Biological nutrient removal process and process control for same
The present disclosure describes an improved system and method for treating wastewater or other liquid. Furthermore, the present disclosure provides a control program for operating the system and method. In one embodiment, the treatment process utilizes a biological nutrient removal activated sludge process utilizing a continuously sequencing reactor (CSR).
1. A method for the biological treatment of a liquid in a single reactor basin containing an activated sludge material, said method comprising the steps of:
a. subjecting said liquid to an oxic phase by creating in said reactor basin an oxygen-rich environment and maintaining said oxygen-rich environment until a oxic phase ending criteria has been achieved;
b. after said oxic phase endpoint has been achieved, subjecting said liquid to an anoxic phase by creating in said reactor basin a limited oxygen environment and maintaining said limited oxygen environment until an anoxic phase ending criteria has been achieved;
c. after said anoxic phase endpoint has been achieved, subjecting said liquid to an anaerobic phase by creating in said reactor basin an oxygen-starved environment and maintaining said oxygen-starved environment until an anaerobic phase ending criteria has been achieved, said anaerobic phase ending criteria selected from the group consisting of: (i) the expiration of the minimum time period for the anaerobic phase and a rate of change of phosphate concentration falling below a pre-set value; and (ii) the occurrence of an anaerobic phase preemptive end criteria, where said anaerobic phase preemptive end criteria is an ammonia concentration of about 5 mg/L or greater or a phosphate concentration of about 3 mg/L or greater;
d. And repeating steps a)-c) until a desired level of treatment of said liquid is achieved.
2. The method of claim 1 where said anaerobic phase generates an increased phosphate release, wherein the uptake of said phosphate contained in such increased phosphate release is enhanced as compared to treatment methods not incorporating said anaerobic phase.
3. The method of claim 2 where said enhancement is a two- to five-fold enhancement.
4. The method of claim 1 where said oxic phase ending criteria is selected from the group consisting of: (i) an oxic phase endpoint is achieved and the minimum time period for the oxic phase has expired; (ii) the maximum time period for the oxic phase has expired; and (iii) an oxic phase preemptive end criteria is met.
5. The method of claim 4 where said oxic phase endpoint is selected from the group consisting of: (i) an ammonia concentration of substantially 0 mg/L; (ii) a soluble phosphate concentration of substantially 0 mg/L; (iii) or both an ammonia and a soluble phosphate concentration of 0 mg/L, and said oxic phase preemptive end criteria is a nitrate concentration of about 5 mg/L or greater.
6. The method of claim 5 where said ammonia concentration and said phosphate concentration are continuously monitored during said treatment to determine when said oxic phase endpoint is achieved.
7. The method of claim 4 where the minimum time period for the oxic phase is about 30 minutes and the maximum time period for the oxic phase is about 12 hours.
8. The method of claim 4 further comprising subjecting said liquid to the anoxic phase on the occurrence of the oxic phase preemptive end.
9. The method of claim 1 where a nitrate concentration increases during said oxic phase.
10. The method of claim 1 where said anoxic phase ending criteria is selected from the group consisting of: (i) an anoxic phase endpoint is achieved and the minimum time period for the anoxic phase has expired; (ii) the maximum time period for the anoxic phase has expired; and (iii) an anoxic phase preemptive end criteria is met.
11. The method of claim 10 where said anoxic phase endpoint is a nitrate concentration of substantially 0 mg/L and said anoxic phase preemptive end criteria is an ammonia concentration of about 3 mg/L or greater.
12. The method of claim 11 where said nitrate concentration is continuously monitored during said treatment to determine when said anoxic phase endpoint is achieved.
13. The method of claim 10 where the minimum time period for the anoxic phase is about 20 minutes and the maximum time period for the oxic phase is about 4 hours.
14. The method of claim 10 further comprising subjecting said liquid to the oxic phase on the occurrence of the anoxic phase preemptive end.
15. The method of claim 1 where an ammonia concentration increases during said anoxic phase.
16. The method of claim 1 where the minimum time period for the anaerobic phase is about 5 minutes.
17. The method of claim 1 further comprising subjecting the liquid to the oxic phase on the occurrence of the anaerobic phase ending criteria.
18. The method of claim 1 where said rate of change of phosphate concentration is determined after a minimum time period.
19. The method of claim 18 where said minimum time period is automatically governed by a timer.
20. The method of claim 1 where an ammonia concentration increases during said anaerobic phase.
21. The method of claim 1 where said method further comprises the addition of a chemical additive during at least one of the oxic phase, the anoxic phase or the anaerobic phase.
22. The method of claim 21 where said chemical additive is selected from the group consisting of a carbon source and a metal salt.
23. The method of claim 22 where said metal salt is added during the oxic phase and said carbon source is added during the anoxic phase, the anaerobic phase or both the anoxic phase and the anaerobic phase.