WO1997033839A1 - Process and device for sewage treatment - Google Patents

Abstract

According to the invention, in a process and device for sewage treatment by the activated sludge process (5) followed by digestion (11) of the separated sewage sludge and sludge water extraction (14, 15, 16) from the treated activated sludge, the extracted sludge water is subjected to a nitrification/denitification treatment (22) before being led back to the activated sludge process, and the return water is removed by a separator (23), thus permitting high nitrogen extraction.

Description

 METHOD AND DEVICE FOR PURIFYING WASTE WATER

The invention relates to a process for the purification of wastewater, in which the wastewater is microbially converted by a biological treatment with activated sludge, the activated sludge is separated from the microbially converted waste water and subjected to a sludge treatment, the treated activated sludge Sludge water is withdrawn and return water obtained from the sludge water is returned to the biological treatment, and to a device for carrying out this method.

In such known processes, the activated sludge which has been separated off is subjected to the sludge treatment together with primary sewage sludge, and the sludge removed from this waste water sludge Mud water is returned directly to the biological treatment and passes through the latter together with the wastewater supplied to it. This sludge water originating from the sludge treatment of the waste water sludge has a relatively high nitrogen content, as a result of which a high nitrogen input into the biological treatment takes place. So that the microbially converted wastewater separated from the wastewater dam can be discharged into a receiving water after the biological treatment, for example, its nitrogen content must be reduced to a low value according to the legal regulations. This can hardly be achieved with the direct return of the sludge water, especially when the biological treatment is used to a high degree.

The invention is based on the object of developing a method of the type mentioned at the outset such that the efficiency for nitrogen removal is increased and of specifying an apparatus for carrying out the method according to the invention.

With regard to the method, this object is achieved according to the invention in that the sludge water is subjected to an microbial nitrification / denitrification treatment and the return water from the nitrification / denitrification treatment is separated off by centrifugation.

The nitrification / denitrification treatment results in a nitrogen removal from the sludge water of around 80 to 90%, but this can also be increased up to 100%. The return water remaining after the nitrification / denitrification treatment therefore does not lead to excessive nitrogen input when it is returned to the biological treatment. In this way, the removal of nitrogen can be achieved with high room-specific degradation rates. By separating the return water from the nitrification / denitrification treatment by centrifugation, the microbial nitrification / denitrification processes for biomass efficiently and gently separated from the return water. This enables high biomass concentrations to be achieved, which are, for example, 5 to 10 al as high as in the known processes. Therefore, only a correspondingly small reaction volume is required.

In a further advantageous embodiment of the method according to the invention it is provided that the nitrification / denitrification treatment is carried out in a denitrification stage fed by the sludge water and in a nitrification stage downstream of the denitrification stage, from which the return water is separated off and from the one obtained during the nitrification process nitrogenous sludge-water mixture is returned to the denitrification stage. The upstream connection of the denitrification stage compared to the nitrification stage is particularly favorable with regard to the reaction rate. Optimal conditions are created in that from the nitrification stage downstream of the denitrification stage a multiple of the amount of sludge water supplied to the denitrification stage per unit of time is recycled in order to obtain a sufficient amount of nitrate for the denitrification. The performance can also be increased further by connecting several cascades of denitrification and nitrification stages in series.

Starting from this embodiment, a further increase in performance can be achieved in that the nitrification stage is followed by a further denitrification stage from which the return water is separated. While around 80 to 90% of the nitrogen compounds are denitrified in the denitrification stage upstream of the nitrification stage, depending on the degree of recycle of the nitrogenous sludge, a further denitrification stage downstream of the nitrification stage can higher degree of nitrogen removal, up to 100%.

In domestic wastewater, nitrogen is mainly in the form of urea and proteins. About 90% of urea, based on nitrogen, is already converted into ammonium in the sewer network and in the primary settling tank of the wastewater treatment plants. The conversion of the proteins is considerably more complicated over several phases of heterotrophic bacteria in the activated sludge of the biological treatment. In the end, however, the protein nitrogen is also in the form of ammonium. This phase of ammonification of the organically bound nitrogen therefore does not require any special process engineering equipment. The nitrification of the ammonium is brought about by various aerobic chemilithotrophic microorganism types of the two genera Nitrosomonas and Nitrobacter under oxygen consumption, whereby the nitrogen is finally converted into the form of nitrites or nitrates. In an expedient embodiment of the method according to the invention, air is therefore supplied for the treatment in the nitrification stage.

