AU1643300A - Waste water treatment - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant/s: Actual Inventor/s: Address for Service: Invention Title: BOC Gases Australia Limited Mervyn R Ogston BALDWIN SHELSTON WATERS MARGARET STREET SYDNEY NSW 2000 'WASTE WATER TREATMENT'

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Details of Associated Provisional Application No. PP8692 dated 15 FEB 1999 The following statement is a full description of this invention, including the best method of performing it known to me/us:- File: 27122AUP00 a -2- WASTE WATER TREATMENT Field of the Invention The invention relates to a system for the treatment of waste. It has been developed primarily for use in the treatment of industrial waste water streams and will be described with reference to this application. It will be appreciated however, that the invention is not limited to that particular field of use.

Background of the Invention In the past, treatment of waste water streams with biologically active materials such as activated sludge process has suffered from a number of limitations. One such limitation results from the necessity of removing the sludge or biomass from the treated effluent stream. Typically, this removal has been carried out by use of large settling tanks or clarifiers. Practical limitations on the size of clarifiers may unduly limit the treatment facility's capacity due to the limited quantity of biomass with which the clarifier could cope. An additional limitation is that the biomass requires a certain supply of oxygen in order to support the bioreactions which break down the organic S" matter in the waste stream.

In combination, these limitations minimise the upgradability of existing water \treatment facilities, as well as necessitating overly large plants for the treatment of waste water.

The object of the invention is to overcome or substantially ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

Disclosure of the Invention According to a first aspect of the invention there is provided a method of increasing the capacity of an existing system for the treatment of waste water, the system including; a vessel for containing a reaction mixture of waste water and biomass whilst the mixture undergoes an aerobic bioreaction and an effluent stream leaving the vessel; the method including the steps of; removing a recycle stream from the effluent stream for recycle back to the vessel; conducting microfiltration of the recycle stream, to remove the biomass from the recycle stream and provide a treated discharge stream and a filtered biomass stream; enriching the oxygen content of at least part of the filtered biomass stream; and returning the oxygenated biomass stream to the vessel whereby at least part of the 9. .9 oxygen is dispersed into the mixture in the vessel.

10 According to a second aspect, the invention provides a system for increasing the capacity of an existing treatment facility for waste water, the existing facility having: a vessel for containing a mixture of waste water and biomass whilst the mixture r. undergoes an aerobic bioreaction and an effluent stream leaving the vessel; the system including: 15 providing a recycle stream to recycle at least part of effluent stream back to the vessel, a microfiltration means in the recycle stream, for removal of the biomass from 999.9.

S•the recycle stream to thereby provide a treated discharge stream and a filtered biomass stream, and an oxygenation means for enriching the oxygen content of at least part of the filtered biomass stream; with the oxygen enriched biomass stream being returned to the vessel.

According to a third aspect of the invention there is provided a system for the treatment of waste water, the system including: -4a vessel for containing a mixture of waste water and biomass whilst the mixture undergoes an aerobic bioreaction; means for passing at least a portion of the mixture from the vessel to a microfiltration means for removal of the biomass to provide a treated discharge stream and a filtered biomass stream; oxygenation means for. enriching the oxygen content of at least a part of the filtered biomass stream prior to recycling back to the vessel; wherein, the filtered biomass stream is pressurised and then contacted with an oxygen containing gas by increasing the velocity of the biomass stream and thereby decreasing 10 its pressure relative to the oxygen containing gas; and a recycle means for returning the oxygen enriched biomass stream to the vessel whereby at least part of the oxygen is dispersed into the mixture in the vessel.

According to another aspect of the invention there is provided a method of treating waste water, the method including the steps of: *15 mixing waste water with biomass in a vessel and allowing the mixture to undergo :an aerobic bioreaction; passing at least a portion of the mixture from the vessel to a microfiltration means for removal of the biomass to provide a treated discharge stream and a filtered biomass stream; enriching the oxygen content of at least a portion of the filtered biomass stream by pressurising the filtered biomass stream and then contacting it with an oxygen containing gas by increasing the velocity of the filtered biomass stream and thereby decreasing its pressure with respect to said oxygen containing gas; and returning the oxygen enriched biomass stream to the vessel so that at least part of the oxygen is dispersed into the reaction mixture.

