AU784076B2

AU784076B2 - Improved chemical treatment methods and apparatus

Info

Publication number: AU784076B2
Application number: AU63642/01A
Authority: AU
Inventors: Michael Everton
Original assignee: Alcos Technologies Pty Ltd
Current assignee: Alcos Technologies Pty Ltd
Priority date: 2000-06-02
Filing date: 2001-06-01
Publication date: 2006-02-02
Anticipated expiration: 2021-06-01
Also published as: AU6364201A

Description

WO 01/92165 PCT/AU01/00655 IMPROVED CHEMICAL TREATMENT METHODS AND APPARATUS The present invention relates generally to chemical processing of materials in industry and particularly to improvements in individual steps involved in the overall processes used in chemical processing industries, particularly in industries involved in the separation of different materials from each other or the treatment of materials such as for example, the treatment of waste waters or the like to remove contaminants prior to discharging the treated waste waters.

More particularly, the present invention relates to improvements in chemical processing of two or more dissimilar materials where the dissimilar materials are to be separated from each other by method and apparatus which allow the dissimilar materials to be at least partially recycled or recirculated in order to improve the amount and/or rate of separation of the two materials from each other.

Even more particularly, the present invention relates to an improved mixing step as a part of an overall process of separating two or more different materials from each other wherein the rate of mixing the materials with a further material, such as a gas or similar in an aeration step, can be controlled independently of the rate of admission of incoming feed material for subsequent treatment, ie., the improvement relates to the recirculation steps for the different materials, particularly the reincarnation of partially treated materials still containing contaminants.

The present invention finds particular application in methods and apparatus using hydrocyclones to mix two fluids together prior to separating materials from WO 01/92165 PCT/AU01/00655 2 each other as part of the overall processing that involves separation of waste materials where the hydrocyclone mixer can be used more or less continuously at a fixed rate to maintain aeration conditions promoting separation of the contaminants in the waste water even when the supply of incoming waste water is interrupted or terminated thereby obviating the need to clean the separation vessel in which separation of the materials take place due to fouling of the vessel caused by being able to maintain aeration within the vessel and operation of the separation process.

Although the present invention will be described with particular reference to the use of a recirculation loop having a hydrocyclone mixer for aerating at least partially treated waste water in order to maintain aeration conditions in a separation tank when the supply of incoming waste water feed is interrupted or terminated, it is to be noted that the scope of the present invention is not limited to the described embodiment but rather the scope of the present invention is more extensive so as to include other arrangements of the apparatus, other uses of the apparatus and the application of the apparatus and methods in industries other than specifically described.

In co-pending patent application no.

PCT/AU98/00691 the use of a hydrocyclone to aerate materials such as waste liquids to aid separation of contaminants from the waste water was described. The hydrocyclone mixers were used in a pre-treatment step to aerate fluids prior to separation of the fluids from each other. It is to be noted that the term "aeration" as used in the present specification is being used in its generic sense and includes the intimate mixing of a water material with any gas or gaseous mixture or combination of gases, such as for example, nitrogen, carbon dioxide, air, oxygen WO 01/92165 PCT/AU01/00655 3or the like. Accordingly, the use of the word aeration is not limited to oxygen or air only but includes any suitable gaseous materials depending upon the particular application of the invention.

In the previously described methods when incoming feed of material being treated stopped the aeration of this material had to stop also since the aeration means being the hydrocyclone mixer was located in line so that when there was no incoming feed material there was nothing to aerate. This presented problems in the apparatus down stream of the aeration site, such as, in the separation tank included as part of the overall apparatus or plant used in the process of separating materials since the sludge at the top of the separation tank became increasing deaerated as time went by with no aeration since no fresh aeration material was added to the separation tank to maintain the sludge in the aerated condition. This in turn resulted in the particles formerly entrapped or entrained in the air bubbles being released and gradually sinking to the bottom of the separation tank and collecting in the clean zone located at the base of the separation tank.

