METHOD AND ARRANGEMENT FOR SEPARATING SOLIDS AND LIQUIDS IN SUSPENSIONS, IN PARTICULAR SEWAGE SLUDGE, BY ADDING FLOCCULANTS

Abstract

The invention relates to a method for separating solids and liquids in suspensions, in particular sewage sludge (K), said method working by adding flocculants (F1) and/or flocculating agents. The suspension, in particular the sewage sludge (K), is observed by means of a sensor (S1). In a first method step, flocculants (F1) and/or flocculating agents are added to a first mixing stage (M1) until the sensor (S1) detects the formation of first flocs. The addition of the flocculant (F1) and/or the flocculating agent is then interrupted so that the suspension, in particular the sewage sludge (K), has a defined, specifically a first, floc-comprising state at that moment. The suspension, in particular the sewage sludge (K), is now fed to a further mixing stage (M2, MM). In this further mixing stage (M2, MM), the same (F1) or another (F2, F3) flocculant or flocculating agent is added in a quantity which is predefined and which, starting from the defined state of the suspension, in particular the sewage sludge (K), causes a desired amount of flocs in the suspension, in particular the sewage sludge (K). The resulting mixture is then fed directly or indirectly to a solid/liquid separation system.

Claims

1. A method for separating solids and liquids in suspensions, in particular sewage sludge (K), by adding flocculants (F1) and/or flocculating agents, in which, the suspension, in particular the sewage sludge (K), is observed by means of a sensor (S1), is hereby characterized in that, in a first method step, flocculants (F1) and/or flocculating agents are added to a first mixing stage (M1) until the sensor (S1) detects the formation of first flocs; in that the addition of the flocculant (F1) and/or the flocculating agent is then interrupted, so that the suspension, in particular the sewage sludge (K), has a defined, specifically a first floc-comprising state at that moment; in that the suspension, in particular the sewage sludge (K), is now fed to a further mixing stage (M2, MM); in that, in this further mixing stage (M2, MM), the same flocculant (F1) or a different flocculant (F2) or flocculating agent is added in a quantity which is predefined and which, starting from the defined state of the suspension, in particular the sewage sludge (K), causes a desired proportion of flocs in the suspension, in particular the sewage sludge (K); and in that the resulting mixture is then fed directly or indirectly to a solid-liquid separation system.

2. The method according to claim 1, further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used.

3. The method according to claim 1, further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K).

4. The method according to claim 1, further characterized in that the quantity of the flocculant (F1 or F2) and/or flocculating agent fed to the further mixing stage (M2) is constant and is determined in advance.

5. The method according to claim 1, further characterized in that the quantity of flocculants (F1 or F2) and/or flocculating agents fed to the further mixing stage (M2, MM) is determined; in that the floc structure in the suspension, in particular the sewage sludge (K), is detected transversely with respect to the flow direction by one-dimensional photo-optical incident light measurement of image rows of the grayscale profiles of a view from the top onto the suspension, in particular the sewage sludge (K), in that chord lengths of the detected floc structure are determined from the grayscale profiles, with the chord length being the distance between a relative grayscale maximum value and an adjacent relative grayscale minimum value, with the frequency for the distribution of the chord lengths being calculated and a concentration factor being determined as a function of parameters that are determined from the chord lengths with the frequency distribution of the chord lengths.

6. The method according to claim 1, further characterized in that a third mixing stage (MM) is provided, which, after the addition of the same or a different flocculant (F1 or F2) and/or flocculating agent to the suspension, in particular the sewage sludge (K), forming in the intermediate mixing stage (MM), is observed using a further sensor (SM), in particular a concept operating by image analysis, in particular with a camera, in order to control the addition of the flocculant.

7. An arrangement for separating solids and liquids in suspensions, in particular sewage sludge (K), by adding flocculants (F1) and/or flocculating agents, in which, the suspension, in particular the sewage sludge (K), is observed by means of a sensor (S1), is hereby characterized in that a first mixing stage (M1) is provided, in which, in a first method step, flocculants (F1) and/or flocculating agents are added until the sensor (S1) detects the formation of first flocs; in that the addition of the flocculant (F1) and/or the flocculating agent is then interrupted, so that the suspension, in particular the sewage sludge (K), has a defined state, namely first floc-comprising state at this moment; in that a further mixing stage (M2, MM) is provided, to which the suspension, in particular the sewage sludge (K), is fed, in that, in this further mixing stage (M2, MM), the same flocculant (F1) or a different flocculant (F2) or flocculating agent is added in a quantity that is predefined and, starting from the defined state of the suspension, in particular the sewage sludge (K), brings about a desired proportion of flocs in the suspension, in particular the sewage sludge (K); and in that the resulting mixture is then fed directly or indirectly to a solid-liquid separation system.