Brief Description of the Figures The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a first embodiment system for the treatment of waste water in accordance with the invention; Figure 2 shows a second embodiment system for the treatment of waste water in accordance with the invention; i 10 Figure 3 shows a third embodiment system for the treatment of waste water in accordance with the invention; Figure 4A shows a conventional system for the treatment of waste water; and S" Figure 4B shows the system of Figure 4A up graded in accordance with the invention.

15 Preferred Embodiment of the Invention Referring to Figure 1, a system 1 is shown for the treatment of waste water. The system includes a vessel 2, in the form of a bioreactor, for maintaining a mixture of waste water and biomass under aerobic conditions. An effluent stream 3 of the mixture is removed from the vessel and pumped through a microfilter 4 to separate at least a substantial portion of the biomass therefrom to provide a treated discharge stream 5 and a filtered biomass stream 8.

The treated discharge stream 5 leaving the microfilter may be discharged or proceed to further treatment. To support the increased concentrations ofbiomass the -6oxygen supplied to the bioreactor must be increased proportionately. Therefore, the filtered biomass stream is then recycled back to the vessel 2 via oxygenation means 6 to enrich it's oxygen content prior to entry into the bioreactor 2. Oxygen or another oxygen containing gas such as air or ozone may be provided to the oxygenation means from any conventional oxygen supply means 7.

The system 1, as described above, can support a higher concentration of biomass than previously possible due to the use of the microfilter 4 to separate the biomass from the treated effluent. The concentration of biomass within the bioreactor 2 is no longer limited by the capacity of a clarifier. Accordingly, higher concentrations of biomass 10 may be used.

As will be appreciated by those skilled in the art, in most systems the gravity separation of the biomass in a clarifier is relatively slow and can indeed be the rate determining step in the process. To increase the level of biomass requires a corresponding increase in the size of the clarifier. Further, if the feed to an already existing plant increases the clarifier may not be sufficiently large to provide an appropriate residence time for setting of the biomass floc. The use of the microfilter enables the separation of the biomass from the treated effluent without the need for a very large clarifier or other separating means. It is not necessary for all the biomass to be removed by microfiltration. It is preferred that substantially all biomass is removed, however, if any remains in the treated discharge stream it may undergo further clarification.

The use of the BOC VITOX injector system 6, 7, as disclosed in US patent no.

4,163,712 and herein included by reference, enables the supply of sufficient oxygen to -7support the increased flow and/or biomass levels. Another advantage of the VITOX system is that the recycle stream is returned to the bioreactor under turbulent conditions thus providing an effective form of mixing for the contents of the bioreactor As disclosed in the applicant's earlier US Patent, by use of the VITOX process it is possible to mix far more oxygen or oxygen containing gas with the filtered biomass stream than is possible by dissolution alone. Indeed, the oxygenated biomass stream may be foam like in appearance due to the large amount of small bubbles (0.2 to 2 mm).

After the oxygenation step, the flow rate/ pressure of the biomass stream is maintained sufficiently high to prevent the separation of the foam into discrete liquid and gas 10 phases.

The foamed mixture is returned to the bioreactor under turbulent conditions so that the small bubbles are smashed or sheared into even smaller bubbles that are either dissolved in the reaction mixture in the bioreactor or consumed by the biomass before they reach the liquid surface.

It has been found that the oxygenated foam can be effectively generated by pressurising the biomass stream and then contacting it with an oxygen containing gas by increasing the velocity of the biomass stream and thereby decreasing its pressure relative to the oxygen containing gas. This can be done by increasing the velocity of the biomass stream from 4 6 ms to 9 11 ms'. Ideally, this velocity increase occurs over a length of pipework less than 0.2d where d is the biomass stream diameter. By continuing control of the flow parameters, the oxygenated biomass stream can be maintained in the foamed form until it reaches the bioreactor.

-8- The applicant has found that this oxygenation step is particularly effective in a venturi mixer having one or more annular arrays of gas holes. The fine foam formed by such venturis offers significant benefits over gas/water mixtures produced by other mixing apparatus such as micronisers and spargers. Moreover, venturis are less prone to blockages from streams with high solids contents and can be used in plants of all sizes.

