Process and device for treating wastewater or sludge

Abstract

The invention relates to a process for treating wastewater or sludge, in which a wastewater or sludge stream (2) is conveyed through a first mixing unit (15), wherein a base/alkaline solution (17) or a phosphate-fixing compound/liquid containing a phosphate-fixing compound (17) is metered or mixed into the first mixing unit (15).

The invention further relates to a device (100) for treating a wastewater or sludge stream (2), especially for carrying out the aforementioned process.

Claims

1. Process for treating wastewater or sludge, in which a wastewater or sludge stream (2) is conveyed through a first mixing unit (15), wherein a base/alkaline solution (17) or a phosphate-fixing compound/liquid containing a phosphate-fixing compound (17) is metered or mixed into the first mixing unit (15).

2. Process according to claim 1, wherein the wastewater or sludge stream (2) is conveyed through a mixing chamber (33) of the first mixing unit (15) via an opening (32) of a diaphragm (31) of the first mixing unit (15).

3. Process according to claim 1, wherein sparingly soluble phosphate is not removed from the wastewater or sludge stream (2).

4. Process according to claim 1, wherein the first mixing unit (15) is at least sectionally tubular.

5. Process according to claim 1, wherein the wastewater or sludge stream (2) is conveyed at a volume flow rate of from 1 m3/h to 150 m3/h through the first mixing unit (15).

6. Process according to claim 2, wherein the opening (32) of the diaphragm (31) has a diameter of from ≥10 mm to 500 mm and/or the mixing chamber (33) has a volume of from 1 l to 250 l.

7. Process according to claim 1, wherein the first mixing unit (15) has a coating which prevents deposition of sparingly soluble phosphate in the first mixing unit (15).

8. Process according to claim 1, wherein the base/alkaline solution (17) or the phosphate-fixing compound/liquid containing a phosphate-fixing compound (17) is metered or mixed into the first mixing unit (15) via an annular gap (37) or a number of annularly arranged openings.

9. Process according to claim 1, wherein the pH in the first mixing unit (15) is increased to from 7.2 to 11 as a result of the base/alkaline solution (17) being metered in or mixed in.

10. Process according to claim 1, wherein the base (17) used is sodium hydroxide and/or potassium hydroxide or the alkaline solution used is sodium hydroxide solution and/or potassium hydroxide solution and/or calcium hydroxide solution.

11. Process according to claim 1, wherein the phosphate-fixing compound (17, 27) used is a magnesium or calcium salt and/or a calcium silicate.

12. Process according to claim 1, wherein the wastewater or sludge stream (2) is furthermore conveyed through a degassing unit (5) for degassing of the wastewater or sludge stream (2), which degassing unit (5) is upstream of the first mixing unit (15).

13. Process according to claim 1, wherein the wastewater or sludge stream (2) is furthermore conveyed through a second mixing unit (25) downstream of the first mixing unit (15).

14. Process according to claim 13, wherein the wastewater or sludge stream (2) is conveyed through a mixing chamber (33′) of the second mixing unit (25) via an opening of the diaphragm (31′) of the second mixing unit (25).

15. Process according to claim 13, wherein a base/alkaline solution (17) is metered or mixed into the first mixing unit (15 and a phosphate-fixing compound/liquid containing a phosphate-fixing compound (27) is metered or mixed into the second mixing unit (25).

16. Process according to claim 13, wherein the wastewater or sludge stream (2) is furthermore conveyed through a third mixing unit (35) downstream of the second mixing unit (25).

17. Process according to claim 13, wherein neither a base/alkaline solution nor a phosphate-fixing compound/liquid containing a phosphate-fixing compound is metered or mixed into the second mixing unit (25) or third mixing unit (35).

18. Device (100) for carrying out a process according to claim 1, comprising a first mixing unit (15) and a metering tank (19) for metering or mixing of a base/alkaline solution (17) or a phosphate-fixing compound/liquid containing a phosphate-fixing compound (17) into the first mixing unit (15), which metering tank (19) is connected to the first mixing unit (15) in a fluid-conducting manner.

19. Device (100) according to claim 18, wherein the device (100) furthermore comprises a degassing unit (5) for degassing of the wastewater or sludge stream (2), which degassing unit (5) is upstream of the first mixing unit (15).

20. Device (100) according to claim 18, wherein the device (100) furthermore comprises a second mixing unit (25) downstream of the first mixing unit (15).

21. Device (100) according to claim 20, wherein the device (100) furthermore comprises a metering tank (29) for metering or mixing of a phosphate-fixing compound/liquid containing a phosphate-fixing compound (27) into the second mixing unit (25), which metering tank (29) is connected to the second mixing unit (25) in a fluid-conducting manner.

22. Device (100) according to claim 20, wherein the device (100) furthermore comprises a third mixing unit (35) downstream of the second mixing unit (25).

23. Device (100) according to claim 20, wherein the device (100) does not comprise a metering tank, connected to the second mixing unit (25) or third mixing unit (35) in a fluid-conducting manner, for metering or mixing of a base/alkaline solution or a phosphate-fixing compound/liquid containing a phosphate-fixing compound into the second mixing unit or third mixing unit.

24. Process according to claim 3, wherein the sparingly soluble phosphate is magnesium ammonium phosphate.

25. Process according to claim 7, wherein the coating prevents deposition of sparingly soluble phosphate in the mixing chamber (33) of the first mixing unit (15).

26. Process according to claim 8, wherein the base/alkaline solution (17) or the phosphate-fixing compound/liquid containing a phosphate-fixing compound (17) is metered or mixed into the mixing chamber (33) of the first mixing unit (15).

