The present invention relates to a method and system for processing organic waste including an anaerobic bioreactor for fermenting the organic waste to generate biogas and an aerobic bioreactor covering at least in part the anaerobic bioreactor. The invention relates particularly, but not exclusively, to thermally regulating the anaerobic bioreactor using decomposing further organic waste, such as compost material, contained in the aerobic bioreactor. The present invention has particular, but not exclusive, application in processing piggery waste from a piggery and decomposing compost material in the aerobic bioreactor.

BACKGROUND OF THE INVENTION

Existing examples of systems for processing organic waste and generating biogas employ an anaerobic bioreactor, in the form of a pit or a tank, to ferment the organic waste, such as piggery waste or other animal waste, to generate the biogas. One of the major advantages of these existing systems is that they require low initial capital investment. However, both the biogas-generating pit and tank systems have a major shortcoming in their batch operation. That is, these traditional pits and tanks require batch input and discharge of the organic waste to be processed. As such, there is the problem of efficiently inputting the organic waste and discharging residue of the waste following biogas generation after the fermentation process is completed. In addition, the yields of biogas from these biogas generating tanks and pits are affected by external factors such as ambient air temperature, presence of bacteria in the organic waste, etc. As a result, biogas yields can fluctuate substantially across, say, the different seasons.

Furthermore, discharging of the waste after biogas production is also a problem for these traditional pit or tank systems as the residue typically has a high nutrient content with high levels of Dissolved Organic Carbon (DOC) which can cause significant pollution if the waste is released directly into the environment. Biogas production using these traditional batch fermentation systems is thus inefficient and these systems potentially generate secondary contaminants which ultimately can cause the biogas produced in this way to be relatively expensive. Another existing example of a system for processing organic waste includes an anaerobic bioreactor having a biogas fermentation tank with a feeding pipe and a discharge outlet for allowing organic waste to pass therethrough whilst being fermented. That is, the traditional batch based fermentation tank is modified for continuous operation by having a suitable inlet and outlet and by being set at a certain angle to the mounting surface when it was installed to ensure that the organic waste being fermented flows from upstream to downstream. Accordingly, the fermentation residue can be easily discharged from the outlet after the fermentation process. The fermentation process taking place in this example of an existing fermentation tank, however, is still readily affected by external factors, such as changes in ambient air temperatures, which can cause unstable production of biogas.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a system for processing organic waste, the system including:

an anaerobic bioreactor for fermenting the organic waste to generate biogas, the anaerobic bioreactor including:

an inlet for receiving said organic waste in the anaerobic bioreactor; an outlet for outputting said organic waste from the anaerobic bioreactor;

a fermentation tank disposed between the inlet and the outlet for fermenting the organic waste passing therethrough to generate the biogas; and a biogas outlet for outputting the biogas generated in the fermentation tank; and

an aerobic bioreactor covering at least in part the anaerobic bioreactor and containing a further organic waste, whereby the further organic waste in the aerobic bioreactor decomposes and thermally regulates the anaerobic bioreactor.

Preferably, the organic waste includes piggery waste from a piggery and the further organic waste includes biomass compost material. In addition, the organic waste is in the form of a slurry of piggery waste including pig manure, urine and water. As such, the inlet of the anaerobic bioreactor receives the slurry and the outlet of the anaerobic bioreactor outputs the slurry after it passes through the fermentation tank. In an example, the slurry has a solid to liquid ratio of around 20:1 ; nonetheless it will be appreciated by those persons skilled in the art that the slurry can be prepared to have a different solid to liquid ratio depending on, say, the size of the fermentation tank. In an embodiment, the aerobic bioreactor covers at least an upper surface of the anaerobic bioreactor. In the embodiment, the inlet, the outlet and the biogas outlet protrude from the upper surface of the anaerobic bioreactor and protrude from the aerobic bioreactor covering at least the upper surface of the anaerobic bioreactor. Preferably, the biomass compost in the aerobic bioreactor decomposes to act as a heating source and a thermal isolation layer to maintain a relatively stable

temperature inside the anaerobic bioreactor to achieve a relatively constant generation of biogas. In one example, a thick layer of compost covering the upper surface of the anaerobic bioreactor generates heat from aerobic composting to warm the anaerobic bioreactor and to insulate the anaerobic bioreactor from cold wintry conditions so as to thermally regulate the anaerobic bioreactor to ensure stable and optimal anaerobic reaction and to ensure optimal biogas production. In the example, the biomass is cut into 2 to 5cm lengths, mixed with water and placed over the top of the upper surface of the fermentation tank and around fermentation tank of the anaerobic reactor for 50 to 60 days. The compost undergoes an aerobic composting process over this time which warms the anaerobic fermentation tank to ensure that an optimum fermentation temperature is maintained in the fermentation tank. The composted biomass can also be removed and used as fertilizer, with new batches of biomass added to the top of the bioreactor to ensure the bioreactor's temperature remains steady.

