WO2012112042A1

WO2012112042A1 - Device and method for disinfecting plant seeds

Info

Publication number: WO2012112042A1
Application number: PCT/NL2012/050084
Authority: WO
Inventors: Wilhelmus Antonius Maria Van Lith; Barthelomeus Johannes Theodorus Smit
Original assignee: Synthesis B.V.
Priority date: 2011-02-16
Filing date: 2012-02-16
Publication date: 2012-08-23
Also published as: NL2006212C2

Abstract

The invention relates to a device for disinfecting plant seeds (2) and in particular the seed surface of the plant seeds (2). The invention moreover relates to a method of disinfecting plant seeds (2). The invention furthermore relates to a method of disinfecting plant seeds (2) by using a device for disinfecting plant seeds (2) according to the invention.

Description

Device and method for disinfecting plant seeds

The invention relates to a device for disinfecting plant seeds. The invention moreover relates to a method of disinfecting plant seeds, in particular by using such a device according to the invention.

Most seed treatment products are fungicides or insecticides applied to seed before planting. Fungicides are used to control diseases of seeds and seedlings; insecticides are used to control insect pests. Some seed treatment products are sold as combinations of fungicide and insecticide. Fungicidal seed treatments are used for three reasons: (i) to control soil-borne fungal disease organisms (pathogens) that cause seed rots, damping- off, seedling blights and root rot; (ii) to control fungal pathogens that are surface-borne on the seed, such as those that cause covered smuts of barley and oats, bunt of wheat, black point of cereal grains, and seed-borne safflower rust; and (iii) to control internally seed-borne fungal pathogens such as the loose smut fungi of cereals. Most fungicidal seed treatments, however, do not control bacterial pathogens and most will not control all types of fungal diseases. It is therefore important to carefully choose a treatment that provides the best control of the disease organisms present on the seed or potentially present in the soil.

The invention has for its object to provide an improved method for disinfecting plant seeds, using which seeds of an improved seed quality can be obtained.

The invention provides for this purpose a device of the type stated in the preamble, comprising: at least one accommodating space for plant seeds to be disinfected, at least one plasma generating unit for generating a plasma extending to said at least one accommodating space, and at least one gas flow generating element for generating a gas flow causing at least partial displacement of the plasma generated by the plasma generating unit to surround the plant seeds substantially entirely by plasma. It has been found that by generating and using a plasma the seed surface of the plant seeds can be disinfected in a relatively effective manner. The plasma will efficiently deactivate and often kill micro-organisms, such as saprophytes, pathogens, mycotoxines, viruses, and bacteria which allows improved control of the seed-borne mycoflora of the plant seeds while maintaining good germination properties of the plant seeds after disinfection. In order to realise complete contact of the plant seeds by the disinfecting plasma a gas flow is generated to displace the plasma cloud at least partially in the direction of the plant seeds. In this manner the plant seeds will be fully immersed into the disinfecting plasma. Commonly this displacement will or may be in the magnitude of several centimetres. Different kinds of plant seeds, like wheat and vegetable seeds, may be treated by using plasma. Plasma is often described as the fourth state of matter.

Typically it contains charged electrons and ions as well as chemically active species such as ozone, hydroxyl radicals, nitrous oxides, electronically excited atoms and molecules. Electronic excitation of some atoms and molecules in plasma produces ultraviolet radiation (hereinafter "UV"), which may have a positive effect to the core of the plant seeds. Plasma can also be a good electrical conductor due to the presence of charged particles in the plasma. In a room-temperature environment, plasma is usually supported by electro-magnetic fields. Light electrons absorb energy from an electric field and transfer part of this energy to heavy particles in the plasma. Plasma is considered to be thermal if the rate of the electron energy transfer is fast relative to the rate of energy losses by heavy particles. In this case heavy particles reach energies comparable with the energy of electrons and the plasma becomes hot. In other cases, when electrons are not given sufficient opportunity to transfer their energy, heavier plasma components remain at much lower temperatures than the electrons. Such plasmas are called non-thermal and their gas temperatures can be as low as room temperature. The plasma generating unit used in the device according to the invention is preferably configured to generated a non-thermal plasma in order to prevent thermal damage of the plant seeds. Commonly the plant seeds will be able to withstand temperatures up to 40 to 50 degrees Celsius. The working pressure wherein the plasma is generated is substantially atmospheric which is relatively cost-effective, although the presence of the gas flow may lead to a slight overpressure.

