Biological nutrient removal process and process control system for same

1. A method for automatically controlling a treatment process for a liquid, wherein said treatment process comprises subjecting said liquid to an oxic phase, an anoxic phase and an anaerobic phase in a sequential order until a desired level of treatment is achieved, said method for controlling comprising:

a. monitoring the concentration of ammonia, nitrate, phosphate and dissolved oxygen in said oxic phase with an ammonia analyzer, a nitrate analyzer, a phosphate analyzer and a dissolved oxygen analyzer, said analyzers transmitting said ammonia, phosphate and dissolved oxygen concentrations to a processor, and said processor terminating said oxic phase and initiating said anoxic phase when said processor determines an oxic phase ending criteria is met;

b. monitoring the concentration of nitrates and ammonia in the anoxic phase with a nitrate analyzer, and an ammonia analyzer, said analyzers transmitting said nitrate and ammonia concentrations to a processor and said processor terminating the anoxic phase and initiating the anaerobic phase when said processor determines an anoxic phase ending criteria is met;

c. monitoring the concentration of phosphate and ammonia in the anaerobic phase with said phosphate analyzer, and an ammonia analyzer, said analyzers transmitting said concentration to said processor, said processor calculating a rate of change of phosphate concentration and said processor terminating the anaerobic phase and initiating the oxic phase when said processor determines an anaerobic phase ending criteria is met.

2. 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.

3. The method of claim 2 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.

4. The method of claim 2 where on the occurrence of the oxic phase preemptive end, said processor terminates the oxic phase and initiates the anoxic phase.

5. The method of claim 2 where the minimum time period and the maximum time period for the oxic phase are automatically governed using a timer in communication with said processor.

6. The method of claim 5 where the minimum time period for the oxic phase is 30 minutes and the maximum time period for the oxic phase is 12 hours.

7. 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.

8. The method of claim 7 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 5 mg/L or greater.

9. The method of claim 7 where on the occurrence of the anoxic phase preemptive end, said processor terminates the anoxic phase and re-initiates the oxic phase.

10. The method of claim 7 where the minimum time period and the maximum time period for the anoxic phase are automatically governed using a timer in communication with said processor.

11. The method of claim 10 where the minimum time period for the oxic phase is 20 minutes and the maximum time period for the oxic phase is 4 hours.

12. The method of claim 1 where said anaerobic phase ending criteria is selected from the group consisting of: (i) an anaerobic phase endpoint is achieved and the minimum time period for the anaerobic phase has expired; (ii) the maximum time period for the anaerobic phase has expired; and (iii) an anaerobic phase preemptive end criteria is met.

13. The method of claim 12 where said anaerobic phase endpoint is a rate of change of phosphate concentration of substantially 0 mg/L per hour and 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.

14. The method of claim 13 where said rate of change of phosphate concentration is determined after a minimum time period.

15. The method of claim 14 where said minimum time period for the determination of said rate of change of phosphate concentration is automatically governed by a timer in communication with said processor.

16. The method of claim 12 where on the occurrence of the anaerobic phase preemptive end, said processor terminates the anaerobic phase and initiates the oxic phase.

17. The method of claim 12 where the minimum time period and the maximum time period for the anaerobic phase are automatically governed using a timer in communication with said processor.

18. The method of claim 17 where the minimum time period for the anaerobic phase is 10 minutes and the maximum time period for the anaerobic phase is 1.5 hours.

19. The method of claim 1 further comprising the addition of a chemical additive.

20. The method of claim 19 where the chemical additive is a metal salt or a carbon source.

21. The method of claim 20 where the metal salt addition is determined using a rate based approach or a preset approach.

22. The method of claim 21 where said rate based approach comprises using said processor to derive an actual rate of phosphate elimination from the phosphate concentration determined by said phosphate analyzer and comparing said actual rate of phosphate elimination to a target rate of phosphate elimination and adding said metal salt only when said processor determines the actual rate of phosphate elimination is not sufficient to drive the phosphate concentration to substantially 0 mg/L by the end of the oxic phase.

23. The method of claim 22 where the actual rate of phosphate elimination is determined after a preset time period by a timer in communication with said processor.

24. The method of claim 22 where a quantity of metal salt added is determined by the difference between the actual rate of phosphate elimination and the target rate of phosphate elimination.

25. The method of claim 21 where said preset approach comprises using said phosphate analyzer to determine the phosphate concentration and adding a quantity of the metal salt based on the phosphate concentration.

26. The method of claim 19 where the carbon source addition is determined using a rate based approach or a preset approach.

27. The method of claim 26 where said rate based approach comprises using said processor to derive an actual rate of nitrate elimination from the nitrate concentration determined by said nitrate analyzer and comparing said actual rate of nitrate elimination to a target rate of nitrate elimination and adding said carbon source only when said processor determines the actual rate of nitrate elimination is not sufficient to drive the nitrate concentration to substantially 0 mg/L by the end of the anoxic phase.

28. The method of claim 27 where the actual rate of nitrate elimination is determined after a preset time period by a timer in communication with said processor.

29. The method of claim 27 where a quantity of carbon source added is determined by the difference between the actual rate of nitrate elimination and the target rate of nitrate elimination.

30. The method of claim 26 where said preset approach comprises using said nitrate analyzer to determine the nitrate concentration and adding a quantity of the carbon source based on the phosphate concentration.