It will be appreciated by those persons skilled in the art that the term "covering" is used to encompass completely and partially covering of at least the exposed areas of the anaerobic bioreactor by the aerobic bioreactor. The term "aerobic bioreactor" refers to a zone in which the further organic waste is substantially contained. For example, the anaerobic bioreactor is partially submerged in the ground and the aerobic reactor is the zone including the exposed upper surface of the anaerobic bioreactor and the partially exposed side walls of the anaerobic bioreactor. In this zone, the further organic waste decomposes to thermally regulate the anaerobic bioreactor. In another example, the aerobic reactor is the zone including just the exposed upper surface of the anaerobic bioreactor and the further organic waste is heaped on top of the anaerobic bioreactor to decompose and thermally regulate the anaerobic bioreactor.

In an example, the fermentation tank of the anaerobic bioreactor that produces biogas by anaerobic fermentation (e.g. digestion) of piggery waste is a substantially horizontally constructed column shaped tank with a gradient of 3 to 5 degrees from the entry inlet down to the exit outlet to allow the digested slurry to slowly move from the entry to the exit during the process of fermentation over say thirty days. Also, the long column shaped fermentation tank design has several advantages: it is easy to operate continuously, it is able to be kept gastight, waste can be discharged conveniently, it produces biogas with high yield, and the unit construction cost is low. Thus, in use, the slurry of piggery waste is pumped into the fermentation tank of the anaerobic bioreactor and the slurry will flow slowly, under gravity, to the outlet. As it flows, the slurry comes into contact with bacteria and microbes under anaerobic conditions to produce the biogas.

As described, the anaerobic bioreactor anaerobically ferments the organic waste to generate the biogas using bacteria in the organic waste. For example, the piggery waste slurry is pumped into the inlet of the anaerobic reactor with biogas-producing bacteria for digestion of the waste under anaerobic conditions. The piggery waste comprises pig manure, pig urine and wastewater (generally used to maintain hygiene of the piggery); the piggery waste normally prepared containing 20% by weight total solids with a carbon-to-nitrogen ratio of about 20-30: 1 . It will be appreciated by those persons skilled in the art that the organic waste can include other types of waste; for example, other types of animal waste discharged through livestock farming that fit the above criteria can also be used as feed material for biogas production. In an embodiment, the anaerobic bioreactor further includes a mixing mechanism to mix the bacteria in the organic waste in the fermentation tank. The mixing

mechanism can break down large aggregates in the slurry and improve contact of waste with the biogas (e.g. methane) producing microbes and bacteria. In the embodiment, the mixing mechanism includes piping disposed along a bottom surface of the fermentation tank, whereby the piping has a gas piped therethrough and has a plurality of holes for bubbling the gas into the fermentation tank. For example, biogas is pumped through the piping from the bottom of the tank to mix the slurry evenly so that the fermentation process in the anaerobic bioreactor takes place smoothly and thoroughly.