In an embodiment of the device the plasma generating unit is configured to generate a plasma by dielectric barrier discharge or by corona discharge. Dielectric barrier discharge (DBD), in particular surface dielectric barrier discharge (SDBD), is commonly preferable since by using this type of discharge a relatively homogeneous plasma can be generated resulting in a relatively homogeneous surface treatment of the plant seeds. Corona discharge treatment can also be used for disinfecting the plant seeds. A corona discharge is typically produced by applying a high voltage (approximately 5 to 10 kV) relatively high frequency (e.g. 10 kHz) signal to electrodes in air at atmospheric pressure. However, whilst corona discharge treatment does have the advantage of operating at atmospheric pressure, there are several significant limitations to the usefulness of corona discharge treatments. In particular corona discharges are produced from point sources, and as such produce localised energetic discharges, which are commonly known as streamers or filaments. The production of localised energetic discharges which may result in a non-uniform treatment of the plant seeds. Hence a DBD plasma, in particular a SDBD plasma will commonly be preferred to be used in the plasma generating unit of the device according to the invention. The ionisable gas for use in the plasma treatment process by the plasma generating unit may be, for example, an oxygen-containing gas, e.g. 0₂, N0₂, H₂0 and air, or an inert gas, such as N₂. It has been found that formation of plasmatic ozone (0₃) will contribute to the disinfection process of the plant seeds. The ionisable gas may be provided by or via the plasma generating unit, though it may also be imaginable that the gas generating element is configured to generate a flow of gas to be ionised by the plasma generating unit.

As already indicated above a particular type of DBD is known as Surface Dielectric Barrier Discharge (SDBD). In contrast to Volume Dielectric Barrier Discharges (VDBD) where the plasma develops in a gas gap in between two surfaces (at least one is covered by a dielectric layer), in SDBD electrode configurations the electrodes are integrated with a single solid dielectric structure thereby creating a plasma which is concentrated on the dielectric surface of this structure. The discharge structure includes streamers (also called micro- discharges), mainly developing on the dielectric in the same direction parallel to each other. In order to sustain SDBD plasma continuously, alternating polarity voltage or a series of pulses must be applied to the electrodes. During each change of the voltage-time gradient dV/dt streamers of the opposite polarity are generated on the dielectric. As result of the repulsive Coulomb force between streamers having the same excess charge, the branches never overlap each other. There appears to be an approximate linear relationship between the peak value of the applied voltage and streamer length. The physical properties of SDBD plasma of known electrode configurations have been widely studied through experiment and numerical modelling. When comparing SDBD with VDBD and atmospheric pressure glow discharge (APGD) technologies, the following can be noted. SDBD has a streamer-like nature like the VDBD on a microscopic scale but due to the built-up charge on the surface of a dielectric from one streamer, a developing path of next streamer is not identical with the path of the previous one (it is adjacent) so that the discharge is macroscopically uniform and the treatment is homogeneous. Furthermore, and in contrast to VDBD, streamers are parallel to a surface supporting the plant seeds to be disinfected, which result in a good contact between plasma and the treated material and, therefore, to higher efficiency i.e. relatively short treatment times. The contact is further improved by inducing a gas flow intensifying the mutual contact between the plasma and the plant seeds. Since the plasma is not generated in volume but only where the treated material is, i.e. in a thin layer on the surface of dielectric barrier, more efficient operation and lower power consumption is associated with SDBD compared to VDBD. Further, as plasma is not generated in volume but only where the treated material is, i.e. in a thin layer on the surface of dielectric barrier, rest products of plasma polymerization (deposition) will only be present on the surface of the dielectric, which can easily be cleaned. SDBD is characterized by high density plasma compared to VDBD or other forms of non-thermal plasmas. The high density of chemically active environment is another factor that makes the treatment more efficient and may lead to even shorter treatment times.

