AU772365B2

AU772365B2 - Denitrification process

Info

Publication number: AU772365B2
Application number: AU49001/00A
Authority: AU
Inventors: Leonid Charuckyj; Peter A. Cooksey
Original assignee: Zeolite Australia Ltd
Current assignee: Individual
Priority date: 1999-06-01
Filing date: 2000-05-31
Publication date: 2004-04-22
Anticipated expiration: 2020-05-31
Also published as: AU4900100A

Description

WO 00/73214 PCT/AU00/00622 1 DENITRIFICATION PROCESS The present invention relates to denitrification of waste water, of particular but by no means exclusive application in the treatment of the nitrate containing liquor from the biological regeneration of zeolite beds.

Ammonium exchange systems utilising zeolite have been accepted technology for some years, but have not found wide application owing, it appears, to difficulties and expenses associated with regeneration, treatment and disposal of the regenerant stream.

All systems were originally regenerated using highly saline backwash streams, resulting in regenerant streams high in ammonium which then had to be disposed of or used beneficially. Even though a number of methods have been employed to address this problem (such as by air stripping the ammonium, or using this liquor as or in the manufacture of fertiliser), the above mentioned problems have none the less led to the limited acceptance of these existing systems.

In the late 1970s investigations into regeneration systems involving nitrification biological regeneration or biologically regenerant restoration systems) were reported.

Early systems recirculated nitrifying organisms across an exchange bed in a saline regenerant solution, or employed suspended nitrifiers for treatment of the regenerant solution after use. In some subsequent systems, the nitrifiers were grown on the exchange medium.

Biological regeneration systems offer the advantage of reduced salt requirements for ammonium release, by keeping the ammonium level in the solution adjacent to the regenerating medium low, but result in conversion of the ammonium to nitrate. This is not a problem if low effluent 1. WO 00/73214 PCT/AU00/00622 2 ammonium is desired, but is initially of little benefit if low effluent total nitrogen is sought, as is usually the case.

A principal shortcoming of existing systems that include the biological regeneration of an ammonium exchange bed, therefore, is the high cost and/or difficulty of denitrifying either the system effluent (if regeneration is carried out on-line) or the regenerant stream (if regeneration is carried out off-line).

In on-line regeneration systems, zeolite loading and nitrification are able to take place simultaneously, although zeolite loading will only occur when the ammonia feed rate exceeds the available nitrification rate, and regeneration would subsequently occur when the ammonium feed rate fell below the available nitrification rate.

If nitrification is to occur while the system is on-line, the system must remain aerobic at essentially all times, and while virtually all ammonium should be removed from the waste stream an equivalent amount of nitrate will be discharged in the effluent (though nitrogen peaks will be reduced owing to the exchange/regeneration mechanism).

On-line exchange/regeneration systems appear generally to have little advantage over alternative nitrificationdenitrification systems apart from their ability to absorb (or exchange) ammonium peaks but are a viable option where oxidized nitrogen in the effluent is acceptable.

In off-line regeneration, zeolite loading occurs on-line as in a normal exchange system, while nitrification on-line is prevented even if nitrifiers are present by a lack of oxygen. This condition will occur naturally provided that the system is not aerated during loading. During loading the system effluent contains virtually no ammonium, but it WO 00/73214 PCT/AU00/00622 3 will contain most of whatever oxidised nitrogen is present in the feed to the exchange system: this may thus limit total nitrogen removal in some instances, such as in effluent from partially nitrifying filters.

The organic carbon from raw sewage is commonly used for denitrification in an anoxic zone located near the head of an activated sludge plant by recycling mixed liquor from a subsequent nitrification zone. A disadvantage of such systems is that high rates of mixed liquor recycle are required to denitrify the majority of the oxidised nitrogen generated, since a proportion of the nitrate is always discharged without passing through the anoxic zone.

Wastewater treatment ponds may be defined as aerobic, anaerobic, or facultative depending on the dominance of various groups of organisms.