It has been found that the combination of mixing techniques to produce the oxygenated biomass stream together with the turbulent mixing of the oxygenated biomass with the bioreactor contents provide synergistic benefits resulting in improved dissolution of the oxygenating gas through contents of the bioreactor.

i 10 Figure 2 shows a system similar to that shown in Figure 1 wherein the oxygenation provided by the VITOX injector 6 is augmented by conventional air based aeration means 9. This can be provided by air blowers or surface aeration technologies. This additional aeration provides a convenient method of stripping the carbon dioxide 1 produced by aerobic biological processes.

15 A further embodiment, similar to Figure 2, is shown in Figure 3 and includes the further treatment of effluent in an ozone contact vessel 10. The ozone is effective in S•removing any colour in the effluent as well as killing any remaining bacteria or the like.

This capability is useful in applications where the waste water has a high organic content such as that produced as a by-product of wineries. The ozone can be produced by a conventional ozone generator provided with a conventional oxygen source. The effluent may be contacted with the ozone by way of a second VITOX injector 11 or any other suitable gas injection system. On contact with the effluent the ozone substantially decomposes to gaseous oxygen which is recycled to the first VITOX injector 6 after -9being passed through an ozone destruct unit 12 to decompose any remaining ozone in the off-gas stream.

It will be appreciated that the capacity of a conventional system for the treatment of waste water may be increased by adding the microfilter in isolation or in conjunction with the features described above. Such systems may include some form of separation devices such as clarifiers or alternately the effluent may be discarded. The addition of a microfilter will reduce the load ofbiomass that an existing clarifier, if present, will be required to accommodate whilst increasing the biomass that can be used to treat the waste water. The addition of oxygenation means such as a VITOX injector will ensure 9 10 that adequate oxygen is available to support the increased flow and/or concentration of biomass. To counteract the increased production of carbon dioxide, additional aeration 9 may be provided by conventional means to strip the carbon dioxide from the bioreaction 9 mixture.

A further variation of the invention provides for the diversion of at least part of the discharge stream to further oxygenation means such as a VITOX injector. Alternatively, the diverted discharge may be combined with the biomass residue and oxygenated in the VITOX injector 6. After oxygenation, the oxygen enriched stream is then recycled to the vessel under turbulent conditions to disperse at least part of the oxygen into the mixture in the vessel.

Figure 4A shows one example of an existing system and Figure 4B shows the same system upgraded in accordance with the invention.

The original system includes a bioreactor 12 for maintaining a mixture ofbiomass and waste water under aerobic conditions. An effluent stream 13 of the mixture is removed from the reactor and passed into a conventional separator 14, shown here as a clarifier to separate at least a portion of the biomass therefrom. The biomass stream 8 is then recycled to the bioreactor 12 whilst the clarified discharge stream 5 may be discharged or proceed to further treatment. A further stream 15 is removed from the bioreactor and is oxygenated using a VITOX injector 16 or equivalent before returning to the bioreactor. Conventional aeration means 17 are also provided.

In the event of an increase in the required duty of the existing system past its design limit waste water may not be sufficiently treated. The simple addition of extra biomass to the system is likely to result in the blockage or insufficient separation in the 9 10 clarifier. Conventional wisdom dictates a substantially larger clarifier would be required 9 i. resulting in substantial cost increases. With the present invention however, the capacity of the plant is substantially increased by augmenting the biomass removal in the clarifier with a microfilter 18 as illustrated in Figure 4B. While microfilter 18 is preferably o* o. positioned downstream of clarifier 14, it may also be placed upstream or even parallel with the clarifier.

The filtered biomass stream 21 can then be combined with stream 15 for subsequent oxygenation in VITOX injector 16 and recycle back to the reactor 12.

The filtered discharge stream 19 may then be discharged to the environment or, as illustrated, undergo further treatment in an ozone contact tank 20 as previously described.

Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims (33)

1. A method of increasing the capacity of an existing system for the treatment of waste water, the system including; a vessel for containing a reaction mixture of waste water and biomass whilst the mixture undergoes an aerobic bioreaction and an effluent stream leaving the vessel; the method including the steps of; removing a recycle stream from the effluent stream for recycle back to the vessel; conducting microfiltration of the recycle stream, to remove the biomass from the recycle stream and provide a treated discharge stream and a filtered biomass stream; 10 enriching the oxygen content of at least part of the filtered biomass stream; and returning the oxygenated biomass stream to the vessel whereby at least part of the oxygen is dispersed into the mixture in the vessel.

2. A method according to claim 1, wherein the oxygen containing gas is fed to the filtered biomass stream under turbulent conditions and at a rate to provide 100% to 15 1500% by weight of gas in excess of the equilibrium saturation value of said gas in the S filtered biomass stream.

3. A method according to any one of the preceding claims, wherein the filtered biomass stream is pressurised and then contacted with an oxygen containing gas by increasing the velocity of the biomass stream and thereby decreasing its pressure with respect to the oxygen containing gas.

4. A method according to claim 3 wherein the velocity of the biomass stream is increased from 4 6 ms to 9 11 ms 1 -12- A method according to claim 4 wherein the velocity increase occurs over a length ofpipework less than O.2d where d is the biomass stream diameter.

6. A method according to any one of the preceding claims wherein the oxygen containing gas is selected from oxygen gas, air, ozone, oxygenated air, ozonated air or a mixture thereof.

7. A method according to any one of the preceding claims, wherein oxygenation of said filtered biomass stream occurs in a venturi having an annular array of gas holes in a restricted throat section. o..

8. A method according to any one of the preceding claims, wherein the oxygen 10 enriched biomass stream forms a fine foam dispersion.

9. A method according to any one of the preceding claims wherein the oxygen enriched biomass stream is maintained as a fine foam dispersion after oxygenation. A method according to any one of the preceding claims wherein the oxygen enriched biomass stream is returned to the vessel under turbulent conditions whereby o. finely dispersed bubbles of undissolved oxygen containing gas are broken into even finer bubbles which either dissolve or are consumed within the reaction mixture.

11. A system for increasing the capacity of an existing treatment facility for waste water, the existing facility having: a vessel for containing a mixture of waste water and biomass whilst the mixture undergoes an aerobic bioreaction and an effluent stream leaving the vessel; the system including: providing a recycle stream to recycle at least part of effluent stream back to the vessel, a microfiltration means in the recycle stream, for removal of the biomass fr-om -13- the recycle stream to thereby provide a treated discharge stream and a filtered biomass stream, and an oxygenation means for enriching the oxygen content of at least part of the filtered biomass stream; with the oxygen enriched biomass stream being returned to the vessel.

12. A system according to claim 11 wherein the discharge stream leaving the microfiltration means is directed towards a clarifier for further treatment.

13. A system according to claim 11 or claim 12, wherein the filtered biomass stream is pressurised and then contacted with an oxygen containing gas by increasing the velocity of the biomass stream and thereby decreasing its pressure with respect to the oxygen 10 containing gas.

14. A system according to any one of claims 11 to 3 wherein the velocity of the biomass stream is increased from 4 6 ms" to 9 11 ms 1

15. A system according to any one of claims 11 to 14 wherein the velocity increase occurs over a length of pipework less than 0.2d where d is the biomass stream diameter.

16. A method according to any one of claims 11 to 15 wherein the oxygen containing gas is selected from oxygen gas, air, ozone, oxygenated air, ozonated air or a mixture *oooo thereof.

17. A system according to any one of claims 11 to 16, wherein oxygenation of said filtered biomass stream occurs in a venturi having an annular array of gas holes in a restricted throat section.

18. A system according to any one of claims 11 to 17 wherein the oxygen enriched biomass stream is returned to the vessel under turbulent conditions whereby finely -14- dispersed bubbles of undissolved oxygen containing gas are broken into even finer bubbles which either dissolve or are consumed within the reaction mixture.

