Water purification reactor and a method for the purification of contaminated water

Abstract

The invention regards a water purification reactor (1) for purifying contaminated water through mixing of said water with an ozone-comprising gas, comprising: - a reactor (1) housing (2) with a first water supply channel (14) for supplying a first portion of the contaminated water to the reactor (1) and a water discharge channel (10) for discharging purified water from the reactor (1), wherein the first water supply channel (14) is configured to discharge the first portion of the contaminated water into the reactor (1) in a first outflow direction (R); and - a mixing device (24) for mixing an ozone-comprising gas into the contaminated water. The reactor (1) further comprises a second water supply channel (22) for supplying a second portion of the contaminated water to the reactor (1), wherein the mixing device (24) is provided in the second water supply channel (22) for mixing an ozone-comprising gas into the second portion of the contaminated water, and wherein the second water supply channel (22) is configured to discharge the second portion of the contaminated water into the reactor (1) in a second outflow direction (R) that is parallel to the first outflow direction.

Description

[0001] Title: Water purification reactor and a method for the purification of contaminated water

[0002] OBJECT OF THE INVENTION

[0003] The invention regards a water purification reactor, a module for in the water purification reactor and a method for the purification of contaminated water.

[0004] BACKGROUND OF THE INVENTION

[0005] Ozone is globally recognized as a powerful oxidant for removing micropollutants from contaminated water. It is effective in breaking down organic contaminants, but it also has disadvantages. A major issue is the formation of bromate, a potentially harmful byproduct that can form when ozone reacts with bromide ions, especially in water with high bromide concentrations. In addition, conventional ozone dissolution systems also dissolve oxygen gas, which can negatively impact downstream treatment steps that rely on oxygen-free (anaerobic) conditions.

[0006] Several methods have been developed for ozone treatment of wastewater, each with its own advantages and disadvantages. A commonly used technique is the bubble column, in which water flows vertically while ozone gas is introduced from the bottom in the form of bubbles. This promotes continuous exchange between ozone and water, thereby enhancing the breakdown of contaminants. However, bubble columns have the disadvantage of their large height of typically at least six meters, resulting in higher investment, operational, and maintenance costs, as well as the potential for uneven ozone distribution. In addition, given the long path the gas bubbles travel in such a column, a relatively high amount of oxygen will also dissolve.

[0007] Another method is the Venturi injector system, where ozone is injected into a side flow via a mixing device and eventually mixed with the bulk liquid. These systems have the advantage of being very compact and achieving high ozone concentrations at the injection point, which is efficient for rapid pollutant removal. However, this temporary, local excess of ozone can also lead to the presence of free ozone in the water, which is the main factor in converting bromide to bromate. In addition, precise control of ozone dosing is desirable to avoid excessive oxygen input, which could be detrimental to downstream anaerobic treatment processes.

[0008] In addition, there are systems such as those described in US2021031153 A1 , in which ozone is either directly injected into the supplied water or a portion of the contaminated water is injected with ozone via a side flow. Such systems have relatively poor mixing of ozone in the water, resulting in locally high ozone concentrations. This can lead to significant bromate formation. This increases the need for additional measures to mitigate bromate formation or additional treatment steps to remove bromate, which raises operational costs and reduces the overall efficiency of the system.

[0009] DESCRIPTION OF THE INVENTION

[0010] It is an objective of the present invention to at least partially overcome one or more of the above-mentioned disadvantages or to provide a suitable alternative.

[0011] In particular, the objective of the present invention is to provide a water purification reactor and method for purifying water in which less bromate is formed.

[0012] Another objective of the present invention is to provide a reactor with a smaller footprint.

[0013] In a first aspect, the invention provides a water purification reactor for purifying contaminated water by mixing said water with an ozone-comprising gas, comprising:

[0014] - a reactor housing comprising a first water supply channel for supplying a first portion of the contaminated water to the reactor, and a water discharge channel for discharging purified water from the reactor, wherein the first water supply channel is configured to discharge the first portion of the contaminated water from the first water supply channel into the reactor in a first outflow direction; and

[0015] - a mixing device for mixing an ozone-comprising gas into the contaminated water.

[0016] The reactor further comprises a second water supply channel for supplying a second portion of the contaminated water to the reactor. The mixing device is provided in the second water supply channel, such that the mixing device is configured to mix an ozone-comprising gas into the second portion of the contaminated wastewater. This second portion of the contaminated water is preferably raw (untreated) contaminated water, but it may also be previously treated contaminated water. According to the inventive concept, the second water supply channel is configured to discharge or inject the second portion of the contaminated water from the second water supply channel into the reactor in a second outflow direction that is parallel to the first outflow direction. The parallel outflow directions are preferably oriented in the same direction, meaning that both water flows run parallel and in the same direction through the reactor, i.e. , not in opposite directions.

