WO2006137736A2

WO2006137736A2 - Device and method for treatment of waste water

Info

Publication number: WO2006137736A2
Application number: PCT/NL2006/050143
Authority: WO
Inventors: Sjoerd Hubertus Josef Vellinga; Cornelia Theresia Maria Johanna Frijters
Original assignee: Paques B.V.
Priority date: 2005-06-21
Filing date: 2006-06-21
Publication date: 2006-12-28
Also published as: WO2006137736A3; NL1029302C2

Abstract

The invention relates to a device and method in which nitrate is removed by partially feeding aerobic effluent and aerobic biomass originating from the aerobic treatment to the anaerobic effluent from the anaerobic treatment, subjecting this aerobic effluent, that aerobic biomass and that anaerobic effluent to an anoxic treatment, and feeding the anoxic effluent from the anoxic treatment to the aerobic treatment. The device comprises an anaerobic reactor (2) , an aerobic reactor (3) and an anoxic intermediate compartment (4) located between them, which can all be accommodated in a single vertical column. The anoxic intermediate compartment (4) is connected on one side to that part of the anaerobic reactor which is located above the gas collectors, and is connected on the other side to the aerobic reactor. Between the aerobic reactor and the anoxic compartment there is a return system (8) for feeding part of the aerobic effluent and aerobic biomass from the aerobic reactor (3) back to the anoxic intermediate compartment.

Description

Device and method for treatment of waste water

The invention relates to a device and method for treatment of waste water, more particularly to such a device and method that also makes nitrogen removal (denitrification) possible.

In biological denitrification, heterotrophic bacteria convert nitrate into molecular nitrogen (N₂). These bacteria need an electron donor in this process. Some denitrifying bacteria are lithotrophic and use hydrogen or sulphur compounds as electron donor. It is the object of the present invention to provide a compact device and method for the treatment of waste water, with which nitrogen can also be removed from the waste water, which device and method are practicable and economically feasible.

The present invention is based on WO 98/19971. This publication discloses the opening part of device claim 1 and also the opening part of method claim 10. WO 98/19971 discloses an anaerobic reactor, in the form of a UASB reactor, on top of which an aerobic reactor is placed. Influent and waste water to be treated are fed in at the bottom of the anaerobic reactor. Above it lies the so-called fermentation chamber, where pollutants are converted into biogas, in particular methane, with the aid of anaerobic biomass. In the top part of the anaerobic reactor there are gas collection hoods for collecting the biogas. In WO 98/19971 the anaerobic UASB reactor is separated from the aerobic reactor by a partition wall with openings, in such a way that between the gas hoods and the partition wall a buffer chamber is formed in which anaerobic biomass that has passed through the gas hoods can accumulate and come to rest, in order to settle, while the openings in the partition wall allow transport of anaerobic effluent originating from the anaerobic reactor upwards, to the aerobic reactor. Air, or at any rate a gas containing oxygen, is fed in at the bottom of the aerobic reactor. In the aerobic reactor organic pollutants are converted mainly into carbon dioxide and aerobic biomass.

The object mentioned earlier is achieved according to the invention by providing a device for the treatment of waste water comprising:

• an anaerobic reactor for anaerobic treatment of the waste water with an anaerobic biomass;

• an aerobic reactor for aerobic treatment of the waste water; and

• an intermediate compartment located between the anaerobic reactor and the aerobic reactor; where the anaerobic reactor comprises a fermentation chamber; where the aerobic reactor comprises aerators on the underside for the supply of gas containing oxygen; where the anaerobic reactor, the intermediate compartment and the aerobic reactor in a column above each other are provided with the intermediate compartment between the anaerobic reactor and the aerobic reactor to receive anaerobic effluent from the anaerobic reactor - originating from that part of the anaerobic reactor which is located above the gas collectors - and also to provide intermediate effluent originating from the intermediate compartment as aerobic influent for the aerobic reactor characterized in that between the aerobic reactor and the intermediate compartment a return system is provided for feeding part of the aerobic effluent and aerobic biomass from the aerobic reactor back to the intermediate compartment. By providing, between the anaerobic reactor and the aerobic reactor linked thereto, an anoxic intermediate compartment through which the anaerobic effluent is conveyed before entering the aerobic reactor as aerobic influent, and by feeding part of the aerobic effluent and aerobic biomass back into this anoxic intermediate compartment (instead of feeding aerobic effluent back into the anaerobic reactor, as WO 98/19971 specifies), the invention makes it possible for the nitrate present in the aerobic effluent to be denitrified in the anoxic intermediate compartment with the aid of aerobic biomass that is also fed back from the aerobic reactor. In this process the nitrate is converted into, inter alia, N₂. This usually takes place by the equation: 4 NO₃ + 4H⁺ + 5[c] - 5 CO₂ + 2N₂ + 2H₂O, where [c] denotes carbon from COD, for example. If a carbon-free COD is used, the formula will be different. The removal of the N₂ gas can take place after the anoxic intermediate compartment, in the aerobic reactor, together with the venting of the aerobic reactor, but might also take place in the anoxic intermediate compartment itself. The vertical arrangement in a column reduces the floor space needed to a minimum and minimizes the number of parts needed, such as pipes.

