WO2015085365A1

WO2015085365A1 - Apparatus and method for producing a plant growth medium

Info

Publication number: WO2015085365A1
Application number: PCT/AU2014/050411
Authority: WO
Inventors: Paul Power
Original assignee: Foxworth Pty Ltd
Priority date: 2013-12-11
Filing date: 2014-12-10
Publication date: 2015-06-18

Abstract

An apparatus for manufacture of organic plant growth media from a starting material comprises; a conveyor comprising a screw auger rotatably housed in an inclined tubular body having an inlet port located at a lower end and an outlet port at an upper end, wherein the screw augur in use conveys the starting material along the inclined tubular body; and a dewatering station which receives treated material from the outlet port, comprising one or two screw augurs which, in use, facilitate at least partial dewatering of the treated material. Alternatively, the dewatering station comprises at least one piston or ram, which in use facilitates at least partial dewatering of the treated material. The apparatus may further comprise a sediment tank. The organic plant growth medium may be a potting mix, orchid mix, bulb mix, hanging basket mix, peat alternative and/or seedling propagation mix.

Description

TITLE

"APPARATUS AND METHOD FOR PRODUCING A PLANT GROWTH

MEDIUM"

FIELD OF THE INVENTION THIS INVENTION relates to an apparatus for the production of plant growth media using starting materials primarily of plant origin.

BACKGROUND OF THE INVENTION

There is a large demand for plant growth media such as potting mixes, orchid mixes, bulb mixes, hanging basket mixes and seedling propagation mixes.

It is known to use plant materials such as sawmill waste in the manufacture of plant growth media. Accordingly, apparatus have been designed which automatically convey the plant material through a treatment stage, such as including at least partial submersion of the plant material in water at elevated pH, temperature and pressure, after which the treated plant material i dewaiered prior to storage in mulching heaps or windrows where bacterial fermentation can assist the mulching process.

However, apparatus such as described above can be subject to clogging, particularly when treated plant material is transferred from the treatment stage to the dewatering stage. Also, it is often not possible to control the extent of dewatering in such apparatus, in which oase it can be difficult to achieve a desired moisture content for the treated material. SUMMARY OF THE INVENTION

It is therefore an object of the invention to address one or more of the deficiencies of the prior art or at least provide a commercially useful alternative.

In a broad form, the invention provides an apparatus for manufacture of organic plant growth media from a starting material, said apparatus comprising a dewatering station which receives treated material from a conveyor, said dewatering station comprising at least one dewatering device which, in use, facilitates at least partial dewatering of said treated material.

In one embodiment, the dewatering device is, or comprises, at least one screw augur.

In another embodiment, the dewatering device is, or comprises, at least one ram or piston, preferably at least one hydraulic ram or piston or alternatively a ram or piston driven by a connecting rod.

In one aspect, the invention provides an apparatus for manufacture of organic plant growth media from a starting material, said apparatus comprising:- a conveyor comprising a screw auger rotatably housed in an inclined tubuiar body having an inlet port located at a lower end of said tubular body and an outlet port at an upper end of said tubular body, said screw augur in use conveying the starting material along said inclined tubular body; and a dewatering station which receives treated material from said outlet port, said dewatering station comprising at least one screw augur which, in use, facilitates at least partial dewatering of said treated material.

Preferably, the dewatering station comprises a dewatering tube, within which dewatering tube is at least partly located the at least one screw augur. The at least one screw augur is operable to convey treated material from an inlet of the dewatering tube to an outlet of the dewatering tube. Suitably, in use at least partly dewatered, treated material exits the dewatering station via the outlet.

The dewatering tube may further comprise a drain whereby fluid exits the dewatering station. Typically, the drain is located between the inlet and the outlet of the dewatering tube. The outlet may be fluidicaily connected to a vessel, whereby fluid exiting the drain of the dewatering station may be collected in the vessel for subsequent treatment.

