Fertilisation and disinfection system using plasma activated water

Abstract

The invention provides a fertilisation and disinfection system (1) adapted for use in a greenhouse water circulation system, the fertilisation and disinfection system comprising: - a Plasma Activated Water, PAW, supply (11); - a mixing unit (12) connected to the PAW supply and configured to receive inlet water from an inlet water supply (13) of the greenhouse water circulation system and to provide processed water (14) to the greenhouse water circulation system; - a mixing unit controller (10) connected to the mixing unit and configured to control at least one of the duration of PAW and inlet water mixing and the ratio of PAW to inlet water mixing.

Description

[0001] Fertilisation and disinfection system using plasma activated water

[0002] FIELD OF THE INVENTION

[0003]

[0001] The present invention relates to a method or system that can be used in precision agriculture or greenhouse cultivation for the disinfection of (feed / drain) water and nitrogen fixation.

[0004] BACKGROUND OF THE INVENTION

[0005]

[0002] Uptake of soil nitrogen by plants should be replenished by chemical fertilizers, so intensive agriculture relies on the high-energy-consuming Haber- Bosch process (HB) for nitrogen fixation. The HB process is energy demanding, exploiting non-renewable resources, and significantly contributing to greenhouse gas (GHG) emissions.

[0006]

[0003] A separate issue concerns the recirculation of water for agriculture, such as in a greenhouse. It is necessary to disinfect the circulation water (also known as drain, feed, or irrigation water) in order to reduce microbe concentrations and enable recirculation.

[0007]

[0004] Document CN115005080A discloses a leaf vegetable hydroponic system and a leaf vegetable hydroponic method using a low-temperature plasma assisted nutrient solution, which take leaf vegetables as a culture target and are matched with the characteristic that plasma activated water is rich in nitrogen. The system adopts a plasma-assisted nutrient solution form which is different from an existing mode that only plasma activated water is used for treating seeds or plants for a short time, and the hydroponic process starts from the seed germination stage to the crop harvesting stage, and the hydroponic process is complete.

[0008]

[0005] The aim of the present invention is to provide a method and system to disinfect circulation water combined with adding nitrogen to it.

[0009] SUMMARY OF THE INVENTION

[0010]

[0006] Since gaseous nitrogen in the atmosphere cannot be used directly by plants, it should be converted into water-soluble forms. The present invention involves nitrogen fixation, which converts gaseous nitrogen into reactive nitrogen compounds in water that can ultimately be assimilated by plants.

[0011]

[0007] Nitrogen fixation (NF) is a process by which nitrogen molecules (N2) in air or nitrogen gas, which are relatively nonreactive molecules, are converted into nitrogenous compounds. A plasma in air can create reactive nitrogen and oxygen species that form nitric and nitrous acid in an aqueous environment. First, an arc plasma is applied to convert nitrogen / oxygen into nitric oxide (NO), which is subsequently further oxidized into nitrogen dioxide (NO2) by cooling the hot gases and mixing them with atmospheric oxygen.

[0012]

[0008] This results in the formation of plasma-activated water (PAW). PAW typically contains hydrogen peroxide, nitrates, nitrites, and other molecules that are present for a short period of time. PAW typically has a low pH ranging from 0 to 7. The production of nitrate as a result of the activation process (during PAW production) is shown to be very energy efficient and can be used as an energyefficient alternative for the production of nitrogen components in fertilizers, currently produced by HB. The components of PAW and the low pH have proven synergistic antimicrobial effects against bacteria, biofilms, yeasts, and other microorganisms.

[0009] To transform drain water into irrigation water, the irrigation water must be disinfected. In addition, volume (fresh water) and nutrients, including nitrogen / nitrate, are added. The invention provides a system and method for disinfecting circulation water combined with the addition of nitrogen and fresh water using PAW as a disinfectant and fertilizer.

[0013]

[0010] 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 in the order of seconds, but high concentrations of SLS in PAW can remain present in detectable quantities for multiple minutes, up to a quarter of an hour, half an hour or an hour after activation.