Alternatively, or in addition, the mixing mechanism includes a mechanical mixer adapted to move along a length of the fermentation tank. For example, the mechanical mixer includes a moving cart adapted to move along a bottom surface of the fermentation tank along the length of the fermentation tank to say break up large blocks of piggery waste and shift the waste towards the exit outlet. The mechanical stirring system can be operated externally with a metal cable pulling the moving cart in either direction along the length of the tank. In an embodiment, the anaerobic bioreactor further includes a safely pressure release mechanism (e.g. safety-relief valve) for preventing pressure build up above a threshold pressure in the fermentation tank. It will be appreciated by those persons skilled in the art that the fermentation tank is kept airtight and is isolated from the inlet and outlet of the anaerobic bioreactor. In addition, the anaerobic bioreactor includes several sensor and sampling outlets for monitoring the fermentation process in addition to the safety-relief valve to prevent over-accumulated biogas. The anaerobic bioreactor can thus be operated continuously and can produce large amounts of gas along the horizontal length of the fermentation tank. The fermented or digested waste from the anaerobic reactor is discharged and separated, and the liquid portion undergoes aerobic remediation to reduce the nutrient content and Dissolved Organic Carbon (DOC) in the wastewater; thus allowing the remediated liquid fraction to be discharged safely into the environment. In an embodiment, the system for processing organic waste further includes a separator for separating liquids and solids from the slurry of organic waste. The separator includes a separator inlet for inputting the slurry from the output of the anaerobic bioreactor, a liquid outlet for outputting substantially liquid from the separator, and a solids output for outputting substantially solids from the separator. In an example, the waste from the anaerobic bioreactor is pumped into a settlement tank of the separator for say 24 hours, after which the solid fraction moves to the bottom of the tank, allowing the liquid waste to flow out into a regulating tank and then to one or more remediation ponds. In the example, the solid waste residue separated is less than 3% of the total slurry weight and can be used for say composting to improve soil quality. If the solid content in the waste is high, it can be also used as raw material to produce bio-char. In this case, the waste material is dehydrated to have a moisture content of less than 1 0% and then undergoes biomass pyrolysis to convert waste residue to bio-char. The biomass pyrolysis involves heating biomass, such as agricultural and forestry waste, in a low/zero -oxygen atmosphere, resulting in solid, liquid and gas products. Bio-char is the solid residue of biomass pyrolysis performed at 400-600°C, with particle size of less than 2mm in diameter. The conversion rate of bio-char from biomass is typically around 30-35%.

In an embodiment, the separated liquid fraction in the regulating tank is diluted 1 :1 with totally remediated wastewater recycled from the system, as described below, to reduce the initial contaminant load for further remediation. In an embodiment, the system further includes remediation ponds for remediating liquid from the separator. The remediation ponds include a pond inlet for inputting said liquid from the separator or the regulating tank, an algae film layer for aerobically remediating the liquid in the pond, and a pond outlet for outputting the liquid from the pond. For example, the diluted wastewater is pumped into a remediation pond, which has a suspended bio- algae membrane which degrades the wastewater to reduce the nutrient and DOC contents over seven days. In an embodiment, the system further includes an algae removal tank for removing the algae from the liquid from the pond. The algae removal tank includes an algae removal tank inlet for inputting said liquid from the remediation pond, a sand filtration layer for filtering the algae from the liquid, and an algae removal tank outlet for outputting the liquid from the algae removal tank.

In an embodiment, the system further includes an adsorbent tank for removing heavy metals from the liquid, the adsorbent tank including an adsorbent tank inlet for inputting said liquid from the algae tank, an adsorbent layer for removing heavy metals from the liquid, and an adsorbent tank outlet for outputting the liquid from the adsorbent tank. The adsorbent layer includes an adsorbent such as activated carbon, bio-char produced from the system, or a modified clay product.

As described, a portion (e.g. 50%) of the liquid from the outlet of the adsorbent tank is mixed with the liquid from the separator before being inputted into the remediation pond to reduce the amount of nutrients and Dissolved Organic Carbon (DOC) in the liquid from the separator, and a further portion (e.g. 50%) of the liquid from the outlet of the adsorbent tank is discharged to environment. Once free of heavy metals, the wastewater can be classified as totally remediated wastewater (TRWW), which meets the appropriate guidelines for wastewater discharged from say piggeries.

Accordingly, in an embodiment, the system processes organic waste from a piggery in two stages. The first stage is to generate biogas using the anaerobic bioreactor, which can be used to say generate energy using the methane in the biogas. It will be appreciated by those persons skilled in the art that the biogas predominantly includes methane as well as carbon dioxide, hydrogen sulphide, etc. The second stage is to remediate the solid waste, which can be used for say production of fertilisers and biochar, and liquid in the form of waste water that can be discharged into the environment safely with minimum environmental burden. That is, the system remediates the piggery waste by removing pathogens, reducing carbon, nitrogen and DOC contents by the algae film and adsorbing heavy metals in the waste water waste.

