Method for wastewater treatment and wastewater treatment system

1. A method for wastewater treatment comprising the steps of:

taking off excess sludge (ES) from primary sludge (PS), and then

anaerobically treating said primary sludge (PS) in a digestion vessel and

separately treating said excess sludge (ES), wherein the excess sludge (ES) is disrupted and liquefied in a hydrolysis treatment and, independently of the primary sludge (PS), subjected to a separate anaerobic treatment such that the anaerobic treatment of primary sludge (PS) takes place separately from the anaerobic treatment of the excess sludge (ES).

2. The method as claimed in claim 1 , wherein the hydrolysis treatment comprises one or more of thermal and chemical hydrolysis of the excess sludge (ES).

3. The method as claimed in claim 2 , wherein the thermal hydrolysis comprises the steps of heating the excess sludge (ES) to a temperature in the range from 130 to 180° C., disrupting the heated excess sludge (ES) in a hydrolysis reactor, and expanding the heated excess sludge (ES) after a residence time in the hydrolysis reactor.

4. The method as claimed in claim 3 , wherein the residence time of the excess sludge (ES) in the hydrolysis reactor for disruption of cells is 15 to 60 minutes.

5. The method as claimed in claim 1 , further comprising the step of injecting steam into the excess sludge (ES) for the hydrolysis treatment.

6. The method as claimed in claim 2 , further comprising the steps of raising the pH of the excess sludge (ES) to values between 9 and 14 and increasing the temperature to 50 to 130° C. for the one or more of chemical and thermal hydrolysis.

7. The method as claimed in claim 1 , further comprising the step of homogenizing the excess sludge (ES) before the hydrolysis treatment.

8. The method as claimed in claim 1 , further comprising the step of cooling the hydrolyzed excess sludge (ES) to a temperature in the range from 30 to 55° C.

9. The method as claimed in claim 1 , wherein the anaerobic treatment of the hydrolyzed excess sludge (ES) in the separately treating step proceeds in a fixed-bed reactor or a fluidized-bed reactor.

10. The method as claimed in claim 9 , wherein the fixed-bed reactor or fluidized-bed reactor is a pellet reactor.

11. The method as claimed in claim 1 , further comprising filtering, centrifuging and/or precipitating the anaerobically treated excess sludge (ES) for extracting solids and/or recovering raw materials.

12. The method as claimed in claim 11 , further comprising the step of feeding solids separated off from the anaerobically treated excess sludge (ES) to the primary sludge (PS) before or during the separate anaerobic treatment of the primary sludge (PS).

13. The method as claimed in claim 1 , further comprising the step of heating the primary sludge (PS) for sanitation by means of heat energy occurring on hydrolysis of the excess sludge (ES).

14. The method as claimed in claim 1 , wherein the anaerobic treatment of the hydrolyzed excess sludge (ES) in the separately treating step is carried out for a time of less than 5 days.

15. The method as claimed in claim 1 , further comprising the step of discharging, for further use, methane gas (M) occurring from the anaerobic treatment of the primary sludge (PS) and the separate anaerobic treatment of the excess sludge (ES).

16. A wastewater treatment system for treating at least one of wastewaters and sludges comprising

separate processing trains for excess sludge (ES) and primary sludge (PS)

a digestion vessel in said processing train for said primary sludge (PS) for anaerobic treatment of said primary sludge (PS) after taking off said excess sludge (ES) from said primary sludge (PS),

a hydrolysis reactor in said processing train for said excess sludge (ES) for the hydrolysis treatment of excess sludge (ES) taken off said primary sludge (PS), wherein the excess sludge (ES) is disrupted and liquefied, and

a separate reactor for the anaerobic treatment of hydrolyzed excess sludge (ES) such that the anaerobic treatment of the primary sludge (PS) takes place separately from the anaerobic treatment of the excess sludge (ES), said reactor being connected so as to communicate directly or indirectly with the outlet of the hydrolysis reactor.

17. The wastewater treatment system as claimed in claim 16 , further comprising

a homogenizer for disintegrating the excess sludge (ES), said homogenizer being connected upstream of the hydrolysis reactor.

18. The wastewater treatment system as clainied in claim 16 , wherein the separate reactor for the anaerobic treatment of hydrolyzed excess sludge (ES) is a fixed-bed reactor or a fluidized-bed reactor.

19. The wastewater treatment system as claimed in claim 18 , wherein the fixed-bed reactor or fluidized-bed reactor is a pellet reactor.

20. The wastewater treatment system as claimed in claim 16 , wherein the hydrolysis reactor has a downstream expansion tank.

21. The wastewater treatment system as claimed in claim 16 , further comprising

a precipitation unit following downstream of an outlet of the separate reactor for the anaerobic treatment of the excess sludge (ES), said precipitation unit having a feed for precipitant for precipitating phosphates from the hydrolyzed and anaerobically treated excess sludge (ES).

22. The wastewater treatment system as claimed in claim 16 , further comprising

one or more of a centrifuge and filter for separating off solids from the hydrolyzed and anaerobically treated excess sludge (ES), said one or more centrifuge and filter following downstream of the outlet of the separate reactor for the anaerobic treatment of the excess sludge (ES).

23. The wastewater treatment system as claimed in claim 16 , further comprising

a line for heat conduction medium between the expansion tank and a sanitation vessel for primary sludge (PS), wherein the sanitation vessel has a heating unit for heating primary sludge (PS) by means of heat energy which can be transferred by the heat conduction medium from the expansion tank via the line.

24. The wastewater treatment system as claimed in claim 16 , further comprising

a heat exchanger between the hydrolysis reactor and the separate reactor for the anaerobic treatment of the hydrolyzed excess sludge (ES) for cooling the excess sludge (ES).

25. The method as claimed in claim 4 , wherein said residence time is from 15 to 45 minutes.

26. The method as claimed in claim 6 , wherein the pH of the excess sludge (ES) is raised to values between 9 and 12 and the temperature is increased to 60 to 100° C. for the one or more of chemical and thermal hydrolysis.

27. The method as claimed in claim 8 , wherein said cooling is to a temperature in the range from 35 to 38° C.

28. The method as claimed in claim 14 , wherein said anaerobic treatment is carried out for a time of 5 to 20 hours.