Simultaneous anoxic biological phosphorus and nitrogen removal with energy recovery

• US 8,685,246 B2
• Filed: 12/30/2010
• Issued: 04/01/2014
• Est. Priority Date: 09/20/2010
• Status: Active Grant

• Current Assignee: American Water Works Company Incorporated
• Original Assignee: American Water Works Company Incorporated
• Inventors: Giraldo, Eugenio
• Primary Examiner(s): Prince, Fred
• Application Number:
  US12/981,984
• Publication Number:
  US 20120067817A1
• Time in Patent Office: 1,188 Days
• Field of Search: 210/603, 210/605, 210/621, 210/623, 210/252, 210/259, 210/903, 210/906
• US Class Current: 210/603
• CPC Class Codes: C02F 2303/10 Energy recovery
• CPC Class Codes: C02F 2303/16 Regeneration of sorbents, filters
• CPC Class Codes: C02F 3/1215 Combinations of activated sludge treatment with precipitation, flocculation, coagulation and separation of phosphates
• CPC Class Codes: C02F 3/1268 Membrane bioreactor systems
• CPC Class Codes: C02F 3/1273 Submerged membrane bioreactors
• CPC Class Codes: C02F 3/28 Anaerobic digestion processes
• CPC Class Codes: C02F 3/2846 using upflow anaerobic sludge blanket [UASB] reactors
• CPC Class Codes: C02F 3/302 Nitrification and denitrification treatment C02F3/308 takes precedence
• CPC Class Codes: C02F 3/307 characterised by direct conversion of nitrite to molecular nitrogen, e.g. by using the Anammox process
• CPC Class Codes: C02F 3/308 Biological phosphorus removal
• CPC Class Codes: Y02E 50/30 Fuel from waste, e.g. synthetic alcohol or diesel
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage
• CPC Class Codes: Y02W 10/30 Wastewater or sewage treatment systems using renewable energies

Abstract

Methods and systems are provided for treating wastewater to simultaneously remove nitrogen, carbon, and phosphorus, while recovering energy in the form of methane and carbon dioxide. An ammonia-containing stream is directed to a pretreatment tank that produces excess sludge, biogas, and a pretreated stream. The pretreated stream has at least 45% less carbon than the ammonia-containing stream. The pretreated stream is then directed to an anoxic tank, which promotes phosphorus release and fermentation of particulate and dissolved organic matter. The mixed liquor is transferred to an aerated tank having low dissolved oxygen concentrations to promote development of phosphorus-release bacteria that is eventually recycled to the anoxic tank by way of the return activated sludge. Simultaneous nitrification, denitrification, and phosphorus release occur in the aerated tank. A membrane tank separates treated effluent from activated sludge in a membrane tank.

Claims

1. A process for treating wastewater to simultaneously remove organic matter, nitrogen, and phosphorus with energy recovery, the process comprising:

providing an ammonia-containing stream in a pretreatment tank that produces, at least, excess sludge, biogas, and a pretreated stream, wherein the pretreated stream has at least 45% less carbon than the ammonia-containing stream, and wherein the biogas comprises at least methane and carbon dioxide;

flowing the pretreated stream and return activated sludge to an anoxic tank operating under anoxic conditions;

mixing the pretreated stream and the return activated sludge in the anoxic tank to form a mixed liquor, thereby initiating phosphorus release and fermentation of particulate organic matter and dissolved organic matter;

transferring the mixed liquor to an aerated tank operating under microaerophilic conditions, wherein a concentration of dissolved oxygen in the aerated tank is less than 1.0 mg/l of the mixed liquor, which is effective to promote simultaneous nitrification, denitrification, phosphorous release, and phosphorus uptake in the aerated tank; and

transferring the mixed liquor to a membrane tank that separates treated effluent from activated sludge containing microorganisms, wherein a first portion of the activated sludge is returned to the anoxic tank as the return activated sludge.

