WO2025017016A1

WO2025017016A1 - System and a method for treating plasma-activated water

Info

Publication number: WO2025017016A1
Application number: PCT/EP2024/070129
Authority: WO
Inventors: Pieter Polo VAN OOIJ; Danique Anouk VAN DER KRIEKEN; Rohit Chaudhary
Original assignee: VitalFluid B.V.
Priority date: 2023-07-17
Filing date: 2024-07-16
Publication date: 2025-01-23
Also published as: NL2035400B1

Abstract

The present disclosure relates to a system for treating a plasma-activated fluid comprising a fluid pipe configured to transport a first plasma activated fluid, and at least one pump apparatus configured to provide an oxidizing agent into the fluid pipe, when the first plasma-activated fluid flows in it, thereby generating a second plasma-activated fluid, wherein the first plasma-activated fluid has previously been generated and comprises a first amount of reactive oxygen species, ROS, and reactive nitrogen species, RNS, and wherein the oxidizing agent is selected in order to create the second plasma-activated fluid, thereby providing a second amount of ROS and RNS, which is greater than the first amount of ROS and RNS.

Description

System and a method for treating plasma-activated water

FIELD OF THE INVENTION

[ 01 ] The invention relates to a system and a method for treating plasma- activated water that has been previously generated.

BACKGROUND OF THE INVENTION

[ 02 ] Plasma-activated water (PAW) is produced by using water, air, and electricity. Ambient air is brought into the plasma phase with electrical energy; the activated air is then brought into contact with water. Reactive oxygen and nitrogen dissolve into the water, creating PAW. PAW typically contains hydrogen peroxide, nitrates, nitrites, and other reactive oxygen and nitrogen species (RONS) with a short half-life time. PAW typically has a pH ranging from 0 to 7. The composition of PAW after production is not stable. Each RONS in PAW has its own half-life time, and molecules present in PAW are typically separated into two groups: 'long-lived species (LLS)' with a half-life time of hours, days, or even years, and 'short-lived species (SLS)'. SLS have a half-life time of less than seconds, but high concentrations of SLS in PAW can remain present for multiple minutes, up to approximately 15 minutes after activation.

[ 03 ] The components in PAW and the low pH have proven synergistic antimicrobial effects against bacteria, biofilms, yeasts, and other microorganisms. All molecules present in PAW are antimicrobial to varying degrees. SLS are considered a very potent antimicrobial molecules. Despite the fact that the LLS in PAW are less reactive, their presence in PAW provides an environment for SLS to be antimicrobial.

[ 04 ] However, since the SLS have short lifetimes, they will disappear within a certain period of time, so that the above-mentioned advantageous effects of the PAW will weaken or even disappear as the storage time prolongs. Thus, this phenomenon will affect the application of the PAW.

[ 05 ] In order to avoid the loss of the advantageous effects of the PAW, current systems locate a reaction chamber for generating the plasma-activated water on a site where the freshly generated plasma-activated water can be immediately discharged. However, this requires the installation of a relatively big and costly system for generating PAW on the site, and this will result in installation and maintenance problems of the system.

[ 06 ] Document KR 10 2 548 895 B1 discloses a system for manufacturing plasma activated water intended to maximize the amount of plasma active species produced by including a plasma generating unit, a nitrogen oxide discharge unit connected to the plasma generating unit, a nitrogen oxide cooling unit connected to the nitrogen oxide discharge unit, a nitrogen oxide conversion unit connected to the nitrogen oxide cooling unit, and a plasma active species dissolved reaction unit connected to the nitrogen oxide conversion unit.

[ 07 ] Wang Sitao et al.: "Plasma re-activation: a promising approach to enhance chemical activity for plasma activated water" (J. Phys. D: Applied Physics, 55, 18, 4 Februari 2022) describes plasma re-activation aimed at enhancing the chemical activity of PAW again before it entirely decays. Results indicate that the PAW generated by re-activation displays superior physicochemical properties and higher production of RONS.

