Destruction of airborne pathogens, and microorganisms on grains and dried food using ultrasound

Abstract

To provide an apparatus and a method for destroying microorganisms on surfaces of grains using sound.SOLUTION: Provided is a method for the destruction of microorganisms present on the surface of a plurality of grains or dried food products disposed in a container having a surface, the method including: subjecting the surface of the container to a first periodic vibrational excitation having a first amplitude effective to cause the plurality of grains or dried food products disposed in the container to become airborne; subjecting the plurality of airborne grains or dried food products to a second periodic vibrational excitation having a second amplitude relative to the surface of the container effective to increase collisions therebetween, whereby the microorganisms are destroyed by the collisions of the airborne grains or dried food products.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 040,259, filed June 17, 2020, for “Destruction Of Airborne Pathogens, And Microorganisms On Grains And Dried Food Using Ultrasound,” the entire contents of which are hereby specifically incorporated by reference herein for all that it discloses and teaches. [Background technology]

[0002] Microorganisms, especially heat-resistant bacterial spores, are widely used in food processing and often contaminate grains, legumes (peas, beans, and lentils), spices, and dried vegetables, resulting in spoilage. The bacterial spores that contaminate these dry food ingredients cannot be completely inactivated by heating processes such as steaming and boiling in food processing plants. Thus, dry ingredients for food processing need to be decontaminated to prevent food spoilage and food-borne illness. Decontamination techniques including fumigation with ethylene oxide gas (EOG), irradiation with ionizing radiation, and treatment with superheated steam have been applied to some of the dry food ingredients.

[0003] However, these techniques are not without their drawbacks. EOG fumigation is banned in certain countries due to the carcinogenic effects of the residues. Irradiation with gamma rays or electron beams can effectively inactivate bacterial spores that contaminate spices and dried vegetables with minimal quality changes, and irradiation of spices is practiced commercially in more than 20 countries. However, irradiation of foods other than potatoes is not approved in several countries. Irradiation at high doses for decontamination is not applicable to cereals such as rice and wheat because ionizing radiation leads to oxidation and deterioration of components such as lipids and starch molecules, which leads to deterioration of the aroma and texture of cereal products such as noodles and rice cakes. Irradiation also leads to chemical changes in foods, producing substances that are not known to be present in non-irradiated foods. These substances are called "radiolysis products". However, any processing leads to chemical changes in foods. For example, heat treatment or cooking produces chemicals known as "pyrolysis products", which have been found to mirror those produced by cooking.

[0004] Treatment with superheated steam is the only method widely used to decontaminate dried ingredients in Japan, but superheated steam can result in changes in the aroma and color of dried vegetables and herbs.

[0005] The recent pandemic involving COVID-19 has placed greater emphasis on eliminating airborne pathogens than was the case before the emergence of this deadly virus. As is now well established, person-to-person transmission via the dispersal of virus-laden droplets is the most common route of infection. Summary of the Invention

[0006] In accordance with the purposes of the present invention, as embodied and broadly described herein, an embodiment of a method herein for the destruction of microorganisms present on a surface of a plurality of grains or dry foods disposed in a container having a surface includes the steps of: subjecting the surface of the container to a first periodic vibrational excitation having a first amplitude effective to cause the plurality of grains or dry foods disposed in the container to be in an airborne state; and subjecting the airborne plurality of grains or dry foods to a second periodic vibrational excitation having a second amplitude effective to increase collisions therebetween, whereby the microorganisms are destroyed by collisions of the airborne grains or dry foods.

[0007] In another aspect of the invention, according to its objects, an embodiment of a method herein for the destruction of microorganisms present on a surface of a plurality of grains and dry foods includes the steps of depositing a plurality of grains or dry foods on a surface of a moving conveyor belt, subjecting the conveyor belt to a first periodic vibration excitation having a first amplitude effective to form a fluidized bed of the plurality of grains or dry foods on the surface of the conveyor belt, and subjecting the fluidized plurality of grains or dry foods to a second periodic vibration excitation having a second amplitude effective to increase collisions therebetween, whereby the microorganisms are destroyed by the collisions of the grains or dry foods.