[0014]

[0011] Nitrites have a longer half-life, measured in days. Some plants are damaged when irrigated with irrigation water with significant concentrations of nitrites. In that case, measures should be taken to neutralize the nitrites before the PAW processed water is fed to the plants. One way of doing this is by introducing an oxidizing agent such as hydrogen peroxide in the correct proportion, so that the hydrogen peroxide and the nitrites will be converted to nitrates. Since an oxidizing agent such as hydrogen peroxide is typically harmful for plants as well, the introduction of the oxidizing agent should be done in the correct proportion so that both the oxidizing agent and the nitrites are essentially fully eliminated by their reaction.

[0015]

[0012] 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 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.

[0016]

[0013] However, since the SLS have short lifetimes, they will disappear within a certain period of time. This is intentional because some of these SLS would also have a detrimental effect on the plants. In addition, there may be other components such as oxidizing agents which need time to react with other constituents. For example, hydrogen peroxide and nitrites, which are both harmful to plants, can neutralize each other when mixed in the correct proportion and given enough time to react. It is therefore important to make sure that SLS and other components that are detrimental to plants are mostly gone from the recirculation water by the time it arrives at the plants.

[0017]

[0014] The invention provides a fertilisation and disinfection system for use in a greenhouse water circulation system, the fertilisation and disinfection system comprising:

[0018] - a Plasma Activated Water (PAW) supply;

[0019] - a mixing unit connected to the PAW supply and adaptable to be receive inlet water from an inlet water supply of the greenhouse water circulation system and to provide processed water to the greenhouse water circulation system;

[0020] - a mixing unit controller connected to the mixing unit and configured to control at least one of the duration of PAW and inlet water mixing and the ratio of PAW to inlet water mixing.

[0021]

[0015] Mixing PAW with inlet water has the twin benefits of adding some nutrients to the inlet water and disinfecting the water. The nutrients can be nitrogen based. The nutrients can be nitrates and / or nitrites that are later converted to nitrates. The controller may control the mixing in order to reach a target nutrient addition and / or a target disinfection level. The target may be calibrated in terms of a target ROS and / or RNS level in the processed water.

[0022]

[0016] In an embodiment according the invention, the controller is configured to set the duration of PAW and inlet water mixing so that a target reduction of microbes is obtained or a target ROS and / or RNS concentration is obtained. In an embodiment according the invention, the controller is configured to set the ratio of PAW to inlet water mixing so that a target reduction of microbes is obtained or a target ROS and / or RNS concentration is obtained. The ROS or RNS concentration can be measured in the processed water.

[0023]

[0017] In an embodiment according the invention, the mixing unit comprises a PAW addition point and a mixing tank. The mixing tank can be used to control the treatment time of the PAW. It is also possible to mix the PAW with the inlet water without using a mixing tank (e.g. by directly mixing into a conduit).

[0024]

[0018] In an embodiment according the invention, the controller is configured to control the mixing so that a concentration of a selected species in the processed water is reduced, through decay or a reaction with another species, to below a target threshold concentration before the processed water is supplied to plants.

[0025]

[0019] Selected species can be a nitrite species and / or an oxidizing agent such as hydrogen peroxide or ozone or in general a molecule with peroxide linkage.

[0026]

[0020] In an embodiment according the invention, a measuring means for measuring at least one of a reactive oxygen species, ROS, and reactive nitrogen species, RNS, concentration in the inlet water or the processed water is provided.

[0027]

[0021] In an embodiment according the invention, the means for measuring at least one of a ROS and RNS concentration is configured to measure in the processed water.

[0028]

[0022] In an embodiment according the invention, the means for measuring at least one of a ROS and RNS concentration is calibrated to estimate a microbe concentration in the inlet or processed water.

[0029]

[0023] In an embodiment according the invention, the fertilisation and disinfection system comprises a PAW reactivation unit connected to a reactivation agent supply for reactivating PAW.

[0030]

[0024] In an embodiment according the invention, the fertilisation and disinfection system comprises a PAW storage connected to the PAW reactivation unit.

[0031]

[0025] In an embodiment according the invention, the reactivation agent supply is configure to supply an oxidizing agent. In an embodiment according the invention, the oxidizing agent is one of ozone and hydrogen peroxide and a molecule with peroxide linkage.

[0032]

[0026] In an embodiment according the invention, the oxidizing agent is supplied in proportion to the nitrite concentration of the processed water, in order to convert the nitrites to nitrates. Preferably, all or essentially all of the oxidizing agent consumed in the reaction to form the nitrates.

