PROCESS FOR CONTROLLING THE NITRIFICATION AND DENITRIFICATION PHASE

The present invention concerns a process and a device for controlling and regulating the nitrification and denitrification phase in waste water treatment, the redox potential (U.sub.R) of the waste water being measured. In a first embodiment, the inflection point of the redox potential is determined statistically. For this a series of measurements of the redox potential are carried out at separate intervals of time, which measurements first are determined and then combined for determining an increase value. The difference between sequential increase values is compared, and a first switch signal (S1) is generated which contains information concerning this result. In a another embodiment, the difference of the redox potential (U.sub.R) between maximum and switching off the denitrification phase is determined and compared with the corresponding value of the previous measurement cycle. Depending on the comparison result, a second switch signal (S2) is generated. The switch signals (S1, S2) thus obtained also can be connected via a logic circuit, preferably a fuzzy logic, with one another for issuing switch signals (S.sub.D) at least for the ending of the denitrification time.