[0008] In yet another aspect of the invention, according to its object, an embodiment of a method herein for the destruction of a plurality of pathogens attached to a plurality of airborne particles includes the steps of flowing air in a selected direction, generating a first periodic acoustic wave having a first wavelength within a volume of a first air flow, and reflecting said first periodic acoustic wave within said first air flow volume such that a first standing wave pattern of parallel nodal planes having a first selected spacing is generated, thereby generating a plurality of clusters of a plurality of airborne particles having a plurality of pathogens attached thereto, said plurality of clusters being the first airflow volume having a first periodic acoustic wave and a second periodic acoustic wave having a second wavelength; and reflecting the second periodic acoustic wave downstream of the first airflow volume to generate a second standing wave pattern of parallel nodal planes having a second selected spacing greater than the first selected spacing, thereby generating multiple collisions between the clusters of the plurality of airborne particles having a plurality of pathogens attached thereto, such that the pathogens are destroyed by the collisions of the clusters.

[0009] In yet another aspect of the invention, according to its objects, an embodiment of an apparatus herein for the destruction of microorganisms present on a surface of a plurality of grains and dry foods comprises a conveyor belt having a trough-like conveying surface on which a plurality of grains or dry foods are deposited and an underside supported by at least one set of three-roller trough idlers, each idler having an axis, at least one head pulley and at least one tail pulley, at least one of said head pulleys being powered to move said conveyor belt; a first vibration source for providing a first periodic vibration excitation to said at least one set of three-roller trough idlers having a first amplitude effective to form a fluidized bed of said plurality of grains or dry foods above the surface of said conveyor belt; and a second periodic vibration excitation source having a second amplitude for vibrating said fluidized plurality of grains or dry foods effective to increase collisions therebetween, whereby said microorganisms are destroyed by collisions of said grains or dry foods.

[0010] Benefits and advantages of the present invention include, but are not limited to, providing an apparatus and method for disrupting microorganisms, such as viruses, by using sound to cause numerous collisions between larger particles, exploiting the mechanically fragile outer membranes of the microorganisms that are attached to the larger particles. [Brief description of the drawings]

[0011] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0012] [Figure 1] 1 is a schematic side perspective view of an embodiment of an apparatus for the bulk processing of grain for the destruction of surface microorganisms. Two ultrasonic frequencies effective to induce vibrations in a container holding the grain are used. [Diagram 2]Figure 2 illustrates an embodiment of the use of the device in Figure 1 in a proof of principle: after sonication of an infected sample at a chosen frequency for a selected period of time, the grain is rinsed, the bacteria are cultured and enumerated, and the results are compared to another grain sample that has not been sonicated as a control set. [Diagram 3] FIG. 3A is a schematic cross-sectional view of an embodiment of a conveyor system for continuous processing of grain for the destruction of surface microorganisms. Rollers are placed under the belt so that as the grain is transported from one location to another, the belt maintains an open concave shape while riding on a suitable set of rollers to contain the grain. FIG. 3B is a schematic cross-sectional view of two types of eccentric rollers for generating a fluidized bed of grain or any other type of feed material. The fluidized bed is generated by vibrating the belt, causing the grain to be suspended above the bed, and a high power and higher frequency acoustic source is placed above the belt to collide the suspended grains with each other. [Figure 4] 4 is a schematic cross-sectional view of an alternative embodiment in which a cylindrical roller does not impart vibration to the belt.An alternative embodiment for imparting external vibration to a conveyor belt using an acoustic transducer. [Diagram 5] 5 is a schematic side view of an apparatus for the destruction of airborne pathogens. A plurality of small particles in the air with attached viruses are agglomerated in a rectangular first acoustic chamber having a small depth using high frequency (in the range between about 60 kHz and about 100 kHz), while a second rectangular acoustic chamber having a depth larger than that of the first rectangular acoustic chamber is vibrated at a low frequency (in the range between about 20 Hz and about 200 Hz) to collide the agglomerated particles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A. Bulk destruction of microorganisms in dry food grains

