Actuators monitoring system for real-time control of nitrification–denitrification via nitrite on long term operation

Abstract A real-time control strategy for SBR was designed in order to control the length of the reaction phases for an integrated nitrification–denitrification process via nitrite, by using an actuators monitoring system instead of monitoring pH or oxygen signals. The real-time control strategy was validated during 220 days at a low dissolved oxygen concentration (1–2.0 mg/L), C/N ratio of 1–2 g COD/g N, and at initial ammonia nitrogen concentrations in a range of 50–600 mg N/L. The aerobic reaction was conducted under control of pH and dissolved oxygen concentration and their manipulated variables: air valve opening and inorganic carbon consumption were used to detect bending points and the end of nitrification, whereas ORP and pH curves were used to detect the end of denitrification. This strategy led to a removal of total nitrogen over 94%, with a nitrite accumulation of 80% and a simultaneous nitrification denitrification of up to 60%. Additionally, a dosage strategy of adding external carbon during denitrification was developed by evaluating the pH derivative, and it was found that the anoxic time was able to reach values as low as 8% of the total reaction time.