In one embodiment, the at least one screw augur of the dewatering station comprises respective, helical screws. Suitably, the respective helical screws are spaced apart on a common, rotatable shaft. The spacing between the helical screws facilitates compression of the treated starting material in the dewatering station, thereby enhancing the ability of the dewatering station to extract fluid from the treated material.

In certain embodiments, the first and/or second helical screws may be releasably connectable to the common, rotatable shaft, to thereby allow adjustment of the spacing between the first and/or second helical screws. Preferably, the second helical screw is releasably mountable to the common, rotatable shaft. This may be achieved by releasably connecting the second helical screw to the common, rotatable shaft via a sleeve.

In a particular embodiment, the first helical screw is located approximately or substantially adjacent to, or in the proximity of, the drain. In another particular embodiment, the second helical screw is located approximately or substantially adjacent to, or in the proximity of, the outlet.

Preferably, the at least one screw augur is operatively connected to a variable speed motor.

in an alternative embodiment, the first and second helical screws are of respective, separate screw augurs. Typically, the separate screw augurs are operatively coupled to respective motors that independently drive rotation of the separate screw augurs. Preferably, the respective motors are variable speed motors.

In another aspect, the invention provides an apparatus for manufacture of organic plant growth media from a starting material, said apparatus comprising:- a conveyor comprising a screw auger rotatably housed in an inclined tubular body having an inlet port located at a lower end of said tubular body and an outlet port at an upper end of said tubular body, said screw augur in use conveying the starting material along said inclined tubular body; and a dewatering station which receives treated material from said outlet pott, said dewatering station comprising at least one ram or piston, which in use, facilitates at least partial dewatering of said treated materia!.

Suitably, the dewatering station is oriented substantially perpendicula to a longitudinal axis of the conveyor. Preferably, the dewatering station is operably connected to the conveyor by way of a collar which connects the outlet port of the conveyor to an inlet of the dewatering station.

Preferably, the dewatering station comprises a dewatering tube, within which dewatering tube is at least partly located the at least one ram. The at least one ram is operable to convey treated material from an inlet of the dewatering tube to an outlet of the dewatering tube. Typically, the ram comprises a ram member which is slidably located within the dewatering tube. Preferably, the at least one ram is a hydraulic ram.

The dewatering tube may further comprise a drain whereby fluid exits the dewatering station. Typically, the drain is located between the Inlet and the outlet of the dewatering tube. Suitably, in use at least partly dewatered, treated material exits the dewatering station via the outlet. The outlet may be fiuidically connected to a vessel, whereby fluid exiting the drain of the dewatering station may be collected in the vessel for subsequent treatment. In one embodiment, the vessel is a sediment tank.

Suitably, according to the aforementioned aspects, the dewatering tube is inclined, preferably at an angle of about 30° to horizontal. Preferably, the drain is located at a lower end of the dewatering tube. Accordingly, this facilitates flow of fluid under gravity towards the drain.

Preferably, the screw augur housed in the inclined tubular body of the conveyor is capable of submerging said starting material in said body of heated water for a predetermined period of time to produce a treated a starting material whilst transporting said treated a starting material towards the outlet port of said housing.

In a particular embodiment, the screw augur comprises a helical screw that terminates before the outlet port of the inclined tubular body. In use, this creates "back pressure" within the inclined tubular body because of the accumulation of treated a starting material between the end of the augur and the outlet port and backflow of the fluid in the conveyor, This "back pressure" facilitates fluid permeation through the starting material and allows some initial dewatering of the treated material before reaching the dewatering station.

Suitably, said inlet port comprises an upright tubular member in fluid communication with the lower end of said tubular body.

Preferably, said inlet port, in use, is able to accommodate a portion of the body of water located within said conveyor. Typically, an upper surface of said portion is located above a feed end of said screw auger, This effectivefy forms a liquid seal between said inlet port and a bore of said tubular body.

The inlet port may include a screw augur to assist in conveying a starting material to the screw auger rotatably housed in the inclined tubular body.

