The invention pertains to a method and system for the purification of contaminated water.

For the purification of water that is contaminated with organic contaminants, in particular non-persistent organic contaminants, generally either reverse osmosis and/or biological purification processes, such as microbial purification, are used.

In reverse osmosis, a selectively permeable membrane is used to separate the contaminants and the water. A pressure is applied over the membrane so as to effect the separation of the water and the contaminants. The applied pressure must be higher than the natural osmotic pressure.

Reverse osmosis has several drawbacks. One drawback is that the application of the pressure over the membrane requires quite a lot of energy. A further drawback is that the process results in a purified fraction and a fraction in which the contaminants are highly concentrated. The contaminants are not broken down into smaller, generally less harmful molecules. The fraction with the concentrated contaminants is hard to dispose of in a sustainable manner.

In microbial purifications, micro-organisms such as bacteria are used to break down the contaminants. In other biological purification processes, plants and/or algae are used to break down the contaminants. The advantage of this type of purification processes is that the contaminants are broken down into smaller, generally less harmful molecules. The drawback of this type of purification processes is however that they take a long time and require a large surface area.

It is the object of the invention to provide an improved method and system for water purification.

In accordance with the invention, this object is achieved by a method for the purification of contaminated water, which method comprises the following steps:

- adding a coagulant to contaminated water, which contaminated water contains organic contaminants,

- then, generating hydrodynamic cavitation in the contaminated water, thereby mixing the contaminated water with the coagulant and forming agglomerates of organic

contaminants present in the contaminated water, - then, separating the formed agglomerates from the water, thereby obtaining partly purified water which contains remaining organic contaminants,

- then, oxidizing remaining organic contaminants in the partly purified water, thereby obtaining purified water.

In accordance with the method according to the invention, first a coagulant is added to the contaminated water. The coagulant is for example an iron salt, an aluminum salt, a titanium salt, a zirconium salt, e.g. iron hydroxide or aluminum hydroxide.

The contaminated water contains organic contaminants, for example non-persistent organic contaminants. The contaminated water is for example one of municipal waste water, waste water from a farm e.g. a dairy farm, waste water from a food production plant e.g. a dairy factory, or leachate from a landfill.

In a subsequent step of the method according to the invention, hydrodynamic cavitation is generated in the contaminated water. To this end, the contaminated water with the coagulant is brought to a hydrodynamic cavitator, in which hydrodynamic cavitation is generated.

In hydrodynamic cavitation, vapour bubbles are generated in a liquid, which bubbles then implode. Hydrodynamic cavitation can for example be generated by subjecting the liquid to rapid changes in pressure. The implosion of the bubbles generates shock waves, high local pressure gradients and high local shear stresses at and in the vicinity of the bubbles. Also, locally high temperatures and generally high fluid velocities occur at and in the vicinity of the bubbles.

The hydrodynamic cavitation results in an efficient and effective mixing of the

contaminated water with the coagulant, and an intense interaction between the contaminated water with the coagulant. Due to the interaction between the contaminated water and the coagulant, agglomerates are formed of organic contaminants that are present in the contaminated water.

The coagulant is often added in the form of particles, e.g. microparticles (i.e. particles with a size that is generally between 0.5 and 10 micrometers). The highly turbulent flow of the contaminated water breaks down the coagulant into smaller particles, which increases the total surface area of the coagulant. Furthermore, the turbulent flow continuously cleans the surface of the coagulant particles, which makes that all the time there is a fresh coagulant surface to interact with the contaminants in the contaminated water.

Therewith, the hydrodynamic cavitation significantly increases the speed and

effectiveness of the mixing of the coagulant with the contaminated water, and also

significantly increases the speed and effectiveness of the formation of agglomerates from the organic contaminants that are present in the contaminated water. The agglomerates are e.g. non-soluable agglomerates. The agglomerates may be dispersed in the contaminated water.

The hydrodynamic cavitation furthermore shreds large organic molecules available in the contaminated water. After cavitation, the contaminated water contains a large number of small molecules. This allows an increase in the chemical kinetics, hence the rate of the chemical processes increases significantly.

As a subsequent step in the method according to the invention the formed

agglomerates are separated from the water. The contaminated water with the coagulants and the agglomerates is transported from the hydrodynamic cavitator to a separator.

As in general not all contaminants will be removed from the contaminated water in this process, the water that leaves the separator is partly purified water which contains remaining organic contaminants.

In accordance with the method of the invention, in order to further purify the partly purified water which is obtained by the separator, remaining organic contaminants in the partly purified water are oxidized. Thereby, purified water is obtained.

The oxidation of remaining organic contaminants may lead to the formation of oxidation products in the form gases, such as nitrogen (N ₂ ), hydrogen (H ₂ ), carbon dioxide (CO ₂ ) and oxygen (O ₂ ). Alternatively or in addition, oxidation products in the form of liquids may be formed, e.g. water (H ₂ O) and/or hydrogen peroxide (H ₂ O ₂ ). Alternatively or in addition, solid or semi-solid oxidation products may be formed.

Optionally, all or at least one of the formed oxidation products are removed from the partly purified water. In particular when water is formed as an oxidation product, removal of this particular oxidation product (i.e. water) is not necessary.

In an embodiment of the method according to the invention, the separator that is used is a hydrocyclone.

A hydrocyclone allows to separate the agglomerates from the water based on their difference in the ratio of their centripetal force to fluid resistance. This ratio is high for the agglomerates and low for the water. The contaminated water with the agglomerates is injected into the hydrocyclone in such a way as to create a vortex inside the hydrocyclone.

The centrifugal acceleration that is caused by the vortex causes the agglomerates to move towards the walls of the hydrocyclone, while the water will remain closer to the centre of the hydrocyclone. This allows separation of the agglomerates from the water.

Furthermore the hydrocyclone raises light particles upward and heavy particles are pressed downward. The hydrocyclone offers a fast, effective and energy-efficient way to remove the agglomerates from the contaminated water, and therewith contributes to a fast, effective and energy-efficient water purification process.

In an embodiment of the method according to the invention, in addition to the coagulant, an additive is added to the contaminated water, which additive increases or accelerates the formation of the agglomerates of organic contaminants that are formed by mixing the contaminated water with the coagulant.

Suitable additives are for example clay, or dispersed layered silicates (e.g. highly dispersed layered silicates), which include for example natural smectites and palygorskite. Smectites are clays that swell when they are immersed in a liquid. Examples of smectites are zeolite, montmorillonite and bentonite. These additives further have the advantage that they may be able to assist in the removal of metals, e.g. heavy metals, from the contaminated water.

In general, these additives are not expensive, which makes that the method according to the invention can be carried out at relatively low costs.

In variants of this embodiment, alternatively or in addition other additives then the ones mentioned above may be added, including additives for different purposes than increasing or accelerating the formation of the agglomerates of organic contaminants.

Additives may be added to the contaminated water in liquid form, solid form (e.g. in the form of a powder) or in gaseous form.

In an embodiment of the method according to the invention, the contaminated water and the coagulant are mixed to before the hydrodynamic cavitation is generated. This mixing is considered to be a pre-mixing or initial mixing, and can for example be carried out by a mechanical mixer or stirrer in a tank in which both contaminated water and coagulant are present. The mixture of the contaminated water and coagulant is then fed into the cavitator to be subjected to the hydrodynamic cavitation in accordance with the invention.

