the invention is a method and an apparatus for continuously controlling denitrification in wastewater purification in a sewage treatment plant having at least one denitrification stage under varying nitrogen loads comprising the steps a ) provision of excess sludge , b ) treatment of the excess sludge according to running parameters determined in advance , c ) separation of the treated excess sludge into an organic fraction and an inorganic fraction , d ) measurement of actual values for dissolved organic carbon in the organic fraction , e ) recirculation of the organic fraction to one of the denitrification stages , f ) comparison of actual values with predetermined setpoint values for doc fractions and , in the event of difference between actual values and setpoint values , determination of altered running parameters for treatment of the excess sludge in step b ), g ) repetition of steps a ), to f ).