layers and/or biological fouling layers, on the ceramic filtration means.

The water into which the ozone bubbles are provided may be at least partially filtered water obtained from method step d. Thereby the stability of the ultra-fine ozone bubbles may be increased. This is as filtered water is free from pollutants and ozone gas is not wasted during dissolution in filtered water by reacting with the pollutants. Hence, less ozone gas may be used such that the number of pumps being required for the dissolution of ozone gas may be reduced. In other words; a part of the ceramically filtrated feed water is branched off to be supplied with the ultra-fine ozone bubbles and then led back and mixed with the untreated feed water before the mixture is supplied to the ceramic filtration means.

The method may further comprise the step of backwashing, wherein backwashing water is backwashed through the ceramic filtration means to clean the ceramic filtration means, wherein the backwashing water comprises filtered water of step d. and ozonated water. Thereby at least part of the ozonated water from step b. may be mixed with filtered water of step d. It is conceivable that the present invention may not eliminate the need for backwashing completely. However, with the backwashing water comprising ozonated water, oxidation processes and/ or implosion processes can take place during backwashing. Thereby the permeability of the ceramic filtration means can be efficiently restored before a next filtration stage. Moreover, the amount of backwashing water can be reduced.

The backwashing water may comprise ozonated water and filtered water in a mixing ratio of ozonated water to filtered water which lies in the range from i:iooo to 1:2, preferably from 1:500 to 1:3, more preferably from 1:100 to 1:4, even more preferably from 1:50 to 1:4.5, and most preferably from 1:8 to 1:5. These ranges have proven to optimize the relation between efficient cleaning of the ceramic filtration means and at the same time reducing the amount of required backwashing water.

The ceramic filtration means may comprise a ceramic ultra-filtration membrane. Thereby the term ultra-filtration refers to a variety of membrane filtration in which forces like pressure and/or concentration gradients lead to a separation through a semipermeable membrane. Suspended solids and/or solutes of high molecular weight are retained in a retentate, while water and/or low molecular weight solutes pass through the ultra-filtration membrane in the permeate, i.e. the filtrate. By means of the ceramic filtration means comprising a ceramic ultra-filtration membrane the impact of the ultra-fine ozone bubbles can be even further increased.

Further, in step b. 1 gram to 2000 gram, preferably 5 gram to 900 gram, more preferably 8 gram to 800 gram, even more preferably 10 gram to 700 gram, and most preferably too gram to 600 gram of ozone gas maybe provided per ton of water, wherein preferably at least 5 %, more preferably at least 10 %, even more preferably at least 40 %, and most preferably at least 85 % of the ozone gas are provided in the water as ultra-fine ozone bubbles. By these amounts of ozone gas per ton of water and the percentages of the ozone gas being provided in the water as ultra-fine ozone bubbles the effect of the ultra-fine ozone bubbles is significant, while at the same time the amount of required ozone gas is kept moderate.

Furthermore, one ton of the ozonated water which is mixed with the feed water in step c. may comprise 1 gram to 2000 gram, more preferably 5 gram to 800 gram, even more preferably 10 gram to 700 gram, and most preferably 100 gram to 600 gram of ozone gas, wherein preferably at least 5 %, more preferably at least 10 %, even more preferably at least 40 %, and most preferably at least 85 % of the ozone gas are ultrafine ozone bubbles. By means of these amounts of ozone gas per ton of water and the percentages of the ozone gas in the water as ultra-fine ozone bubbles the effect of the ultra-fine ozone bubbles is significant, while at the same time the amount of required ozone gas is kept moderate.

The ultra-fine ozone bubbles may have a diameter from 25 nm to 800 nm, preferably from 30 nm to 700 nm, more preferably from 50 nm to 600 nm, even more preferably from 60 nm to 400 nm, and most preferably from 70 nm to 200 nm. These diameter ranges allow for improving the oxidation of organic material by means of the ultra-fine bubbles. Further, these diameter ranges allow for an improved continuous mechanical cleaning due to a higher emission of ultrasound waves by the imploding ultra-fine ozone bubbles. In summary the above diameters improve the filtering performance and/or at least partially avoid a biological fouling and/or a buildup of sediment layers at the ceramic filtration means. It will be understood that if e.g. 10 % of the ozone gas provided in the water are provided as ultra-fine ozone bubbles and the ultra-fine ozone bubbles are specified to have a diameter from 25 nm to 800 nm, then 10 % of the ozone gas are ultra-fine ozone bubbles with a diameter from 25 nm to 800 nm and the remaining 90% may have a different diameter and may not necessarily be in the form of ultra-fine bubbles.

