The two-stage anaerobic-aerobic treatment is applied by preference for the purification of high-concentrated industrial wastewaters. With regard to the elimination of nitrogen compounds by denitrification the far-reaching reduction of organic carbon during the anaerobic pre-treatment is problematic.

A new process of nitrification/denitrification via nitrite wais found to be available in half-technical experiences with high operation security. The carbon consumption amounts only to 60 % in comparison with denitrification via nitrate. The essential parameter for regulating the process is the concentration of free ammonia in the reactor. Concentrations of 1 to 5 mg NH3/l inhibit the nitratation but not the nitritation. The content of ammonia was controlled by means of continuous NH4− and pH-measuring. The inhibition limit for denitrification was found to be at 0.13 mg HN02/l.

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