This required the separation tank to be dismantled and cleaned before the process could recommence. Not only was the cleaning of the separation tank costly, it also involved down time since there was a loss of production in that the waste material could not be treated until the tank was cleaned and the separation process was recommenced.

Such separation systems used a fixed flow incoming aerated material.

A major drawback of the fixed flow system is that if there is no flow coming forward from the processing plant to the hydrocyclone mixer there is no aeration taking place and therefore no aerated liquid is being processed WO 01/92165 PCT/AU01/00655 4 into the separation tank. With no air to support the sludge on top of the liquid in the separation tank the sludge becomes saturated with liquid and the solids sink to the bottom of the separation tank and enter the clean water zone beneath the diffusion plate. If this is allowed to happen the only way to remove the sunken sludge is to drain the tank and clean by hand.

Additional problems suffered with the previously available system included that the use of the hydrocyclone mixer required an accurate and fixed flow feed rate of incoming feed material for the particular-application in which the particular hydrocyclone mixer was being used.

This did not allow the operating parameters of the plant in which the hydrocyclone mixer was located to be varied, particularly variations in the rate of aeration and/or the rate of incoming feed material could not be easily tolerated. Furthermore, the hydrocyclone mixer could only be used in accordance with its design parameters of say 3m 3 per hour irrespective of the feed rate of incoming waste material. This in turn meant that the hydrocyclone was specific to a particular type of waste material and a particular capacity of treatment in a particular plant, ie., there was no flexibility or adjustability of using the hydrocyclone. Thus, the operation rate of the in line hydrocyclone mixer could not be adjusted and the hydrocyclone could not be used in other applications since it was dedicated to one specific separation process.

Therefore, there is a need for a system which allows aeration of material, particularly in the separation tank to be maintained when there is an interruption to the flow of incoming waste material for treatment.

Additionally, there is a need for a hydrocyclone mixer arrangement that can be adjusted to take into account WO 01/92165 PCT/AU01/00655 5 different operating conditions and parameters, particularly different feed rates of incoming waste material to be treated, and different materials to be treated.

Accordingly, it is an aim of the present invention to address these needs by providing a method and apparatus suitable for use in separating materials from each other in which there is a recirculation loop that allows material in a separation tank to be continuously aerated or enabling aeration to be maintained even when supply of incoming waste material for treatment is interrupted.

According to a first aspect of the present invention there is provided an apparatus for use in treating a waste material by aeration to substantially separate contaminants from the waste material including: an incoming waste material feed stream; a separation means for at least partially separating the waste material of the incoming feed stream into an aerated portion containing a major amount of the contaminants separated from the incoming feed stream and a partially treated portion containing a residual or minor amount of contaminants; and a recirculation loop provided with a mixer means for aerating the partially treated portion for return to the separation means in an aerated condition such that the recirculation loop can be operated independently of the incoming waste material feed stream in order to maintain aeration conditions in the separation means thereby preventing the aerated portion from substantially deaerating and fouling the separation means.

According to a further aspect of the present invention there is provided a method of treating waste material by aeration or similar to substantially separate WO 01/92165 PCT/AU01/00655 6 contaminants from the waste material including the steps of providing an incoming waste material feed stream; at least partially separating the waste material in a separation means into a substantially aerated portion containing a major amount of the contaminants separated from the incoming feed stream and a partially'.treated portion containing a residual or minor amount of contaminants passing the partially treated portion through a recirculation loop having a mixer means; aerating the partially treated portion by the use of the mixer means and returning the aerated partially treated portion to the separation means; such that the returned aerated partially treated portion maintains aeration conditions in the separation means thereby preventing the substantially aerated portion containing the major amount of contaminants from deaerating and fouling the separation means.

Typically, the rate of incoming waste material is variable. More typically, the rate is between about 0 and 30m 3 /HR. However, it is to be noted that the incoming feed can be at any rate.

Typically, the waste material is a waste water.

More typically, the waste is from a food or beverage processing plant. Even more typically, the waste water is from a coconut processing plant. However, it is to be noted that the apparatus and process of the present invention is applicable to all types of industrial, chemical, food or beverage waste water processing.

