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A batch respirometric test was developed to measure the response of activated sludge communities degrading low concentrations of organic chemicals. The low substrate concentrations used in the assay ensure that minimal changes occur in the physiological state of the degrading community. The estimated kinetic parameters are, therefore, extant, that is, representative of the existing condition of the biomass in the continuous bioreactor. Monte Carlo and sensitivity analyses were performed to verify the robustness of the technique for determining unique and accurate estimates of the parameters describing Monod and Andrews kinetics. Application of the technique to a laboratory‐scale activated sludge system showed that kinetic parameter estimates were reproducible and independent of the substrate concentration within the range tested (0.2–4.0 mg/L as chemical oxygen demand [COD]). Low Ks values (<0.1 mg/L as COD) were measured by the assay for the biodegradation of phenol and 4‐chlorophenol, both of which exhibited an inhibitory response (Andrews kinetics). The biodegradation of ethylene glycol, acrylamide, and acetate exhibited Monod kinetics.

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