8. The arrangement according to claim 7, further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used.

9. The arrangement according to claim 7, further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K).

10. The arrangement according to claim 7, further characterized in that the quantity of the flocculant (F1 or F2) and/or flocculating agent fed to the further mixing stage (M2) is constant and is determined in advance.

11. The arrangement according to claim 7, further characterized in that the quantity of flocculants (F1 or F2) and/or flocculating agents fed to the further mixing stage (M2, MM) is determined; in that the floc structure in the suspension, in particular the sewage sludge (K), is detected transversely with respect to the flow direction by one-dimensional photo-optical incident light measurement of image rows of the grayscale profiles of a view from the top onto the suspension, in particular the sewage sludge (K); in that chord lengths of the detected floc structure are determined from the grayscale profiles, with the chord length being the distance between a relative grayscale maximum value and an adjacent relative grayscale minimum value, with the frequency for the distribution of the chord lengths being calculated and a concentration factor being determined as a function of parameters that are determined from the chord lengths with the frequency distribution of the chord lengths.

12. The arrangement according to claim 7, further characterized in that a third mixing stage (MM) is provided, which, after the addition of the same or a different flocculant (F1 or F2) and/or flocculating agent to the suspension, in particular the sewage sludge (K), forming in the intermediate mixing stage (MM), is observed using a further sensor (SM), in particular a concept operating by image analysis, in particular with a camera, in order to control the addition of the flocculant.

13. The method according to claim 1 further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used; and in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K).

14. The method according to claim 1, further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K); and in that the quantity of the flocculant (F1 or F2) and/or flocculating agent fed to the further mixing stage (M2) is constant and is determined in advance.

15. The method of claim 1, further characterized in that the quantity of the flocculant (F1 or F2) and/or flocculating agent fed to the further mixing stage (M2) is constant and is determined in advance; in that the quantity of flocculants (F1 or F2) and/or flocculating agents fed to the further mixing stage (M2, MM) is determined; in that the floc structure in the suspension, in particular the sewage sludge (K), is detected transversely with respect to the flow direction by one-dimensional photo-optical incident light measurement of image rows of the grayscale profiles of a view from the top onto the suspension, in particular the sewage sludge (K), in that chord lengths of the detected floc structure are determined from the grayscale profiles, with the chord length being the distance between a relative grayscale maximum value and an adjacent relative grayscale minimum value, with the frequency for the distribution of the chord lengths being calculated and a concentration factor being determined as a function of parameters that are determined from the chord lengths with the frequency distribution of the chord lengths.

16. The method according to claim 1, further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used; further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K); further characterized in that the quantity of the flocculant (F1 or F2) and/or flocculating agent fed to the further mixing stage (M2) is constant and is determined in advance; further characterized in that the quantity of flocculants (F1 or F2) and/or flocculating agents fed to the further mixing stage (M2, MM) is determined; in that the floc structure in the suspension, in particular the sewage sludge (K), is detected transversely with respect to the flow direction by one-dimensional photo-optical incident light measurement of image rows of the grayscale profiles of a view from the top onto the suspension, in particular the sewage sludge (K), in that chord lengths of the detected floc structure are determined from the grayscale profiles, with the chord length being the distance between a relative grayscale maximum value and an adjacent relative grayscale minimum value, with the frequency for the distribution of the chord lengths being calculated and a concentration factor being determined as a function of parameters that are determined from the chord lengths with the frequency distribution of the chord lengths; further characterized in that a third mixing stage (MM) is provided, which, after the addition of the same or a different flocculant (F1 or F2) and/or flocculating agent to the suspension, in particular the sewage sludge (K), forming in the intermediate mixing stage (MM), is observed using a further sensor (SM), in particular a concept operating by image analysis, in particular with a camera, in order to control the addition of the flocculant.

17. The arrangement according to claim 7, further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used; further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K).

18. The arrangement according to claim 7, further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K); further characterized in that the quantity of the flocculant (F1 or F2) and/or flocculating agent fed to the further mixing stage (M2) is constant and is determined in advance.

19. The arrangement according to claim 7, further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used; further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K); further characterized in that the quantity of flocculants (F1 or F2) and/or flocculating agents fed to the further mixing stage (M2, MM) is determined; in that the floc structure in the suspension, in particular the sewage sludge (K), is detected transversely with respect to the flow direction by one-dimensional photo-optical incident light measurement of image rows of the grayscale profiles of a view from the top onto the suspension, in particular the sewage sludge (K); in that chord lengths of the detected floc structure are determined from the grayscale profiles, with the chord length being the distance between a relative grayscale maximum value and an adjacent relative grayscale minimum value, with the frequency for the distribution of the chord lengths being calculated and a concentration factor being determined as a function of parameters that are determined from the chord lengths with the frequency distribution of the chord lengths.