Typically, the process of the present invention results in significant reductions in the amounts of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and Fats, Oils and Greases Content(FOG).

WO 01/92165 PCT/AU01/00655 7 Typically, the incoming waste water feed stream is pre-treated before being admitted to the separation means. Typically, the separation means is a separation vessel, preferably a tank and more preferably provided with a diffuser and a means for discharging the fraction containing the major amount of contaminants.

Typically, the mixer means is a hydrocyclone mixer. More typically, the hydrocyclone aerates the waste water by mixing air or other gas under conditions of shear.

Even more typically, the hydrocyclone mixer is operated at a predetermined rate irrespective of the rate of the incoming feed of waste water. Even more typically, this rate can vary from 1 to 50m 3 /HR, preferably from 5 to 3 /HR, more preferably from 10 to 30m 3 /HR and most preferably at about 20m 3

/HR.

Typically, the hydrocyclone mixer is described in International Patent Application No. PCT/AU98/00691.

Typically, the recirculation loop returns aerated partially treated waste water either directly or indirectly to the separation tank. More typically, the return of the recirculation loop is at a location or level corresponding to the position, level or location of the diffuser which is typically a diffuser plate or similar. Even more typically, the return of the recirculation loop is at a location remote from the separation tank.

Typically, the recirculation loop returns the aerated partially treated waste water to an intermediate location remote from the separation tank where it is mixed with incoming feed material prior to being introduced into the separation tank. It is to be noted that material being aerated in the recirculation loop can be returned at any convenient or suitable location in accordance with requirements to operate the plant in an efficient manner WO 01/92165 PCT/AUOI/00655 8 for optimal removal of the contaminants from the feed waste material being treated.

The present invention will now be described by way of example with reference to the accompanying drawings in which Figure 1 is a schematic flow chart representing one form of using the method and process of the present invention allowing for recirculation of partially treated waste water through the mixing hydrocyclone in order to facilitate further treatment of the waste water and to maintain aeration conditions in the separation tank.

In Figure 1 is shown a flow chart of the paths for the different materials involved in the process of the present invention. Although this form of the present invention will be described with particular reference to experimental investigations conducted with respect to a coconut processing plant, it is to be noted that this is only one example of use of the method and apparatus of the present invention. The present invention can be used in a wide variety of diverse applications for treating different materials in a number of different ways.

Waste water or other effluent from a coconut processing plant is introduced to the treatment apparatus depicted schematically in the flow chart of Figure 1 at feed point 2 as an incoming feed stream of waste water containing the contaminants which are to be removed from the feed stream before it is disposed of or undergoes subsequent treatment. Typically, the water admitted at feed point 2 has a BOD value of 6,720 ppm, a COD value of 33,600 ppm and a FOG value of 33,012 ppm. A chemical additive, such as a coagulant, polymer or other material is provided through feed line 4 from a suitable source such as a feed tank or other reservoir or container and added to WO 01/92165 PCT/AU01/00655 9 the waste water at mixing point 6 in a suitable dosage rate in accordance with the nature and amount of material to be separated from the waste water. A particularly preferred material added to the incoming feed of waste water is a coagulant to combine or agglomerate particles in the waste water to assist in their separation later in this separation process.

A second feed line 8 is provided from feed line 4 to admit coagulant or similar additive to one or more remote locations of the apparatus as will be described in more detail later in this specification depending upon the particular waste water being treated. The waste water with added coagulant flows through feed line 10 from mix point 6 to retarder tank 12, where a chemical reaction can take place to coagulate or flocculate the contaminants of the waste water, such as for example, forming individual fibres of the waste water into clumps of fibres or the like.

Retarder tank 12 can be of any suitable shape, size and type in accordance with requirements to ensure a substratial rate of reaction of coagulation or similar, including ensuring that the correct chemical reactions take place, and that the necessary specific contaminants are flocculated, coagulated or the like.

