Context
The environmental behavior of trace metals in soils and waters largely depends on the chemical form (speciation) of the metals. Speciation software programs combining models for the binding of metals to soil and sediment constituents are powerful tools in environmental risk assessment. We published a new combination of speciation software ORCHESTRA with the fitting program PEST to optimize geochemical model parameters that describes proton and metal binding to humic substances. The examples provided in this publication will help users to set up their own parameter estimation calculations for the NICA-Donnan model and all other sorption models implemented in ORCHESTRA.
PEST-ORCHESTRA, a tool for optimizing advanced ion-binding model parameters: derivation of NICA-Donnan model parameters for humic substances reactivity
Janot, N., J.P. Pinheiro, W.G. Botero, J.C.L. Meeussen and J.E. Groenenberg
Environmental Chemistry (2016), http://dx.doi.org/10.1071/EN16039
This paper describes the coupling of the chemical speciation software ORCHESTRA with the parameter estimation software PEST. This combination enables the computation of optimized model parameters from experimental data for the ion binding models implemented in ORCHESTRA. For testing this flexible tool the NICA-Donnan model parameters for proton-, Cd- and Zn-binding to Laurentian fulvic acid were optimized. The extensive description of the method implementation and the provided examples facilitate the use of this tool by students and researchers. Three procedures were compared to derive the proton binding parameters, differing in the way they constrain the model parameters and in the implementation of the electrostatic Donnan model. Although the different procedures resulted in significant different sets of model parameters, the experimental data fit obtained was of similar quality. The choice of the relation between the Donnan volume and the ionic strength appears to have a strong influence on the derived set of optimal model parameters, especially on the values of the protonation constants, as well as on the Donnan potential and Donnan volume. Optimized results are discussed in terms of their physico-chemical plausibility. Coherent sets of NICA-Donnan parameters were derived for Cd and Zn binding to Laurentian fulvic acid.
The ORCHESTRA and PEST files of these examples can be downloaded here:
Links to software used
ORCHESTRA. ORCHESTRA is a computer program for calculating chemical speciation and reactive transport. It includes various advanced models for ion binding, such as the NICA-Donnan model for ion binding to dissolved and particulate organic matter and the Generalized Two Layer Model (GTLM) and the CD-MUSIC model for ion binding to iron (hydr)oxides. The program includes databases with default model parameters for a large set of cations for the NICA-Donnan model and default parameters for cations and anions for the GTLM model. For inorganic speciation in solution the Minteq V4.0 database is included. With the graphical user interface of the program chemical equilibrium calculations can be set up by selecting the elements and sorption models. ORCHESTRA is written in Java and runs on Windows, Linux and Apple OSX. A special feature of ORCHESTRA in comparison with other chemical speciation programs is the possibility for users to add (mathematical) expressions and models in text format.
ORCHESTRA can be downloaded free from: www.orchestra.meeussen.nl
This website also provides further information on how to get started with the program and includes various examples
PEST. To be able to derive model-parameters for the sorption models from experimental data the model ORCHESTRA can be used in combination with the freely available parameter estimation program PEST. PEST can be downloaded free from www.pesthomepage.org
For further information contact Bert-Jan Groenenberg bert-jan.groenenberg (at) univ-lorraine.fr / bertjan.groenenberg (at) wur.nl