WO2008025098A1

WO2008025098A1 - A treatment process and apparatus

Info

Publication number: WO2008025098A1
Application number: PCT/AU2007/001281
Authority: WO
Inventors: Tito Pica; David Halliday
Original assignee: Active Research Pty Ltd
Priority date: 2006-09-01
Filing date: 2007-08-31
Publication date: 2008-03-06
Also published as: AU2007291890A1

Abstract

The present invention is directed to a method of treating aqueous organic waste to form a treated product, the method comprising introducing the aqueous waste into a vessel having an upper section and a lower section wherein microbes capable of converting the aqueous organic waste into a treated product reside in the upper and lower sections of the vessel; and maintaining the aqueous waste within the vessel in a fluidised and suspended state by the introduction of a fluidising medium into the lower section of the vessel. The present invention is also directed an apparatus for treating aqueous organic waste comprising a vessel and one or more waste circulating systems located therein.

Description

"A treatment process and apparatus"

Cross-Reference to Related Applications

The present application claims priority from Australian Provisional Patent Application No 2006904803 filed on 1 September 2006, the content of which is incorporated herein by reference.

Field of the Invention

The present invention relates to waste treatment processing, in particular, processing of waste such as, for example, aqueous based organic waste, winery effluent, sewage or industrial grease trap waste.

Background of the Invention

In addition to sewage waste, large quantities of wastewater are generated by industries such as breweries, sugar mills, distilleries, food-processing industries, tanneries, paper and pulp industries and livestock industries. The nature of the wastewater depends on its source and also its treatment process. Depending on its source, the wastewater may contain not only organic and inorganic matter, but also bacteria, viruses, oil, grease, nutrients such as nitrogen and phosphorous, heavy metals and organochlorines. The discharge of industrial waste water is subject to what is known as a "Trade

Waste Agreement" with the local water authority in which industrial waste must be treated so that it meets certain quality standards before discharge or reuse. The most common way of treating trade waste is physio/chemical where the pH is adjusted and a polymer is added to flocculate the solids in the waste. Such treatment produces masses of residual waste known as sludge.

Once the wastewater has been treated, the treated water may be recycled, used for irrigation or released into the sewer. Disposal of sludge to land is widely practised, but is coming under increasing pressure as (a) suitable sites become scarce (b) the higher costs associated with landfilling and (c) the introduction of tighter controls on the discharge of hazardous substances into the environment. As such, the volume of sludge has to be reduced.

One common method of sludge treatment is digestion in lagoons which may occur under anaerobic or aerobic conditions. Anaerobic lagoons are more widely used since anaerobic bacteria decompose more organic matter per unit lagoon volume than aerobic bacteria. In addition, since the anaerobic process is not dependent on the maintenance of dissolved oxygen, the lagoons can be much deeper thereby reducing the amount of required surface area and the need for agitation of the lagoon to introduce oxygen is eliminated which can otherwise be quite expensive to operate. A drawback with anaerobic lagoons, however, is that they can produce an offensive odour if not properly managed. Another drawback with both aerobic and anaerobic lagoons is the lengthy treatment turnaround time which is, on average, about 15 to 20 days.

For many waste processes, particularly those with an organic background, traditional treatment such as lagoon digestion has been satisfactory, however, such processes generate an excess amount of sludge which must be transported and disposed to landfill or incinerated. For instance, digestion of sludge using anaerobic bacteria to break down the organic matter into a gaseous mixture of methane/CC^ converts only about 30-40% of the organic matter to methane/CO₂. Although this reduction in organic matter is normally sufficient to allow the sludge to be stabilised and disposed to land, a large volume remains for transport and disposal which is not only expensive, but possibly not feasible in the future due to the restriction of available land for landfill disposal.

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 before the priority date of each claim of this application.

Disclosure of the Invention In a first aspect, the present invention provides a method of treating aqueous organic waste to form a treated product, the method comprising introducing the aqueous waste into a vessel having an upper section and a lower section wherein microbes capable of converting the aqueous organic waste into a treated product reside in the upper and lower sections of the vessel; and maintaining the aqueous waste within the vessel in a fluidised and suspended state by the introduction of a fluidising medium into the lower section of the vessel.

Preferably the fluidising medium is fluid recycled from the vessel, however any type of fluid such as, for example, fresh aqueous organic waste may be used.

The treated product substantially comprises a mixture of methane gas and water. In a preferred embodiment, the methane gas is collected from the upper section of the vessel and used as a fuel source to heat the vessel contents. Preferably the lower section of the vessel houses acidogenic microbes which convert organics in the aqueous organic waste primarily into a mixture of organic acids and the upper section houses methanogenic microbes which convert the mixture of organic acids primarily into methane. Desirably, and in order to minimise the disturbance of the microbial population (which tend to form floes with the methanogens in the upper section and the acidogens in the lower section of the vessel) and avoid, as much as possible, mixing of the acidogenic and methanogenic microbial populations, the introduction of the fluidising medium into the lower section of the vessel is achieved through intermittent injection. Preferably, fluidising medium is injected into the vessel lower section no more than about 5 times per 24 hours with each injection lasting about 1 to 2 minutes. It will be appreciated, however, that aqueous organic waste with higher BOD loadings will produce more sludge and therefore the duration and the number of times the fluidisation medium is injected into the vessel will depend on the BOD of the aqueous organic waste. It will be appreciated that if no fluidisation takes place, the aqueous organic waste will have a tendency to settle forming a sludge blanket at the bottom of the vessel. In addition, any pH adjustment of the aqueous organic waste through the use of, for example, magnesium hydroxide, tends to promote the settling of the heavier components within the waste. Such settling of the sludge may lead to the formation of sludge blanket which may cause mixing and temperature problems within the vessel thereby adversely affecting the microbial population and lowering the conversion efficiency of aqueous organic waste into treated product. As such, the fluidisation of the sludge allows temperature control to be more readily achieved throughout the reactor. In a second aspect, the present invention provides a method of treating aqueous waste containing organic material to form a treated product, the method comprising: anaerobically digesting at least a portion of the organic material into, primarily, a mixture of organic acids with acidogenic bacteria and converting the organic acids primarily into methane with methanogenic bacteria, wherein the overall conversion of the organic material into methane is capable of being achieved in about, or less than about, 24 hours.