Coagulated/flocculated waste water is discharged from retarder tank 12 through conduit 14 and conveyed to a mixing point in conduit 14 which mixing point is denoted by reference number 16 where a stream of partially treated and aerated waste water in conduit 18 is also introduced into conduit 14 so as to mix with the untreated waste water stream in conduit 14 thereby reducing the concentration of contaminants in the untreated waste water stream and at least partially aerating the incoming feed stream. It is to be noted that the two flows in conduits 14 and 18 WO 01/92165 PCT/AU01/00655 10 respectively which are joined at point 16 are mixed in a ratio that is predetermined to best suit the requirement of operation of the method and process to ensure optimum separation of the contaminants of the waste water.

Accordingly, the flow rates in conduits 14 and 18 can be adjusted within wide limits, can be variable or can be fixed.

The partially aerated mixture is conveyed from mixing point 16 in conduit 20 and is conducted to mixing point 22 where further coagulant, flocculant, polymer or similar additive is introduced from feed ine -24 at a dosage rate which has been predetermined to suit the process and requirements of the system. Feed line 24 has been provided with a suitable receptacle for containing and supplying the additive. Conduit 20 continues past mixing point 22 and is connected to separation tank 26 at a location into intermediate the top and base of the tank.

The contaminants of the waste water being treated in tank 26 are separated from the waste water as a sludge which can be collected at or towards the top of separation tank 26.

Separation tank 26 is provided with a diffuser, baffle arrangement or similar, such as for example, a diffuser plate 28.located part way along the height of tank 26 for dividing tank 26 into a sludge collection zone 30 located at or towards the top of tank 26 and a clear zone 32 at and towards the lower part of tank 26. The contaminants separated from the waste water are collected as sludge at the top of tank 26 in the sludge collection zone In operation of separation tank 26 aerated waste water is introduced through diffuser plate 28 so that the particles of contaminants are entrapped or otherwise entrained within or by air or other gas bubbles rising to the surface of tank 26 so that the contaminants collect as WO 01/92165 PCT/AU01/00655 11 an aerated sludge at the top of tank 26. Aeration conditions are maintained in tank 26 by fresh incoming material supplied through conduit 20. A rotating scraper 34 having a scraper blade 35 is located at or towards the top of separation tank 26 and rotates so as to direct the sludge accumulating at the top of the tank in a direction towards the mouth of a collection hopper or chute 36 located at the top of tank 26 towards one side and extending from the side wall. Sludge collected in chute 36 is discharged through an outlet located at the base of chute 36 which is provided with a sloping side wall to aid in collection of the sludge and disposal through the side wall of tank 26. Conduit 38 is used to convey the sludge from tank 26 to a suitable remote location for ultimate disposal or recycling or further treatment as required or desired. Outlet 40 is provided at the lowermost point of tank 26 for removing any solid material from tank 26.

Clean or relatively clean waste water including some or a minor amount of unseparated contaminants such as suspended solids, fibres or the like are collected in clean zone 32 located beneath the level of diffuser 8. It is to be noted that the waste water in clean zone 32 and the conditions that exist in this part of the tank are substantially unaerated. Heavier solid particles removed from the incoming waste water stream fall to the extreme bottom of tank 26 which is provided with sloping walls so as to collect the heavier solid material at the very bottom of tank 26 for periodic discharge through outlet 40 as solid material for either ultimate disposal or further treatment.

Partially treated waste water, including some contaminants and suspended solids and the like which had settled into clean zone 32, is discharged from a suitably WO 01/92165 PCT/AUOI/00655 12 positioned outlet located at or towards the bottom of clean zone 32 into one end of conduit 42 which forms the beginning of a recirculation loop for returning the partially treated waste water material back to the separation tank 26. The other end of conduit 42 is connected to second retarder tank 44. Another.mixing point 46 is provided in conduit 42 intermediate separation tank 26 and retarder tank 44.

Second feed line 8 extending from feed line 4 is connected to mixing point 46 for introducing further additives, such as coagulant/flocculant or -similar which is added at mixing point to the partially treated waste water in a predetermined dosage rate so that the mixture flows to retarder tank 44 where further chemical reactions can take place in a manner similar to that described previously in connection with retarder tank 12. A typical residence time for the waste water in retarder tank 44 is from about secs to 1 hour or- more.