27. Process according to claim 26, wherein the annular gap (37) or the number of annularly arranged openings is arranged coaxially in relation to the opening (32) of a diaphragm (31) of the first mixing unit (15).

28. Process according to claim 9, wherein the pH in the mixing chamber (33) of the first mixing unit (15) is increased to from 7.2 to 11 as a result of the base/alkaline solution (17) being metered in or mixed in.

29. Process according to claim 11, wherein the magnesium or calcium salt is magnesium chloride and/or magnesium oxide and/or calcium chloride and/or the calcium silicate is calcium silicate hydrate.

30. Process according to claim 15, wherein the base/alkaline solution (17) is metered or mixed into the mixing chamber (33) of the first mixing unit (25) and the phosphate-fixing compound/liquid containing a phosphate-fixing compound (27) is metered or mixed into the mixing chamber (33′) of the second mixing unit (25).

31. Process according to claim 16, wherein the wastewater or sludge stream (2) is conveyed through a mixing chamber (33″) of the third mixing unit (35) via an opening of a diaphragm (31″) of the third mixing unit (35).

32. Device (100) according to claim 20, wherein the second mixing unit (25) has a diaphragm (31′) and a mixing chamber (33′).

33. Device (100) according to claim 22, wherein the third mixing unit (35) has a diaphragm (31″) and a mixing chamber (33″).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0073] FIG. 1 shows schematically one embodiment of a process according to the invention,

[0074] FIG. 2 shows schematically one embodiment of a device according to the invention, especially for carrying out the process depicted in FIG. 1,

[0075] FIG. 3 shows schematically a further embodiment of a process according to the invention,

[0076] FIG. 4 shows schematically a further embodiment of a device according to the invention, especially for carrying out the process depicted in FIG. 3,

[0077] FIG. 5 shows schematically a further embodiment of a process according to the invention,

[0078] FIG. 6 shows schematically a further embodiment of a device according to the invention, especially for carrying out the process depicted in FIG. 5,

[0079] FIG. 7 shows schematically one embodiment of a mixing unit usable according to the invention and

[0080] FIG. 8 shows schematically one embodiment of a degassing unit usable according to the invention.

DETAILED DESCRIPTION OF THE FIGURES

[0081] In the process schematically depicted in FIG. 1, a wastewater or sludge stream 2 is conveyed through a first mixing unit 15. The arrow depicted in FIG. 1 indicates the conveying direction of the wastewater or sludge stream 2. The wastewater or sludge stream 2 is usually taken from a storage tank 1. The storage tank 1 can be, for example, a digestion tower of a wastewater treatment plant or biogas plant. Accordingly, the wastewater or sludge stream 2 can be, for example, a digested sludge stream.

[0082] The wastewater or sludge stream 2 is preferably conveyed through the first mixing unit 15 and optionally through a second mixing unit 25 with the aid of a pump 3.

[0083] The first mixing unit 15 preferably comprises a diaphragm 31 having an opening, and a mixing chamber 33. The mixing chamber 33 is preferably arranged immediately after the diaphragm 31 and/or the opening of the diaphragm 31 in the conveying direction of the wastewater or sludge stream 2. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33 via the opening of the diaphragm 31, i.e. through the opening of the diaphragm 31. Preferably, the diaphragm 31 has an opening diameter of from 50 mm to 150 mm. Furthermore, the mixing chamber 33 can have, for example, a volume of from 5 l to 45 l.

[0084] Furthermore, the first mixing unit 15 is preferably tubular.

[0085] A base/alkaline solution 17 or a phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 is metered or mixed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15. To this end, the base/alkaline solution 17 or a phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 is preferably taken from a metering tank 19. Preferably, the base/alkaline solution 17 or the phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 is conveyed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, by means of a metering pump 18.

[0086] The alkaline solution used can be, for example, sodium hydroxide solution, especially 50% sodium hydroxide solution.

[0087] As a result of the alkaline solution 17 being metered or mixed in, there is an increase in pH in the first mixing unit 15, especially in the mixing chamber 33 of the first mixing unit 15. Preferably, the pH in the first mixing unit 15, especially in the mixing chamber 33 of the first mixing unit 15, is increased to from 8 to 8.5. This advantageously promotes the formation of sparingly soluble phosphates, especially of magnesium ammonium phosphate.

[0088] The phosphate-fixing compound used can be, for example, a magnesium salt, especially magnesium chloride, magnesium oxide or a mixture thereof. Preferably, a solution containing magnesium chloride, magnesium oxide or a mixture thereof is conveyed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15.

[0089] As a result of the metering or mixing of the phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, it is particularly advantageously possible to achieve comprehensive binding of soluble phosphate ions contained in the wastewater or sludge stream 2, in the form of sparingly soluble phosphates, especially in the form of magnesium ammonium phosphate.

[0090] In the first mixing unit 15, what arises—in the conveying direction of the wastewater or sludge stream 2—after the diaphragm 31 and/or the diaphragm opening is a so-called free jet, around which there is establishment of a secondary flow which ensures intensive mixing of the metered-in or mixed-in base/alkaline solution 17 or the metered-in or mixed-in phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 with the wastewater or sludge stream 2. Preferably, the base/alkaline solution 17 or the phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 is metered or mixed into the mixing chamber 33 of the first mixing unit 15 via an annular gap or a number of annularly arranged openings, wherein the annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31 and/or diaphragm opening of the first mixing unit 15. What is achievable as a result is particularly efficient mixing of the metered-in or mixed-in base/alkaline solution 17 or the metered-in or mixed-in phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 with the wastewater or sludge stream 2.