The ultra-fine ozone bubbles may have an average diameter which lies in the range from 25 nm to 700 nm, preferably from 40 nm to 600 nm, more preferably from 50 nm to 500 nm, even more preferably from 60 nm to 400 nm, and most preferably from 70 nm to 200 nm. These average diameter ranges have proven to further increase the effect of continuous mechanical cleaning due to an increased emission of ultrasound waves by the imploding ultra-fine ozone bubbles. It will be understood that the ultra- fine ozone bubbles may be exemplarily specified to have a diameter from 25 nm to 800 nm and have an average diameter which lies in the range from 60 nm to 400 nm.

The mixing ratio of ozonated water to feed water in step c. may lie in the range from 1:1000 to 1:1, preferably from 1:500 to 1:1.5, more preferably from 1:100 to 1:2, even more preferably from 1:10 to 1:2.5, and most preferably from 1:5 to 1:3. These ranges have proven to optimize the relation between efficient feed water treatment and at the same time reducing the amount of required ozonated water. Hence, by reducing the amount of required ozonated water the amount of feed water may be increased, and the efficiency of feed water treatment is enhanced.

The method may further comprise the step of injecting a coagulant into the feed water before filtering. The coagulant may comprise iron salt, aluminum salt, titanium salt, zirconium salt and/or salt of any other metal. Coagulants are compounds that promote the clumping of fines into larger floc so that they can be more easily separated from the water. Thereby the injection of a coagulant in combination with the use of ultra-fine ozone bubbles allows for improved coagulation. This is as the ultra-fine ozone bubbles enhance coagulation on a micro scale since particles bond to the ultra-fine ozone bubbles. Hence, with the same amount of coagulant or even less coagulant, an improved coagulation may be achieved.

Thereby at least part of the ozonated water may be mixed with the feed water prior to injecting the coagulant, wherein at least another part of the ozonated water may be mixed with the feed water after injecting the coagulant. Mixing part of the ozonated water with the feed water prior to injecting the coagulant allows for an improved coagulation. This is as coagulation on a micro scale prior to adding the coagulant enhances and/or accelerates the overall coagulation process. Moreover, mixing part of the ozonated water with the feed water after injecting the coagulant allows to provide a stable amount of ultra-fine ozone bubbles in the mixture before it enters the ceramic filtration means. In summary, the improved coagulation, and the mixing of ozonated water with the feed water before the ceramic filtration means allows for a high and/or stable permeability of the ceramic filtration means.

The ozonated water which is mixed with the feed water prior to injecting the coagulant may be mixed with the feed water in a mixing ratio which lies in the range from 1:2000 to 1:1, preferably from 1:1000 to 1:2, more preferably from 1:500 to 1:3, even more preferably from 1:100 to 1:4, and most preferably from 1:10 to 1:5, wherein preferably the ozonated water which is mixed with the feed water after injecting the coagulant is mixed with the feed water in a mixing ratio which lies in the range from i:iooo to 1:1, preferably from 1:500 to 1:1.5, more preferably from 1:100 to 1:2, even more preferably from 1:10 to 1:2.5, and most preferably from 1:5 to 1:3. Thereby it will be understood that the feed water after adding the coagulant may still comprise ultra-fine ozone bubbles. Said ranges have proven to optimize the relation between efficient coagulation and/or efficient filtering and at the same time reducing the amount of required ozonated water.

The object is further achieved, at least partly by a system for treating feed water, in particular for use in a reverse osmosis process. Hence, the system may serve to treat a feed water prior to entering the reverse osmosis process.

The system comprises an inlet for receiving feed water. Further the system comprises ceramic filtration means for filtering the feed water. The ceramic filtration means may comprise a material with macropores. Further, a pore size of the ceramic filtration means may range from 0.09 pm to 1.2 pm, preferably from 0.092 pm to 1.1 pm, more preferably from 0.095 pm to 1.0 pm, even more preferably from 0.097 pm to 0.9 pm, and most preferably from 0.1 pm to 0.2 pm. These pore sizes allow an enhanced filtering performance and a sufficient flow rate. The ceramic filtration means may comprise at least one ceramic filtration membrane. Further, the ceramic filtration means may comprise at least one flat sheet ceramic filtration membrane. The ceramic filtration means is preferably installed in a low-pressure filtration tank.