One end of conduit 48 is connected to the outlet of retarder tank 44 and the other end is connected to a suitable mixing apparatus 50 which is typically a hydrocyclone or aerator, known under the title of an IC- SEP. A valve, typically a trottle valve 52, is provided in line in conduit 48. Trottle valve 52 is pre-set to create a partial vacuum in the suction side of pump 54 for pumping partially treated material through the recirculation loop.

This allows a predetermined volume of free air to be admitted into the partially treated waste water flowing in conduit 48 at mixing point 56 located between trottle valve 52 and pump 54 in order to form an aerated partially treated waste water in conduit 48. It is to be noted that adding coagulant at mixing point 56 from feed line 57 as a separation media prior to entering mixer 50 in the form of WO 01/92165 PCT/AU01/00655 13 the IC-SEP stimulates growth of flocs thereby enhancing the performance of the aeration and/or separation steps of the apparatus. The growth of flocs results from controlling the volume of air mixture into the coagulant/waste water mixture which produces a relatively homogenous/uniform mixing of air, coagulant and waste water materials.

Conduit 18 is connected between the outlet of mixer 50 and mixing point 16 located between conduits 14 and 20 to return the aerated partially treated waste water in the recirculation loop back to separation tank 26 in a mixture with untreated waste water inthe incoming feed stream. In this manner there is always a continuous supply of aerated waste water being supplied to separation tank 26, even if there is little or not supply of waste water to feed point 2. A back pressure valve 51 is provided in conduit 18 intermediate mixer 50 and mixing point 16 to regulate the rate of return of partially treated material in conduit 18 and/or the amount of aeration of the material in conduit 18.

The resulting fully aerated/coagulated liquid formed in mixer 50 is pumped from the outlet of mixer 50 to mixing point 16 through conduit 18 where it is mixed in line with fresh untreated waste water flowing in conduit 14 which had previously been treated with coagulant/flocculant in retarder tank 12. The mixed waste water ie the essentially unaerated untreated waste water from conduit 14 and the aerated partially treated waste water from mixer are conveyed to separation tank 26 where further treatment is undertaken so that more of the contaminants are removed as sludge from the waste water in tank 26. The thus treated essentially clean waste water can then be recirculated through the recirculation loop once again or as many times as required if necessary by passing this WO 01/92165 PCT/AUOI/00655 14 material through retarder tank 44 for further treatment and further aeration in mixer 50 for readmission to tank 26 where further separation occurs. In this manner the waste water can be recirculated as many times as possible until it is sufficiently clean for ultimate discharge and/or reuse whilst always maintaining aerated conditions in tank 26. Further, the recirculation loop can be operated by recycling partially treated waste water substantially continuously even when there is no new supply of waste water material being introduced through feed point 2. When the waste water in clean zone 32 is ready--for -discharge it is discharged from a suitably located clean water outlet located in the separation tank 26 at a level above that of the recirculation outlet to conduit 42 and then through conduit 58 for disposal. Conduit 58 is provided with a mamometer 60 or similar arrangement and vent 62 for maintaining the level of the waste water in tank 26 at a predetermined level to ensure scrapper blade 35 contacts the sludge at the top of the liquid level in tank 26 as it rotates to direct the sludge into chute 36 for disposal of the contaminants of the waste water. Thus, clean waste water free of contaminants is produced by the apparatus and method of the present invention, and additionally aerated conditions can be maintained in tank 26 as long as required by operating mixer 50 in the recirculation loop, including when there is no supply of waste water from feed point 2.