20. The arrangement according to claim 7, further characterized in that, as a second flocculant (F2), a macromolecule or polymer that is identical in charge to the first flocculant (F1) is used; further characterized in that the sensor (S1) has a camera and/or carries out an image analysis measurement of the suspension, in particular the sewage sludge (K); further characterized in that a third mixing stage (MM) is provided, which, after the addition of the same or a different flocculant (F1 or F2) and/or flocculating agent to the suspension, in particular the sewage sludge (K), forming in the intermediate mixing stage (MM), is observed using a further sensor (SM), in particular a concept operating by image analysis, in particular with a camera, in order to control the addition of the flocculant.

Description

[0074] Two exemplary embodiments of the conduct of the method according to the invention will be explained below on the basis of the drawings. Shown are:

[0075] FIG. 1 a first alternative of a method according to the invention;

[0076] FIG. 2 a second alternative of a method according to the invention; and

[0077] FIG. 3 a comparison of a single addition and a twofold addition of flocculants to a sewage sludge suspension (polymer input in kg/t dry residue)

[0078] In a first illustrated embodiment, the method according to the invention serves for processing sewage sludge K by means of flocculants F1 and/or F2.

[0079] In the first embodiment of the method according to the invention, illustrated in FIG. 1, sewage sludge K is fed in the form of a suspension containing a substantial amount of water to a mixer or to a mixing stage M1. A flocculant F1, such as, for example, a polymer, is fed to the mixing stage M1 at the same time.

[0080] Attached to this mixing stage M1 is a sensor S1, which preferably operates by image analysis and has a camera for this purpose. The sensor S1 observes whether, during the addition of the flocculant F1, flocs are already formed in the suspension of the sewage sludge K in the mixing stage M1 or whether this is not the case. The sensor therefore does not undertake or does not necessarily undertake closer investigations as to the kind of flocs. What is important is whether the existence of flocs can already be affirmed.

[0081] If this is the case, then the sensor S1 interrupts the further addition of flocculant F1 to the mixing stage M1 and/or reports this circumstance to a control device (not shown), which controls the dosing and quantity of the flocculant F1 fed to the next batch or the next sections of a continuously fed quantity of sewage sludge K.

[0082] In any case, after this observation of the suspension of the sewage sludge K, the new mixture resulting in the mixing stage M1 and containing no flocs or only a very small quantity of flocs is fed to a second mixing stage M2. In the case of a continuous conduct of the method, the sensor S1 can also be arranged on the conveyor line of the sewage sludge K from the mixing stage M1 to the mixing stage M2 and, from there, can make use of its observation of the flowing sewage sludge K with the just forming flocs for control of the further feeding of the flocculant F1.

[0083] Also, further flocculant F1 (or, in certain applied cases, another flocculant F2) is fed to the mixing stage M2 at the same time. The quantity of flocculant F1 or F2 that is fed to the mixing stage M2 is calculated exactly in advance in the embodiment illustrated, because the exact flocculation amounts of the fed suspension are known and, accordingly, when further flocculant F1 is added, in many cases, exactly predictable or at least sufficiently exactly predictable flocculation effects start to occur.

[0084] After the addition of this flocculant to the mixing stage M2 and the formation of the exactly intended, optimized number of flocs, the resulting suspension K.sub.F obtained from the sewage sludge, the water contained in it, and the flocked particles, is fed to a further processing stage (not illustrated) for dewatering.

[0085] It has been found in tests that, by using a procedural approach of this kind, it is possible to achieve very good results. A two-stage dosing and mixing leads to very advantageous dosing possibilities for the minimum dosed quantity in the first mixing stage in comparison to a conventional one-stage dosing and mixing. The tests were carried out on the example of a dewatering of a digested sludge.

[0086] In the case of the digested sludge, values of about 3 kg of active substance per ton of dry matter have been obtained as values for the quantity of flocculant F1 that is to be fed.

[0087] In the case of conventional methods carried out in one stage, the quantity of flocculant F1 to be used was about 18 kg of active substance per 1 ton of dry matter. This is the quantity of flocculant F1 for which, in conventional methods, the highest dewatering results were obtained.

[0088] In carrying out the method in accordance with the invention using a two-stage design composed of two mixing stages and two additions of flocculants, it was possible to reduce the total quantity of flocculant to be added to 11.25 kg of active substance per 1 ton of dry matter.

[0089] The tests also have already shown that there should be neither a shortfall nor an exceeding of the minimum dosed quantity, because, in both cases, the dewatering results worsen in comparison to an exact dosing.

[0090] This confirms the advantages of the invention, for which a minimum dosed quantity to be adjusted in the first mixing stage M1 for the flocculant F1 to be added is very crucial for the functioning of the twofold or multifold mixing process.