Preferably, the anaerobic digestion is performed at about 38⁰C and at a pH of about 7.3.

In a preferred embodiment of the method according to the second aspect, the methane is collected and used as fuel source to heat the vessel contents and to maintain the anaerobic digestion at about 38⁰C. Treatment of the aqueous organic waste according to the method of the first and second aspects of the invention may be preceded by a separation step comprising a screening step and/or clarification. Such a screening step preferably removes solids greater than about 20 mm in size and clarification allows the settling of particulate matter.

Treatment of the aqueous organic waste according to the method of the first and second aspects of the invention may also be followed by one or more disinfection steps.

In a preferred embodiment, the treatment is followed by an ozonation step. The treatment step and/or the ozonation step may also be followed by a filtration step. In a preferred embodiment, the filtration step comprises zeolite filtration.

In accordance with the method according to the first and second aspect of the invention, aqueous organic waste having a Biological Oxygen Demand (BOD) of about 2,000 to 80,000 ppm may be treated. In a preferred embodiment of the invention, aqueous organic waste having a BOD of about 6,000 to about 10,000 ppm, preferably about 8,000 ppm, is continuously introduced into the lower section of the vessel and caused to move from the lower section of the vessel to the upper section of the vessel such that it is substantially converted into the treated product in about 24 hours - that is, the retention time of the vessel is preferably about 24 hours. It will be appreciated, however, that the retention time of the vessel will be dependent on the BOD of the aqueous organic waste with longer retention times being required for aqueous organic waste having higher BOD loadings.

Preferably the vessel contents are maintained at a temperature of 36⁰C - 38°C. Most preferably, the vessel contents are maintained at a temperature of about 38⁰C.

Preferably the vessel contents are maintained at a pH of about 7.0 to about 7.5 Most preferably, the vessel contents are maintained at a pH of about 7.3.

In a third aspect, the present invention provides an apparatus for treating aqueous organic waste to form a treated product, the apparatus comprising a vessel having an upper section and a lower section and at least one waste circulation system that retains the aqueous organic waste in a suspended state. In a fourth aspect, the present invention provides an apparatus for treating aqueous organic waste to form a treated product, the apparatus comprising a vessel and one or more heating means, the vessel comprising: a lower section housing acidogenic microbes which convert organics in the aqueous organic waste primarily into a mixture of organic acids; and an upper section housing methanogenic microbes which convert the mixture of organic acids primarily into methane; and at least one waste circulation system that retains the aqueous organic waste in a suspended state as it moves from the lower section to the upper section of the vessel. Preferably the vessel is operated in continuous mode and the residence time of the aqueous organic waste in the vessel is about 24 hours or less. In a fifth aspect, the present invention provides an apparatus for treating aqueous organic waste to form a treated product, the apparatus comprising: a receiving tank in which the aqueous organic waste is introduced wherein any particulate material is allowed to settle; an anaerobic digester comprising a vessel in which a mixture of acidogens and methanogens reside, wherein the acidogens convert at least a portion of any organic material in the aqueous organic waste into, primarily, volatile fatty acids and wherein the methanogens convert at least a portion of the volatile fatty acids into, primarily, methane; at least one waste circulating system, and optionally, an ozone tower and/or a filter unit.

The vessel according to the third aspect of the invention may be of any shape, although, preferably, the vessel has a base that is of an inverted conical configuration extending from a cylindrical vessel body. It will be appreciated that the inverted conical shape of the vessel base assists in the collection and/or disposal of any solid matter which settles in the trough of the inverted cone.

Preferably the vessel according to any aspects directed to the apparatus of the invention further comprises a platform on which a microbial population may grow. The platform advantageously allows the passage of fluids like gas and water therethrough, however substantially prevents the passage of microbes such as, for example, bacteria, yeast or fungi. Preferably also, the platform is of a mesh configuration and may be made from any material, for example, polypropylene. In a preferred embodiment of the invention, the platform is an extruded polypropylene mesh. The platform is desirably positioned within the vessel in a manner that serves to substantially separate the mixing of the contents in the upper section with those in the lower section, thereby avoiding the mixing of the acidogenic and methanogenic microbial populations. The platform also advantageous serves to prevent washout of the microbial population from the vessel during bulk fluid flow of the vessel contents from the bottom to the top of the vessel.

To assist in maintaining the aqueous organic waste in an agitated and suspended state, the apparatus preferably comprises one or more waste circulating systems located in the lower section of the vessel through which a fluidising medium is introduced into the vessel.

Preferably, the one or more waste circulating systems are located and arranged to allow the fluidising medium to be introduced into the vessel in a direction that is substantially at right angles to the bulk flow of waste as it moves from the lower section to the top section of the vessel. In one embodiment, the waste circulation system comprises three pipes arranged in a pronged and planar configuration. It will be appreciated however that other configurations are possible such as a single, dual or multi-pipe configuration. In one embodiment, the one or more waste circulating systems comprise three pipes arranged in a pronged configuration which are orientated so that the flow direction of the fluidising medium ejected from the pipes is substantially at right angles to the bulk flow of the waste as it moves from the lower section to the top section of the vessel. Preferably the fluidising medium is at least a portion of the treated product recirculated from the vessel contents, however, it will be understood that any liquid capable of achieving fluidisation of vessel contents is suitable.

In another embodiment of the invention, the apparatus according to the second or third aspects of the invention comprises at least one waste circulating system comprising a nozzle positioned substantially at the base of the vessel through which a fluid is fed and ejected in the upward direction under pressure by means of a pump, for example, a circulating pump. The fluid fed through the nozzle may be any fluid, for example, water or recycled matter from the vessel, ie digestate.