[0014] It is generally recognized that the majority of microorganisms that contaminate dry food ingredients reside on the surface of the food, so that the interior does not need to be exposed to heat, gas, or radiation for decontamination. A vibrating surface is used to vibrate the layers of grain to be decontaminated so that they collide with each other in succession, effectively forming a fluidized bed suspended in air (a fluidized bed is a physical phenomenon that occurs when any amount of solid particulate matter is placed under the right conditions to cause a solid / fluid mixture to behave as a fluid). Such collisions do not cause chemical changes in the food and therefore have no adverse effect on its taste. It was determined that a single vibration source from above was not very effective in creating such collision conditions. The effectiveness of collisions was determined by using dyed grains mixed with clean grains. The extent of the spread of color in the grains was a quick visualization of the effectiveness of the collision process, and the extent of the process. At high frequencies (between 60 kHz and 80 kHz), the upper grain material shielded the lower grains. This also occurred when the grains were irradiated with ultrasound from below. In the frequency range between 6 kHz and 15 kHz, the grain bed could be fluidized (suspended in the air) only when ultrasonicated from below, but did not exhibit circulation. In the lowest frequency range, between about 20 Hz and about 80 Hz, a fixed pattern circulation was present in the grain, but there were isolated areas with little or no grain movement. The sterilization effect was expected to be a function of the number of collisions. Thus, the low frequencies were considered unacceptably slow for practical applications. To address these concerns, a dual swept frequency system was used.

[0015] The system found to be effective employed a low frequency shaker / circulating platform and a higher frequency grain impingement section. Any vibration source may be used, including but not limited to a low frequency audio speaker employed to circulate the grain in the grain sample. Square wave electrical excitation of the audio speaker was found to be effective as it generated higher harmonics that helped to eliminate areas where no excitation occurred. Additionally, to avoid fixed patterns in the vibration or circulation of the grain, the square wave frequency was varied linearly between about 20 Hz and about 100 Hz at various rates, typically with a period of 2 seconds, and with a duty cycle of 20% to 50% (50% was used in the following examples). This frequency range was effective for the grains used, but may be varied for other grains. A medium frequency (between about 6 kHz and about 10 kHz) piezoelectric transducer was attached and positioned directly beneath the lightweight plastic grain container. Grain temperature was measured using an inserted thermocouple.

[0016] For non-invasive batch processing, the grain may be held inside the chamber so that the material remains inside the selected volume for the duration of the processing. As mentioned before, the vibration frequency may be on the order of 10 kHz. Frequency modulation or other means may be employed so that standing wave patterns are not created in the grain, since grains in the region of the nodes do not experience many collisions. However, any periodic waveform, variable or fixed frequency, may be employed with varying efficiency. Additionally, the grain must remain in airborne condition during the microbial destruction process so that grain collisions are not diminished. The temperature of the system does not need to be controlled, since any heat generated by the vibration and collisions will aid the process of microbial destruction. The temperature inside the chamber has been measured using thermocouples and found to not rise more than 4°C during grain processing. However, the temperature rise depends on the duration of excitation.

[0017] If the grains are subjected to millions of collisions, the physical impact of one grain against another is likely to destroy the microorganisms on the grain's surface. Moreover, the destruction process is accelerated in the case of grains with sharp edges.

[0018] Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the various figures, like structures are identified using the same reference characters. It is to be noted that the various figures are presented for the purpose of illustrating particular embodiments of the invention and are not intended to limit the invention thereto. Referring now to FIG. 1, shown is a schematic cross-sectional view of an embodiment of an apparatus 10 for the non-invasive bulk processing of a plurality of grains 12 for the destruction of surface microorganisms. The plurality of grains was placed in a lightweight plastic container or chamber 14 having a lid 16 and a base 18 resting on a vibrating surface 20. The vibrating surface 20 may itself be a transducer or may be driven by a transducer 22 in response to a selected signal from a periodic waveform generator 24. The signal is amplified by an amplifier 26 to a selected voltage. The transducer is used to agitate the plurality of grains 12 once suspended in air. The transducer 22 was a medium frequency (between about 6 kHz and 10 kHz) piezoelectric disc transducer rated at 100 W. The temperature of the grains was measured using an inserted thermocouple. Frequencies of a few tens of kHz, e.g. 10 kHz, have been shown to induce numerous collisions between multiple grains. For grains with smaller volume and weight, higher frequencies (up to 100 kHz) are more effective.