The above described process continues as previously described with suitable chemical additives such as coagulants/flocculants being added at the various mixing points, particularly at mixing point 6 where the first dosage is added to the incoming waste water. This process continues until a suitably placed detector (not shown or described) senses that the flow of waste water in conduit 2 WO 01/92165 PCT/AU01/00655 15 or 10 has stopped whereupon the introduction of additives at dosing points 6 and 22 is also stopped. Whilst the flow in conduits 10 and 14 is stopped, pump 54 can continue pumping partially treated and aerated waste water in the recirculation loop formed of conduits 20, 42, 48 and 18, separation tank 26, retarder tank 44 and mixer 50 thus ensuring that the waste water continues to be treated and that aeration conditions are maintained in the upper part of tank 26 to keep the sludge accumulating at the top of tank 26 aerated so as to prevent the contaminants from falling to the base of tank 26 or fouling the lower parts of the tank 26 or from entering the clean zone 32, thereby keeping tank 26 relatively clean. During this process free air continues to be admitted at point 56 to ensure that aeration continues and that the sludge in separation tank 26 does not deaerate and settle to the bottom of separation tank 26 which would have required the whole process to be stopped and tank 26 dismantled for cleaning. Thus, the recirculation loop can continue independently of the introduction of fresh incoming waste water for treatment.

Further, the ratio of aerated waste water to incoming waste water can be adjusted easily by altering the rate of recirculation in the recirculation loop. Additionally, the amount of aeration produced in mixer 50 can be adjusted in accordance with requirements.

The mixer 50 can be operated continuously at a fixed rate. Typically, the mixer is operated at 20m 3

/HR.

However, mixer 50 can be operated at any suitable rate.

An analysis of the treated waste water being discharged from tank 26 through conduit 58 demonstrates that almost all of the contaminants have been removed. A typical analysis of the water being discharged through conduit 58 in trials conducted on the coconut processing WO 01/92165 PCT/AUO/00655 16 plant include the following; the BOD is 371 ppm, the COD is 509 ppm and the FOG is 28 ppm. As a comparison a similar analysis of the treated waste water from a plant using an mixer/aerator with no recirculation loop revealed the following figures; BOD is 1,319 ppm, COD is 4,224 ppm and the FOG is 98 ppm. The difference in values clearly demonstrates there has been a significant reduction in the contaminants remaining in the waste water after treatment often using the independently operated recirculation loop.

This demonstrates the improvement of the process and apparatus of the present invention.

The described arrangement has been advanced by explanation and many modifications may be made without departing from the spirit and scope of the invention which includes every novel feature and novel combination of features herein disclosed.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope.