The apparatus may be operated at ambient temperature or may be operated at an elevated temperature. Accordingly, the apparatus may further comprise a heating device for heating said body of water. Suitably, said heating device is capable of heating said body of water to a temperature in the range 20° to 125°C. Preferably said body of water is heated to a temperature in the range 50° to 110°C or more preferably about 70^ΰΟ, which is a temperature at which beneficial micro-organisms may survive. Said heating device may be located adjacent said lower end of said tubular body. The heating device may be a heat exchanger throug which a heated fluid (e,g water) is circulated or it may comprise one or more electrical heating elements. In other embodiments, said heating device comprises a steam generator fluidically coupled adjacent a lower end of said tubular body.

The starting material may comprise organic and/or inorganic material, tn some embodiments the starting material is a waste materia!. Organic material may be of plant and/or animal origin. The starting material may include sawmill waste that comprises sawdust, bark and/or woodchips alone or mixed with other materials such as peat, spent mushroom compost, animal manure (e.g. chicken, cow, pig, horse, sheep, fish), sewerage sludge, waste vegetables or vegetable scraps, meat or bone meal of animal origin or the like or selected combinations thereof.

in some embodiments, the starting material may comprise particulate pine bark having a layer of exogenous bark adhering to endogenous bark. It may be advantageous to at least partially separate said endogenous bark and said exogenous bark during treatment in the apparatus. At least partial separation of said exogenous bark and said endogenous bark may be effected in said apparatus by the application of mechanical force to said particulate pine bark in said conveyor and/or in said dewatering station. For example, exogenous bark and endogenous bark may be subjected to mechanical shear under pressure to loosen fibrous bonds in said particulate pine bark to enhance moisture retention therein.

The starting material may be comminuted to a particle size where substantially all the comminuted starting material passes through a 12mm screen.

In some embodiments, the body of water may comprise a chemical treatment composition selected from a pH modifier, plant nutrients, inorganic salts, pesticides, micrabicides, parasiticides, fungicides or the like. Suitably, the body of water comprises an alkaline pH modifier. In some embodiments, the body of water comprises ferrous sulphate. These chemical treatments may be formed as a "premix" with the starting material or may be added to the starting material at the beginning of, or during treatment.

The pH of the water may preferably be about pH 5 to ?, or more preferably about pH 5.5-6.8. Relatively acidic conditions may be used to produce an organic plant growth medium for certain plants that enjoy such acidic conditions.

Another aspect of the invention provides a method for producing an organic plant growth medium including the step of treatring a starting material in the apparatus of the previous aspects.

Typically, the method is performed at above atmospheric pressure.

A further aspect of the invention priovides an organic plant growth medium produced according to the method of the previous aspect.

In some embodiments, the organic plant growth medium is a potting mix, orchid mix, bulb mix, hanging basket mix, peat alternative and/or seedling propagation mix.

Throughout this specification unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood and put into practical effect, reference will now be made to preferred embodiments described with reference to the accompanying drawings In which

FIG, 1 illustrates schematically a side elevation view of a treatment apparatus;

FIG, 2 illustrates an embodiment of dewatering station of the treatment apparatus of FIG. 1 , the dewatering station comprising first and second screw augurs;

FIG. 3 illustrates an embodiment of dewatering station of the treatment apparatus of FIG, 1 , the dewatering statio comprising a ram or piston; and

FIG. 4 illustrates extension tubes connected to a dewatering tube of a dewatering station.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows apparatus 100 comprising central conveyor 10 having substantially tubular housing 11 defining interior 12 in which is located screw auger 13 that comprises helical flyte 14 located on shaft 5 which is operatively coupled to variable-speed motor 16 that drives rotation of screw augur 13. Centra! conveyor 10 is inclined relative to horizontal, comprising lower end 17 and upper end 18. Adjacent lower end 17 of central conveyor 10 is inlet port 20 having substantially tubular housing 21 defining interior 22 in which is located screw auger 23 that comprises helical flyte 24 located on shaft 25 which is operatively coupled to variable-speed motor 26 that drives rotation of screw augur 23. Inlet port 20 is substantially upright and comprises lower end 27 and upper end 28. Upper end 28 of inlet port 20 comprises feed inlet 29 into which starting material is fed, such as by belt conveyor 200. Lower end 27 of inlet port 20 is connected to lower end 17 of centra! conveyor 10, whereby respective interiors 12 and 22 form an essentially continuous space through which starting material can be conveyed from inlet 20 to centra! conveyor 10.

