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

• US 7,083,715 B2
• Filed: 05/25/2005
• Issued: 08/01/2006
• Est. Priority Date: 02/09/2001
• Status: Expired due to Term

• Current Assignee: OTV SA SA
• Original Assignee: OTV SA SA
• Inventors: Binot, Patrick
• Primary Examiner(s): Hruskoci, Peter A.
• Application Number:
  US11/136,971
• Publication Number:
  US 20050218056A1
• Time in Patent Office: 433 Days
• Field of Search: 210/188
• US Class Current: 210/112
• 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/l.

Claims

1. A plant for thickening sludge derived from water treatment comprising at least one wastewater or water treatment unit including a ballasted flocculation zone with floc ballasted with sand or other granular material, a settling zone for separating settled sludge, a recirculating line for circulating settled sludge from the settling zone to a separator that separates the settled sludge into ballast and sludge, a line from the separator to a sludge thickening system for directing sludge from said separator to degassing zone having a minimum surface corresponding to a degassing speed of 100 m/hr relative to the flow rate of said sludge;

a thickening system flocculation zone adapted to enable at least one flocculation agent to be mixed with the sludge to be thickened;

at least one sludge thickener settler forming a part of a lamellar sludge thickening system and including a lamellar decantation zone including a series of plates, a thickening zone disposed under the plates, an extraction device associated with the thickener settler for extracting thickened sludge, and a clarified water zone above the plates.

2. The plant of claim 1 including a thickening system coagulating zone disposed upstream of the thickening system flocculating zone.

3. The plant of claim 1 wherein the maximum total surface of the degassing zone corresponds to a degassing speed of 60 m/hr relative to the flow rate of entering sludge.

4. The plant of claim 1 wherein the thickening system flocculation zone includes an agitation tank.

5. The plant of claim 1 wherein the plates are of a length of approximately 0.5 to 3 meters and are spaced apart approximately 5 to 15 cm;

and wherein the plates are disposed at an angle relative to a horizontal reference line of approximately 55; and

wherein the thickener settler includes a sludge raking device and at least one sensor for monitoring a height of a sludge blanket within the thickener settler.

6. The plant of claim 1 including a recirculation loop extending between the thickener settler and the thickening system flocculation zone.

7. The plant of claim 1 wherein the treatment unit includes a coagulation zone.

8. The plant of claim 7 wherein the ballasted flocculation zone is a sand ballasted flocculation zone including a hydrocyclone for separating the settled sludge into sand and sludge.