[0091] The thus treated wastewater or sludge stream 2 can furthermore be conveyed through a second mixing unit 25 downstream, especially immediately downstream, of the first mixing unit 15. The second mixing unit 25 preferably comprises a diaphragm 31′ having an opening, and a mixing chamber 33′. Preferably, the mixing chamber 33′ of the second mixing unit 25 is—in the conveying direction of the wastewater or sludge stream 2—arranged immediately after the diaphragm 31′ and/or the diaphragm opening. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33′ via the opening of the diaphragm 31′, i.e. through the opening of the diaphragm 31′. Especially preferably, the second mixing unit 25 is also tubular. The downstream second mixing unit 25 can particularly advantageously additionally improve the mixing of the wastewater or sludge stream 2 and especially the formation of sparingly soluble phosphates, especially of magnesium ammonium phosphate.

[0092] Further preferably, neither a base/alkaline solution nor a phosphate-fixing compound/liquid containing a phosphate-fixing compound is metered or mixed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25.

[0093] Furthermore, especially the first mixing unit 15 and/or the second mixing unit 25 can be provided with a coating on the inside, which coating prevents deposits or encrustations of sparingly soluble phosphates, especially of magnesium ammonium phosphate. The coating can be, for example, a material commercially available under the name Sikafloor®-220 W Conductive.

[0094] Furthermore, the pH of the wastewater or sludge stream 2 can be measured by means of a pH measurement unit 16 downstream of the first mixing unit 15.

[0095] Further preferably, the wastewater or sludge stream 2 is conveyed into a dewatering unit 45 downstream of the first mixing unit 15 or the second mixing unit 25 without separation or removal of sparingly soluble phosphate, especially of magnesium ammonium phosphate (MAP, struvite).

[0096] The advantages of the process depicted in FIG. 1 consist especially in low process- and equipment-related complexity, the binding of soluble phosphates (for improvement of subsequent dewatering), and in the avoidance of encrustations due to sparingly soluble phosphates, especially due to magnesium ammonium phosphate.

[0097] FIG. 2 shows schematically one embodiment of a device 100 according to the invention for treating a wastewater or sludge stream 2 that is especially suitable for carrying out the process schematically depicted in FIG. 1.

[0098] The device 100 comprises a first mixing unit 15. The first mixing unit 15 preferably comprises a diaphragm 31 having an opening, and a mixing chamber 33. The mixing chamber 33 is preferably arranged immediately after the diaphragm 31 and/or the opening of the diaphragm 31.

[0099] Furthermore, the device comprises a metering tank 19 for metering or mixing of a base/alkaline solution 17 or a phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, which metering tank 19 is connected to the first mixing unit 15 in a fluid-conducting manner. Preferably, the first mixing unit 15 comprises an annular gap or a number of annularly arranged openings for metering or mixing of the base/alkaline solution 17 or the phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15. The annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31 and/or the opening of the diaphragm 31. Preferably, the first mixing unit 15 is tubular or designed as a pipe mixer.

[0100] Furthermore, the device can comprise a metering pump 18 for conveyance of the base/alkaline solution 17 or the phosphate-fixing compound/liquid containing a phosphate-fixing compound 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, which metering pump 18 is connected between the metering tank 19 and the first mixing unit 15.

[0101] Furthermore, the device can be connected to a storage tank 1 for wastewater or sludge, especially sewage sludge, preferably digested sludge, in a fluid-conducting manner. The storage tank 1 can be, for example, a digestion tower of a wastewater treatment plant or of a biogas plant.

[0102] Furthermore, the device can comprise a pump 3 for conveyance of the wastewater or sludge stream 2, which pump 3 is connected between the storage tank 1 and the first mixing unit 15.

[0103] Preferably, the device furthermore comprises a second mixing unit 25 downstream, especially immediately downstream, of the first mixing unit 15. The second mixing unit 25 preferably comprises a diaphragm 31′ having an opening, and a mixing chamber 33′. Preferably, the mixing chamber 33′ of the second mixing unit 25 is arranged immediately after the diaphragm 31′ and/or the opening of the diaphragm 31′. Especially preferably, the second mixing unit 25 is also tubular or designed as a pipe mixer.

[0104] Furthermore, especially the first mixing unit 15 and/or the second mixing unit 25 can be provided with a coating on the inside, which coating prevents deposits or encrustations of sparingly soluble phosphates, especially of magnesium ammonium phosphate. The coating can be, for example, a material commercially available under the name Sikafloor®-220 W Conductive.

[0105] Furthermore, the device 100 can comprise a pH measurement unit 16 for measurement of the pH of the wastewater or sludge stream 2, which pH measurement unit 16 is downstream of the first mixing unit 15 or the second mixing unit 25.

[0106] Furthermore, the device can comprise a dewatering unit (not depicted) for dewatering of the wastewater or sludge stream 2, which dewatering unit is downstream of the first mixing unit 15 or the second mixing unit 25.

[0107] The advantages of the device depicted in FIG. 2 likewise consist especially in low process- and equipment-related complexity, the binding of soluble phosphates (for improvement of subsequent dewatering), and in the avoidance of encrustations due to sparingly soluble phosphates, especially due to magnesium ammonium phosphate.

