AU2020103790A4 - Beneficial utilisation of unwanted vegetation - Google Patents

Abstract

The invention provides for the beneficial utilisation of unwanted vegetation, in particular the transforming of declared weeds into useful products including feedstocks for biofuels and into compost by way of a process wherein viable seeds in harvested weed biomass are rendered innocuous by means of elevated temperature or size reduction treatments. SHEET1of1 10 12 harvest 14 pile 16 Allow temperature to rise 18 Stable temperature 20 Cooling 22 Seed treatment 24E Store or spread FIGURE 1

Description

SHEET1of1

12 harvest

14 pile

16 Allow temperature to rise

18 Stable temperature

20 Cooling

22 Seed treatment

24E Store or spread

FIGURE 1

BENEFICIAL UTILISATION OF UNWANTED VEGETATION

Field of invention

[01] This invention relates to the beneficial utilisation of unwanted vegetation, in particular the transforming of declared weeds into useful products.

Background to the invention

[02] A significant cost borne by mining operations relates to the rehabilitation of mined terrain. Dropping commodity prices and the need to maintain rehabilitation initiatives whether or not compelled by environmental laws can lead to the scaling back of operations, mothballing or even entire mine closures.

[03] Invasive weeds are among the most serious threats to a natural environment and primary production industries. Weeds have major economic, environmental and social impacts, causing damage to natural landscapes, agricultural lands, waterways and coastal areas.

[04] In Australia, for example, the invasive flora species Mesquite (all varieties and hybrids), Parkinsonia (all varieties and hybrids) and Prickle bush Acacia (all varieties and hybrids), collectively known as Prickle Bush Weeds, have been declared invasive weeds by the Federal, State and Territory Governments. Parkinsonia has been declared a 'Weed of National Significance', being regarded as one of the worst because of its invasiveness, potential for spread, and economic and environmental impacts. Parkinsonia has the potential to invade more than three quarters of mainland Australia. Prickle bush Acacia and Mesquite have also been declared Weeds of National Significance, for similar reasons.

[05] Parkinsonia can dam watercourses, cause erosion, and lower water tables. It is a very hardy plant that can withstand long dry spells. Its seeds remain viable for many years (Smith 2002). Parkinsonia infestations provide refuges for feral animals, especially pigs (CRC 2003; Deveze 2004).

[06] Conventional weed eradication methods include mechanical harvesting and poisoning, and incineration of harvested matter. The highest probability of success is

achieved when the final step is incineration. This step increases aggregate releases of

carbon dioxide and other combustion by-products, arguably causing environmental damage without maximising potential benefits of the incinerated material.

[07] Nowadays, when a mine closes, the mine site is required to be safe, stable, non-polluting and have sustainable land uses. However, regulations in the past were less

stringent and community expectations lower than at present, giving rise to a legacy of mines that do not meet today's standards.

[08] Abandoned mines are largely historic, have no clear ownership and rarely meet current community and regulatory mine rehabilitation and closure expectations.

Australian governments and local communities have become responsible for managing

these mines and their rehabilitation.

[09] Rehabilitation is the process used to repair the impacts of mining on the

environment. The long-term objectives of rehabilitation can vary from simply converting an area to a safe and stable condition, to restoring the pre-mining conditions as closely as

possible to support the future sustainability of the site. The process of restoring indigenous or native flora to denuded tracts of land requires that top soil is reinstated and

or bio mas replete with viable, beneficial microorganisms, is introduced. Composting provides an effective solution to the problem of preparing disturbed ground for

restoration.

[010] Composting is a process that relies on the presence of a multitude of organisms, bacteria in particular. Various aerobic bacteria are known that work in

composting piles. Their populations will vary according to the pile temperature. Psychrophilic bacteria work in the lowest temperature range. They are most active at 132C

(about 55 2F) and will work in the pile if the initial pile temperature is less than about 202C (or 702F). They give off a small amount of heat in comparison to other types of bacteria.

The heat they produce is enough, however, to help build the pile temperature to the point where another set of bacteria, mesophilic bacteria, start to dominate the composting.

[011] Mesophilic bacteria rapidly decompose organic matter, producing acids, carbon dioxide and heat. Their working temperature range is generally between 202C to

382C (702F to 1002F). When the pile temperature rises above about 402C, the mesophilic

bacteria begin to die off or move to the outer parts of the heap. They are replaced in the decomposition process by thermophilic bacteria, which thrive at even higher

temperatures.