If a relatively large amount of biogas is developed in the fermentation chamber, it is of advantage according to the invention if gas collectors are provided on the top of the anaerobic reactor to collect the biogas. Anaerobic reactors/processes are also known, however, in which a relatively small amount of biogas is produced, even in which no or hardly any biogas bubbles are observed. The biogas may then be entirely, or at any rate almost entirely, in solution.

If the aerobic effluent has insufficient COD for the amount of nitrate to be denitrified, it is of advantage according to the invention if means of supply are provided which are connected on one side to a COD source and on the other side to the intermediate compartment, so as to supply 'COD substance' thereto. The COD source can be an external COD source, such as a storage tank with COD, such as methane gas or a liquid containing sugar, or a supply line originating from another process. The COD source can also be an internal COD source, however. Thus it is of particular advantage according to the invention if the COD substance originates from the anaerobic process. The gas collectors can be used for this purpose, in which case the COD source will comprise the gas collectors. COD substance present in the anaerobic effluent can also be used, however. This may be dissolved COD substance or COD substance in bubble form/gas form. Where COD source is talked about here, this means a physical part of the installation. Where 'COD substance' is talked about here, this means a composition needed for the chemical, in particular biological, treatment process, in particular denitrification.

For practical considerations, if the COD substance is in gas form, it is of advantage according to the invention if the means of supply are connected to the return system so as to supply carbon to the intermediate compartment via the return system. It is thus possible to add 'COD substance' in the return system and at the same time to feed the effluent and aerobic biomass returned from the aerobic reactor back into the anoxic compartment via the same means of supply. It is furthermore of advantage according to the invention if the anaerobic reactor is an Upflow Sludge Blanket (USB) reactor in terms of its construction.

In order to prevent interchange between the media present in the aerobic reactor and the intermediate compartment, in particular of oxygen from the aerobic reactor to the intermediate compartment, the intermediate compartment and the aerobic reactor are separated by a partition which has one or more openings going through it. This partition can be a membrane, such as a perforated plate, with sufficient resistance (across the perforations) to prevent backflow of gas bubbles or oxygen-rich water through the membrane/perforations.

According to a further aspect, the object of the invention is achieved by providing a method for treatment of waste water in which the waste water in a vertical arrangement is subjected to an anaerobic treatment and an aerobic treatment, one after the other and from bottom to top, characterized in that nitrate is removed by:

• partially feeding aerobic effluent and aerobic biomass originating from the aerobic treatment, such as aerobic effluent containing aerobic biomass, to the anaerobic effluent from the anaerobic treatment,

• subjecting that aerobic effluent, that aerobic biomass and that anaerobic effluent to an anoxic treatment, and

• feeding the anoxic effluent from the anoxic treatment to the aerobic treatment. Insofar as the advantages achieved with the method according to the invention and the effects achieved therewith are concerned, reference can be made to the preceding description with regard to the device according to the invention. This applies also to the dependent method claims, which for this reason will not be separately discussed further here. According to yet another aspect, the invention relates to the use of a device according to one of claims 1-7 for carrying out the method according to one of claims 9-14.

The desired ratio of the aerobic recirculation stream to the anoxic intermediate compartment and the influent stream to the anaerobic reactor is about 4 to 5 for sewage waste water, i.e. 4 to 5 parts of recirculation stream to 1 part of influent stream. A different ratio can be calculated for other waste water streams, depending on the amount of nitrogen to be removed.

The present invention will be further explained below on the basis of an embodiment example shown schematically in the drawing. The only figure shows a device 1 for the treatment of waste water. This device comprises an anaerobic reactor 2, an aerobic reactor 3 and an anoxic intermediate compartment 4. The anaerobic reactor 2, aerobic reactor 3 and the anoxic intermediate compartment 4 are illustrated very schematically in this example as accommodated in a vertical arrangement in which they are placed above each other in a column- type construction. The implementation may involve a single column unit in which the anaerobic reactor, the aerobic reactor and the anoxic intermediate compartment are accommodated. It is also conceivable, however, that the anaerobic reactor, the intermediate compartment and the aerobic reactor are implemented in 2, 3 or more units which are stacked to form one column. In this example the anaerobic reactor is a so-called UASB reactor. In this reactor pollutants are converted into methane. Gas collectors 5, such as so-called gas collection hoods, are fitted in the top of the anaerobic reactor 2. In the case of a UASB reactor a 3-phase separation system can be used for the gas hoods, as described in EP 1.291.326. As is indicated with the arrow to the right (from the right-hand side), collected biogas can be removed to somewhere else. As is described further on, it can also be fed back wholly or partially via line 9a or in some other way into the device according to the invention.