Moreover, the system comprises a first fluidic connection between the inlet and the ceramic filtration means for guiding the feed water from the inlet to the ceramic filtration means. The fluidic connection maybe any means which allows to guide the feed water from the inlet to the ceramic filtration means, such as a tube, a pipe, a hose, a channel and/or the like.

Furthermore, the system comprises an ozone bubble generation unit for generating ozonated water, wherein the ozone bubble generation unit is configured to provide ultra-fine ozone bubbles in water, wherein ultra-fine bubbles are defined as having a diameter from 10 nm to 900 nm.

The ozone bubble generation unit may comprise a hydrodynamic cavitation device. Further, the ozone bubble generation unit may comprise a multi-stage hydrodynamic cavitation device. Particularly, the ozone bubble generation unit may be based on a hydrodynamic cavitation phenomenon. Thereby, in detail, kinetic energy delivered by a centrifugal pump may be utilized to create a vortex flow with a high turbulence. Thereby in a core of the vortex flow a vacuum region is generated and outside the core a high-pressure region is generated and centrifugal forces in the vortex flow throw out gas bubbles from the vacuum region into the high-pressure region. This leads to cavitation and the generation of ultra-fine bubbles. Moreover, for providing the ultrafine ozone bubbles the ozone bubble generation unit may rely on a pressurized dissolution method, a shear force method and/ or porous film permeation method.

Even further, the system comprises at least one mixing means for mixing the ozonated water with the feed water before the feed water is guided to the ceramic filtration means. Mixing may be understood as introducing the ozonated water into the feed water. Moreover, mixing may be understood as merging a flow of the ozonated water and a flow of the feed water. An active mixing may take place, however, is not required. For example, the mixing means may comprise a static mixer. Moreover, the mixing means may be a port in the first fluidic connection for mixing the ozonated water with the feed water.

Mixing the ozonated water with the feed water before filtering with the ceramic filtration means improves the filtering performance and/ or at least partially reduces the need for maintenance, backwashing and/ or chemical cleaning. First, mixing the ozonated water with the feed water before filtering with the ceramic filtration means allows for a continuous oxidation of organic material by means of oxidation processes. This already leads to an at least partial purification of the feed water. Further, a biological fouling and/ or a buildup of sediment layers at the ceramic filtration means can be at least partially avoided. Thus, a decrease of the permeability of the ceramic filtration means may be at least partially avoided and/ or slowed down. Second, a continuous mechanical cleaning of the ceramic filtration means can be achieved. This is as at least part of the ultra-fine ozone bubbles implode what emits ultrasound waves being able to destroy physical build up, such as sediment layers and/or biological fouling layers, on the ceramic filtration means.

The system may further comprise a second fluidic connection between a source of backwashing water and the ceramic filtration means for introducing backwashing water into the ceramic filtration means to clean the ceramic filtration means. Thereby the system preferably comprises a third mixing means for mixing part of the ozonated water with the backwashing water. The advantages of introducing ozonated water into IO the backwashing water are described in further detail above regarding the method according to the present invention.

The third mixing means may be configured to provide backwashing water that comprises ozonated water and filtered water in a mixing ratio of ozonated water to filtered water which lies in the range from 1:1000 to 1:2, preferably from 1:500 to 1:3, more preferably from 1:100 to 1:4, even more preferably from 1:50 to 1:4.5, and most preferably from 1:8 to 1:5. As described above regarding the method according to the present invention, these ranges have proven to optimize the relation between efficient cleaning of the ceramic filtration means and at the same time reducing the amount of required backwashing water.

The system may further comprise a reservoir for receiving filtered water which was filtered by the ceramic filtration means, wherein the reservoir is preferably fluidically connected to the ozone bubble generation unit such that the water into which the ozone bubbles are provided may at least partially be filtered water. The advantages of introducing ozone bubbles into filtered water are described in further detail above regarding the method according to the present invention.

The reservoir is preferably at least partially the source of backwashing water such that the filtered water may be used as backwashing water. The advantages of using filtered water as backwashing water are described in further detail above regarding the method according to the present invention.

The ceramic filtration means may comprise a ceramic ultra-filtration membrane. Further details on the ceramic ultra-filtration membrane are provided above regarding the method according to the present invention. As also above-mentioned, the ceramic filtration means may comprise at least one silicon carbide-based membrane and/or at least one AI2O3 based ceramic membrane.

