In order to support environmental scientists in finding an "adequate" model of the system they are investigating, a computer program is necessary, which allows its users to perform simulations using different models, to assess the identifiability and to estimate the values of model parameters (using measured data), and to estimate prediction uncertainty. The computer program AQUASIM was developed to perform such analyses for technical and natural aquatic systems.
AQUASIM allows its users to define the spatial configuration of the system to be investigated as a set of compartments, which can be connected to each other by links. Currently, the available compartment types include mixed reactors, biofilm reactors (consisting of a biofilm and a bulk fluid phase), advective-diffusive reactors (e.g. plug flow with or without dispersion) and river sections (describing water flow and substance transport and transformation in open channels). It is planned to extend this set of compartment types in future versions of the program. Compartments can be connected by two types of links. Advective links represent water flow and advective substance transport between compartments, including bifurcations and junctions. Diffusive links represent boundary layers or membranes, which can be penetrated selectively by certain substances. The user of the program is free in specifying any set of state variables and transformation processes to be active within the compartments. For the model as defined by the user, the program is able to perform simulations, sensitivity analyses and parameter estimations using measured data. These features make the program a very useful research tool. Calculated results can be plotted to the screen (window interface version only), written to a PostScript file for transfer to a printer, or written to a text file for external postprocessing.
Due to the possibility of starting with a simple model and gradually increasing model complexity later on by considering additional variables and processes, AQUASIM is also well suited for application by students in exercises accompanying a lecture on environmental modelling. The possibility of comparing different models and the capability of the program to estimate the uncertainty of calculated results (for a given, certain model) also stimulate discussions on the limits of the reliability of model predictions.
Three versions of the program are available. The window interface version (w) uses the graphical user interface of a machine, the character interface version (c) can be run on a primitive teletype terminal, and the batch version (b) is designed for long calculations to be submitted as batch jobs.
Reichert, P., "Design techniques of a computer program for the identification of processes and the simulation of water quality in aquatic systems", to appear in Environmental Software 10, 1995.
Reichert, P., von Schulthess, R. and Wild, D., "The use of AQUASIM for estimating parameters of activatReichert, P., von Schulthess, R. and Wild, D., "The use of AQUASIM for estimating parameters of activated sludge systems", Water Sci. Tech., 31(2), 135-147, 1995. ed sludge systems", Water Sci. Tech., 31(2), 135-147, 1995.
Reichert, P., Concepts underlying a computer program for the identification and simulation of aquatic systems, Schriftenreihe der EAWAG Nr. 7, Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Dübendorf, Switzerland, 386 p., 1994.