[012] Thermophilic bacteria continue the decomposition process, raising the pile

temperature to about 702C, where it usually stabilizes. The highest temperatures typically last no more than three to five days, because the thermophilic bacteria consume too much

of the degradable materials to sustain their population for longer. As the thermophilic bacteria decline, the heap gradually cools off, the mesophilic bacteria again becoming

dominant, consuming what compostable organic matter remains, helped by other

organisms.

Objects of the invention

[013] It is an object of this invention to address the shortcomings of the prior art and, in doing so, to provide a method of utilising available biomass derived from unwanted vegetation, such as the officially declared weeds, Mesquite, Parkinsonia, and Prickle Bush

Acacia (including all hybrids of each).

[014] A further object of the invention is to provide by-products of an unwanted

biomass.

[015] The preceding discussion of the background to the invention is intended to

facilitate an understanding of the present invention. However, it should be appreciated

that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or elsewhere as at the

priority date of the present application.

[016] Further, and unless the context clearly requires otherwise, throughout the

description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense - that is to say, in the sense of "including, but not being limited to" - as opposed to an exclusive or exhaustive sense - that is to say meaning "including this and nothing else".

Summary of invention

[017] The invention provides, according to a first aspect, feedstock for a vegetation beneficiation process, the feedstock comprising a biomass having in it an unwanted species of vegetation.

[018] Preferably, the feedstock comprises neutralised seed matter of the species.

[019] Further preferably, the feedstock is substantially free of viable seeds of the species.

[020] In a preferred form of the invention, the biomass comprises destroyed weeds.

[021] In a preferred embodiment of the invention, the destroyed weeds are derived from one or more declared weeds selected from prickle bush weeds. The group known as prickle bush weeds includes Parkinsonia, Mesquite and Prickle Bush Acacia.

[022] According to a second aspect of the invention, there is provided a biomass adapted for transformation into economically useful end products.

[023] In a preferred form of the invention, the biomass is adapted to be substantially free of viable seeds of an unwanted vegetation species.

[024] In an embodiment, the biomass is rendered substantially free of viable seeds by reason of exposure to temperatures in a range effective for rendering seeds of the species innocuous. In a further embodiment, the biomass is adapted so that alternatively, or in addition, it consists of particles of mean size less than that of the seeds of the species. Preferably the mean particle size of the biomass is adapted by mechanical maceration.

[025] Preferably, the end products comprise organic seed bed material and compost.

[026] According to a third aspect of the invention, there is provided a method of utilising unwanted vegetation including

a. harvesting said vegetation, b. transforming said vegetation, by one or more of mechanical, hydraulic and biological manipulation, into an economically useful product.

[027] In a preferred form of the invention, the method includes transforming the

vegetation by bacterial treatment into a product in a group consisting of fuels, animal feeds, building materials, mulches, composts, and soil-enriching, erosion-stabilizing and

organic seed-bed material.

[028] In a further preferred form of the invention, in transforming the vegetation, the method includes rendering seeds present in the vegetation innocuous. Preferably, the product of transformation is substantially free of viable seeds of the unwanted vegetation

species.

[029] In an embodiment, the step of rendering the seeds innocuous includes

subjecting the vegetation including the seeds to a temperature in the range of effective

seed neutralising temperatures.

[030] Preferably, the method includes attaining effective seed-neutralising

temperatures by allowing composting in the presence of thermophilic bacteria.

[031] In a preferred embodiment, the seed-neutralising temperature range is

between 55°C and 72°C.

[032] The method preferably further includes causing mechanical maceration of the

vegetation so as to reduce particle size thereof to below the seed sizes of unwanted vegetation.

[033] In a preferred embodiment, the unwanted vegetation is a species of prickle

bush weed.

[034] According to a fourth aspect of the invention, there is provided a method of

combatting soil erosion, comprising the steps of providing a biomass comprising an unwanted vegetation species, allowing the biomass to become compost, and blanketing

a disturbed area of soil with a layer of the compost.

[035] In a preferred form of the invention, the species is a declared weed species.

[036] According to a fifth aspect of the invention, there is provided a method of preparing a denuded tract of land for restoration of vegetation thereto, the method

including the steps of providing a biomass comprising an unwanted vegetation species,

allowing the biomass to become compost, and blanketing the tract with a layer of the compost.

