Systems and methods for treating wastewater

1. A wastewater treatment system comprising:

one or more aeration tanks for receiving wastewater;

a controller for controlling the amount of air delivered to each of the one or more aeration tanks by a blower assembly; and

a sensor assembly for periodically measuring values corresponding to the amount of dissolved oxygen in at least one of the one or more aeration tanks, wherein:

when the sensor assembly measures values that are less than a low setpoint value, the controller causes the blower assembly to incrementally deliver more air until the sensor assembly measures values that are not less than the low setpoint value;

when the sensor assembly measures values that exceed the low setpoint value, the controller causes the blower assembly to incrementally deliver less air until either the sensor assembly measures values that are not greater than the low setpoint value, or the blower assembly reaches a preselected low operating threshold; and

when the blower assembly is operating at the preselected low operating threshold, and the sensor assembly measures values that exceed a high setpoint value for a first designated period of time, the controller causes the blower assembly to shut down for a second designated period of time.

2. The wastewater treatment system of claim 1 , wherein the low setpoint value corresponds to a dissolved oxygen concentration in at least one aeration tank that is between about 0.1 mg/L and about 4.0 mg/mL.

3. The wastewater treatment system of claim 1 , wherein the high setpoint value corresponds to a dissolved oxygen concentration in at least one aeration tank that is between about 0.5 mg/mL and about 5.0 mg/mL.

4. The wastewater treatment system of claim 1 , wherein when the blower assembly is operating at the preselected low operating threshold, the blower assembly delivers sufficient air to agitate biosolids in each tank receiving air from the blower assembly.

5. The wastewater treatment system of claim 1 , wherein the preselected low operating threshold is dependent on the operating mode of the controller.

6. The wastewater treatment system of claim 1 , wherein the one or more aeration tanks include a first aeration tank adapted to receive wastewater, and a second aeration tank adapted to receive wastewater from the first aeration tank, and wherein the controller operates in a plurality of modes including a first mode that causes the blower assembly to deliver air to the first aeration tank but not to the second aeration tank, and a second mode that causes the blower assembly to deliver air to the second aeration tank but not to the first aeration tank.

7. The wastewater treatment system of claim 6 , further comprising an anoxic tank for receiving an influent of wastewater containing biosolids and ammonia, wherein the first aeration tank is adapted to receive wastewater from the anoxic tank.

8. The wastewater treatment system of claim 7 , further comprising:

a third aeration tank adapted to receive wastewater from the anoxic tank; and

a fourth aeration tank adapted to receive wastewater from the third aeration tank.

9. The wastewater treatment system of claim 8 , wherein when the controller is in the first mode, the controller causes the blower assembly to deliver air to the third aeration tank but not to the fourth aeration tank, and when the controller is in the second mode, the controller causes the blower assembly to deliver air to the fourth aeration tank but not to the third aeration tank.

10. The wastewater treatment system of claim 8 , wherein when the controller is in the first mode, the controller causes the blower assembly to deliver air to the fourth aeration tank but not to the third aeration tank, and when the controller is in the second mode, the controller causes the blower assembly to deliver air to the third aeration tank but not to the fourth aeration tank.

11. A method of treating wastewater, the method comprising:

receiving an influent of wastewater;

aerating the wastewater while periodically measuring values corresponding to the amount of dissolved oxygen in the wastewater;

when the measured value is less than a designated lower limit, incrementally increasing the amount of aeration until the measured value is not less than the lower limit;

when the measured value is greater than the lower limit, incrementally decreasing the amount of aeration until either the measured value is not greater than the lower limit or a designated low aerating threshold has been reached; and

when the designated low aerating threshold has been reached, and the measured value is greater than a designated upper limit for a first designated period of time, terminating aerating for a designated period of time.

12. The method of claim 11 , wherein the lower limit corresponds to an amount of dissolved oxygen between about 0.1 mg/L and about 4.0 mg/mL.

13. The method of claim 11 , wherein the upper limit corresponds to an amount of dissolved oxygen between about 0.5 mg/L and about 5.0 mg/mL.

14. The method of claim 11 , wherein a blower assembly is used to aerate the wastewater.

15. The method of claim 14 , wherein the designated low aerating threshold has been reached when the blower assembly is operating at a preselected low operating threshold, and wherein when the blower assembly is operating at the preselected low operating threshold, the blower assembly is delivering sufficient air to agitate biosolids in each tank receiving air from the blower assembly.

16. The method of claim 11 , wherein the preselected low operating threshold is dependent on the operating mode of the controller.

17. The method of claim 11 , comprising receiving wastewater in a first aeration tank, and receiving wastewater in a second aeration tank from the first aeration tank, wherein the step of aerating the wastewater comprises aerating the wastewater in the first aeration tank while not aerating the wastewater in the second aeration tank, and aerating the wastewater in the second aeration tank while not aerating the wastewater in the first aeration tank.

18. The method of claim 17 , wherein a blower assembly is used to aerate the wastewater.

19. The method of claim 17 , wherein the influent of wastewater is received into an anoxic tank, and wherein the step of receiving wastewater in the first aeration tank comprises receiving wastewater in the first aeration tank from the anoxic tank.

20. The method of claim 19 , further comprising:

receiving wastewater in a third aeration tank from the anoxic tank; and

receiving wastewater in a fourth aeration tank from the third aeration tank.

21. The method of claim 20 , further comprising either aerating the wastewater in the first and third aeration while not aerating the wastewater in the second and fourth aeration tanks, or aerating the wastewater in the first and fourth aeration tanks while not aerating the wastewater in the second and third aeration tanks.