[0017] The two separate supply channels, each independently discharging a portion of the contaminated water from its respective supply channel into the reactor, wherein one of the supply channels is provided with a mixing device, ensure that the ozone-comprising gas does not need to be mixed or injected into the entire volume of contaminated water. The directly mixing into only a portion of the contaminated water has, on the one hand, the advantage that part of the ozone immediately reacts with the organic contaminants, thereby preventing the formation of excessive free ozone in the contaminated water, which could otherwise lead to excessive bromate formation. Furthermore, when a consistent amount of gas is mixed into a relatively small volume of contaminated water, the efficiency of gas dissolution in the liquid is reduced, resulting in a reduced solubility of the injected gas mixture. However, this reduction in solubility is disproportionate: while the solubility of oxygen decreases significantly, the solubility of ozone is relatively less affected due to its inherently better solubility in water. Consequently, the desired concentration of dissolved ozone in the side flow can be maintained, while the amount of dissolved oxygen is greatly reduced. This, in turn, has the advantage that the oxygen concentration remains low, which benefits further (anaerobic or anoxic) treatment processes. Another advantage is that the ozone is mixed under pressure into the second portion of the contaminated water, allowing the gas to dissolve more effectively locally.

[0018] To ensure sufficient mixing of the two portions of contaminated water and to evenly distribute the ozone from the second portion of the contaminated water across both water flows, the inventors of the present invention have found that favorable mixing occurs when the first water supply channel and the second water supply channel discharge the first and second portions of the contaminated wastewater, respectively, from the water supply channel into the reactor in a parallel outflow direction. In particular, the mixing is further optimized when the first outflow direction is substantially coaxially aligned with the second outflow direction. This means that both water flows are introduced into the reactor along the same central axis and flow in the same orientation. Due to this coaxial, or concentric, alignment, there is maximum overlap between the flow of the first portion of the contaminated water and the flow of the second portion of the contaminated water. When the two flows are aligned in extension of one another, more intense vortices are generated at the interfaces between the flows, leading to faster and more thorough mixing. The concentric alignment optimizes the mixing of ozone into the two water flows, allowing the ozone in the second portion of the contaminated water to come rapidly into contact with the first portion of the contaminated water. Because of this fast and thorough mixing, the ozone quickly reacts with the contaminants present and there is a short contact time between ozone and water. This has the advantage that little free ozone can form in the contaminated water, thereby reducing bromate formation as previously discussed. In addition, due to the effective mixing of the two flows, a smaller reactor volume is required, resulting in a reactor with a smaller footprint and reduced height.

[0019] In one embodiment of the invention, the first and second outflow directions are directed vertically, in particular downwardly. By positioning both outflow directions vertically, it is prevented that the flows deviate excessively, for example due to differences in density (since one of the flows is provided with a gas). It is particularly advantageous when both flows are directed downward. The outflow directions can, for instance, both be arranged in a central portion of the reactor and directed downward, such that, upon impacting the reactor bottom, the mixed flow spreads laterally, preferably substantially uniformly in all directions, and flows upward along a surrounding wall. The inventors have found that such a flow profile within the reactor promotes mixing. This improved mixing leads to rapid distribution of the introduced ozone throughout the contaminated wastewater in the reactor and minimizes the likelihood of bromate formation.

[0020] In an embodiment of the invention, the first water supply channel and / or the second water supply channel is at least partially provided within the reactor housing. For example, the respective water supply channels may be located within a reactor volume defined by the reactor housing, which includes a bottom, a top, and enclosing walls. The point at which each portion of the contaminated water enters the reactor from the water supply channel is located at the respective outlet openings of those channels. By placing the first and / or second water supply channel at least partly inside the reactor housing, the mixing can be more easily optimized. It has been found particularly advantageous to position a portion of the first water supply channel, preferably provided within the reactor housing, and at least a portion of the second water supply channel, preferably also within the reactor housing, concentrically. This means that one supply channel is positioned coaxially within the other supply channel, such that both outlet openings share a common outflow axis. This concentric configuration ensures that the first and second water flows enter the reactor in exactly the same direction and along the same central axis. Optionally, the second water supply channel, comprising the ozone mixing device, is at least partially concentrically positioned within the first water supply channel.

[0021] Preferably, the concentrically positioned supply channels are also centrally located within the reactor, meaning that the common outflow axis of the supply channels coincides with the central axis of the reactor. This results in a symmetrical flow profile in which both water flows flow substantially coaxially along the reactor’s central axis. Such central and concentric positioning prevents asymmetric flow patterns and promotes a uniform distribution of the mixed flow throughout the reactor.

[0022] In a further preferred embodiment, the invention provides a central gas supply channel positioned concentrically within the second water supply channel. This gas supply opens into the mixing device provided in the second supply channel. In this way, the ozone-comprising gas is introduced precisely into the core of the second water flow. In a particularly advantageous embodiment, the reactor housing, the first water supply channel, the second water supply channel, and the central gas supply are all positioned concentrically with respect to one another, with their axes coinciding with the central axis of the reactor. This fully concentric configuration creates a symmetrical flow profile in the reactor, prevents undesired asymmetric vortices, and promotes a highly uniform distribution of ozone throughout the entire water mass. The result is rapid and efficient mixing, improved ozone utilization, and the ability to design the reactor with a relatively compact volume.

[0023] In an embodiment of the invention, the second water supply channel has an outlet opening located lower than the outlet opening of the first water supply channel. When all outlet openings are positioned at the same height, the flows may interfere with one another, leading to unstable flow, vortices that cancel each other out, or dead zones where the liquid does not mix properly. By positioning the outlet openings at different heights, the outflowing liquids or gases can mix at different points. This results in more turbulent and efficient mixing. By placing the outlet opening of the second water supply channel, in which the the portion of contaminated water mixed with ozone-comprising gas is present, lower, the ozone can be mixed more efficiently into the first portion of the contaminated wastewater. Moreover, the flow velocity from the second supply channel is typically higher than that from the first; if the outlet opening of the second supply channel were positioned higher within the first channel, part of the water could be deflected backward.