The nitrite and nitrate oxygen is used by facultative heterotrophic bacteria instead of dissolved oxygen as an electron acceptor under certain circumstances. This respiration of oxidized nitrogen, referred to as denitrification, corresponds biochemically to oxygen respiration. It becomes effective to the extent that the proportion of dissolved oxygen is reduced. On the one hand, this makes it possible to recover part of the ventilation energy applied for the nitrification and, at the same time, releases the nitrogen in gaseous form through the nitrite and nitrate reduction. Many facultative bacteria, which are normally abundant in all activated sludge systems, can switch from oxygen respiration to nitrate respiration in an anoxic environment without difficulty. Electron donors are also required for nitrate respiration. derlieh, which must be provided in the form of organic carbon compounds. If they are not present in the activated sludge, they must be supplied externally. For this reason, an expedient variant of the method according to the invention is that the denitrification treatment is carried out with the supply of an external carbon carrier. Possible carbon carriers are, for example, methanol or acetic acid.

Furthermore, in order to increase the space-time yield, it is particularly advantageous in the process according to the invention to carry out the nitrification / denitrification treatment under excess pressure, in particular in a pressure range up to 5 bar.

In particular, the method according to the invention is designed in such a way that the sludge treatment of the activated sludge has a fouling treatment. The digestion treatment causes a partial decomposition of the activated sludge from the biological treatment with the formation of digestion gas. The sludge water separated from the digested treatment of the activated sludge is subjected to the nitrification / denitrification treatment.

A plant according to the invention for carrying out the method according to the invention with a biological treatment device serving for the microbial conversion of the waste water by activated sludge, a separating device serving for separating the activated sludge from the microbially converted waste water, and a sludge treatment device serving for the treatment of the separated activated sludge , a device used for the removal of sludge from the treated activated sludge and a return circuit serving to feed the return water obtained from the removed sludge water into the biological treatment device is characterized in that in the return circuit a nitrifying agent charged on the inlet side with the sludge water cation / denitrification device is provided to the a separator is connected on the output side, at the one outlet of which the return water is obtained and the other outlet which supplies a concentrate is returned to the nitrification / denitrification device. After the biological removal of nitrogen in the nitrification / denitrification device by microorganisms, the return water returned to the biological treatment device no longer has excessive nitrogen contents.

The separator, in which the return water is separated from the solid constituents of the sludge active in the nitrification / denitrification device by centrifugal force, enables the required degree of separation and the pressures which occur to be set individually.

In this regard, it proves to be particularly advantageous that the separator is a plate centrifuge, preferably in the form of a nozzle separator or a nozzle separator.

To ensure that the separator functions properly, a screening device is connected upstream of the separator. Furthermore, it is expedient to alternatively or additionally connect a cyclone separator.

A construction of the plant within the scope of the invention consists in that the nitrification / denitrification device has a denitrification tank, on the inlet side of which the sludge water is fed, to the outlet of which a nitrification tank is connected with its inlet, from which nitrogen-containing sludge obtained during the nitrification process Water mixture can be returned to the denitrification tank by means of a return path. While with low nitrogen loads in different areas of a single container it could be nitrified and denitrified at the same time or by targeted intermittent In this embodiment, the nitrification container and the denitrification container are provided as separate units, so that the optimal conditions for the respective processes can be set independently of one another.

Further features, details and advantages of the invention emerge from the following description, in which an exemplary embodiment of the method according to the invention is explained in more detail using an exemplary embodiment of the system according to the invention with reference to the drawing. This shows:

1 shows an overall diagram of the device and of the method,

FIG. 2 shows a more detailed illustration of a part of the scheme from FIG. 1 related to a nitrification / denitrification treatment, and

FIG. 3 shows a diagram corresponding to FIG. 2 of a special embodiment.