Optionally, an additive is added to the contaminated water along with the coagulant. In that case, the contaminated water, the coagulant and the additive are optionally mixed to before the hydrodynamic cavitation is generated. This mixing is considered to be a pre-mixing or initial mixing, and can for example be carried out by a mechanical mixer or stirrer in a tank in which contaminated water, coagulant and additive are present. The mixture of

contaminated water, coagulant and additive is then fed into the cavitator to be subjected to the hydrodynamic cavitation in accordance with the invention. In an embodiment, when during the oxidation of the remaining organic contaminants in the partly purified water, solids are formed, these solids are removed from the partly purified water or from the purified water. For example, such solids are removed using one or more filters and/or using a hydrocyclone. If a hydrocyclone is used, this can be a different hydrocyclone than the one that is used to remove the agglomerates of organic contaminants, or the same hydrocyclone.

In an embodiment of the method according to the invention, the step of oxidizing remaining organic contaminants in the partly purified water comprises:

- adding an oxidizing gas to the partly purified water, and

- generating hydrodynamic cavitation in the partly purified water.

In this embodiment, the hydrodynamic cavitation is used to provide a good mixing of the oxidizing gas with the partly purified water. In addition, the hydrodynamic cavitation generates a large surface area of the interface between the partly purified water and the oxidizing gas, which increases the speed and effectiveness of the oxidation.

For example, air, oxygen and/or ozone are used as oxidizing gas.

Optionally, the generation of hydrodynamic cavitation for mixing the contaminated water with the coagulant and the generation of hydrodynamic cavitation for oxidizing remaining organic contaminants in the partly purified water are carried out in the same hydrodynamic cavitator. Alternatively, separate hydrodynamic cavitators are used for these two steps of the method according to the invention.

In a variant of this embodiment, no oxidizing gas is added to the partly purified water during the hydrodynamic cavitation. In this variant, only hydrodynamic cavitation is generated in the partly purified water, optionally in combination with other oxidizing processes such as irradiation with ultraviolet radiation or vortex aeration. In this variant, the hydrodynamic cavitation breaks up molecules of the remaining organic contaminants, e.g. due to increase of temperature and/or pressure. The hydrodynamic cavitation itself may also lead to the formation of oxidizing gas, e.g. inside the bubbles which are created by the cavitation.

So, in an embodiment of the invention, the step of oxidizing remaining organic contaminants in the partly purified water comprises:

- generating hydrodynamic cavitation in the partly purified water, and

- optionally, adding an oxidizing gas to the partly purified water.

In an embodiment of the method according to the invention, the step of oxidizing remaining organic contaminants in the partly purified water comprises irradiating the partly purified water with ultraviolet radiation and/or vortex aeration. The irradiation with ultraviolet radiation and/or vortex aeration can be carried out instead of or in addition to oxidation by injecting an oxidizing gas and generating hydrodynamic cavitation.

The ultraviolet radiation can for example be generated by an ultraviolet lamp, for example an excimer ultraviolet lamp.

A reaction that may typically occur during the oxidation is the dissociation of ammonia (NH3) to nitrite (NO2), then the dissociation of nitrite (NO2) to nitrate (NO3) and the dissociation of nitrate (NO3) to nitrogen gas, water and oxygen, in accordance with the following reactions:

NH ₃ + 4 0 ₃ NOs + H ⁺ + H2O + 4 0 ₂ ,

2 NOs + H ₂ N ₂ + 2 H2O + 2 0 ₂ .

During the oxidation, for example amine compounds and/or ammonium salts may be formed. Ozone easily and quickly interacts with these substances to form hydroxylamines, nitro compounds, nitrons and nitroxide radicals. Such substances may for example settle down as a residue and then be removed, or filtered out, or separated in a hydrocyclone.

When the partly purified water is irradiated with ultraviolet radiation, for example photolysis of H2O2 may occur, which generates hydroxyl radicals and reduces Fe(lll) to Fe(ll). For example, a classical and/or a heterogenous Fenton’s reaction may take place. The iron in this reaction can initially be in the Fe(ll) or Fe(lll) form, because the reaction of Fe(lll) with H2O2 regenerates Fe(ll). The effectiveness of the Fenton process can be improved by using external non-chemical energy sources such as ultraviolet radiation, electrical current and/or ultrasound and/or an inerton field, which can be generated in the hydrodynamic cavitator. At the same time, the radicals (R) may initiate the degradation of explosives to carry out the oxidation of bio-organic compounds by abstracting a hydrogen atom:

RH + OH· R· + H2.

The Fenton reaction is effective in the degradation of seven explosives. The rate of explosive oxidation significantly increases with increasing the concentration of Fe2+ in the Fenton system.

Thus, gases such as nitrogen N2 and hydrogen H2 are released from the partly purified water and the contaminant as a residue can be separated, e.g. in a semi-dry form.

In an embodiment of the method according to the invention, the hydrodynamic cavitation is generated by using a nozzle with a pseudospherical shape, e.g. a

pseudospherical shape according to Lobachevsky. A pseudospherical shape is a shape with a constant negative Gaussian curvature. For example, the surface of the nozzle has the shape of a tractricoid.

It has been found that this particular nozzle shape produces good results in generating hydrodynamic cavitation, It has also been found to be particularly effective when used in the method and system according to the invention.

In an embodiment of the method according to the invention, the purified water which is obtained, is filtered to obtain further purified water.

As already indicated before, the oxidation of the partly purified water may result in the formation of solid particles. Alternatively or in addition, solid particles from a different origin may still be present in the purified water (i.e. after the oxidation of remaining organic contaminants). The solid particles may be removed for example by filtration, in one filtration step or in multiple filtration steps. By doing this, water of higher purity level (i.e. further purified water) may be obtained.

In general, filters that are used for this step will have a relatively long life span, as the water that passes through these filters is already relatively clean.

For example, the filtering is carried out by using one or more of an ultrafilter, nanofilter, an electrostatic filter e.g. a passive electrostatic polymer filter and/or an activated carbon filter.

Optionally, the filtering is carried out in two filtration steps, wherein in the first step an ultrafilter, nanofilter, or an electrostatic filter e.g. a passive electrostatic polymer filter is used, and in the second step an activated carbon filter.

The method according to the invention can be carried out using a system according to the invention.

The invention provides two types of systems that can be used to carry out the method according to the invention. The first type of system is a linear type system, which can be used in a continuous way. Alternatively, it can be used to treat batches of contaminated water. In the linear type system, all steps of the method are carried out in individual parts of the system, so all steps in the method can be carried out simultaneously. This system is in particular suitable for treating large volumes of contaminated water, if desired on a continuous basis.

The second type of system is a recirculating type system, in which multiple steps of the method are carried out sequentially by a single part of the system. For example, a single hydrodynamic cavitator is used for both mixing the contaminated water with the coagulant as well as for oxidizing the partly purified water. So, not all steps of the method can be carried out simultaneously, and only batches of contaminated water can be processed. However, this type of system can be built significantly compacter that the linear type system, and also at lower cost because less components are required.