The UASB reactor 2 is provided with a supply pipe 11 for supplying influent waste water to be treated. This waste water to be treated is distributed over the UASB reactor via a schematically illustrated distribution device 15. This distribution device for distribution of the influent from the anaerobic reactor, especially in the case of an anaerobic reactor with gas lift, can be a perforated plate, as described in WO 98/19971. The distribution device can also be constructed in a different way, however, for example as a tube system. The waste water goes up through a bed 14 of anaerobic biomass. In this process gas is formed, in particular methane, which rises as gas bubbles 13 and in so doing also takes anaerobic biomass up with it. In the top of the UASB reactor the gas, which is also called biogas, is collected by the gas collectors 5. The gas collectors 5 form part of a so-called three-phase separator, so that the rising biomass is also intercepted. What is then left over is the effluent from the anaerobic reactor, rid of biogas and biomass, which is here also called the anaerobic effluent. This anaerobic effluent, indicated schematically by means of the arrows 16, then comes into the intermediate compartment 4. From the intermediate compartment 4 this anaerobic effluent then goes up further to form the influent of the aerobic reactor 3 which is located higher. It is also possible for the gas collectors to be omitted or to be partially used to intercept biogas. In these cases the anaerobic effluent (16) contains biogas bubbles which are fed into the anoxic space together with that anaerobic effluent.

Between the intermediate compartment 4 and the aerobic reactor 3 there is a partition wall 10 which has one or more openings going through it, which partition wall can have the form of a perforated plate through which liquids and gas bubbles can pass upwards, but not downwards. The perforated plate can for example be made of metal or synthetic material.

Oxygen, or at any rate gas containing oxygen, such as air, is fed into the aerobic reactor 3 via a supply system 7. In this aerobic reactor pollutants are converted mainly into carbon dioxide, water and biomass by means of aerobic bacteria. The bubbles of exhaust air, air from which oxygen has been absorbed and to which carbon dioxide and nitrogen have been added, are illustrated by means of bubbles 12. The aerobic biomass is illustrated by means of flakes 17. In the top of the aerobic reactor 3 there is a plate separator 19 in which the aerobic biomass 17 is given the opportunity to settle and then fall back into the actual reactor chamber 21 of the aerobic reactor 3. From the separator 19 the final effluent, which has been rid of biomass and gases, is then removed via a pipe 18 for direct discharge or possibly further processing. In this example the aerobic reactor 3 is provided with a discharge pipe 20 for collected gases. The anaerobic reactor 3 can also very well be completely or partially open at the top, however. It will be clear to a person skilled in the art that a different system can also be chosen for the separation of aerobic sludge, such as a flotation unit for example.

The device as described hitherto on the basis of the figure does not in essence differ from the device described in WO 98/19971. For examples of further details, reference can then be made to WO 98/19971 by way of example. For examples of the gas collectors, reference can be made to the 3-phase separator as described in EP-1.291.326.

In accordance with the invention, a return pipe 8 is now provided. A pump 23 is optionally incorporated in the return pipe. From the aerobic reactor 3 this return pipe 8 removes a part of the effluent 22 from the reactor chamber 21 of the aerobic reactor 3. In this example this effluent includes both liquid which is still to receive further treatment, because it contains nitrates, and aerobic biomass 17. Via return pipe 8 this effluent containing aerobic biomass is fed back to the anoxic compartment 4. In the anoxic compartment 4 the aerobic biomass, which contains COD, will convert the nitrates into, inter alia, nitrogen gas. This nitrogen gas is allowed to pass through the membrane to the aerobic reactor, in order to be removed there together with the bubbles of exhaust air 12.

