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Practical identifiability of biokinetic parameters of a model describing two‐step nitrification in biofilms
Author(s) -
Brockmann D.,
Rosenwinkel K.H.,
Morgenroth E.
Publication year - 2008
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.21932
Subject(s) - identifiability , collinearity , nitrification , sensitivity (control systems) , analytical chemistry (journal) , physics , mathematics , statistics , combinatorics , thermodynamics , chemistry , environmental chemistry , nitrogen , quantum mechanics , electronic engineering , engineering
Parameter estimation and model calibration are key problems in the application of biofilm models in engineering practice, where a large number of model parameters need to be determined usually based on experimental data with only limited information content. In this article, identifiability of biokinetic parameters of a biofilm model describing two‐step nitrification was evaluated based solely on bulk phase measurements of ammonium, nitrite, and nitrate. In addition to evaluating the impact of experimental conditions and available measurements, the influence of mass transport limitation within the biofilm and the initial parameter values on identifiability of biokinetic parameters was evaluated. Selection of parameters for identifiability analysis was based on global mean sensitivities while parameter identifiability was analyzed using local sensitivity functions. At most, four of the six most sensitive biokinetic parameters were identifiable from results of batch experiments at bulk phase dissolved oxygen concentrations of 0.8 or 5 mg O 2 /L. High linear dependences between the parameters of the subsets ${\rm (}K_{{\rm O}_{\rm 2} {\rm ,AOB}} {\rm ,}\,\mu _{{\rm AOB}} {\rm )}$ and ${\rm (}K_{{\rm O}_{\rm 2} {\rm ,NOB}} {\rm ,}\,\mu _{{\rm NOB}} {\rm )}$ resulted in reduced identifiability. Mass transport limitation within the biofilm did not influence the number of identifiable parameters but, in fact, decreased collinearity between parameters, especially for parameters that are otherwise correlated (e.g., µ AOB and $K_{{\rm O}_{\rm 2} {\rm ,AOB}} $ , or µ NOB and $K_{{\rm O}_{\rm 2} {\rm ,NOB}} $ ). The choice of the initial parameter values had a significant impact on the identifiability of two parameter subsets, both including the parameters µ AOB and $K_{{\rm O}_{\rm 2} {\rm ,AOB}} $ . Parameter subsets that did not include the subsets µ AOB and $K_{{\rm O}_{\rm 2} {\rm ,AOB}} $ or µ NOB and $K_{{\rm O}_{\rm 2} {\rm ,NOB}} $ were clearly identifiable independently of the choice of the initial parameter values. Biotechnol. Bioeng. 2008;101: 497–514. © 2008 Wiley Periodicals, Inc.