The linear type system according to the invention is a system for the purification of contaminated water, which system comprises:

- a hydrodynamic cavitator, which comprises:

- a cavitator feed section which is adapted to receive contaminated water and a coagulant, and

- a cavitator outlet section,

- a cavitation chamber which is in fluid communication with the cavitator feed section and the cavitator outlet,

which hydrodynamic cavitator is adapted to generate hydrodynamic cavitation in the contaminated water in the cavitation chamber, thereby mixing the contaminated water with the coagulant and promoting the formation of agglomerates of organic contaminants,

- a separator, which is adapted to separate the agglomerates of organic contaminants from the water, thereby obtaining partly purified water which contains remaining organic contaminants, which separator comprises:

- a separator inlet, which is connected to the cavitator outlet section, which separator inlet is adapted to receive the contaminated water with the agglomerates of organic contaminants from the cavitator outlet section, and,

- a separator water outlet which is adapted to discharge the partly purified water with remaining organic contaminants from the separator, and,

- a separator contaminants outlet which is adapted to discharge the agglomerates of organic contaminants from the separator,

- an oxidizer system, which is adapted to oxidize remaining organic contaminants in the partly purified water, thereby forming gas and obtaining purified water, which oxidizer system comprises:

- an oxidizer water outlet which is adapted to discharge purified water from the oxidizer system.

The linear type system according to the invention comprises a hydrodynamic cavitator. When the system is in operation, in this hydrodynamic cavitator hydrodynamic cavitation is generated for mixing the contaminated water with the coagulant and promoting the formation of agglomerates of organic contaminants.

The hydrodynamic cavitator comprises a feed section, a cavitation chamber and a cavitator outlet section. The cavitation chamber is where the actual hydrodynamic cavitation takes place. The cavitation chamber comprises for example at least one nozzle for generating the pressure conditions and flow conditions which lead to hydrodynamic cavitation. The cavitation chamber receives contaminated water with coagulant (and optionally also one or more additives) from the feed section. Contaminated water and agglomerates of organic contaminants (and optionally non-used coagulant and non-used additives) are discharged from the cavitation chamber to the cavitator outlet section, through which they leave the hydrodynamic cavitator.

The feed section of the hydrodynamic cavitator is adapted to receive the contaminated water and a coagulant, and optionally one or more additives. An additive may be added in liquid form, in solid form (e.g. in the form of a powder) or in gaseous form.

The contaminated water, coagulant and optionally one or more additives may be supplied to the feed section in a pre-mixed form, as a single flow. In this case, the feed section of the hydrodynamic cavitator comprises a combined inlet, which is adapted and arranged to receive the mixture of contaminated water, coagulant and optionally one or more additives. In this case, the system according to the invention may further comprise a contaminated water tank, in which the contaminated water, coagulant and optionally one or more additives are combined. Optionally this contaminated water tank may comprise a mixer or stirrer, e.g. a mechanical mixer or stirrer.

Alternatively, the contaminated water, coagulant and optionally one or more additives are supplied to the hydrodynamic cavitator separately. In that case, the feed section of the hydrodynamic cavitator comprises multiple dedicated inlets, e.g. one for contaminated water, one for coagulant and optionally one or more for additives.

Combinations of those two alternatives are also possible, e.g. wherein the feed section of the hydrodynamic cavitator comprises a combined inlet for contaminated water with coagulant, and a dedicated inlet for additives.

The linear type system according to the invention further comprises a separator. The separator is adapted to separate the agglomerates of organic contaminants from the water, thereby obtaining partly purified water which contains remaining organic contaminants.

The separator comprises a separator inlet, a separator chamber, a separator water outlet and a separator contaminants outlet.

The separator inlet is connected to the cavitator outlet section. The separator inlet is adapted to receive the contaminated water with the agglomerates of organic contaminants from the cavitator outlet section.

The separator chamber is where the actual separation of the agglomerates from the water takes place. The contaminated water with the agglomerates enters the separator chamber via the separator inlet. The partly purified water (i.e. the water from which the agglomerates are removed) leaves the separator chamber via the separator water outlet. The separator water outlet is adapted to allow discharge of the partly purified water with remaining organic contaminants from separator.

The agglomerates leave the separator chamber via the separator contaminants outlet. The separator contaminants outlet is adapted to allow discharge the agglomerates of organic contaminants from the separator.

Optionally, the separator is a hydrocyclone, the separator inlet is a cyclone inlet, the separator chamber is a vortex chamber, the separator water outlet is a cyclone water outlet and the separator contaminants outlet is a cyclone contaminants outlet. The hydrocyclone offers a fast, effective and energy-efficient way to remove the agglomerates from the contaminated water.

The linear type system according to the invention further comprises an oxidizer system. The oxidizer system is adapted to oxidize remaining organic contaminants in the partly purified water, thereby obtaining purified water. The oxidizer system receives the partly purified water from the separator, in particular from the separator water outlet of the separator.

The oxidizer system comprises an oxidizer water inlet and an oxidizer water outlet. The oxidizer water inlet is connected to the separator water outlet of the separator. The oxidizer water outlet is adapted to allow discharge of purified water from the oxidizer system.

Optionally, the oxidizer system further comprises an oxidizer gas outlet. The oxidizer gas outlet is adapted to allow discharge of gas from the oxidizer system, which gas is formed during the oxidation of remaining contaminants.

Optionally, the oxidizer system further comprises an oxidizer liquid outlet. The oxidizer liquid outlet is adapted to allow discharge of liquid from the oxidizer system, which liquid is formed during the oxidation of remaining contaminants.

Optionally, the oxidizer system further comprises an oxidizer solids outlet. The oxidizer solids outlet is adapted to allow discharge of solids from the oxidizer system, which solids are formed during the oxidation of remaining contaminants.

The recirculating type system according to the invention is a system for the purification of contaminated water, which system comprises:

- a cavitator feed system which comprises:

- a contaminated water feed section, which comprises a contaminated water feed line which is connectable to a source of contaminated water, and a coagulant feed line which is connectable to a source of coagulant, which contaminated water feed section further comprises a valve,

- a partly purified water feed section, which comprises a partly purified water feed line and a partly purified water reservoir which is adapted to accommodate a volume of partly purified water, wherein the partly purified water feed line is connectable to the partly purified water reservoir, which partly purified water feed section further comprises a valve,

- a hydrodynamic cavitator, which comprises:

- a cavitation chamber,

- a cavitator inlet section, which is connectable to the contaminated water feed section and to the partly purified water feed section, which cavitator inlet section is in communication with the cavitation chamber, and

- a cavitator outlet section, which cavitator outlet section is in communication with the cavitation chamber,

which hydrodynamic cavitator is adapted to generate hydrodynamic cavitation in a fluid in the cavitation chamber,

- a feed system control device which is adapted to control the valves of the cavitator feed system such that either the contaminated water feed section or the partly purified water feed section is in fluid communication with the cavitator inlet section,

- a separator which is adapted to separate solid particles from fluid, which separator comprises:

- a separator inlet, which is connectable to the cavitator outlet section of the hydrodynamic cavitator to receive contaminated water with agglomerates of organic contaminants from the hydrodynamic cavitator when the contaminated water feed section is in fluid communication with the hydrodynamic cavitator,

- a separator chamber, which is in fluid communication with the separator inlet,

- a separator fluid outlet which is adapted to allow discharge of fluid from the separator and

- a separator contaminants outlet which is adapted to allow discharge of solids or semi-solids from the separator,

wherein the separator fluid outlet is connectable to the partly purified water reservoir,

- a purified water discharge which is adapted to allow discharge of purified water and/or further purified water from the system. The recirculating type system according to the invention is a system for the purification of contaminated water, which system comprises a cavitator feed system, a hydrodynamic cavitator, a feed system control device, a separator and a purified water discharge.

