WO2010020002A1

WO2010020002A1 - Aeration device for use in a biopele

Info

Publication number: WO2010020002A1
Application number: PCT/AU2009/001066
Authority: WO
Inventors: Richard John Stewart; Benjamin Dearman
Original assignee: Ziltek Pty Ltd
Priority date: 2008-08-20
Filing date: 2009-08-19
Publication date: 2010-02-25

Abstract

The present invention relates to a device for placing within and enhancing aeration of a particulate mass, a liquid substance or a combination thereof (eg a biopile). The device comprises a three dimensional structure (for example, of a substantially spherical shape) comprising a surface provided with at least one pore therein, and wherein said structure defines a minimum cross-sectional dimension of about greater than 10mm. Preferably, the device comprises a biodegradable material.

Description

AERATION DEVICE FOR USE IN A BIOPELE

FIELD OF THE INVENTION

The present invention relates to devices for use within a biopile to enhance aeration.

BACKGROUND OF THE INVENTION

Sources of major environmental contamination events most commonly arise from agricultural waste, industrial waste and tanker spills. The release of contaminants into the environment may cause toxicity to animal and plant life as well as the subsequent direct and indirect exposure to humans through food and water sources, for example via the leaching of waste streams into ground waters. Toxic compounds often found in environmental contaminants can include, for example, petrochemicals, heavy metals and xenobiotics (eg chlorinated or aromatic compounds). Common sources of xenobiotics in the environment include pesticides and herbicides, industrial solvents and degreasing agents. Many of these compounds can persist in the environment and several are particularly recalcitrant. Recalcitrant compounds often include aromatic or chlorinated compounds although many compounds can be resistant to biodegradation under certain conditions, for example, hydrocarbon contaminants degrade very slowly in anoxic environments as can be observed following tanker spills at sea.

It can be expensive to collect and transport contaminated soils due to the costs involved in attaining the required regulatory permits, the appropriate handling of contaminated materials, and the requisite containment of contaminated soils during transport and handling. Following collection and transport, further costs are incurred in undertaking the decontamination (ie remediation) process. The cost of remediation activities can be extremely high, particularly following large contamination events. For example, following the eleven million gallon petrochemical spill from the Exxon Valdez tanker in Alaska in 1989, the clean up costs were estimated to be around US$1.5 billion. This does not include the ecological cost of the spill on surrounding environments.

The safe management of soil contaminants can be undertaken through a number of remediation processes.

These may include bioremediation, chemical stabilisation, micro-encapsulation, thermal destruction, chemical oxidation, or the construction of onsite repositories. Bioremediation of contaminated soils or the biodegradation/bioconversion of environmental contaminants involves the use or manipulation of living organisms to degrade or convert toxic environmental contaminants to safer compounds and/or derivatives.

Biodegradation or bioconversion is most commonly undertaken by bacteria although plants, fungi, moulds, yeasts, cyanobacteria and algae have also been known to be capable of degrading hydrocarbons or converting heavy metals or xenobiotic compounds to safer compounds and/or derivatives. Often symbiotic relationships between several organisms can lead to the enhanced biodegradation or bioconversion of contaminants. The efficiency of biodegradation or bioconversion can be enhanced by optimising the environmental conditions for microbial growth or metabolism. Conditions requiring adjustment may include temperature and/or pH, the addition of micronutrients and/or macronutrients, and/or the dosing of microorganisms to provide a consortium of microorganisms for co-metabolism. For example, hydrocarbon contaminants undergo aerobic biodegradation and therefore require optimal oxygen conditions. Achieving adequate aeration is often the most limiting factor for the breakdown of hydrocarbon contaminants in soil.

For the bioremediation treatment of hydrocarbon contaminated soils, the soil is generally formed into engineered biopiles that have been positioned and configured to allow gaseous movement within the piles. To enhance aeration, the biopiles will often comprise reticulated aeration systems which involve the pumping of air through the pile so as to increase oxygen availability to microorganisms present and thereby enhance aerobic biodegradation rates (ie static aerated biopiles). However, these reticulated aeration systems can be expensive to install and operate, and can cause soil in the biopiles to dry which, in turn, can create the need for the installation and operation of irrigation systems. Further, over time, biopiles require turning or loosening to reduce compaction and further assist in the movement of gases within the piles.

Despite current efforts to enhance aeration in biopiles, further measures are desired in order to enhance aeration within biopiles and hence optimise, particularly, the biodegradation of hydrocarbons. Such measures preferably ought to require little infrastructure cost, will facilitate the ease of operation of aeration systems such that the intervention of operators is minimised (eg by removing or reducing the need for soil turning), and possibly, reduce costs by alleviating the need for additional resources, such as energy to run pumps and the like, and/or irrigation to prevent soil drying. Further, measures to enhance aeration within biopiles may increase the rate of biodegradation of contaminants, in particular hydrocarbons, and/or result in an increase in complete biodegradation of contaminants to safer compounds and/or derivatives.

