Monitoring of pH inhibition on microbial activity in a continuous flow reactor by pseudo toxic concentration (C<SUB>PT</SUB>) concept and time delay model

The pseudo toxic concentration (C<SUB>PT</SUB>) concept was introduced as a quantification method to describe pH as an inhibitor concentration. In this research, the applicability of the C<SUB>PT</SUB> concept model for the detection of pH inhibitions was expanded for a continuous flow activated sludge reactor. A pilot equipped with an inhibition detection system was installed. Inhibitory wastewater was injected for 1 h and the relative activity was calculated by the maximum respiration rate. At the same time, the coefficients for the C<SUB>PT</SUB> concept model were estimated. At the dynamic conditions, the estimated relative activity by the C<SUB>PT</SUB> concept model showed time lag compared to the measured one. However, the time lag problem was successfully resolved by introducing a transfer function into the C<SUB>PT</SUB> concept model. The C<SUB>PT</SUB> concept model combined with a transfer function (C<SUB>PT</SUB> + TF model) successfully tracked the variation of the relative activity under dynamic conditions. The C<SUB>PT</SUB> + TF model could detect 50% inhibition faster than the respirometry based method by approximately 10 min. Moreover, it had additional advantages such as being inexpensive, easy to install and simple to operate. In conclusion, the C<SUB>PT</SUB> þ TF model was an effective and convenient detection method of pH inhibition.