WASTEWATER TREATMENT PLANT AND METHOD FOR TREATING WASTEWATER

Abstract

A method for treating wastewater in a wastewater treatment plant includes passing the wastewater passes through a rake system and, thereafter, a sand trap to separate from the wastewater, solids having different particle sizes. A screening device screens the wastewater emerging from the sand trap to yield a primary sludge that fails to pass through the screening device and a suspension passing through the screening device. The suspension is fed to at least one further treatment stage, and the primary sludge is thickened with the aid of at least one thickener. The thickened primary sludge is fed to one or several further treatment stages. Moreover, a wastewater treatment plant for treating wastewater is described.

Claims

1. A method for treating wastewater in a wastewater treatment plant, the method comprising the steps of: passing the wastewater through a rake system and, thereafter, a sand trap, wherein solids having different particle sizes are separated out of the wastewater with the aid of the rake system and the sand trap, wherein the wastewater emerging from the sand trap is screened with the aid of a screening device, wherein this yields a primary sludge and a suspension passing through the screening device, feeding the suspension to a first further treatment stage, and wherein the primary sludge is thickened with the aid of at least one thickener and the thickened primary sludge is fed to a second further treatment stage.

2. The method as claimed in claim 1, wherein the primary sludge is thickened with the aid of a static thickener, wherein the residence time of the primary sludge in the static thickener is between 1 h and 10 h.

3. The method as in claim 2, wherein the primary sludge thickened with the aid of the static thickener is fed to a mechanical thickener and, there, is further thickened.

4. The method as in claim 3, wherein the thickened primary sludge emerging from the static thickener or the thickened primary sludge emerging from the mechanical thickener is fed to a digester.

5. The method as claimed in claim 2, wherein the wastewater in the screening device is screened with the aid of a screen surface, the mesh size of which is between 1 m and 10 mm, wherein the solids which have been separated out via screening are fed, as a portion of the primary sludge separated from the wastewater, to the static thickener.

6. The method as in claim 5, wherein the solids retained by the screen surface are removed from the screen surface continuously or at intervals with the aid of an air flow and/or a cleaning fluid, wherein the primary sludge emerging from the screening device comprises liquid from the wastewater which is carried along by the solids which have been separated out via screening, and, in the event that a cleaning fluid is utilized, also at least a portion of the introduced cleaning fluid.

7. The method as in claim 2, wherein the primary sludge emerging from the screening device has a solid content per unit mass of 0.01% to 10%.

8. The method as in claim 1, wherein the primary sludge emerging from the screening device is thickened with the aid of the static thickener to a solid content per unit mass of 0.1% to 15%.

9. The method as in claim 2, wherein the primary sludge emerging from the static thickener is thickened with the aid of the mechanical thickener to a solid content per unit mass of 1% to 15%.

10. The method as in claim 1, wherein the suspension emerging from the screening device is fed to a an activated sludge tank, and, there, is biologically clarified, wherein the wastewater emerging from the activated sludge tank is fed to a secondary clarification tank and, there, undergoes secondary treatment.

11. The method as in claim 2, wherein wastewater is separated from the primary sludge during the thickening of the primary sludge in the static thickener, wherein the wastewater which has been separated out is also fed to a biological treatment stage, wherein the wastewater subsequently emerging from the biological treatment stage is fed to a secondary clarification tank.

12. A wastewater treatment plant for treating wastewater, the wastewater treatment plant comprising: a rake system and a sand trap installed downstream from the rake system in the flow direction of the wastewater, wherein solids having different particle sizes are separated out of the wastewater with the aid of the rake system and the sand trap, a screening device installed downstream from the sand trap in the flow direction of the wastewater, with the aid of which the wastewater emerging from the sand trap is screened to yield a primary sludge, which fails to pass through the screening device, and a suspension passing through the screening device, and a thickener, with the aid of which the primary sludge emerging from the screening device is thickened.

