Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L2/00—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
  • A61L2/02—Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using physical phenomena
  • A61L2/14—Plasma, i.e. ionised gases
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/2406—Generating plasma using dielectric barrier discharges, i.e. with a dielectric interposed between the electrodes
  • H05H1/2439—Surface discharges, e.g. air flow control
• • A—HUMAN NECESSITIES
  • A01—AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
  • A01C—PLANTING; SOWING; FERTILISING
  • A01C1/00—Apparatus, or methods of use thereof, for testing or treating seed, roots, or the like, prior to sowing or planting
  • A01C1/08—Immunising seed
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/2406—Generating plasma using dielectric barrier discharges, i.e. with a dielectric interposed between the electrodes
  • H05H1/2425—Generating plasma using dielectric barrier discharges, i.e. with a dielectric interposed between the electrodes the electrodes being flush with the dielectric

Definitions

• 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.
• 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
• 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.
• 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.
• 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.
• UV ultraviolet radiation
• 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.
• 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.
• the plasma generating unit is configured to generate a plasma by dielectric barrier discharge or by corona discharge.
• Dielectric barrier discharge DBD
• surface dielectric barrier discharge SDBD
• 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.
• a high voltage approximately 5 to 10 kV
• relatively high frequency e.g. 10 kHz
• 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.
• 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. 0 2 , N0 2 , H 2 0 and air, or an inert gas, such as N 2 . It has been found that formation of plasmatic ozone (0 3 ) 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.
• SDBD Surface Dielectric Barrier Discharge
• VDBD Volume Dielectric Barrier Discharges
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the one or multiple electrodes configured for inducing a plasma are positioned at one side of, commonly below or above, the accommodating space.
• 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).
• 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.
• 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.
• 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.
• the accommodating space is configured for holding the plant seeds to be disinfected.
• 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.
• 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.
• the bed is said to be fluidized and will exhibit fluidic behaviour.
• 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.
• the plant seeds can be surrounded by plasma in a relatively efficient and controlled manner.
• 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.
• the device comprises at least one heating element for realizing such an elevated temperature in the accommodating space.
• 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.
• 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).
• 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.
• 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.
• at least one administering element for administering at least one additive to the generated plasma and/or to the seeds to be disinfected.
• 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 (H 2 O 2 ) 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
• 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.
• 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.
• 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.
• the method comprises step D) comprising moisturizing the plant seeds to be disinfected.
• 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.
• 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
• FIG. 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.
• figure 6b shows a schematic top view of a part of the device according to figure 6a.
• FIG 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.
• a plasma 5 is present which is generated in this example by SDBD technology.
• 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.
• 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.
• 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.
• 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.
• 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.
• FIG. 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.
• a plasma is present which is generated by a plasma generator 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.
• 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.
• 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.
• FIG. 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.
• 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.
• FIG. 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.
• 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.
• FIG. 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.
• 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.
• 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.
• FIG. 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.
• 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.
• 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.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Health & Medical Sciences (AREA)
• Environmental Sciences (AREA)
• Soil Sciences (AREA)
• Epidemiology (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Pretreatment Of Seeds And Plants (AREA)

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Cited By (29)

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• 2011
  • 2011-02-16 NL NL2006212A patent/NL2006212C2/en not_active IP Right Cessation
• 2012
  • 2012-02-16 WO PCT/NL2012/050084 patent/WO2012112042A1/en active Application Filing

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