Central conveyor 10 and inlet port 20 are partly filled with water 50 to the level 51 indicated in FIG. 1. Water 50 is in fluid communication with interior 12 of central conveyor 10 via apertures 19 and in inlet port 20 via apertures 29. Screw augur 13 terminates above water level 51 in or near upper end 18 of central conveyor 10. Water level 51 is maintained within apparatus 10 by a float valve or the like coupled to a source of pressurized water.

A the terminus of upper end 18 of central conveyor 10 is collar 30 connected to dewatering station 40. Collar 30 comprises wall 31 and interior 32. As best seen in FIG.2, dewatering station 40 comprises dewatering tube 41 having interior 42 in which is located screw augur 43 having shaft 44 and respective helical flytes 45, 46 which are spaced apart, the function of which will be discussed in more detail hereinafter. Shaft 44 is operatively coupled to variable-speed motor 47 which drives rotation of screw augur 43. Interior 11 of conveyor 10 is in communication with interior 42 of dewatering station 40 by way of interior 32 of collar 30. Dewatering station 40 is oriented perpendicular to the longitudinal axis of central conveyor 10 and inclined at about 30° relative to horizontal, Dewatering station 40 sits below central conveyor 10 to enable gravity feed of treated material from interior 11 of central conveyor 10 via interior 32 of collar 30. Lower end 411 of dewatering station 40 comprises drain 48 in dewatering tube 41 and upper end 4 2 of dewatering station 40 comprises outlet 49 in dewatering tube 41.

Referring again to FIGS 1 and 2 and also FIG. 3, apparatus 100 further comprises sediment tank 60 which is located below dewatering station 40 in a position which enables sediment tank 60 to collect fluid from dewatering station 40. Sediment tank 60 also acts as a support for dewatering station 40 and conveyor 20, by way of concave upper surface 63. Steam or super-heated steam is supplied to inlet port 20, central conveyor 10 and sediment tank 60 byway of pipe 70 which is fluid icaUy connected thereto by way of valves 71 , 72 and 73, respectively.

Water 50 in central conveyor housing 11 and inlet port housing 21 is heated to boiling by introducing steam via pipe 70 below water level 51. Because of th head of water (between 2 to 3 metres) in apparatus 100, temperature of about 70" or above (e.g u to about 100-1 0°C) can be maintained in water 50 inside central conveyor housing 1 1 and inlet port housing 21. In some embodiments, the starting material comprises sawmill waste of predominantly bark having an exogenous layer adhering to an endogenous sapwood layer together with varying quantities of other material. Because the bark portion of coniferous barks is quite acid due to a high level of phenolic compounds (tannins) it is desirable to partially neutralize these surface tannins as many plants are sensitive to excessively acid growth media.

Starting material is conveyed to feed inlet 29 by belt conveyor 200 and additives such as dolomite or lime in a powdered form is added to produce a treated material having a pH in the range of 5.8 to 6.5 to meet AS 3743- 96 requirements, although it is preferred to maintain pH in the range 6.2 to 6,4 for the sake of product consistency, except where a more acidic piant growth medium is required. Plant nutrents containing nitrogen, phosphorus and potassium compounds, minerals and trace elements may also be added in a liquid, slurry or dry powder form. If required, a colorant may also be added. At this point, ferrous sulphate may also be added. Ferrous sulphate may provide a source of iron for plants and may also assist creating a darkened product which is of asthetic value. The starting material and additives may be formed as a "premix" which is added to feed iniet 29 or may be added separately to feed inlet 29.