[0033]

[0027] The invention further provides a greenhouse water circulation system comprising: - a fertilisation and disinfection system as described above;

[0034] - a water and nutrients addition unit configured to add water and / or nutrients to the processed water.

[0035]

[0028] The invention further provides a method for disinfecting inlet water and adding nitrogen thereto in a greenhouse water circulation system, the method comprising:

[0036] - a Plasma Activated Water, PAW, supply;

[0037] - a mixing unit connected to the PAW supply and adaptable to be receive inlet water from a inlet water supply of the greenhouse water circulation system and to provide processed water to a the greenhouse water circulation system;

[0038] - a mixing unit controller connected to the mixing unit and configured to control at least one of the duration of PAW and inlet water mixing and the ratio of PAW to inlet water mixing.

[0039]

[0029] The method can be combined with any of the features described in reference to the fertilisation and disinfection system.

[0040] BRIEF DESCRIPTION OF THE DRAWINGS

[0041]

[0030] 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.

[0042]

[0031] 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 .

[0043]

[0032] Figure 1 schematically shows a fertilisation and disinfection system for use in a greenhouse water circulation system according to the invention;

[0044]

[0033] Figure 2 schematically shows a greenhouse water circulation system according to the invention;

[0045]

[0034] Figure 3 schematically shows a logarithmic reduction of bacteria as a function of the ratio of PAW to drain water;

[0046]

[0035] Figure 4 schematically shows a logarithmic reduction of bacteria as a function of the treatment time; and

[0047]

[0036] Figure 5 schematically shows a fertilisation and disinfection system for use in a greenhouse water circulation system according to the invention having a PAW reactivation unit. DETAILED DESCRIPTION OF EMBODIMENTS

[0048]

[0037] 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.

[0049]

[0038] Throughout the detailed description, reference is made to plasma- activated water. But the present invention is not limited to "water" as such, but water can also referred "liquid" such as process water, drain water, or any other liquid suitable for plasma activation.

[0050]

[0039] Figure 1 schematically shows a fertilisation and disinfection system 1 for use in a greenhouse water circulation system according to the invention.

[0051]

[0040] The system 1 comprises a controller 10 connected to a PAW supply 11 and a mixing unit 12. The mixing unit 12 has an inlet 13 for inlet water and an outlet 14 for processed water. Inside the mixing unit 12, the mixing unit can mix PAW with drain water under control from the controller 10. The controller may be able to control the ratio of PAW to inlet water and / or the duration of the time in which the PAW and inlet water is being mixed before the mixture leaves the mixing unit through the processed water outlet 14. The inlet water can be drain water from the greenhouse water circulation system, fresh water, rain water, water from other sources, or a mixture of those. In the below, for brevity reference will be made to drain water as water that is to be disinfected, but it is to be understood that this drain water can also be fresh water, rain water, other water, or a mixture.

[0052]

[0041] The PAW supply 11 will typically be a PAW generator using a plasma source. Such systems are commercially available and described in the literature. A variant uses a PAW storage for storing previously generated PAW in combination with a PAW reactivation unit. That variant is described in the context of figure 5. The PAW supply 11 can also be a storage of PAW, with our without reactivation unit. The PAW might be generated at a distance and be brought to the PAW supply 11 through a conduit or in a suitable container. More information about PAW generation using a plasma source can be found in the applicant's published applications EP3954181 "Plasma activated fluid processing system" and EP3235350 "Plasma activated water". The relevant details of the PAW generation methods and systems are hereby incorporated by reference.

[0053]

[0042] The system 1 , as shown in figure 1, may further comprise a sensor 15, 16 for measuring an amount of reactive oxygen species (ROS) and / or reactive nitrogen species (RNS) (together also called RONS). In an exemplary embodiment, the sensor 15,16 may be a spectrometry-based sensor, such as an absorption spectrometry-based sensor. The sensor can be placed to measure in the drain water (on the inlet side 13 of the system) and / or in the processed water (the outlet side 14) of the system. The sensor or sensors 15, 16 are connected to the controller 10. The sensors 15 and / or 16 may be sensor packages that are able to measure bacteria or microbe concentrations in the drain water or the processed water, respectively. A sensor (not shown) may be provided to sense the bacteria or microbe concentration inside the mixing unit 12. In another alternative, a RNS or ROS concentration is linked to an expected microbe concentration, so that the microbe concentration is estimated based on the determined RNS and / or ROS concentration.