In yet another embodiment of the invention, the apparatus according to the second or third aspects of the invention may further include a waste circulating system fitted within the vessel base. In this embodiment, the vessel base is of an inverted conical configuration thereby assisting in the collection of matter. The waste circulating system preferably comprises an elongate conduit positioned centrally within the vessel base having a first end positioned at or near the trough region of said inverted cone and a second end positioned at about 20% of the vessel height wherein the conduit is provided with a internal co-axially mounted screw-like device. . It will be appreciated that the screw-like device serves as an Archimedes screw so that solid matter that settles at the base of the vessel is swept up by the screw-like device within the conduit and is moved (or lifted) in the upward direction. Preferably, the point at which the solid matter exits the conduit comprises an overhanging lip that extends in the downward direction toward the base or trough of the vessel and is outwardly extended to about 20% of the vessel width. By this configuration, solid matter that settles at the base of the vessel is able to be moved by the circulating system in the upward direction and flows over the extending lip from the conduit and into the vessel where it is mixed and comes into contact with the microbial population.

It will be appreciated that two or more waste circulating systems may be adopted within the vessel simultaneously. This assists in preventing or minimising the settling of solid matter, for example, residual sludge, at the vessel base thereby improving the mixing and heat transfer characteristics of the apparatus. As a result, high rates of conversion of the aqueous organic waste into a treated product are able to be achieved. In another embodiment of the invention, the apparatus alternatively or additionally includes a heating means in the form of a heating coil located in the lower section of the vessel and a waste circulating system.

In another embodiment, the waste circulating system comprises three pipes arranged in pronged configuration wherein the centre pipe of the three pipes is angled so that fluidising medium is ejected directly onto the heating coil. In this way, the sludge is prevented from forming a blanket around the heating coil and the vessel contents are maintained in a mixed and suspended state thereby achieving uniform heating throughout the vessel.

In another embodiment of the invention, the apparatus according to any one of the third, fourth or fifth aspects of the invention, may have one or more sweeper arms attached to a centrally located rotatable longitudinal member extending from between the top and the bottom of a vessel.

The one or more sweeper arms may be attached to the longitudinal member proximate to and above the vessel liquid surface. At this location, the one or more sweeper arms desirably break up any surface scum that may accumulate at the liquid surface as the longitudinal member is rotated. Alternatively or additionally to the above, one or more sweeper arms may be attached to the longitudinal member proximate to and under the platform on which microbes grow. At this location, the one or more sweeper arms desirably break up or disengage gas bubbles which may occur at the platform surface as the longitudinal member is rotated. This is desirable as gas bubbles tend to cause particulate matter to accumulate under the platform which is sometimes referred to as "raft". Alternatively or additionally to the above, one or more sweeper arms may be attached to the longitudinal member proximate to the base of the vessel. At this location, the one or more sweeper arms desirably move settled matter, for example, heavy inorganic material, that accumulates at the base of the vessel. This allows for easier collection and eventual removal of such matter from the vessel. The one or more sweeper arms may comprise brushes (or a broom), chains or the like extending therefrom. These desirably assist in disengaging or breaking up any settled or accumulated matter or floating scum.

In a sixth aspect, the present invention provides a method of treating aqueous organic waste to form a treated product, the method comprising treating the aqueous organic waste in an apparatus according to any one of the third, fourth or fifth aspects of the invention.

In a seventh aspect, the present invention provides the use of an apparatus according to any one of the third, fourth or fifth aspects of the invention to treat aqueous waste and to form a treated product.

In an eighth aspect, the present invention provides a product produced in accordance with the method of the first or second aspects of the invention.

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.

The present invention will now be described in more detail with reference to the following non-limiting figures and embodiments.

Brief description of the Figures

Figure 1 is a schematic diagram of the apparatus in accordance with an embodiment of the invention.

Figure 2 is a photograph of the waste circulating system in accordance with an embodiment of the invention. Figure 3 is a photograph of the waste circulating system shown from a different perspective.

Figure 4 is a photograph of the fluidising pump connected to the waste circulating system used to pump and inject the fluidising medium into the vessel via the waste circulating system. Figure 5 depicts a flowchart of the process in accordance with an embodiment of the invention.

Figure 6 is a schematic diagram of the apparatus in accordance with an embodiment of the invention.

Figure 7 is a schematic diagram of a base plate in accordance with an embodiment of the invention. ' Figure 8 is a schematic diagram of the apparatus in accordance with an embodiment of the invention.

Figure 9 is a diagram showing the waste circulating system of figures 2 and 3 in plan view.

Detailed Description of the Invention

The treatment technology of the present invention is based on managed anaerobic digestion of aqueous organic waste. Various anaerobic acidogenic and methanogenic bacteria convert the organic load into methane, water, CO₂ and a small amount of residual sludge. The process is preferably contained in an above ground reactor vessel which incorporates a gas/liquid/solid disengagement zone dominated by a microbial population held in the reactor. The acidogenic and methanogenic bacteria are capable of converting aqueous organic waste into, primarily methane, which may be recycled and used as a fuel source, or transported off site for alternative use. One of the more common reasons that leads low rates of conversion and long retention times in anaerobic digesters is improper mixing of the digester contents. Improper mixing of the digester contents tends to result in a build-up of sludge barriers at the bottom of the digester and pockets of poor integration of new feed material with existing microbial populations. In addition, some products which when exposed to anaerobic digestion tend to become extremely buoyant as gas bubbles adhere to particulate matter and form rafts of floating solid matter. In the case of a fixed film apparatus, the raft will be trapped under the film and eventually block the entire system. Slime layers are not uncommon on the surface water of the digester which causes poor water/gas separation and potential blocking of discharge vents by the slimes.