Aerobic ponds are either lightly loaded, or provided with sufficient oxygen (naturally or artificially) that the dominant organisms throughout the pond are aerobic. Since denitrification occurs only in the absence of free oxygen such ponds are ineffective for denitrification.

In anaerobic ponds loading is so high that any oxygen introduced into the pond is utilised very quickly, and virtually all the biological activity occurring is anaerobic. This can lead to the production of odours, but because anaerobic growth is (biologically) inefficient little sludge is produced in relation to the oxygen demand destroyed, and a significant amount of treatment can be obtained in a relatively small volume. Introduction of either oxygen or nitrate to such a system interferes with the anaerobic activity, and hence the performance of the pond, although it can be a very effective means of denitrification since adequate organic carbon is readily available.

4 Facultative ponds are those in which aerobic activity may be dominant in some regions (usually the upper levels) and anaerobic activity in others (usually the lower regions).

The proportions of aerobic and anaerobic activity affect the degree of treatment of different kinds, but are not important in terms of pond type definition, and frequently vary with changes in temperature, light intensity, etc.

Unless pond loading is very heavy, and hence conditions approach being fully anaerobic, increased aerobic activity is usually preferable to increased anaerobic activity.

Both nitrification and denitrification can occur in facultative ponds, but total nitrogen removal is limited either by limitations on nitrification (since this must i* *occur first) or subsequent transfer of the nitrate to anaerobic zones where denitrification can occur. Aerobic reactions in facultative ponds are very much related to retention time, so increased flows adversely affect 20 performance, but considerable spare capacity for denitrification normally exists, and this can be utilised if low volume streams of nitrate (particularly at high concentration) can be introduced into the anaerobic regions S of the pond.

g SUMMARY OF THE INVENTION 0i According to the present invention there is provided a process for reducing nitrogen in a waste stream, having the steps of: removing ammonium and/or ammonia from said stream in a reactor, thereby producing an effluent with reduced nitrogen content; WO 00/73214 PCT/AU00/00622 5 biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; discharging said regenerant stream to either the lower portions of a facultative pond or to an anaerobic pond; and denitrifying said regenerant stream by means of said facultative pond or said anaerobic pond.

Preferably said discharging is performed at a low rate.

Thus, available carbon is used for denitrification without adversely affecting performance of the pond system. From a denitrification point of view, anaerobic ponds would be no different to facultative ponds, hence reference to both facultative and anaerobic ponds.

If the original waste stream includes organic nitrogen pollution, the process preferably additionally includes the step of converting the organic nitrogen to ammonia/ammonium biologically.

Preferably said reactor includes a zeolitic medium for removing ammonium from said waste stream by exchange onto said zeolitic medium Regenerating said reactor, to release said removed ammonium from said zeolitic medium, may comprise allowing said reactor to regenerate.

Preferably said reactor includes a zeolite exchange bed including said zeolitic medium.

This pond system need not be involved in treatment of the original waste stream treated by the zeolite exchange bed.

Preferably said process includes interrupting flow of said 6 waste stream into said reactor when the effluent ammonium concentration reaches a predetermined concentration, or after a specified period of time. The waste stream is then preferably diverted to a further reactor.

During the regeration phase, the reactor may be aerated in order to induce nitrifying organisms either growing on the zeolitic medium, or introduced in suspension, to nitrify.

The process may include introducing a saline solution to accelerate the release of ammonium from the zeolitic medium.

The process may include recirculation. The recirculation rates are preferably controlled on the basis of salt requirements for ammonium release, alkalinity restoration in view of alkalinity consumption during nitrification, and/or to limit nitrate concentration in the regenerant stream.

According to the present invention there is provided a process for reducing nitrogen in a waste stream, having the steps of: removing ammonium and/or ammonia from said stream 25 in a reactor, thereby producing an effluent with reduced nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; and denitrifying said regenerant stream by anoxically digesting waste sludge in said regenerant stream.

Digesting the waste sludge in said regenerant stream is preferably performed in a purpose built reactor, in an existing digester, or in a sludge lagoon.