[0108] With regard to further features and advantages of the device 100 depicted in FIG. 2, full reference is made to the figure description relating to FIG. 1. The features and advantages described there also apply analogously to the device 100 depicted in FIG. 2.

[0109] In the case of the process schematically depicted in FIG. 3, a wastewater or sludge stream 2 is conveyed through a first mixing unit 15 and through a second mixing unit 25 downstream, preferably immediately downstream, of the first mixing unit 15. The arrow depicted in FIG. 3 indicates the conveying direction of the wastewater or sludge stream 2.

[0110] The wastewater or sludge stream 2 is usually taken from a storage tank 1. The storage tank 1 can be, for example, a digestion tower of a wastewater treatment plant or biogas plant. Accordingly, the wastewater or sludge stream 2 can be, for example, a digested sludge stream.

[0111] Preferably, the wastewater or sludge stream 2 is conveyed through the first mixing unit 15, the second mixing unit 25 and optionally through a third mixing unit 35 with the aid of a pump 3.

[0112] The first mixing unit 15 preferably comprises a diaphragm 31 having an opening, and a mixing chamber 33. The mixing chamber 33 is preferably arranged immediately after the diaphragm 31 and/or the opening of the diaphragm 31 in the conveying direction of the wastewater or sludge stream 2. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33 via the opening of the diaphragm 31, i.e. through the opening of the diaphragm 31. The first mixing unit 15 is preferably tubular.

[0113] A base/alkaline solution 17 is metered or mixed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15. To this end, the base/alkaline solution 17 is preferably taken from a metering tank 19. Preferably, the base/alkaline solution 17 is conveyed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, by means of a metering pump 18. The alkaline solution used can be, for example, sodium hydroxide solution, especially 50% sodium hydroxide solution.

[0114] In the first mixing unit 15, what arises—in the conveying direction of the wastewater or sludge stream 2—after the diaphragm 31 and/or the diaphragm opening is a free jet, around which there is establishment of a secondary flow which ensures intensive mixing of the metered-in or mixed-in base/alkaline solution 17 with the wastewater or sludge stream 2. Preferably, the base/alkaline solution 17 is metered or mixed into the mixing chamber 33 of the first mixing unit 15 via an annular gap or a number of annularly arranged openings, wherein the annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31 and/or diaphragm opening of the first mixing unit 15. What is achievable as a result is particularly good mixing of the metered-in or mixed-in base/alkaline solution 17 with the wastewater or sludge stream 2.

[0115] The second mixing unit 25 preferably comprises a diaphragm 31′ having an opening, and a mixing chamber 33′. The mixing chamber 33′ is preferably arranged immediately after the diaphragm 31′ and/or the opening of the diaphragm 31′ in the conveying direction of the wastewater or sludge stream 2. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33′ via the opening of the diaphragm 31′, i.e. through the opening of the diaphragm 31′. The second mixing unit 25 is preferably tubular.

[0116] A phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is metered or mixed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25. To this end, the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is preferably taken from a metering tank 29.

[0117] Preferably, the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is conveyed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25, by means of a metering pump 28. The phosphate-fixing compound used can be, for example, a magnesium salt, especially magnesium chloride, magnesium oxide or a mixture thereof. Preferably, a solution containing magnesium chloride, magnesium oxide or a mixture thereof is conveyed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25.

[0118] In the second mixing unit 25, what arises—in the conveying direction of the wastewater or sludge stream 2—after the diaphragm 31′ and/or the diaphragm opening is likewise a free jet. Around the free jet, there is establishment of a secondary flow which ensures intensive mixing of the metered-in or mixed-in phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 with the wastewater or sludge stream 2. Preferably, the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is metered or mixed into the mixing chamber 33′ of the second mixing unit 25 via an annular gap or a number of annularly arranged openings, wherein the annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31′ and/or diaphragm opening of the second mixing unit 25. What is achievable as a result is particularly effective mixing of the metered-in or mixed-in phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 with the wastewater or sludge stream 2.

[0119] The thus treated wastewater or sludge stream 2 can furthermore be conveyed through a third mixing unit 35 downstream, especially immediately downstream, of the second mixing unit 25. The third mixing unit 35 preferably comprises a diaphragm 31″ having an opening, and a mixing chamber 33″. Preferably, the mixing chamber 33″ of the third mixing unit 35 is—in the conveying direction of the wastewater or sludge stream 2—arranged immediately after the diaphragm 31″ and/or the diaphragm opening. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33″ via the opening of the diaphragm 31″, i.e. through the opening of the diaphragm 31″. Especially preferably, the third mixing unit 35 is also tubular. The downstream third mixing unit 35 can particularly advantageously additionally optimize the mixing of the wastewater or sludge stream 2 and especially the formation of sparingly soluble phosphates, especially of magnesium ammonium phosphate.

[0120] Further preferably, neither a base/alkaline solution nor a phosphate-fixing compound/liquid containing a phosphate-fixing compound is metered or mixed into the third mixing unit 35, especially into the mixing chamber 33″ of the third mixing unit 35.

[0121] Furthermore, especially the first mixing unit 15 and/or the second mixing unit 25 and/or the third mixing unit 35 can be provided with a coating on the inside, which coating prevents deposits or encrustations of sparingly soluble phosphates, especially of magnesium ammonium phosphate. The coating can be, for example, a material commercially available under the name Sikafloor®-220 W Conductive.

[0122] Further preferably, the wastewater or sludge stream 2 is conveyed into a dewatering unit 45 downstream of the second mixing unit 25 or the third mixing unit 35 without separation or removal of sparingly soluble phosphate, especially of magnesium ammonium phosphate (MAP, struvite).