[ 08 ] There is a need for an effective system or method to increase the antimicrobial activity of the PAW, providing opportunities for storing and transporting the PAW without loss of antimicrobial action, and providing easy maintenance.

SUMMARY OF THE INVENTION

[ 09 ] It is an objective of the invention to provide a system and method that increase the antimicrobial activity of plasma-activated water.

[ 10 ] It is another or alternative objective of the invention to provide a system and method that provides an application of plasma-activated water without loss of antimicrobial action.

[ 11 ] It is yet another or alternative objective of the invention to provide a system and method for providing plasma-activated water that has the optimal/highest disinfection power at the moment of application.

[ 12 ] Thus, the present invention strives to provide an improved system and a method for re-activating the PAW by upgrading both the disinfecting properties of PAW and the oxidizing agent, as a synergistic action relating to the disinfection occurs. The present invention provides that the optimal/highest disinfection power of PAW will take place at the moment of application. Besides, the hyperactivation of the disinfection power of PAW with a shortened shelf life will also result in no reactive residue after the application of PAW when the disinfection is no longer required.

[ 13 ] According to an aspect, the invention provides a plasma-activated fluid system comprising; a fluid pipe configured to transport a first plasma-activated fluid. at least one apparatus configured to provide an oxidizing agent into the fluid pipe when the first plasma-activated fluid flows in it, thereby creating a second plasma-activated fluid. wherein the first plasma-activated fluid has previously been generated and contains a first amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS). The oxidizing agent is selected to generate the second plasma- activated fluid, providing a second amount of ROS and RNS that is greater than the first amount of ROS and RNS.

[ 14 ] In an embodiment, the first plasma-activated fluid comprises, immediately after generation, an original amount of ROS and RNS that subsequently degenerates to a lower first amount of ROS and RNS than the original amount.

[ 15 ] In an embodiment, the second amount of ROS and RNS is greater than the original amount of ROS and RNS.

[ 16 ] In an embodiment, the fluid pipe has an inlet configured to receive the first plasma-activated fluid from a reaction chamber that is configured to generate the first plasma-activated water.

[ 17 ] In an embodiment, the system further comprises. a plasma-activated fluid reservoir has an inlet designed to receive the first plasma-activated fluid generated in the reaction chamber, and an outlet configured to transport the first plasma-activated fluid from the reservoir to the fluid pipe.

[ 18 ] In an embodiment, the oxidizing agent comprises at least one of ozone, hydrogen peroxide, and a molecule with peroxide linkage. While ozone and hydrogen peroxide are readily available and relatively easy to use, in general a molecule with peroxide linkage can be used as oxidizing agent.

[ 19 ] In an embodiment, the at least one apparatus comprises a first apparatus with a reaction conduit configured to receive fresh air from a fresh air port, thereby generating ozone in gas form.

[ 20 ] In an embodiment, the at least one apparatus comprises a second apparatus with a reaction conduit configured to receive oxygen, thereby generating ozone, in gas form.

[ 21 ] In an embodiment, the at least one apparatus comprises a third apparatus with a reaction conduit configured to generate hydrogen peroxide.

[ 22 ] In an embodiment, the fluid pipe comprises an outlet configured to allow the second plasma-activated fluid to flow onto a plant.

[ 23 ] In an embodiment, the at least one apparatus is arranged at the outlet of the fluid pipe.

[ 24 ] In an embodiment, the system further comprises. a sensor is configured to determine whether the second amount of ROS and RNS is at least equal to a predetermined amount of ROS and RNS before the second plasma-activated fluid flows onto the plant.

[ 25 ] In another aspect, the invention provides a method for re-activating a plasma-activated fluid by using the system according to the aforementioned embodiments, comprising the steps of: providing a first plasma-activated fluid that has been previously generated, containing a first amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS), into a fluid pipe. providing, via at least one apparatus, an oxidizing agent into the fluid pipe when the first plasma-activated fluid flows in it, thereby creating a second plasma-activated fluid. wherein the oxidizing agent is selected in order to provide a second amount of ROS and RNS, which is greater than the first amount of ROS and RNS.