The ozone bubble generation unit may be configured to provide 1 gram to 2000 gram, preferably 5 gram to 900 gram, more preferably 8 gram to 800 gram, even more preferably 10 gram to 700 gram, and most preferably too gram to 600 gram of ozone gas per ton of water, wherein preferably at least 5 %, more preferably at least 10 %, even more preferably at least 40 %, and most preferably at least 85 % of the ozone gas are provided in the water as ultra-fine ozone bubbles. Respective advantages are described in further detail above regarding the method according to the present invention. The ozone bubble generation unit maybe configured to provide ultra-fine ozone bubbles having a diameter from 25 nm to 800 nm, preferably from 30 nm to 700 nm, more preferably from 50 nm to 600 nm, even more preferably from 60 nm to 400 nm, and most preferably from 70 nm to 200 nm. The advantages of the above diameters are described in further detail above regarding the method according to the present invention.

The ozone bubble generation unit maybe configured to provide ultra-fine ozone bubbles having an average diameter which lies in the range from 25 nm to 700 nm, preferably from 40 nm to 600 nm, more preferably from 50 nm to 500 nm, even more preferably from 60 nm to 400 nm, and most preferably from 70 nm to 200 nm. The advantages of the above average diameters are described in further detail above regarding the method according to the present invention.

The at least one mixing means may be configured to provide a mixing ratio of ozonated water to feed water which lies in the range from 1:1000 to 1:1, preferably from 1:500 to 1:1.5, more preferably from 1:100 to 1:2, even more preferably from 1:10 to 1:2.5, and most preferably from 1:5 to 1:3. The advantages of the above mixing ratios are described in further detail above regarding the method according to the present invention.

The system may further comprise a coagulant injection means for injecting a coagulant into the feed water before the feed water is guided to the ceramic filtration means. Thereby preferably a first mixing means for mixing part of the ozonated water with the feed water is located between the inlet and the coagulant injection means, and further preferably a second mixing means for mixing part of the ozonated water with the feed water is located between the coagulant injection means and the ceramic filtration means. Respective advantages are described in further detail above regarding the method according to the present invention. The first mixing means and/or the second mixing means may form part of the first fluidic connection.

The first mixing means may be configured to provide a mixing ratio of ozonated water to feed water which lies in the range from 1:2000 to 1:1, preferably from 1:1000 to 1:2, more preferably from 1:500 to 1:3, even more preferably from 1:100 to 1:4, and most preferably from 1:10 to 1:5, wherein preferably the second mixing means is configured to provide a mixing ratio of ozonated water to feed water which lies in the range from 1:1000 to 1:1, preferably from 1:500 to 1:1.5, more preferably from 1:100 to 1:2, even more preferably from 1:10 to 1:2.5, and most preferably from 1:5 to 1:3. The advantages of the above mixing ratios are described in further detail above regarding the method according to the present invention.

In a preferred embodiment the system according to the present invention exactly comprises the first mixing means, the second mixing means and the third mixing means. Thereby further preferably the first mixing means, the second mixing means and the third mixing means are supplied with ozonated water from a ozone bubble generation unit. By keeping the number of injection points of ozonated water in feed water and/or ozone gas in water, safety can be increased.

4. Brief description of the accompanying figures

In the following, the accompanying figures are briefly described:

Fig. 1 shows an exemplary system for treating feed water according to the present invention,

Fig. 2 shows another exemplary system for treating feed water according to the present invention in more detail, and

Fig. 3 shows an exemplary method for treating feed water according to the present invention.

5. Detailed description of the figures

Fig. 1 shows an exemplary system 50 for treating feed water according to the present invention. The system comprises an inlet 1 for receiving feed water. Further the system 50 comprises ceramic filtration means 2 for filtering the feed water. Moreover, the system 50 comprises a first fluidic connection 3 between the inlet 1 and the ceramic filtration means 2 for guiding the feed water from the inlet 1 to the ceramic filtration means 2. Furthermore, the system 50 comprises an ozone bubble generation unit 6 for generating ozonated water. Thereby the ozone bubble generation unit 6 is configured to provide ultra-fine ozone bubbles in water. The ozone bubble generation unit 6 is connected to a gas providing unit 9 which provides a gas which is required for providing the ultra-fine ozone bubbles in the water. The gas supply 54 from the gas providing unit 9 to the ozone bubble generation unit 6 in addition to ozone may comprise oxygen and/or carbon dioxide. By introducing gas at only one point into the system 50 the safety can be increased. Even further, the depicted system comprises a first and a second mixing means 4, 5 for mixing the ozonated water with the feed water before the feed water is guided to the ceramic filtration means 2.