Due to the buoyancy of the starting material, screw auger 22 is necessary to urge the starting material below water level 51 in inlet port 20 and into central conveyor 10 in the proximity of screw auger 13. Screw auger 13 rotates at a speed sufficient to give a submerged residence time of from 5 to 20 minutes for the starting material while transported below water level 51 in central conveyor 10. Suitably, the respective rotational speeds of screw augur 13 and screw augur 23 are independently variable through being coupled to respective, variable speed motors 16 and 26. This enables control of the rate at which starting materials are fed from inlet port 20 into centra lconveyor 10 and also the period of submersion of the starting material below water level 51 inside inlet port 20 and/or central conveyor 10. Starting material moves through inlet port 20 and central conveyor 10 in the directions indicated by the arrows.

Helical flyte 14 of screw augur 13 terminates in upper end 18 of housing 11 before collar 30. This causes some compaction of treated material emerging from upper end 8 of central conveyor 10 and thereby provides some initial dewatering of the treated material, wherein fluid from the treated material can drain from upper end 18 of central conveyor 0 back into water 50.

In the embodiment shown in FIG. 1 , at the terminus of upper end 18 of central conveyor 10 prior to dewatering station 40, super-heated air injection valve^' 74 may foe provided. This provides a source of steam or hot air direct from a furnace, boiler or other heat production unit {now shown) in fluid communication with valve 74. At this stage the treated material, typically comprising plant material, has been thoroughly saturated, which is an optimal point for delivery of steam or hot air, which has the effect of swelling the plant material such as by opening the pores of the plant material, so that the plant material will adopt the physical properties of a superior growing media by ensuring a superior air water ratio . Because the pores of the plant material have been opened, the aqueous alkaline nutrient- containing solution is forced deep within the plant material, especially during the dewatering process, thereby ensuring superior physical and chemical properties.

Treated material then moves from central conveyor 10 through interior 32 of collar 30 and then into and through interior 41 of dewatering station 40 in the direction indicated by the arrow. Rotation of screw augur 43 is driven by variable-speed motor 47, Helical flytes 45, 46 are spaced apart on shaft 44 so that rotatio of helical flyte 46 urges treated material towards helical flyte 46, but the spacing between helical flytes 45, 46 results in a slowing of movement of the treated material which is compressed betwee helical flytes 45, 46, thereby enhancing fluid extraction (i.e dewatering) from the treated material. Oewatered, treated material 150 is then urged by helical flyte 46 through outlet 49, A desired level of dewatering can be achieved by controlling the rate of rotation of screw augur 43 driven by variable-speed motor 47 and/or by adjusting the spacing beteen helical flytes 45 , 46 , Either or both helical flytes 45, 46 may be releasably mounted to shaft 44 (suc as b a sleeve) to facilitate adjusting the spacing beteen helical flytes 45, 46. The rate of dewatering can also be modified by adjusting the angle to horizontal of dewatering station 40, whereby an increased angle causes greater back-pressure. A preferred angle is about 30° to horizontal . The end edges and faces of flytes 45, 46 may be hardened to facilitate gouging, shearing and/or tearing of the dewatered material.

It will be appreciated that by providing spaced apart helical flytes 45, 46 to create a "dual augur" dewaterin station 40, control of moisture retention is far more readily achieved than with a single augur or ffyte as the rotation speed of the single augurorflyte is the only determinant of treatment time. In order to overcome compaction and expel dewatered material at a suitable rate, the rotation speed of the single augur is typically greater than the optimal speed to properly dewater the treated material.

Dewatering station 40 further comprises drain 48 at lower end 41 1 of dewatering tube 41 to enable fluid to exit dewatering station 40 and be collected in sediment tank 60. The inclined angle of dewatering tube 41 facilitates exit of fluid from dewatering station 40. Alternatively, a pipe or other conduit may fiutdfcaHy connect drain 48 and sediment tank 60.