[ 26 ] In an embodiment, the first plasma-activated fluid comprised, immediately after generation, an original amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS), subsequently degenerating to the first amount of ROS and RNS, which is lower than the original amount.

[ 27 ] In an embodiment, the second amount of ROS and RNS is greater than the original amount of ROS and RNS.

[ 28 ] In an embodiment, the oxidizing agent comprises at least one of ozone, hydrogen peroxide, and a molecule with peroxide linkage.

[ 29 ] In an embodiment, the at least one apparatus comprises a first apparatus with a reaction conduit configured to receive fresh air from a fresh airport, thereby generating ozone in gas form.

[ 30 ] In an embodiment, the at least one apparatus comprises a second apparatus with a reaction conduit configured to receive oxygen, thereby generating ozone, in gas form.

[ 31 ] In an embodiment, the at least one apparatus comprises a third apparatus with a reaction conduit configured to generate hydrogen peroxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[ 32 ] Further features and advantages of the invention will become apparent from the description of the invention through non-limiting and non-exclusive embodiments. These embodiments should not be seen as limiting the scope of protection. The person skilled in the art will realize that other alternatives and equivalent embodiments of the invention can be conceived and implemented without deviating from the scope of the present invention.

[ 33 ] Embodiments of the invention will be described with reference to the accompanying drawings, in which like or same reference symbols denote like, same, or corresponding parts, and in which .

[ 34 ] Figure 1 schematically shows an instrumentation diagram of a reactivation system of a plasma-activated water according to the invention.

[ 35 ] Figure 2 schematically shows the antimicrobial activity of plasma- activated water according to the invention.

[ 36 ] Figure 3a schematically shows concentrations for short-lived species (SLS) of a reactive oxygen species (ROS) and a reactive nitrogen species (RNS) in a plasma-activated water combined with an oxidizing agent.

[ 37 ] Figure 3b schematically shows an SLS concentration in plasma- activated water as a function of an oxidizing agent concentration.

[ 38 ] Figure 4a schematically shows a diagram for the antimicrobial effect of plasma-activated water immediately after re-activation with an oxidizing agent.

[ 39 ] Figure 4b schematically shows a diagram for the delayed antimicrobial effect of plasma-activated water 30-seconds after re-activation.

DETAILED DESCRIPTION OF EMBODIMENTS

[ 40 ] Various other embodiments of the invention will be apparent to the skilled person when having read the above disclosure in connection with the drawings, all of which are within the scope of the invention and accompanying claims.

[ 41 ] Throughout the detailed description, reference is made to plasma- activated water. But the present invention is not limited to (pure) water but can also relate to any liquid with is suitable for plasma activation. For example, it also includes process water, drain water, etc.

[ 42 ] Figure 1 schematically shows an instrumentation diagram of a reactivation system 100 of plasma-activated water according to the invention. The system 100 may comprise a fluid pipe 140 for transporting a first plasma-activated water (PAW) that was previously generated in a reaction chamber, a first supply arrangement 110 attached to the fluid pipe 140 and configured to provide the first PAW into the fluid pipe 140, and a second supply arrangement 120 comprising at least one apparatus that is configured to provide an oxidizing agent into the fluid pipe 140. The first supply arrangement 110 may comprise a pump or a venturi. The second supply arrangement 120 may comprise at least one pump or venturi for providing an oxidizing agent into the fluid pipe 140.

[ 43 ] The first PAW can be fed to the fluid pipe by the first supply arrangement 110, either directly from the reaction chamber or from a reservoir that stores the first PAW previously generated in the reaction chamber. The reservoir can have an inlet to receive the first PAW generated in the reaction chamber and an outlet to transport the first PAW to the fluid pipe 140 through the first supply arrangement 110. Other arrangements, such as using portable storage tanks for previously generated PAW, are also possible.