[0024] Preferably, the water purification reactor comprises a cylindrical enclosing wall, so that when the mixed flow spreads laterally, it also moves evenly along this wall. However, it is also possible for the assembly of supply channels and discharge channel to be installed in existing, for example rectangular, reactors. In such cases, mixing in the reactor’s corners can be problematic. Preferably, a conical, pyramidal, or similar flow-distribution element is positioned at the reactor bottom beneath the outlet openings of the first and second water supply channels. This helps to guide the contaminated water portions emerging from the respective outlet openings more effectively toward the reactor walls.

[0025] In an embodiment of the invention, the reactor further comprises an overflow plate provided higher than an outlet opening of the first supply channel and an outlet opening of the second water supply channel. The overflow plate has a discharge volume in fluid connection with the water discharge channel. This allows the overflow plate to direct water from the discharge volume to the discharge channel. During operation, the reactor is filled with (contaminated) water until the water flows over the edges of the overflow plate and is discharged from the reactor. By allowing the water to flow over an overflow plate before being discharged, it passes along a large portion of the reactor walls before leaving the reactor, rather than being immediately drawn into the discharge channel. This enhances mixing. Moreover, the flow profile in which the water first moves downward and then upward increases the contact time between the water and the ozone, further improving the efficiency of the ozone treatment. It also helps to prevent dead zones where water stagnates or flows slowly, which could otherwise lead to insufficient ozone mixing. A uniform distribution of ozone throughout the reactor ensures that all parts of the water are effectively treated and that the risk of bromate formation is reduced.

[0026] In an embodiment of the invention, the water discharge channel is provided lower than the overflow plate. The overflow plate has an opening toward the discharge channel for discharging overflowed water from the discharge volume to the discharge channel. By positioning the discharge channel lower, the overflowed water can easily drain away from the overflow plate.

[0027] In another embodiment, the overflow plate is provided with a profiled, in particular sawtooth-shaped, edge, preferably along the entire length of the plate. The profiled edge ensures that the water flows evenly over the overflow plate. In the absence of such a profiled edge, the water could develop a preferred flow direction, for instance toward the section of the overflow plate nearest to the discharge opening. This preferred direction would deteriorate mixing within the reactor. Additionally, the profiled edge helps prevent large variations in flow rate across the edge.

[0028] In an embodiment of the invention, the first water supply channel is provided with a gas outlet for discharging gases from the first water supply channel. The path of gas bubbles formed during the mixing of ozone-comprising gas into the contaminated water is difficult to predict within the reactor. To prevent accumulation of gas bubbles in the first water supply channel, the channel is provided with a gas outlet, for example in the form of a pipe, to discharge gas from the channel.

[0029] In an embodiment of the invention, the mixing device comprises a gas supply conduit and a liquid supply conduit arranged substantially coaxially therearound. This liquid supply conduit preferably corresponds to the second water supply channel. In this way, the gas from the gas supply conduit is directly mixed into the second portion of the contaminated water.

[0030] The gas supply conduit terminates in a gas nozzle having a preferably smaller crosssection than that of the gas supply conduit, the gas nozzle being located in a preferably narrowed portion of the liquid supply conduit, hereafter referred to as the gas mixing chamber. The gas mixing chamber opens downstream into a preferably narrowing (funnel- shaped) liquid outlet nozzle with an outlet opening configured to discharge (inject) the mixed chamber liquid contained in the gas mixing chamber into the reactor. Thus, by means of the mixing device, the second portion of the contaminated water is injected forcefully into the reactor. Within the reactor liquid, a mixing zone is formed in which the first portion of the contaminated water, and thereby the ozone, are significantly more mixed. Experimental results have shown that this invention provides an effective reactor system for ozone transfer in wastewater, enabling the removal of micropollutants. At the same time, bromate formation and oxygen transfer into the water are minimized.

[0031] In the mixing device according to the invention, ozone is dissolved in the water while oxygen dissolves only to a limited extent. This offers significant advantages for wastewater treatment, since subsequent processes following ozonation, such as the removal of organic micropollutants and nutrients (mainly nitrogen via nitrification and denitrification), can operate much more efficiently. The denitrification process requires low-oxygen conditions; therefore, the proposed ozone-mixing system is particularly beneficial as it operates under low-oxygen conditions ideal for denitrification. Excess oxygen will be discharged from the reactor as offgas, which can optionally be reused in further aerobic treatment processes.

[0032] In an embodiment, the mixing device is configured for mixing hydrogen peroxide (H2O2) into the second portion of contaminated water. In particular, the mixing device is configured for introducing the hydrogen peroxide into the liquid supply conduit upstream of the gas mixing chamber. Hydrogen peroxide is effective in removing organic contaminants. Additionally, the presence of hydrogen peroxide has the advantage of regulating ozone concentration to prevent the formation of free ozone in the contaminated water.