According to FIG. 1, wastewater to be cleaned is introduced from a schematically illustrated inlet 1 via a rake 2 used to hold larger foreign bodies and a downstream sand trap 3 into a primary clarifier 4. The pre-clarified wastewater passes from the pre-clarification tank 4 into a biological treatment facility, the core of which is an aeration tank 5, in which the contents of the wastewater are reacted microbially with activated sludge. A secondary clarifier 6 downstream of the activated sludge 5, from which the clarified waste water separated from the activated sludge at 7 is derived, serves as the device for separating the activated sludge from the microbially converted waste water. Through a return line 9 provided with a pump 8, the contents of the secondary clarifier 6, a partial stream can be returned to the entrance of the aeration tank 5.

By means of a line 10, the activated sludge separated from the microbial u-deposited wastewater is fed from the clarifier 6 to a sludge treatment device, the core of which is a digester 11. Pre-treatment sludge from pre-treatment tank 4 can also be introduced into this digester 11 via a line 12. The sewage sludge formed by the activated sludge drawn off via line 10 together with the primary sewage sludge taken off via line 12 undergoes a fermentation treatment in the digestion chamber 11, by which biogas is produced, which is withdrawn from the digestion chamber 11 via a line 13.

The digester 11 is followed by a device through which sludge water is extracted from the sewage sludge subjected to the digestion treatment. This device has a thickener 14, a machine drain 15 and a drying device 16 connected in series. As a result, the sludge water is increasingly removed from the treated sewage sludge. The latter is composed of the digested water separated in the thickener 14 and obtained at an outlet 17, that in the mechanical dewatering 15, for example by filtration or centrifugation, which is obtained at an outlet 18 and the filtrate or centrate and the in the vapors separated from the dryer 16 and accumulating at an outlet 19. The sewage sludge freed from the sludge water in this way is discharged from the dryer 16, as symbolically indicated at 20, as dried sludge.

The extracted sludge water is collected in a surge tank 21 connected to the outputs 17, 18 and 19. This is located in a recirculation circuit in which a nitrification / denitrification device 22, a separator 23 and the primary settling tank 4 are located, so that the return circuit leads back to the activation tank 5. In the nitrification / denitrification device 22, the nitrogen is biologically extracted from the sludge water, which has a high nitrogen load, by the action of microorganisms, in that it is released in gaseous form in molecular form and can, for example, be released into the atmosphere. The separator 23 connected downstream of the nitrification / denitrification device 22 serves to separate the return water returned from the recirculation circuit to the biological treatment device from the bacterial sludge causing the nitrification / denitrification reactions, which separator 23 as a concentrate to the nitrification / denitrification device 22 is returned.

FIG. 2 shows, for a special embodiment, the part of a plant which corresponds to the scheme of FIG. 1 and which is related to the nitrification / denitrification treatment and the separation of the return water. In FIG. 2, to the left is the surge tank 21 of FIG. 1, which is fed with the sludge water at an inlet 24. The nitrification / denitrification device 22 has a denitrification tank 27, which is charged with the sludge water, from the surge tank 21 via a feed line 25, into which a feed pump 26 is switched, to which a downstream nitrification tank 29 is connected via a discharge line 28 is connected with its entrance. A return path 30, which extends from the nitrification tank 29 to the denitrification tank 27, serves to return the nitrogen-containing sludge-water mixture in the nitrification tank 29 during the nitrification process, in which the nitrogen is present as nitrate or also nitrite nitrogen, to the denitrification tank 27 . The amount returned via the return path 30 is selected to be significantly higher than the amount of sludge water newly flowing in via the feed line 25, for example the amount returned is approximately that Ten times the amount fed through the feed line 25. The continuous process running between the denitrification container 27 and the nitrification container 29 advantageously achieves high nitrate or nitrite concentrations, as a result of which, in the denitrification, the nitrogen present in the oxidized form can be converted into gaseous molecular nitrogen at a high reaction rate. The gaseous nitrogen produced in this way is discharged via an exhaust air line 31 which is connected to both the denitrification tank 27 and the nitrification tank 29.

