Method of Removing Phosphorus from Wastewater

• US 20080314830A1
• Filed: 06/22/2007
• Published: 12/25/2008
• Est. Priority Date: 06/22/2007
• Status: Active Grant

• Current Assignee: I. Kruger Inc. (Veolia Environnement SA)
• Original Assignee: I. Kruger Inc. (Veolia Environnement SA)
• Inventors: Schrader, John Charles, Blumenschein, Charles D., Banerjee, Kashi
• Granted Patent: US 7,828,976 B2
• Time in Patent Office: Days
• US Class Current: 210/631
• CPC Class Codes: C02F 1/52 by flocculation or precipitation of suspended impurities C02F1/463 takes precedence
• CPC Class Codes: C02F 1/5245 using basic salts, e.g. of aluminium and iron
• CPC Class Codes: C02F 1/56 Macromolecular compounds
• CPC Class Codes: C02F 2101/105 Phosphorus compounds
• CPC Class Codes: C02F 2209/001 Upstream control, i.e. monitoring for predictive control
• CPC Class Codes: C02F 2209/06 pH
• 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 9/00 Multistage treatment of water, waste water or sewage
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage
• CPC Class Codes: Y10S 210/906 Phosphorus containing

Abstract

A process for removing phosphorus from wastewater wherein an iron or aluminum salt is added to the wastewater. The iron or aluminum salt results in the precipitation of certain iron or aluminum species that include phosphorus adsorption sites. These iron or phosphorus species are settled and become a part of sludge produced in the course of the wastewater treatment process. By recycling substantial portions of the sludge, the concentration of these iron or aluminum species in the wastewater is increased. This increased concentration results in the presence of large quantities of unused phosphorus adsorption sites that attract and adsorb phosphorus, resulting in phosphorus being removed from the wastewater.

Claims

1. A ballasted flocculation process for removing phosphorous from wastewater comprising:

a. adding iron or aluminum salt to influent wastewater;

b. mixing a flocculant with the wastewater;

c. mixing an insoluble granular material with the wastewater that results in the formation of ballasted flocs;

d. directing the wastewater and ballasted flocs to a settling tank and separating clarified effluent from sludge which includes the insoluble granular material and iron or alum;

e. directing the settled sludge to a separator and separating the insoluble granular material from the sludge;

f. concentrating the iron or aluminum in the wastewater by recycling a substantial portion of the iron or aluminum containing sludge and mixing the recycled iron or aluminum containing sludge with the influent wastewater; and

g. removing phosphorous from the wastewater by adsorbing phosphorous onto the iron or alum.

2. The method of claim 1 wherein mixing iron or aluminum salt with the wastewater results in the formation of iron or aluminum adsorption material having phosphorous adsorption sites, and the wherein the sludge includes the iron and aluminum adsorption material and the method further includes continuously recycling the sludge with the iron or aluminum adsorption material and utilizing the phosphorus adsorption sites thereof to adsorb phosphorous.

3. The method of claim 2 wherein the ratio of the iron or aluminum to phosphorous added to the influent wastewater is approximately 15-50 to 1.

4. The method of claim 3 wherein the ratio of the iron or aluminum to phosphorous added to the influent wastewater is approximately 35 to 1.

5. The method of claim 2 including dividing the sludge into at least two streams, a recycle stream and a waste stream, and wherein the recycle stream constitutes at least 90% of the sludge.

6. The method of claim 1 wherein the amount of sludge recycled is based, in part at least, on the amount of solids precipitated from the wastewater by adding the iron or aluminum salt to the wastewater.

7. The method of claim 6 including recycling sludge at a rate such that the solids content of the sludge recycled is approximately 10 to 30 times the solids precipitated from the wastewater by adding the iron or aluminum salt to the wastewater.

8. The method of claim 1 wherein the dosage of iron or aluminum added to the wastewater is a function of the phosphorous concentration of the influent wastewater.

9. The method of claim 8 wherein the sludge recycle rate is based in part at least on the amount of solids precipitated from the wastewater as a result of adding the iron or aluminum salt to the wastewater.

10. The method of claim 2 wherein the concentration of phosphorous in the influent wastewater is greater than 0.7 mg/l and wherein the method includes utilizing the iron or aluminum adsorption material to adsorb phosphorous and produce an effluent having a phosphorous concentration of 0.05 mg/l or less.

11. The method of claim 2 including maintaining the pH of the wastewater at approximately 6.5 to 8.5.

12. The process of claim 2 wherein the ballasted flocculation process is preceded by a biological treatment process, and wherein the ballasted flocculation process functions as a polishing process for removing phosphorous from the effluent of the biological treatment process.

13. The method of claim 7 including recycling sludge at a rate such that the solids content of the sludge recycled is approximately 20 times the solids precipitated from the wastewater by adding the iron or aluminum salt to the wastewater.

14. The method of claim 1 including splitting the sludge into two streams, a recycle stream and a waste stream, and adjusting the flow of the two streams such that the flow of the waste stream is based in part at least on the amount of solids precipitated by adding the iron or aluminum salt.

15. A method of removing phosphorous from wastewater comprising:

adding an iron or aluminum salt to the wastewater;

removing phosphorous from the wastewater by precipitating phosphorous as ferric hydroxyphosphate or aluminum hydroxyphosphate;

in addition to precipitating phosphorous from the wastewater, forming iron or aluminum adsorption material having phosphorous adsorption sites thereon;

clarifying the wastewater and producing a sludge having the iron or aluminum adsorption material therein;

concentrating the iron or aluminum adsorption material in the wastewater by recycling a substantial portion of the sludge having the iron or aluminum adsorption material therein and mixing the recycled sludge with the wastewater being treated; and

removing phosphorous from the wastewater by absorbing phosphorous onto the concentrated iron or aluminum adsorption material in the wastewater.

16. The method of claim 15 including basing, in part at least, the amount of iron or aluminum salt added to the wastewater on the phosphorous concentration of the wastewater before treatment.

17. The method of claim 15 wherein adding the iron or aluminum salt causes solids to be precipitated from the wastewater, and wherein the amount of sludge recycled is based, in part at least, on the amount of solids precipitated by the addition of the iron or aluminum salt.

18. The method of claim 16 wherein the iron or aluminum salt is added to the wastewater in an amount such that the ratio of iron or aluminum to phosphorous is approximately 5-50 to 1.

19. The method of claim 18 wherein the iron or aluminum salt is added to the wastewater in an amount such that the ratio of the iron or aluminum to phosphorous is approximately 35 to 1.

20. The method of claim 15 wherein the sludge includes solids and the method includes recycling sludge at a rate such that the solids content of the sludge recycled is approximately 10-30 times the solids precipitated by adding iron or aluminum salt.

21. The method of claim 20 wherein the amount of sludge recycled is equal to approximately 20 times the amount of solids precipitated from the wastewater by adding the iron or aluminum salt to the wastewater.

22. The method of claim 15 including producing a clarified influent having a phosphorous concentration of 0.05 mg/l or less.

23. The method of claim 15 including selecting a sludge recycle rate, determining the phosphorous concentration in a clarified effluent, and adjusting the sludge recycle rate until the phosphorous concentration in the clarified effluent is 0.05 mg/l or less.

24. The method of claim 15 including maintaining the pH of the water in a range of approximately 6.5 to 8.5.