WO 00/73214 PCT/AU00/00622 7 The rate of stabilisation of solids under various conditions can be calculated, as can be the rate of denitrification under similar conditions. The degree of solids stabilisation will depend on their initial condition and the plant operating conditions (particularly solids retention time), and the availability of nitrate depends on the nitrate content of the regenerant stream and the plant operating conditions (particularly its hydraulic retention time), so it should be possible within certain limits to balance sludge stabilisation and denitrification requirements by separately adjusting the solids retention time and hydraulic retention of the system, provided that proper control can be exercised over separation of the solids from the liquid stream.

Preferably sufficient anoxic substrate is provided for denitrification, or alternatively if insufficient sludge stabilisation is provided anoxically the substrate can be supplemented by subsequent anaerobic or aerobic stabilisation.

Preferably said process includes interrupting flow of said waste stream into said reactor when the effluent ammonium concentration reaches a predetermined concentration, or after a specified period of time. The waste stream is then preferably diverted to a further reactor.

8 During the regeration phase, the reactor may be aerated in order to induce nitrifying organisms either growing on the zeolitic medium, or introduced in suspension, to nitrify.

According to the present invention there is further provided a process for denitrifying a waste stream, having the steps of: S 20 removing ammonium and/or ammonia from said stream in a reactor, thereby producing an effluent with reduced nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; and denitrifying said regenerant stream using an organic carbon bearing waste stream as a source of organic carbon for denitrification.

Preferably said organic carbon bearing waste stream includes raw sewage, trade waste or digester supernatant.

Preferably, the organic carbon bearing waste stream and the regenerant stream are mixed for sufficient time for full denitrification to take place. In order to reduce the contact time necessary, and hence the reactor volume, it -9 may be desirable to increase organism concentration, such as by operating the unit in an activated sludge mode (i.e.

with solids retention in order to increase the denitrifier concentration) or by promoting attached growth, such as in a submerged bed.

This aspect of the invention has the advantage of low regenerant flow required to introduce oxidised nitrogen to the denitrification unit.

Where the original waste stream also comprises raw sewage, the raw sewage being used as the source of organic carbon may be obtained from the original waste stream.

Regenerating the reactor, to release said removed ammonium from said zeolitic medium, may comprise allowing said reactor to regenerate.

0:0. By using an ammonium exchange bed for nitrogen removal from the waste stream, and biological regeneration of this bed, it becomes possible to return a large proportion of the oxidised nitrogen from the system to the anoxic zone in a very small volume of liquid.

C

09 25 The invention also provides a process for denitrifying a waste stream, having the steps of: 0 •g *removing ammonium and/or ammonia from said stream in a reactor, thereby producing an effluent with reduced Goo# nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; and denitrifying said regenerant stream by discharging the regenerant stream to wetlands or overland.

Wetlands and overland discharge may be more effective, WO 00/73214 PCT/AU00/00622 10 however, at denitrification than nitrification, depending on operating conditions. It may be difficult to maintain aerobic conditions in a wetland, particularly if organic loading is relatively high, and this may inhibit nitrification. Alternatively, the area available may be insufficient to achieve both nitrification and denitrification. In either case, utilisation of an ammonium exchange filter for ammonium removal and nitrification would allow optimisation, and maximum utilisation, of the wetland for denitrification. Overland flow can be considered an extension of wetland systems involving plants not as water dependent as wetland plants, and while not likely to be as effective as other wetland systems for denitrification, may be used where topography, etc., dictate their adoption.

Preferably said reactor includes a zeolitic medium for removing ammonium from said waste stream by exchange onto said zeolitic medium Regenerating said reactor, to release said removed ammonium from said:zeolitic medium, may comprise allowing said reactor to regenerate.

The process may include introducing a saline solution to WO 00/73214 PCT/AU00/00622 11 accelerate the release of ammonium from the zeolitic medium.

In each of the above aspects of the invention, the reactor is preferably an ion exchange reactor.