[0019] The vibrating surface 28 is used to circulate or agitate the grains 12 so that they are effectively suspended in air. The vibrating surface 28 may itself be a transducer or may be driven by a transducer 30 in response to a selected signal from a periodic waveform generator 32, amplified by an amplifier 34 to a selected voltage. The surface 20 rests on a rigid structure 36, which may comprise, for example, a cylindrical or conical shape, constructed of plastic or metal, resting on the surface 28. As previously mentioned, frequencies of tens of Hz have been found to generate a fluidized bed condition in the grains 12 within the vessel 14, whereby the grains are repeatedly ejected from the bottom 18 of the vessel 14, effectively suspended in air, while continually colliding with one another under the combined influence of the vibrations from the transducers 22 and 30. The signal from the periodic waveform generator 32 may be swept in frequency. In this apparatus, the vibrating surface 28 was equipped with a mid-range audio speaker (tweeter) rated at 30 W generating a displacement between about 2 mm and 5 mm to circulate the grains in the grain sample, although the invention is not limited to the audio speaker used. Square wave electrical excitation was found to be effective in eliminating fixed standing wave vibration or circulation patterns in the grains where no excitation occurred because it generated higher harmonics. Furthermore, to avoid fixed patterns in the vibration or circulation of the grains, the square wave frequency was varied linearly at various speeds between about 20 Hz and about 100 Hz with a typical period of 2 seconds and a duty cycle of 50%.

[0020] Amplifiers 26 and 34 (Pro PT-2000 units by Pyle) have a bandwidth of 80 kHz and are rated up to 350 watts. An Agilent 34970A data acquisition switch unit with a 20 channel multiplexer for the 34970A and a Type T thermocouple (not shown in FIG. 1) was used for temperature measurements.

[0021] Figure 2 illustrates an embodiment of the use of the apparatus in Figure 1 in a proof of principle. In step 38, grain is contaminated with a known amount of microorganisms, in this case bacteria, prior to placement 40 in a treatment vessel or chamber 14. After exposure to ultrasound at a selected frequency for a selected period of time 42, the grain is rinsed (44), the bacteria are cultured (46), and after incubation for a selected period of time, counted (48), and the results are compared (50) to another grain sample that has not been exposed to ultrasound, i.e., a control set. The following example illustrates an embodiment of the bulk method of the present invention.

[0022] Example 1 A layer of about 1 / 4 inch thick was formed with 4 g of wheat kernels on the bottom 18 of the container 12. A thickness of 5 to 10 layers is expected to work effectively. The kernels were then artificially contaminated with Salmonella cholerae suis (14028, Source: BD Diagnostic Systems, Inc. Trade Name: BD BBL™ QualiSwab™ Quality Control Organisms, per ITOCHU Procedure for Contamination of Grains). An identical sample was contaminated as a reference sample for comparison. The vibration frequency, amplitude, FM modulation, etc. used were not optimized, but multiple impacts of the grain on the grain were evident. One sample was then subjected to the vibration contamination method depicted in FIG. 2 for 10 minutes. The control sample was not sonicated. Following sonication, both samples were rinsed with distilled water and incubated. Each test was repeated three times, and the reported values ​​are in CFU (colony forming units). The first column shows the values ​​from the control sample and the second column shows the results of bulk grain sonication.

[0023] The applied low frequency vibration was a linearly swept square wave between 28Hz and 72Hz for 2 seconds with a displacement between 2mm and 5mm, while the higher frequency vibration was a linearly swept square wave of 15V peak-to-peak between 6kHz and 9kHz for 2 seconds, resulting in the following: TIFF2025060906000002.tif4599

[0024] Example 2 A second culture of Salmonella was prepared and a second batch of grain was infected separately.

[0025] The applied low frequency vibration was a linearly swept square wave between 37Hz and 58Hz for 2 seconds with a displacement between 2mm and 5mm, while the higher frequency vibration was a linearly swept square wave of 15V peak-to-peak between 6kHz and 9kHz for 2 seconds, resulting in the following: TIFF2025060906000003.tif4495

[0026] B. Continuous destruction of microorganisms in dry food grains

[0027] As mentioned above, bulk pathogen destruction in grain is a combination of two processes: (1) forming a fluidized bed of grain above a surface by vibrating said surface at a low frequency, and (2) then vibrating the grain at a much higher frequency so that individual grains can collide with adjacent grains. For continuous processing of significantly larger volumes of grain, a similar approach can be applied to grain transported on a trough-like conveyor belt.

