Optimizing experimental design to estimate ammonia and nitrite oxidation biokinetic parameters from batch respirograms

Knowledge of relative NH4+–N to NO2−–N oxidation and NO2−–N to NO3−–N oxidation dynamics is essential before application of either single-step or two-step nitrification models to fit batch nitrification respirograms. We have previously shown that two step nitrification models based on respirometry permit the estimation of kinetic parameters for both nitrification steps from a single respirogram associated with NH4+–N to NO3−–N oxidation. However, two-step model parameter estimates are meaningful only under circumstances when the respirograms contain sufficient kinetic information pertaining to both steps. In this study, we present an operationally amenable extant batch nitrification respirometric assay to engender maximal information content in the resulting respirograms with respect to both constituent nitrification steps. The developed design consists of an initial NH4+–N pulse to a nitrifying biomass sample followed by an additional NO2−–N pulse at an optimal time point, which can be rigorously determined by maximizing the value of the determinant of the Fisher information matrix, Det(F) or, alternatively, by visually identifying the point of NH4+–N depletion during the respirometric assay. The proposed design is applicable for accurate determination of the Monod kinetic parameter estimates for both nitrification steps from batch respirograms even when the pseudo-first order rate coefficients for the two nitrification steps are nearly equal; a condition under which standard NH4+–N to NO3−–N respirograms typically lack information with respect to NO2−–N oxidation.