[037] In a preferred form of the invention, the unwanted vegetation species is a declared weed species. In an embodiment, the weed species is a prickle bush weed

species.

[038] In a further preferred form of the invention, the method includes the step of

neutralising viable seeds in the biomass.

[039] In an embodiment, the method includes neutralising the seeds by exposure to

heat in an effective seed neutralising range for an effective seed neutralising period.

[040] In a preferred form of the invention, the method includes the step of neutralising viable seeds by maceration.

[041] The invention in another aspect extends to the use of a biomass derived from a species of unwanted vegetation, such as a prickle weed species, in the production of an

economically valuable commodity. In an embodiment, the commodity is suitable for soil enrichment, whereby to promote gains in agricultural production.

[042] In a further aspect, the invention provides a compost comprising neutralised seed matter of environmentally unwanted vegetation. Preferably, the vegetation

comprises a declared weed species.

[043] In an embodiment, the weed species is a prickle bush weed species.

[044] Further the invention provides a commodity comprising vegetative matter

derived from a species of prickle bush weed selected from Parkinsonia, Mesquite and Prickle bush Acacia.

[045] In an embodiment, the commodity is a fuel. The fuel may be in liquid, gaseous or solid form.

[046] In an alternative embodiment, the commodity is a compost comprising neutralised seeds of the species.

Brief description of drawings

[047] In order that the invention may be readily understood, and put into practical effect, reference will now be made to the accompanying figure. Thus:

Figure 1 shows in schematic form a block-flow diagram of a preferred embodiment of the method of this invention for producing compost from an unwanted vegetation species.

Detailed description of an embodiment of the invention

[048] The invention provides for the beneficial utilisation of unwanted species of vegetation. In particular, the utilisation of unwanted vegetation to form a biomass for transforming into compost is described. The compost is then utilisable in various applications, including, but by no means limited to the restoration, by revegetation with desired species, of land disturbed by human activities such as mining, or by soil erosion from wind or water, whether or not directly or indirectly caused by the activities of man and his livestock.

[049] The proposed composting of undesired vegetation, such as invasive weeds, will reduce the amount of greenhouse gases released into the atmosphere as a result of conventional eradication processes. Figure 1 illustrates a process of utilising invasive weeds according to the invention. The process is denoted generally by the numeral 10.

[050] The process of composting the invasive weeds begins with collecting harvested weed material 12 and forming it onto a composting pile 14. The pile isof known structure, generally having a rigid wire grid wall defining an internal space into which the weed matter is located and allowed to stand. The grid wall permits ingress and egress of air and composting fluids, including water from rainfall or artificial wetting. Other composting structures may of course be implemented depending on the scale or outcome required. Options are discussed below.

[051] As composting organisms present in the pile become active, emitting heat in the exorthermic digestion and decomposition processes they perform, the pile

temperature rises. This is represented by the numeral 16 in Figure 1. The heat tends to be

greatest in a core zone of the pile, the temperature profile showing a diminishing tendency from the core to the fringes of the pile.

[052] While pile temperatures above 602C (about 1402F) are known to kill certain pathogenic organisms and weed seeds, temperatures exceeding 712C (1602F) tend to

cause the composting vegetative material to become sterile and lose its pathogen or disease-fighting capacity. Therefore, the biomass being combusted, when derived from

the harvesting of prickle bush weed is kept at a temperature in a range between 60C and 722C (about 1602F and 1402F), as shown at the step marked 18.

[053] The temperature is maintained at this plateau level for a limited period of time

in order to render the seeds innocuous or neutral, so as to be incapable of germinating. It is found that when prickle bush weed being composted is kept in the stated temperature

range for a period of time from 2 hours to 350 hours depending on ambient conditions, the rendering of seeds innocuous is greater than 99.9%.

[054] The biomass formed with this processed matter is substantially free of viable seeds and can be used for composting without significant risk of allowing unwanted

species to thrive in the tract being composted.

[055] Various aerobic bacteria are known that work in composting piles. Their

populations will vary according to the pile temperature. Psychrophilic bacteria work in a

first, lowest temperature range. They are most active at 132C (about 552F) and will work in the pile if the initial pile temperature is less than 202C (or 702F). They give off a small

amount of heat in comparison to othertypes of bacteria. The heatthey produce is enough, however, to help build the pile temperature to the point where another set of bacteria,

mesophilic bacteria, start to dominate the composting. In hot climates, the activity of psychrophilic bacteria may be limited to non-existent if the vegetation added to form the

pile is at an ambient temperature above the first temperature range above.

