INTECH   27907
Unidad Ejecutora - UE
congresos y reuniones científicas
Natural Time Scales of the Monod type kinetics: experimental support by photocatalysis and oxygen consumption in saturated porous media
Congreso; InterPore 2019; 2019
Institución organizadora:
Universitat Politécnica de Valencia
An accurate characterization of kinetic parameters related to degradation processes in saturated porous media is key for a proper modeling of reactive solute transport and the coupled mixing and dispersion processes. Degradation processes, as well as microbial growth, are often described by non-linear kinetics with consumption rate laws, r = ±dC/dt, of the form r = kKC / (1 + KC). This is the case, for example, of: (1) the Monod model, describing degradation processes related to organic matter preservation, denitrifcation or trace metal speciation and mobility linked to the iron cycle in shallow-water sediment, (2) the Langmuir-Hinselwook (L-H) model, describing heterogeneous catalysis processes and widely used in water treatment or, (3) the Michaellis?Menten (M-M) model describing enzymatic catalysis. The kinetic parameters k ([M][T]-1) and K ([M]-1) are commonly estimated from measured time (t) series of the reactant concentration (C) using non-linear regression analysis. However, data heterogeneity in time, low data density and the intrinsic non-linearity of the method can result in a substantial parameter uncertainty. By identifying the Natural Time Scales (NTS) of the general reactive Monod type cycles, this work presents a new procedure, the NTS method, to extract robust kinetic information from arbitrary distributed experimental reactant concentration-time data. Two natural scales are identified: (i) tf=kK, describing the fastest time to perform one run of the catalytic cycle, and (ii) ts=C0/k, the slowest time it would take to chemically transform an initial amount of matter, being C0 the initial concentration. Thus, the reactive transport equation results in a linear combination of functions weighted by the tf and ts time scales, from which the kinetic parameters can be easily computed using a linear regression. The NTS method has been first tested using experimental data from the heterogeneous photocatalysis of naphthalene (as reactant) and TiO2 (as photocatalyst) in a tubular bench reactor under different physical, chemical and flow conditions. Then, the method was tested using field measurements of the dissolved oxygen (DO) consumption in heterogeneous sediments of a shallow lagoon under different climate conditions. In both cases, the NTS method shows an excellent behavior, with smaller regression errors than those of the standard non-linear analysis. Moreover, the density, distribution or extension of the data has no significant influence on the estimation of the kinetic parameters.Finally, the Kinetic Family (KF) concept is presented to analyze the roll of the inhibition factor, KC, on the natural time scales (tf to ts ) calculated for the two study cases. The KF concept is probed to be useful to analyze the influence of physicochemical variables, such as flow, radiance and temperature, on the NTS and the kinetic behaviour of complex biogeochemical processes.