In contrast to VDBD, APGD and other plasma sources, SDBD is stable at atmospheric pressure at almost any composition of the process gas and precursor (even at relatively relatively high concentration) and at high electrical power. In addition, in contrast to VDBD and APGD, SDBD is stable at low flow rates of gas to be ionised to form the plasma, and is even stable when no flow of ionisable gas is present. SDBD plasma may penetrate to some extent into (the pores of) the plant seeds and, unlike to VDBD and other plasma sources, the treatment may be both on the outer surface of the plant seeds and on the inside of the plant seeds. When applying SDBD, the one or multiple electrodes configured for inducing a plasma are positioned at one side of, commonly below or above, the accommodating space. In addition to the advantages mentioned above, an additional advantage of SDBD is that the unilateral positioning of the electrodes allows easy optimisation of the design of the accommodating space located above - on top of - the electrode(s). Commonly the accommodating space is provided with a support structure for the plant seeds to be disinfected. The support structure may be stationary and fixed with respect to the plasma generating unit, though in order to disinfect larger quantities of plant seeds it is often preferable to use a movable (mobile) support structure. To this end, the mobile support structure may be formed by an endless belt. It is conceivable to use the device according to the invention during a batch process or a continuous process for disinfecting plant seeds. It is preferable in case the support structure is configured for flow-through of the gas flow generated by the gas flow generating element. The support structure may be formed by a wire mesh made of metal and/or polymer.

The gas flow generating element may be configured to regulate the magnitude of the gas flow which may be dependent on various process parameters, such as the composition of the gas for flowing, the composition of the gas to be ionised, the nature of the plant seeds to be disinfected, and the disinfection time of the plant seeds. In order to secure good physical contact between the plant seeds to be disinfected and the plasma it is advantageous in case the gas flow generating element is configured to generate a gas flow in a direction enclosing an angle with a part of the support structure supporting the plant seeds. This angle is preferably between 15 and 175, preferably between 30 and 160, more preferably between 45 and 135 degrees.

The gas flow generating element is preferably configured to generate an air flow. Air is relatively cheap and has moreover a composition which is suitable to be ionised to form a disinfecting plasma. The air flow may be enriched by additives, such as nitrogen and/or water, in order to improve the disinfection of the plant seeds. It is imaginable to add other additives to the gas flow, in particular air flow, generated, such as specific coatings or fungicides. These latter additives will commonly be present in the gas flow and plasma formed thereof in atomized form.

In a preferred embodiment of the device according to the invention, the accommodating space is configured for holding the plant seeds to be disinfected. By holding or keeping the plant seeds in the accommodating space the disinfection time of the plant seeds can be entirely controlled as a result of which the degree of disinfection can be controlled relatively easily while the device can be construed in a relatively compact manner. The accommodating space can be formed on top of a conveyor belt on which the plant seeds to be disinfected are situated. It is also conceivable that the accommodating space is enclosed by a container in which the plant seeds to be disinfected are situated. This container may or may not be closable by means of a closing element. Within the container the plant seeds may be blown around by means of the generated gas flow which may result in a relatively turbulent process. It is further imaginable that a fluidization bed is formed within the container wherein the plant seeds are moved such that they behave as a fluid. This can be achieved by the introduction of the gas flow through the bottom of a bed of plant seeds kept in the container, as a result of which the gas flow will move upwards through the bed via the empty spaces between the plant seeds. At low gas velocities, aerodynamic drag on each plant seed is also low, and thus the bed remains in a fixed state. Increasing the velocity, the aerodynamic drag forces will begin to counteract the gravitational forces, causing the bed to expand in volume as the plant seeds move away from each other. Further increasing the velocity, it will reach a critical value at which the upward drag forces will exactly equal the downward gravitational forces, causing the plant seeds to become suspended within the fluid. At this critical value, the bed is said to be fluidized and will exhibit fluidic behaviour. By further increasing gas velocity, the bulk density of the bed will continue to decrease, and its fluidization becomes more violent, until the plant seeds no longer form a bed and are "conveyed" upwards by the gas flow. In the fluidized state the plant seeds can be surrounded by plasma in a relatively efficient and controlled manner. Preferably, the accommodating space and the at least one gas flow generating element are oriented such that the plant seeds are exposed to plasma for a period of at least 1 second, preferably at least 5 seconds. A typical period for disinfecting relatively dry plant seeds (water activity < 0,8 aW) is between 1 second and 15 minutes, and a typical period for disinfecting relatively wet plant seeds (water activity > 0,8 aW) is between 5 seconds and 15 minutes, commonly dependent on the energy density (intensity) of the plasma.

It has been found that an increased temperature, preferably a temperature of between 30 and 50 degrees Celsius, in the accommodating space can be in favour of the disinfection process. It is therefore preferred that the device comprises at least one heating element for realizing such an elevated temperature in the accommodating space.

