AU682200B2 - Peat moss alternative - Google Patents

Description

WO 95/03371 PCT/AU94/00,07 1

TITLE

PEAT MOSS ALTERNATIVE FIELD OF THE INVENTION This invention is concerned with a method and apparatus for the manufacture of a peat moss alternative useful as a plant growth or culture medium.

BACKGROUND ART While naturally occurring peat moss is generally satisfactory for use as a plant growth medium it suffers a number of disadvantages.

A major disadvantage is the harvesting of naturally occurring peat moss. Peat moss or sphagnum is associated with deposits of peat which in turn is a highly organic soil ?omprised of decomposed vegetable matter.

Peat deposits are not widespread and thus substantial cost overheads are incurred in the collection, transportation and storage of peat mosses.

Being a naturally occurring product, it is generally not possible to culture peat moss as a renewable crop in a meaningful time frame. Moreover, natural peat moss contains a high abundance of naturally occurring bacteria, viruses, protozoa, insect and other parasites and, in particular, fungi.

As many of the micro-organisms and insect parasites associated with naturally occurring peat mosses are pathogenic to a wide variety of cultured plant species, it is desirable to sterilise peat moss or potting mixtures made therewith to ensure not only the health of plants but also the health of humans handling this material. For example, bacterial legionella infections in humans have been traced to potting mixes.

An effective way of sterilising peat moss (and thereby reducing transportation mass) is to allow the peat moss to dry in the sun. This process is slow and adds still further to the cost of the product. Once the peat moss has dehydrated, it is quite difficult and time consuming to re-hydrate.

Yet another disadvantage of peat moss is that it is often contaminated with peat which can be acidic.

Plant species intolerant to an acidic growth medium may be affected by peat moss growth media.

According to one aspect of the invention there is provided a method for the manufacture of a peat moss alternative, said method comprising the steps of:treating granules of tree or plant bark at a temperature in the range 50 0 c 130°c in the presence of an aqueous alkali solution to kill heat labile plant pathogens and to at least partially dissolve lignins contained in said bark; immersing said bark granules while heated into water at ambient temperature to cause separation of exogenous and endogenous portions of said bark granules; collecting said endogenous bark portions; and, tshredding said endogenous bark portions to cause at least partial separation of the cellulosic fibres 2' therein.

Suitably said granulated bark has a particle size in the range 5 mm to 50 mm.

4 0 Preferably the pH of said aqueous alkaline solution is chosen to produce an endogenous particulate q. bark material having a substantially neutral pH.

The aqueous alkaline solution suitably is selected from an expensive readily obtainable material such as sodium or potassium chloride or hypochlorite, quicklime, soda ash, powdered limestone, slaked lime, dolomite or mixtures thereof.

IH^A/ Preferably the alkaline solution comprises a mixture of powdered limestone and dolomite at least partially dissolved in water.

If required the alkaline solution may also include trace elements, plant nutrients, fungicides, pesticides and the like, either alone or in a preselected combination.

Heating of the bark may be achieved by any suitable means such as a hot air oven, steam oven, radiant heaters or microwave radiation. Preferably heating is effected by heating the bark granules in a body of water at an elevated temperature at atmospheric or at elevated pressure in a pressure vessel.

The bark granules are preferably heated at a temperature in the range 95 0 C 105 0

C.

SUMMARY OF THE INVENTION According to another- aspect of the invention there is provided an apparatus for the manufacture of a peat moss alternative, said apparatus comprising:o a heat treatment vessel including means to heat a 2 body of liquid contained in the vessel; conveyor means adapted to move bark particles through said heat treatment vessel at a predetermined rate; 5*9 a separation vessel containing, in use, a body of unheated water; transfer means to transfer treated particulate

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bark from said heat treatment vessel to said separation vessel; collection means to collect particles of treated exogenous bark from said separation vessel; collection means to collect particles of treated endogenous bark from said separation vessel; and, shredding means adapted to shred particles of treated endogenous bark collected from said separation vessel to produce a fibrous mass of separated or partially cellulosic fibres.

In order that the invention may be more readily understood, reference will now be made to a preferred embodiment of the invention illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG 1 illustrates a flow chart of the method.

FIG 2 illustrates schematically an apparatus according to the invention.

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a r WO 95/03371 PCT/AU94/00407 4 DETAILED DESCRIPTION In Fig 1, saw mill waste such as pine bark is granulated in a hammer mill 1 and is then graded into selected particle size ranges by passing through a series of graded screens 2. A suitable range of particle sizes may be between say 6 mm and 30 mm in 6 mm steps.

After grading into suitable particle size ranges the particle size ranges the particulate bark with attached sapwood is fed into a reaction vessel 3 containing an aqueous suspension of pulverised limestone or a mixture of pulverised limestone and dolomite. The particulate bark is maintained in the reaction vessel 3 with gentle agitation to allow neutralisation of at least the surface layer of the bark which is acidic due to the presence of tannins and the lignaceous material.

During the chemical treatment process one or more trace elements 4 may be added to the reaction vessel 3.

The trace elements are selected according to the intended purpose of the peat moss alternative.