SUMMARY OF THE INVENTION In a first aspect, the present invention provides an aeration device for placing within a particulate mass, a liquid substance or a combination thereof, said device comprising a three dimensional structure comprising a surface provided with at least one pore therein, and wherein said structure defines a minimum cross-sectional dimension of about greater than 10mm and is substantially resistant to damage caused by placement within said particulate mass, liquid substance or combination thereof.

The three dimensional structure of an aeration device according to the present invention preferably defines an interior space containing gas (eg air or oxygen). The at least one pore provided in the surface of the device may therefore "communicate" with the interior space so as to allow gases to pass between the interior space and the exterior of the device. The shape of an aeration device according to the present invention may comprise any three dimensional structure, although, a substantially spherical shape is preferred. Preferably, an aeration device according to the present invention will comprise a biodegradable material.

In a second aspect, the present invention provides a method for aerating a particulate mass, a liquid substance or a combination thereof comprising, at least in part, some organic matter, wherein said method comprises the step of; (i) incorporating a plurality of an aeration device according to the first aspect within said particulate mass, liquid substance or combination thereof.

The method of the second aspect preferably enhances the composting and/or decontamination of a biopile.

The method may further comprise the step of:

(ii) adding one or more materials that enhance the composting and/or decontamination of said particulate mass, liquid substance or combination thereof.

The method of the second aspect may also further comprise a step of recovering the aeration devices following the composting and/or decontamination of said particulate mass, liquid substance or combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 provides schematic views of various embodiments of the aeration device according to the present invention: A. spherical aeration device (1) comprising multiple pores (2) produced by bonding or ultrasonic welding of two hemispherical pieces; B. spherical aeration device (1) comprising pores (2) produced by uniting hemispherical pieces provided with snap-fittings (3); C. an array (4) of the aeration devices (1) as shown in A linked by short lengths of a small gauge wire; and D. a mat (5), shown in cross- section, comprising a resilient, flexible sheet material (6) including aeration devices (1) comprising pores (2) and a hollow interior space (7);

Figure 2 provides a front sectional view of a soil biopile with a conventional reticulated aeration system provided at the base of the biopile;

Figure 3 provides a side sectional view of the reticulated biopile of Figure 2, showing reticulation along the length of the biopile; Figure 4 provides a schematic view of a plurality of aeration devices according to an embodiment of the invention wherein the flow of gases between devices is indicated with arrows;

Figure 5 provides a front sectional view of a soil biopile formed according to methods of the invention wherein the aeration devices of Figure 4 are distributed therein. The biopile is typically about 2m³ formed into a conical pile (10) and placed on a lined hardstand area (11) and may be covered with a water- resistant sheeting (12); and

Figure 6 provides graphical results showing carbon dioxide output and temperature profile for organic waste contained in an in-vessel composting bin with and without a plurality of aeration devices according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to devices to enhance aeration, and to a method involving their use, preferably suitable for the composting and/or decontamination of a particulate mass comprising, at least in part, some organic matter.

Thus, in a first aspect, the present invention provides an aeration device for placing within a particulate mass, a liquid substance or a combination thereof, said device comprising a three dimensional structure comprising a surface provided with at least one pore therein, and wherein said structure defines a minimum cross-sectional dimension of about greater than 10mm and is substantially resistant to damage caused by placement within said particulate mass, liquid substance or combination thereof.

Preferably, the aeration device is suitable for placing within a particulate mass such as soil or organic refuse, liquid substance such as water or wastewater, or a combination thereof such as sludge. More preferably, the aeration device is suitable for placing within a biopile or for use with organic waste contained within an in-vessel composting bin.

As used herein, the term "biopile" refers to any heaped mass of particulate matter comprising, at least in part, some organic matter. Heaped particulate matter for forming biopiles may therefore include, for example, soil and/or compost, biosolids derived from sewage and/or wastewaters, organic refuse (such as food waste) or other substantially particulate matter comprising organic matter collected from other sources of waste.

The shape of an aeration device according to the present invention may comprise any three dimensional structure, although, a substantially spherical shape is preferred. Spherical shapes provide greater structural integrity to the aeration device however other shapes such as ovoid, cuboid, cylindrical, polyhedral and irregular shapes are also suitable. Preferred aeration devices, with a substantially spherical structure (eg a ball-like structure), are illustrated in Figure IA and B.

The aeration device has a structure with a minimum cross-sectional dimension (eg a width or diameter) of about greater than 10mm. However, preferably, the minimum cross-sectional dimension is in the range of 1 lmm to 500mm, more preferably in the range of 15mm to 150mm and, most preferably, about 30 to 60mm.

The aeration device may be provided in an array with a plurality of other aeration devices, which may be the same, similar or different (ie the plurality of aeration devices may have, for example, the same or similar structure and/or composition). For example, aeration devices may be linked together by a flexible linking means including, for example, wire, mesh or mat to form a substantially flat array of aeration devices. Examples of such arrays are illustrated in Figure 1C and D. An array of aeration devices may assist in applying the devices to in-vessel composting bins in a uniform manner (eg a layer or organic waste material may be introduced into the bin followed by an array of aeration devices followed, in turn, with another layer of organic waste, etc.) or preventing "escape" of the devices from a biopile. However, other means such as spikes or wires may be provided on the surface of aeration devices provided in single, non-array form so as to prevent their escape (eg by rolling down the sloped sides) from a biopile.