By the novel reactor configuration and/or the novel process described herein, much higher conversion rates of aqueous organic waste to clean water are able to be achieved thereby allowing much lower conversion times (eg about 24 hours or less) to be realised. This compares to the average 15 to 30 day conversion time observed with conventional anaerobic digestion systems.

By the novel reactor configuration and/or the novel process described herein, a treated product of a high quality standard (ie clean water with a BOD 10 mg/1) is able to be attained. This clean water may be used, for example, for irrigation of vegetable crops. Some advantages associated with the apparatus of the present invention includes the elimination or minimisation of rafting (floating) material at the gas/liquid (eg digester water level) or solid/liquid interface (eg underside of Bioblock/liquid interface) and the release of gas which can become trapped in the slime layer at the water/gas disengagement zone. Such advantages lead to:

• An even, continuous and thorough mixing of the digester contents resulting in more efficient temperature control throughout the digester.

• Immediate and efficient contact of the aqueous organic waste with the microbial population.

• The maintenance of material having a higher specific gravity than the liquid phase in suspension eg magnesium hydroxide used for pH adjustment is prevented from collecting in the base of the digester which tends to form a thick sludge barrier. This results in a more efficient usage of the magnesium hydroxide introduced into the digester.

• Enhanced digestion of waste and improved gas production.

• Prevention of raft and scum blockages. The novel apparatus and process steps will now be generally described. Persons skilled in the art will appreciate that the below represents a general description of the invention. As such, numerous variations and/or modifications may be made to the invention as described below without departing from the spirit or scope of the invention as broadly described.

Solids separation and waste stream conditioning in a receiving tank Aqueous organic waste may be pre-treated prior to entry into the receiving tank. This may be achieved by the use of a bar screen (eg 20 mm bar screen) to capture any solid objects which may exist in the waste stream. The aqueous organic waste (or pretreated aqueous organic waste) is transferred to the receiving tank by a transfer pump, eg a positive displacement pump. Persons skilled in the art will understand that other methods of feeding the waste into the receiving tank are possible, such as, for example, gravity feed.

The receiving tank preferably comprises a cone base that allows for ready collection and draw-off of the settled solid matter. The draw-off of the settled matter is preferably achieved through vacuum, however persons skilled in the art will understand that other methods of collection are possible. The tank may also be fitted with an override switch which cuts power to the transfer pump in the event the tank is in danger of overfilling. The receiving tank may be fabricated from any suitable material known to persons skilled in the art such as, for example, reinforced vinyl ester fibreglass. The receiving tank may also be equipped with a level indicator so that the level of the tank may be deduced externally of the tank by visual means.

The receiving tank primarily serves as an initial separation device and also acts as a buffer to minimise process variances and surges. As such, a more uniform aqueous organic waste composition is fed to the digester.

Preferably also, any air discharged from the receiving tank is passed through a filtration system (discussed below) to minimise odour emissions. In this regard, the waste is preferably transferred under substantially isolated (sealed) conditions, eg from a truck, to minimise the emission of unpleasant odours.

Anaerobic digestion

Treatment of the aqueous organic waste is preferably achieved in a vessel comprising an upper section and a lower section wherein a microbial population is retained within the upper and lower sections of the vessel. The vessel may be of any configuration, for example, circular or rectangular. Preferably, aqueous organic waste is introduced into the lower section of the vessel and caused to flow in the upward direction towards the upper section of the vessel. As the aqueous organic waste travels from the lower to the upper section of the vessel, it comes into intimate contact with the microbial population retained in the reactor and is converted by anaerobic digestion into a mixture of products such as organic acids, methane, water and carbon dioxide.

The microbial population is preferably a mixture of acidogens and methanogens. The acidogens are preferably retained within the lower section of the vessel and convert the aqueous organic waste into a mixture of organic acids. The methanogens are preferably retained within the upper section of the vessel and convert the mixture of organic acids primarily into methane. In order to assist microbial growth, a platform made from, for example, polypropylene extruded mesh may be suspended within the vessel which serves as a support on which the bacteria are able to adhere and grow. The platform also serves in minimising or preventing the microbial population from being carried upward with the bulk flow of the aqueous organic waste at the waste moves from the lower section of the vessel to the upper section of the vessel.

The treatment process in accordance with the invention focuses on managed anaerobic digestion in which the anaerobic bacteria convert the organic load into water and methane gas and small amount of residual sludge. The methane gas produced may be utilised elsewhere in the process, transported offsite or subsequently converted to a mixture of water and carbon dioxide. Methane production and collection

The methane generated through the anaerobic digestion process may be captured and used as fuel source on-site or may be transported off-site.

Preferably, the digester has a domed top, fixed or floating, in which any methane that is generated is collected and drawn from the digester. The methane drawn from the digester may dried and burnt immediately, or alternatively, may be burnt in an internal combustion engine which in turn drives an alternating current generator which can supply electrical power on-site.

The methane gas may be collected and used to fuel a burner which in turn heats water used to heat the digester by way of a closed loop water-filled coil. The heating of the digester may also be supplemented with LPG, or LPG may also be used as the primary fuel source during start-up of the process and before any methane is generated.

It will be understood that the volume of methane produced is dependent on the nature and volume of the waste being treated. For example, the higher the BOD load the greater the amount of organic material to be consumed. The ultimate amount of gas produced is directly proportional to the BOD load. In addition, it will be appreciated that the rate of methane gas production will vary according to digester temperature, movement, pH and the microbial population in the vessel.

Disinfection

Effluent from the digester is preferably subjected to disinfection to produce a high quality effluent. Persons skilled in the art will appreciate that while various methods of disinfection are available such as, for example, chlorination, ozonation and ultraviolet (UV) disinfection, according to a preferred embodiment of the invention, disinfection is achieved through ozonation.

