NL2006212C2

NL2006212C2 - Device and method for disinfecting plant seeds.

Info

Publication number: NL2006212C2
Application number: NL2006212A
Authority: NL
Inventors: Wilhelmus Antonius Maria Lith; Barthelomeus Johannes Theodorus Smit
Original assignee: Synthesis B V
Priority date: 2011-02-16
Filing date: 2011-02-16
Publication date: 2012-08-20
Also published as: WO2012112042A1

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 5 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 10 fungicide and insecticide. Fungicidal seed treatments are used for three reasons: (i) to control soil-bome fungal disease organisms (pathogens) that cause seed rots, damping-off, seedling blights and root rot; (ii) to control fungal pathogens that are surface-bome 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 15 seed-bome 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.

20

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, 25 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 30 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-bome myco flora of the plant seeds while maintaining good germination properties of the plant seeds after disinfection. In 2 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 5 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 10 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 15 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 20 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 25 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 30 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 3 (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 5 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 10 ionisable gas for use in the plasma treatment process by the plasma generating unit may be, for example, an oxygen-containing gas, e.g. O2, NO2, H20 and air, or an inert gas, such as N2. It has been found that formation of plasmatic ozone (O3) 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 15 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 20 (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 25 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 30 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 4 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, 5 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 10 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, 15 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 20 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 25 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 30 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) 5 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 5 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 10 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 15 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 20 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.

25

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 30 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 has 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 6 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 5 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 YDBD 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 10 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.

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

20

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 25 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 30 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 7 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 5 (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 10 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 15 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 20 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 25 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 30 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 8 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 5 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 10 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 15 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.

20 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 25 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.

30

Claims

Device for disinfecting plant seeds, comprising: - at least one accommodation space for plant seeds to be disinfected, 5. at least one plasma-generating unit for generating a plasma extending to the at least one accommodation space, and - at least one gas-flow generating unit element for producing a gas stream that at least partially displaces the plasma generated by the plasma generating unit to completely surround the plant seeds with plasma.

Device as claimed in claim 1, wherein the plasma generating unit is designed such that it generates a plasma by means of a discharge over a dielectric barrier. 15

The device of claim 1, wherein the plasma generating unit is configured to generate a plasma by corona discharge.

4. Device as claimed in any of the foregoing claims, wherein the plasma-generating unit comprises a plurality of electrodes between which a plasma can be generated, wherein all electrodes are situated on one side of the accommodation space.

5. Device as claimed in any of the foregoing claims, wherein at least one plasma generating unit comprises at least one electrode which is located below the accommodation space.

6. Device as claimed in any of the foregoing claims, wherein at least one plasma generating unit comprises at least one electrode which is situated above the accommodation space.

The device of any one of claims 4 to 6, wherein the plasma generating unit comprises at least one dielectric element that at least partially covers the at least one electrode.

The device of any one of claims 4 to 7, wherein the plasma generating unit comprises a plurality of electrodes, wherein at least one dielectric element is located at least partially between the electrodes. 5

Device as claimed in any of the foregoing claims, wherein the accommodation space is provided with a support structure for the plant seeds to be disinfected.

Device as claimed in claim 9, wherein the support structure is adapted to flow through the gas flow generated by the gas-generating element.

Device as claimed in claim 9 or 10, wherein the support structure is movable through the accommodation space. 15

Device as claimed in claim 11, wherein the support structure is formed by an endless conveyor belt.

13. Device as claimed in any of the foregoing claims, wherein the gas flow generating element is adapted to generate a gas flow in a direction which encloses an angle with a part of the supporting structure supporting the plant seeds.

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

15. Device as claimed in any of the foregoing claims, wherein the gas flow generating element is adapted to generate an air flow.

Device as claimed in any of the foregoing claims, wherein the gas flow generating element is adapted to generate a gas flow that contains more than 80 volume percent nitrogen.

17. Method for disinfecting plant seeds, in particular with the aid of a device according to one of claims 1 to 16, comprising: A) providing at least one accommodation space with plant seeds to be disinfected, B) generating a plasma extending into the accommodation space, and C) inducing a gas flow along a gas flow path that causes an at least partial displacement of the plasma to surround the plant seeds substantially entirely with plasma.

The method of claim 17, wherein the gas flow path is substantially transversely oriented with respect to a treatment surface of a structure to be treated by the unit. 15

The method of claim 17 or 18, wherein the plasma is generated by applying a voltage between an internal electrode disposed in an internal space of a fixed dielectric structure and a further electrode.

The method of any one of claims 17-19, wherein the gas stream is formed by an air stream.