According to another aspect of the present invention, there is provided a method of processing organic waste, the method including:

inputting the organic waste into an anaerobic bioreactor for fermenting the organic waste to generate biogas

fermenting the organic waste passing through the anaerobic bioreactor to generate said biogas;

outputting the organic waste from the anaerobic bioreactor;

outputting the biogas from the anaerobic bioreactor; and

thermally regulating the anaerobic bioreactor using decomposing further organic waste in an aerobic bioreactor covering at least in part the anaerobic bioreactor. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in more detail by way of non- limiting embodiments and with reference to the accompanying drawings, wherein:

Figure 1 is a top view of a system for processing organic waste according to an embodiment of the present invention;

Figure 2 is a sectional view of the system taken at A-A of Figure 1 ;

Figure 3 is a sectional view of the system taken at B-B of Figure 1 ;

Figure 4 is a sectional side view of a separator of the system for processing organic waste according to an embodiment of the present invention;

Figure 5 is a sectional top view of the separator of Figure 4;

Figure 6 is a sectional view of a remediation pond showing an algae bio- membrane of the system for processing organic waste according to an embodiment of the present invention;

Figure 7 is a sectional side view of the remediation pond of Figure 6;

Figure 8 is a sectional view of an adsorbent tank of the system for processing organic waste according to an embodiment of the present invention;

Figure 9 is a flow chart of a method of processing organic waste according to an embodiment of the present invention; and

Figure 1 0 is another flow chart of a method of processing organic waste according to an embodiment of the present invention.

DETAILED DESCRIPTION

According to an embodiment, there is provided a system 100 for processing organic waste as shown in Figures 1 to 3. The system 100 includes an anaerobic bioreactor 1 1 0 for fermenting the organic waste to generate biogas and an aerobic bioreactor 7 covering at least in part the anaerobic bioreactor 1 10 and containing a further organic waste that decomposes to thermally regulate the anaerobic bioreactor 1 1 0. The anaerobic bioreactor 1 10 includes an inlet 1 for receiving the organic waste in the anaerobic bioreactor 1 10. As described, the organic waste is preferably prepared in the form of a slurry of piggery waste having a certain solid to liquid ratio based on designated properties of the anaerobic bioreactor 1 10. In one embodiment, the slurry is piggery waste having a solid to liquid ratio of 20:1 . The system 100 is thus used in this case for processing piggery waste to produce biogas containing methane which can be used in, for example, energy production. Also, the prepared piggery waste slurry is pumped using a pump (not shown) into the inlet 1 of the anaerobic reactor 1 1 0 with biogas-producing bacteria for digestion of the waste under anaerobic conditions.

The anaerobic bioreactor 1 10 also includes an outlet 6 for outputting the piggery waste from the anaerobic bioreactor 1 10 after it passes through a fermentation tube 8 of a fermentation tank 9 disposed between the inlet 1 and the outlet 6 for fermenting the piggery waste to generate the biogas. As described, the slurry passes from the entry inlet 1 to the exit outlet 6 over say thirty days. During this period, the bacteria digest the piggery waste to anaerobically ferment the waste to produce the biogas. The biogas generated by the anaerobic bioreactor 1 1 0 is outputted from a biogas outlet 4 disposed on the upper surface of the fermentation tank 9.

Furthermore, the anaerobic bioreactor 1 1 0 has a pressure gauge 3 for monitoring pressure within the fermentation tube 8 of the fermentation tank 9. It will be appreciated by those persons skilled in the art that the pressure gauge 3 is used in connection with a pressure relief valve (not shown) that relieves pressure in the fermentation tube 8 when the pressure gauge 3 senses pressure exceeding a designated threshold value. In another embodiment, an operator of the system 100 is alerted when the sensed pressure exceeds a designated threshold value.

In addition, the fermentation tube 8 has a first panel 2 and a second panel 5 disposed inside the fermentation tube 8 which extend inwardly from its upper surface. In the embodiment, the input 1 is a feed pipe joined with the fermentation tube 8 at one end and the first panel 2 is set above the join to isolate the fermentation tube 8 from the upside of the feed pipe 1 . The other end of fermentation tube 8 is connected with the outlet pipe 6 and the second panel 5 is set above this join to isolate the digested organic waste from re-entering the fermentation tube 8.

