Method of Removing Phosphorus from Wastewater

• US 20110036772A1
• Filed: 10/26/2010
• Published: 02/17/2011
• Est. Priority Date: 06/22/2007
• Status: Active Grant

• Current Assignee: I. Kruger Inc.
• Original Assignee: I. Kruger Inc.
• Inventors: Schrader, John Charles, Blumenschein, Charles D., Banerjee, Kashi
• Granted Patent: US 8,147,695 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 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 ferric hydroxyphosphate or aluminum hydroxyphosphate from the wastewater, precipitating iron or aluminum phosphorus adsorption species having phosphorous adsorption sites thereon;

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

concentrating the iron or aluminum phosphorus adsorption species in the wastewater by recycling portions of the sludge having the iron or aluminum phosphorus adsorption species 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 phosphorus adsorption species in the wastewater.

2. The method of claim 1 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.

3. The method of claim 1 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.

4. The method of claim 2 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.

5. The method of claim 4 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.

6. The method of claim 1 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.

7. The method of claim 6 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.

8. The method of claim 1 including producing a clarified influent having a phosphorous concentration of 0.05 mg/l or less.

9. The method of claim 1 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.

10. The method of claim 1 including maintaining the pH of the water in a range of approximately 6.5 to 8.5.

11. The method of claim 9 wherein the wastewater, prior to treatment, includes a phosphorus concentration of 0.7 mg/l or more.

12. The method of claim 1 including:

basing, in part at least, the amount of iron or aluminum salt added to the wastewater on the phosphorus concentration of the wastewater before treatment; and

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.

13. The method of claim 1 including:

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; and

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.

14. The method of claim 1 wherein concentrating the iron or aluminum phosphorus adsorption species includes recycling at least 90% of the sludge produced by clarifying the wastewater and mixing the recycled sludge with the wastewater to be treated.

15. The method of claim 1:

wherein the iron or aluminum salt is added to the wastewater in amounts such that the ratio of the iron or aluminum to phosphorus in the wastewater is approximately 5-50 to 1;

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 the iron or aluminum salt; and

wherein the phosphorus concentration in the wastewater before treatment is 0.7 mg/l or greater, and wherein the method substantially removes phosphorus from the wastewater by producing a clarified effluent having a phosphorus concentration of 0.05 mg/l or less.

16. The method of claim 16 wherein the iron or aluminum phosphorus adsorption species include iron hydroxide, iron oxy-hydroxide, aluminum hydroxide, or aluminum oxy-hydroxide.

17. A ballasted flocculation process for removing phosphorus from wastewater, comprising:

directing the wastewater to a mixing tank;

mixing an iron or aluminum salt with the wastewater in the mixing tank;

co-precipitating from the wastewater iron or aluminum hydroxyphosphate and other iron or aluminum phosphorus adsorption species having phosphorus adsorption sites;

mixing a flocculant with the wastewater;

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

directing the wastewater and ballasted flocs to a settling tank and separating clarified effluent from sludge which includes the insoluble granular material, iron or aluminum hydroxyphosphate and the other iron or aluminum phosphorus adsorbing species;

after separating the clarified effluent from the sludge, directing the sludge to a separator and separating the insoluble granular material from the sludge to yield separated sludge;

concentrating the iron or aluminum phosphorus adsorption species in the wastewater by recycling a substantial portion of the separated sludge and mixing the separated sludge with the wastewater causing the wastewater to be concentrated with the iron or aluminum phosphorus adsorption species;

wasting a portion of the separated sludge; and

removing phosphorus from the wastewater by adsorbing phosphorus onto the phosphorus adsorption sites of the iron or aluminum phosphorus adsorption species that are concentrated in the wastewater.

18. The method of claim 17 including concentrating the iron or aluminum phosphorus adsorption species by adding iron or aluminum salt to the wastewater such that the ratio of iron or aluminum to phosphorus added to the wastewater is approximately 15-50 to 1;

and continuously recycling separated sludge and mixing a substantial portion of the separated sludge with the influent wastewater.

19. The method of claim 17, wherein concentrating the iron or aluminum phosphorus adsorption species includes recycling at least 90% of the separated sludge to the mixing tank and mixing the recycled separated sludge with the wastewater.

20. The method of claim 17 wherein the ratio of the iron or aluminum to phosphorous added to the influent wastewater is approximately 35 to 1.

21. The method of claim 17 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.

22. The method of claim 17 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 phosphorus adsorption species to adsorb phosphorous and produce an effluent having a phosphorous concentration of 0.05 mg/l or less.

23. The process of claim 17 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.

24. The method of claim 17 including splitting the separated sludge into two streams, a sludge recycle stream and a sludge waste stream, and adjusting the flow of the two streams such that the flow of the sludge recycle stream is based in part at least on the amount of solids precipitated by adding the iron or aluminum salt.

25. The method of claim 24 wherein adjusting the flow of the sludge recycle stream and sludge waste stream results in the sludge recycle stream including a solids content of approximately 10 to 30 times the solids precipitated from the wastewater by adding the iron or aluminum salt to the wastewater.