[ 44 ] The system 100, as shown in Figure 1 , may further include a first sensor for measuring the amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in the first PAW before it is treated with the oxidizing agent from the second supply arrangement 120.

[ 45 ] The first PAW is generated with an original amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS) that are provided by the reaction chamber. This original amount of ROS and RNS may be degraded during a storage time in the reservoir and/or during the transportation within the fluid pipe 110. The degraded ROS and RNS correspond to a first amount of ROS and RNS in the first PAW, wherein the first amount of ROS and RNS, evidently, is lower than the original amount of ROS and RNS. Therefore, there is at least a need for reactivating the degraded ROS and RNS in said first PAW.

[ 46 ] In an exemplary embodiment, as shown in Figure 1 , the fluid pipe 140 may comprise a mixing point 141 for treating the first PAW supplied through the first supply arrangement 110 with the oxidizing agent supplied through the second supply arrangement 120. The mixing point 141 may be a multiport manifold that is attached to the first and second supply arrangements 110, 120. The at least one pump of the second supply arrangement 120 in Figure 1 is configured to provide the oxidizing agent into the fluid pipe 110 when the first PAW flows in it, thereby creating a second PAW. The at least one pump in the second supply arrangement 120 may provide the oxidizing agent that is selected for creating or generating the second PAW. In an embodiment, the mixing ratio is based on the original amount and/or the first amount of ROS and RNS that is measured by the first sensor 130. The second PAW is provided with a second amount of ROS and RNS which is greater than the first amount of ROS and RNS.

[ 47 ] The oxidizing agent selected to provide the second amount of ROS and RNS may not only re-activate the degenerated ROS and RNS in the first PAW, but also hyperactivate them, resulting in a second amount of ROS and RNS that is greater than the original amount provided in the first PAW generated in the reaction chamber.

[ 48 ] In order to hyper- or re-activate the first PAW, an amount of short-lived species, SLS, in the ROS and RNS of the first PAW must be increased or preserved as long as possible. This is achieved by treating the first PAW with the oxidizing agent.

[ 49 ] The second supply arrangement 120 may comprise more than one pump, each of which is configured to provide a different oxidizing agent from the others. For example, the second supply arrangement 120 may comprise a first pump or venturi with a reaction conduit that is configured to receive fresh air from a fresh air port, thereby generating ozone in the gas form as an oxidizing agent to be combined with the first PAW.

[ 50 ] As another example, the second supply arrangement 120 may comprise a second pump or venturi with a reaction conduit configured to receive oxygen, thereby generating ozone, in gas form as an oxidizing agent to be combined with the first PAW

[ 51 ] As another example, the second supply arrangement 120 may comprise a third pump or venturi with a reaction conduit configured to generate hydrogen peroxide as an oxidizing agent to be combined with the first PAW.

[ 52 ] As another example, the second supply arrangement 120 may comprise a fourth pump or venturi with a reaction conduit configured to generate nitrogen oxides as an oxidizing agent to be combined with the first PAW.

[ 53 ] In the shown instrumentation diagram of Figure 1 , the system 100 may further comprise a second sensor 150 for measuring the formation of SLS, including the amount of RONS in the second PAW. In this way, the system allows the sensor to determine whether a predetermined value of RONS for maximal SLS production is achieved by the provided second amount of RONS in the second PAW.

[ 54 ] In an exemplary embodiment, the sensor 150 may be a spectrometrybased sensor. For example, the first PAW with the first amount of RONS may be supplied through the first pump arrangement 110 and may be combined with one or more oxidizers via at least one of the above-mentioned pumps in the second supply arrangement 120, through the multiport manifold, thereby providing the second PAW with the second amount of RONS. The second PAW may be transported to the spectrometer 150 through the fluid pipe 140. The RONS values, and indeed the SLS production, of the second PAW may be measured via the spectrometer 150.