In an alternative embodiment shown in FIG. 3, dewatering station 40 may comprise ram or piston 80 comprising shaft 81 and head 82 inside dewatering tube 41 which urges treated material towards outlet 49. In this embodiment, central conveyor 10 and inlet port 20 are essentially as hereinbefore described. A desired level of dewatering can be achieved by controlling the speed of movement of ram or piston 80 along dewatering tube 41 in the direction indicated by the solid arrow. Typically, ram or piston 80 is hyadraulicaily driven. Suitably, in this embodiment outlet 49 is in the form of a substantially open end of dewatering tube 41 , as the treated material is significantly compressed by the ram or piston 80 and will not readily break apart and fall through an outlet 49 such as shown in FIG. 2.

The dewatering process can be further assisted by providing one or more perforations 48B in dewatering tube 41 {in addition to perforations 48A) following the point at which ram or piston 80 i fully extended (i.e distal to head 82 at its limit of travel). Water and sludge exiting perforatiions 48B can be collected in casing 90 directed towards sediment tank 60 by way of conduit 91. To further assist dewatering, piston head 82 may also comprise on or more perforations (not shown).

In another embodiment, ram or piston 80 may alternatively be driven by a crankshaft conrod-type drive mechanism (not shown).

Generally, it will be appreciated that an advantage of ram or piston 80

(compared to screw augur 43 shown in FIG. 2) is that considerably greater egress of treated material 150 can be achieved by using ram or piston 80 in dewatering tube 41.

Referring to FIG. 4, it will also be appreciated that a desired level of dewatering may achieved by varying the length of dewatering tube 41 prior to outlet 49, as an increased length and/or taper increases back pressure. This increased length may be achieved by fastening one or more additional short tube lengths 92 to dewatering tube 41. These short tube lengths 92 can be attached using a quick release bracket fastener or by a collar 93 and bolts 94A, B. In one embodiment, short tube length 92A is non-tapered. Another embodiment may comprise one or more tapered or reduced diameter short tube lengths 92B to further create extra back-pressure.

As shown in FIGS. 2 and 3, sediment tank 60 may comprise internal, sloped surface 65 to facilitate collection of sludge 300 in sediment tank 60. Pump 61 is connected to pipe 62 which can transfer fluid from sediment tank 60 back into inlet port 20. Sludge pump 61 is connected to pipe 62 which can transfer fluid from sediment tank 60 back into inlet port 20 by way of sludge augur 64. Fluid 400 and sludge 300 from sediment tank 60 may therefore be recycled back into apparatus 10. With this in mind, chemical additives such as previously described may be added to sediment tank 60 to replenish any depleted chemicals. Optionally, sediment tank 60 may be heated so that fluid and/or sludge recycled back into apparatus 10 may be at an appropriate temperature. Sediment tank 60 enables returning the fluid and/or sludge to re-enter the treatment process, thereby ensuring the consistency of the end product. This is an important factor when judging the quality of plant growth media. Because there are reduced or insignificant waste residues from the process there is no wastage of energy and resources. This has the effect of a very environmentally friendly and cost effective process. Furthermore, the fluid and/or sludge returned to the process are at high temperature, the treatment process achieves far greater energy efficiency, having captured and retained the heat contained in the fluid and/or sludge.

Referring again to FIGS. 2 and 3, dewatered, treated material 150 exits dewatering station 40 via outlet 49 in upper end 412 of dewatehng tube 41. Dewatered, treated material 150 typically contains a desired, residual moisture content which may be controlled during dewatering as previously described. The moisture content may be in the range of about 10% to 40% w/w or preferably, about 20% to 25% w/w. Preferably, dewatered, treated material 50 may be placed in piles, heaps or windrows for a desired period so as to reach about 60°C, which would normally destroy any pathogens or seeds. The resultant material may then be size-graded, such as by using a vibrating screen to eliminate material of an undesired size and/or shape and also to aerate the material. Alternatively, a hammer mill may be used to produce finer particles such that the resultant material resembles a high quality peat This resultant material may have about 80% water holding capacity and about 10% air-filled porosity.

It will be appreciated that the resultant material may be packaged and sold as a plant growth medium such as a potting mix, orchid mix, bulb mix, hanging basket mix, peat alternative and/or seedling propagation mix, although without limitation thereto.