[0054]

[0043] The controller is configured to measure the sensor data and adjust either the ratio of PAW to drain water in the mixing unit or the duration of the treatment in the mixing unit, to control the treatment duration, the mixing unit can have one or more interconnected mixing tanks.

[0055]

[0044] The controller will typically make use of data from sensor 15 and / or sensor 16 and / or a sensor inside the mixing unit 12. These sensors may be able to determine bacteria or microbe concentrations. The controller can control the mixing ratio of PAW to drain water and / or the duration of mixing in order to reduce the bacteria or microbe concentrations by a preset factor or to a target threshold level in the processed water.

[0056]

[0045] The PAW is generated with an original amount of reactive oxygen species (ROS) and reactive nitrogen species (RNS). One of the species in the PAW may be nitrite (NO2-)- Over time, this species may be transformed into nitrate (NCh' ) which, unlike nitrite, is safe and beneficial for plants. In an embodiment, system 1 is configured, using the controller, so that the nitrite is sufficiently reduced before the processed water reaches a crop.

[0057]

[0046] The disinfecting properties of PAW are combined with the fertilisation needs of feedwater (in the form of processed water) for agricultural irrigation applications. PAW has multiple forms of reactive oxygen and nitrogen species (ROS, RNS) that create disinfecting properties. After the initial reactivity, stable molecules of NOs' are formed, which are of nutritional value for crops. A balance between the amount of NOs' and the disinfecting properties needs to be guaranteed for optimal disinfection and fertilisation properties.

[0058]

[0047] In an optional embodiment, a reactivation with an oxidizing component such as hydrogen peroxide or ozone or more generally a molecule with peroxide linkage, further disinfection can be achieved while maintaining a target nitrate concentration in the output stream. A predefined contact time of the strongly disinfecting components of the (reactivated) PAW, controlled by the controller, results in a constant disinfecting property of the setup.

[0059]

[0048] Figure 2 schematically shows a greenhouse water circulation system according to the invention, in which a fertilisation and disinfection system 1 is used. For simplicity, the sensors 15 and 16 are not shown. In this example, the mixing unit 12 comprises a PAW addition point 20, where PAW is added to drain water, and a mixing tank 21 where the mixture can rest for a while. The mixture tank 21 can also be a series of multiple interconnected tanks. It is to be understood that the mixing tank 21 can also be omitted. For example, a buffer tank 22 of the greenhouse water circulation system can be used instead.

[0060]

[0049] The outlet of system 1 is connected to an optional buffer tank 22 of the greenhouse water circulation system 2. The buffer tank is connected to a nutrition tank 23, which is connected to a fresh water supply 26 and nutrients 27, such as nitrogen species, specifically additional fertilizers. These additional fertilizers can be created using a traditional Haber-Bosch procedure. An advantage of the invention is that, by using the PAW supply for disinfection and nutrition, there is less need for HB-produced fertilizer.

[0061]

[0050] After the processed water is mixed with the fresh water 26 and the nutrients 27 in the nutrition tank 23, the water is supplied to crops 24. It is important that at this point the toxic species , such as nitrite but also hydrogen peroxide, are sufficiently reduced. In addition, it is important that the water, which comprises previously drained water, is sufficiently disinfected. That is, the water should have a sufficiently low microbe or bacteria concentration (for the purposes of this application, the terms microbes and bacteria may be used interchangeably and are meant to indicate microorganisms such as bacteria that can be detrimental to crops).

[0062]

[0051] The water is drained from the crops as drain water and may be stored in a drain water tank 25. The drain water is then supplied to the drain water inlet 13 of the mixing unit, where the measurement unit 15 may measure the remaining ROS / RNS concentration. In addition, the sensor 15 may measure microbe or bacteria levels in the drain water.

[0063]

[0052] The controller 10 will typically make use of data from sensors 15, 16. These sensors may be able to determine bacteria or microbe concentrations. The controller can control the mixing ratio of PAW to drain water and / or the duration of mixing in order to reduce the bacteria or microbe concentrations by a preset factor or to a target threshold level in the processed water.

[0064]

[0053] The system 2 will generally be provided with one or more pumps in order to circulate the water. These pumps are not shown in figure 2.