[ 55 ] If the measured SLS production of the second PAW with the second amount of RONS is lower than the predetermined amount of RONS, the hyperactivation or re-activation process may be repeated by providing the oxidizing agents through the pumps in the second supply arrangement 120 to the manifold 141. In this case, a different concentration of the oxidizing agent can be combined with the previously generated second PAW with the lower second amount of RONS in order to achieve the predetermined amount of RONS.

[ 56 ] The above-mentioned process may be repeated until the predetermined amount of RONS is achieved by the second amount of RONS in the second PAW.

[ 57 ] For example, the pumps in the second supply arrangement 120 may further include valves that are adapted to be controlled remotely by a control unit to which system 100 is connected. In this way, the optimal combination of the oxidizing agent(s) with the first PAW can be determined. Based on the predetermined amount of RONS, the control unit may activate and/or deactivate the valves of the respective pumps in the second supply arrangement 120.

[ 58 ] The system 100 may be arranged at an outlet of the fluid pipe 140, where the second PAW is discharged onto a plant. Such an arrangement of the system 100 allows the first PAW to be stored and re-circulated within the system before its application. Even though the first PAW degenerates RONS during the storage and flowing time, and loses its advantageous effects, the system 100 located at the discharge will hyper- and/or re-activate the first PAW before its application.

[ 59 ] Such system 100 is relatively smaller and easier to set up than a regular reaction chamber for generating plasma-activated water in the field. Therefore, instead of placing a regular reaction chamber at a site where the plasma-activated water is discharged onto the plant, the system 100 that uses stored plasma- activated water that has been previously activated far away from the site may be located at the discharge for economical and maintenance reasons.

[ 60 ] Figure 2 illustrates the antimicrobial activity of the first PAW before treatment with the oxidizing agent. More specifically, Figure 2 shows a diagram indicating the log reduction of the first PAW over time. The y-axis of the diagram represents the log reduction, which expresses the relative number of living microbes eliminated by disinfection in the First PAW over time after the production of the first PAW indicated on the x-axis of the diagram.

[ 61 ] Due to the unstable composition of the first PAW after production, a decay of antimicrobial activity may be observed over time, as shown in Figure 2. As SLS disappears from the first PAW, a decrease in antimicrobial activity can be observed within the first 30 minutes after production of the first PAW. The presence of long-lived species, LLS, in the first PAW results in an antimicrobial effect for a longer period of time.

[ 62 ] As evidently shown in Figure 2, since the composition of PAW is not stable, the antimicrobial activity will decrease over time. Within 30 minutes, the SLS is expected to have disappeared in the first PAW, which results in a steep decrease in antimicrobial activity of the first PAW. The LLS amount in the first PAW with a longer half-life time may provide a more stable level of antimicrobial activity for a period up to a week.

[ 63 ] In order to achieve a high antimicrobial action, the presence of SLS is desired. The original PAW, just after generation, comprised SLS. However, in the first PAW, several minutes, hours or days after generation, these SLS have largely decayed. The SLS can be generated again during the plasma re-activation process. Therefore, in order to induce the formation of SLS for achieving increased antimicrobial action, the system 100 combines the first PAW containing first RONS amounts with an oxidizing agent in an acidic environment, as demonstrated in Figures 3a and 3b.

[ 64 ] Reaction 1 , indicated below, evidently demonstrates that when the first PAW is combined with the oxidizing agent, it can provide a hyperactivation of the ROS and RNS, thereby providing SLS, e.g., peroxynitrite, regardless of the degeneration of ROS and RNS (RONS) in the first PAW. The oxidizing agent can be provided through the at least one pump in the second supply arrangement 120 and can comprise at least one of ozone, hydrogen peroxide, and nitrogen oxides.

[ 65 ] As seen in reaction 1 below, not only peroxynitrite will be formed with the treatment of the first PAW, but many SLS are present after the addition of hydrogen peroxide, as the oxidizing agent, to the first PAW.

