Continuous process for the partial sterilization of mushroom casing

• US 4,978,501 A
• Filed: 12/21/1988
• Issued: 12/18/1990
• Est. Priority Date: 09/26/1984
• Status: Expired due to Fees

• Current Assignee: The Minister Of Agriculture Fisheries and Food
• Original Assignee: The Minister Of Agriculture Fisheries and Food
• Inventors: Evans, Geoffrey H., Diprose, Michael F.
• Primary Examiner(s): Warden, Robert J.
• Assistant Examiner(s): Santiago, Amalia
• Application Number:
  US07/287,654
• Time in Patent Office: 727 Days
• Field of Search: 422/22, 422/186.29, 422/186.01, 422/32, 422/23, 422/186.04-186.06, 422/186.2, 219/388
• US Class Current: 422/22
• CPC Class Codes: A01G 18/20 Culture media, e.g. compost
• CPC Class Codes: A01G 18/30 Accessories for use before inoculation of spawn, e.g. sterilisers
• CPC Class Codes: A01M 21/046 by electricity
• CPC Class Codes: A61L 2/12 Microwaves

Abstract

A process and apparatus are provided for the sterilization of horticultural material, which may be substrate, fertilizer, peat or especially mushroom casing. The sterilization may be complete or may be partial, removing only harmful organisms while leaving beneficial organisms unharmed. The horticultural material is passed through a tunnel and is exposed to radiofrequency electromagnetic waves for a period sufficient for sterilization. In a preferred process and apparatus the horticultural material is heated to a suitable temperature by the waves and is then maintained in a region not exposed to the waves for a period long enough to sterilize the material, before allowing it to cool to ambient temperature.

Claims

1. Apparatus for at least partially sterilizing wet horticultural material comprising:

an open ended tunnel having a channel extending therethrough, said tunnel defined by steam tight walls, constructed of low loss dielectric material in at least a central portion of said tunnel;

radio frequency wave electromagnetic applicator means positioned at least on opposite sides of said central portion of said tunnel for heating wet horticultural material passing through said tunnel to a predetermined temperature in the range of about 90°

-100°

C., said tunnel having no other heat generating means associated therewith, and wherein said radio frequency wave applicator means is capable of emitting RF radiation at a frequency of 13 to 100 MHz, and of applying an RF power density of up to 90 KW m^-2 ;

means for continuously passing the wet horticultural material through said tunnel at a speed such that the material is exposed to the heating effect of the radio frequency waves when applied by the applicators for a period of 1-2 minutes, said tunnel being provided with a first extended region immediately adjacent and upstream of said radio frequency wave applicator means adapted to expose incoming material when in the said first extended region to steam given off from the heated material,

and said tunnel being provided with a second extended region immediately adjacent and downstream of said radio frequency applicator means and wherein the said downstream extended region includes insulation means for maintaining the wet horticultural material at substantially said predetermined temperature and exposes outgoing material to steam given off from said heated material.

2. A sterilizer according to claim 1 wherein said first extended region has a length of about 0.5 to 1.0 meter.

3. A sterilizer according to claim 1 wherein said second extended region has a length of at least about 0.5 meter.

4. A sterilizer according to claim 1 wherein the said means to continuously pass material through said tunnel comprise a conveyor belt passing through and along the length of the tunnel.

5. Apparatus according to claim 1 wherein said radio frequency wave applicator means is capable of applying an RF power density of up to 60 KWm^-2.

6. Apparatus according to claim 1 wherein said radio frequency wave applicator means comprises a pair of parallel radiating plates.

7. Apparatus according to claim 1 wherein said tunnel is substantially rectangular in shape with a cross-sectional dimension of about 30×

10 cm².

8. Apparatus according to claim 1 wherein said radio frequency wave applicator means comprises a 20 KW, 27 MHz generator.

9. A process for at least partially sterilizing wet horticultural material comprising the steps of:

(a) providing an open ended tunnel having radio frequency wave applicator means positioned at least above and below a central portion of the tunnel, said tunnel being defined by steam tight walls constructed of low loss dielectric material in at least a central portion of said tunnel;

(b) continuously passing wet horticultural material through said tunnel; and

(c) exposing at least a part of said wet horticultural material to radio frequency waves in a frequency range of 13 to 100 MHz and at a power density of up to 90 KWm^-2 for a period of 1-2 minutes to heat said material to a predetermined temperature of 90°

-100°

C., and thereafter to the heat generated by said waves for a period of time in the range of about 30 seconds to about 20 minutes sufficient to destroy fungi and invertebrate pests, and further wherein as a result of heating said wet horticultural temperature to said predetermined temperature, steam is generated;

the process including the further step of;

(d) utilizing said steam upstream of said radio frequency wave applicator means to preheat the wet horticultural material, and downstream of said radio frequency wave applicator means to maintain the wet horticultural material at a temperature within about 10°

to 15°

C. of said predetermined temperature without utilization of additional heating means.

10. A process according to claim 9 wherein said horticultural material comprises fertilizer.

11. A process according to claim 9 wherein said horticultural material comprises peat.

12. A process according to claim 9 wherein said horticultural material comprises mushroom casings.

13. A process according to claim 9 and including the further step of cooling said wet horticultural material immediately after step (d).

14. A process for partially sterilizing wet mushroom casing material comprising the steps of:

(a) providing an open ended tunnel having radio frequency wave applicator means positioned at least above and below a central portion of the tunnel, said tunnel being defined by steam tight walls constructed of low loss dielectric material in at least a central portion of said tunnel;

(b) continuously passing wet mushroom casing material through said tunnel; and

(c) exposing at least a part of said wet mushroom casing material to radio frequency waves in a frequency range of 13 to 100 MHz for a period of 1-2 minutes to heat said material to a temperature of 90°

to 100°

C., and thereafter to the heat generated by said waves for a period of time in the range of about 30 seconds to about 20 minutes sufficient to destroy fungi and invertebrate pests and wherein as a result of heating said wet mushroom casing to said predetermined temperature, steam is generated;

the process including the further step of;

(d) utilizing said steam upstream of said radio frequency wave applicator means to preheat the wet mushroom casing and downstream of said radio frequency wave applicator means to maintain the wet mushroom casing at a temperature within about 10°

to 15°

C. of said predetermined temperature without utilization of additional heating means.

15. A process according to claim 14 and including the further step of cooling said mushroom casing immediately after step (d).