The exemplary system 50 of Fig. 1 further comprises a coagulant injection means 7 for injecting a coagulant from a coagulant providing means 17 into the feed water before the feed water is guided to the ceramic filtration means 2. Thereby the first mixing means 4 for mixing part of the ozonated water with the feed water is located between the inlet 1 and the coagulant injection means 7. Further, the second mixing means 5 for mixing part of the ozonated water with the feed water is located between the coagulant injection means 7 and the ceramic filtration means 2. As depicted in Fig. 1, the first and the second mixing means 4, 5 as well as the coagulant injection means 7 form part of the first fluidic connection 3.

As illustrated with an arrow having a solid line, the ceramic filtration means 2 is connected to a reservoir of filtered water 20. From this reservoir 20 the filtered water maybe provided to a reverse osmosis process. Moreover, the reservoir 20 is fluidically connected to the ozone bubble generation unit 6 such that the water into which the ozone bubbles are provided is at least partially filtered water. It will be understood that further sources of water may also provide water to the ozone bubble generation unit 6.

Further, the system 50 comprises a second fluidic connection 10 between a source of backwashing water 20 and the ceramic filtration means 2 for introducing backwashing water into the ceramic filtration means 2 to clean the ceramic filtration means 2. The flow of backwashing water is illustrated with dashed lines. In the system of Fig. 1 the reservoir 20 is at least partially the source of backwashing water such that the filtered water may be used as backwashing water. However, it will be understood that further sources may provide backwashing water. Moreover, the system 50 comprises a third mixing means 11 for mixing part of the ozonated water with the backwashing water. As depicted, the third mixing means 11 forms part of the second fluidic connection 10. The backwashing water which was transferred through the ceramic filtration means 2 is disposed in a sludge discharge tank 8.

Fig. 2 shows another exemplary system 60 for treating feed water according to the present invention. This exemplary system 60 essentially corresponds to the system 50 in Fig 1. However, the system 50 further comprises a second filtering circuit, which comprises respective ceramic filtration means 12 and second mixing means 15. The use of a second filtering circuit may allow for a continuous supply of filtered water even while one of the ceramic filtration membranes 2 or 12 of the respective filtering circuits is backwashed.

Further in the exemplary system 6o of Fig. 2 valves 51 are illustrated which may be automatic pressure driven ball valves. Moreover, several fluidic connections 52 form part of the system 60. The fluidic connections may exemplarily be pipelines. Furthermore, the system 60 comprises pumps 53 which serve to transport the fluids and/or gases. The filtered water outlet 55 may directly provide filtered water to a reverse osmosis process. The reference sign 54 represents the gas supply.

Fig. 3 shows an exemplary method 100 for treating feed water according to the present invention. The method 100 comprises the steps of providing 110 feed water; generating 120 ozonated water, wherein ozone gas is provided in water at least partially as ultrafine ozone bubbles; mixing 130, 150 the ozonated water with the feed water, and after that filtering 160 the mixture by means of a ceramic filtration means 2.

The exemplary method too comprises the step of injecting 140 a coagulant into the feed water before filtering 160. Thereby in the exemplary method at least part of the ozonated water is mixed 130 with the feed water prior to injecting 140 the coagulant, wherein at least part of the ozonated water is mixed 150 with the feed water after injecting 140 the coagulant.

The exemplary method too further comprises the step of backwashing 170, wherein backwashing water is backwashed through the ceramic filtration means 2 to clean the ceramic filtration means 2.

List of reference signs

1 inlet for receiving a feed water

2 ceramic filtration means

3 first fluidic connection

4 first mixing means

5 second mixing means

6 ozone bubble generation unit

7 coagulant injection means

8 sludge discharge tank

9 gas providing unit

10 second fluidic connection

11 third mixing means 12 ceramic filtration means of second filtering circuit

15 second mixing means of second filtering circuit

17 coagulant providing means

20 reservoir of filtered water

50 system for treating feed water

51 valve

52 fluidic connection

53 pump

54 gas supply

55 filtered water outlet

6o further system for treating feed water

100 method for treating feed water no providing feed water

120 generating ozonated water

130 introducing the ozonated water into the feed water prior to injecting coagulant

140 injecting a coagulant into the feed water

150 introducing the ozonated water into the feed water prior to filtering

160 filtering the feed water

170 backwashing