[0065]

[0054] In an embodiment, the controller is also connected to the water 26 and / or nutrient 27 supply, in order to control the amount of water and / or nutrients that are mixed into the nutrition tank 27 depending on the measurements done on the processed or drain water. For example, the controller can add nutrients where needed to increase the concentration of nitrates. The controller can also add water where needed to reduce the concentration of microbes or bacteria even further.

[0066]

[0055] Figure 3 schematically shows a logarithmic reduction of bacteria as a function of the ratio of PAW to drain water, for a treatment time of one minute. The disinfection activity of mixing PAW with dirty, nutrient-rich drain water can be observed in figure 3. The composition of PAW (molecules present and concentrations), the ratio of PAW to drain water, and the microbes exposed will influence the measured disinfecting capacity. A ratio of 60% PAW results in a 3 Iog10 reduction. Even a ratio of PAW to drain water of 1:2 (e.g. 33%) results in disinfection and could be used to keep bacterial levels under control.

[0067]

[0056] A higher PAW to drain water ratio results in more disinfection power (and nitrogen addition). A logarithmic reduction of 6 typically means complete eradication of all pathogens. Logarithmic reductions were calculated by relating the bacterial survival to the survival in Phosphate Buffer Saline (PBS).

[0068]

[0057] Figure 4 schematically shows a logarithmic reduction of bacteria as a function of the treatment time.

[0069]

[0058] Longer incubation times and PAW activity / composition can further improve disinfection rates. Figure 4 shows that disinfection rates continue to increase over time. The solid curve relates to a PAW percentage of 40% and the dashed curve relates to a PAW percentage of 60%. The higher dose of PAW, represented by the dashed curve in the graph exhibits greater antimicrobial activity, resulting in easier eradication of bacteria. Gram-negative bacteria are more susceptible to eradication compared to Gram-positive bacteria through this application, as the RNS and ROS (RONS) in PAW directly target the bacterial membrane.

[0070]

[0059] As PAW contains RONS, the combination of PAW with inlet water will result in a higher nitrogen content of the water. As PAW mostly contains NOXcomponents, the end result that is expected in the disinfected water is nitrate. The amount of disinfection in the water will therefore always be linked to the amount of nitrogen delivered to the water.

[0071]

[0060] Figure 5 schematically shows a fertilisation and disinfection system 1 for use in a greenhouse water circulation system according to the invention having a PAW reactivation unit 51 as part of the PAW supply 11. The PAW supply 11 further comprises a PAW storage 50, for storing PAW that has been previously generated (possibly at a different location) and a reactivation agent supply 52. The reactivation agent supply 52 supplies a reactivation agent, typically an oxidizing agent which will be described below. In the PAW reactivation unit 51, the stored PAW and the reactivation agent are mixed, thereby reactivating the PAW.

[0072]

[0061] In the optional example where an oxidizing agent is used to reactivate PAW, the oxidizing agent that is selected for providing the second amount of ROS and RNS may not only reactivate the degenerated ROS and RNS in the first PAW but also hyperactivate them, resulting in a second amount of ROS and RNS being greater than the original amount provided in the originally produced PAW.

[0073]

[0062] In order to hyper- or reactivate the PAW, an amount of short-lived species, SLS, in the ROS and RNS of the PAW must be increased or preserved as long as possible. This is achieved by treating the PAW with the oxidizing agent.

[0074]

[0063] A PAW supply 12 that reactivates or hyperactivates previously generated PAW is relatively smaller and easier to set up than a PAW supply 12 that has a regular reaction chamber for generating plasma-activated water in the field.

[0075]

[0064] Due to the unstable composition of the PAW after production, a decay of antimicrobial activity may be observed over time. As SLS disappears from the 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.

[0076]

[0065] 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 of up to a week.

[0077]

[0066] In order to achieve a high antimicrobial action, the presence of SLS is desired. The SLS can be regenerated during the plasma activation process by combining the previously generated PAW containing RONS with the oxidizing agent.

[0078]

[0067] Equation 1, mentioned 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 pump arrangement 120 and can comprise at least one of ozone, hydrogen peroxide, and generally molecules with peroxide linkage.

[0079] NO2- + H2O2+H+- O=NOOH + H2O - NO3’ + H++ H2O (1)

[0080]

[0068] As seen in reaction 1 , 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.

[0081]

[0069] Following reactions (reactions 2 and 3) describe the inactivation of the second PAW by the addition of the oxidizing agents. The first PAW is a source of RONS, and hydrogen peroxide or ozone are used as exemplary oxidizers.