The cavitator feed system comprises a contaminated water feed section and a partly purified water feed section.

The contaminated water feed section comprises a contaminated water feed line which is connectable to a source of contaminated water, and a coagulant feed line which is connectable to a source of coagulant. The contaminated water feed section further comprises a valve.

The partly purified water feed section comprises a partly purified water feed line, a partly purified water reservoir and a valve. The partly purified water reservoir is adapted to accommodate a volume of partly purified water. The partly purified water feed line is connectable to the partly purified water reservoir.

Optionally, the partly purified water feed section further comprises the an oxidizing gas feed line which is connectable to a source of oxidizing gas.

The hydrodynamic cavitator of the recirculating type system according to the invention comprises a cavitation chamber, a cavitator inlet section and a cavitator outlet section. The hydrodynamic cavitator is adapted to generate hydrodynamic cavitation in a fluid in the cavitation chamber when this fluid is flowing through the cavitation chamber. Depending on the settings of the valves of the cavitator feed system, this fluid is or comprises either contaminated water with a coagulant and optionally one or more additives, or partly purified water, optionally partially purified water with oxidizing gas.

The cavitator inlet section is connectable to the contaminated water feed section and to the partly purified water feed section. The cavitator inlet section is in communication with the cavitation chamber. So, the cavitator inlet section receives the fluids in which hydrodynamic cavitation has to be generated. These fluids enter the cavitation chamber via the cavitator inlet section.

The cavitator outlet section is also in communication with the cavitation chamber. The cavitator outlet section receives fluids from the cavitation chamber and allows to discharge these fluids from the hydrodynamic cavitator.

The contaminated water feed section is adapted and arranged to supply contaminated water, coagulant and optionally one or more additives to the hydrodynamic cavitator. The partly purified water feed section is adapted and arranged to supply partly purified water and oxidizing gas to the hydrodynamic cavitator. The contaminated water feed section and the partly purified water feed section do not operate simultaneously. Either the contaminated water feed section is active, or the partly purified water feed section.

The feed system control device is adapted to control the valves of the cavitator feed system such that either the contaminated water feed section or the partly purified water feed section is in fluid communication with the hydrodynamic cavitator, in particular with a cavitator inlet section of the hydrodynamic cavitator.

When the contaminated water feed section is in fluid communication with the cavitator inlet section of the hydrodynamic cavitator, the hydrodynamic cavitator is set to mix the contaminated water and coagulant, and optionally also one or more additives, and to therewith promote the formation of agglomerates of organic contaminants which are present in the contaminated water.

When the partly purified water feed section is in fluid communication with the cavitator inlet section of the hydrodynamic cavitator, the hydrodynamic cavitator is set to promote oxidation of remaining organic contaminants in the partly purified water, e.g. by mixing the partly purified water with an oxidizing gas.

The separator of the recirculating type system according to the invention is adapted to separate solid particles from fluid. The separator comprises a separator inlet, a separator chamber, a separator fluid outlet and a separator contaminants outlet.

The separator chamber is where the actual separation of the solids from the fluid takes place. The mixture of fluid and solids enters the separator chamber via the separator inlet. The mixture of fluid and solids is for example the contaminated water with the agglomerates, or the purified water in which still some solids may be present, e.g. due to the oxidation of the partly purified water.

The separator inlet is connectable or connected to the cavitator outlet section of the hydrodynamic cavitator to receive contaminated water and agglomerates of organic contaminants from the hydrodynamic cavitator when the contaminated water feed section is in fluid communication with the hydrodynamic cavitator. Optionally, the separator inlet is also connectable or connected to the cavitator outlet section of the hydrodynamic cavitator to receive purified water in which still some solids are or may be present, e.g. due to the oxidation of the partly purified water from the hydrodynamic cavitator when the partly purified water feed section is in fluid communication with the hydrodynamic cavitator.

The separator fluid outlet is adapted to allow discharge of fluid from the separator and the separator contaminants outlet is adapted to allow discharge of solids or semi-solids from the separator.

The separator fluid outlet is connectable or connected to the partly purified water reservoir. This way, the partly purified water that leaves the separator is collected in the partly purified water reservoir so that later it can be supplied to the hydrodynamic cavitator for oxidation.

The system further comprises a purified water discharge which is adapted to allow discharge of purified water and/or further purified water (e.g. purified water that has been subjected to filtration downstream of the separator) from the system. Depending on the set-up of the system, the purified water discharge can for example be arranged at the cavitator outlet section, between the hydrodynamic cavitator and the separator, or downstream of the separator.

Optionally, the separator fluid outlet of the separator is selectively connectable to either the partly purified water reservoir or the purified water discharge.

Optionally, the separator is a hydrocyclone, the separator inlet is a cyclone inlet, the separator chamber is a vortex chamber, the separator water outlet is a cyclone water outlet and the separator contaminants outlet is a cyclone contaminants outlet. The hydrocyclone offers a fast, effective and energy-efficient way to remove the solids from the water.

In an embodiment of the linear type system according to the invention, and in an embodiment of the recirculating type system according to the invention, the hydrodynamic cavitator comprises a cavitation nozzle with a pseudospheric shape.

In an embodiment of the linear type system according to the invention, and in an embodiment of the recirculating type system according to the invention, the hydrodynamic cavitator comprises a first stage, which has a single cavitation nozzle, and a second stage, which has multiple cavitation nozzles.

Optionally, in the second stage, multiple cavitation nozzles are arranged in series with each other.

Optionally, in the second stage, multiple cavitation nozzles are arranged in series with each other to form a nozzle array, and multiple nozzle arrays are arranged parallel to each other.

Optionally, the nozzle in the first stage has a pseudospheric shape.

In an embodiment of the linear type system according to the invention, and in an embodiment of the recirculating type system according to the invention, the system further comprises at least one filter which is arranged downstream of the separator.

Optionally, the filter is or comprises an ultrafilter, nanofilter, an electrostatic filter e.g. a passive electrostatic polymer filter and/or an activated carbon filter. In an embodiment of the recirculating type system according to the invention, the system further comprises at least one filter which is arranged downstream of the separator.

Optionally, the filter is or comprises an ultrafilter, nanofilter, an electrostatic filter e.g. a passive electrostatic polymer filter and/or an activated carbon filter.

In an embodiment of the linear type system according to the invention, the oxidizer system comprises a source of ultraviolet radiation which is adapted to irradiate the partly purified water.

Optionally, the source of ultraviolet radiation is an ultraviolet lamp, e.g. an excimer ultraviolet lamp.

