REGULATION STRATEGIES
a) Prioritised Regulation of Compressors with NH4-N Measuring Instrument 
Upon output of nitrification, the NH4-N is measured. With the help of this measured value of NH4-N, the desired value of oxygen is passed on from the process control system where all lines can be controlled independently of each other.
If the measured value of NH4-N is smaller than an adjustable minimum (1 mg/l), an adjustable minimal desired value of oxygen (0.8 mg/l) is passed on from the process control system; if the measured value of NH4-N is larger than an adjustable maximum value (2 mg/l), an adjustable desired value of oxygen (2.5 mg/l)is passed on from the process control system; if the measured value of NH4-N is in an interim (1.0 < NH4-N < 2.0), an adjustable mean desired value of oxygen (1.5 mg/l) is passed on from the process control system.
The desired value of oxygen controls the glare-regulating valve in the air conductors, with reliance on the principal deviation. These end in a collector where a manometer controls a frequency regulated rotating piston blower.
The operation has confirmed that through the different desired value of oxygen guidelines, which are determined by the NH4-N measurements, a complete nitrification (98.5 % decomposition) can be guaranteed. For the most part, a minimal desired value of oxygen of 0.80 - 1.0 mg/l (70% of the time) is taken, and only during NH4-N daily maximums and seasonal maximum, a higher desired value of oxygen is controlled. Through this an optimal nitrification, with minimal transfer of oxygen, occurs and thus a minimal demand of electricity from the compressors is guaranteed.
b) Regulation of the Denitrification with NO3-N Measuring Instruments
NO3-N is measured upon outlet of the denitrification. With the help of this measured value of NO3-N, the re-circulation pumps and the bypassing of the preliminary clarification are piloted by the process control system where all lines can be controlled independently of each other. If the measured value of NO3-N is smaller than an adjustable value (3 mg/l), the re-circulation pumps are regulated by the process control system at a maximal value (400% of QDW in influx).
If the measured value of NO3-N is larger than an adjustable value (3 mg/l), the re-circulation pumps are controlled by the process control system at a minimal value (100% of QDW in influx).
If the measured value of NO3-N is still larger than an adjustable value (3 mg/l) at the next measurement (one hour later), the primary clarifiers are additionally dealt with by the process control system so that more carbon enters the denitrification zone. T
he operation has shown that with this regulation strategy, the concentration of nitrate in the outlet can be kept low (yearly mean = 3.65 mg/l).
c)Regulation of Phosphate Precipitation with PO4-P Measuring Instruments 
PO4-P is measured upon outlet of nitrification in influx and outlet of the wastewater treatment plant.
The precipitant dosing takes place in the third cycle of the nitrification. The frequency controlled metering pumps can be regulated according to the following possibilities:
- according to the amount of influx
- according to the PO4-P concentration in the nitrification outlet
- according to the PO4-P loading in influx
- according to pre-set maximal PO4-P loading in outlet
- according to work and break periods
In operation, the regulation of the precipitant metering pumps, according to the PO4-P concentration, has proved to be the most optimal plant management.
d)Regulation of Excess Sludge Extraction
The excess sludge is extracted from the return-sludge stream. A solid matter meter, which is recorded in the process control system, is placed in the nitrification basins.
The regulation of the frequency controlled excess sludge pumps occurs automatically over a given dried matter content. This dried matter content is dependent on the deviation, although it shouldn't fall under a certain adjustable daily minimum.
In addition to these possibilities, a daily quantity can be given, or work and break period can be selected through the process control system. As a further possibility, the regulation of the excess sludge extraction was programmed according to a pre-determined sludge age.
The computer adopts the dried matter excess from the laboratory protocol, the sludge age is pre-determined, dried matterExcess is measured and so the amount of excess sludge is automatically subtracted. This method of regulation covered a period of about four months and functioned flawlessly. At this time, the excess sludge extraction is controlled according to dried matterAeration tank.
e) Regulation of pH Value Activated Sludge Tanks 
A pH measuring devise is installed in each activated sludge tank. A set point value is given in the process control system and depending on the principal deviation, the lime milk metering pumps are controlled. These pumps are equipped with frequency rotary converters.
A lime milk dissolving station with a lime silo, in which lime Ca(OH)2 exists in powder, is added. The metering of lime milk is necessary in order to keep the acid carryover capacity upright and to guarantee nitrification.