As showed in the sectional views of Figures 2 and 3, the system 100 includes the aerobic bioreactor 7 covering nearly all of the upper surface of the fermentation tank 9 of the anaerobic bioreactor 1 10, except for the biogas outlet pipe 4, the inlet 1 and the outlet 6, and covering an upper portion (around 50%) of the side walls of the fermentation tank 9 of the anaerobic bioreactor 1 10. In the embodiment shown in Figure 1 , the aerobic bioreactor 7 surrounds the fermentation tank 9 of the anaerobic bioreactor 1 1 0 and is connected to the fermentation tank 9 with supports 13. That is, the aerobic reactor 7 is bound by side walls, connected to the fermentation tank 9 with the supports 13, a lower surface, and the sidewalls and upper surface of the fermentation tank 9 of the anaerobic bioreactor 1 10. In this way, for example, the system 100 including the anaerobic bioreactor 1 10 and the aerobic reactor 7 can be prefabricated and easily installed in the ground say adjacent a piggery. Also, as described above, when installing the system 100, the inlet end 1 of the fermentation tank 9 should be slightly higher by, say, one to ten degrees than the outlet end 6. This ensures that the fermenting piggery waste flows slowly downstream under gravity in the fermentation tube 8; thus allowing fermentation residues to be discharged easily via the outlet 6.

As described, the aerobic reactor 7 contains further organic waste (e.g. biomass) that decomposes to thermally regulate the anaerobic bioreactor 1 1 0 when it covers at least part of the anaerobic bioreactor 1 10. The further organic waste is in the form of compost which can be seen in Figures 2 and 3 as a thick layer of compost covering the upper surface of the fermentation tank 9 and part of the side walls of the fermentation tank 9. The decomposing organic waste generates heat to warm the anaerobic bioreactor 1 10 to insulate the anaerobic bioreactor 1 1 0 from cold wintry conditions and to thermally regulate the anaerobic bioreactor 1 1 0 to ensure stable and optimal anaerobic fermentation for optimal biogas production. In the example described above, the compost is mixed with water and placed in the anaerobic reactor 7 for 50 to 60 days before it is removed and used for say fertiliser.

In addition, Figures 2 and 3 show the anaerobic bioreactor 1 10 having a mixing mechanism disposed in the fermentation tank 9 to mix the bacteria in the piggery waste to improve contact of the waste with the biogas producing microbes and bacteria within the fermentation tank 9. The mixing mechanism is shown as a mechanical mixer 10 adapted to move along a length of the fermentation tube 8 of the fermentation tank 9. Specifically, the mechanical mixer 10 is a moving cart, or shell frame, adapted to move along a bottom surface of the fermentation tube 8 with wheels to break up large blocks of piggery waste and to shift the waste towards the exit outlet 6 using metal cables fixed to both ends of the moving cart 10 to move the cart in either direction along the length of the fermentation tube 8. The metal cables are pulled externally from the fermentation tube 8, and a first pulley 1 1 and a second pulley 1 2 are set at opposed ends in the fermentation tube 8 to guide movement of the moving cart 10 along the length of the fermentation tube 8. It will be appreciated by those persons skilled in the art that the metal cables are pulled using pulling means (not shown), such as a winch, external to the fermentation tank 9- as such, the metal cable extend through the inlet 1 and the outlet 6 of the fermentation tank 9. It will also be appreciated that the moving cart 1 0 is made of light weight material and is corrosion resistant.

In an experimental example demonstrating the system 100 in use, the raw materials for aerobic composting in the aerobic reactor 7 and for biogas fermentation in the anaerobic reactor 1 1 0 are a mixture of manure, straw and grass. A portion of these raw materials is crushed into small pieces, say about 1 -5 cm in size, and added to the aerobic reactor 7. The remainder of the raw materials are finely shredded into particles about 5 mm in size and added into the mixture of the manure and fed into the fermentation tank 9. The length and volume of the fermentation tank 9 used in this example is 21 m and 200 m3, respectively. The impact of temperature on the anaerobic fermentation in the fermentation tank 9 for this experimental example is shown in Tables 1 and 2.

Fermentation temperature /°C 3 5 14 23 30 40 50

Fermentation cycle /d 248 128 62 35 28 19 12

Table 1. The effect of temperature on the anaerobic fermentation cycle Raw material Temperature/°C Gas yield/(m3/kg)

Manure, straw and grass 45-51 198.35

34-43 170.52

26-32 148.35

22-25 120.61

10-16 80.12

2-7 30.12

Table 2. Effect of temperature on gas production by anaerobic fermentation

In summer conditions in Australia, for example, the average summer temperature can be around 28°C. In these temperatures, the temperature of aerobic composting can be maintained at 50-60°C which allows the temperature of the fermentation tank 9 to be maintained at 45-52°C. Using the system 1 00 and extrapolating from the collected results shown in the Tables, biogas yield of about 1 .4 times that of known digesters can be obtained at these temperatures, as well as nearly having the fermentation cycle.

