Regulation of Denitrification Using Continually Measured ORP and pH Signal

The use of pH and oxidation-reduction potential (ORP) as control parameters for the nitrificationdenitrification process is compared and discussed. The signals were measured in a sequencing batch reactor activated sludge system and in a completely mixed activated sludge reactor. The termination of denitrification was clearly identified not only by an ORP signal, but also by a pH signal. However, in some cases the ORP measurement failed (e.g. in the case of high organic substrate concentrations in the system). pH measurement failed in the case of low substrate concentration or under the conditions of endogenous denitrification. The combined measurement of pH and ORP signals is proposed to indicate the end of denitrification as a result.