[056] Mesophilic bacteria rapidly decompose organic matter, producing acids, carbon dioxide and heat. Their working temperature range is generally between 202C to

382C (702 to 1002F). When the pile temperature rises above 382C (1002F), the mesophilic

bacteria begin to die off or move to cooler, generally outer parts of the heap. They are replaced in the decomposition process by thermophilic bacteria, which thrive at

temperatures in the range between 452C and 722C (1132F and 1602F).

[057] Thermophilic bacteria continue the decomposition process, raising the pile

temperature to plateau in the range from 552C to 712C (1302F or 1602F). Unless a pile is constantly fed new compostable material and is turned at strategic times, the high range

temperatures typically last no more than three to five days, as the thermophilic bacteria consume too much of the degradable materials to sustain their population for longer. As

the thermophilic bacteria decline and the temperature of the pile gradually cools off, the

mesophilic bacteria again become dominant. The mesophilic bacteria consume remaining compostable organic matter with the help of other organisms.

[058] The rate of seed neutralization to reach an innocuous state is improved when one or more of the following seed treatment steps is added to or included in the

composting process:

a. the application of a neutralising compound including chemicals, nutrients

or hormones or selected combinations thereof,

b. the application of a biological agent including micro-organisms,

c. a wetting and drying process,

d. an energy form including heat, radiation, electricity or magnetism, and

a. maceration of the composting matter to achieve mean particle sizes less

than mean seed sizes.

[059] Biological agents include sources of thermophilic bacteria. This group is widely

distributed in nature, occurring, by way of example, in dust particles, on clothes, in soil, in sewage, in the gastro-intestinal contents and faeces of herbivorous animals, and the like.

[060] The quantity of energy to which the pile is preferably subjected is selected to be effective for neutralising 99.9% of seeds present.

[061] It is found that larger seeds in the size range of a prickly bush species are more

likely than smaller seeds of the species to survive neutralisation by temperature alone, when the temperature is maintained in the plateau of the effective range above.

Therefore, by adding a maceration step, the probability that all seeds will be made innocuous is increased to a value exceeding 99%. The seed sizes are found to range from

mm to 12 mm. Maceration is carried out, by way of example, using a tub grinder of the type supplied by Mobark LLC of South Winn Road, Winn, Michigan.

[062] The seed treatment step, when comprising maceration, is shown added after the cooling stage 20, as denoted by the number 22 in the diagram. However, maceration

may be carried out alternatively at other stages, or even at or after more than one stage

of the process. For example, it may be carried out before forming of the pile 14. The size reduction inherent in the maceration process increases the active surface area of each

particle, enabling improved access by participating bacteria at the different temperature ranges of the composting process.

[063] The size reduction step may be delayed until after the compost core temperature has reached a transition stage between different bacterial species activity.

In the diagram, this example of seed treatment is therefore performed during the temperature rise of step 16, before the thermophilic bacterial activity becomes

significant.

[064] Bacteria use carbon for energy and protein to grow and reproduce. Carbon and nitrogen levels vary with each organic material. Carbon-rich materials tend to be dry and

brown, being found in leaves, straw, and dried wood chips. Nitrogen materials tend to be wet and green, for example fresh foliage and green wood chips. A process of grinding

drying, blending and incremental agitation is required to limit the requirement for the introduction of biomass other than that derived from the processing of prickle bush

weeds.

[065] Decomposer organisms need water to live. Microbial activity occurs most rapidly in thin water films on the surface of organic materials. Microorganisms can only

utilize organic molecules that are dissolved in water. The optimum moisture content for

a compost pile should range from 40% to 60% by weight.

[066] A wetting and drying process, by way of example, comprises hosing down or

using a sprinkler system to distribute water at a temperature of about 24°C. The quantity of water applied per hour per tonne of composting matter is between 20 and 360 litres,

depending on moisture content of macerated biomass and ambient conditions.

[067] Particle size affects the rate of organic matter breakdown. The more surface

area available, the easier it is for microorganisms to work, because activity occurs at the interface of particle surfaces and air. Microorganisms are able to digest more, generate

more heat, and multiply faster with smaller pieces of material.

[068] Therefore, in a preferred embodiment of the process, the mechanical maceration of the prickle bush weed biomass is included so as to reduce particle size to

below the seed sizes of the weeds being transformed.