[0028] A typical conveyor system is generally circular and includes a trough-like belt made of various types of rubber and polymers that is moved over rollers by motor-driven drive wheels or pulleys not shown in FIG. 3A or FIG. 4. FIG. 3A is a schematic cross-sectional view of an embodiment of a conveyor system 52. A plurality of idler rollers 54a-54c are disposed under the belt 56 so that as the grain 12 is transported by the belt 56 from one location to another, the belt 56 maintains an open, concave shape while riding on a plurality of sets of rollers 54a-54c suitable for accommodating a plurality of grains 12. The base 28 supports a series of vertical roller supports 60a, 60b, and 62a, 62b. The supports 60a and 62a hold an axle 64a on which the idler roller 54a rotates. The supports 62a and 62b hold an axle 64b on which the idler roller 54b rotates. Supports 62b and 60b carry an axle 64c on which idler roller 54c rotates.

[0029] The belt 56 is vibrated to generate a fluidized bed of grain or any other type of feed material. FIG. 3B is a schematic cross-sectional view of two types of eccentric rollers 54a-54c. The upper part of the roller surface vibrates as the roller rotates, providing a suitable vibration of the belt 56. The rollers 54 have an elliptical shape with a central cylindrical hole 66 configured to receive one of the axes 64a-64c. The surface 68 thereby moves periodically between two heights. The cylindrical roller 58, shown as having an off-center cylindrical hole 66 configured to receive one of the axes, has a similar function. Thus, when the belt 56 passes through any of these rollers, the belt vibrates, thereby causing the grains 12 to be suspended a small distance above the belt 56.

[0030] A high power and higher frequency (tens of kHz, e.g. 20 kHz) acoustic source 68 is positioned above the belt 56 and is driven by the waveform generator 24 and power amplifier 26. The waveform generator 24 determines the frequency of the high frequency source and its waveform characteristics and is controlled by the microcontroller 70. The high frequency acoustic waves collide the multiple suspended grains. There may be multiple such sources positioned along the belt 56 and at various angles so that each volume of grain 12 is treated multiple times to ensure that pathogen reduction is effective.

[0031] 4 is a schematic cross-sectional view of another embodiment for applying external vibration to a belt 56. A transducer 30, driven by an acoustic frequency source 32 via an amplifier 34 and controlled by a microcontroller 70, is attached to a fixture or surface 28 supporting a number of rollers 54a-54c. In this embodiment, the rollers 54a-54c are cylindrical with a number of axial holes 66 along their cylindrical axes. Although the acoustic transducer is shown as being attached to the surface 28, it is not limited to this location and may also be attached to the vertical roller supports 60a, 60b, and 62a, 62b. Acoustic sources having high power are commercially available and are used in the food and beverage industry. Low frequency vibration sources are also commercially available.

[0032] C. Destruction of Airborne Pathogens

[0033] In normal indoor air (e.g., class ISO 9), there are many different kinds of particles, including dust, pollen, bacteria, etc. As can be seen in the table, the most numerous particles are larger than 0.5 μm in diameter. When multiple pathogens such as bacteria or viruses are present in the air, they attach to other particles due to electrostatic charges, hydrodynamically induced attraction, van der Waals forces, and several other forces, as well as random collisions. When air is vibrated by low-frequency sound (e.g., below 20 kHz), the amplitude of the vibration is large and particles can collide with each other efficiently. Therefore, mechanical impact plays an important role in destroying (inactivating) these pathogens, due to increased collisions between particles that carry the pathogens. In many cases, viruses such as Covid-19 (which has spikes (protrusions) of 0.125 μm in length, 0.085 μm in diameter, and 0.020 μm in length) and other viruses are mechanically fragile, and the outer membrane of such viruses can be easily broken, thereby inactivating the viruses. [Table 1]

[0034] The microorganism destruction embodiments presented above can be modified and extended to destroy multiple airborne pathogens as well. In the case of multiple airborne pathogens, the step of making these objects equivalent to a fluidized bed in the air, as in the case of grains, is unnecessary because they are already free-floating. On the other hand, the size of small particles, and the size of viruses, requires a pretreatment process that causes the small particles to aggregate into small clusters, which then appear as larger particles, because the small particles are entrained in the air and therefore move with the air current.

[0035] This embodiment of the invention applies the well-known acoustic radiation force (ARF) to first move airborne particles to the standing wave node plane within the resonator chamber, which results in the formation of small clusters. The force on the particles due to the acoustic wave F is TIFF2025060906000005.tif1279, where Po is the pressure amplitude, k is the wavelength constant, λ is the wavelength, t is time, x is the local position within the transducer and reflector, Vp is the particle volume, βf is the fluid compressibility, and φ is a material constant. See, for example, K. Yoshioka and Y. Kawashima, "Acoustic Radiation Pressure on a Compressible Sphere," Acustica, Vol. 5, pp. 167-173, 1955.