A separating device 33 is connected to the nitrification tank 29 via an outlet line 32 and is used to separate the sludge formed by the microorganisms involved in the nitrification / denitrification reactions in the form of a concentrate from the return water, that from an outlet 34 of the separating device 33 is returned to the biological treatment facility. This concentrate is returned to the nitrification tank 29 via a concentrate return line 36 provided with a concentrate return pump 35. An excess concentrate can be removed through an excess sludge discharge line 37 branching off from the concentrate return line 36 and shown in broken lines and subjected to a concentrate or sludge treatment.

An alternative further embodiment of the embodiment shown in FIG. 2 consists in that the nitrification container 29 is not connected directly to the separating device 33, but, as indicated by a line 38 shown in dashed lines, between the nitrification container 29 and the separation device 33 is connected to a further denitrification tank 39, which is also connected to the exhaust air line 31. In this further denitrification tank 39, the degree of nitrogen removal that is in the inlet-side denitrification tank 27 can be after the degree of recirculation of the recirculation path 30, a denitrification of approximately 80 to 90% of the nitrogen compounds can be increased to up to 100%.

Via a schematically illustrated metering device 40, a carbon carrier, for example methanol or acetic acid, can be selectively added to the denitrification container 27 as well as the nitrification container 29 and the optionally provided further denitrification container 39 from a carbon source 41. In addition, the nitrification tank 29 and the optionally provided further denitrification tank 39 are connected via an air supply line 42 to a compressor 43 serving for the air supply. Through the metered supply of the carbon carrier to the denitrification tank 27, denitrification can be carried out there in the absence of atmospheric oxygen. In the nitrification tank 29, on the other hand, the aeration represents the normal operation. However, just like in the further denitrification tank 39, alternating operation between denitrification and nitrification could be carried out there by intermittent aeration, so that the two tanks 29 and 39 are both in the function of a denitrification part and also the function of a nitrification part can be used. A further variety of the operating mode is created by a bypass line 44 which extends from the feed line 25 to the nitrification tank 29 and through which the sludge water can be introduced directly into the nitrification tank 29.

The embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 2 only in the construction of the separating device 33, while with respect to all other elements labeled with the same reference symbols, there is complete agreement between FIG. 2 and FIG. 3 exists, so that in this respect reference is made to the description of FIG. 2. In detail, in the separating device 33 of the embodiment from FIG Output of the nitrification / denitrification device 22 is first connected to a screening device 45 in the form of a rotary brush screen and a cyclone separator 46 connected downstream of the screening device 45. The solids separated in the screening device 45 and the cyclone separator 46 are discharged at outlets 47 and 48 and can be fed to a further treatment.

In all exemplary embodiments, the actual separation of the return water is provided by the separator 23 or 49 provided in the separation device, at the centrifugate outlet 50 of which the return water is obtained. The concentrate separated from the treated sludge water in the separator 49 is introduced from the concentrate outlet 51 into a concentrate receiver 52, from where it passes via the concentrate return pump 35 into the concentrate return line 36 already described with reference to FIG. 2.

The nitrification / denitrification device 22 is designed as a pressure vessel. The system pressure of up to 5 bar is applied through the air supply line 42. A pressure maintaining device 53 provided in the outlet 50 of the separator 23 or 49 serves to maintain this system pressure.

Plate centrifuges in which conical jacket plates rotate, on which the solid components are conducted into the radially outer region of the plate centrifuge, have proven to be particularly suitable separators, while the lighter liquid components collect near the axis and are derived therefrom. Nozzle separators have proven particularly useful, in which the separated solids, that is to say the concentrate, are discharged via nozzles distributed over the outer circumference and then flow off without pressure. Alternatively, however, a separator type with a self-emptying drum is also possible, in which the separated concentrate accumulates in a concentrate space and periodically through an annular gap is carried out. The time interval and the duration of the discharge can be set individually according to the required degree of separation via a control device. Another possible separator type is the nozzle separator. In this case, both the centrate and the concentrate for the discharge are each conveyed by a rotating gripper. Furthermore, the concentrate is discharged via nozzles arranged at the bottom of the concentrate chamber. If the concentrate is too high, centrifugal valves on the periphery of the concentrate space also open due to the increased pressure and allow a further concentrate discharge. The degree of separation can be regulated particularly well by means of these measures.