19. A system for the treatment of waste water, the system including: a vessel for containing a mixture of waste water and biomass whilst the mixture undergoes an aerobic bioreaction; means for passing at least a portion of the mixture from the vessel to a microfiltration means for removal of the biomass to provide a treated discharge stream and a filtered biomass stream; and g.. oxygenation means for enriching the oxygen content of at least a part of the filtered 10 biomass stream prior to recycling back to the vessel; wherein, the filtered biomass stream is pressurised and then contacted with an oxygen containing gas by increasing the velocity of the biomass stream and thereby decreasing its pressure relative to the oxygen containing gas; and a recycle means for returning the oxygen enriched biomass stream to the vessel o* whereby at least part of the oxygen is dispersed into the mixture in the vessel. A system according to claim 19, wherein the oxygen containing gas is fed to the :oo i filtered biomass stream under turbulent conditions and at a rate to provide 100% to 1500% by weight of gas in excess of the equilibrium saturation value of said gas in the filtered biomass stream.

21. A system according to claim 19 or claim 20 wherein the velocity of the biomass stream is increased from 4 6 ms i to 9 11 ms 1

22. A method according to claim 21 wherein the velocity increase occurs over a length of pipework less than 0.2d where d is the biomass stream diameter.

23. A system according to any one of claims 19 to 22, wherein said oxygenation means is a venturi having an annular array of gas holes in a restricted throat section.

24. A system according to any one of claimsl9 to 23, wherein the oxygen enriched biomass stream forms a fine foam dispersion. A system according to any one of claims 19 to 24 wherein the oxygen enriched biomass stream is maintained as a fine foam dispersion after oxygenation.

26. A system according to any one of claims 19 to 23 wherein the oxygen enriched biomass stream is returned to the vessel under turbulent conditions whereby finely dispersed bubbles of undissolved oxygen containing gas are broken into even finer bubbles which either dissolve or are consumed within the reaction mixture.

27. A method of treating waste water, the method including the steps of: mixing waste water with biomass in a vessel and allowing the mixture to undergo S. :an aerobic bioreaction; passing at least a portion of the mixture from the vessel to a microfiltration means for removal of the biomass to provide a treated discharge stream and a filtered biomass stream; enriching the oxygen content of at least a portion of the filtered biomass stream by pressurising the filtered biomass stream and then contacting it with an oxygen containing gas by increasing the velocity of the filtered biomass stream and thereby decreasing its pressure with respect to said oxygen containing gas; and returning the oxygen enriched biomass stream to the vessel so that at least part of the oxygen is dispersed into the reaction mixture. -16-

28. A method according to claim 27, wherein the oxygen containing gas is fed to the filtered biomass stream under turbulent conditions and at a rate to provide 100% to 1500% by weight of gas in excess of the equilibrium saturation value of said gas in the filtered biomass stream.

29. A method according to claim 27 or claim 28 wherein the velocity of the biomass stream is increased from 4 6 ms to 9 11 ms A method according to claim 29 wherein the velocity increase occurs over a length of pipework less than 0.2d where d is the biomass stream diameter.

31. A method according to any one of claims 27 to 30, wherein said biomass stream is 10 contacted with the oxygen containing gas in a venturi having an annular array of gas holes in a restricted throat section.

32. A method according to any one of claims 27 to 31, wherein the oxygen enriched biomass stream forms a fine foam dispersion.

33. A method according to any one claims 27 to 32, wherein the oxygen enriched 9e biomass stream is maintained as a fine foam dispersion after oxygenation.

34. A method according to any one of claims 27 to 33 wherein the oxygen enriched biomass stream is returned to the vessel under turbulent conditions whereby finely dispersed bubbles of undissolved oxygen containing gas are broken into even finer bubbles which either dissolve or are consumed within the mixture in the vessel.

35. A method of increasing the capacity of an existing system for the treatment of waste water substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings. -17-

36. A system for increasing the capacity of an existing treatment facility for waste water substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings.

37. A system for the treatment of waste water substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying drawings.

38. A method of treating waste water substantially as herein described with reference to any one of the embodiments of the invention illustrated in the accompanying S. drawings. 10 DATED this 15th day of February, 2000 BOC GASES AUSTRALIA LIMITED Attorney: JOHN D. FORSTER Fellow Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS se p