[0036] If the constant φ is positive, the force pulls the particle towards the node, and if φ has the opposite sign, the force moves the particle towards the anti-node. The material constant φ is given by TIFF2025060906000006.tif1279, where β f and β p are the material compressibilities of the fluid medium (air) and the particle, respectively. See, for example, LA Cruz, "Acoustic Force on a Liquid Droplet in an Acoustic Stationary Wave," J. of the Acoustical Society of America, Vol. 50, pp. 157-163, 1971.

[0037] As can be seen from equation (1), the acoustic force is proportional to the volume of the particle, so larger particles experience more force. The main factors in acoustic particle agglomeration are the properties of the acoustic signal, i.e., acoustic frequency, acoustic intensity, and residence time. In general, higher frequencies in the ultrasonic range work better for particle agglomeration of submicron particles, while lower frequencies are effective for particles in the micron range. This is because small particles are entrained in the air at low frequencies and move with the air. These particles do not collide or follow the vibration of the acoustic wave. Although the use of high frequencies to destroy airborne pathogens seems trivial, there are two challenges to consider. First, high frequencies above 200 kHz are highly attenuated in air, so shorter distances and smaller geometries must be used for devices to induce standing waves and cause particle agglomeration. For example, the sound absorption coefficient in air at 25°C, 50% humidity, and 10kHz is 0.131dB / m compared to 17.4dB / m at 300kHz. Furthermore, for practical devices, i.e., those with a reasonable amount of airflow throughput, the residence time becomes too long. Secondly, the acoustic forces are small and collisions between small particles are not very effective. Large particles are stationary at these high frequencies and do not move from their equilibrium positions. Thus, collisions between large particles are almost nonexistent.

[0038] An effective approach is a two-step process. Figure 5 is a schematic side view of an apparatus 80 for non-invasive destruction of airborne pathogens. Air pre-treatment is achieved at high frequency (in the range between about 100 kHz and about 500 kHz) in a rectangular first acoustic chamber (20 cm x 15 cm) 82 with a depth (2 cm) 84. Air 86 is pumped into the chamber 82 at its inlet 90 using a fan 88. Acoustic waves are generated by a piezoelectric transducer 92 in vibrational communication with one side 94 of the chamber 82. The piezoelectric transducer 92 is driven by the waveform generator 24 via the amplifier 26 and controlled by the electronic circuitry 70, while the opposite side 96 acts as a reflector such that a standing wave pattern of parallel nodal planes is generated inside the chamber 82. The spacing between the nodal planes is related to the wavelength of the applied sound in air (e.g., 1 mm wavelength at 340 kHz). The dimensions of the chamber are based on the size of the transducer to be driven. A larger rectangular transducer or smaller transducers driven by the same drive signal can correspond to a larger chamber. The purpose of this RF pretreatment is to create clusters of particles that behave as larger particles. The clusters carry pathogens that are attached to the particles. During the aggregation process as the particles approach each other, there are secondary acoustic forces that promote the collision process and the bonding of the particles. The first acoustic chamber 82 is less effective at destroying or inactivating pathogens, but a certain amount of inactivation is possible depending on the pathogen.

[0039] The second rectangular acoustic chamber 98 has a greater depth 100 (up to 2.5 times as much and depending on the low frequency used and the acoustic power applied) than the first rectangular acoustic chamber 82, but has substantially the same volume as chamber 82 to keep air throughput reasonably constant. A transition member 102 connects chamber 82 and chamber 98 to reduce air turbulence. A low frequency (in the range between about 5 kHz and about 50 kHz) transducer 104 in vibrational communication with one side 106 of chamber 98 is driven by waveform generator 107 via amplifier 34 and controlled by electronic circuitry 70 to generate acoustic waves within chamber 98. The opposite side 108 acts as a reflector such that a parallel nodal plane standing wave pattern is generated inside chamber 98. The nodal planes are much further apart (e.g., 3.4 cm at 10 kHz) than in chamber 82. The configuration of chamber 98 is selected based on the desired flow rate of the device.