[0033] In an embodiment of the invention, the gas mixing chamber has a length in the second flow direction in the range of 5-25 cm, preferably 7-20 cm. The inventors have found that such a length in the flow direction of the gas mixing chamber is optimal for achieving the desired residence time of the ozone within the gas mixing chamber and the corresponding linear velocity.

[0034] In an embodiment of the invention, at least the first water supply channel, the water discharge channel, and preferably the overflow plate are interconnected to form a module. This module is preferably removable from the reactor as a whole. Maintaining or replacing an entire module is faster and more cost-efficient than replacing individual pipes or components one by one. If one or more parts of the module fail or need replacement, the entire module can be quickly and easily replaced without requiring prolonged reactor downtime.

[0035] In a second aspect, the invention provides such a module for use in a water purification reactor according to the invention, the module comprising at least a first water supply channel, a water discharge channel, and preferably an overflow plate, which are interconnected, the module preferably being removable from the reactor as a unit.

[0036] In a third aspect, the invention provides a water purification system comprising two or more water purification reactors according to the invention. These reactors may for example be connected in series and / or in parallel. The advantage of two or more reactors in series is that in each reactor ozone can be mixed into a portion of the contaminated water supplied to the reactor, thereby reducing the amount of ozone that must be dissolved per reactor while maintaining purification capacity and reducing bromate formation. The advantage of reactors connected in parallel is that they can treat larger volumes of contaminated water without adverse effects on mixing.

[0037] Preferably, in each reactor of the two or more reactors, at least the second water supply channel receives untreated contaminated water, i.e. , contaminated water that has not yet undergone a purification process. This contaminated water has a relatively high content of organic contaminants (such as micropollutants). By adding ozone only to this untreated water, the ozone reacts relatively quickly, preventing the formation of excess free ozone in the water, which would otherwise lead to bromate formation.

[0038] In a fourth aspect, the invention provides a method for purifying contaminated water by mixing the contaminated water with an ozone-comprising gas, comprising the steps of:

[0039] - supplying a first portion of the contaminated water to a water purification reactor via a first water supply channel, wherein the first portion of the contaminated water flows from the first water supply channel into the reactor in a first outflow direction,

[0040] - supplying a second portion of the contaminated water to the reactor via a second water supply channel, wherein a mixing device is provided in the second water supply channel for mixing an ozone-comprising gas into the second portion of the contaminated water; and wherein the second portion of the contaminated water flows from the second water supply channel into the reactor in a second outflow direction parallel to the first outflow direction.

[0041] As previously described, the inventors have found that the parallel discharge of the two liquid flows improves their mixing. It is particularly preferred that the first outflow direction of the first portion of the contaminated water is substantially coaxially aligned with the second outflow direction of the second portion of the contaminated wastewater. The two outflow directions may, in particular, be oriented vertically, preferably downwardly.

[0042] Through coaxial (and preferably downward) outflow directions, a flow profile is created in the reactor in which both flows emerge from the respective supply channels and, upon impacting a wall (i.e. , the bottom, top, or enclosing wall), spread laterally outward. This flow profile has been found to be highly conducive to mixing the two supply flows. Due to the effective mixing, the ozone quickly contacts contaminants in the contaminated water, thereby reducing the formation of free ozone in the water. Moreover, because of the improved mixing, a relatively small reactor volume is sufficient. To further promote even distribution throughout the reactor, both outflow directions are preferably positioned centrally within the reactor.

[0043] Preferably, the first portion of the contaminated water is supplied to the reactor without having ozone-comprising gas premixed prior to entering the reactor. That is, ozone is only mixed into the second water supply channel and not into the first water supply channel. The mixing of ozone with the first portion of the contaminated water therefore only occurs after both the first and second portions of the contaminated water have been discharged into the reactor and mixed therein.

[0044] In an embodiment of the invention, the flow velocity of the second portion of the contaminated water discharged from the second water supply channel is higher than that of the first portion of the contaminated water discharged from the first water supply channel. In particular, the second portion of the contaminated water flows from an outlet opening of the second water supply channel into the reactor at a velocity in the range of 5-20 m / s, preferably 10-18 m / s, and more preferably around 15 m / s. This relatively high flow velocity has the advantage of entraining surrounding water with it and of impacting a wall, preferably the reactor bottom, with considerable force. This enhances the aforementioned advantage of evenly mixing the fluid through lateral spreading at the bottom of the reactor.

[0045] In an embodiment of the invention, the mixing device comprises a gas supply conduit and a liquid supply conduit arranged substantially coaxially therearound, wherein the gas supply conduit terminates in a gas nozzle, which gas nozzle is located within the liquid supply conduit, hereafter referred to as the gas mixing chamber. The liquid supply conduit of the mixing device preferably corresponds to the second water supply channel.

[0046] The mixed chamber liquid present in the gas mixing chamber preferably has a residence time in the range of 10-1000 milliseconds, preferably 50-200 milliseconds, and more preferably around 100 milliseconds. The inventors have discovered that, due to the effective mixing and very short residence time, ozone gas exists only briefly at high concentration within the gas mixing chamber before being mixed into the first portion of contaminated water. Consequently, the ozone quickly contacts contaminants in both the first and second portions of the contaminated water, reacting rapidly and preventing the formation of free ozone that could otherwise lead to bromate formation. Optionally, hydrogen peroxide is mixed into the second portion of the contaminated water upstream of the gas mixing chamber, preferably in a concentration of 1-5 ppm at the mixing point of the hydrogen peroxide.