BRIEF DESCRIPTION OF THE FIGURES In order that the invention may be more fully ascertained, preferred embodiments will now be described, by way of example, by reference to the accompanying drawing, in which: Figure 1 is a schematic diagram of a general system for denitrifying waste water according to a preferred embodiment of the present invention; Figure 2 is a schematic diagram of a pond denitrification system for denitrifying waste water according to a preferred embodiment of the present invention; Figure 3 is a schematic diagram of a system incorporating an anoxic digester for denitrifying waste water according to a preferred embodiment of the present invention; Figure 4 is a schematic diagram of a system incorporating an anoxic system for denitrifying waste water using an organic carbon bearing waste stream according to a preferred embodiment of the present invention; and Figure 5 is a schematic diagram of a system utilising wetland and overland flow systems for denitrifying waste water according to a preferred embodiment of the present invention.

WO 00/73214 PCT/AU00/00622 12 DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a system for denitrifying waste water according to a preferred embodiment of the present invention. Waste oxidised nitrogen bearing backwash from an ammonium removal unit 10 is mixed, in the absence of free dissolved oxygen, with an organic carbon source 12 in a reactor 14 which contains a biomass including a substantial quantity of denitrifying organisms. After contact for several minutes to a few days, the treated effluent 16 is separated from the biomass and discharged.

If it is necessary to limit the amount of biomass in the reactor, a proportion of the biomass may be wasted periodically as a sludge stream 18.

This system differs from existing systems in that the feed to the reactor 14, being the regenerant stream from a biologically regenerated ammonium removal system, carries a high concentration of oxidised nitrogen in a small flow of waste.

Figure 2 shows a particular example of such a system, for performing a denitrifying process according to a further preferred embodiment. The system includes a denitrification reactor in the form of a facultative or anaerobic pond 20 (or series of ponds) in a treatment system served by ammonium exchange units 24 and 28 generating the stream to be denitrified. The original waste stream 22, or anaerobic breakdown of organisms in the reactor 20, provides the organic carbon needed for denitrification.

Ammonium exchange bed 24 is shown on-line and hence being loaded, resulting in an effluent 26 which is low in ammonium. Exchange bed 28 is shown as previously loaded and now off-line and being regenerated biologically (i.e.

aerated in the presence of nitrifying organisms). During WO 00/73214 PCT/AU00/00622 13 this process regenerant stream 30a, which may be saline if desired to improve the release rate of ammonium, may be recirculated (at 30b). Nitrification will result in conversion of released ammonia to an oxidised form, predominantly nitrate.

During or after regeneration of the exchange bed 28 some or all of the regenerant is wasted to the anaerobic zone of the pond (or one of the ponds) in the treatment system, where denitrification will occur.

The advantage of this system is that the ammonium exchange beds will remove nearly all ammonium exiting from the treatment system, resulting in low ammonium levels in the effluent, while biological regeneration of the beds and denitrification of the regenerant stream in the ponds will result in actual removal of this nitrogen from the effluent, rather than mere conversion to a less environmentally harmful form.

The system shown in figure 2 is a simple embodiment of the invention, but it is not essential that the treatment system served by the ammonium exchange beds includes facultative or anaerobic ponds. The treatment system served by these units could be activated sludge, biological filters, or some other form of treatment, provided only that facultative or anaerobic ponds are available in the vicinity (possibly on a sidestream treatment, treatment for a portion of the flow not served by the exchange beds, or in an unconnected system which may be available in the area). Further, the ponds could constitute all of the main treatment system, or part of the main treatment system (in which case, for example, upstream of other units).

Figure 3 shows a further system for performing a denitrifying process according to a further preferred embodiment of the invention, where the denitrification unit WO 00/73214 PCT/AU00/00622 14 is an anoxic digester.

The figure shows the treatment system 42 which is served by the ammonium exchange system (parallel units 44 and 46).

As illustrated, the exchange unit 44 is shown on-line, while unit 46 is shown off-line for regeneration.

Waste regenerant 48 enters the denitrification unit which contains a denitrifying biomass. Organic carbon is provided by waste sludge 50 from the treatment system 42 served by the ammonium exchange system (or by any other treatment system in the area which has a waste stream high in particulate organic carbon). Periodically, solids in the denitrification unit 40 are separated from the liquor, with the latter being returned (at 52) to the treatment system 42 for disposal with the treated effluent 54. A proportion of the solids from the denitrification unit may be wasted 56 periodically to maintain a suitable concentration of denitrifying organisms in the system.