[0123] The advantages of the process depicted in FIG. 3 consist especially in low process- and equipment-related complexity, comprehensive binding of soluble phosphates (for improvement of subsequent dewatering), and in the avoidance of encrustations due to sparingly soluble phosphates, especially due to magnesium ammonium phosphate.

[0124] With regard to further features and advantages of the process depicted in FIG. 3, full reference is made to the previous figure descriptions. The features and advantages described there can also apply analogously to the process depicted in FIG. 3.

[0125] FIG. 4 shows schematically one embodiment of a device 100 according to the invention for treating a wastewater or sludge stream that is especially suitable for carrying out the process schematically depicted in FIG. 3.

[0126] The device 100 comprises a first mixing unit 15 and a second mixing unit 25 downstream, especially immediately downstream, of the first mixing unit 15.

[0127] The first mixing unit 15 and the second mixing unit 25 each preferably comprise a diaphragm 31, 31′ having an opening, and a mixing chamber 33, 33′, wherein the mixing chamber 33, 33′ is preferably arranged immediately after the diaphragm 31, 31′ and/or the opening of the diaphragm 31, 31′. Preferably, the first mixing unit 15 and the second mixing unit 25 are both tubular or designed as a pipe mixer.

[0128] Furthermore, the device 100 comprises a metering tank 19 for metering or mixing of a base/alkaline solution 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, which metering tank 19 is connected to the first mixing unit 15 in a fluid-conducting manner. Preferably, the first mixing unit 15 comprises an annular gap or a number of annularly arranged openings for metering or mixing of the base/alkaline solution 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15. The annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31 and/or the opening of the diaphragm 31.

[0129] Furthermore, the device 100 can comprise a metering pump 18 for conveyance of the base/alkaline solution 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, which metering pump 18 is connected between the metering tank 19 and the first mixing unit 15.

[0130] Furthermore, the device 100 can comprise a pH measurement unit 16 for measurement of the pH of the wastewater or sludge stream 2, which pH measurement unit 16 is downstream of the first mixing unit 15 and is especially connected between the first mixing unit 15 and the second mixing unit 25.

[0131] Furthermore, the device 100 comprises a metering tank 29 for metering or mixing of a phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25, which metering tank 29 is connected to the second mixing unit 25 in a fluid-conducting manner. Preferably, the second mixing unit 25 comprises an annular gap or a number of annularly arranged openings for metering or mixing of the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25. The annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31′ and/or the opening of the diaphragm 31′ of the second mixing unit 25.

[0132] Furthermore, the device 100 can comprise a metering pump 28 for conveyance of the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25, which metering pump 28 is connected between the metering tank 29 and the second mixing unit 25.

[0133] Furthermore, the device 100 can be connected to a storage tank 1 for wastewater or sludge, especially sewage sludge, preferably digested sludge, in a fluid-conducting manner. The storage tank 1 can be, for example, a digestion tower of a wastewater treatment plant or of a biogas plant.

[0134] Furthermore, the device 100 can comprise a pump 3 for conveyance of the wastewater or sludge stream 2, which pump 3 is connected between the storage tank 1 and the first mixing unit 15.

[0135] Furthermore, the device 100 can comprise a third mixing unit 35 downstream, especially immediately downstream, of the second mixing unit 25. The third mixing unit 35 preferably comprises a diaphragm 31″ having an opening, and a mixing chamber 33″. Preferably, the mixing chamber 33″ of the third mixing unit 35 is arranged immediately after the diaphragm 31″ and/or the opening of the diaphragm 31″. Especially preferably, the third mixing unit 35 is also tubular or designed as a pipe mixer.

[0136] Furthermore, especially the first mixing unit 15 and/or the second mixing unit 25 and/or the third mixing unit 35 can be provided with a coating on the inside, which coating prevents deposits or encrustations of sparingly soluble phosphates, especially of magnesium ammonium phosphate. The coating can be, for example, a material commercially available under the name Sikafloor®-220 W Conductive.

[0137] Furthermore, the device 100 can comprise a dewatering unit (not depicted) for dewatering of the wastewater or sludge stream 2, which dewatering unit is downstream of the second mixing unit 25 or the third mixing unit 35.

[0138] The advantages of the device 100 depicted in FIG. 4 likewise consist especially in low process- and equipment-related complexity, comprehensive binding of soluble phosphates (for improvement of subsequent dewatering), and in the avoidance of encrustations due to sparingly soluble phosphates, especially due to magnesium ammonium phosphate.

[0139] With regard to further features and advantages of the device depicted in FIG. 4, full reference is made to the previous figure descriptions. The features and advantages described there can also apply analogously to the device 100 depicted in FIG. 4.

[0140] In the case of the process schematically depicted in FIG. 5, a wastewater or sludge stream 2 is conveyed through a degassing unit 5 for degassing of the wastewater or sludge stream 2, through a first mixing unit 15 downstream, especially immediately downstream, of the degassing unit 5 and through a second mixing unit 25 downstream, especially immediately downstream, of the first mixing unit 15. The arrow depicted in FIG. 5 indicates the conveying direction of the wastewater or sludge stream 2.

[0141] The wastewater or sludge stream 2 is usually taken from a suitable storage tank 1. The storage tank 1 can be, for example, a digestion tower of a wastewater treatment plant or biogas plant. Accordingly, the wastewater or sludge stream 2 can be, for example, a digested sludge stream. The wastewater or sludge stream 2 can be either conveyed into the degassing unit 5 with the aid of a pump 3 or sucked into the degassing unit 5 with the aid of a regulating valve 4 for regulation of the volume flow rate of the wastewater or sludge stream 2.

