Simultaneous nitrification/denitrification (SNDN) in sequencing batch reactor applications

1. A method of operating a sequencing batch reactor process comprising:

introducing wastewater to be treated into the sequencing batch reactor; and

subjecting the wastewater to treatment in the sequencing batch reactor in an aerated anoxic mode in which a quantity of oxygen is supplied at a level insufficient to meet a biological oxygen demand of the wastewater, but sufficient to cause simultaneous nitrification and denitrification reactions to occur in the wastewater, the sequencing batch reactor being operated in a first treatment regime for a first set amount of time, in a second treatment regime immediately following the first treatment regime for a second set amount of time less than the first set amount of time, and in a third treatment regime immediately following the second treatment regime for a third set amount of time less than the second set amount of time, a concentration of dissolved oxygen in the wastewater being maintained at or below an average of between 0.2 mg/L and 0.4 mg/L throughout operation in the first treatment regime, the concentration of dissolved oxygen in the wastewater being maintained at or below an average of between 0.5 mg/L and 0.8 mg/L throughout operation in the second treatment regime, the treatment of the wastewater in the sequencing batch reactor not including introducing sludge from any treatment process downstream of the sequencing batch reactor into the sequencing batch reactor.

2. The method of claim 1 , further comprising operating the sequencing batch reactor the first, second, and third treatment regimes within a single operation cycle, each of the first, second, and third treatment regimes being characterized by a different concentration of dissolved oxygen in the wastewater.

3. The method of claim 2 , wherein the sequencing batch reactor is operated in the first treatment regime with the concentration of dissolved oxygen in the wastewater at a first level, operated in the second treatment regime with the concentration of dissolved oxygen in the wastewater at second level higher than the first level, and operated in the third treatment regime with the concentration of dissolved oxygen in the wastewater at third level higher than the second level.

4. The method of claim 3 wherein operating the sequencing batch reactor in the first treatment regime and operating the sequencing batch reactor in the second treatment regime each include maintaining the concentration of dissolved oxygen in the wastewater at a level sufficient to provide for simultaneous nitrification and denitrification to occur in the wastewater.

5. The method of claim 4 , wherein operating the sequencing batch reactor in the third treatment regime includes maintaining the concentration of dissolved oxygen in the wastewater at a level greater than a concentration at which denitrification occurs in the wastewater.

6. The method of claim 5 , further comprising:

measuring the concentration of dissolved oxygen in the wastewater; and

maintaining the concentration of dissolved oxygen in the wastewater at single predetermined setpoints in each of the first, second, and third treatment regimes.

7. The method of claim 6 , wherein the concentration of dissolved oxygen in the wastewater is maintained between 1.8 mg/L and 2.2 mg/L in the third treatment regime.

8. The method of claim 6 , wherein maintaining the concentration of dissolved oxygen in the wastewater at the single predetermined setpoints in each of the first, second, and third treatment regimes includes modulating flow of an oxygen-containing gas into the wastewater in response to results of comparisons between measured dissolved oxygen concentrations of the wastewater and the predetermined setpoints.

9. The method of claim 1 , further comprising performing a settling operation, a decant operation, and an idle operation in the sequencing batch reactor immediately following operating in the third treatment regime.

10. The method of claim 9 , wherein the sequencing batch reactor is operated in the first treatment regime during filling of the sequencing batch reactor.

11. The method of claim 10 , wherein the second treatment regime is conducted immediately following the first treatment regime and through completion of filling of the sequencing batch reactor and continues through a first portion of a react step, and the third treatment regime begins immediately after the second treatment regime and through completion of the react step.