In an embodiment of the recirculating type system according to the invention, the system further comprises a source of ultraviolet radiation which is arranged between the hydrodynamic cavitator and the separator, or downstream of the separator.

Optionally, the source of ultraviolet radiation is an ultraviolet lamp, e.g. an excimer ultraviolet lamp.

Optionally, the source of ultraviolet radiation can be switched on and off depending on whether the contaminated water feed section is in fluid communication with the hydrodynamic cavitator or the partly purified water feed section is in fluid communication with the

hydrodynamic cavitator. Optionally, the feed system control device is adapted to switch the source of ultraviolet radiation on and off.

In an embodiment of the linear type system according to the invention, the oxidizer system further comprises an additional hydrodynamic cavitator. The additional hydrodynamic cavitator comprises a water inlet which is adapted to receive the partly purified water, and optionally a gas inlet which is adapted to receive an oxidizing gas. So, in this embodiment, the system comprises two hydrodynamic cavitators, one for mixing the contaminated water and the coalugant, and one for the oxidation of remaining contaminants in the partly purified water.

In an embodiment of the recirculating type system according to the invention, the contaminated water feed section further comprises a contaminated water tank. The coagulant feed line is connectable to the contaminated water tank to feed coagulant to the contaminated water tank. The contaminated water tank comprises a mixer which is adapted to mix the contaminated water which is present in the contaminated water tank with the coagulant. The contaminated water tank has a contaminated water tank outlet, and the contaminated water feed line extends between the contaminated water tank outlet and the cavitator inlet section. The valve of the contaminated water feed section is arranged in the contaminated water feed line.

The invention will be described in more detail below under reference to the drawing, in which in a non-limiting manner exemplary embodiments of the invention will be shown. The drawing shows in:

Fig. 1 : a first embodiment of a linear type system according to the invention,

Fig. 2: a first embodiment of a recirculating type system according to the invention,

Fig. 3: an example of a hydrodynamic cavitator which can be used in the method and system according to the invention.

Fig. 1 shows a first embodiment of a linear type system according to the invention.

In the embodiment of fig. 1 , the system comprises a contaminated water tank 4. The contaminated water tank 4 is connectable to a source of contaminated water via

contaminated water tubing 1. The contaminated water tubing 1 optionally comprises a valve 7. When the valve is open, the contaminated water tank 4 is connected to and in fluid communication with a source of contaminated water and the contaminated water tank 4 can receive contaminated water from the source of contaminated water. When the valve in the contaminated water tubing 1 is closed, the connection between the contaminated water tank 4 and the source of contaminated water is blocked.

The contaminated water contains organic contaminants, for example non-persistent organic contaminants. The contaminated water is for example one of municipal waste water, waste water from a farm e.g. a dairy farm, waste water from a food production plant e.g. a dairy factory, or leachate from a landfill.

The contaminated water tank 4 is connectable to a source of coagulant via coagulant tubing 2. The coagulant tubing 2 optionally comprises a valve 8. When the valve is open, the contaminated water tank 4 is connected to and in fluid communication with a source of coagulant and the contaminated water tank 4 can receive coagulant from the source of coagulant. When the valve in the coagulant tubing 2 is closed, the connection between the contaminated water tank 4 and the source of coagulant is blocked.

The coagulant is for example an iron salt, an aluminum salt, a titanium salt, a zirconium salt, e.g. iron hydroxide or aluminum hydroxide.

The contaminated water tank 4 is connectable to a source of additive via additive tubing 3. The additive tubing 3 optionally comprises a valve 9. When the valve is open, the contaminated water tank 4 is connected to and in fluid communication with a source of additive and the contaminated water tank 4 can receive additive from the source of additive. When the valve in the additive tubing 3 is closed, the connection between the contaminated water tank 4 and the source of additive is blocked.

In the embodiment of fig. 1 , there is only one additive tubing 3, but alternatively there are multiple additive tubings 3, each connected to a different source of additive, so that different additives can be added to the contaminated water. Alternatively, there is a single additive tubing 3, which is connected to a manifold, which manifold in turn is connected to different sources of additives. This way, also different additives can be added to the contaminated water. Alternatively or in addition, the contaminated water tank may comprises an opening through which additive can be added to the contents of the contaminated water tank 4. The additive may be added in the form of a liquid, a solid (e.g. in the form of a powder) or in the form of a gas.

Suitable additives are for example clay, or dispersed layered silicates (e.g. highly dispersed layered silicates), which include for example natural smectites and palygorskite. Smectites are clays that swell when they are immersed in a liquid. Examples of smectites are zeolite, montmorillonite and bentonite.

Optionally, in the embodiment of fig. 1 , the contaminated water tank 4 is provided with a mechanical mixer 5. This allows to pre-mix the contaminated water, coagulant and additive.

The mixture of contaminated water, coagulant and optionally additive is transported to a hydrodynamic cavitator 10 via tubing 71. The arrow shown at tubing 71 in fig. 1 indicates the direction of the flow.

In this hydrodynamic cavitator 10, during operation of the system, hydrodynamic cavitation is generated for mixing the contaminated water with the coagulant and promoting the formation of agglomerates of organic contaminants.

The hydrodynamic cavitator 10 comprises a feed section 11 , a cavitation chamber 15 and a cavitator outlet section 12. The cavitation chamber 15 is where the actual

hydrodynamic cavitation takes place. The cavitation chamber 15 comprises for example at least one nozzle for generating the pressure conditions and flow conditions which lead to hydrodynamic cavitation. The cavitation chamber receives contaminated water with coagulant (and optionally also one or more additives) from the feed section 1 1. Contaminated water with agglomerates of organic contaminants (and optionally non-used coagulant and non-used additives) is discharged from the cavitation chamber 15 to the cavitator outlet section 12, through which they leave the hydrodynamic cavitator 10.

The feed section 11 of the hydrodynamic cavitator 10 is adapted to receive

contaminated water and a coagulant, and optionally one or more additives. In the embodiment of fig. 1 , the contaminated water, coagulant and optionally one or more additives may be supplied to the feed section in a pre-mixed form, as a single flow. In this case, the feed section of the hydrodynamic cavitator comprises a combined inlet 1 1a, which is adapted and arranged to receive the mixture of contaminated water, coagulant and optionally one or more additives.

The contaminated water with the agglomerates of organic contamination is transported from the cavitator outlet section 12 of the hydrodynamic cavitator 10 to a separator which is a hydrocyclone 20, via tubing 72. The arrow shown at tubing 72 in fig. 1 indicates the direction of the flow.

The hydrocyclone 20 is adapted to separate the agglomerates of organic contaminants from the water, thereby obtaining partly purified water which contains remaining organic contaminants.

The hydrocyclone 20 comprises a cyclone inlet 21 , a vortex chamber 25, a cyclone water outlet 22 and a cyclone contaminants outlet 23.

The cyclone inlet 21 is connected to the cavitator outlet section 12. The cyclone inlet 21 is adapted to receive the contaminated water with the agglomerates of organic contaminants from the cavitator outlet section 12.

The vortex chamber 25 is where the actual separation of the agglomerates from the water takes place. The contaminated water with the agglomerates enters the vortex chamber 25 via the cyclone inlet 21.