In some places, the average winter temperature is 5°C. In these conditions, the temperature of aerobic composting can be maintained at 20-25°C using the system 100. At this temperature of the aerobic reactor 7, the temperature of the fermentation tank can be maintained at 14-18°C. In these conditions, the biogas yield is about 2.7 times that of known digesters, and the fermentation cycle is shorted by nearly one third.

In an embodiment, the system 100 further processes the piggery waste to remediate the waste after it is digested in the anaerobic reactor 1 10 to produce biogas. The digested waste from the anaerobic reactor 1 10 is discharged from the outlet 6 and separated into solids and liquids using a separator 20, as shown in Figures 4 and 5. The separator 20 of the system 100 includes a separator inlet 21 for inputting the discharged slurry from the output of the fermentation tank 9 of the anaerobic bioreactor 1 1 0 and an overflow port 22 to allow excess slurry to be discharged without affecting operation of the separator 20. As with the panels in the fermentation tube 8, the separator 20 also includes a division panel to stop liquid from the slurry entering the outlet 6 of the fermentation tank 9. The separator 20 in the embodiment shown in Figure 4 is a tank and includes a liquid outlet 26 for outputting the substantially liquid portion of the waste from the separator 20. The outlet 26 is disposed at the top of the separator tank 20 and a solids output 28 for outputting substantially solids from the separator 20 is disposed substantially at the bottom of the separator tank 20. The liquid output 26 is connected to a central pipe 24 extending substantially into the separator tank 20, which has a floating object separator panel (e.g. filter) 27 disposed at the end in the separator tank 20. The liquid output 26 also has a further filter in the form of a collection channel 25 to further separate the liquids from the solids before the liquid is discharged from the separator tank 20. As described, the discharged waste from the anaerobic bioreactor 1 1 0 is pumped into the separator tank 20 for say 24 hours so that the solids move to the bottom of the tank 20 for removal and used for say bio-char production, and the liquids flow out the liquid output 26 for further remediation.

Indeed, in an embodiment, the liquid waste from the separator 20 is outputted into a regulating tank (not shown) and then to one or more remediation ponds 30, as shown in Figures 6 and 7 to be further remediated. As described, the separated liquid fraction in the regulating tank is diluted 1 :1 with totally remediated wastewater recycled from the system 1 00 to reduce the initial contaminant load on the

remediation ponds 30 for further remediation. The remediation ponds 30 of the system 100 include a waste water inlet 31 to receive waste water from the regulating tank of the system 100. The received waste water then undergoes aerobic remediation to reduce the nutrient content and Dissolved Organic Carbon (DOC) in the waste water using suspended algae bio-membranes in each of the ponds 30. The algae bio-membrane is formed on elastic polyethylene packing 33 supported by framework 32 suspending the algae in the ponds between baffle retaining walls 5 and 6. In this way, the inputted waste water flows through the suspended algae bio- membrane, over say a week, and is discharged from the remediation ponds 30 at a pond outlet 37.

Figure 7 shows one of the remediation ponds 30 in further detail. In this embodiment, the pond 30 includes an aeration pipe 34 having a plurality of holes for distributing air along the length of the pipe into the pond 30. The pipe 34 is disposed beneath the framework 32 suspending the algae in the ponds 30 to discharge air directly into the ponds 30 to assist in the aerobic degradation of organic material in the waste water. Rapid regrowth of algae bio-membrane will consume nutrients in the waste water. This aeration system has an air inlet 38 arranged to take in air from the environment, a pumping means (not shown), and an air distributing manifold 39 to distribute the pumped air to one or more of the aeration pipes 34 in the remediation ponds 30.