[0040] A programmable electronic controller 70, such as an Arduino or Raspberry Pi electronic board, may be used to control the dual output waveform generator 107. The amplitude and frequency of each channel of the dual output generator 107 is programmable. Thus, both the high and low frequency output signals of the device 80 are provided by the waveform generator 107 through respective power amplifiers 26 and 34 (one per channel to drive respective converters 92 and 104).

[0041] The vibration frequency applied to the two chambers is adjusted so that small clusters more efficiently aggregate to form larger particles as a result of the larger acoustic force in chamber 82. Chamber 98 is where a large number of interparticle collisions take place, because particles tend to accumulate in fewer nodal planes after moving from their original positions. In chamber 98, particles vibrate due to the applied acoustic waves and collide with their nearest neighbors. For example, at 10 kHz, particles collide nearly 10,000 times per second. To improve pathogen inactivation, the length of chamber 98 (pathogen treatment length) can be increased as needed, because the length of the chamber determines the retention, which is dependent on the flow rate.

[0042] Chambers 82 and 98, and transition member 102 may comprise metals such as steel, brass, or copper, by way of example. Transducers 92 and 104 may comprise piezoelectric transducers, although any transducer that generates effective vibrations in the required frequency range may be used. The transducers are typically epoxied to the exterior surface of the chamber, vibrating a majority of the chamber walls beyond the transducer's surface area. Although transducers 92 and 104 are shown as single transducers, multiple transducers may be used to address larger surface areas, if desired.

[0043] It is well known that heat destroys most airborne pathogens, including various types of influenza viruses. The temperature of air 86 may be increased by attaching an electric heater 110 controlled by a temperature controller 112 to the exterior of one or both of chambers 82 and 99. Air 114 exiting pathogen treatment device 80 may be filtered by a filter 116 effective to remove particles larger than 5 μm. HEPA type filters are not utilized because that type of filtration significantly reduces flow rate.

[0044] The foregoing description of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously, many modifications and variations are possible in light of the above teachings. The present embodiments have been chosen and described to best explain the principles of the invention and its practical application, and thereby enable those skilled in the art to best utilize the invention in various embodiments and with various modifications as suited to the particular uses envisioned. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims

1. 1. A method for the destruction of microorganisms present on the surfaces of a plurality of grains or dry foods disposed in a container having a surface, comprising: applying a first periodic vibrational excitation to the surface of the container having a first amplitude effective to cause the plurality of grains or dry foods disposed within the container to become airborne; subjecting the suspended plurality of grains or dry foods to a second periodic vibrational excitation having a second amplitude effective to increase collisions therebetween with respect to the surface of the container; Equipped with A method whereby said microorganisms are destroyed by impact of said grains or dry foods which are kept in air suspension.

2. The method of claim 1 , wherein the first periodic vibration excitation comprises a fixed frequency vibration excitation.

3. The method of claim 1 , wherein the first periodic vibration excitation comprises a swept frequency vibration excitation.

4. The method of claim 3 , wherein the first periodic vibration excitation comprises a square wave.

5. The method of claim 4 , wherein the square wave is swept in frequency between 10 Hz and 100 Hz.

6. The method of claim 1 , wherein the second periodic vibration excitation comprises a fixed frequency vibration excitation.

7. The method of claim 1 , wherein the second periodic vibration excitation comprises a swept frequency vibration excitation.

8. The method of claim 7 , wherein the second periodic vibration excitation comprises a square wave.

9. The method of claim 8 , wherein the square wave is swept in frequency between 5 kHz and 100 kHz.

10. The method of claim 1 further comprising the step of measuring air temperature during the step of providing the second periodic vibration excitation.

11. 1. A method for the destruction of microorganisms present on the surfaces of a plurality of grains and dry foods, comprising: depositing a plurality of grains or dry foods onto a surface of a moving conveyor belt; subjecting the conveyor belt to a first periodic vibratory excitation having a first amplitude effective to form a fluidized bed of the plurality of grains or dry food products on a surface of the conveyor belt; subjecting the fluidized plurality of grains or dry food products to a second periodic vibrational excitation having a second amplitude effective to increase collisions therebetween. Equipped with A method whereby said microorganisms are destroyed by impaction of said grain or dry food.

12. The method of claim 11 , wherein the first periodic vibration excitation comprises a fixed frequency vibration excitation.

13. The method of claim 11 , wherein the first periodic vibration excitation comprises a swept frequency vibration excitation.