[0082]

[0070] Neutralization of the PAW with hydrogen peroxide:

[0083] NO2’+ H2O2 +H+NO3‘ + H++ H2O (2)

[0084]

[0071] Neutralization of the PAW with ozone:

[0085] NO2- + O3+ 3H+- NO3- + H++ H2O + O2(3)

[0086]

[0072] The skilled person will be readily able to describe other reactions involving a molecule with peroxide linkage as the oxidizing agent.

[0087]

[0073] 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(s).

[0088]

[0074] 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.

[0089]

[0075] 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.

[0090]

[0076] 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.

[0091]

[0077] 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

CLAIMS1. A fertilisation and disinfection system (1) adapted for use in a greenhouse water circulation system, the fertilisation and disinfection system comprising:- a Plasma Activated Water, PAW, supply (11);- a mixing unit (12) connected to the PAW supply and configured to receive inlet water from an inlet water supply (13) of the greenhouse water circulation system and to provide processed water (14) to the greenhouse water circulation system;- a mixing unit controller (10) connected to the mixing unit and configured to control at least one of the duration of PAW and inlet water mixing and the ratio of PAW to inlet water mixing.

2. The fertilisation and disinfection system (1) of claim 1, wherein the controller (11) is configured to set the duration of PAW and inlet water mixing so that a target reduction of microbes is obtained or a target reactive oxygen species, ROS, and / or reactive nitrogen species, RNS, concentration is obtained.

3. The fertilisation and disinfection system of claim 1 or 2, wherein the controller (11) is configured to set the ratio of PAW to inlet water mixing so that a target reduction of microbes is obtained or a target ROS and / or RNS concentration is obtained.

4. The fertilisation and disinfection system (1) of any one of the preceding claims, wherein the mixing unit (12) comprises a PAW addition point (20) and a mixing tank (21).

5. The fertilisation and disinfection system (1) of any one of the preceding claims, wherein the controller is configured to control the mixing so that a concentration of a selected species in the processed water is reduced, through decay or a reaction with another species, to below a target threshold concentration before the processed water is supplied to plants.

6. The fertilisation and disinfection system (1) of any one of the preceding claims, comprising a sensor means (15, 16) for measuring at least one of a ROS and RNS concentration in the inlet water or the processed water.

7. The fertilisation and disinfection system of claim 6, wherein the means (16) formeasuring at least one of a ROS and RNS concentration is configured to measure in the processed water.

8. The fertilisation and disinfection system of claim 6 or 7, wherein the means (16) for measuring at least one of a ROS and RNS concentration is calibrated to estimate a microbe concentration in the inlet or processed water.

9. The fertilisation and disinfection system of any one of the preceding claims, further comprising a PAW reactivation unit (51) connected to a reactivation agent supply (52) for reactivating PAW.

10. The fertilisation and disinfection system of claim 9, further comprising a PAW storage (50) connected to the PAW reactivation unit.

11. The fertilisation and disinfection system of claim 9 or 10, wherein the reactivation agent supply (52) is configure to supply an oxidizing agent.

12. The fertilisation and disinfection system of claim 11, wherein the oxidizing agent is one of ozone, hydrogen peroxide, and a molecule with peroxide linkage.

13. The fertilisation and disinfection system of claim 11 or 12, wherein the oxidizing agent is supplied in proportion to the nitrite concentration of the processed water, in order to convert the nitrites to nitrates.

14. A greenhouse water circulation system (2) comprising:- a fertilisation and disinfection system (1) of any one of claims 1-12- a water and nutrients addition unit (23, 26, 27) configured to add water and / or nutrients, such as nitrogen-based nutrients, to the processed water.

15. Method for disinfecting inlet water and adding nitrogen thereto in a greenhouse water circulation system, the method comprising:- a Plasma Activated Water, PAW, supply;- a mixing unit connected to the PAW supply and adaptable to be receive inlet water from a inlet water supply of the greenhouse water circulation system and to provide processed water to a the greenhouse water circulation system;- a mixing unit controller connected to the mixing unit and configured to control at least one of the duration of PAW and inlet water mixing and the ratio of PAW to inletwater mixing.

16. The method of claim 15 combined with any of the features of claims 2 - 14.

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