INSTALLATION FOR OBTAINING PHOSPHATE SALTS AND METHOD FOR OPERATING THIS INSTALLATION

Abstract

The invention provides an installation (10) for separating phosphate from phosphate-containing liquids and obtaining phosphate salts, having one or more reactors (12) which each have two electrodes of opposing polarity and which, between them, span a reaction area, wherein each reactor (12) has an inlet (14) and an outlet (16), in which the outlet (16) is separated into a recirculation (22) and a discharge stream (24) and the recirculation (22) supplies part of the liquid from the outlet (16) of the reactor (12) to the inlet of the same reactor or a different reactor (12); and to a method for this and to a biological wastewater treatment plant and to a method for operating the latter.

Claims

1. An installation (10) for separating phosphate from phosphate-containing liquids and for obtaining phosphate salts having one or more reactors (12) that each comprise two electrodes of opposing polarity and that span a reaction space between them, each reactor (12) having an inlet (14) and an outlet (16), characterized in that the outlet (16) is separated into a recirculation (22) and a discharge stream (24), the recirculation (22) supplies a part of the phosphate-containing liquids from the outlet (16) of the one or more reactors (12) to the inlet (14) of a same one of the one or more reactor (12), or to another one of the one or more reactors (12), and an extraction device is provided for the phosphate salts.

2. The installation according to claim 1, characterized in that the outlet (16) of the one or more reactors (12) opens out into a storage tank (16), from which the recirculation (22) branches off.

3. The installation according to claim 1, characterized in that the one or more reactors (12), the recirculation 22 and/or the outlet (16), in particular the storage tank (18), has an extraction device for phosphate salts.

4. The installation according to claim 1, characterized in that the one or more reactors (12), the outlet (16) and/or the recirculation (22) have a unit for collecting and separating gasses, in particular hydrogen and/or in particular gaseous ammonia, from liquids, in particular liquids containing ammonium.

5. The installation according to claim 1, characterized in that the discharge stream (24), in particular downstream of a last reactor (12), has a pH value of 8, in particular 8.5, preferably 9.

6. The installation according to claim 1, characterized in that the one or more reactors (12) can be connected in series or in parallel.

7. The installation according to claim 1, characterized in that a ratio of a flow (Q.sub.R) of the recirculation (22) to a flow (Q.sub.D) of the inlet (14) is 1, in particular 2, in particular 3, in particular 4, in particular 5.

8. The installation according to claim 1, characterized in that one of the two electrodes is a sacrificial electrode that comprises in particular a material containing magnesium.

9. The installation according to claim 1, characterized in that the phosphate salts and volatile ammonia in liquids containing ammonia, and in particular also hydrogen, can be formed simultaneously and in particular can be simultaneously separated.

10. A method for separating phosphate from a phosphate-containing liquid using the installation according to claim 1, comprising one or more reactors for electrolytic reaction of phosphates in the phosphate-containing liquids to the phosphate salts, the phosphate-containing liquids being supplied to a reactor via the inlet (14) and leaving the inlet (14) via the outlet (16) and precipitated phosphate salts are drawn off via an extraction device, characterized in that an outlet stream is separated into a discharge stream and a recirculation stream, and the recirculation steam is supplied to the inlet (14) of a same one of the one or more reactors (12), or a different reactor and is mixed with this.

11. The method according to claim 10, characterized in that a ratio of the recirculation stream to the inlet stream is set a 1, in particular a 2, in particular 3, in particular a 4, in particular 5.

12. The method according to claim 10, characterized in that a plurality of reactors is arranged in series and/or in parallel.

13. The method according to claim 10, characterized in that the recirculation stream is set so that the pH value in at least one of the reactors becomes a pH 8, in particular a pH 8.5, preferably a pH 9.

14. The method according to claim 10, characterized in that volatile ammonia is separated out from the outlet and/or the recirculation stream and/or the reactor.

15. The method according to claim 10, characterized in that the phosphate salts and volatile ammonia are formed simultaneously in the presence of liquids containing ammonium and, in particular, also hydrogen, and in particular are simultaneously separated.

16. A biological wastewater treatment plant comprising the installation (10) according to claim 1.

17. A biological wastewater treatment plant according to claim 16, further comprising a biological stage (100), a biomass separation (102) and a unit for dewatering the biomass (104) connected downstream of the biomass separation (102), a resulting filtrate water (24, 108, 130) being suppliable to an inlet stream (132) of the biological stage (100), characterized in that the installation (10) is arranged for obtaining the phosphate salts in the resulting filtrate water (108, 130), and the installation (10) having an extraction device (20,30) for the phosphate salts and a unit for collecting and separating ammonia.