The partly purified water (i.e. the water from which the agglomerates are removed) leaves the vortex chamber 25 via the cyclone water outlet 22. The cyclone water outlet 22 allows discharge of the partly purified water with remaining organic contaminants from hydrocyclone 20.

The separated agglomerates leave the vortex chamber 25 via the cyclone contaminants outlet 23. The cyclone contaminants outlet 23 allows discharge of the agglomerates of organic contaminants from the hydrocyclone via tubing 74. The arrow shown at tubing 74 in fig. 1 indicates the direction of the flow.

The partly purified water is transported from the cyclone water outlet 22 of the hydrocyclone 20 to an oxidizer system 30 via tubing 73. The arrows shown at tubing 73 in fig. 1 indicates the direction of the flow.

The oxidizer system 30 is adapted to oxidize remaining organic contaminants in the partly purified water, thereby obtaining purified water. The oxidizer system 30 comprises an oxidizer water inlet 31 , an oxidizer water outlet 32 and optionally an oxidizer gas outlet 33.

The oxidizer water inlet 31 is connected to the cyclone water outlet 22 of the hydrocyclone 20 via tubing 73. The oxidizer water outlet 32 allows discharge of purified water from the oxidizer system 30 and the optional oxidizer gas outlet 33 allows discharge of gaseous oxidation products from the oxidizer system 30 via tubing 76. The arrow shown at tubing 76 in fig. 1 indicates the direction of the flow.

In the embodiment of fig. 1 , the oxidizer system 30 comprises an additional

hydrodynamic cavitator 40 and an ultraviolet irradiation device 50, which are arranged in series with each other.

In the embodiment of fig. 1 , the additional hydrodynamic cavitator 40 comprises an inlet section 41 with a water inlet 41 a and optionally a gas inlet 41 b.The water inlet 41 a receives the partly purified water via tubing 73. Optionally a gas inlet 41 b is provided which receives an oxidizing gas via tubing 75. The arrow shown at tubing 75 in fig. 1 indicates the direction of the flow.

The ultraviolet irradiation device 50 comprises a source 55 of ultraviolet radiation which is adapted to irradiate the partly purified water which passes through the oxidizer system 30. The source 55 of ultraviolet radiation is for example an ultraviolet lamp, e.g. an excimer ultraviolet lamp.

Tubing 77 brings the water that is treated in the oxidizer system from the additional hydrodynamic cavitator 40 to the ultraviolet irradiation device 50. The arrow shown at tubing 77 in fig. 1 indicates the direction of the flow.

In the embodiment of fig. 1 , the system further comprises a filtration system 60. In the embodiment of fig. 1 , the filtration system 60 comprises a first filter 61 and a second filter 62. In the embodiment of fig. 1 , the first filter is one of an ultrafilter, nanofilter, and/or an electrostatic filter e.g. a passive electrostatic polymer filter. The second filter 62 is an activated carbon filter.

Tubing 78 brings the purified water that has been treated in the oxidizer system 30 from the oxidizer system 30 to the filtration system 60. By the filtration in filtration system 60, further purified water is obtained. The arrow shown at tubing 78 in fig. 1 indicates the direction of the flow.

The further purified water is discharged from the system via tubing 79. The arrow shown at tubing 79 in fig. 1 indicates the direction of the flow.

Fig. 2 shows a first embodiment of a recirculating type system according to the invention. In the embodiment of fig. 2, the system comprises a cavitator feed system 100, a hydrodynamic cavitator 110, a feed system control device 180, a separator which is a hydrocyclone 120, and a purified water discharge 150.

The cavitator feed system comprises a contaminated water feed section 100 and a partly purified water feed section 130.

The contaminated water feed section 100 comprises a contaminated water feed line 102 which is connectable to a source of contaminated water.

The contaminated water feed section 100 further comprises a coagulant feed line 103 which is connectable to a source of coagulant.

The contaminated water feed section further comprises a valve 105.

In the embodiment of fig. 2, the contaminated water feed section 101 further comprises an additive feed line 104 which is connectable to a source of additive.

In the embodiment of fig. 2, the contaminated water feed section 100 further comprises a contaminated water tank 106. The coagulant feed line 103 is connectable to the

contaminated water tank 106 to feed coagulant to the contaminated water tank 106.

Optionally, the contaminated water tank 106 comprises an opening through which e.g. a solid additive can be added, e.g. an additive in powder form. The contaminated water tank 106 comprises a mixer 107 which is adapted to mix the contaminated water which is present in the contaminated water tank 106 with the coagulant. The contaminated water tank 106 has a contaminated water tank outlet 108, and the contaminated water feed line 102 extends between the contaminated water tank outlet 108 and a cavitator inlet section 1 11 of the hydrodynamic cavitator 110. The valve 105 of the contaminated water feed section 100 is arranged in the contaminated water feed line 102.

In this embodiment, the contaminated water tank 106 receives contaminated water from a source of contaminated water via contaminated water supply line 101. So, in this embodiment, the contaminated water feed line 102 which is connectable to a source of contaminated water via contaminated water tank 106 and contaminated water supply line 101.

The partly purified water feed section 130 comprises a partly purified water feed line 131 , a partly purified water reservoir 132, an optional oxidizing gas feed line 133 and a valve 134. The partly purified water reservoir 132 is adapted to accommodate a volume of partly purified water. The partly purified water feed line 131 is connectable to the partly purified water reservoir 132. The optional oxidizing gas feed line 133 which is connectable to a source of oxidizing gas. The hydrodynamic cavitator 1 10 of the embodiment as shown in fig. 2 comprises a cavitation chamber 1 15, a cavitator inlet section 11 1 and a cavitator outlet section 112. The hydrodynamic cavitator 110 is adapted to generate hydrodynamic cavitation in a fluid that flows through the cavitation chamber 1 15. Depending on the settings of the valves 105,134 of the cavitator feed system, this fluid is or comprises either contaminated water with a coagulant and optionally one or more additives, or partly purified water, optionally partly purified water with oxidizing gas.

The cavitator inlet section 11 1 is connectable to the contaminated water feed section 100 and to the partly purified water feed section 130. The cavitator inlet section 11 1 is in communication with the cavitation chamber 115. So, the cavitator inlet section 1 11 receives the fluids in which hydrodynamic cavitation has to be generated. These fluids enter the cavitation chamber 1 15 via the cavitator inlet section 11 1.

The cavitator outlet section 1 12 is also in communication with the cavitation chamber 1 15. The cavitator outlet section 1 12 receives fluids from the cavitation chamber 115 and allows to discharge these fluids from the hydrodynamic cavitator 110.

The contaminated water feed section 100 is adapted and arranged to supply contaminated water, coagulant and optionally one or more additives to the hydrodynamic cavitator 1 10. The partly purified water feed section 130 is adapted and arranged to supply partly purified water and optionally oxidizing gas to the hydrodynamic cavitator 1 10. The contaminated water feed section 100 and the partly purified water feed section 130 do not operate simultaneously. Either the contaminated water feed section 100 is active, or the partly purified water feed section 130 is active.