NO₂- + H₂O₂ +H⁺ - O=NOOH + H₂O - NO₃’ + H⁺ + H₂O (1)

[ 66 ] Figure 3a schematically shows an illustrative example of nitrous acid (top right) and peroxynitrite (bottom right) concentrations after, in chronological sequence, three different concentrations of hydrogen peroxide (bottom left) as oxidizing agent have been added to first PAW with a constant concentration of nitric acid (top left). The shown diagrams of the concentration of components in the second PAW (being the first PAW after addition of the oxidizing agent) indicate the concentration balance of different components added (H2O2) and formed (ONOO-) and the components that have reacted (NC>2' and HNO2).

[ 67 ] In the diagrams shown, various volumes of hydrogen peroxide were added to the first PAW that contained LLS nitric acid and nitrous acid. This resulted in the production of peroxynitrite (ONOO-), which is an SLS, while the nitrous acid (HNO2) concentration varies inversely proportional to the hydrogen peroxide (H2O2) concentration because the nitrous acid is consumed in the reaction with hydrogen peroxide to from the SLS.

[ 68 ] Figure 3b shows an SLS concentration of the second PAW that is generated from the combination of the first PAW and the oxidizing agent(s) as a function of the oxidizing agent concentration. The x-axis indicates a concentration of the oxidizing agent H2O2 that is combined with the first PAW, and the y-axis indicates a concentration of ONOOFT in the second PAW that has been generated by the re-activation.

[ 69 ] In view of Figure 3b, it can be observed that a higher volume of hydrogen peroxide results in a higher concentration of peroxynitrite measured in the RONS amount of the second PAW, meaning the amount of peroxynitrite formed is linearly proportional to the amount of hydrogen peroxide added to the first PAW.

[ 70 ] The creation of a high SLS content in the second PAW will be provided by re- or hyper-activation of the antimicrobial properties of the first PAW. In that way, a low antimicrobial activity of the first PAW combined with a non-existent or negligible antimicrobial concentration of the oxidizing agent will result in high antimicrobial activity, reaching 5 logarithmic reductions of microbes. This is called a synergistic effect.

[ 71 ] The benefit of this synergistic effect of the system 100 provides a high disinfection power, which can be gained at the moment of application. Because of this, storage and transport of PAW is possible, and the relatively short shelf-life (due to SLS) is no longer a limitation for effectively using PAW for its SLS concentrations. [ 72 ] Figure 4a schematically shows a diagram of the antimicrobial effect of the second PAW, which is created by treating the first PAW with the oxidizing agent H2O2. In particular, Figure 4a shows a test result of a logarithmic reduction of bacteria by comparing the amount of bacteria present in the RONS of a PAW without treatment (i.e. , the first PAW), and after treatment with the oxidizing agent H2O2 (i.e. , the second PAW). During the test, the first PAW has been exposed to bacteria and afterwards has been treated, immediately, with H2O2. As seen from the diagram, the treatment immediately provides a relatively good logarithmic reduction of the bacteria in the second PAW (white bar), better than the reduction in the untreated first PAW (black bar). In contrast, the experiment on the right hand side of figure 4a, where various amounts of H2O2 have ben added to demineralized water show that H2O2 by itself and in the quantities used has no discernible disinfecting activity.

[ 73 ] The system 100 described in the above-mentioned embodiments provides increased antimicrobial activity after adding the oxidizing agent to the first PAW, known as re-activation or hyperactivation. The treatment of the first PAW reduces the number of viable microbes in suspension compared to the initial number.

[ 74 ] On the other hand, the rapid and high generation of SLS in the second PAW will result in a faster formation of nitrate in water. Therefore, the system 100 also provides a way to remove reactive species from the first PAW or to deactivate them. In certain situations, such a short shelf life is required, as the reactive component in a PAW could also have negative effects.