In a preferred embodiment the intensity of the plasma is relatively high in order to improve the disinfection of the plant seeds and to decrease the disinfection time of the plant seeds. To this end, it is favourable in case the plasma generating unit is configured to generate a plasma with an energy density (power density) of at least 10 Watt per millimetre (w/mm). In another preferred embodiment the device comprises at least one moisturizing element for moisturizing the plant seeds to be disinfected. Moisturizing the plant seeds can be favourable for typically two reasons. Moisturizing the plant seeds prevents drying out and therefore harming the plant seeds during the disinfection process, in particular when an elevated temperature is present in the accommodating space. Moreover, it has been found that the presence of water on the plant seeds may allow formation of hydroxyl radicals which may further improve the disinfecting process.

The device according to the invention preferably comprises at least one administering element for administering at least one additive to the generated plasma and/or to the seeds to be disinfected. Commonly the purpose of adding one or multiple additives to the plasma and/or directly onto the plant seeds is to improve the disinfection process. It has been found that adding hydrogen peroxide (H₂O₂) is well suitable to improve the disinfection process due to the easy formation of effective disinfection hydroxyl radicals.

The invention also relates to a method of disinfecting plant seeds, in particular using a device according to the invention, comprising: A) providing at least one

accommodating space with plant seeds to be disinfected, B) generating a plasma extending to said accommodating space, and C) inducing a gas flow, in particular an air flow, along a gas flow path causing at least partial displacement of the plasma to surround the plant seeds substantially entirely by plasma. Advantages of applying the method of disinfecting plant seeds and further embodiments of the method according to the invention have already been described above in a comprehensive manner. Prior to generating the plasma according to step B) it is thinkable to slightly moisten the plant seeds to be disinfected. Too much moisture will lead to obstruction of seed pores which is undesired. Commonly the maximum quantity of moisture to be applied to the plant seeds will be about 10% of the absolute moisture content of the seeds. The gas flow path is preferably oriented substantially transverse with respect to a treating plane of a supported structure to be treated by the unit. Using SDBD technology for generating a plasma, this transverse direction will blow the plasma away from the electrode(s) generating the plasma resulting in a substantially complete immersion of the plant seeds in the plasma. Commonly, in particular when using SDBD or VDBD technology, the plasma is generated by applying a voltage between an interior electrode arranged in an interior space of a solid dielectric structure and a further electrode. The gas flow may have a bilateral functionality: (i) the gas may be ionisable and therefore applicable to form the plasma, and (ii) since the gas is flowing it will distribute the plasma formed within the accommodating space causing the plant seeds to be surrounded substantially completely by plasma. In a preferred embodiment the method comprises step D) comprising moisturizing the plant seeds to be disinfected. In an alternative preferred embodiment the method comprises step E) comprising administering at least one additive, in particular hydrogen peroxide, to the generated plasma and/or the plant seeds to be disinfected. Step D) and E) both leads to formation of hydroxyl radicals which could further increase the disinfection process as mentioned above.

The invention is illustrated by way of the following non-limitative example, wherein: figure 1 shows a schematic view of a device for disinfecting plant seeds according to the invention,

figure 2 shows a schematic view of another device for disinfecting plant seeds according to the invention,

figure 3 shows a schematic view of further device for disinfecting plant seeds according to the invention,

figure 4 shows a schematic view of yet another device for disinfecting plant seeds according to the invention,

figure 5 shows a schematic view of another device for disinfecting plant seeds according to the invention,

figure 6a shows a schematic view of an alternative device for disinfecting plant seeds according to the invention, and

figure 6b shows a schematic top view of a part of the device according to figure 6a.