13. The wastewater treatment plant as in claim 12, wherein the thickener is a static thickener.

14. The wastewater treatment plant as in claim 13, further comprising a mechanical thickener configured for further thickening the primary sludge emerging from the static thickener.

15. The wastewater treatment plant as in claim 12, further comprising: a biological treatment stage in the form of an activated sludge tank that is configured for biologically clarifying the suspension passing through the screening device, and a secondary clarification tank that is configured for subjecting the wastewater emerging from the biological treatment stage to a secondary treatment.

16. The method as in claim 1, wherein the primary sludge is thickened with the aid of a static thickener during a residence time therein of between 2 hours and 8 hours.

17. The method as in claim 2, wherein the wastewater in the screening device is screened with the aid of a screen surface, the mesh size of which is between 10 m and 1 mm, and further comprising the step of feeding to the static thickener the solids which have been separated out via screening as a portion of the primary sludge separated from the wastewater.

18. The method as in claim 2, wherein the primary sludge emerging from the screening device has a solid content per unit mass of 0.2% to 3.5%.

19. The method as in claim 1, wherein the primary sludge emerging from the screening device is thickened with the aid of the static thickener to a solid content per unit mass of 2% to 6%.

20. The method as in claim 2, wherein the primary sludge emerging from the static thickener is thickened with the aid of the mechanical thickener to a solid content per unit mass of 4% to 8%.

Description

[0034] Further advantages of the invention are described in the following exemplary embodiment.

[0035] FIG. 1 schematically shows the essential treatment stages of a wastewater treatment plant according to the invention.

[0036] It is apparent from FIG. 1 that the wastewater treatment plant comprises a rake system 1, with the aid of which relatively large solids, such as stones or branches, can be separated from a wastewater flow. The rake system 1 can be, in principle, a multi-rake bar screen which comprises a bar screen and several traveling rakes, with the aid of which retained solids can be removed from the bar screen.

[0037] A sand trap 2 is installed downstream from the rake system, wherein the transport path of the wastewater emerging from the rake system 1 is marked by the arrow A.

[0038] In the sand trap 2, smaller settleable solids, such as glass chips, which have not been removed from the wastewater by the rake system 1, are at least partially separated from the wastewater.

[0039] Thereafter, the wastewater emerging from the sand trap 2 enters a screening device 7 which preferably comprises a filter drum 13 which can be set into rotary motion with the aid of a drive and which includes a screen surface 5 (the transport direction of the wastewater from the sand trap 2 to the screening device 7 is marked by the arrow B).

[0040] The wastewater flows, in this case, into the filter drum 13 via an end face. Solids which are larger than the mesh size of the filter drum 13 are retained by the screen surface 5 of the filter drum 13. One or several spray nozzles 3 is/are present in the upper area, with the aid of which cleaning fluid 4 (water, or wastewater passing through the screen surface 5) can be sprayed from the outside onto the screen surface 5. As a result, the solids adhering to the inside of the screen surface 5 are loosened and drop, together with the cleaning fluid 4, into a discharge outlet 6 situated within the filter drum 13. Alternatively or additionally, the screen surface 5 can also be cleaned with the aid of the above-described air flow.

[0041] The wastewater passing through the screen surface 5 is fed to a biological treatment stage 8 in the form of an activated sludge tank (arrow C), for example, while the primary sludge (=mixture of solids, wastewater, and cleaning fluid 4, if utilized, discharged from the screen device 7 via the discharge outlet 6) is fed to a static thickener 10 (arrow D).

[0042] There, the primary sludge is thickened by way of the separating-out of wastewater, i.e., the solid content of the primary sludge is increased. The wastewater emerging from the static thickener 10 is also fed to the biological treatment stage 8, wherein this can take place via a direct path. Alternatively, the wastewater can also be mixed with the wastewater flow between the screening device 7 and the biological treatment stage 8 (arrow E).