It should be noted that this system is primarily designed for denitrification of the ammonium exchange regenerant stream, and in some cases it may be difficult to control the denitrifying unit to achieve this while simultaneously providing full digestion of the solids in the sludge providing the organic carbon. It may therefore be desirable to incorporate anaerobic or aerobic phases into the operation of the denitrification unit 40, or to operate this unit in conjunction with other digesters designed primarily for full stabilisation of the organic matter in the waste sludge being used for denitrification of the ammonium exchange regenerant.

Figure 4 shows another system for performing denitrification according to a further preferred embodiment of the invention, which uses organic carbon from an organic carbon bearing waste stream (such as raw sewage, trade waste or digester supernatant) for denitrification. The WO 00/73214 PCT/AU00/00622 15 system includes a denitrification unit in the form of an anoxic system 60 placed at the upstream end of the treatment system 62 served by the ammonium exchange units 64 and 66 generating the regenerant stream 68 to be denitrified. Raw sewage waste 70 is admitted into the treatment system 62, while the organic carbon bearing waste stream 71 needed for denitrification is admitted into denitrification unit 60. This organic carbon bearing waste stream 71 may comprise raw sewage waste, and in that case may be drawn from the original raw sewage waste Indeed, raw sewage waste may be used for denitrification in applications where the original waste 70 is other than raw sewage waste. Depending on the denitrification rate required, this system may include a means of increasing organism concentrations (such as a clarifier and sludge return system as commonly used for activated sludge, or a submerged growth bed).

Ammonium exchange bed 64 which is shown on-line and hence being loaded, resulting in an effluent 72 which is low in ammonium. Exchange bed 66 is shown off-line and being regenerated biologically aerated in the presence of nitrifying organisms). During this process regenerant 68, which may be saline if desired to improve the release rate of ammonium, may be recirculated (at 74). Nitrification will result in conversion of released ammonia to an oxidised form, predominantly nitrate.

During or after regeneration of the exchange beds 64 and 66, some or all of the regenerant is wasted to the anoxic system 60, where denitrification occurs.

The advantage of this system over existing systems incorporating an anoxic zone is the low flow rate of the stream returning the oxidised nitrogen to the denitrification system.

WO 00/73214 PCT/AU00/00622 16 Figure 5 shows another system (similar to that shown in figure 2) for performing denitrification according to a further preferred embodiment of the invention, incorporating the use of a wetland or overland flow system.

The system uses a denitrification unit 80 in the form of a wetland or overland flow system to denitrify the regenerant stream. Organic carbon for denitrification is provided by detritus from plants grown in the wetland or overland flow system.

The system again includes an ammonium exchange bed 82 shown on-line and hence being loaded, producing an effluent 86 which is low in ammonium. The system also includes an exchange bed 84 shown off-line and being regenerated biologically aerated in the presence of nitrifying organisms). During this process regenerant stream 88, which may be saline if desired to improve the release rate of ammonium, may be recirculated (at 90). Nitrification will result in conversion of released ammonia to an oxidised form, predominantly nitrate.

During or after regeneration of the exchange bed 84 some or all of the regenerant stream 88 is wasted to the wetland or overland flow system 80, where denitrification will occur.

This wetland or overland flow system 80 may receive flow only from.the ammonium exchange backwash, or it may also receive flow from the system served by the ammonium exchange unit (if so desired for solids reduction, etc., for that stream).

The advantage of this system over wetland and overland flow systems currently in use (particularly if the system receives regenerant liquor only) is that it can be tailored towards denitrification alone, without having to satisfy conflicting requirements for nitrification and denitrification, and that much smaller hydraulic loadings need be applied.

17

CONCLUSION

The practical application of this system is that it provides a novel, cost-effective solution to produce an effluent that has total nitrogen both ammonia and nitrate) reduced significantly, or value in reducing nutrients to waterways from waste water treatment plants, which are the cause of significant water pollution of the receiving water-body.