18. A method for operating a biological wastewater treatment plant according to claim 16, the method comprising supplying again a filtrate water stream obtained after the biomass separation (102) and dewatering of a biomass to a biological stage, characterized in that the method comprising subjecting beforehand in the installation (10) for obtaining phosphate salts the filtrate water stream to an electrolytic reaction in at least one reactor of the installation via a sacrificial anode containing magnesium in order to obtain phosphate salts from the filtrate water stream, suppling the filtrate water stream to the one or more reactors (12) via the inlet (14) and then leaving the filtrate water stream via the outlet (16) and precipitated phosphate salts being drawn off via an extraction device, separating an outlet stream into a discharge stream and a recirculation stream in the installation, and supplying the recirculation stream to the inlet (14) of a same one of the one of more reactors (12) or a different reactor, and mixing the discharge stream with an inflow stream of a biological stage (100) and also ammonia becoming volatile and being separated in the installation for separating phosphate, in particular simultaneously.

19. The method according to claim 18, characterized in that the method comprises increasing the pH, via the setting of the ratio of the flow of the recirculation stream to the inlet stream, to 8, in particular 8.5 and in particular 9.0.

20. The method according to claim 18, characterized in that the method comprises setting a ratio of the recirculation stream to the inlet to a 1, in particular >2, in particular 3, in particular a 4, in particular >5.

21. An installation according to claim 1, wherein the installation is used in, or forms part of, in a biological wastewater treatment plant.

Description

[0036] The invention is explained below in reference to a drawing.

[0037] Shown are:

[0038] FIG. 1 an installation according to a first embodiment,

[0039] FIG. 2 an alternative embodiment of the installation having reactors connected in parallel,

[0040] FIG. 3 an additional embodiment of the installation having reactors connected both in parallel and in series,

[0041] FIG. 4 a cascaded connection of the installation,

[0042] FIG. 5 a schematic for the electrolytic reaction,

[0043] FIG. 6 a schematic representation of a biological wastewater treatment plant according to the invention.

[0044] FIG. 1 shows an installation according to a first embodiment that is provided as a whole with the reference character 10. The installation comprises a reactor 12 having an inlet 14 and an outlet 16. The reactor 12 is an electrolytic reactor in which phosphorous from phosphorous-containing liquids can be crystallized out in particular into MAP or KMP via the consumption of a sacrificial anode made of magnesium. This can take place in a purely galvanic manner or with the application of a current. The flow in the region of the inlet 14 is indicated with QD.

[0045] The pH value of liquids, in particular wastewater and other liquids containing phosphorous, is approx. 5 to 7. By means of the electrolytic conversion in the reactor (see FIG. 5), OH.sup. ions are released so that the pH value in the reactor increases. The pH value upstream of the reactor 12 is therefore lower than downstream of the reactor 12.

[0046] The outlet 16 now leads into a storage tank 18, to which is connected a crystal separator 20, via which the phosphate salts can be drawn off. A partial stream of the outlet 16 is then combined with the inlet 14 and resupplied to the reactor 12 as recirculation 22. The flow in the recirculation 22 is indicated here with Q.sub.R. Q.sub.R is preferably Q.sub.R5Q.sub.D.

[0047] An additional part of the outlet 16 is extracted from the installation 10 as discharge stream 24, wherein measurements are taken here of the pH value using a probe 26 and of the phosphorous using a probe 28, and the discharge stream in turn has a flow of QD. The pH value at discharge stream 24 is 8 to 9.5 or above. The pH value is again increased compared to a one-time passage through the repeated exposure in the reactor 12 by means of the circulation of a part of the outlet 16 because there is a concentration of OH.sup. ions (see FIG. 5). A supplementary addition of alkali can therefore be omitted.

[0048] In particular, the flow speed can be adjusted so that the best-possible mixing and reaction takes place in the reactor 12 and an unwanted sedimentation of salt crystals is prevented.

[0049] In addition or alternatively to the crystal separator 20 in the storage tank 18, a separation can also take place in the recirculation 22, for example, wherein this separation is provided with the reference character 30.