Figure 1 shows a schematic view of a device 1 for disinfecting plant seeds 2 according to the invention. The device 1 comprises a supply container 3 partially filled with plant seeds 2 to be disinfected. The supply container 3 is configured to release dosed quantities of plant seeds 2 to an rotating fine-meshed endless belt 4 leading the plant seeds through an disinfection zone 5, also referred to as an accommodating space, after which the disinfected seeds 2 are collected by a storage container 6. In the disinfection zone 5 a plasma 5 is present which is generated in this example by SDBD technology. To this end, the device 1 comprises two electrodes 7a, 7b between which an alternating voltage V is applied. Between the electrodes 7a, 7b a dielectric structure 8 is located resulting in the formation of the plasma 5 above the dielectric structure 8. In order to secure complete surrounding of the plant seeds 2 to be disinfected a compressor 9 is applied blowing air into a hollow structure 10 of the dielectric structure 8. Via small channels 11 facing the endless 4 and via the fine-meshed endless belt 4 air is blown into the disinfection zone 5 expanding the plasma cloud 5. The diameter of each channel 11 is typically about 1 millimetre or smaller. Narrowing the channels 11 will lead to an acceleration of air which is commonly in favour of the extent of expansion of the plasma cloud 5. The (ionisable) air blown via the hollow structure 10 into the disinfection zone 5 also functions as feedstock for formation of the plasma 5. The (substantially vertical) direction in which the air is blown into the disinfection zone 5 is substantially transverse to the (substantially horizontal) transport direction of the plant seeds 2. Alternatively, the orientation of the channels 11 may be inclined as a result of which the channels are orientated diagonally and therefore also extent in a horizontal direction. Air blown through these inclined channels 11 may be blown in the transport direction of the plant seeds 2 which may facilitate and improve transport of the plant seeds 2 in the desired direction. Optionally one or multiple additives, such as nitrogen or water, may be mixed with atmospheric air in a mixing unit 12 to enrich the air prior to be sucked into the compressor 9. Alternatively, the one or more additives are added to the flow air after being led through the compressor 9. The working air pressure is substantially atmospheric. The electric source V is a high-frequency and high-voltage electric source, preferably with a frequency range from 50 Hz to 20 kHz and the voltage range is preferably between 1 kV and 10 kV. The plant seeds 2 are treated by the plasma between 5 and 130 seconds in this example. It is also conceivable to treat the plant seeds simultaneously as a batch, wherein the plant seeds are e.g. positioned in a disinfection chamber. In this disinfection chamber a plasma is generated to treat the plant seeds, wherein a gas flow is created to allow the plasma to surround the plant seeds. The gas flow may further be applied to dry the seeds. Alternatively, the plant seeds may be dried by controlled heating. Treatment of a batch of plant seeds with plasma in such a disinfection chamber may last longer than 130 seconds. A typical treatment time is 180 seconds. Dependent on the intensity of the plasma treatment the treatment time may be extended up to several minutes.

Figure 2 shows a schematic view of another device 13 for disinfecting plant seeds 14 according to the invention. The device 13 comprises a supply container 15 partially filled with plant seeds 14 to be disinfected. The supply container 15 is configured to release dosed quantities of plant seeds 14 to a fine-meshed vibrating plate 16 leading the plant seeds 14 through an disinfection zone 17, also referred to as an accommodating space, after which the disinfected seeds 14 are collected by a storage container 18. In the disinfection zone 17 a plasma is present which is generated by a plasma generator 19. As shown in figure 19 the plant seeds 14 are transported between the vibrating plate 16, acting as support structure, and the plasma generator 19, wherein the plasma generator 19 is substantially positioned above the vibrating plate 16, which will commonly be favourable from a constructive point of view. Moreover, since it has been found that a turbulent plasma flow could relatively easily cause degradation of the plasma due to intraplasmatic reactions, the shown orientation of the plasma generator 19 and vibrating plate 16 is commonly preferred, since this orientation allows generation of a substantially laminar plasma flow which will be in favour of the plasma quality. In order to secure complete surrounding of the plant seeds 14 to be disinfected the air may be blown by using a compressor or fan from the plasma generator 19 towards the vibrating plate 16 and/or by using a vacuum pump a vacuum is applied below the fine- meshed vibrating plate 16 sucking the plasma towards the vibrating plate 16 (see vertical arrows). Both methods generate a gas flow leading to a desired expansion of the plasma. The vibrating plate 16 is supported by two diagonal vibrating arms 20a, 20b causing the plate 16 to vibrate in diagonal direction as a result of which the seeds 14 will bumped from the supply container 15 through the disinfection zone 17 to the storage container 18. Instead of using a mesh-like plate 16 it is also conceivable to apply a solid (impermeable) plate. Figure 3 shows a schematic view of further device 21 for disinfecting plant seeds 22 according to the invention by using plasma. The device 21 comprises a container 23 enclosing an accommodating space 24 which is partially filled with plant seeds 22 to be disinfected. The container 23 is provided with a plasma generating unit 25 for generating a plasma extending to said accommodating space 24. The container 23 is further provided with a heating element 26 for heating the atmosphere within the accommodating space 24 to a temperature of between 30 and 50 degrees Celsius. At the bottom the of the container 23 a gas flow generating element 27 is provided for generating a gas flow towards a distribution element 28 via which the gas flow is led into the accommodating space, preferably in multiple directions. The gas flow velocity is relatively high, such that the plant seeds 22 in the accommodating space 24 are blown and displaced throughout the (entire) accommodating space 25. This turbulence created in the accommodating space 24 facilitates both heating and disinfecting of the plant seeds 22.