After a suitable reaction time in vessel 3, the chemically treated particles, impregnated with trace elements are fed into a container 5 of clean unheated water. As the hot bark particles start to cool, any sapwood and endpgenous bark.separates from the exogenous bark and settles to the bottom of container 5. This is believed to occur due to differentials in thermal expansion and water absorption between the sapwood and endogenous bark on the one hand and exogenous bark on the other.

The floating treated exogenous bark particles are then collected and subjected to initial drainage before being dried in a rotary kiln and after drying, the particulate bark is hermetically sealed in plastic bags or the like to prevent ingress of contaminants, particularly of the bacterial or fungal kind. This particulate product is used as a plant growth medium, particularly orchids as described in Australian Patent No. 634573.

jy I WO 95/03371 PCT/AU94/00407 The product according to this part of the process comprises a graded particulate exogenous bark product which is substantially pH neutral at least on the surface layer of the particles and is packaged in a clean sterile form. If required the product may be impregnated with trace elements or other plant nutrients.

This -nv-:-.tion however concerns the further treatment of the sapwood, endogenous bark and the unspent limestone/dolomite mixture previously treated as a waste product from the process of Australian Patent No. 634573.

It has now been found, surprisingly, that if the sapwood and endogenous bark particles, having a relatively high moisture content of between 20 50% or higher, are then subjected to a milling action to coarsely shred the particulate matter, a coarse fibrous material is obtained with an appearance not dissimilar to coconut fibre or relatively dry peat moss or a mixture thereof.

Accordingly, as shown in FIG 1 after collection of the sapwood, a proportion of exojenous bark which sinks to the bottom of container 5 during processing, endogenous bark and the majority of the undissolved limestone/dolomite from container 5, this material is drained on a mesh conveyor belt 6 through which a current of dry heated air may be passed to reduce the moisture content of the sapwood/endogenous bark mixture.

When the particulate mixture is dried to a moisture content of between about 20% 40% by weight, the particulate mixture is then fed into a shredder 7.

During the shredding action a coarse fibrous material is produced by separation of the cellulosic fibres rather than by a cutting or pulverising action which would otherwise occur with dry untreated material.

The shredding action to produce the fibrous mass is believed to arise frcm at least a partial removal of lignaceous matter which serves to bond the cellulose fibres together and swelling and softening of the cellulosic fibres due to the high moisture content.

i -I WO 95/03371 PCT/AU94/00407 6 Fig 2 illustrates one embodiment of an apparatus for substantially continuous production of peat moss alternative.

Oraded pulverised bark mill waste is fed via hopper 10 onto a conveyor belt 11 for transfer to reaction vessel 12 at a predetermined feed rate. Feed rate may be controlled or varied by any suitable means such as a rotary feeder 13 on hopper 10 or adjusting the speed of conveyor 11 or both.

A further hopper 14 contains a mixture of pulverised limestone and magnesium silicate and this powdered material is metered onto the conveyor belt 11 by means of a vibratory feeder Reaction vessel 12 is substantially filled with water which is maintained at or near 100 0 C by a fuel fed boiler (not shown).

As the particulate bark is added to the reaction vessel it floats on the surface of the aqueous limestone suspension within the tank. The floating layer of bark is conveyed from one end of the vessel to the other at a predetermined rate by a walking beam conveyor 23 which momentarily elevates a layer of bark above the water surface as the layer progresses forwardly towards the outlet end of the vessel 12. Conveyor 23 comprises a plurality of rotating cranks 24 connected via link arms to a bed 26 in the form of a wire mesh rack, timber platform or the like.

The oscillatory motion of the walking beam conveyor 23 not only serves to control the duration of treatment of the bark in reaction vessel 12, it also serves to continuously agitate the bark particles to ensure complete and even chemical treatment.

'r-cated in the base of vessel 12 is a chain scraper 17 comprising spaced slats 18 extending between chain and sprocket drives 16 on each side of vessel 12.

As the bark particles progress along the surface of the water in vessel 12, particles of sapwood, exogenous bark, WO 95/03371 PCT/AU94/00407 7 endogenous bark, dirt and other contaminants sink to the floor of vessel 12. The reaction product of the limestone, the lignaceous material and the soluble acidic components of the bark settles to the floor of vessel 12 as a viscous red-brown liquid containing at least some unreacted limestone.

Reaction time in the reaction vessel is dependent upon surface area of the bark particles. For finer grades having an average particle size around 6mm, a residence time of about 10 minutes is sufficient to neut~-1'4e the acidic bark residues, impregnate with trace 7 and to sterilise the particles. For larger partic, is of say, 30 mm, a residence time of up to one hour may be required to fully treat the bark.

The combined effects of walking beam conveyor 23 and chain scraper 17 transfer the treated bark particles and the reaction vessel residues, under the influence of gravity, to a separation vessel 19 containing clean, unheated water at ambient temperature. As the hot treated bark particles come into contact with the cold water the exogenous bark portion separates from the sap wood and endogenous bark portions and the latter sink to the floor of vessel 19 while the exogenous bark portion continues to float.