[ 75 ] Reactions (2) and (3) are provided to describe the inactivation of the second PAW by the addition of the oxidizing agents mentioned below. The first PAW is a source of RONS, and hydrogen peroxide or ozone are used as exemplary oxidizers.

[ 76 ] Reaction (2) describes neutralization of the first PAW with hydrogen peroxide:

NO₂’+ H₂O₂ +H⁺ NO₃’ + H⁺ + H₂O (2)

[ 77 ] Reaction (3) describes neutralization of the first PAW with ozone:

NO₂- + O₃ + 3H⁺ - NO₃’ + H⁺ + H₂O + O₂ (3)

[ 78 ] The reactions with other peroxide-linked molecules as oxidizing agent will be readily apparent to the skilled person.

[ 79 ] The removal of reactive components in PAW will also result in a loss of antimicrobial activity. Due to the short half-life time of SLS, this reduction in antimicrobial activity (after the hyperactivation) will happen within a minute.

[ 80 ] Figure 4b schematically shows a diagram of the antimicrobial effect of the first PAW being treated with hydrogen peroxide and exposed to bacteria after 30 seconds waiting time. Specifically, Figure 4b shows a test result of a logarithmic reduction of bacteria by comparing the amount of bacteria present in the RONS of the first PAW and after being treated with the oxidizing agent H2O2 and being exposed to bacteria after 30 seconds waiting time. As such, figure 4b is an example of the de-activation of PAW (after a short period of time such as 30 seconds). The striped bars in figure 4b show, as a control, that adding the oxidizing agent H2O2 to demi water does not have a significant effect on the bacteria.

[ 81 ] A RONS amount in the un-activated first PAW still possesses antimicrobial activity (indicated as a black bar in Figure 4b). The addition of hydrogen peroxide results in a second PAW having formation of SLS with high antimicrobial potency, but quickly after their formation, they will further react to nitrate. Nitrate itself has almost no antimicrobial activity, resulting in a lower antimicrobial activity of the second PAW after at least 30 seconds after activation. After the addition of the oxidizer and a waiting period, the antimicrobial activity is decreased (indicated as a white bar in Figure 4b). A higher dose of hydrogen peroxide results in more nitrate formation and fewer reactive molecules, followed by a lower reduction in microbial levels upon exposure to bacteria. When hydrogen peroxide is added in a concentration that all reactive components are converted to nitrate, no antimicrobial activity is observed in this microbial test setup.

[ 82 ] From the test results it is clear that an oxidizing agent can be used to reactivate or hyper-activate previously generated PAW. The disinfecting properties of the (hyper)activated PAW will be increased compared to the un-activated PAW, but will last less long. The addition of an oxidizing agent (ozone, hydrogen peroxide, or in general a molecule with peroxide linkage) to previously PAW thus provides a control to indicate how intense the disinfecting properties should be, and how long they should last. This can be advantageous in many processes where intensive but short-lasting disinfection is needed, for example in the treatment of (drain) water for agriculture that is to be fed back to the plants.

[ 83 ] In the preceding description of the figures, the invention has been described with reference to specific embodiments. However, It will be evident that various modifications and changes may be made to it without departing from the scope of the invention as summarized in the attached claims.

[ 84 ] In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

[ 85 ] In particular, combinations of specific features of various aspects of the invention may be made. An aspect of the invention may be further advantageously enhanced by adding a feature that was described in relation to another aspect of the invention.

[ 86 ] It is understood that the invention is limited by the attached claims and its technical equivalents only. In this document and in its claims, the verb "to comprise" and its conjugations are used in their non-limiting sense to mean that items following the word are included, without excluding items not specifically mentioned. Additionally, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one".