The present invention has the added advantage that it can be applied to biological filtration and pond systems as well as activated sludge systems, incorporation of an anoxic reactor into such systems not normally being practicable due to the high flow rates resulting from recirculation, or due to the absence of suitable anoxic zones.

i Modifications may be made to the invention as will be apparent to a person skilled in the art. These and other 20 modifications may be made without parting from the ambit of the current invention, the nature which may be ascertained from the foregoing description and the drawing.

Further, any reference herein to prior art is not intended to imply that such prior art forms or formed a part of the ocommon general knowledge.

0.como ::o

Claims

1. A process for reducing nitrogen in a waste stream, having the steps of: removing ammonium and/or ammonia from said stream in a reactor, thereby producing an effluent with reduced nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; discharging said regenerant stream to either the lower portions of a facultative pond or to an anaerobic pond; and denitrifying said regenerant stream by means of said facultative pond or said anaerobic pond.

2. A process as claimed in claim 1, wherein said discharging is performed at a low rate. 20 3. A process as claimed in either claim 1 or 2, wherein, if said waste stream before treatment includes organic nitrogen pollution, said process additionally includes the step of converting the organic nitrogen to ammonia/ammonium biologically.

4. A process as claimed in any one of the preceding claims, wherein said reactor includes a zeolitic medium for removing ammonium from said waste stream by exchange onto said zeolitic medium A process as claimed in claim 4, wherein said reactor includes a zeolite exchange bed including said zeolitic medium.

6. A process as claimed in claim 5, wherein said pond is not involved in treatment of said waste stream before being treated by the zeolite exchange bed. 19

7. A process as claimed in any one of the preceding claims, wherein said regenerating of said reactor comprises allowing said reactor to regenerate.

8. A process as claimed in any one of the preceding claims, wherein said process includes interrupting flow of said waste stream into said reactor when the effluent ammonium concentration reaches a predetermined concentration, or after a specified period of time.

9. A process as claimed in claim 8, including subsequently diverting said waste stream to a further reactor.

10. A process as claimed in any one of the preceding claims, including, during said regenerating, aerating said reactor to induce nitrifying organisms either growing on 0 the zeolitic medium, or introduced in suspension, to nitrify.

11. A process as claimed in any one of claims 4 to 6, including introducing a saline solution to accelerate the release of ammonium from the zeolitic medium.

12. A process as claimed in any one of the preceding claims, including recirculation. So13. A process as claimed in claim 12, wherein the oo..recirculation rates are controlled on the basis of salt 30 requirements for ammonium release, alkalinity restoration in view of alkalinity consumption during nitrification, and/or to limit nitrate concentration in the regenerant stream.

14. A process for reducing nitrogen in a waste stream, having the steps of: removing ammonium and/or ammonia from said stream WO 00/73214 PCT/AU00/00622 20 in a reactor, thereby producing an effluent with reduced nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; and denitrifying said regenerant stream by anoxically digesting waste sludge in said regenerant stream.

15. A process as claimed in claim 14, wherein said digesting of said waste sludge in said regenerant stream is performed in a purpose built reactor, in an existing digester, or in a sludge lagoon.

16. A process as claimed in either claim 14 or including providing sufficient anoxic substrate for denitrification.

17. A process as claimed in either claim 14 or including providing anoxic substrate for denitrification and supplementing said substrate by subsequent anaerobic or aerobic stabilisation if insufficient sludge stabilisation is provided anoxically.

18. A process as claimed in any one of claims 14 to 17, wherein said reactor includes a zeolitic medium for removing ammonium from said waste stream by exchange onto said zeolitic medium

19. A process as claimed in claim 18, wherein said regenerating said reactor, to release said removed ammonium from said zeolitic medium, comprises allowing said reactor to regenerate.

20. A process as claimed in either claim 18 or 19, wherein said reactor includes a zeolite exchange bed including said zeolitic medium. 21

21. A process as claimed in any one of claims 18 to including, during said regenerating, aerating said reactor to induce nitrifying organisms either growing on the zeolitic medium, or introduced in suspension, to nitrify.