The feed system control device 180 is adapted to control the valves 105, 134 of the cavitator feed system such that either the contaminated water feed section 100 or the partly purified water feed section 130 are in fluid communication with the hydrodynamic cavitator 1 10, in particular with a cavitator inlet section 11 1 of the hydrodynamic cavitator 1 10.

When the contaminated water feed section 100 is in fluid communication with the cavitator inlet section 1 11 of the hydrodynamic cavitator 110, the hydrodynamic cavitator 1 10 is set to mix the contaminated water and coagulant, and optionally also one or more additives, and to therewith promote the formation of agglomerates of organic contaminants which are present in the contaminated water.

When the partly purified water feed section 130 is in fluid communication with the cavitator inlet section 1 11 of the hydrodynamic cavitator 110, the hydrodynamic cavitator 1 10 is set to oxidize remaining organic contaminants in the partly purified water. In the embodiment of fig. 2, the hydrocyclone 120 is adapted to separate solid particles from fluid. The hydrocyclone 120 comprises a cyclone inlet 121 , a vortex chamber 125, a cyclone fluid outlet 122 and a cyclone contaminants outlet 123.

The vortex chamber 125 is where the actual separation of the solids from the fluid takes place. A mixture of fluid and solids enters the vortex chamber 125 via the cyclone inlet 121. The mixture of fluid and solids is for example the contaminated water with the agglomerates, or the purified water in which still some solids may be present, e.g. due to the oxidation of the partly purified water.

The cyclone inlet 121 is connectable or connected to the cavitator outlet section 1 12 of the hydrodynamic cavitator to receive contaminated water and agglomerates of organic contaminants from the hydrodynamic cavitator 110 when the contaminated water feed section 100 is in fluid communication with the hydrodynamic cavitator 110. Optionally, the cyclone inlet 121 is also connectable or connected to the cavitator outlet section 112 of the hydrodynamic cavitator 110 to receive purified water in which still some solids are or may be present, e.g. due to the oxidation of the partly purified water from the hydrodynamic cavitator 1 10 when the partly purified water feed section 130 is in fluid communication with the hydrodynamic cavitator 110.

The cyclone fluid outlet 122 allows discharge of fluid from the hydrocyclone 120 and the cyclone contaminants outlet 123 allows discharge of solids or semi-solids from the hydrocyclone 120.

The cyclone fluid outlet 122 is connectable or connected to the partly purified water reservoir 132. This way, the partly purified water that leaves the hydrocyclone 120 is collected so that later it can be supplied to the hydrodynamic cavitator 110 for oxidation. In the embodiment of fig.2, tubing 135 extends between the cyclone fluid outlet 122 and the partly purified water reservoir 132. In tubing 135, valve 136 is provided. When this valve 135 is open, partly purified water which is discharged from the hydrocyclone 120 can be transported to and received by partly purified water reservoir 132.

In the embodiment of fig. 2, the system further comprises a purified water discharge 150. The purified water discharge 150 is adapted to allow discharge of purified water and/or further purified water (e.g. purified water that has been subjected to filtration downstream of the hydrocyclone) from the system. Depending on the set-up of the system, the purified water discharge 150 can for example be arranged at the cavitator outlet section 112, between the hydrodynamic cavitator 110 and the hydrocyclone 120, or downstream of the hydrocyclone 120.

In the embodiment of fig. 2, optionally a second purified water discharge 152 is present in addition to the purified water discharge 150. The purified water discharge 150 is arranged downstream of the hydrocyclone 120, and the second purified water discharge 152 is arranged between the hydrodynamic cavitator 110 and the hydrocyclone 120. Depending on the settings of valves 151 and 153, the water that leaves the hydrodynamic cavitator goes to the hydrocyclone 120 or to the second purified water discharge 152.

In the embodiment of fig. 2, the system further comprises filtration system 160, which comprises a first filter 161 and a second filter 162. The filtration system with the filters 161 ,

162 is arranged downstream of the hydrocyclone 120 and upstream of the purified water discharge 150. For example, the first filter 161 is or comprises one of an ultrafilter, nanofilter, and/or an electrostatic filter e.g. a passive electrostatic polymer filter, and the second filter

162 is or comprises an activated carbon filter.

In the embodiment of fig. 2, the cyclone fluid outlet 122 of the hydrocyclone 120 is selectively connectable to either the partly purified water reservoir 132 or the purified water discharge 150. Tubing 163 extends between the cyclone water outlet 122 and the filtration system 160, which is arranged between the cyclone water outlet 122 and the purified water discharge 150. Valve 164 is arranged in tubing 163. When the valve 136 in the tubing 135 is open and the valve 164 in the tubing 163 is closed, the fluid that is discharged from the hydrocyclone 120 via cyclone fluid outlet 122 flows towards and into the partly purified water reservoir 133. When the valve 136 in the tubing 135 is closed and the valve 164 in the tubing

163 is open, the fluid that is discharged from the hydrocyclone 120 via cyclone fluid outlet 122 flows towards and into the filtration system 160, and from there towards the partly purified water discharge 150.

In the embodiment of fig. 2, the system further comprises ultraviolet irradiation device 140 which is arranged between the hydrodynamic cavitator 1 10 and the hydrocyclone 120. Alternatively, the ultraviolet irradiation device may be arranged downstream of the

hydrocyclone 120. The ultraviolet irradiation device 140 comprises a source of ultraviolet radiation which is adapted to irradiate the fluid passing the source of ultraviolet radiation, e.g the purified water which has left the hydrodynamic cavitator 110.

For example, the source of ultraviolet radiation is an ultraviolet lamp, e.g. an excimer ultraviolet lamp.

In the embodiment of fig. 2, the source of ultraviolet radiation of the ultraviolet irradiation device 140 can be switched on and off depending on whether the contaminated water feed section 100 is in fluid communication with the hydrodynamic cavitator 110 or the partly purified water feed section 130 is in fluid communication with the hydrodynamic cavitator 1 10. For example, the feed system control device 180 is adapted to switch the source of ultraviolet radiation of the ultraviolet irradiation device 140 on and off. Alternatively, the ultraviolet irradiation device 140 is always on.

The operation of the embodiment of fig. 2 is as follows.

First, the valve 105 in the contaminated water feed line 102 of the contaminated water feed section 100 is closed. Contaminated water is fed into the contaminated water tank 106 via supply line 101. Coagulant is fed into the contaminated water tank 106 via coagulant feed line 103. Additive is fed into the contaminated water tank 106 via additive feed line 104 or via an opening in the tank 104. The contaminated water, coagulant and additive are mixed with each other by the mixer 107, e.g. during 10 to 20 minutes.

Then, after it has been made sure that the valve 134 is the partly purified feed line 131 is closed, valve 105 in the contaminated water feed line 102 is opened and the mixture of contaminated water, coagulant and additive is supplied to the hydrodynamic cavitator 1 10. In the cavitation chamber 115, hydrodynamic cavitation is generated, which causes further mixing of the contaminated water, coagulant and additive and promotes the formation of agglomerates of organic contaminants.

The contaminated water with the agglomerates of organic contaminants then leaves the hydrodynamic cavitator 115 and flows into the hydrocyclone 120. The ultraviolet irradiation device 140 which is present between the hydrodynamic cavitator 110 and the hydrocyclone 120 remains switched off when the contaminated water with the agglomerates of organic contaminants passes the source of ultraviolet radiation.