2. The process of claim 1, wherein the ammonia-containing stream is plant influent wastewater that is to be treated by converting the ammonia to nitrogen gas and water.

3. The process of claim 1, wherein the biogas comprises about 60% of the methane.

4. The process of claim 1, wherein the pretreatment tank is an upflow anaerobic sludge blanket (UASB) reactor.

5. The process of claim 2, wherein the biogas is treated such that it can be used to power a wastewater treatment plant that treats the plant influent wastewater by offsetting energy requirements of the wastewater treatment plant.

6. The process of claim 1, wherein the microaerophilic conditions in the aerated tank promote the fermentation of the particulate organic matter in the mixed liquor and allow for development of a microbial population used for phosphorus removal.

7. The process of claim 1, wherein a portion of the ammonia-containing stream bypasses the pretreatment tank and is directed to the anoxic tank.

8. The process of claim 1, wherein the pretreatment tank utilizes chemically enhanced primary treatment (CEPT).

9. The process of claim 1, wherein the pretreatment tank utilizes a one-stage activated sludge system.

10. A method for reducing ammonia in a stream while recovering energy, the method comprising:

providing a stream containing ammonia in a pretreatment tank that comprises anaerobic microorganisms that react with the ammonia-containing stream to produce biogas and a pretreated stream;

contacting the pretreated stream with an oxygen-containing stream in an anoxic tank under effective treatment conditions to form a first product stream, the ratio of ammonia in the pretreated stream to oxygen in the oxygen-containing stream being about 2.28 g O₂/g N—

NH₃ (2.28 grams of oxygen per gram of nitrogen in ammonia) or less; and

exposing the first product stream to organic matter in an aerated tank under effective treatment conditions in a ratio of about 0.57 g COD/g N—

NH₃ (0.57 grams of chemical oxygen demand (COD) per gram of nitrogen in ammonia) or less.

11. The process of claim 10, wherein the biogas comprises at least 45% of the carbon present in the ammonia-containing stream.

12. The process of claim 10, wherein phosphorus release occurs in the anoxic tank.

13. The process of claim 10, wherein nitrification, denitrification, phosphorus release, and phosphorus uptake occur simultaneously in the aerated tank.

14. The process of claim 10, wherein a concentration of dissolved oxygen in the aerated tank is less than 1.0 mg/l of fluid.

15. A system for treating wastewater to simultaneously remove organic matter, nitrogen, and phosphorus with energy recovery, the system comprising:

a pretreatment tank that receives plant influent wastewater and that comprises anaerobic microorganisms that reacts with the plant influent wastewater to produce, at least, biogas comprising methane, excess sludge, and a pretreated stream, the pretreated stream having at least 45% less carbon than the plant influent wastewater;

an anoxic tank that receives the pretreated stream and return activated sludge, wherein the anoxic tank operates under anoxic conditions to promote denitrification, phosphorus release and fermentation of particulate organic matter and dissolved organic matter;

an aerated tank that receives a mixed liquor from the anoxic tank, wherein a concentration of dissolved oxygen in the aerated tank is less than 1.0 mg/l to effectively promote development of phosphorus-release bacteria that is present in the return activated sludge received into the anoxic tank, and wherein the phosphorus-release bacteria in the return activated sludge allows for the phosphorus release and fermentation of particulate organic matter in the anoxic tank; and

a membrane tank that separates plant effluent wastewater from activated sludge, a portion of which is recycled to the anoxic tank as the return activated sludge.

16. The system of claim 15, wherein the aerated tank comprises one or more aerated tanks.

17. The system of claim 15, wherein the aerated tank operates under microaerophilic conditions.

18. The system of claim 17, wherein nitrification, denitrification, phosphorus release, and phosphorus uptake occur simultaneously in the aerated tank.

19. The system of claim 15, wherein the concentration of dissolved oxygen in the second tank is less than 0.3 mg/l of the mixed liquor.