The use of ozone as a disinfectant has the following advantages:

• ozone is more effective than chlorine in destroying viruses and bacteria

• short contact times are required (10 to 30 minutes)

• as ozone rapidly decomposes, removal of harmful residual is not required • the is little or negligible microorganism regrowth after ozone treatment

• ozone may be generated onsite

• ozone is a strong oxidiser and is therefore able to reduce odour emissions arising from components such as hydrogen sulphide and ammonia present in waste streams such as sewage sludge In a preferred embodiment of the invention, the ozone is generated onsite and passed through an ozonation tower through which effluent from the digester is also passed and contacted with the ozone.

It will be a appreciated that any conventional method may be used to generate ozone. Ozone is produced when an oxygen molecule(O₂) is dissociated by an energy source into oxygen atoms and subsequently collide with another oxygen atom to form an unstable gas, ozone (O₃). Ozone may be generated by, for example, imposing UV irradiation or a high voltage alternating current (6 to 20 kV) across a dielectric discharge gap that contains an oxygen-bearing gas. As ozone is a highly unstable gas and rapidly decomposes to elemental oxygen, it is preferably generated onsite.

Following ozonation, the treated water may be subject to a zeolite filtration step. Zeolite filtration is desirable to trap any residual particulate matter. Zeolite filtration is also desirable to collect heavy metals such as, for example, zinc, copper or lead that may be present in the treated product.

Odour control

Preferably, any air expelled from the process is passed through a filtration system to remove odour components, for example, hydrogen sulphide and ammonia.

While it will be appreciated that there a numerous filtration systems that are able to be adopted to remove various odour components, in a preferred embodiment, the expelled air is passed through an activated carbon filter (eg Riga-Sorb).

In order to further control odour emission, any waste material is preferably unloaded into the receiving tank through a direct connection piping system from, for example, a truck to the receiving tank. This not only minimises odour emission, but also minimises the risk of any spill of waste material.

Storage prior to use or transport

Treated water may be tested and stored in tanks for reuse onsite, transported for reuse offsite or released into the sewer.

Embodiments

With reference to figure 1, the vessel or digester 1 is shown according to an embodiment of the invention. The digester 1 has a height of 4.5 metres, a diameter of

2.5 metres, a minimum wall thickness of 6 mm at the top and is manufactured from reinforced fibreglass in accordance with Australian Standards. The digester 1 comprises an off-centre cone 2 in the base angled towards a 100mm ball valve 3 through which drainage of the vessel contents may be achieved. This cone configuration assists in the collection and removal of dead bacterial cells and any residual sludge. To this end, a connection point (by way of a 100 mm Kamlock) is built into the base of the cone to allow for any drainage that may be required. The digester 1 is sealed and all flow streams in and out of the digester 1 are contained within pipe work that are sealed and connected to other components (eg a truck loaded with waste) or a vessel (eg the receiving tank or ozonator) so as so as to minimise contamination of, or the release of offensive odours into, the external environment.

Still referring to figure 1, aqueous organic waste (distillery waste having a BOD of about 8,000 ppm) is pumped from a receiving tank (as shown in figure 5) to the digester 1 using a 3ph 2.5 KW positive displacement pump fitted with a variable speed gearbox at a rate of 1 kL/h through 40 mm piping. Flow measurement is achieved with a Magflow meter and the waste is fed into the digester 1 at inlet port 4. The aqueous organic waste moves from the lower section 5 of the digester 1 to the upper section 7 of the digester 1. Acidogenic bacteria residing in the lower section 5 convert the organic matter in the waste to organic acid (eg acetic acid) which is subsequently converted to methane gas and water by methanogenic bacteria residing in the upper section 7 of the digester 1.

Situated approximately midway between the top and bottom of the digester 1 is a 1.5m layer of extruded polypropylene mesh 9 (BioBlok) which serves as a growing platform for the bacteria. The polypropylene mesh 9 also serves to slow down or minimise wash-out of the bacteria as the waste flows from the lower section 5 to the upper section 7 of the digester 1.

The top of the digester 1 is of a domed configuration 11 which provides strength and also allows for the collection and draw-off of methane gas that is produced during anaerobic digestion of the waste.

Heat transfer to the vessel contents is achieved by way of a stainless steel heat coil 13 situated in the lower section 5 of the digester 1 through which circulating hot water (75⁰C) is continuously passed. The heat coil 13 (2 loops) is approximately 12 metres long and 50 mm in diameter. Temperature control is achieved with a reactor temperature device (RTD) 15 situated in the top of the digester 1 in which a temperature probe 17 is inserted. The RTD 15 switches a circulating hot water pump (not shown) on and off as required. In this way, the vessel contents are maintained at about 37-38⁰C. Temperature control is further aided by providing external insulation to the vessel (side and bottom) using insulation rubber (19 mm in thickness) (not shown). About 200 mm from the top of the digester 1 is an overflow port 19 where the treated product (water) flows to the ozonator by gravity.

The concave (domed) top 11 comprises a collection point (25 mm) 21 where the generated methane gas is collected and piped away. Adjacent to the collection point 21 is a temperature controller, a temperature probe and relay (not shown). The domed top 11 also comprises a sealable insertion point for a pH probe (not shown).

Situated externally to and near the base of the tank is a small positive displacement pump (0.5 kW) 23 to circulate a portion of the vessel contents through piping (25 mm) 25 from either the middle or the top of the digester 1. Built into this pipe work is a pH probe 27 which controls a magnesium hydroxide dosing pump (20 mm peristaltic pump, not shown). In this way, the pH of the recirculated feed into the digester 1 may be controlled and maintained at a desired setpoint (ie 7.3). A temperature sensor is also included with the pH probe (not shown).

