Method and plant for thickening sludge derived from water treatment by flocculation-decantation with ballasted floc

• US 6,966,993 B2
• Filed: 02/08/2002
• Issued: 11/22/2005
• Est. Priority Date: 02/09/2001
• Status: Expired due to Term

• Current Assignee: Veolia Water Solutions & Technologies Support
• Original Assignee: OTV S.A. (Veolia Environnement SA)
• Inventors: Binot, Patrick
• Primary Examiner(s): Hruskoci, Peter A.
• Application Number:
  US10/470,934
• Publication Number:
  US 20040055961A1
• Time in Patent Office: 1,383 Days
• Field of Search: 210/609, 210/710, 210/711, 210/713, 210/714, 210/724, 210/725, 210/727, 210/718, 210/738, 210/188, 210/195.1, 210/195.3, 210/709, 210/712, 210/715
• US Class Current: 210/711
• CPC Class Codes: B01D 21/0039 Settling tanks provided with contact surfaces, e.g. baffles, particles
• CPC Class Codes: B01D 21/0045 Plurality of essentially parallel plates
• CPC Class Codes: B01D 21/01 using flocculating agents for purifying water C02F1/52; for liquid radioactive waste G21F9/10
• CPC Class Codes: B01D 21/08 provided with flocculating compartments
• CPC Class Codes: B01D 21/2427 The feed or discharge opening located at a distant position from the side walls
• CPC Class Codes: B01D 21/2488 bringing about a partial recirculation of the liquid, e.g. for introducing chemical aids
• CPC Class Codes: B01D 21/2494 provided with means for the removal of gas, e.g. noxious gas, air
• CPC Class Codes: B01D 21/34 Controlling the feed distribution; Controlling the liquid level ; Control of process parameters
• CPC Class Codes: C02F 1/20 by degassing, i.e. liberation of dissolved gases degasification of liquids in general B01D19/00; arrangement of degassing apparatus in boiler feed supply F22D
• CPC Class Codes: C02F 1/38 by centrifugal separation
• CPC Class Codes: C02F 1/52 by flocculation or precipitation of suspended impurities C02F1/463 takes precedence
• CPC Class Codes: C02F 1/5281 Installations for water purification using chemical agents
• CPC Class Codes: C02F 11/147 using organic substances C02F11/148 takes precedence
• CPC Class Codes: C02F 2001/007 Processes including a sedimentation step
• CPC Class Codes: C02F 2103/001 Runoff or storm water
• CPC Class Codes: C02F 2305/12 Inert solids used as ballast for improving sedimentation C02F3/1226 takes precedence

Abstract

A method is provided for thickening sludge produced through a ballasted flocculation process. The sludge and granular material from the ballasted flocculation process are directed to a sludge separator where the sludge is separated from the granular material. Thereafter the separated sludge is sent to a degassing area and the sludge is degassed. A flocculating agent is mixed or injected into the sludge. The sludge is directed to a sludge thickener with a load at a sill calculated on the surface of the thickener greater than 200 kgMIS/m²/day. This process produces a thickened sludge having a concentration greater than 10 gm/I.

Claims

1. A method for thickening sludge produced by a ballasted flocculation water or wastewater treatment system comprising:

a. directing a mixture of sludge and granular material from the ballasted flocculation water or wastewater treatment system to a sludge separator and separating the sludge from the granular material;

b. directing the separated sludge to a degassing area and degassing the sludge;

c. injecting a flocculation agent into the sludge; and

d. directing the sludge to a sludge thickener with a load at a sill calculated on the sill surface of the thickener greater than 200 kgMIS/m²/day, and producing a thickened sludge having a concentration greater than 10 gm/l.

2. The method of claim 1 wherein the degassing of the sludge is implemented over a degassing surface corresponding to a superficial degassing speed of less than 100 m/hr.

3. The method of claim 1 including injecting at least one coagulating agent into the sludge.

4. The method of claim 3 wherein the injection of the coagulating agent occurs upstream from the injection of the flocculating agent.

5. The method of claim 1 wherein the degassing of the sludge is implemented over a degassing surface corresponding to a superficial degassing speed lower than 60 m/hr.

6. The method of claim 1 wherein the flocculating agent is mixed with the sludge in an agitated flocculation zone.

7. The method of claim 6 wherein the residency time of the sludge within the agitated flocculation zone is 10 minutes or less.

8. The method of claim 1 wherein the sludge thickening is carried out in a lamellar thickener.

9. The method of claim 8 wherein a sludge blanket is formed in the sludge thickener and the sludge thickener includes a series of plates that are spaced approximately 2 to 4 meters above a bottom portion of the thickener, and wherein the height of the sludge blanket is monitored and maintained between two predetermined heights.

10. The method of claim 1 wherein the sludge is produced from tertiary sewage treatment and the thickening process is carried out with a load at the sill greater than 300 kgMIS/m²/day and produces a concentration of thickened sludge greater than 15 gm/l.

11. The method of claim 1 wherein the sludge is produced from a primary sewage treatment or from combined sewage overflows resulting from rain, and wherein the thickening process is carried out with a load at the sill greater than 1000 kgMIS/m²/day and produces a thickened sludge having a concentration greater than 25 gm/l.

12. The method of claim 1 wherein the sludge to be thickened is produced from the settling treatment of surface waters other than carbonate removal treatment, and wherein the thickening process is carried out with a load at the sill greater than 200 kgMIS/m²/day and produces a sludge concentration of more than 10 gm/l.

13. The method of claim 1 including separating water from the thickened sludge and returning the separated water to the water or wastewater treatment system that produced the sludge.

14. The method of claim 1 wherein the flocculating agent is injected into the sludge in an area, and returning at least a portion of the thickened sludge from the sludge thickener to the area where the flocculating agent is injected into the sludge.