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

Abstract

A combination of a titration experiment and a biokinetic parameter estimation procedure is proposed as an experimental tool to study the kinetics of NH 4 -oxidizing bacteria in activated sludge. The method was used to quantify the effect of low concentrations of a toxic compound on the maximum substrate removal capacity and the substrate af®nity constant (K NH ) of NH 4 -oxidizing bacteria in activated sludge samples. Experiments in the presence of increasing concentrations of a toxic compound (CN À , 3,5-DCP, Cu 2 and phenol) were performed with nitrifying activated sludge samples obtained from two full-scale wastewater treatment plants. The repeatability of the proposed procedure was found to be suf®cient to deduce trends in the behavior of the NH 4 -N-oxidizing bacteria based on one series of experiments with increasing 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 titration curves did not correspond any longer to a simple Monod model. In this case, titration curves could be described by a model including both nitri®cation inhibition by phenol and degradation of the phenol by heterotrophic bacteria.

Response of Nitrobacter spp. Ribosomal Gene and Transcript Abundance Following Nitrite Starvation and Exposure to Mechanistically Distinct Inhibitors

“…Solid black lines are SigmaPlot fits of the combined inhibition data (four-parameter sigmoid model for the 3,5-DCP and H + data, three-parameter logistic model for the azide data). Previously published 3,5-DCP inhibition results are provided for AOB (gray, open diamond , gray, open, inverted triangle , gray, open triangle, and gray open box ) and mixed or heterotrophic cultures (gray, filled, inverted triangle , gray, filled triangle , gray, filled circle , and gray, filled square ). Previously published azide inhibition results for NOB (open circle and open triangle ) are provided.…”

Testing the toxicity of influents to activated sludge plants with the Vibrio fischeri bioassay utilising a sludge matrix

“…The extent of the response will depend on the quality of the microbial population with some microorganisms being more sensitive than others to a particular compound challenge. Nitrifiers, for example, are considered one of the most sensitive groups in activated sludge and other environments and are affected by various toxic compounds (Gernaey et al, 1999). One factor affecting toxicity relates to toxicant immobilisation owing to sorption onto flocs containing mineral and organic constituents.…”

Acute and Chronic Toxicity of Acid Mine Drainage to the Activated Sludge Process

“…Although differences between toxic effects on sludge from different source WWTPs have been reported elsewhere (Gernaey et al 1999), many previous studies have found that activated sludge from different sources can be used indistinctly in toxicity studies, giving similar results in respiration inhibition tests (Christofi et al 2000;Dalzell and Christofi 2002;Gutiérrez et al 2002). The EC 50 results using Swords activated sludge and Leixlip II activated sludge sampled on different dates indicated that the toxic effect of synthetic AMD to activated sludge sampled from a single WWTP can also change significantly over time.…”