The three dimensional structure of an aeration device according to the present invention preferably defines an interior space containing gas (eg air or oxygen). The at least one pore provided in the surface of the device may therefore "communicate" with the interior space so as to allow gases to pass between the interior space and the exterior of the device. In addition to defining an interior space, a preferred aeration device is, further, substantially resistant to damage caused by placement within a particulate mass, a liquid substance or a combination thereof. For example, preferred aeration devices suitable for placement in a biopile may be substantially resistant to damage (particularly crushing or collapse) whilst being compressible. Preferred aeration devices may typically be compressed to a volume that is no less than 60%, more preferably no less than 80% and, most preferably no less than 90%, of the uncompressed volume of the device.

A preferred aeration device according to the present invention comprises a substantially uniform mass composed of a foamed or sponge-like material.

The diameter and number of the pore(s) may vary depending on the size of the device and the nature of the particulate matter. Thus, for use in a biopile comprising soil, for example, the size of the pore(s) may be restricted to substantially prevent the ingress of soil particles therein and therefore avoid clogging of the interior space. Moreover, the diameter of the pore(s) may be varied depending upon the nature of the soil in the biopile, for example, clay soil particles have a greater tendency to adhere to one another forming larger clumps or masses which are less likely than sandy soil particles to enter the interior space through the pore(s).

The interior space may also be adapted to prevent ingress of the particulate matter of the biopile through the pore(s). For example, the interior space may be partially or wholly filled with a network of interconnected channels and/or chambers (eg the interior space may have a foamed or sponge-like appearance, and/or comprise a number of baffle members).

While the device size (ie as defined by the minimum cross-sectional dimension) and pore number and pore diameter of an aeration device according to the present invention may depend on several factors including the nature of the particulate matter, the nature of any contaminant sought to be biodegraded, bioconverted and/or decomposed within the biopile is also a consideration. Hydrocarbon contaminants, for example, are predominantly degraded by aerobic degradation, such that the device size and pore number and diameter should be selected so as to improve the growth conditions (eg by optimising the oxygen and/or carbon dioxide environment) for hydrocarbon-degrading microorganisms present in the biopile.

While the shape of the aeration device may contribute to structural integrity and, thereby, resistance to damage by compression (eg when the device is placed within a biopile), structural integrity may be improved by selecting an appropriately rigid or resilient material for the manufacture of the device. Suitable rigid materials may include hard synthetic or natural polymeric materials (eg polyvinyl chloride (PVC)), metals or metal alloys (eg steel), composite materials such as glass reinforced plastic (GRP), or mixtures thereof. Suitable resilient materials may include compressible and/or foamed natural and synthetic polymeric materials (eg natural and synthetic rubber). Rigid materials are particularly suitable for the manufacture of aeration devices that are hollow, substantially hollow or include baffle members in the interior space, whereas resilient materials are particularly suitable for the manufacture of aeration devices that comprise an interior space with a foamed or sponge-like appearance.

The structural integrity of aeration devices according to the present invention may also be provided by or within the interior space. For example, the interior space may comprise a core formed to provide further structural support to the device. The core may comprise a foamed or sponge-like material and wholly or partially fill the interior space. Alternatively, where the aeration device is hollow or substantially hollow, the interior space may include one or more cross members to prevent compression of the aeration device when placed in the particulate mass, liquid substance or combination thereof. Preferably, aeration devices according to the present invention will comprise a biodegradable material. For example, a synthetic biodegradable polymeric material such as a polyalkylene ester, polyacetic acid or a copolymer thereof, a polyamide ester, a polyvinyl ester, polyvinyl alcohol, polyanhydride or mixtures thereof, and/or a natural biodegradable polymeric material such as cellulose or starch-based polymers, and mixtures thereof). Preferably, the biodegradable material degrades at temperatures in the order of 60° to 8O⁰C which is typical of actively composting organic waste material.

Composite biodegradable materials may also be suitable, for example, composite materials formed from any combination of biodegradable materials in which a small proportion of non-biodegradable material is present. Suitable composite materials may be formed by cross-polymerising polymeric materials or by integrating other structural compounds within polymeric materials such as structural fibres including fibres of proteinaceous materials and/or lignin- or chitin-containing materials.

Where the aeration device comprises a biodegradable material or a composite material, it will be understood that the device is substantially resistant to damage (particularly crushing or collapse) caused by placement within said particulate mass, liquid substance or combination thereof, while the biodegradable or composite material is substantially undegraded. Preferably, such aeration devices will remain substantially undegraded for a period of at least one week, more preferably at least two weeks, after placement within said particulate mass, liquid substance or combination thereof.