[0142] The degassing unit 5 is preferably operated under reduced pressure or vacuum, especially under a reduced pressure of from −0.6 bar to −0.95 bar. The reduced pressure or the vacuum can be adjusted using a reduced-pressure or vacuum pump 6. The reduced-pressure or vacuum pump 6 can be, for example, a liquid-ring vacuum pump. The degassing unit 5 preferably comprises fittings 7, especially a cascade of fittings 7. Foaming of the wastewater or sludge stream 2 and consequently the formation of gas bubbles is particularly advantageously achievable as a result. This supports the process to degas the wastewater or sludge stream 2 that is taking place in the degassing unit 5. A gas or gas mixture escaping from the wastewater or sludge stream 2 preferably comprises carbon dioxide and methane. The escaping gas is preferably digester gas, i.e. a gas mixture containing methane, carbon dioxide, carbon monoxide, ammonia, hydrogen sulfide and oxygen. The removal of carbon dioxide from the wastewater or sludge stream 2 causes a (slight) rise in the pH in the wastewater or sludge stream 2. This advantageously promotes the formation of sparingly soluble phosphates, especially of magnesium ammonium phosphate.

[0143] Furthermore, the wastewater or sludge stream 2 can be conveyed through the degassing unit 5 multiple times or repeatedly by means of a circulation pump 14 upstream of the degassing unit 5, especially by means of one connected between the pump 3 or regulating valve 4 and the degassing unit 5. In this connection, a ratio of wastewater or sludge stream 2 to wastewater or sludge stream 20 circulating through the degassing unit 5 can be chosen in the range from 1 to 0 to 1 to 8, preferably 1 to 3.

[0144] The gas or gas mixture which issues from the degassing unit 5 can be conveyed into an incineration unit 10, for example into a furnace or a cogeneration system, as a gas stream 8 by means of a pump 9. Issuing of methane as a gas which is particularly damaging to the climate can thereby be avoided in later dewatering of the wastewater or sludge stream 2. A high saving of CO.sub.2 equivalents is realizable altogether.

[0145] The wastewater or sludge stream 2 which issues from the degassing unit 5 is preferably conveyed through the first mixing unit 15, the second mixing unit 25 and optionally through a third mixing unit 35 with the aid of a pump 11. The pump 11 is preferably upstream of the first mixing unit 15. In particular, the pump 11 is connected between the degassing unit 5 and the first mixing unit 15.

[0146] The first mixing unit 15 preferably comprises a diaphragm 31 having an opening, and a mixing chamber 33. The mixing chamber 33 is preferably arranged immediately after the diaphragm 31 and/or the opening of the diaphragm 31 in the conveying direction of the wastewater or sludge stream 2. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33 via the opening of the diaphragm 31, i.e. through the opening of the diaphragm 31. The first mixing unit 15 is preferably tubular.

[0147] A base/alkaline solution 17 is metered or mixed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15. To this end, the base/alkaline solution 17 is preferably taken from a metering tank 19. Preferably, the base/alkaline solution 17 is conveyed into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, by means of a metering pump 18. The alkaline solution used can be, for example, sodium hydroxide solution, especially 50% sodium hydroxide solution.

[0148] A rise in pH caused by the degassing unit 5 can advantageously reduce the amount of base/alkaline solution.

[0149] The second mixing unit 25 preferably comprises a diaphragm 31′ having an opening, and a mixing chamber 33′. The mixing chamber 33′ is preferably arranged immediately after the diaphragm 31′ and/or the opening of the diaphragm 31′ in the conveying direction of the wastewater or sludge stream 2. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33′ via the opening of the diaphragm 31′, i.e. through the opening of the diaphragm 31′. The second mixing unit 25 is preferably tubular.

[0150] A phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is metered or mixed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25. To this end, the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is preferably taken from a metering tank 29. Preferably, the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 is conveyed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25, by means of a metering pump 28. The phosphate-fixing compound used can be, for example, a magnesium salt, especially magnesium chloride, magnesium oxide or a mixture thereof. Preferably, a solution containing magnesium chloride, magnesium oxide or a mixture thereof is conveyed into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25.

[0151] The thus treated wastewater or sludge stream 2 can furthermore be conveyed through a third mixing unit 35 downstream, especially immediately downstream, of the second mixing unit 25. The third mixing unit 35 preferably comprises a diaphragm 31″ having an opening, and a mixing chamber 33″. Preferably, the mixing chamber 33″ of the third mixing unit 35 is—in the conveying direction of the wastewater or sludge stream 2—arranged immediately after the diaphragm 31″ and/or the diaphragm opening. Accordingly, the wastewater or sludge stream 2 preferably gets into the mixing chamber 33″ via the opening of the diaphragm 31″, i.e. through the opening of the diaphragm 31″. Especially preferably, the third mixing unit 35 is also tubular. The downstream third mixing unit 35 can particularly advantageously additionally optimize the mixing of the wastewater or sludge stream 2 and especially the formation of sparingly soluble phosphates, especially of magnesium ammonium phosphate.

[0152] Further preferably, neither a base/alkaline solution nor a phosphate-fixing compound/liquid containing a phosphate-fixing compound is metered or mixed into the third mixing unit 35, especially into the mixing chamber 33″ of the third mixing unit 35.