In some cases, the remediated water is safe to be discharged straight from the remediation ponds 30. Alternatively, it undergoes further filtration to remove the algae and any heavy metals present in the remediated water before it can be discharged safely to the environment. That is, the system 100 includes an algae removal tank 40, as shown in Figure 8, for removing the algae from the liquid discharged from the ponds 30. The algae removal tank 40 includes an inlet for inputting liquid from the remediation pond, a sand filtration layer 43 for filtering the algae from the liquid, a support panel 44 supporting the sand layer 43 and a filtering panel 45 also supported by the support panel 44. The filtering panel 45 further filters the liquid so that the filtered water 46 can be outputted from the algae removal tank 40 at output 47.

Figure 8 also shows the water level 42 in the algae removal tank 40 being full and an overflow panel 41 stopping any overflowing liquid being inputted back into the inlet.

As described, the system 100 further includes an adsorbent tank (not shown) for removing heavy metals from the liquid outputted from the algae removal tank 40 using activated carbon or bio-char. A portion (e.g. 50%) of the liquid from the outlet of the adsorbent tank is then mixed in the regulating tank with the liquid from the separator 20 before being inputted into the remediation ponds 30 to reduce the amount of nutrients and Dissolved Organic Carbon (DOC) in the liquid from the separator. The remaining portion (e.g. 50%) of the liquid from the outlet of the adsorbent tank is then discharged safely to environment. In another embodiment, liquid from the algae removal tank 40 is mixed with liquid from the separator 20 in the regulating tank.

An example of a method of processing piggery waste using the system 100 is described with respect to the flow chart of Figure 9. As described, the piggery waste 50 is first prepared into the slurry by performing, for example, the steps of fine crushing, fluidization and picking out sand and massive fibrosis from the raw piggery waste. The slurry is then piped into the fermentation tank or biogas digester 52 and, because of the liquidity of the solid-liquid mixture of starting crude piggery waste and water, the slurry flows slowly downstream under gravity. During this flowing progress, biogas is produced by methane-producing microbes and bacteria in the fermenting slurry. As will be appreciated by those persons skilled in the art, there is a high concentration of microbes in the starting crude piggery waste, and the anaerobic environment characteristic of the fermentation process promotes microbial

propagation. Accordingly, biogas is generated and outputted from the process. As described, compost materials (e.g. biomass) are placed in an aerobic composting reactor around the fermentation tank, or biogas digester 52, to thermally regulate the biogas digester 52. That is, the raw compost material is aerobically composted to generate heat and insulate the biogas digester 52 to ensure optimal biogas production. The raw materials are also replaced in batches to ensure a steady temperature in the biogas digester 52. Also, the starting crude slurry is stirred by a mechanical device to speed up the rate of gas production in the biogas digester 52 and to prevent the formation of a crust in the slurry.

The digested piggery waste is outputted from the biogas digester 52 and both solid and liquid wastes from the biogas digester 52 are piped out and separated as biogas residues and biogas slurry through a solid-liquid separator 54. The solid biogas residues can be used as raw material for the production of bio-char through biomass pyrolysis following dehydration to bring the moisture content below 10%. The predominantly liquid biogas slurry from the separator 54 is further treated to degrade the nutrients in the liquid and is first diluted in a water regulating tank 56 before being piped into an algae biofilm pond 58 to degrade the nutrients. As described, the liquid from the algal biofilm pond 58 is then filtered using a sand filtration tank 60 to remove the algae from the liquid. Part of the filtered liquid is then piped back to the water regulating tank 56 to dilute the liquid from the separator 54 and the remaining part is piped to an adsorption tank 62 where bio-char from the separator 54 is used to adsorb heavy metals in the liquid. The liquid from the adsorption tank 62 is piped from the tank as effluent 64 that can be used for, say, agricultural irrigation. The bio- char containing adsorbed heavy metals can be used as landfill for, say, carbon sequestration. Referring now to Figure 10, there is shown a summary of the method 70 of

processing organic waste. The method including the steps of inputting 72 the organic waste into an anaerobic bioreactor for fermenting the organic waste to generate biogas, fermenting 74 the organic waste passing through the anaerobic bioreactor to generate said biogas, outputting 76 the organic waste from the anaerobic bioreactor, outputting 78 the biogas from the anaerobic bioreactor, and thermally regulating 80 the anaerobic bioreactor using decomposing further organic waste in an aerobic bioreactor covering at least in part the anaerobic bioreactor.

It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the spirit and scope of the invention; in particular, it will be apparent that certain features of the embodiments of the invention can be employed to form further embodiments.

It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art in any country.