An aeration device according to the present invention may be manufactured from a variety of methods which will be readily apparent to persons skilled in the art (eg by injection moulding or extrusion). In one preferred embodiment, the aeration device is manufactured in an integral form such as, for example, a hollow ball composed of a single rigid or resilient material, or a ball comprising a single, substantially uniform mass of a foamed or sponge-like material (ie wherein the chambers located, at least partially, at the surface of the foamed or sponge-like material form the required pore(s) of the surface of the device). For the latter form, the method of manufacture may include the preparation of resilient rubbery materials to generate a foamed or sponge-like mass prior to moulding the mass into a desired shape. Alternatively, such a form may be manufactured by forming a desired shape from reactive polymers, wherein a foamed or sponge-like material is produced during the polymerisation process.

Alternatively, aeration devices according to the present invention may be formed from two or more pieces (eg two hemispheres to produce a ball, or a spherical core comprising a single, substantially uniform mass of a foamed or sponge-like material and an outer covering comprising a rigid material and provided with at least one pore therein to communicate, in the formed ball, with the core of the interior space).

Accordingly, methods of manufacture may involve a joining (eg by snap-fitting) or adhering step (eg involving ultrasonic welding processes) for uniting such pieces. In embodiments of the aeration device which comprise a core of a foamed or sponge-like material and an outer covering comprising a rigid material, the outer covering will preferably have a thickness in the range of about 0.1mm to 1.5mm, more preferably in the range of about 0.25mm to 0.75mm and, most preferably, about 0.5mm. In any case, the ratio of the volume of the outer covering (including pore volume) to the volume of the interior space is preferably no greater than about 1:1, more preferably no greater than 1:10 and, most preferably, is about 1:60.

An aeration device according to the present invention, in use, will be dispersed or incorporated within the biopile along with a plurality of others, which may be the same or similar (ie the plurality of aeration devices may have, for example, the same or similar structure and/or composition), to enhance biodegradation, bioconversion and/or decomposition. As mentioned above, aeration devices may be provided in an array.

Non-biodegradable aeration devices according to the present invention, having a cross-sectional dimension of greater than about 10mm may, if desired, be readily recovered from the particulate mass, liquid substance or combination thereof, following bioremediation by simple sieving. On the other hand, there may be no need to recover biodegradable aeration devices following the bioremediation treatment. Alternatively, in one preferred embodiment, the aeration device comprises a biodegradable core (including dosing materials) and a non-degradable outer covering comprising a rigid material, such that hollow or substantially hollow, "spent" devices may be recovered for reuse following bioremediation.

An aeration device according to the present invention, particularly those comprising biodegradable materials, may optionally exhibit absorbent characteristics such that the device may be utilised as a means for dosing the particulate mass, liquid substance or combination thereof, with materials that enhance biodegradation, bioconversion and/or decomposition (eg a device may comprise phosphate and/or nitrogen) or which adjust environmental conditions (eg a device may comprise buffer solutions). Otherwise, such materials may be coated onto the surface of the aeration device or contained within the interior space within, for example, a permeable sachet.

Preferably, absorbent aeration devices retain sufficient structural integrity (ie when placed in the particulate matter) to allow adequate gases to pass between the interior space and the exterior of the device but permitting slight compression to effect the slow and controllable release of the dosing material.

Alternatively, where the device comprises a biodegradable material, the dosing material may be released or become dissolved/resuspended as the device degrades within the pile. This may be assisted through generation of heat (ie naturally or through the application of heat) within the particulate matter or irrigation.

Suitable dosing materials and their concentrations can be readily determined by persons skilled in the art and preferably include micronutrients (eg phosphate such as superphosphate fertiliser and/or nitrogen such as urea), oxidising agents (eg iron nano-particles), macronutrients (eg vitamins and the like), and/or bacteria (eg Bacillus spp. or Pseudomonas spp.).

In the context of a biopile, and while not wishing to be bound by theory, it is believed that once dispersed or incorporated into a biopile, the plurality of aeration devices provide enhanced aeration therethrough by establishing a network of channels that allow for the movement of gases within the biopile and with the external environment, and assist to prevent compaction of the particulate matter, to further enhance biopile aeration. This is depicted schematically in Figure 4 wherein the flow of gases between aeration devices in a biopile is indicated with arrows. The aeration devices (1) illustrated comprise hollow spheres of 40mm diameter comprising 5mm diameter pores (2) on the surface.

In order to achieve optimal gaseous exchange of aeration devices in a biopile, a preferred ratio of the void volume of aeration devices to biopile volume is at least 1:100. However, ideal ratios may depend on the dimensions of the devices and the pattern of device distribution within the pile. More preferably, the ratio of the void volume of aeration devices to biopile volume is at least 1:50, more preferably about 1:10, more preferably 1:4, even more preferably 1:2 and most preferably, about 1:1.