[0091] In comparison to conventional methods, there results an overall reduction in the consumption of flocculant, that is, in the sum total of all flocculant quantities from the first mixing stage and the second mixing stage. Furthermore, there results an improvement in the thickening and dewatering result and in the solid-liquid separation properties.

[0092] A sensor with an image-analysis evaluation of photo-optically recorded images of a CCD camera has proven to be especially suitable for the sensor S1. In this way, the start of the flocculation, which is the crucial factor, can be detected especially well.

[0093] In order to determine concrete values for a control device, it is possible, for example, to choose an increase in the number of detected flocs with diameters of greater than 500 μm and/or a decrease in detected flocs with a diameter of less than 500 μm or less than 125 μm.

[0094] Shown in FIG. 2 is a second embodiment of the method according to the invention.

[0095] The start of the method proceeds here as in the first embodiment. Sewage sludge K is fed to the mixing stage M1. In the process, flocculant F1 is added to it. A sensor S1 detects whether, during the mixing operation, flocs have formed and, when the first flocs have formed, interrupts the further feeding of flocculant F1 to the mixing stage M1.

[0096] In contrast to the first embodiment, the sewage sludge K containing the added flocculant F1 and the first flocs that have formed is now fed to an intermediate mixing stage MM. Here, the addition of another different flocculant F2 now takes place. In this mixing stage MM, a dual flocculation therefore occurs. This is an addition of different flocculants to the same substance, namely, the sewage sludge K. By way of such a dual flocculation, the circumstance that oppositely charged polymers have specific attraction properties can be exploited.

[0097] In this way, additional effects that are very advantageous for the solid-liquid separation are achieved. Preferably, a specific predetermined dosed quantity is employed in this intermediate mixing stage MM with the added flocculant F2.

[0098] A further sensor SM of the intermediate mixing stage MM now establishes the impact of the addition of the flocculant F2.

[0099] This has the advantage that, in the case of fluctuating sludge and water characteristics of the sewage sludge K, a customized and thus optimal control of the dosed quantity is possible. The sensor SM can operate by an image analysis of the flocculation.

[0100] Conceivable are a control both of the addition of the flocculant F1 to the mixing stage M1 and also of the flocculant F2 to the mixing stage MM.

[0101] After the image analysis of the flocculation in the sensor SM, the sewage sludge proceeds, in turn, now with addition of the flocculants F1 and F2, to the second mixing stage M2. On account of the intermediate connection of the intermediate mixing stage MM in the sequence, this second mixing stage M2 is now the third mixing stage. However, it has the function of the second mixing stage M2 of the first exemplary embodiment, so that, here, for better differentiation, the term second mixing stage M2 is used.

[0102] Here, too, the flocculant F1 or, if need be, also the flocculant F2 or a third flocculant F2 is added to the mixing stage M2.

[0103] In this case, the resulting suspension K.sub.F also leaves the second mixing stage M2.

[0104] Schematically depicted in FIG. 3 are the measurement results and laboratory tests that correspond essentially to the first alternative of the method according to the invention of the twofold dosing. As a comparison, the curve for the single dosing of flocculant is also depicted.

[0105] Plotted at the right is the quantity of flocculant F and, namely, the numerical values refer to the polymer input in kilograms of active substance in relation to the quantity of the dry matter to be treated in tons.

[0106] Plotted at the top is a prognosis for the value E of the floc formation effects. The given numbers refer to the dry matter of the floc formation effects E in percent.

[0107] As a comparison, two curves D1 and D2 are drawn here. The bottom curve D1, drawn as a solid line, refers to the conventional single dosing of a flocculant F and the upper curve D2, drawn as a dashed line, refers to the twofold dosing in accordance with the invention.

[0108] The quantity of flocculant F1 or F2 that is fed to the mixing stage M2 can be calculated exactly in advance by means of the depicted course of the curves for the twofold dosing, because the exact flocculation amounts of the supplied suspension are known and, accordingly, during the addition of further flocculent F1, there occur in many cases exactly predictable or at least sufficiently exactly predictable flocculation effects.

LIST OF REFERENCE CHARACTERS

[0109] D1 dosing, single [0110] D2 dosing, twofold [0111] E effect of floc formation [0112] F flocculant [0113] F1 flocculant 1 [0114] F2 flocculant 2 [0115] F3 flocculant 3 [0116] K sewage sludge containing water portion [0117] K.sub.F sewage sludge containing water portion and flocked particles [0118] M1 mixer 1 [0119] M2 mixer 2 [0120] MM intermediate mixer [0121] S1 sensor 1 [0122] SM sensor of the intermediate mixing stage MM [0123] WS active substance [0124] TR dry residue