The digester 1 further comprises a waste circulation system 29 as will now be described in detail with reference to figures 2 to 4. The waste circulation system 29 comprises a pronged piping arrangement which allows a fluidising medium (eg recirculated waste) to be injected into the digester 1. This assists in maintaining the sludge within the vessel contents in a fluidised and suspended state which not only promotes contact with the bacterial population thereby increasing conversion efficiency, but also allows greater mixing of the vessel contents thereby achieving better temperature control throughout the digester 1. As can be seen from figure 2, the waste circulating system comprises a pronged piping arrangement having three pipes (eductors) 31, 33 and 35 arranged in a planar fashion through which fluidising medium is injected. As can be more clearly seen from figures 3 and 9, the centre pipe (eductor) 35, has a bent section which is angled towards the heating coil 13 (shown in figure 1). In this way, the settling of the sludge over the heating coil 13 is prevented thereby preventing the formation of a sludge blanket. This allows greater temperature control to be achieved throughout the digester 1. The fluidising medium is pumped through waste circulating system by means of a fluidising pump (Ebara DWO 200 stainless steel open impeller) 37 as shown in Figure 4. Fluidising medium is intermittently pumped through pipes 31, 33 and 35 at a frequency of about 3 to 5 times per 24 hours each time for a period of 3 to 5 minutes. The pipes 31, 33 and 35 preferably include eductor nozzles (not shown) at each of their ends which increases the volume of medium circulated without having to increase the pump speed or capacity. In this way, sufficient fluidisation is achieved so as to maintain the sludge in a suspended state, but high flows and shear rates are avoided to ensure that the microbial population within the digester is not disturbed. The fluidising pump 37 is located in the lower section 5 of the digester 1 and draws liquid from the digester 1 which serves as the fluidising medium as it is injected into the waste circulating system 29 and through eductors 31, 33 and 35. With reference to figure 5, aqueous organic waste (wine distillery waste having a BOD of 8,000 ppm) is continuously pumped from a receiving tank 41 into the bottom of the digester 1 through a 40 mm pipe 39 fitted with a backflow preventer (not shown). Any air dispelled from the receiving tank 31 is passed through an activated carbon filter 43 prior to discharge into the environment. The wine distillery waste is continuously fed into the digester 1 at a feed rate so as to achieve a retention time of about 24 hours. In this time, the organic matter in the wine distillery waste is substantially converted to methane gas (which is collected and drawn off via piping 20) and water.

The treated water product overflows and travels, by gravity, to the next stage of the process which is ozonation in an ozonation tower 45. To regulate the flow of the overflow treated water and to prevent siphoning of any solids flowing on the surface, the collection point 19 is situated approximately 300 mm below the water line of the digester 1. A goose neck arrangement (as can be seen in piping 18 on figures 1 and 5) is used to maximise the vessel 1 capacity. A vacuum breaking device (not shown) is also mounted atop the gooseneck of piping 18. At the collection point 19, a 40 mm pipe (not shown) having a rectangular cross-section (1.3 m x 1.5 m) is suspended horizontally across the digester 1. This pipe of rectangular cross-section comprises a series of holes (10 mm in diameter) along its uppermost section through which water is able to flow and overflow to the ozonator, yet any particulate matter is prevented from entering. In the ozonation tower 45, ozone is produced in the ozonation tower 45 by pumping water through a 5 mm venturi (not shown) from the bottom of the ozonation tower 45 through an ozone generator 47. The venturi draws air across two UV producing lamps (not shown), each one meter in length and contained in individual stainless tubes. The tubes are jacketed to provide for water cooling of the lamps. Although not shown in figure 5, the receiving tank 41 and finished water tanks

(not shown) are connected by way of a 25 mm pipe line leading to a carbon filtering system. The carbon filters, each 700 mm square are housed in a closed container with an in and out fixture. This means any air emissions from the digester, receiving tank or finished water tanks must pass through the filter thereby eliminating or at least minimising the escape of unpleasant odours from the process. Following ozonation, the treated water product is then passed through a zeolite filter 49 and discharged through piping 51.

Another embodiment of the invention will now be described with reference to figure 6. Liquid organic waste is introduced into the vessel or digester 101 through port 103 into an anaerobic environment. The vessel is essentially divided into three sections, upper, middle and lower, wherein the middle section comprises a polypropylene platform 109 (Bioblok) on which the microbial population is able to grow. Acidogenic bacteria reside in the lower section 105 and convert the organic matter in the waste to organic acid (eg acetic acid) which is subsequently converted to methane gas and water by methanogenic bacteria residing in the upper section 107 of the digester 101.

The digester 101 further comprises a central drive shaft 108 which extends from the top of the digester 101, through the Bioblok platform 109 to a point near the digester base 116 but clear of a base plate 220 (as shown in, and described further with reference to, figure 7) bolted onto the digester base 116. Attached to the drive shaft 108 is a gas sweeper 110, a platform sweeper 112, and a floor sweeper 114 as shown in figure 6. All three sweepers slowly revolve as the drive shaft 108 is rotated (at approximately 5 revolutions per minute).

The gas sweeper 110 is situated approximately 150 mm above the digester 101 water line (WL) and is comprised of two arms attached to the drive shaft 108 protruding to a point just clear of the digester internal wall 102. The gas sweeper 110 further comprises stainless steel chains 118 which hang to a point not more than 20 mm below the digester 101 water line (WL). As the gas sweeper arms 110 rotate, the stainless steel chains 118 disrupt the formation of surface scum and release any entrained gas. The disrupted solids sink to the bottom of the digester 101 and are removed through a drain 236 (as shown in figure 7) of the base plate 220 (see figure 7) bolted onto the digester base 116.