[0047] In an embodiment of the invention, the linear velocity of the mixed chamber liquid in the gas mixing chamber lies in the range of 0.5-5 m / s, more preferably between 0.75-2 m / s, and more preferably around 1.2 m / s.

[0048] In an embodiment of the invention, the gas-to-liquid ratio (Vg / VI) of the mixed chamber liquid in the gas mixing chamber lies in the range of 3-20 vol%, preferably 7-18 vol%, and more preferably around 14 vol%. With these ratios, sufficient ozone is dissolved in the water while simultaneously preventing excessive oxygen dissolution.

[0049] In an embodiment of the invention, the reactor, higher than at least the outlet opening of the first water supply channel and the outlet opening of the second water supply channel, comprises an overflow plate with a discharge volume in fluid connection with a water discharge channel for discharging purified water from the reactor. The method includes discharging water that overflows the overflow plate via the discharge volume into the reactor’s water discharge channel.

[0050] As mentioned before, allowing the water to flow over an overflow plate before being discharged causes it to pass along a large portion of the reactor walls before leaving the reactor, resulting in more effective mixing.

[0051] In an embodiment of the invention, the method is performed in the absence of prior (ozonebased) treatment of the second portion of the contaminated water. In other words, the second portion of the contaminated water is untreated water. This contaminated (untreated) water has a relatively high concentration of organic pollutants (such as micropollutants). By adding ozone only to this untreated water, the ozone reacts relatively quickly, preventing the formation of free ozone, and thus bromate.

[0052] In an embodiment of the invention, purified water discharged from the reactor via the water discharge channel is supplied to a first water supply channel of another water purification reactor, and wherein untreated contaminated water is supplied via the second water supply channel of the other water purification reactor to the other water purification reactor.

[0053] Other features of the first aspect of the invention apply correspondingly to the fourth aspect of the invention. SHORT DESCRIPTION OF THE FIGURES

[0054] The invention will hereinafter be explained with reference to the accompanying figures, wherein,

[0055] Fig. 1 shows a schematic cross-sectional view of a water purification reactor according to an embodiment of the invention;

[0056] Fig. 2 shows a schematic top view of a water purification reactor according to an embodiment of the invention;

[0057] Fig. 3 shows a schematic representation of the liquid flows in the water purification reactor of Fig. 1 ;

[0058] Fig. 4 shows a schematic view of a mixing device according to an embodiment of the invention.

[0059] DETAILED DESCRIPTION OF THE FIGURES

[0060] Figure 1 shows a water purification reactor designated by reference numeral 1. The water purification reactor 1 can be used for purifying contaminated water by mixing ozone into the contaminated water. The reactor 1 comprises a reactor housing 2 having an enclosing wall 4, a bottom 6, and a top 8, which together define a reactor volume. The bottom 6 in fig. 1 has slanted edges towards the enclosing wall 4. Alternatively, the bottom 6 may have rounded or differently shaped edges. Inside the reactor housing 2, a water discharge channel 10 is provided for discharging purified water from the reactor 1 through a water discharge channel 10 discharge opening 12. In fig. 1 , for illustrative purposes, a wall of the water discharge channel 10 has been omitted to show the internal structure.

[0061] A first portion of the contaminated water is supplied to the reactor 1 via a first water supply channel 14. The first water supply channel 14 is partly provided in the reactor housing 2. The first water supply channel 14 comprises a radially positioned channel section, connected to an inlet opening of the channel 14, and an axially positioned channel section having an outlet opening 20 for discharging the first portion of the contaminated water into the reactor 1. The radial and axial channel sections are interconnected by a bend or curvature in the channel 14. When the first portion of the contaminated water is guided into the reactor 1 , it flows through the first water supply channel 14 and exits via the outlet opening 20, entering the reactor 1 in a downward direction R towards the bottom 6 of the reactor housing 2. The outlet opening 20 of the first water supply channel 14 is located in a central part of the reactor housing 2, preferably centered within the reactor 1.

[0062] The water purification reactor 1 further comprises a second water supply channel 22 for supplying a second portion of the contaminated water to the reactor 1. This second water supply channel 22 is also centrally located within the reactor. In this second water supply channel 22, upstream of an outlet opening of the second water supply channel 22, a mixing device 24 is provided for mixing an ozone-comprising gas into the second portion of the contaminated water. A detailed view of an embodiment of the mixing device 24 is shown in fig. 4 and 5.