Figure 4 shows a schematic view of yet another device 29 for disinfecting plant seeds 30 according to the invention by using plasma as disinfecting medium. The device 29 comprises a container 31 enclosing an accommodating space 32 which is partially filled with plant seeds 30 to be disinfected. The container 31 is provided with a heating element 33 for heating the accommodating space 32 to a temperature, preferably 40 degrees Celsius, at which disinfection is improved. The bottom of the container 31 is formed by a diffuser plate 34 comprising multiple small channels 35 connecting opposing sides of the diffuser plate 34. The channel diameter is smaller than the average diameter of the plant seeds 30 to prevent plant seeds 30 to enter the channels 35.

Underneath the diffuser plate 34 a collecting space 36 is positioned for collecting air sucked up by an air flow generating element 37, such as a ventilator of compressor, as well as for collecting plasma generated by a plasma generating unit 38. Plasma generated in the collecting space 36 is displaced by the air flow, generated by the air flow generating element 37, via the diffuser plate 34 into the accommodating space 32 to disinfect the plant seeds 30. Due to the presence of the diffuser plate 35 the air/plasma flow can be led in a relatively homogeneous manner into the accommodating space, wherein the flow speed can be such that the bed of plant seeds 30 is fluidized. This plant seed fluidization is favourable for bringing the plant seeds 30 into intensive contact with the disinfecting plasma, as a result of which the disinfection process of the plant seeds 30 can be performed in a relatively controlled manner.

Figure 5 shows a schematic view of yet another device 39 for disinfecting plant seeds 40 according to the invention by using plasma as disinfecting medium. The device 39 comprises a container 41 enclosing an accommodating space 42 which is partially filled with plant seeds 40 to be disinfected. A bottom part of the container 41 is connected to a conduit 43 for leading plasma and heated air into the container 41. The container 41 and the conduit 43 are separated by means of a sieve plate 44 preventing the plant seeds 40 to enter the conduit 43. In the conduit a heating element 45 is provided for heating air to be led into the accommodating space 42. An outer end of a plasma generator 46 is also positioned in bthe conduit 43 near the sieve plate 44. In the accommodating space 42 a guiding sleeve 46 to guide the plasma cloud, the heated air, and the plant seeds 40 in the accommodating space 42, wherein the plant seeds 40 will be circulated within the accommodating space 42 according to a more or less heart-shaped pattern.

Figure 6a shows a schematic view of an alternative device 47 for disinfecting plant seeds according to the invention by using plasma as disinfecting medium. The device 47 comprises a drum 48 enclosing an accommodating space 49, which is partially filled with plant seeds to be disinfected. A top part of the drum 48 is provided with a heating element 50 for heating the atmosphere within the accommodating space 49 to a temperature of typically 45 degrees Celsius. A bottom part of the container 48 is provided with a sieve screen 51 provided with openings 52 which are sufficiently small to prevent the plant seeds to pass through, though which are sufficiently large to allow air or other gas to pass through. Each opening 52 is provided with a guiding element 53 to guide and direct an air stream, generated by a ventilator 54 positioned underneath the sieve screen 51, according to a circular pattern (see figure 6b) into the accommodating space which results in the generation of a rotating fluidization bed of plant seeds which will commonly improve the disinfection efficiency and effectivity. Between the ventilator 54 and the sieve screen 51 multiple plasma generating units 55 are positioned. Disinfecting plasma generated by these units 55 are blown by the generated air stream into the accommodating space 49 in order to disinfect the moving plant seeds in the accommodating space.

It should be noted that the above-mentioned embodiments and experiment illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. Device for disinfecting plant seeds, comprising:

at least one accommodating space for plant seeds to be disinfected,

- at least one plasma generating unit for generating a plasma extending to said at least one accommodating space, and

at least one gas flow generating element for generating a gas flow causing at least partial displacement of the plasma generated by the plasma generating unit to surround the plant seeds substantially entirely by plasma.