[0153] Furthermore, especially the first mixing unit 15 and/or the second mixing unit 25 and/or the third mixing unit 35 can be provided with a coating on the inside, which coating prevents deposits or encrustations of sparingly soluble phosphates, especially of magnesium ammonium phosphate. The coating can be, for example, a material commercially available under the name Sikafloor®-220 W Conductive.

[0154] Further preferably, the wastewater or sludge stream 2 is conveyed into a dewatering unit 45 downstream of the second mixing unit 25 or the third mixing unit 35 without separation or removal of sparingly soluble phosphate, especially of magnesium ammonium phosphate (MAP, struvite).

[0155] The advantages of the process depicted in FIG. 5 consist especially in low process- and equipment-related complexity, comprehensive binding of soluble phosphates (for improvement of subsequent dewatering), in the avoidance of methane release (during subsequent dewatering), in the saving of high CO.sub.2 equivalents, in a lower demand for base/alkaline solution, and in the avoidance of encrustations due to sparingly soluble phosphates, especially due to magnesium ammonium phosphate.

[0156] With regard to further features and advantages of the process depicted in FIG. 5, full reference is made to the previous figure descriptions, especially to the description relating to FIG. 3. The features and advantages described there, especially in the description relating to FIG. 3, can also apply analogously to the process depicted in FIG. 5.

[0157] FIG. 6 shows schematically one embodiment of a device 100 according to the invention for treating a wastewater or sludge stream that is especially suitable for carrying out the process schematically depicted in FIG. 5.

[0158] The device 100 comprises a degassing unit 5 for degassing of a wastewater or sludge stream 2, a first mixing unit 15 downstream, especially immediately downstream, of the degassing unit 5, and a second mixing unit 25 downstream, especially immediately downstream, of the first mixing unit 15.

[0159] The degassing unit 5 preferably comprises fittings 7, especially a cascade of fittings 7.

[0160] The first mixing unit 15 and the second mixing unit 25 each preferably comprise a diaphragm 31, 31′ having an opening, and a mixing chamber 33, 33′, wherein the mixing chamber 33, 33′ is preferably arranged immediately after the diaphragm 31, 31′ and/or the opening of the diaphragm 31, 31′. Preferably, the first mixing unit 15 and the second mixing unit 25 are both tubular or designed as a pipe mixer.

[0161] Furthermore, the device 100 comprises a metering tank 19 for metering or mixing of a base/alkaline solution 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, which metering tank 19 is connected to the first mixing unit 15 in a fluid-conducting manner. Preferably, the first mixing unit 15 comprises an annular gap or a number of annularly arranged openings for metering or mixing of the base/alkaline solution 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15. The annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31 and/or the opening of the diaphragm 31.

[0162] Furthermore, the device 100 can comprise a metering pump 18 for conveyance of the base/alkaline solution 17 into the first mixing unit 15, especially into the mixing chamber 33 of the first mixing unit 15, which metering pump 18 is connected between the metering tank 19 and the first mixing unit 15.

[0163] Furthermore, the device 100 comprises a metering tank 29 for metering or mixing of a phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25, which metering tank 29 is connected to the second mixing unit 25 in a fluid-conducting manner. Preferably, the second mixing unit 25 comprises an annular gap or a number of annularly arranged openings for metering or mixing of the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25. The annular gap or the number of annularly arranged openings is preferably arranged coaxially in relation to the diaphragm 31′ and/or the opening of the diaphragm 31′.

[0164] Furthermore, the device 100 can comprise a metering pump 28 for conveyance of the phosphate-fixing compound/liquid containing a phosphate-fixing compound 27 into the second mixing unit 25, especially into the mixing chamber 33′ of the second mixing unit 25, which metering pump 28 is connected between the metering tank 29 and the second mixing unit 25.

[0165] Furthermore, the device 100 can be connected to a storage tank 1 for wastewater or sludge, especially sewage sludge, preferably digested sludge, in a fluid-conducting manner. The storage tank 1 can be, for example, a digestion tower of a wastewater treatment plant or of a biogas plant.

[0166] Furthermore, the device 100 can comprise a regulating valve 4 for regulation of the volume flow rate of the wastewater or sludge stream 2, which regulating valve 4 is upstream of the degassing unit 5 and is especially connected between the storage tank 1 and the degassing unit 5.

[0167] Alternatively, the device 100 can comprise a pump (not depicted) for conveyance of the wastewater or sludge stream 2 in the direction of the and/or through the degassing unit 5, which pump is upstream of the degassing unit 5 and is especially connected between the storage tank 1 and the degassing unit 5.

[0168] Furthermore, the device 100 can comprise a separator unit, especially a two-stage separator unit, 12. By means of the separator unit 12, water which is carried away by a gas stream leaving the degassing unit 5 can be removed from the wastewater or sludge stream 2. The separator unit 12 is expediently downstream of the degassing unit 5.

[0169] Furthermore, the device 100 can comprise a vacuum pump, especially a liquid-ring vacuum pump, 6 which is connected between the degassing unit 5 and the separator unit 12.

[0170] Furthermore, the device 100 can comprise a pump 11 for conveyance of the wastewater or sludge stream 2 through the first mixing unit 15, the second mixing unit 25 and optionally through a third mixing unit 35, which pump 11 is upstream of the first mixing unit 15 and is especially connected between the degassing unit 5 and the first mixing unit 15.

[0171] Furthermore, the device 100 can comprise a pH measurement unit 13 for measurement of the pH of the wastewater or sludge stream 2, which pH measurement unit 13 is upstream of the first mixing unit 15 and is especially connected between the degassing unit 5 and the first mixing unit 15 and is preferably connected between the pump 11 and the first mixing unit 15.