[0063] The second water supply channel 22 extends through the top 8 of the reactor housing 2 into the reactor housing, and passes through a wall of the first water supply channel 14 such that part of the second water supply channel 22 is concentrically arranged within the axially positioned portion of the first water supply channel 14. In the second water supply channel 14, a mixing device 24 is provided by means of which an ozone-comprising gas is mixed into a second portion of the contaminated water, which is supplied to the reactor independently of the first portion of the contaminated water. After ozone has been mixed in, the second portion of the contaminated water flows out of the outlet opening 26 of the second water supply channel 22 in a second outflow direction R that is parallel to, and in fig. 1 corresponds with, the first outflow direction R. Due to the parallel or preferably coaxial alignment, there is maximum overlap between the flow of the first portion of the contaminated water and the flow of the second portion of the contaminated water. When the two flows are aligned in extension of one another, more intense turbulence is created at the interfaces between the flows, leading to faster and more thorough mixing. Concentric water supply channels 14, 22 can thereby optimize the mixing and distribution of the ozone in the contaminated water. A gas supply conduit 27 may be concentrically provided within the second water supply channel 22 for supplying gas to the mixing device 24. This results in a channel-in-channel-in-channel structure of gas supply conduit 27, second water supply channel 22, and first water supply channel 14, all concentrically arranged, preferably within the reactor volume defined by the reactor housing 2, as illustrated in fig. 3. The outlet opening 26 of the second water supply channel 22 is located lower than the outlet opening 20 of the first water supply channel 14. The outflow velocity from the second supply channel 22 is higher than that from the first supply channel 14; if the outlet opening of the second water supply channel were positioned higher than that of the first, part of the flow could be redirected backward into the channel. By placing the outlet openings at different vertical levels, the outflowing liquids or gases can mix at different positions. This creates more turbulent and efficient mixing, since the flows interact at multiple levels rather than in a single plane.

[0064] The two contaminated water flows that exit their respective outlets 20, 26 in the downward direction R will (if sufficient velocity is achieved), strike the bottom 6 of the reactor 1. Upon hitting the bottom 6, part of the flows will move upward along the enclosing wall 4. This upward flow along the wall 4 creates upward circulation of the water that contributes to effective mixing of the two flows and, consequently, the ozone. At the same time, another part of the water mixes within the central portion of the reactor 1. This mixing within reactor 1 itself ensures that the contaminated water and the ozone are distributed throughout the entire reactor volume. Through these two mechanisms — upward wall circulation and internal mixing — a complex mixing profile develops within the reactor 1. The inventors have found that this mixing profile significantly enhances the efficiency of ozone mixing throughout the reactor 1.

[0065] In reactor 1, further an overflow plate 28 is provided. This overflow plate 28 is located in a higher part of reactor 1, specifically above the water discharge channel 10 and the outlet opening 12 of the water discharge channel 10, and extends across the cross-section of reactor 1. The overflow plate 28 has a central portion that forms an outflow volume 30 and (raised) edges 32 that delimit the central portion. The water flowing upward in the reactor 1 will flow over the edges 32 of the overflow plate 28 and subsequently enter the central portion of the plate, where it collects in the outflow volume 30. This outflow volume 30 is in fluid connection with the water discharge channel 10 via an opening 34 in a substantially central part of the overflow plate 28 (see fig. 2). The water that has flowed over the edges 32 of the overflow plate 28 passes through this opening 34 into the water discharge channel 10 and ultimately exits the reactor 1. The water discharge channel 10 comprises an inclined section, allowing the overflowed water to be easily guided toward the outlet opening 12. The (raised) edges 32 of the overflow plate 28 are profiled, in particular in a sawtooth shape. These profiled edges 32 have the advantage that the water flows evenly over the edges 32 of the overflow plate 28. Without profiled edge 32, a preferential flow direction could arise in which a greater amount of water flows over the edge 32 near the opening 34 (see fig. 2) of the overflow plate 28. Such a preferential direction would impair mixing in the rest of the reactor.

[0066] The bubbles formed in the contaminated water after ozone mixing create a less predictable flow pattern in reactor 1. It is possible that, after flowing out of the outlet opening 26 of the second water supply channel 22, the bubbles move upward and enter the outlet opening 20 of the first water supply channel 14, where they could accumulate. To prevent this unwanted accumulation of gas in the first water supply channel 14, a gas discharge 36 is provided in the first water supply channel 14, allowing gas to be discharged from the first water supply channel 14 toward the top 8 of reactor 1. The top 8 of the reactor housing 2 itself is also provided with an opening 38 for the discharging of excess gas.

[0067] In fig. 1, the first water supply channel 14, the water discharge channel 10, and the overflow plate 28 are connected to each other so that together they form a single module. This module can therefore be easily removed as a whole from the reactor housing 2, for example for maintenance purposes.

[0068] In fig. 1, a reactor 1 with a cylindrical enclosing wall 4 is shown. It is possible that the assembly of the supply channels 14, 22, the discharge channel 10, and the overflow plate 28 may also be installed in existing, for example rectangular, reactors 1. In this case, mixing in the corners of reactor 1 can be problematic. It may be advantageous to place a conical, pyramid-shaped, or similar distribution element on the bottom 6 of the reactor, preferably centrally beneath the outlet openings 20, 26 of the first and second water supply channels 14, 22. This has the advantage that the portions of contaminated water discharged from the respective outlet openings are better directed toward the walls of reactor 1 .

[0069] Fig. 2 schematically shows a top view of the reactor, with the reactor housing 2 comprising the first water supply channel 14 and the second water supply channel 22, which is partially concentrically positioned within a portion of the first water discharge channel 10. Furthermore, a gas discharge 36 is provided in the first water discharge channel 10. The flows in the reactor 1 are schematically illustrated in Figure 3. The first portion of the contaminated water 37 flows downward in the first outflow direction R from the outlet opening 20 of the first water supply channel 14 into the reactor, and the second portion of the contaminated water 39 flows in the same outflow direction R (through the concentrically arranged supply channels) from the outlet opening 26 of the second water supply channel 22 into the reactor. As a result, the two portions of the contaminated water mix, distributing ozone between them. The mixed water flows downward until it reaches the bottom 6, then moves upward along the reactor walls. A portion of the upward-flowing water passes over the overflow plate 28 and is subsequently discharged from the reactor through the opening 34 via the water discharge channel 10.