For use in a biopile, a plurality of aeration devices according to the present invention will, preferably, be dispersed or incorporated into a biopile in a pattern that is substantially uniform throughout the biopile as illustrated in Figure 5. However, other patterns of distribution may also be suitable such as, for example, a distribution of aeration devices predominantly at the base of the pile, either in a single layer or intermittently at the base. Alternatively, aeration devices may be placed in layers throughout the pile by placing one layer of devices at the base of the pile, followed by a covering layer of biopile particulates, followed by a further layer of devices thereon and so forth until the final desired structure of the biopile is achieved.

A plurality of aeration devices according to the present invention may also be used in a biopile, in combination with another aeration system, such as a conventional reticulated aeration system known in the art and illustrated in Figures 2 and 3. Air or oxygen is conventionally pumped into a reticulated system (8) via, for example, pump (9) placed at the base of a biopile. Air or oxygen is forced into the base of the pile which in turn promotes the egress of gases from within the pile to the surrounding atmosphere. The combined use of aeration devices according to the present invention, with an additional aeration system such as a reticulated aeration system, should further enhance the movement of gases within the biopile and with the external environment. The use of combined aeration systems may optionally require the addition of further additives to the biopile, for example, the addition of water to prevent drying of the particulate matter (eg by irrigation).

In a second aspect, the present invention provides a method for aerating a particulate mass, a liquid substance or a combination thereof comprising, at least in part, some organic matter, wherein said method comprises the step of;

(i) incorporating a plurality of an aeration device according to the first aspect within said particulate mass, liquid substance or combination thereof.

The method may further comprise the step of:

The optional further step of adding one or more materials that enhance or improve the biodegradation, bioconversion and/or decomposition of the particulate matter may involve adding water, micronutrients and/or macronutrients such as those discussed above, microbial inocula to augment the population of microorganisms present in the particulate matter or introduce different microorganisms, for example, to initiate co-metabolism of contaminating compounds, and/or materials such as sand or gypsum that alter the characteristics of the particulate matter (especially useful for clay soils) which, in turn, result in changes to the "bioavailability" of contaminants (and/or micronutrients, macronutrients etc).

Preferably, the addition of water may be made at any stage of the composting and/or decontamination process (eg by irrigation) and with variable frequency. The need for the addition of water may be readily ascertained by persons skilled in the art, who will recognise that such a need will depend according to several factors and, particularly, environmental conditions such as temperature, humidity and external wind velocity.

Preferably, the addition of micronutrients and/or macronutrients is achieved by the addition of further waste streams such as woodchips or green organic waste.

An aeration device according to the present invention, when used in the method of the second aspect, is preferably dispersed or incorporated within said particulate mass, liquid substance or combination thereof, along with a plurality of other devices, which may be the same, similar or different (ie the plurality of aeration devices may have, for example, the same or similar structure and/or composition), by mixing into and through the particulate matter by hand, with the use of a manually operated implement (eg a bucket or shovel), or by other automated or mechanical means such as a front end loader, a windrow top turner or soil blending machinery. The exact method used for dispersing and/or incorporating a plurality of aeration devices according to the present invention within a biopile will be primarily determined by the particular pile size. However, since piles typically comprise several tonnes of particulate matter, the use of a front end loader will generally be the preferred means.

The method of the second aspect may also further comprise the step of recovering the aeration devices following the composting and/or decontamination of said particulate mass, liquid substance or combination thereof. Thus, the devices can be collected (eg by simple sieving) and reused in subsequent biodegradation, bioconversion and/or decomposition methods. Alternative means for recovering aeration devices may involve, for example, magnetically separating aeration devices which comprise, at least in part, a metal or metal alloy (eg steel) or which have been otherwise coated with a metal or metal alloy (eg a metal film).

The present invention is hereinafter further described by way of the following, non-limiting examples and accompanying figures.

EXAMPLES

Example 1

Initial laboratory scale experiments were conducted to assess any enhancement of the rate of hydrocarbon biodegradation in soils containing aeration devices. Further, these experiments were conducted to trial the physical characteristics of aeration devices, for example to determine whether the devices are susceptible to compaction under the weight of a biopile and whether or not they are easily recoverable for reuse.

Methods and Materials Test soils were obtained from soils that had previously been contaminated following a petrochemical spill. Two piles of approximately 2m³ were formed from the test soils side by side in a field environment.

Aeration devices comprising hollow polyvinyl chloride (PVC) spheres of 40mm diameter (1), with about 0.5-1.0 mm thick walls and comprising 5mm diameter perforations (2) on the surface thereof as illustrated in Figure IA, were used to treat one of the two piles of test soils. In particular, around 500 of such aeration devices were homogenously combined into the "first pile". The "second pile" remained untreated as a control. Urea, superphosphate and water were added to each pile to achieve a total carbon to nitrogen ratio of 25: 1 (w/w) and a moisture content of approximately 60% (w/w). Water was added to prevent drying throughout the following 120 days, although no additional turning or aeration was undertaken during this period. After 120 days, the change in total petroleum hydrocarbons (TPH) from the initial concentrations was determined.

Results

Samples were collected in duplicate at the initial and 120 day time points and the mean change in TPH was measured. Average TPH concentrations for each treatment at the two time points are provided in Table 1.

