A new pH-based procedure to model toxic effects on nitrifiers in activatedsludge

A combination of a titration experiment and a biokinetic parameter estimati on procedure is proposed as an experimental tool to study the kinetics of N H4+-oxidizing bacteria in activated sludge; The method was used to quantify the effect of low concentrations of a toxic compound on the maximum substr ate removal capacity and the substrate affinity constant (K-NH) of NH4+-oxi dizing bacteria in activated sludge samples. Experiments in the presence of increasing concentrations of a toxic compound (CN-, 3,5-DCP, Cu2+ and phen ol) were performed with nitrifying activated sludge samples obtained from t wo full-scale wastewater treatment plants. The repeatability of the propose d procedure was found to be sufficient to deduce trends in the behavior of the NH4+-N-oxidizing bacteria based on one series of experiments with incre asing toxicant concentrations. The experimental results showed that the two sludge samples reacted completely differently in the presence of a certain concentration of the same toxic compound. For phenol, the shape of the tit ration curves did not correspond any longer to a simple Monod model. In thi s case, titration curves could be described by a model including both nitri fication inhibition by phenol and degradation of the phenol by heterotrophi c bacteria. (C) 1999 Society of Chemical Industry.