Combined biological and ballasted flocculation process for treating wastewater

• US 7,323,108 B1
• Filed: 04/17/2007
• Issued: 01/29/2008
• Est. Priority Date: 04/17/2007
• Status: Expired due to Fees

• Current Assignee: I. Kruger Inc.
• Original Assignee: I. Kruger Inc.
• Inventors: Garbett, Ross Alan, Hendley, Barry Wayne, Hudson, Branden Edmond, Gutshall, Michael Leon
• Primary Examiner(s): Barry; Chester T.
• Application Number:
  US11/736,229
• Time in Patent Office: 287 Days
• Field of Search: 210/607, 210615-618, 210620-626, 210/631
• US Class Current: 210/607
• CPC Class Codes: C02F 1/5209 Regulation methods for flocculation or precipitation
• CPC Class Codes: C02F 1/5281 Installations for water purification using chemical agents
• CPC Class Codes: C02F 2001/007 Processes including a sedimentation step
• CPC Class Codes: C02F 2209/10 Solids, e.g. total solids [TS], total suspended solids [TSS] or volatile solids [VS]
• CPC Class Codes: C02F 2209/40 Liquid flow rate
• CPC Class Codes: C02F 2305/12 Inert solids used as ballast for improving sedimentation C02F3/1226 takes precedence
• CPC Class Codes: C02F 3/12 Activated sludge processes
• CPC Class Codes: C02F 3/286 including two or more steps
• CPC Class Codes: C02F 3/30 Aerobic and anaerobic processes
• CPC Class Codes: C02F 9/00 Multistage treatment of water, waste water or sewage
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage

Abstract

A wastewater treatment process is provided that entails both a biological or activated sludge process and a ballasted flocculation process. A first stream of wastewater is directed to a biological system for biologically treating the wastewater. The biological treatment process produces a first effluent and a first sludge. In cases where the biological system is an activated sludge process, the first sludge is recycled. A second stream of wastewater is directed to a ballasted flocculation system. The second stream of wastewater can be a stream independent of the first stream of wastewater or can be derived from the wastewater passing through the biological system. Sludge in the form of activated sludge or mixed liquor from the biological system is mixed with a second stream of wastewater in the ballasted flocculation system for the purpose of biologically treating the second stream of wastewater. Forming a part of the ballasted flocculation system is a settling tank that produces a second effluent and a second sludge. The second sludge is routed to a separator where granular material that forms a ballast in the process is separated and recycled. To effectively remove suspended solids from the wastewater passing through the ballasted flocculation system, the second sludge recycle rate is controlled or maintained at a flow rate of about 15% and higher of the influent flow rate to the ballasted flocculation system. Furthermore, as the mixed liquor suspended solids (MLSS) concentration increases from, for example, 1000 mg/l to about 4000 mg/l, the recycle rate of the second sludge may be varied from about 15% to about 40% of the influent flow rate to the ballasted flocculation system.

Claims

1. A method of treating wastewater with both a biological system and a ballasted flocculation system, comprising:

a. directing a first wastewater stream to the biological system and biologically treating the first wastewater stream;

b. separating a first sludge from the wastewater in the biological system and producing a first effluent;

c. directing a second wastewater stream to the ballasted flocculation system;

d. transferring at least some of the first sludge from the biological system, and mixing the first sludge with the wastewater in the ballasted flocculation system to biologically treat the second stream of wastewater;

e. in the ballasted flocculation system, separating a second sludge from the wastewater in the ballasted flocculation system to produce a second effluent;

f. recycling the second sludge to a separator and separating ballast from the sludge; and

g. maintaining the second sludge recycle rate such that the flow rate of the second sludge to the separator is 15% or more of the influent flow rate to the ballasted flocculation system.

2. The method of claim 1 including maintaining the second sludge recycle rate such that the flow rate of the second sludge to the separator is 15% to 40% of the influent flow rate to the ballasted flocculation system.

3. The method of claim 1 including varying the second sludge recycle flow rate based, in part at least, on the concentration of mixed liquor suspended solids in the wastewater being treated in the ballasted flocculation system.

4. The method of claim 3 wherein the second sludge recycle flow rate is maintained at 15% to 30% of the influent to the ballasted flocculation system when the wastewater being treated by the ballasted flocculation system has a mixed liquor suspended solid (MLSS) concentration of about 2000 mg/l, and wherein the second sludge recycle flow rate is maintained at 25% to 40% of the influent to the ballasted flocculation system when the wastewater being treated in the ballasted flocculation system has a mixed liquor suspended solid concentration of about 4000 mg/l.

5. The method of claim 1 including mixing insoluble granular material with the wastewater in the ballasted flocculation system and maintaining the concentration of the insoluble granular material at about 20 g/l and above.

6. The method of claim 1 including mixing a flocculant with the wastewater passing through the ballasted flocculation system and varying the concentration of the flocculant based on the concentration of MLSS in the wastewater in the ballasted flocculation system.

7. The method of claim 6 including varying the concentration of the flocculant from 8 mg/l to 24 mg/l.

8. The method of claim 7 including maintaining the concentration of the flocculant at about 8 mg/l when the MLSS concentration is about 1000 mg/l, and maintaining the flocculant concentration at about 24 mg/l when the MLSS concentration is about 4000 mg/l.