Table 1 TPH concentrations (mg/kg) in soil treated with aeration devices and control soil (mean of duplicate samples)

A reduction in TPH concentration of 18,000 mg/kg or 75% total TPH was observed in treated samples in comparison to a reduction of 6,000 mg/kg or 30% total TPH in control samples, representing a 35% improvement in biodegradation with treatment. Further, the aeration devices were found to be easily recovered from the soils and were not substantially damaged during the remediation process. This initial data provided sufficient information to proceed with more comprehensive trials.

Example 2

A trial was conducted utilising biodegradable aeration devices in biopiles.

Methods and Materials

Aeration devices comprising hollow spheres of biodegradable/compostable cornstarch (Biograde-BM, Biograde Limited, Mulgrave, VIC, Australia) were formed by snap-fitting together hemispherical pieces produced by standard injection moulding techniques. The devices (1), which are illustrated in Figure IB, were of 60mm diameter, with about 0.5- 1.0mm thick walls and comprising a regular pattern of "square" shaped perforations (2).

Four biopiles of consistent, homogeneous materials were built in the same dimensions. The homogenous material comprised shredded green organics blended with wet organics in the form of grease trap liquids, potato starch and other food organic by-products. This formed a high moisture, high nutrient, low porosity mixture which is indicative of a composting feedstock that is typically difficult to compost. Two of the biopiles were constructed on top of an aeration bed and the other two on a regular compacted base. The aeration devices were applied to one of the aerated biopiles and one of the non-aerated biopiles. The aeration devices were mixed in evenly using a loader at a rate of about 50 devices per m³. Only about one in every 100 aeration devices was broken in this operation.

The biopiles were left for 40 days to compost and were not mechanically disturbed for the duration of the composting cycle. The two biopiles on the aeration bed received oxygen by pumping through the aeration bed on an on/off duty cycle which was 10 minutes on and 5 minutes off. Temperature readings were taken weekly for all piles. Each biopile was measured in both sides and on the top. Each reading had two temperatures taken at a depth of 0.3m and at Im. The gas production of each biopile was also taken weekly. Readings were taken in one side and in the top of the pile. The gases measured were oxygen, carbon dioxide and methane. The moisture content of the biopiles was observed on a weekly basis to ensure that the piles had sufficient moisture to enable the composting process to occur.

In addition, some aeration devices were also specifically planted in the biopiles and attached to a wire so as they could be retrieved at different time to assess their decomposition rate.

At the conclusion of the 40 days of composting, the biopiles were opened up by using loaders and internally assessed for aeration devices and compost quality indicators. The static biopiles were then also sampled and submitted to microbial testing.

Results Biodegradabilitv assessment

After three days, it was noticed that the aeration devices in the aerated biopile had significantly reduced strength and were starting to crumble. After 21 days, the aeration devices in the static biopile also showed significantly reduced strength and, indeed, some of the devices had become crushed under pile compaction. This was more severe in the aerated biopile at that time, with the aeration devices appearing as flat structures. These devices also now had a rubber-like feel and could be readily pulled apart. By 33 days, it was clear that the biodegradation of the aeration devices in the aerated biopile was more significantly advanced, with only portions of the devices being found. In contrast, the aeration devices in the static biopile had now degraded to the flat structure and rubber-like feel observed previously in the aerated biopile. After 40 days, it was found that in the aerated pile, the only remaining aeration devices were a few that had been located in the very outer 200mm layer. The static biopile, in contrast, had a lot more aeration devices still present, but this amount was still only a small number relative to the amount that was initially added to the pile. Biopile data and observations

After 21 days, it was noticed that the piles had dropped significantly in height. The following approximated height decreases were found: static with no devices (SND), 0.5m; static with aeration devices (SAD), 0.75m; aerated with no devices (AND), Im; and aerated with aeration devices (AAD), 1.5m. After 33 days, the biopiles had dropped in height again by roughly 0.5m for all piles. The biopiles containing the aeration devices were found to be about 0.5m lower than the control biopiles containing no devices. It was also noticed that the SND biopile had a very putrid smell and was likely to be anaerobic. This smell was not detectable in the other piles. Also, fungi development on the biopiles was visually assessed at this time. It was found that the fungi development in the biopiles containing aeration devices was more advanced than the respective control biopiles with no devices. Further, after 40 days, mushroom development was observed on the aerated biopile containing aeration devices (ie the AAD biopile) indicating superior microbial development. When the biopiles were pulled apart at this time, examination of the biopile materials found that the AAD biopile had an organic, well composted odour with good moisture content and lots of fungal development. The AND also had a well composted odour but the fungal development was not as great. There were also very good indicators of macro- invertebrates, in the form of beetles and other bugs, in the AAD biopile. In contrast, the SAD biopile now smelt putrid, had a much higher moisture content (and was extremely sloppy and wet at the bottom), showed very little fungal development and no signs of macro-invertebrates. Indeed, like the SND biopile, this biopile also appeared to be anaerobic.