The apparatus and method disclosed herein provides control over each treatment step in the inlet port, the central conveyor and the dewatering station by coupling the respective augurs to independent, variable speed motors. Furthermore, the augur in the dewatering station minimizes clogging while allowing fine-tuning of the degree of dewatering by way of spaced, counter-rotating screws, the spacing between which screws can be varied as desired.

Throughout the specification, the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features. Various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.

The disclosure of each patent and scientific document, computer program and algorithm referred to in this specification is incorporated by reference in its entirety.

Claims

1. An apparatus for manufacture of organic plant growth media from a starting material, said apparatus comprising:- a conveyor comprising a screw auger rotatably housed in an inclined tubular body and comprising an inlet port located at a tower end of said tubular body and an outlet port at an upper end of said tubular body, said screw augur in use conveying the starting material along said incfined tubular body; and

a dewatering station which receives treated material from said outlet port, said dewatering station comprising at least one dewatering device which, in use, facilitates at least partial dewatering of said treated material.

2. The apparatus of Claim 1 , wherein the dewatering station comprises a dewatering tube, within which dewatering tube is at least partly located the dewatering device.

3. The apparatus of Claim 1 or Claim 2, wherein the dewatering device is, or comprises, at least one screw augur.

4. The apparatus of Claim 3, wherein the at least one screw augur of the dewatering station comprises respective helical screws spaced apart on a common, rotatable shaft or on respective shafts.

5. The apparatus of Claim 4, wherein the first and/or second helical screws may be releasably connectabie to the or each rotatable shaft, to thereby allow adjustment of the spacing between the first and/or second helical screws.

6. The apparatus of Claim 1 or Claim 2, wherein the dewatering device is, or comprises, at least one ram or piston.

7. The apparatus of Claim 6, wherein the at least one ram or piston is operable to convey treated material from an inlet of the dewatering tube to an outlet of the dewatering tube.

8. The apparatus of Claim 6 or Claim 7, wherein the at least one ram or piston comprises a head which is slidably located within the dewatering tube.

9. The apparatus of any one of Claims 6-8, wherein the at least one ram or piston is hydrauiically driven.

10. The apparatus of any preceding claim, wherein the dewatering station is oriented substantially perpendicular to a longitudinal axis of the conveyor.

11. The apparatus of any preceding claim, wherein the dewatering station is operably connected to the conveyor by way of a collar which connects the outlet port of the conveyor to an inlet of the dewatering station.

12. The apparatus of any preceding claim, wherein the dewatering station is inclined.

13. The apparatus of Claim 11 , wherein the dewatering station is at an angle of about 30° to horizontal.

14. The apparatus of Claim 3, wherein a drain is located at a lower end of the dewatering station and an outlet is located at an upper end of the dewatering station.

15. The apparatus of Claim 14, whereby in use at least partly dewatered, treated material exits the dewatering station via the outlet.

16. The apparatus of Claim 14 or Claim 15 wherein fluid exits the drain. 7. The apparatus of Claim 16, wherein the apparatus further comprises a vessel for collecting fluid exiting the drain for subsequent treatment.

16. The apparatus of Claim 17, wherein the vessel is a sediment tank. 19. A method for producing an organic plant growth medium including the step of treating a starting material in the apparatus of any one of Claims 1- 18.

20. The method of Claim 19, wherein the starting material is, or comprises, organic and/or inorganic material inclusive of waste material, organic material of plant and/or animal origin, sawmill waste that comprises sawdust, bark and/or woodchips alone or mixed with other materials such as peat, spent mushroom compost, animal or chicken manure, sewerage sludge, waste vegetables or vegetable scraps, meat or bone meal of animal origin or the iike or selected combinations thereof.

21. The method of Claim 20, wherein the starting material comprises particulate pine bark having a layer of exogenous bark adhering to endogenous bark.

22. An organic pfant growth medium produced according to the method of any one of Claims 19-21.

23. The organic plant growth medium of Claim 22, which is a potting mix, orchid mix, bulb mix, hanging basket mix, peat alternative and/or seedling propagation mix.