The platform sweeper 112 (sometimes also referred to as a "raft" sweeper) is situated approximately 150 mm beneath the under-surface of the Bioblok platform 109. The platfoπn sweeper 112 comprises two opposite arms attached to the drive shaft 108 that protrude to a point just clear of the digester internal wall 102. Attached to the upper side of the platform sweeper arms 112 is a polypropylene "broom" 117 which gently sweeps the underside of the Bioblok platform 109 as the platform sweeper 112 rotates. The effect is to disengage gas bubbles which adhere to particulate matter thereby breaking-up a potentially disruptive raft. The allows the release of trapped gases which then move though the digester 101. The floor sweeper 114 located near the digester base 116 (approximately 150 mm above the digester floor) comprises two arms attached to the drive shaft 108. The floor sweeper arms 114 protrude from the drive shaft 108 to a point just clear of the digester internal wall 102. The arms (one on either side of the drive shaft 108) are upward facing at an angle approximately equivalent to the angle of the conical digester base 116. Attached to the underside of the floor sweeper arms 114 is a polypropylene "broom" 122 which gently sweeps across the digester floor 119 to move heavy inorganic material to the centre of the tank and eventual removal through drain 240 (as shown in, and described with reference to, figure 7). Bolted to the digester base 116 is a base plate 220 as shown in, and as will now be described with reference to, figure 7. Base plate 220 comprises a mixing device 225 having a nozzle 232 fed by circulating pump 234. Under pressure, the nozzle 232 acts in a venturi-like manner by a factor of 4 and creates an inverted conical plume when the material is discharged. The conical plume will consist of newly introduced material together with existing digester contents. Advantageously, the plume will cause a continuous flow of material over the heat exchanger (not shown) thereby preventing (or at least minimising) the accumulation of material on and around the heat exchanger. This helps maintain a uniform temperature throughout the digester and also achieves efficient temperature control. Base plate 220 also is collected and discharged from the digester 101.

Another embodiment of the invention is shown in figure 8. In this embodiment, material to be treated is introduced into digester 301 through port 303 and travels through a longitudinal member in the form of a hollow stainless steel drive shaft 308 and exits the drive shaft 308 at points 340 and 341 into the lower section of digester 301. Digester 301 is much like digester 101 previously described with reference to figure 6. In contrast to digester 101, however, the digester 301 in this embodiment comprises an Archimedes screw 330 which serves to lift and resuspend any mixed settled solids at the digester base or trough 316. The screw 330 is formed by the introduction of grooves to the drive shaft 308. The screw 330 may be encased in a lined fixed conduit 329 to prevent backflow, and rises from the digester base 316 to approximately 20% of the digester height. As the screw 330 rotates with a longitudinal member in the form of a drive shaft 308, material is lifted from the bottom of the digester 301 and rises to a point where it overflows the fixed lined conduit 329. An overhanging lip 331 is located on the top edge of the fixed conduit 329 which faces downwards and outwards to about 20% of the width of the digester 301. As material flows upwards within the fixed conduit 329 by virtue of being entrained within the grooves of the screw 330 as the drive shaft 308 is rotated, entrained material spills over the overhanging lip 330 and slowly sinks towards the digester base 316 wherein further mixing occurs. Although not shown in figure 8, digester 301 may also have a base plate 220 as shown in, and described with reference to, figure 7, bolted to its base 316, with a screw 330 to achieve mixing and suspension of the digester contents instead of a mixing device 225.

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 embodiment 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

CLAIMS:

1. A method of treating aqueous organic waste to form a treated product, the method comprising introducing the aqueous waste into a vessel having an upper section and a lower section wherein microbes capable of converting the aqueous organic waste into a treated product reside in the upper and lower sections of the vessel; and maintaining the aqueous waste within the vessel in a fluidised and suspended state by the introduction of a fluidising medium into the lower section of the vessel.

2. A method according to claim 1 wherein the fluidising medium is fluid recycled from the vessel.

3. A method according to claim 1 wherein the fluidising medium is fresh aqueous organic waste.

4. A method according to any one of the preceding claims wherein the treated product substantially comprises a mixture of methane gas and water.

5. A method according to claim 5 wherein the methane gas is collected from the upper section of the vessel and used as a fuel source to heat the vessel contents.

6. A method according to any one of the preceding claims wherein the lower section of the vessel houses acidogenic microbes which convert, by anaerobic digestion, organics in the aqueous organic waste into a mixture comprising substantially organic acids and the¹ upper section houses methanogenic microbes which convert the organic acids in the mixture substantially into methane.

7. A method according to any one of the preceding claims wherein introduction of the fluidising medium is into the lower section of the vessel and is achieved through intermittent injection.

8. A method according to claim 7 wherein the fluidising medium is injected into the vessel lower section at no more than about 5 times per 24 hours with each injection lasting about 1 to 2 minutes.

9. A method according to claim 8 wherein conversion of the aqueous organic waste into a treated product is capable of being achieved in about, or less than about, 24 hours.

10. A method of treating aqueous waste containing organic material to form a treated product, the method comprising: anaerobically digesting in a vessel at least a portion of the organic material into, primarily, a mixture of organic acids with acidogenic bacteria and converting the organic acids primarily into methane with methanogenic bacteria, wherein the overall conversion of the organic material into methane is capable of being achieved in about, or less than about, 24 hours.

11. A method according to claim 6 or 10 wherein the anaerobic digestion is performed at about 36⁰C to about 38⁰C and at a pH of about 7.0 to about 7.5.

12. A method according to claim 10 or claim 11 wherein the methane is collected and used as fuel source to heat the vessel contents and to maintain the anaerobic digestion at about 36⁰C to about 38⁰C.

13. A method according to any one of the preceding claims wherein the treatment of the aqueous organic waste is preceded by a separation step selected from a screening step, a clarification step or a combination of such steps.

14. A method according to any one of the preceding claims wherein the treatment of the aqueous organic waste is followed by one or more disinfection steps.

15. A method according to claim 14 wherein the one or more disinfection steps comprise ozonation.

16. A method according to any one of the preceding claims wherein the treatment step may also be followed by one or more filtration steps.

17. A method according to claim 16 wherein the one or more filtration steps comprise zeolite filtration.

18. A method according to any one of the preceding claims wherein aqueous organic waste having a Biological Oxygen Demand (BOD) of about 2,000 to about 80,000 ppm is treated.