Results of microbial testing for the SND and SAD are shown in Table 2. The temperature and gas readings taken from each of the biopiles are shown in Tables 3 and 4, respectively.

Discussion

No significant advantages were observed between the control biopiles and those including aeration devices in terms of oxygen and temperature. However, microbial testing and observations did indicate that larger microbial populations and a superior food web were found in the biopiles with aeration devices. This may be due to improved initial composting and, in the case of the static biopiles, the additional one week period where the aeration devices were still functioning, may have given the biopile a "better start" and resulted in a bacterial population that was nearly double that of the relevant control biopile (ie SND biopile).

Table 3

Table 4

Example 3

A trial was conducted utilising biodegradable aeration devices in commercial in-vessel composting bins.

Methods and Materials

The trial used two BiobIN® airtight waste collection bins (Biobin Technologies Pty Ltd, Aldinga, SA, Australia). These bins include air pumps to circulate the air inside to aerate any waste materials placed in the bins and thereby increase the rate of decomposition.

The aeration devices used were as described in Example 2.

To determine any differences in the rate of composting between the two bins, a qualitative and quantitative assessment was performed. The qualitative assessment was conducted by visually inspecting the state of the waste in the bins; assisted by taking photographs periodically. The quantitative assessment was achieved by measuring the following:

(i) Gases: oxygen, carbon dioxide, methane, hydrogen sulphide, ammonia and volatile organic compounds (VOCs); and

(ii) Compost temperature.

The gases were measured using gas tubes installed at three different depths in each bin at 0.1m, 0.6m and at 1.2m. Gases were sampled twice a day using gas analysers and the results tabulated. Carbon dioxide was measured using a WMA-4 CO₂ Analyzer (PP Systems International, Inc., Amesbury, MA, United States of America) and the other gases of interest (ie oxygen, methane, hydrogen sulphide, ammonia and VOCs), were measured using an MX6 iBRID™ gas monitor (Industrial Scientific Corporation, Oakdale, PA, United States of America).The gas measurements from each depth were averaged to ensure an even distribution of data. Temperature probes were set up in each bin to track the changes in temperature of the compost overtime.

A total of about 400 kg of food waste was added to each bin over a period of 41 days. To simulate the rate of conventional waste addition, 20 kg of organic waste was initially added to each bin every day. After two weeks, this was modified to an addition of about 50 kg twice a week to avoid disruption to the sealed internal compost system. In Bin A, forty aeration devices were added as an even layer with every waste addition. In Bin B, in the place of the aeration device treatment, a layer of waste cardboard was added as the control. Cardboard was chosen as the control as this is the material used in current practices with conventional waste bins. Results

Gas Measurements

Over the duration of the trial of 41 days, methane, hydrogen sulphide and ammonia was not detected. An average of 19 % volume of oxygen was detected in the bin including aeration devices (Bin A) and an average of 19.81% volume of oxygen was recorded in the control Bin B. This equates to 0.81 % volume or 8100 ppm of oxygen reduced in Bin A.

In terms of carbon dioxide evolution, Figure 6 displays the daily concentration of carbon dioxide evolved over 41 days. The temperature profile included in the figure suggested that it was unlikely that there was a correlation of the amount of carbon dioxide produced in relation to the temperature inside the bins. The average carbon dioxide concentration was 21738 ppm in Bin A compared with 12809 ppm in the control Bin B. Given that the environmental concentration of carbon dioxide is approximately 400 ppm, this data indicated that respiration was occurring in both bins. From these results, the reduction of 8100 ppm of oxygen and the increase in 8928 ppm of carbon dioxide closely correlates to a 1 : 1 ratio of oxygen to carbon dioxide in the respiration reaction stoichiometry. In addition, given that 8928 ppm or about 70% more carbon dioxide was generated in the Bin A than in the control, the results indicated that respiratory activity was elevated by the use of aeration devices.

With regard to VOCs, Bin A produced 122.52 ppm or 30% less compared to the 175.01 ppm produced in the control Bin B. This result indicates that the aeration devices may have potentially reduced the evolution of odours as, in the absence of hydrogen sulphate, volatile carbon compounds probably represent the contributors to odour in the BiobiN®.

As shown in Figure 6, the temperature profiles from both bins were similar and this suggested that there was no significant difference in the temperatures despite the application of different treatments. In addition, given that the temperatures did not reach the expected levels of 50 ^σC and above, it can be concluded that both the systems did not achieve active composting states. This is likely to have been due to cool environmental conditions since this trial was conducted in the winter months.

Visual Assessment

The state of decomposed matter in both the bins at the end of the trial was observed to be similar. The waste matter was examined from both bins at subsurface levels and it was found that the matter was dense and clay-like. It was found that the aeration devices from prior additions were not degraded. This result was consistent with the temperature profile discussed above which indicated that an active composting state had not been achieved. Discussion

The results of this trial, particularly the evidence of increased respiration in Bin A, indicate that the aeration devices showed significant potential for the treatment of organic waste contained in an in- vessel composting bin to improve the effectiveness of composting. It was also found that there is potential for the aeration devices to reduce the production of odours in in-vessel composting bins.