Claims

claims 1. Process for the purification of waste water, in which the waste water is converted microbially by a biological treatment with activated sludge, the activated sludge is separated from the microbially converted waste water and subjected to a sludge treatment, sludge water is removed from the treated activated sludge and return water obtained from the sludge water to the biological treatment is recycled, characterized in that the sludge water is subjected to a microbial nitrification / denitrification treatment and the return water is separated from the nitrification / denitrification treatment by centrifugation. 2. The method according to claim 1, characterized in that the nitrification / denitrification treatment in a denitrification stage fed by the sludge water and a downstream of the denitrification stage nitrification stage, from which the return water is separated and from the nitrogenous sludge-water mixture obtained during the nitrification process to the denitrification stage is returned, is executed. . 3. The method according to claim 2, characterized in that the nitrification stage is followed by a further denitrification stage from which the return water is separated. 4. The method according to any one of claims 1 to 3, characterized in that air is supplied for the treatment in the nitrification stage. 5. The method according to any one of claims 1 to 4, characterized in that the denitrification treatment is carried out with the supply of an external carbon carrier. 6. The method according to any one of claims 1 to 5, characterized in that the nitrification / denitrification treatment under positive pressure, in particular in a pressure range up to 5 bar, is carried out. 7. The method according to any one of claims 1 to 6, characterized in that the sludge treatment of the activated sludge has a fouling treatment. 8. The method according to any one of claims 1 to 7, characterized in that the sludge treatment of the activated sludge is carried out together with supplied preliminary sewage sludge and the sludge water is removed from the sewage sludge formed and treated from the activated sludge and the preliminary sewage sludge. 9. Plant for performing the method according to one of claims 1 to 8, with a microbial conversion of the wastewater by activated sludge biological treatment device, a separation of the activated sludge from the microbially converted wastewater separating device, a treatment of the separated Activated sludge treatment sludge treatment device, a device used to extract sludge water from the treated activated sludge and a return circuit used to feed return water obtained from the extracted sludge water into the biological treatment device, characterized in that in the return circuit an input side with the Sludge-fed nitrification / denitrification device (22) is provided, to which a separator (23; 49) is connected on the outlet side, to the outlet (50) of which the return water is obtained and whose concentrate 1 The other output (51) is returned to the nitrification / denitrification device (22). 10. Plant according to claim 9, characterized in that the separator (23; 49) is a plate centrifuge. 11. Plant according to claim 10, characterized in that the separator (23; 49) is a nozzle separator. 12. Plant according to claim 10, characterized in that the separator (23; 49) is a nozzle separator. 13. Plant according to one of claims 9 to 12, characterized in that the separator (49) has a screening device (45) is connected upstream. 14. Plant according to one of claims 9 to 13, characterized in that the separator (49) is a cyclone separator (46) is connected upstream. 15. Plant according to one of claims 9 to 14, characterized in that the nitrification / denitrification device (22) has a denitrification tank (27) on the inlet side of the sludge water, at the outlet of which a nitrification tank (29) is connected with its inlet from which the nitrogenous sludge-water mixture obtained during the nitrification process can be returned to the denitrification tank (27) by means of a return path (30). 16. Plant according to claim 15, characterized in that the separator (49) is connected downstream of the outlet of the nitrification tank (29). 17. Plant according to claim 15, characterized in that at the output of the nitrification container (29) another Denitrification tank (39) is connected on the input side, the output of which is followed by the separator (49). 18. Plant according to claim 16 or 17, characterized in that an air supply line (42) is connected to the nitrification tank (29). 19. Plant according to one of claims 9 to 18, characterized in that a metering device (40) for the supply of a carbon carrier is connected to the nitrification / denitrification device (22). 20. Plant according to one of claims 9 to 19, characterized in that the sludge treatment device has a digester (11). 21. Plant according to one of claims 9 to 20, characterized in that the nitrification / denitrification device (22) is designed as a pressure vessel and is kept under a system pressure in a pressure range up to 5 bar. 22. Plant according to claim 18 and 21, characterized gekennzeich¬ net that the system pressure is applied by the air supply. 23. System according to claim 21 or 22, characterized in that the separator (23; 49) has in its outlet (50) supplying the return water a pressure maintaining device (53) for the system pressure.