In the hydrocyclone 120, agglomerates of organic contaminants are separated from the water. The agglomerates leave the hydrocyclone via the cyclone contaminants outlet 123.

The water, which is now partly purified water, leaves the hydrocyclone via the cyclone fluid outlet 122.

At this point of the processing, the valve 164 in the tubing 163 between the

hydrocyclone 120 and the filtration system 160 is closed and the valve 136 in the tubing 135 between the hydrocyclone 120 and the partly purified water reservoir 132 is open. So, the partly purified water which leaves the hydrocyclone 120 via the cyclone fluid outlet 122 flows into the partly purified water reservoir 132.

When sufficient partly purified water is collected in the partly purified water reservoir 132, or when the contaminated water tank 106 is empty, valve 105 in the contaminated water feed line 102 is closed and valve 134 in the partly purified feed line is opened. Now, the partly purified water is supplied from the partly purified water reservoir 132 to the hydrodynamic cavitator 1 10.

In the hydrodynamic cavitator, hydrodynamic cavitation is generated and the partly purified water is optionally mixed with oxidizing gas, e.g. air, oxygen or ozone. As a result, remaining organic contaminants which were still present in the partly purified water are oxidized to obtain purified water. The oxidation for example results in the formation of gases, liquids and/or and in the formation of solid particles. Optionally, formed gases are removed at this point in the process.

The purified water which leaves the hydrodynamic cavitator and passes through the ultraviolet irradiation device 140. The source of ultraviolet radiation is now on and the water is treated with ultraviolet radiation for further oxidation of remaining contaminants. Optionally, any gases that are formed here are again removed from the water.

The water then flows into the hydrocyclone again (depending on the setting of the valves 151 and 153), in which solid particles that may still be present are separated from the water. The particles leave the hydrocyclone via the cyclone contaminants outlet 123. In the meantime, valve 136 has been closed and valve 164 has been opened. So, the purified water that leaves the hydrcyclone 120 via the cyclone fluid outlet 122 now flows towards and into the filtration device 160 for a final filtering. After this filtering, the water leaves the system via the purified water discharge 150.

Alternatively, if the setting of the valves 151 and 153 is different, the purified water does not flow back into the hydrocyclone 120 again, but goes directly to the optional second purified water discharge 152. Before or after the purified water leaves the optional second purified water discharge 152, it may be filtered to even further improve the quality of the water.

Fig. 3 shows an example of a hydrodynamic cavitator 300, which can be used in the method and systems according to the invention, e.g. in the embodiments of fig. 1 and fig. 2.

The hydrodynamic cavitator 300 of fig. 3 has a cavitator inlet 301 and a cavitator outlet 302 and a cavitation chamber 303. The fluid in which hydrodynamic cavitation has to be generated flows from the cavitator inlet 301 , via the cavitation chamber 303 to the cavitator outlet 302.

In the embodiment of fig. 3, the hydrodynamic cavitator 300 comprises a first stage 304, which has a single cavitation nozzle 310, and a second stage 305, which has multiple cavitation nozzles 315. For reasons of clarity, only two of the multiple nozzles 315 have been indicated by reference numeral 315 in fig. 3.

In the embodiment of fig. 3, the cavitation nozzle 310 of the first stage 304 has a pseudospheric shape. In particular, the surface surface 31 1 of the nozzle 310 has a pseudospheric shape. In the embodiment of fig. 3, there are two sets of cavitation nozzles 315 in the second stage 305. The cavitation nozzles of each series are arranged in series with each other to form a nozzle array 316a, 316b. The two nozzle arrays 316a, 316b are arranged parallel to each other. Optionally, the nozzles 315 of the second stage 305 also have a pseudospheric shape.

Example 1

In this experiment, a landfill leachate has been treated in accordance with an embodiment of the method according to the invention. The landfill leachate had, before the treatment according to an embodiment of the invention, an initial chemical oxygen demand (COD) of 5,000 mg of 0 ₂ per liter. The sample of the leachate that was subjected to the experiment had a volume of 10 liters.

The chemical oxygen demand (COD) is indicative for the amount of oxygen that can be consumed by reactions in a water sample. It is commonly expressed as the mass of oxygen consumed over volume of contaminated water. A COD test can be used to easily quantify the amount of organics in water. The most common application of COD is in quantifying the amount of oxidizable pollutants found in surface water (e.g. lakes and rivers) or wastewater.

In the experiment, 200 ml of active colloidal fine-dispersed alumina was added to the leachate sample as a coagulant. The coagulant was added in the form of a powder which mainly comprises microparticles.

Then 200 grams of a mix of bentonite and montmorillonite was added to the leachate as an additive.

The mixture of leachate, coagulant and additive was pre-mixed and introduced into a hydrodynamic cavitator. In the hydrodynamic cavitator, hydrodynamic cavitation was generated and therewith the leachate, the coagulant and the additive were thoroughly mixed and agglomerates of organic contaminants present in the leachate were formed.

Then, the formed agglomerates were separated from the water by using a

hydrocyclone. This resulted in obtaining partly purified water which contains remaining organic contaminants.

Then, remaining organic contaminants in the partly purified water were oxidized, which led to the formation of gas and also some solid particles.

Then, the gas was removed from the partly purified water, thereby obtaining purified water. The purified water was then filtered, to obtain further purified water.

Then, the further purified water was cleaned with fine-dispersed wood charcoal. The COD of the water that resulted from this experiment was equal to 30 mg of O2 per liter. A viscous residue (which was similar to a solid matter) was removed from the system during the experiment.

Example 2

In this experiment, a landfill leachate has been treated in accordance with an embodiment of the method according to the invention. The landfill leachate had, before the treatment according to an embodiment of the invention, an initial chemical oxygen demand (COD) of 50,000 mg of 0 ₂ per liter. The sample of the leachate that was subjected to the experiment had a volume of 15 liters.

In the experiment, 300 ml of colloidal iron hydroxide in the colloidal form was added to the leachate sample as a coagulant. The iron hydroxide was obtained from soluble iron salts. The coagulant was added in the form of a powder which mainly comprises microparticles.

Then 300 grams of montmorillonite was added to the leachate as an additive.

The mixture of leachate, coagulant and additive was pre-mixed and introduced into a hydrodynamic cavitator. In the hydrodynamic cavitator, hydrodynamic cavitation was generated and therewith the leachate, the coagulant and the additive were thoroughly mixed and agglomerates of organic contaminants present in the leachate were formed.

Then, the formed agglomerates were separated from the water by using a

hydrocyclone. This resulted in obtaining partly purified water which contains remaining organic contaminants.

Then, remaining organic contaminants in the partly purified water were oxidized, which led to the formation of gas and also some solid particles.

Then, the gas was removed from the partly purified water, thereby obtaining purified water. The purified water was then filtered, to obtain further purified water.

Then, the further purified water was cleaned with fine-dispersed wood charcoal. The COD of the water that resulted from this experiment was less than 30 mg of O2 per liter.

A viscous residue (which was similar to a solid matter) was removed from the system during the experiment.