If insufficient COD is present in the anaerobic effluent 16 to adequately denitrify the nitrate, extra 'COD substance' can be supplied. This supply can take place via a supply pipe 9a in the return pipe 8, especially in the case of a COD substance in gas form. If the COD substance is in liquid form, the supply can take place via a supply pipe such as 9a in the return pipe or directly into the anoxic compartment 4, as schematically indicated by means of pipe 9b. The supply pipe 9a or 9b will be connected to a so-called COD source. This source can be an outside tank or a feed pipe coming from outside. According to the invention, however, it is preferable to use the gas collectors 5 for this source and in this way to feed biogas collected in the gas collectors 5, or at any rate a part thereof, to the anoxic compartment, preferably via the return pipe 8. To this end the gas collectors are connected to pipe 9a by means of pipe 9. It should be pointed out, however, that the use of biogas collected in the gas collectors does not exclude the possibility of supply also from a COD source originating from outside. This is shown in the Figure by continuing the line of pipe 9a past the junction point with pipe 9, on the right. To explain the terms COD source and 'COD substance'; the gas collection hoods form the COD source and the biogas collected therein forms 'COD substance', which is also simply called COD. COD is a term known to the person skilled in the art, which stands for chemical oxygen demand. According to the invention the COD/the COD substance comprises in particular carbon, but carbon-free COD is also conceivable. It should be pointed out that in the example illustrated the return system 8 feeds effluent containing aerobic biomass [thus a mixture of biomass and effluent] back to the intermediate compartment. It is also possible, however, to use final effluent 18, which has been rid of aerobic biomass, and to add aerobic biomass, collected for example in the separator 19, to this again. This is less efficient, however, because it leads to a separator 19 of much bigger construction. Pagina-einde

Claims

1. A device (1) for the treatment of waste water, comprising:

• an anaerobic reactor (2) for anaerobic treatment of the waste water with an anaerobic biomass;

• an aerobic reactor (3) for aerobic treatment of the waste water with aerobic biomass; and

• an intermediate compartment (4) located between the anaerobic reactor (2) and the aerobic reactor (3); where the anaerobic reactor (2) comprises a fermentation chamber (6); where the aerobic reactor comprises aerators (7) on the underside for the supply of gas containing oxygen; where the anaerobic reactor (2), the intermediate compartment (4) and the aerobic reactor (3) in a column above each other are provided with the intermediate compartment (4) between the anaerobic reactor (2) and the aerobic reactor (3) to receive anaerobic effluent (16) originating from the anaerobic reactor (2) and also to provide intermediate effluent originating from the intermediate compartment

(4) as aerobic influent for the aerobic reactor characterized in that between the aerobic reactor and the intermediate compartment (4) a return system (8) is provided for feeding part of the aerobic effluent and aerobic biomass from the aerobic reactor (3) back to the intermediate compartment (4).

2. The device as claimed in claim 1, in which the anaerobic reactor (2) includes, at the top, gas collectors (5) for collection of biogas, and in which the fermentation chamber (6) is provided under these gas collectors.

3. The device as claimed in claim 1 or 2, in which means of supply (9a, 9b) are provided which are connected on one side to a COD source (5) and on the other side to the intermediate compartment.

4. The device as claimed in claims 2 and 3, in which the COD source includes the gas collectors (5).

5. The device as claimed in claim 3 or 4, in which the means of supply (9) are connected to the return system (8) in order to supply 'COD substance' to the intermediate compartment (4) via the return system.

6. The device as claimed in claim 3 or 4, in which the means of supply lead directly into the intermediate compartment (4) in order to supply 'COD substance' to the intermediate compartment.

7. The device as claimed in one of the preceding claims, in which the intermediate compartment (4) and the aerobic reactor (3) are separated by a partition (10) having one or more holes going through it, which partition preferably comprises a membrane, such as a perforated plate.

8. A method for treatment of waste water, in which the waste water, in a vertical arrangement, is subjected to an anaerobic treatment and an aerobic treatment, one after the other and from bottom to top, characterized in that nitrate is removed by:

• partially feeding aerobic effluent and aerobic biomass originating from the aerobic treatment, such as aerobic effluent containing aerobic biomass, back to the anaerobic effluent from the anaerobic treatment, • subjecting that aerobic effluent, that aerobic biomass and that anaerobic effluent to an anoxic treatment, and

• feeding the anoxic effluent from the anoxic treatment to the aerobic treatment.

9. The method as claimed in claim 8, in which the anaerobic effluent, prior to the anoxic treatment, is separated from biogas and anaerobic biomass, and in which the anaerobic biomass is returned to the anaerobic treatment.

10. The method as claimed in one of claims 8-9, in which the anoxic treatment is carried out in the presence of a 'COD substance', such as an external 'COD substance'.

11. The method as claimed in claim 10, in which the 'COD substance' comprises methane.

12. The method as claimed in one of claims 10-11, in which the 'COD substance' originates at least partially from the anaerobic treatment.

13. The method as claimed in one of claims 10-11, in which the 'COD substance' comprises biogas, in particular biogas originating from the anaerobic treatment.

14. The method as claimed in one of claims 10-11, in which the COD substance is a residual product of the anaerobic treatment, and in which this residual product is supplied with the anaerobic effluent to the anoxic treatment.