A perforated belt conveyor 20 removes from one end of vessel 19 the exogenous bark particles, impregnated with one or more selected trace elements or other plant nutrient media, while sedimentary residues are removed by a chain scraper 21 or the like.

The sapwood and endogenous bark particles are then subjected to partial moisture removal on a mesh conveyor 30 which allows excess liquid to drain away. Dry heated air is passed upwardly through the layer of particulate matter on conveyor 30 to reduce its moisture content to between about 25% The moisture reduced particles are then passed to a shredder 31 such as a Brentwood (TM) AZ-7 or AZ-15 or to WO 95/03371 PCT/AU94/00407 8 a modified hammer mill with spaced rows of enlarged apertures in the screen.

After shredding, the fibrous mass so produced is introduced into a rotary screen dryer 31 or the like to reduce the moisture content of the fibrous mass to between 20% for transportation efficiency.

The partially dried fibrous mass is then compressed and bagged for transport in sealed plastic bags to maintain moisture and sterility in the product.

The fibrous mass produced according to the process has an appearance not dissimilar to a mixture of coconut fibre and peat moss.

The peat moss alternative produced in accordance with the invention possesses most of the advantage of natural peat moss without the main disadvantages.

The peat moss alternative is sterile and otherwise free from plant pathogens, it is pH neutral and optionally may contain trace elements or other plant nutrients, herbicides, pesticides or fungicides which may be impregnated in the material during tne chemical treatment process or added at some subsequent stage in processing.

A typical analysis is as follows:- Air filled porosity Water holding capacity pH Conductivity Chloride Ammonium Nitrogen Nitrate Nitrogen Total Nitrogen Sulphur Phosphorous Potassium Calcium Sodiumn of the peat moss alternative 17% up to 6-7 0.06 ds/m 35 mg/.

1 mg/L 3 mg/L 4 mg/L 2 mg/L 1 mg/L 21 mg/L 30 mg/L 20 mg/L WO 95/03371 PCT/AU94/00407 9 Magnesium 25 mg/L Ca/Mg Ratio 1:1.2 Potassium/Magnesium Ratio 0.84:1 Iron 21 mg/L Manganese 2 mc/L Copper 0.08 mg/L Zinc 1 mg/L Boron 0.21 mg/L Aluminium 22 mg/L It will be readily apparent to a skilled addressee that many modifications and variations may be made to the invention without departing from the spirit and scope thereof.

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Claims (12)

1. A method for the manufacture of a peat moss alternative, said method comprising the steps of:- treating granules of tree or plant bark at a temperature in the range 50 0 c 130°c in the presence of an aqueous alkali solution to kill heat labile plant pathogens and to at least partially dissolve lignins contained in said bark; immersing said bark granules while heated into water at ambient temperature to cause separation of exogenous and endogenous portions of said bark granules; collecting said endogenous bark portions; and, shredding said endogenous bark portions to cause at least partial separation of the cellulosic fibres therein.

2, A method according to claim 1 wherein said bark 0 i. granules have a particle size in the range 5 mm to 50 mm. S*

3. A method as claimed in claim 1 or claim 2 wherein the pH of said aqueous alkaline solution is chosen to 0' produce an endogenous particulate bark material having a substantially neutral pH.

4. A method as claimed in any preceding claim wherein the aqueous alkaline solution is selected from sodium or potassium chloride or hypochlorite, quicklime, j3C soda ash, powdered limestone, slaked lime, dolomite or mixtures thereof.

A method as claimed in claim 4 wherein the alkaline solution comprises a mixture of powdered limestone and dolomite at least partially dissolved in wateZ.

6. A method as claimed in any preceding claim wherein the alkaline solution also includes trace elements, plant nutrients, fungicides, pesticides and the like, either alone or in a preselected combination.

7. A method as claimed in any preceding claim wherein heat treating of the bark is achieved by any suitable means such as a hot air oven, steam oven, radiant heaters or microwave radiation.

8. A method as claimed in claim 7 wherein heat treating is effected by heating the bark granules in a body of water at an elevated temperature at atmospheric or at elevated pressure in a pressure vessel.

9. A method as claimed in any preceding claim wherein the bark granules are treated at a temperature between 950C 105 0 C.

10. An apparatus for the manufacturing of a peat moss alternative in accordance with any one of claims 1 to said apparatus comprising:- a heat treatment vessel including means to heat a body of ,l;'iid contained in the vessel; conveyor means adapted to move bark particles through said heat treatment vessel at a predetermined rate; a separation vessel containing, in use, a body of 0 unheated water; transfer means to transfer treated particulate bark from said heat treatment vessel to said separation vessel; collection means to collect particles of treated exogenous bark from said separation vessel; collection means to collect particles of treated ndogedogenous bark from said separation vessel; and, 1la shredding means adapted to shred particles of treated endogenous bark collected from said separation vessel to produce a fibrous mass of separated or partially separated cellulosic fibres.

11. An apparatus as claimed in claim 11 wherein said milling means comprise a shredder.

12. An apparatus as claimed in claim 11 wherein said milling means comprises a modified hammer mill. *o *6. *9 Otoe a 0