2. Device according to claim 1, wherein the plasma generating unit is configured to generate a plasma by dielectric barrier discharge.

3. Device according to claim 1, wherein the plasma generating unit is configured to generate a plasma by corona discharge.

4. Device according to any of the foregoing claims, wherein the plasma generating unit comprises multiple electrodes between which a plasma can be generated, wherein all electrodes are positioned at one side of the accommodating space.

5. Device according to any of the foregoing claims, wherein at least one plasma generating unit comprises at least one electrode positioned below the accommodating space.

6. Device according to any of the foregoing claims, wherein at least one plasma generating unit comprises at least one electrode positioned above the accommodating space.

7. Device according to one of claims 4-6, wherein the plasma generating unit comprises at least one dielectric element covering the at least one electrode at least partially.

8. Device according to any of claims 4-7, wherein the plasma generating unit comprises multiple electrodes, wherein at least one dielectric element is positioned at least partially between the electrodes.

9. Device according to any of the foregoing claims, wherein the accommodating space is provided with a support structure for the plant seeds to be disinfected.

10. Device according to claim 9, wherein the support structure is configured for flow-through of the gas flow generated by the gas flow generating element.

11. Device according to claim 9 or 10, wherein the support structure is movable trough the accommodating space.

12. Device according to claim 11, wherein the support structure is formed by an endless transport belt.

13. Device according to any of the foregoing claims, wherein the gas flow generating element is configured to generate a gas flow in a direction enclosing an angle with a part of the support structure supporting the plant seeds.

14. Device according to claim 13, wherein the gas flow generating element is configured to generate a gas flow enclosing an angle of between 15 and 175, preferably between 30 and 160, more preferably between 45 and 135 with the part of the support structure supporting the plant seeds.

15. Device according to any of the foregoing claims, wherein the gas flow generating element is configured to generate an air flow.

16. Device according to any of the foregoing claims, wherein the gas flow generating element is configured to generate a gas flow containing more than 80 volume percent of nitrogen.

17. Device according to any of the foregoing claims, wherein the accommodating space is configured for holding the plant seeds to be disinfected.

18. Device according to any of the foregoing claims, wherein the accommodating space and the at least one gas flow generating element are oriented such that the plant seeds are exposed to plasma for a period of at least 1 second, preferably at least 5 seconds.

19. Device according to any of the foregoing claims, wherein the accommodating space and the at least one gas flow generating element are oriented such that the gas flow causes the plant seeds to be disinfected to be moved through the accommodating space.

20. Device according to any of the foregoing claims, wherein the device comprises at least one heating element for realizing an elevated temperature in the accommodating space.

21. Device according to claim 20, wherein the heating element is configured to realize a temperature of between 30 and 50 degrees Celsius in the accommodating space.

22. Device according to any of the foregoing claims, wherein the plasma generating unit is configured to generate a plasma with an energy density of at least 10 Watt per millimetre (w/mm).

23. Device according to any of the foregoing claims, wherein the device comprises at least one moisturizing element for moisturizing the plant seeds to be disinfected.

24. Device according to any of the foregoing claims, wherein the device comprises at least one administering element for administering at least one additive to the generated plasma and/or to the seeds to be disinfected.

25. Device according to claim 24, wherein the administering element is configured to administer hydrogen peroxide, to the generated plasma and/or to the seeds to be disinfected.

26. Method of disinfecting plant seeds, in particular using a device according to any of claims 1-25, comprising:

A) providing at least one accommodating space with plant seeds to be disinfected,

B) generating a plasma extending to said accommodating space, and

C) inducing a gas flow along a gas flow path causing at least partial displacement of the plasma to surround the plant seeds substantially entirely by plasma.

27. Method according to claim 26, wherein the gas flow path is oriented

substantially transverse with respect to a treating plane of a structure to be treated by the unit.

28. Method according to claim 26 or 27, wherein the plasma is generated by applying a voltage between an interior electrode arranged in an interior space of a solid dielectric structure and a further electrode.

29. Method according to any of claims 26-28, wherein the gas flow is formed by an air flow.

30. Method according to any of claims 26-29, wherein the method comprises step D) comprising moisturizing the plant seeds to be disinfected.

31. Method according to any of claims 26-30, wherein the method comprises step E) comprising administering at least one additive, in particular hydrogen peroxide, to the generated plasma and/or the plant seeds to be disinfected.