[0070] Figure 4 shows an example of a mixing device 24. The mixing device 24, designed to mix an ozone-comprising gas into a first portion of the contaminated water, comprises a gas supply conduit 38 and a liquid supply conduit 40 arranged substantially coaxially therearound, through which the gas flow 42 resp. the second portion of the contaminated water 44 are supplied to the mixing device 14. The gas supply conduit 38 terminates in a gas nozzle 46 having a preferably smaller cross-section than that of the gas supply conduit 38, which nozzle 46 is located within a narrowed section of the liquid supply conduit 40, referred to hereafter as the gas mixing chamber 48. Downstream (in the downward direction in fig. 4), the gas mixing chamber 48 discharges into a preferably narrowing (funnel-shaped) liquid outlet nozzle 50 comprising an outlet opening 26 configured to inject the mixed chamber liquid 52, contained in the gas mixing chamber 48, into the reactor 1. By means of the mixing device 14, the first portion of the contaminated water is forcefully injected into the remaining part of the reactor 1 . In the reactor fluid, there is created a mixing zone in which the first part of the contaminated water, and thus the ozone, is mixed significantly more. Experimental results have shown that the invention provides a highly effective reactor system for ozone transfer in wastewater, enabling removal of micropollutants. In the meantime, bromate formation and the transfer of oxygen to the water is minimized.

[0071] The discharge velocity of the gas-mixed first portion of the contaminated water is ejected from the outlet opening with a velocity in the range between 5 and 20 m / s, preferably between 10 and 18 m / s, as around 15 m / s. The residence time of the fluid in the gas mixing chamber is ideally between 10 and 1000 milliseconds, preferably 50 and 200 milliseconds, most preferably around 100 milliseconds. The linear velocity of the liquid in the gas mixing chamber is preferably between 0.5 m / s and 5 m / s, more preferably between 0.75 m / s and 2 m / s, and most preferably around 1.2 m / s. The optimal gas-to-liquid ratio (Vg / VI) preferably lies between 3% and 20%, more preferably 7% and 18%, and most preferably around 14%. In the mixing device according to the invention, ozone dissolves effectively in the water, while oxygen dissolves only to a limited extent. This offers major advantages in wastewater treatment, as other processes running on ozonisation such as micropollutant removal and nutrient elimination (mainly nitrogen via nitrification and denitrification) can operate more efficiently. The denitrification process requires low-oxygen conditions, and thus the proposed ozone mixing system is particularly beneficial because it operates under low- oxygen conditions ideal for denitrification.

Claims

CLAIMS1. Water purification reactor (1) for purifying contaminated water by mixing said water with an ozone-comprising gas, comprising: a reactor housing (2) with a first water supply channel (14) for supplying a first portion of the contaminated water to the reactor (1) and a water discharge channel (10) for discharging purified water from the reactor (1), wherein the first water supply channel (14) is configured to discharge the first portion of the contaminated water into the reactor (1) in a first outflow direction (R); and a mixing device (24) for mixing an ozone-comprising gas into the contaminated water; characterized in that, the reactor (1) further comprises a second water supply channel (22) for supplying a second portion of contaminated water to the reactor (1), wherein the mixing device (24) is provided in the second water supply channel (22) for mixing an ozonecomprising gas into the second portion of the contaminated water, and wherein the second water supply channel (22) is configured to discharge the second portion of the contaminated water into the reactor (1) in a second outflow direction (R) that is parallel to the first outflow direction (R).

2. Water purification reactor (1) according to claim 1, wherein the first outflow direction (R) of the first portion of the contaminated water is substantially coaxially aligned with the second outflow direction (R) of the second portion of the contaminated water.

3. Water purification reactor (1) according to claim 1 or 2, wherein the first and second outflow directions (R) are vertical, particularly downwardly directed.

4. Water purification reactor (1) according to any of the preceding claims, wherein the first water supply channel (14) and / or the second water supply channel (22) is at least partially provided within the reactor (1) housing (2).

5. Water purification reactor (1) according to claim 4, wherein the housing defines a reactor volume, and the first water supply channel (14) and / or the second water supply channel (22) is at least partially provided within the reactor volume.

6. Water purification reactor (1) according to any of the preceding claims, wherein at least part of the first water supply channel (14) and at least part of the second water supply channel (22) are concentrically positioned, particularly wherein at least a portion of thesecond water supply channel (22) is concentrically positioned within at least a portion of the first water supply channel (14).

7. Water purification reactor (1) according to any of the preceding claims, wherein the second water supply channel (22) comprises an outlet opening (26) which is located lower than an outlet opening (20) of the first water supply channel (14).

8. Water purification reactor (1) according to any of the preceding claims, further comprising an overflow plate (28) provided above an outlet opening of the first water supply channel (14) and an outlet opening of the second water supply channel (22), wherein the overflow plate (28) comprises a discharge volume (30) that is in fluid connection with the water discharge channel (10) for discharging water during use from the discharge volume (30) to the water discharge channel (10).