[0043] A further treatment of the wastewater takes place in the biological treatment stage 8. Thereafter, the wastewater is fed to a secondary clarification tank 9, as is already known from the related art (arrow M).

[0044] In the secondary clarification tank 9, a final separating-out of the so-called excess sludge takes place by gravity, wherein this excess sludge can be fed directly to a unit for stabilization (arrow L). The unit is, for example, a digester 12 which can be designed, for example, as a digestion tower.

[0045] The thickened primary sludge emerging from the static thickener 10 can also be fed to the unit for stabilization. Three alternatives are conceivable, in principle.

[0046] According to one alternative, the thickened primary sludge is introduced into the conveying line, via which the excess sludge is transported to the unit for stabilization (arrow K).

[0047] It is also conceivable that the thickened primary sludge is conveyed directly into the unit for stabilization. This option is represented by the arrow H.

[0048] Finally, it is possible that the primary sludge thickened in the static thickener 10 is initially fed to a mechanical thickener 11, as described further above, and, there, is further thickened (arrow G). The primary sludge emerging from the mechanical thickener 11 has a solid content, in this case, which is higher than the solid content of the primary sludge introduced into the mechanical thickener 11.

[0049] After emerging from the mechanical thickener 11, the additionally thickened primary sludge finally enters the unit for stabilization (arrow F).

[0050] The aforementioned alternatives can be implemented at different points in time or even simultaneously during the operation of the wastewater treatment plant. In addition, either only two of the aforementioned alternatives or only one alternative can be implemented in the specific embodiment.

[0051] Finally, it is possible that excess sludge emerging from the secondary clarification tank 9 is also fed to the mechanical thickener 11 and, there, is further thickened together with the primary sludge coming from the static thickener 10 before it is fed to the digester 12 (arrow N). The addition of chemicals (polymers) for pretreating the excess sludge emerging from the secondary clarification tank 9 between the secondary clarification tank 9 and the digester 12 can be dispensed with, in particular, in this case.

[0052] Moreover, it is conceivable that a homogenization of the two sludges can be useful in this process of the joint mechanical thickening of the primary sludge and the excess sludge. This homogenization can take place ahead of or even within the mechanical thickener 11.

[0053] In conclusion, it is pointed out, in general, that the wastewater, the primary sludge, and the excess sludge are preferably transported between the individual treatment stages with the aid of pumps and pipelines.

[0054] The present invention is not limited to the exemplary embodiment which has been represented and described. Modifications within the scope of the claims are also possible, as is any combination of the described features, even if they are represented and described in different parts of the description or the claims or in different exemplary embodiments, provided no contradiction to the teaching of the independent claims results.

LIST OF REFERENCE SIGNS

[0055] 1 rake system [0056] 2 sand trap [0057] 3 spray nozzle [0058] 4 cleaning fluid [0059] 5 screen surface [0060] 6 discharge outlet [0061] 7 screening device [0062] 8 biological treatment stage [0063] 9 secondary clarification tank [0064] 10 static thickener [0065] 11 mechanical thickener [0066] 12 digester [0067] 13 filter drum [0068] A transport direction of the wastewater passing through the rake system [0069] B transport direction of the wastewater passing through the sand trap [0070] C transport direction of the suspension passing through the screening device [0071] D transport direction of the primary sludge emerging from the screening device [0072] E transport direction of the wastewater emerging from the static thickener [0073] F transport direction of the thickened primary sludge emerging from the mechanical thickener [0074] G first possible transport direction of the thickened primary sludge emerging from the static thickener [0075] H second possible transport direction of the thickened primary sludge emerging from the static thickener [0076] K third possible transport direction of the thickened primary sludge emerging from the static thickener [0077] L first possible transport direction of the excess sludge emerging from the secondary clarification tank [0078] M transport direction of the wastewater emerging from the biological treatment stage [0079] N second possible transport direction of the excess sludge emerging from the secondary clarification tank