[069] The subsequent composted material derived from the biomass resulting from

the processing of prickle bush weeds will be used as a vehicle to promote soil improvement as generally required for erosion control, soil stabilization, revegetation,

site disturbance reclamation and rectification, vegetative cover establishment and propagation, production gains in agriculture, mine site restoration and re-forestation of

native and non-native species of flora. It will be applied in its mono-simplistic form or with

the admixtures of preferred seed material and or moisture entrapment chemicals and wetting agents.

[070] In the process of Figure 1, the step labelled 24 entails either placing the compost in storage ready for use, immediately causing it to be transported to a tract of

land that has been substantially denuded of vegetation, and spreading it in an effective vegetation-supporting layer. In this preferred embodiment, the compost comprising the

unwanted vegetation matter is not mixed in with the soil over which it is spread. In this application it forms a moisture-retaining mulch. However, it may be admixed in other embodiments in a more conventional composting application.

[071] With the manufacture viable products from the biomass made available from

invasive weed harvesting and processing, the economic burden on the fiscus may be reduced significantly. Currently, the various Government agencies and pastoral

organizations responsible for invasive weed management struggle to gain control of the spread of these weeds, largely because their funds are limited and there is little economic

gain to be derived for the entities involved. This invention will realise economic value by incentivising and encouraging the engagement of private entities for performing weed

eradication.

[072] Commodities that may be produced, using feedstock comprising the unwanted

vegetation discussed in this invention, include bio-fuels, animal feeds, building materials,

and horticultural products, examples being mulches, composts (as described), and soil enriching, erosion-stabilizing and organic seed-bed materials. It will be appreciated that

seed neutralisation steps need not be performed for fuel manufacture.

[073] Federally declared weeds such as Mesquite, Parkinsonia, and Prickle Bush

Acacia are processed into cellulosic ethanol, which is used as a feedstock in the manufacture of biodiesel.

[074] Cellulosic ethanol is produced by separating cellulose in the unwanted weed plants from the other plant materials, using enzymes to break down the cellulose into

glucose, and then converting the glucose into ethanol by fermentation

[075] Aqueous phase exothermic reactions are utilised, lowering production costs, not least by avoiding the need for distillation, required in the production of conventional

formulations of ethanol.

[076] The method of producing biodiesel can conveniently be summarised in four

main stages: a. A stream of processed biomass consisting of water and sugars (principally glucose) is fed over a nickel-tin catalyst to strip off a portion of the hydrogen present therein.

b. The stream is treated with acids to remove most of the water.

c. The resulting intermediate is then transported over a solid base catalyst,

forming alkanes rich in long carbon chains.

d. Finally, the alkanes are run through a platinum-silica-alumina catalyst at

high temperatures, while the hydrogen from the first step is fed into the reactor.

[077] The resulting liquid has almost the same chemical structure as traditionally refined biodiesel. The only combustion by-products are water and heat.

[078] The present invention provides for a cost-effective and environmentally

sustainable alternative to importing compost and seed-bed material from areas outside the geographical zone where rehabilitation of vegetation is planned, whether from

erosion or mining operations.

[079] These embodiments merely illustrate particular examples of the method, use

and products of the invention providing for the processing of unwanted vegetative species. With the insight gained from this disclosure, the person skilled in the art is well

placed to discern further embodiments by means of which to put the claimed invention into practice.

Claims (5)

Claims The claims defining the invention are:

1. A method of utilising unwanted vegetation including

a. harvesting said vegetation,

b. rendering seeds present in the vegetation innocuous, and

c. transforming said vegetation, by one or more of mechanical, hydraulic and biological manipulation, into an economically useful product.

2. The method of claim 1 including transforming the vegetation by bacterial treatment into a product in a group consisting of fuels, animal feeds, building materials and horticultural products.

3. The method of claim 3 including subjecting the vegetation including the seeds to a temperature in the range of effective seed neutralising temperatures.

4. The method of claim 4 including attaining effective seed-neutralising temperatures by allowing composting in the presence of thermophilic bacteria.

5. The method according to any one of the preceding claims further including causing mechanical maceration of the vegetation so as to reduce the mean particle size thereof to below the mean seed sizes of said unwanted vegetation.

end

SHEET 1 of 1 Nov 2020

10

12 harvest

14 pile 2020103790

16 Allow temperature to rise

18 Stable temperature

20 cooling

22 Seed treatment

24 Store or spread

FIGURE 1