Example 4

Experiments were conducted to "coat" aeration devices with bacteria useful in the decomposition of biopile materials.

Methods and Materials

Three separate experiments were conducted to detect the presence of bacteria that constitutively expressed green fluorescent protein (GFP) on aeration devices as described in Example 2. The following bacterial strains were used: ABl 157 (Yale University, New Haven, CT, United States of America) - an attenuated E. coli strain that does not express GFP (negative control); and pNGFP

(Goodman Laboratory, Flinders University, Bedford Park, SA, Australia) - an attenuated E. coli strain that carries the plasmid pNGFP which permits the bacteria to constitutively express GFP.

The aeration devices were pre-treated as follows: (i) No pre-treatment;

(ii) Fine sandpaper treatment (a fine sandpaper rub was applied over half of each aeration device before bacterial application); and

(iii) Coarse sandpaper treatment (a coarse sandpaper rub was applied over half of each aeration device before bacterial application).

To the "no pre-treatment" devices, two coats of an overnight culture of the E. coli strains were pipetted directly on to separate aeration devices and incubated at room temperature for 60 min.

For the devices pre-treated with the application of sandpaper, aeration devices were placed in sterile nutrient broth in two separate beakers, one containing ABl 157 and the second pNGFP, and cultured overnight. The aeration devices were then extracted from the culture, left to air dry for approximately 40 minutes and photographed. The overnight cultures were also spotted onto a nutrient agar plate and incubated overnight. In a further experiment, devices that had been pre-treated with the application of sandpaper were placed in sterile nutrient broth including 5% glycerol in two separate beakers, one containing ABl 157 and the second pNGFP, and cultured overnight.

Results

With the "no pre-treatment" devices, there was little detectable fluorescence on the aeration devices following incubation, suggesting that the device does not provide a good surface for bacterial adhesion and growth. However, when pre-treated with fine or coarse sandpaper and cultured with the bacteria overnight, there was a clear difference in fluorescence between the devices cultured with the ABl 157 and pNGFP strains. That is, the aeration devices cultured with the pNGFP strain showed fluorescence whilst the aeration devices cultured with ABl 157 did not. This indicated that sandpaper treatment was able to increase bacterial adherence and growth. When 5% glycerol was included in the culture medium, an increase in the overall level of fluorescence was observed.

Discussion

The results of these experiments showed that a simple culturing process could be employed to provide aeration devices with a "dose" of bacteria for composting waste in a biopile. For the cornstarch-based devices used in the experiments, it was necessary to roughen the surface in order to achieve bacterial adherence.

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

All publications mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of each claim of this application.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

1. An aeration device for placing within a particulate mass, a liquid substance or a combination thereof, said device comprising a three dimensional structure comprising a surface provided with at least one pore therein, and wherein said structure defines a minimum cross-sectional dimension of about greater than 10mm and is substantially resistant to damage caused by placement within said particulate mass, liquid substance or combination thereof.

2. An aeration device for placing within a particulate mass, a liquid substance or a combination thereof, said device being comprised of a biodegradable material and comprises a three dimensional structure comprising a surface provided with at least one pore therein, wherein said structure defines a minimum cross-sectional dimension of about greater than 10mm.

3. The device of claim 1 or 2, wherein the three dimensional structure defines an interior space containing gas.

4. The device of claim 3, wherein the three dimensional structure of the interior space is hollow.

5. The device of any one of the preceding claims, wherein the three dimensional structure is of a substantially spherical shape.

6. The device of any one of the preceding claims, wherein the minimum cross-sectional dimension is in the range of 15mm to 150mm.

7. The device of any one of the preceding claims, wherein the minimum cross-sectional dimension is in the range of 30mm to 60mm.

8. The device of any one of the preceding claims, wherein said device is comprised of a biodegradable polymeric material selected from the group consisting of polyalkylene esters, polyacetic acid or a copolymer thereof, polyamide esters, polyvinyl esters, polyvinyl alcohol, polyanhydride or mixtures thereof, cellulose, starch-based polymers, and mixtures thereof.

9. The device of any one of the preceding claims, wherein the device further comprises one or more of phosphate and/or nitrogen, buffer solutions, oxidising agents, macronutrients and bacteria.

10. A method for aerating a particulate mass, a liquid substance or a combination thereof comprising, at least in part, some organic matter, wherein said method comprises the step of; (i) incorporating a plurality of an aeration device according to any one of the preceding claims within said particulate mass, liquid substance or combination thereof.

11. The method of claim 10, further comprising the step of:

12. The method of claim 10 or 11, wherein the particulate mass, a liquid substance or a combination thereof is a biopile.

13. The method of claim 10 or 11, wherein the particulate mass, a liquid substance or a combination thereof is organic waste contained within an in-vessel composting bin.

14. The method of claim 13, wherein a plurality of aeration devices are introduced into the bin as a layer with a covering layer or organic waste.

15. The method of claim 14, wherein the aeration devices are provided as an array.