14. The method of claim 13 , wherein the first periodic vibration excitation comprises a square wave.

15. The method of claim 14 , wherein the square wave is swept in frequency between 10 Hz and 100 Hz.

16. The method of claim 11 , wherein the second periodic vibrational excitation comprises a fixed frequency vibrational excitation.

17. The method of claim 11 , wherein the second periodic vibration excitation comprises a swept frequency vibration excitation.

18. The method of claim 17 , wherein the second periodic vibration excitation comprises a square wave.

19. 20. The method of claim 18, wherein the square wave is swept in frequency between 5 kHz and 100 kHz.

20. The method of claim 11 further comprising the step of measuring air temperature during the step of providing the second periodic vibration excitation.

21. 1. A method for the destruction of a plurality of pathogens attached to a plurality of airborne particles, comprising: directing air in a selected direction; generating a first periodic acoustic wave having a first wavelength within a volume of a first air flow; reflecting the first periodic acoustic wave within the first airflow volume to generate a first standing wave pattern of parallel nodal planes having a first selected spacing, thereby generating a plurality of clusters of airborne particles having a plurality of pathogens attached thereto, the plurality of clusters moving through the flowing air; generating second periodic acoustic waves having a second wavelength within the second air flow volume; reflecting the second periodic acoustic wave downstream of the first airflow volume such that a second standing wave pattern of parallel nodal planes having a second selected spacing greater than the first selected spacing is generated, thereby causing multiple collisions between the clusters of the plurality of airborne particles having a plurality of pathogens attached thereto; such that the plurality of pathogens are destroyed by collision of the plurality of clusters; The process of generating A method for providing the above.

22. 22. The method of claim 21, wherein the first periodic acoustic wave has a frequency between about 100 kHz and about 500 kHz.

23. 22. The method of claim 21, wherein the second periodic acoustic wave has a frequency between about 5 kHz and about 50 kHz.

24. 22. The method of claim 21, further comprising the step of filtering the air subsequent to generating the second periodic acoustic waves in the air.

25. 22. The method of claim 21, further comprising the step of heating the air prior to generating the first periodic acoustic waves in the air.

26. 1. An apparatus for the destruction of microorganisms present on the surfaces of a plurality of grains and dry foods, comprising: a conveyor belt having a trough-like conveying surface on which a plurality of grains or dry foods are deposited and an underside supported by at least one set of three-roller trough idlers, each idler having a shaft, at least one head pulley and at least one tail pulley, at least one of said head pulleys being powered to move said conveyor belt; a first vibration source for providing a first periodic vibration excitation to the at least one set of three-roller trough idlers having a first amplitude effective to form a fluidized bed of the plurality of grains or dry food products above a surface of the conveyor belt; a second periodic vibration excitation source having a second amplitude for vibrating the fluidized plurality of grains or dry foods effective to increase collisions therebetween; and whereby said microorganisms are destroyed by impaction of said grain or dry food.

27. 27. The apparatus of claim 26, wherein the first vibration source comprises a vibration transducer powered by a frequency source driving a power amplifier configured to vibrate the at least one set of three-roller trough idlers.

28. 27. The apparatus of claim 26, wherein the first vibration source comprises an eccentric roller or off-center shaft for each roller within the at least one set of three-roller trough idlers.

29. 28. The apparatus of claim 27, wherein the first periodic vibrational excitation comprises a fixed frequency vibrational excitation.

30. 28. The apparatus of claim 27, wherein the first periodic vibration excitation comprises a swept frequency vibration excitation.

31. 31. The apparatus of claim 30, wherein the first periodic vibration excitation comprises a square wave.

32. 32. The apparatus of claim 31 , wherein the square wave is swept in frequency between 10 Hz and 100 Hz.

33. 27. The apparatus of claim 26, wherein the second periodic vibrational excitation comprises a fixed frequency vibrational excitation.

34. 27. The apparatus of claim 26, wherein the second periodic vibration excitation comprises a swept frequency vibration excitation.

35. 35. The apparatus of claim 34, wherein the second periodic vibration excitation comprises a square wave.

36. 36. The apparatus of claim 35, wherein the square wave is swept in frequency between 5 kHz and 100 kHz.

37. 27. The apparatus of claim 26, further comprising a temperature measurement device for measuring air temperature above the surface of the conveyor belt.

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