Claims

1. A system (100) for treating a plasma-activated fluid, the system comprising; a fluid pipe (140) configured to transport a first plasma activated fluid, a plasma-activated fluid reservoir having an inlet configured to receive the first plasma-activated fluid generated in a reaction chamber, and an outlet configured to transport the first plasma-activated fluid from said reservoir to the fluid pipe (140), and at least one apparatus (120) configured to provide an oxidizing agent into the fluid pipe (140), when the first plasma-activated fluid flows in it, thereby generating a second plasma-activated fluid, wherein the first plasma-activated fluid has previously been generated and comprises a first amount of reactive oxygen species, ROS, and reactive nitrogen species, RNS, and wherein the oxidizing agent is selected in order to create the second plasma- activated fluid, thereby providing a second amount of ROS and RNS, which is greater than the first amount of ROS and RNS.

2. The system (100) according to claim 1 , wherein said first plasma-activated fluid comprises, immediately after generation, an original amount of ROS and RNS, subsequently degenerating to the first amount of ROS and RNS, which is lower than the original amount.

3. The system (100) according to claim 2, wherein the second amount of ROS and RNS is greater than the original amount of ROS and RNS.

4. The system (100) according to claim 1 , wherein the fluid pipe (140) has an inlet configured to receive the first plasma-activated fluid from the reaction chamber that is configured to generate the first plasma-activated fluid.

5. The system (100) according to any one of the preceding claims, wherein the oxidizing agent comprises at least one of ozone, hydrogen peroxide, and a molecule with peroxide linkage.

6. The system (100) according to any one of the preceding claims, wherein the at least one apparatus (120) comprises a first apparatus with a reaction conduit configured to receive fresh air from a fresh air port, thereby generating ozone in gas form.

7. The system (100) according to any one of the preceding claims, wherein the at least one apparatus (120) comprises a second apparatus with a reaction conduit configured to receive oxygen, thereby generating ozone, in gas form.

8. The system (100) according to any one of the preceding claims, wherein the at least one apparatus (120) comprises a third apparatus with a reaction conduit configured to generate hydrogen peroxide.

9. The system (100) according to claim 1 , wherein the fluid pipe (140) comprising an outlet configured to allow the second plasma-activated fluid to be discharged to a plant.

10. The system (100) according to any one of the preceding claims, wherein the at least one apparatus (120) is arranged on the outlet of the fluid pipe (140).

11. The system (100) according to any one of the preceding claims, further comprising: a sensor (150) configured to determine whether the second amount of ROS and RNS is at least equal to a predetermined amount of ROS and RNS, before the second plasma-activated fluid flows onto the plant.

12. A method for re-activating a plasma-activated fluid by using the system (100) according to claims 1 to 11, comprising the steps of; providing, from a plasma-activated fluid reservoir, a first plasma- activated fluid that has been previously generated containing a first amount of reactive oxygen species, ROS, and reactive nitrogen species, RNS, into a fluid pipe (140); and providing, via at least one apparatus (120), an oxidizing agent into the fluid pipe (140), when the first plasma-activated fluid flows in it, thereby creating a second plasma-activated fluid, wherein the oxidizing agent is selected in order to provide a second amount of ROS, and RNS, which is greater than the first amount of ROS and RNS.

13. The method according to claim 12, wherein the first plasma-activated fluid comprised, immediately after generation, an original amount of ROS and RNS subsequently degenerating to the first amount of ROS and RNS which is lower than the original amount.

14. The method according to claim 12 or 13, wherein the second amount of ROS and RNS is greater than the original amount of ROS and RNS.

15. The method according to claims 12 to 14, wherein the oxidizing agent comprises at least one of ozone, hydrogen peroxide, and a molecule with peroxide linkage.

16. The method according to any one of claims 12 to 15, wherein the at least one apparatus (120) comprises a first apparatus with a reaction conduit configured to receive fresh air from a fresh air port, thereby generating ozone, in gas form.

17. The method according to any one of claims 12 to 16, wherein the at least one apparatus (120) comprises a second apparatus with a reaction conduit configured to receive oxygen, thereby generating ozone, in gas form.

18. The method according to any one of claims 12 to 17, wherein the at least one apparatus (120) comprises a third apparatus with a reaction conduit configured to generate hydrogen peroxide.