[0050] Pumps 23 or 15 are provided in the recirculation 22 as well as in the inlet 14.

[0051] Moreover and particularly advantageously, through the recirculation and the increase of the pH value, it can be achieved that the ammonia (NH.sub.3) and the hydrogen (H.sub.2) present are volatile and can be drawn off, for example, in the reactor 12 and/or via the storage tank 18 and/or in the region of the recirculation 22 as indicated respectively with arrows. These two products can be further reprocessed materially and/or for energy purposes.

[0052] In contrast to this simplest form of the installation according to the invention, FIG. 2 shows an installation 10, in which n reactors 12 are connected in parallel. The outlet 16 of all of the reactors 12 is supplied to a storage tank 18 from which the recirculation 22 is supplied, which is in turn fed to the inlet 14 of the installation 10. In this manner, the total output of the installation 10 can be increased without having to change the individual reactors 12. A continuous operation is additionally possible in this manner, insofar as individual reactors 12 must be disconnected and exchanged, for example because of the consumption of the electrodes.

[0053] FIG. 3 now shows an additional embodiment of the invention, wherein, as a modification of FIG. 2, the reactors 12 of the installation 10 are connected not only in parallel, but also in series, wherein a series comprises up to n reactors 12 and up to m reactors are connected in parallel. Thus the outlet 16 of the n reactors arranged in series is then correspondingly supplied to the buffer reservoir 18, wherein this buffer reservoir 18 in turn feeds the recirculation 22. By virtue of the additional series connection of the reactors 12, in the course of the throughflow of the different reactors 1 to n there is as complete a conversion as possible of the phosphorous in the liquid to phosphate salts. The recirculation 22 is guided from the first reactor of the series into the common inlet 14 of all the parallel reactors 12. The remaining elements of the invention, in particular the removal of NH3 as well as H2 and the salts is analogous to the exemplary embodiment according to FIG. 1.

[0054] FIG. 4 shows a cascaded connection. In the cascaded connection of the installation 10 shown in FIG. 4, each cascade stage 40 is designed analogous to FIG. 2. The discharge stream 24 of a cascade stage 40 is thus simultaneously the inlet of the next cascade stage. In addition to the design of the recirculation 22 shown in the corresponding cascade stage 40, it is also possible to provide a recirculation in a previous cascade stage.

[0055] FIG. 6 shows a basic principle of a biological wastewater treatment plant comprising a biological stage 100, wherein the liquid leaving the biological stage is supplied to a biomass separation 102 in order to retain the biomass in particular. The biomass leaving the biomass separation 102 (sludge) is then separated in a step 104 (sludge dewatering) into a filtrate water stream 108 as well as a dewatered biomass (106). The filtrate water stream 108, which still contains nitrogen and phosphate, is supplied to a previously described installation 10 for obtaining phosphate salts and gaseous ammonia, wherein magnesium ammonium phosphate (MAP) 120 as well as ammonium in the form of ammonia 122 being released is preferably obtained in the installation 10.

[0056] Optionally, an anaerobic processing step 103 for reducing and stabilizing the biomass can be connected between the separation and the dewatering, which, however, also frees the phosphorous and ammonia contained in the biomass. As a result, the load of N and P in the filtrate water 108 is increased compared to a wastewater treatment plant without an aerobic processing step 103.

[0057] The liquid 130 (the discharge stream 24) present after leaving the installation 10 is largely free of ammonium and phosphorous or only has them in a sharply reduced amount. This discharge stream 24 of the installation 10 is then supplied again to the inlet 132 of the biological step 100 as treated filtrate water 130 and mixed with the inlet stream 132 so that the biological stage 100 is not loaded with phosphorous and nitrogen during the circulation, and in particular energy for removing nitrogen as N2 (aspiration) and phosphate is no longer needed.

[0058] The flow speeds can be increased by means of a corresponding installation for obtaining phosphate salts and preferably also ammonia from liquids that contain these materials, namely by repeated exposure of the liquid, so that a better mixing and thus more efficient reaction can take place and a sedimentation can be prevented at an earlier instant. A concentration of OH.sup. ions thus takes place so that the pH value increases significantly compared to a simple flowing through of the reaction chamber 12. In this manner, installations can be provided that make possible a particularly cost-efficient, perhaps even lucrative use of wastewater, such as wastewater from agriculture in particular, but also municipal water management. The implementation in a biological wastewater treatment plant is therefore particularly preferred.