[0172] Furthermore, the device 100 can comprise a (further) pH measurement unit 16 for measurement of the pH of the wastewater or sludge stream 2, which pH measurement unit 16 is downstream of the first mixing unit 15 and is especially connected between the first mixing unit 15 and the second mixing unit 25.

[0173] Furthermore, the device 100 can comprise a third mixing unit 35 downstream, especially immediately downstream, of the second mixing unit 25. The third mixing unit 35 preferably comprises a diaphragm 31″ having an opening, and a mixing chamber 33″. Preferably, the mixing chamber 33″ of the third mixing unit 35 is arranged immediately after the diaphragm 31″ and/or the opening of the diaphragm 31″. Especially preferably, the third mixing unit 35 is also tubular or designed as a pipe mixer.

[0174] Furthermore, especially the first mixing unit 15 and/or the second mixing unit 25 and/or the third mixing unit 35 can be provided with a coating on the inside, which coating prevents deposits or encrustations of sparingly soluble phosphates, especially of magnesium ammonium phosphate. The coating can be, for example, a material commercially available under the name Sikafloor®-220 W Conductive.

[0175] Furthermore, the device 100 can comprise a dewatering unit 45 (not depicted) for dewatering of the wastewater or sludge stream 2, which dewatering unit is downstream of the second mixing unit 25 or the third mixing unit 35.

[0176] The advantages of the device depicted in FIG. 6 likewise consist especially in low process- and equipment-related complexity, comprehensive binding of soluble phosphates (for improvement of subsequent dewatering), in the avoidance of methane release (during subsequent dewatering), in the saving of high CO.sub.2 equivalents, in a lower demand for base/alkaline solution, and in the avoidance of encrustations due to sparingly soluble phosphates, especially due to magnesium ammonium phosphate.

[0177] With regard to further features and advantages of the device depicted in FIG. 6, full reference is made to the previous figure descriptions, especially to the description relating to FIG. 4. The features and advantages described there, especially in the description relating to FIG. 4, can also apply analogously to the device depicted in FIG. 6.

[0178] FIG. 7 shows schematically the structure of a mixing unit usable according to the invention, using the example of the first mixing unit 15. Preferably, the first mixing unit 15 is tubular and especially designed in the form of a pipe mixer. The first mixing unit 15 comprises a diaphragm 31 having a diaphragm opening 32, and a mixing chamber 33. The mixing chamber 33 is situated immediately after the diaphragm 31 and/or diaphragm opening 32, i.e. is immediately downstream of the diaphragm 31 and/or diaphragm opening 32. Furthermore, the first mixing unit 15 comprises a meter-in or mix-in opening 34. The meter-in or mix-in opening 34 opens into an annular gap 37. The annular gap 37 is arranged coaxially in relation to the diaphragm 31 and/or diaphragm opening 32.

[0179] If a wastewater or sludge stream 2 is conveyed into the first mixing unit 15, the wastewater or sludge stream 2 is contracted by the diaphragm opening 32. When the contracted wastewater or sludge stream 2 issues into the mixing chamber 33, said stream can re-expand. The result is a free jet 36, around which there is establishment of a secondary flow 38 in the mixing chamber 33. The free jet 36 and the secondary flow 38 cause a particularly intensive mixing of the wastewater or sludge stream 2 to take place. Furthermore, a base/alkaline solution or phosphate-fixing compound/liquid containing a phosphate-fixing compound that is metered or mixed in via the meter-in or mix-in opening 34 is advantageously subjected to better mixing with the wastewater or sludge stream 2 owing to the secondary flow 38. The above-described features and advantages preferably also apply analogously to the optional second mixing unit of the present invention. Apart from the meter-in or mix-in opening 34, the above-described features and advantages can also apply analogously to the optional third mixing unit of the present invention.

[0180] FIG. 8 shows schematically a degassing unit 5 usable in the context of the present invention. The degassing unit 5 can be subdivided into three different zones, namely into a zone 32 having fittings 7, into a defoaming zone 26 situated below the zone 32, and into a degassing zone 27 situated below the defoaming zone 26. The fittings 7 of the zone 32 are preferably designed as a cascade. In said zone, a wastewater or sludge stream 2 entering the degassing unit 5 is foamed up, which promotes the formation of gas bubbles. In the defoaming zone 26 situated therebelow, what occurs is calming of the wastewater or sludge stream 2 and consequently defoaming thereof. In the degassing zone 27 situated therebelow, what occurs is degassing of the wastewater or sludge stream 2. Furthermore, the degassing unit 5 can comprise a foam breaker 42. This can bring about additional defoaming of the wastewater or sludge stream 2, if the defoaming zone 26 is insufficient for this purpose. Gas which forms in the degassing unit 5 can be discharged as a gas stream 41 via a port 39. As an alternative or in combination, gas which forms in the degassing unit 5 can be supplied as a gas stream 8 to, for example, an incineration unit (not depicted). The degassed or largely degassed wastewater or sludge stream 2 leaves the degassing unit 5 via an outlet 29. To optimize the issue of the wastewater or sludge stream 2 from the degassing unit 5, the degassing zone 27 of the degassing unit 5 can comprise a conically shaped region 30. The total residence time of the wastewater or sludge stream 2 in the degassing unit 5 can be from 3 min to 15 min, preferably 5 min to 10 min. Preferably, the fill level 40 in the degassing unit 5 is kept constant.