19. A method according to any one of the preceding claims wherein aqueous organic waste having a BOD of about 6,000 to about 10,000 ppm is treated.

20. A method according to any one of the preceding claims wherein aqueous organic waste having a BOD of about 8,000 ppm is treated.

21. A method according to any one the preceding claims wherein the aqueous organic waste is continuously introduced into the lower section of the vessel and caused to move from the lower section of the vessel to the upper section of the vessel such that it is substantially converted into the treated product in about 24 hours.

22. A method according to any one of the preceding claims wherein the vessel contents are maintained at a pH of about 7.3.

23. An apparatus for treating aqueous organic waste to form a treated product, the apparatus comprising a vessel having an upper section and a lower section and at least one waste circulation system that retains the aqueous organic waste in a suspended state.

24. An apparatus for treating aqueous organic waste to form a treated product, the apparatus comprising a vessel and one or more heating means, the vessel comprising a lower section housing acidogenic microbes which convert organics in the aqueous organic waste primarily into a mixture of organic acids; and an upper section housing methanogenic microbes which convert the mixture of organic acids primarily into methane; and at least one waste circulation system that retains the aqueous organic waste in a suspended state as it moves from the lower section to the upper section of the vessel.

25. An apparatus according to claim 23 or claim 24 wherein the vessel is operated in continuous mode and has a residence time of the aqueous organic waste in the vessel of about 24 hours or less.

26. An apparatus for treating aqueous organic waste to form a treated product, the apparatus comprising: a receiving tank in which the aqueous organic waste is introduced wherein any particulate material is allowed to settle; an anaerobic digester comprising a vessel in which a mixture of acidogens and methanogens reside, wherein the acidogens convert at least a portion of any organic material in the aqueous organic waste substantially into organic acids and wherein the methanogens convert at least a portion of the organic acids substantially into methane; at least one waste circulation system located within the vessel; and optionally, an ozone tower and/or a filter unit.

27. An apparatus according to any one of claims 23 to 26 wherein the vessel has a base that is of an inverted conical configuration extending from a cylindrical vessel body.

28. An apparatus according to any one of claims 23 to 27 wherein the vessel further comprises a platform on which a microbial population may grow yet allows the passage of fluids like gas and water therethrough and substantially prevents the passage of microbes such as, for example, bacteria, yeast or fungi.

29. An apparatus according to claim 28 wherein the platform is of a mesh configuration.

30. An apparatus according to claim 28 or claim 29 wherein the platform is made from polypropylene.

31. An apparatus according to any one of claims 23 to 30 wherein the one or more waste circulating systems are located in the lower section of the vessel through which a fluidising medium is introduced into the vessel.

32. An apparatus according to any one of claims 23 to 31 wherein the one or more waste circulating systems are located and arranged to allow a fluidising medium to be introduced into the vessel in a direction that is substantially at right angles to the bulk flow of waste as it moves from the lower section to the upper section of the vessel.

33. An apparatus according to any one of claims 23 to 32 wherein the one or more waste circulation systems comprise three pipes arranged in a pronged and planar configuration.

34. An apparatus according to any one of claims 23 to 33 wherein the one or more waste circulating systems comprise three pipes arranged in a pronged configuration which are orientated so that the flow direction of the fluidising medium ejected from the pipes is substantially at right angles to the bulk flow of the waste as it moves from the lower section to the top section of the vessel.

35. An apparatus according to any one of claims 23 to 34 wherein the one or more waste circulating systems comprise a nozzle positioned substantially at the base of the vessel through which a fluid is fed and ejected by means of a pump in a direction from the lower section to the upper section of the vessel.

36. An apparatus according to any one of claims 27 to 35 wherein at least one waste circulating system is located within the vessel base.

37. An apparatus according to any one of claims 27 to 36 wherein the at least one waste circulating system comprises an elongate conduit positioned centrally within the vessel base having a first end positioned at or near a trough region of said inverted cone and a second end positioned at about 20% of the vessel height, wherein the conduit is provided with a internal co-axially mounted screw-like device.

38. An apparatus according to claim 37 wherein the screw-like device serves as an Archimedes screw so that any solid matter that settles at the base of the vessel is swept up by the screw-like device within the conduit and is moved from the lower section of the vessel to the upper section of the vessel.

39. An apparatus according to claim 38 wherein the solid matter exits the conduit at a point comprising an overhanging lip that extends in the downward direction toward the base or trough of the vessel and is outwardly extended to about 20% of the vessel width.

40. An apparatus according to any one of claims 23 to 30 further a heating means in the form of a heating coil located in the lower section of the vessel.

41. An apparatus according to claim 40 wherein one or more waste circulating systems comprise three pipes arranged in pronged configuration wherein the centre pipe of the three pipes is angled so that fluidising medium is ejected directly onto the heating coil.

42. An apparatus according to any one of claims 23 to 41 further comprising one or more sweeper arms attached to a centrally located rotatable longitudinal member extending from between the top and the bottom of the vessel.

43. An apparatus according to claim 42 wherein the one or more sweeper arms are attached to the longitudinal member proximate to and above a liquid surface of the vessel.

44. An apparatus according to claim 42 or claim 43 wherein the one or more sweeper arms are attached to the longitudinal member proximate to and under the platform on which microbes grow.

45. An apparatus according to any one of claims 42 to 44 wherein the one or more sweeper arms are attached to the longitudinal member proximate to the base of the vessel.

46. An apparatus according to any one of claims 42 to 45 wherein the one or more sweeper arms comprise any one of, or a combination of, brushes or chains extending therefrom.

47. A method of treating aqueous organic waste to form a treated product, the method comprising treating the aqueous organic waste in an apparatus according to any one of claims 23 to 46.

48. Use of an apparatus according to any one of claims 23 to 46 to treat aqueous waste and to form a treated product.

49. A product produced in accordance with the method of any one of claims 1 to 22.