Method of controlling a circulation-type wastewater treatment plant via a stored parameter relationship in a control unit

1. A method for controlling a plant for treatment of waste water, wherein the plant comprises:

a basin constituted by a circulation channel and configured to contain waste water,

at least one flow generating machine constituted by a submerged mixer machine that is arranged in the basin and configured to generate a liquid flow in the basin,

equipment arranged in the basin and that effects a momentum of the waste water flowing along the circulation channel, wherein an operational speed N of the flow generating machine is (i) higher than a predetermined lowest allowable operational speed Nmin to prevent solid matter from accumulating on a bottom of the basin, and (ii) lower than a predetermined highest allowable operational speed Nmax to prevent the flow generating machine from becoming overloaded, and

a control unit that is operatively connected to said at least one flow generating machine,

the method including the steps of:

storing a predetermined relationship in the control unit between the operational speed N of the flow generating machine and an operational parameter P, which predetermined relationship depends on a predetermined liquid flow speed V in the basin at the flow generating machine, the operational parameter P being defined as either the torque M of the flow generating machine or an operational parameter from which a torque M of the flow generating machine may be derived,

determining the operational speed N of the flow generating machine,

determining a set value of the operational parameter P of the flow generating machine from the determined operational speed N, the set value based on said predetermined relationship between the operational speed N of the flow generating machine and the operational parameter P of the flow generating machine,

determining a real value of the operational parameter P of the flow generating machine using the control unit by measuring a parameter from which the torque M of the flow generating machine can be derived, and

adjusting the operational speed N of the flow generating machine using the control unit if the real value of the operational parameter P of the flow generating machine is different than the set value of the operational parameter P of the flow generating machine.

2. The method according to claim 1 , wherein the plant comprises a treatment plant for treatment of waste water.

3. The method according to claim 1 , wherein the operational parameter P comprises the torque M of the flow generating machine.

4. The method according to claim 1 , wherein the operational parameter P comprises a current I consumed by the flow generating machine.

5. The method according to claim 1 , wherein the operational speed N of the flow generating machine is increased if the real value of the operational parameter P of the flow generating machine is greater than the set value of the operational parameter P of the flow generating machine.

6. The method according to claim 1 , wherein the operational speed N of the flow generating machine is decreased if the true real value of the operational parameter P of the flow generating machine is less than the set value of the operational parameter P of the flow generating machine.

7. The method according to claim 1 , wherein said equipment comprises a mechanical surface aerator.

8. The method according to claim 7 , wherein the mechanical surface aerator comprises a horizontal rotational axis.

9. The method according to claim 7 , wherein the mechanical surface aerator comprises a vertical rotational axis.

10. The method according to claim 1 , wherein said equipment comprises an aeration sector arranged at a bottom of the basin.