22. A process as claimed in any one of claims 18 to 21, including introducing a saline solution to accelerate the release of ammonium from the zeolitic medium.

23. A process as claimed in any one of claims 14 to 21, including interrupting flow of said waste stream into said reactor when the effluent ammonium concentration reaches a predetermined concentration, or after a specified period of time.

24. A process as claimed in claim 23, including i subsequently diverting said waste stream to a further reactor. A process as claimed in any one of claims 14 to 24, including recirculation. oooo

26. A process as claimed in claim 25, wherein recirculation rates are controlled on the basis of salt requirements for ammonium release, alkalinity restoration in view of alkalinity consumption during nitrification, and/or to limit nitrate concentration in the regenerant stream.

27. A process for denitrifying a waste stream, having the steps of: removing ammonium and/or ammonia from said stream in a reactor, thereby producing an effluent with reduced nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized 22 nitrogen, but with reduced ammonia and/or ammonium content; and denitrifying said regenerant stream using an organic carbon bearing waste stream as a source of organic carbon for denitrification.

28. A process as claimed in claim 27, wherein said organic carbon bearing waste stream includes raw sewage, trade waste or digester supernatant.

29. A process as claimed in either claim 27 or 28, wherein said organic carbon bearing waste stream and the regenerant stream are mixed for sufficient time for full denitrification to take place. A process as claimed in claim 29, including increasing organism concentration to reduce required contact time i necessary and hence reactor volume.

31. A process as claimed in claim 30, wherein said organism concentration is increased by operating the unit in an activated sludge mode or by promoting attached growth. 25 32. A process as claimed in any one of claims 27 to 31, wherein said waste stream before treatment also comprises raw sewage, and said process includes obtaining the raw sewage being used as the source of organic carbon from said waste stream before treatment. oooo

33. A process as claimed in any one of claims 27 to 32, wherein said regenerating of said reactor, to release said removed ammonium from said zeolitic medium, comprises allowing said reactor to regenerate.

34. A process for denitrifying a waste stream, having the steps of: WO 00/73214 PCT/AU00/00622 23 removing ammonium and/or ammonia from said stream in a reactor, thereby producing an effluent with reduced nitrogen content; biologically regenerating said reactor and thereby producing a regenerant stream containing oxidized nitrogen, but with reduced ammonia and/or ammonium content; and denitrifying said regenerant stream by discharging the regenerant stream to wetlands or overland. A process as claimed in claim 34, wherein said regenerating of said reactor comprises allowing said reactor to regenerate.

36. A process as claimed in either claim 34 or 35, wherein said reactor includes a zeolitic medium for removing ammonium from said waste stream by exchange onto said zeolitic medium

37. A process as claimed in claim 36, wherein said reactor includes a zeolite exchange bed including said zeolitic medium.

38. A process as claimed in any one of claims 34 to 37, including interrupting flow of said waste stream into said reactor when the effluent ammonium concentration reaches a predetermined concentration, or after a specified period of time.

39. A process as claimed in any one of claims 34 to 38, including subsequently diverting said waste stream to a further reactor. A process as claimed in any one of claims 34 to 38, including, during said regerating, aerating said reactor to induce nitrifying organisms either growing on the zeolitic medium, or introduced in suspension, to nitrify. 24

41. A process as claimed in any one of claims 34 to including introducing a saline solution to accelerate the release of ammonium from the zeolitic medium.

42. A process as claimed in any one of the preceding claims, wherein said reactor is an ion exchange reactor.

43. A process for reducing nitrogen in a waste stream substantially as herein described with reference to any one of the accompanying drawings.

44. A process for denitrifying a waste stream substantially as herein described with reference to any one of the accompanying drawings. Dated this 6th day of February 2004 ZEOLITE AUSTRALIA LIMITED **f By their Patent Attorneys GRIFFITH HACK 20 Fellows Institute of Patent and Trade Mark Attorneys of Australia oo o* o• *oo ago o *ooo