Aerated anoxic membrane bioreactor
View Patent ↗A process for treating biological oxygen demand (BOD), nitrogen and phosphorus containing wastewater, wherein the process includes providing wastewater influent to an oxygen-deficit aeration zone having activated sludge and mixing the wastewater influent with the activated sludge in the oxygen-deficit aeration zone to form a mixed liquor. The process further includes transferring the mixed liquor from the oxygen-deficit aeration zone to an oxygen-surplus aeration zone and transferring a portion of the mixed liquor from the oxygen-surplus aeration zone to a membrane filter wherein a filtrate is separated from sludge. In addition, the process includes recycling at least a portion of the sludge to the oxygen-deficit aeration zone as recycled activated sludge.
1. A process for treating BOD, nitrogen, and phosphorus containing wastewater, the process comprising:
providing wastewater influent to an oxygen-deficit aeration zone having activated sludge;
maintaining an oxygen deficit throughout the oxygen-deficit aeration zone by controlling a rate of oxygen supplied to the oxygen-deficit aeration zone to less than a rate of oxygen consumption by micro-organisms in the oxygen-deficit aeration zone;
mixing the wastewater influent with the activated sludge in the oxygen-deficit aeration zone to form a first mixed liquor;
transferring the first mixed liquor from the oxygen-deficit aeration zone to an oxygen-surplus aeration zone;
mixing the first mixed liquor with activated sludge in the oxygen-surplus aeration zone to form a second mixed liquor;
recycling a portion of the second mixed liquor to the oxygen-deficit aeration zone;
transferring a second portion of the second mixed liquor from the oxygen-surplus aeration zone to an anoxic reactor tank;
mixing the second portion of the second mixed liquor with activated sludge in the anoxic reactor tank to form a third mixed liquor;
transferring a portion of the third mixed liquor from the anoxic reactor tank to a membrane filter;
filtering the third mixed liquor to form a filtrate and an activated sludge; and
recycling at least a portion of the activated sludge from the membrane filter to the oxygen-deficit aeration zone.
2. The process according to claim 1 , wherein the oxygen deficit in the oxygen-deficit aeration zone is maintained by controlling aeration in the oxygen-deficit aeration zone.
3. The process according to claim 1 , wherein the recycled activated sludge includes dissolved oxygen.
4. The process according to claim 3 wherein the dissolved oxygen content of the recycled activated sludge is less than 8 mg/L.
5. The process according to claim 3 wherein the dissolved oxygen content of the recycled activated sludge is in a range of from about 4 mg/L to about 8 mg/L.
6. The process according to claim 3 , wherein the dissolved oxygen comprises oxygen provided to the membrane filter.
7. The process according to claim 1 , wherein the aerator device in the oxygen-deficit aeration zone provides at least some oxygen-containing gas and mixing energy to keep the first mixed liquor in suspension.
8. The process according to claim 1 , wherein the second mixed liquor has a dissolved oxygen concentration of at least about 0.5 mg/L.
9. The process according to claim 1 , wherein the oxygen-deficit aeration zone promotes simultaneous nitrification and denitrification.
10. The process according to claim 1 , further comprising recycling a portion of the second mixed liquor to the oxygen-deficit aeration zone for mixing therein with the wastewater and the recycled activated sludge.
11. The process according to claim 10 , wherein recycling a portion of the second mixed liquor to the oxygen-deficit aeration zone comprises recycling a portion of the second mixed liquor directly from an outlet of the oxygen-surplus aeration zone to the oxygen-deficit aeration zone
12. The process according to claim 1 , wherein the overall dissolved oxygen content in the mixed liquor in the oxygen-deficit aeration zone does not exceed about 0.5 mg/L.
13. The process according to claim 1 including the step of providing a source of carbon to the anoxic reactor tank to assist denitrification.
14. The process according to claim 1 , wherein recycling at least a portion of the activated sludge from the membrane filter to the oxygen-deficit aeration zone comprises recycling at least a portion of the activated sludge directly from the membrane filter to the oxygen-deficit aeration zone.
15. The process according to claim 1 , wherein the membrane filter comprises a membrane bioreactor.
16. The process according to claim 1 , wherein at least one of the oxygen-deficit aeration zone, the oxygen-surplus aeration zone, and the anoxic reactor tank includes a mechanical mixer.
17. The process according to claim 1 , wherein the hydraulic residence time for at least one of the first mixed liquor in the oxygen-deficit aeration zone and the second mixed liquor in the oxygen-surplus aeration zone is between two and twelve hours.