9. Water purification reactor (1) according to claim 8, wherein the water discharge channel (10) is provided lower than the overflow plate (28) and wherein the overflow plate (28) comprises an opening (34) towards the water discharge channel (10) for discharging water during use from the discharge volume (30) to the water discharge channel (10).

10. Water purification reactor (1) according to claim 8 or 9, wherein the overflow plate (28) is provided with a profiled, in particular sawtooth-shaped edge (32), preferably extending along the entire length of the edge (32).

11. Water purification reactor (1) according to any of the preceding claims, wherein the first water supply channel (14) is provided with a gas outlet (36) for removing gases from the first water supply channel (14).

12. Water purification reactor (1) according to any of the preceding claims, wherein the mixing device (24) comprises a gas supply conduit (27, 38) and a liquid supply conduit (22, 40) arranged substantially coaxially therearound, wherein the gas supply conduit terminates in a gas nozzle (46) having a preferably smaller cross-section than that of the gas supply conduit (27, 38), which gas nozzle (46) is located in a preferably narrowed portion of the liquid supply conduit (22, 40), referred to hereafter as the gas mixing chamber (48).

13. Water purification reactor (1) according to claim 12, wherein the gas mixing chamber (48) has a length in the second flow direction within the range of 5-25 cm.

14. Water purification reactor (1) according to claim 12 or 13, wherein the mixing device (24) is configured for introducing hydrogen peroxide into the second portion of the contaminated water, preferably upstream of the gas mixing chamber (48).

15. Water purification reactor (1) according to any of the preceding claims, wherein at least the first water supply channel (14), the water discharge channel (10), and preferably the overflow plate (28) are interconnected to form a module, and wherein the module is preferably removable from the reactor (1) as a unit.

16. Module for use in a water purification reactor (1) according to any of the preceding claims, comprising at least a first water supply channel (14), a water discharge channel (10), and preferably an overflow plate (28) that are interconnected, wherein the module is preferably removable from the reactor (1) as a unit.

17. Water purification system comprising two or more water purification reactors (1) according to any of claims 1-5.

18. Method for purifying contaminated water by mixing said water with an ozonecomprising gas, comprising the steps of:- supplying a first portion of the contaminated water to a water purification reactor (1) via a first water supply channel (14), wherein the first portion flows from the first water discharge channel (10) into the reactor (1) in a first outflow direction (R); and- supplying a second portion of contaminated water to the reactor (1) via a second water supply channel (22), wherein a mixing device (24), provided in the second water supply channel (22), mixes an ozone-comprising gas into the second portion of the contaminated water; wherein the second portion of contaminated water flows into the water purification reactor (1) in a second outflow direction (R) that is parallel to the first outflow direction (R).

19. Method according to claim 18, wherein the first outflow direction (R) of the first portion of the contaminated water is substantially coaxially aligned with the second outflow direction (R) of the second portion of the contaminated water.

20. Method according to claim 18 or 19, wherein the outflow direction (R) is vertical, in particular downwardly directed.21 . Method according to any one of the claims 18-20, wherein the second portion of the contaminated water flows from the outlet opening (26) of the second water supply channel (22) into the reactor (1) at a velocity in the range of 5-20 m / s, preferably 10-18 m / s, more preferably around 15 m / s.

22. Method according to any one of the claims 18-21, wherein the mixing device (24) comprises a gas supply conduit (38) and a liquid supply conduit (40) arranged substantially coaxially therearound, wherein the gas supply conduit (38) terminates in a gas nozzle (46), which gas nozzle is located in the liquid supply conduit (40), referred to hereafter as the gas mixing chamber (11), wherein a mixing chamber fluid (52) present in the gas mixing chamber (11) has a residence time between 10-1000 milliseconds, preferably 50-200 milliseconds, more preferably about 100 milliseconds.

23. Method according to claim 22, wherein the linear velocity of the mixing chamber fluid (52) in the gas mixing chamber lies between 0.5-5 m / s, preferably 0.75-2 m / s, more preferably around 1.2 m / s.

24. Method according to any one of the claims 18-23, wherein the gas-to-liquid ratio (Vg / VI) of the mixing chamber fluid (52) in the gas mixing chamber (48) lies between 3-20 vol%, preferably 7-18 vol%, and more preferably about 14 vol%.

25. Method according to any one of the claims 18-24, further comprising the step of introducing hydrogen peroxide into the second portion of the contaminated water, preferably upstream of the gas mixing chamber (11).

26. Method according to any one of the claims 18-25, wherein the reactor (1) comprises, higher than at least one outlet opening (20) of the first water supply channel (14) and an outlet opening (26) of the second water supply channel (22), an overflow plate (28) having a discharge volume (30) that is in fluid connection with a water discharge channel (10) for discharging purified water from the reactor (1), and wherein the water overflowing the overflow plate (28) flows via said overflow plate (28) to the water discharge channel (10) of the reactor (1) for the discharging of the purified water.

27. Method according to any one of the claims 18-26, wherein purified water discharged via the water discharge channel (10) from the reactor (1) is supplied to a first water supply channel (14) of another water purification reactor (1), and wherein, via the second watersupply channel (22) of the other water purification reactor (1), an untreated portion of contaminated water is supplied to the other water purification reactor (1).

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