Claims

2. A method of treating waste material by aeration or similar for substantially separating contaminants from the waste material including the steps of: providing an incoming waste material feed stream; at least partially separating the waste material in the separation means into a substantially aerated portion containing a major amount of the contaminants separated from the incoming feed stream; and a partially treated portion containing a residual or minor amount of contaminants; characterised in that the method further includes passing the partially treated portion through a recirculation loop WO 01/92165 PCT/AU01/00655 18 having a mixer means; aerating the partially treated portion by the mixer means and returning the aerated partially treated portion to the separation means such that the returned aerated partially treated portion maintains aeration conditions in the separation means thereby preventing the substantially aerated portion containing the major amount of contaminants from the aerating and fouling the separation means.
3. A method and apparatus according to any preceding claim, characterised in that the rate of -incoming waste material is fixed, variable, intermittent and/or can be terminated or interrupted.
4. A method and apparatus according to any preceding claim, in which the rate of incoming waste material is between about 0 and 30 cubic metres per hour. A method and apparatus according to any preceding claim, characterised in that the water.
6. A method and apparatus claim, characterised in that the or beverage processing plant.
7. A method and apparatus claim, characterised in that the coconut processing plant and the coconut fibres.
8. A method and apparatus claim, characterised in that use waste material is a waste according to any preceding waste water is from a food according to any preceding waste water is from a contamination includes according to any preceding of the method and/or apparatus results in significant reductions in the amounts of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS) and Fats, Oils and Greases Content (FOG).
9. A method and apparatus according to any preceding WO 01/92165 PCT/AU01/00655 19 claim, characterised in that incoming waste water feed stream is pre-treated before being admitted to the separation means. A method and apparatus according to any preceding claim, characterised in that the separation means is a separation vessel or tank.
11. A method and apparatus according to any preceding claim, characterised in that the separation tank is provided with a diffuser and a means for discharging the portion of the treated waste water containing the major amount of contaminants.
12. A method 'or apparatus according to any preceding claim, characterised in that the mixer means is a hydrocyclone mixer.
13. A method or apparatus according to any preceding claim, characterised in that the hydrocyclone aerates the waste water by mixing air or other gas under conditions of sheer to aerate the waste material.
14. A method or apparatus according to any preceding claim, characterised in that the hydrocyclone mixer is operated at a pre-determined rate irrespective of the rate of the incoming feed of waste water. A method or apparatus according to any preceding claim, in which the rate of aeration can vary from about 1 to 50 cubic metres per hour, preferably from 5 to 40 cubic metres per hour, or preferably from 10 to 30 cubic metre per hour and most preferably, at about 20 cubic metre per hour.
16. A method or apparatus according to any preceding claim, characterised in that the recirculation loop returns aerated partially treated waste water either directly or indirectly to the separation tank.
17. A method or apparatus according to any preceding WO 01/92165 PCT/AU01/00655 20 claim, characterised in that the recirculation loop return is located at a location or level of the separation tank corresponding to the position of the diffuser.
18. A method or apparatus according to any preceding claim, characterised in that the diffuser is a diffuser plate.
19. A method or apparatus according to any preceding claim, characterised in that the recirculation loop returns the aerated partially treated waste water to an intermediate location where it is mixed with additional incoming feed material prior to being introduced into the separation tank. A method or apparatus according to any preceding claim, characterised in that there is one or more additives added to the conduits or feed lines.
21. A method or apparatus according to any preceding claim, characterised in that the additives include flocculants, coagulants, polymer or like chemical materials to combine, agglomerate or the like contaminants together to form larger sized materials.
22. A method or apparatus according to any preceding claim, characterised in that the additives are added at one or more different locations throughout the process, including being associated with the incoming feed stream, being associated with the partially treated stream in the recirculation loop either before or after aeration, and/or being associated with the combined aerated incoming feed stream and partially treated recirculated stream.
23. A method or apparatus according to any preceding claim, characterised in that the ratio of incoming feed stream to recirculated stream is variable.
24. A method or apparatus according to any preceding claim, characterised in that during operation aerated waste WO 01/92165 PCT/AU01/00655 21 water is introduced into the separation vessel through the diffuser plate so that the contaminants are entrapped or otherwise entrained within or by air or other gas bubbles rising to the surface of the separation tank so that the contaminants are collected as an aerated sludge at the top. of the separation tank. A method or apparatus according to any preceding claim, characterised in that the separation tank is provided with a scraper having a scraper blade for moving or directing the sludge for discharge from the separation tank.
26. A method or apparatus according to any preceding claim, characterised in that the scraper blade rotates at the top of the tank to more or less continually discharge the aerated sludge from the top of the tank.
27. A method or apparatus according to any preceding claim, characterised in that the separation tank is provided with an outlet located at the lowermost point of the tank for removing any solid material accumulating at the base of the tank.
28. A method or apparatus according to any preceding claim, characterised in that the tank is provided with a clean zone located at or towards the base of the tank and a sludge collection zone located at or towards the top of the tank.
29. A method or apparatus according to any preceding claim, characterised in that the contaminants separated from the waste water are collected as sludge in the sludge collection zone.
30. A method or apparatus according to any preceding claim, characterised in that the clean zone is substantially unaerated.
31. A method or apparatus according to any preceding WO 01/92165 PCT/AU01/00655 22 claim, in which the partially treated waste water, including some contaminants and suspended solids or similar, are removed from the clean zone for recirculation through the mixer back to the separation vessel.
32. A method or apparatus according to any preceding claim, characterised in that the recirculation. loop further includes a retarder tank.
33. A method or apparatus according to any preceding claim, characterised in that the partially treated waste water from the clean zone is held in the retarder tank for up to one hour or more, preferably from seconds to one hour.
34. A method or apparatus substantially as hereinbefore described with reference to the accompanying drawings.