9. The method of claim 1 wherein the ballasted flocculation system includes a settling tank that produces a varying rise rate, and wherein the method includes increasing the second sludge recycle flow rate in response to an increase in rise rate.

10. The method of claim 9 including, for rise rates of 15 gpm/sq. ft to 25 gpm/sq. ft utilizing a second sludge recycled flow rate in the range of about 15% to 40% of the influent flow rate to the ballasted flocculation system.

11. The method of claim 1 wherein the ballasted flocculation system includes a settling tank that produces a varying rise rate, and wherein the method includes varying the second sludge recycle flow rate between 15% and 40% of the influent to the ballasted flocculation system, and wherein the second sludge recycle flow rate is dependent on both the rise rate and the MLSS concentration of the wastewater in the ballasted flocculation system.

21. The method of claim 3 wherein the second sludge recycle flow rate is maintained at 15% to 30% of the influent to the ballasted flocculation system when the wastewater being treated by the ballasted flocculation system has a mixed liquor suspended solid (MLSS) concentration of 2000 mg/l, and wherein the second sludge recycle flow rate is maintained at 25% to 40% of the influent to the ballasted flocculation system when the wastewater being treated in the ballasted flocculation system has a mixed liquor suspended solid concentration of 4000 mg/l.

22. The method of claim 1 including mixing insoluble granular material with the wastewater in the ballasted flocculation system and maintaining the concentration of the insoluble granular material at 20 g/l and above.

23. The method of claim 7 including maintaining the concentration of the flocculant at 8 mg/l when the MLSS concentration is 1000 mg/l, and maintaining the flocculant concentration at 24 mg/l when the MLSS concentration is 4000 mg/l.

12. A method of treating wastewater with both a biological system and a ballasted flocculation system, comprising:

a. directing a first wastewater stream to the biological system and biologically treating the first wastewater stream;

b. separating a first sludge from the wastewater in the biological system and producing a first effluent;

c. directing a second wastewater stream to the ballasted flocculation system;

d. transferring at least some of the first sludge from the biological system, and mixing the first sludge with the wastewater in the ballasted flocculation system to biologically treat the wastewater therein;

e. mixing a ballast of insoluble granular material with the wastewater that passes through the ballasted flocculation system and maintaining the concentration of the insoluble granular material to 20 g/l and above;

f. in the ballasted flocculation system, separating a second sludge from the wastewater in the ballasted flocculation system to produce a second influent;

g. recycling the second sludge to a separator and separating the ballast from the sludge; and

h. maintaining the second sludge recycle flow rate such that the flow rate of the second sludge to the separator is 15% or more of the influent flow rate to the ballasted flocculation system.

13. The method of claim 12 including maintaining the second sludge recycle rate at 15%-40% of the influent flow rate to the ballasted flocculation system.

14. The method of claim 12 including varying the second sludge recycle flow rate based, in part at least, on the concentration of MLSS of the wastewater being treated in the ballasted flocculation system.

15. The method of claim 14 wherein the second sludge recycle flow rate is maintained at 15%-30% of the influent to the ballasted flocculation system when the wastewater being treated in the ballasted flocculation system has an MLSS concentration of about 2000 mg/l, and wherein the second sludge recycle flow rate is maintained at 25%-40% of the influent to the ballasted flocculation system when the wastewater being treated and the ballasted flocculation system has an MLSS concentration of about 4000 mg/l.

16. The method of claim 12 including mixing a flocculant with the wastewater passing through the ballasted flocculation and varying the concentration of the flocculant based on the MLSS concentration of the wastewater in the ballasted flocculation system.

17. The method of claim 16 including varying the concentration of the flocculant from 8 mg/l to 24 mg/l.

18. The method of claim 12 wherein the ballasted flocculation system includes a settling tank that produces a varying rise rate, and wherein the method includes increasing the second sludge recycle flow rate in response to an increase in rise rate.

19. The method of claim 18 including for rise rates of 15 gpm/sq. ft to 25 gpm/sq. ft utilizing a second sludge recycle flow rate in the range of about 15% to 40% of the influent flow rate to the ballasted flocculation system.

24. The method of claim 14 wherein the second sludge recycle flow rate is maintained at 15%-30% of the influent to the ballasted flocculation system when the wastewater being treated in the ballasted flocculation system has an MLSS concentration of about 2000 mg/l, and wherein the second sludge recycle flow rate is maintained at 25%-40% of the influent to the ballasted flocculation system when the wastewater being treated and the ballasted flocculation system has an MLSS concentration of 4000 mg/l.

20. A method of treating wastewater with both a biological system and a ballasted flocculation system, comprising:

a. directing a first wastewater stream to the biological system and biologically treating the first wastewater stream;

b. separating a first sludge from the wastewater in the biological system and producing a first effluent;

c. directing a second wastewater stream to the ballasted flocculation system;

d. transferring at least some of the first sludge from the biological system, and mixing the first sludge with the wastewater in the ballasted flocculation system to biologically treat the second stream of wastewater;

e. in the ballasted flocculation system, separating a second sludge from the wastewater in the ballasted flocculation system to produce a second effluent, and wherein the ballasted flocculation system includes a settling tank having a variable rise rate;

f. recycling the second sludge to a separator and separating ballast from the sludge; and

g. controlling the second sludge recycle rate such that the second sludge recycle rate to the separator is 15% to 40% and is based at least partially on the rise rate of the settling tank of the ballasted flocculation system.