A General-Purpose Multiphase and Multicomponent Computational Solver for Biogeochemical Reaction-Advection-Dispersion Processes in Porous and Non-Porous Media (No. R954)

Abstract

Abstract This document describes the functioning principles and practical use of BRTSim framework at its version 1 stage of development. BRTSim (BioReactive Transport Simulator) is a general‐purpose multiphase and multicomponent computational solver for biogeochemical reaction‐advection‐dispersion processes in porous and non‐porous media. BRTSim finds suitable applications to describe water flow in soils and geophysical media, to track transport and dispersion of aqueous and gaseous chemicals, as well as to assess their chemical equilibrium and their decomposition rates in both chemical and biochemical reactions. For these characteristics, BRTSim is an extraordinary computational tool in soil physics and biogeochemistry, soil and water quality assessment and prediction, soil bio‐ and phyto‐remediation potential estimation, and in all environmental engineering contexts where physical, chemical and biological processes co‐exist and affect each other with complex nonlinear feedbacks. BRTSim allows defining a geophysical domain with an arbitrary number of grid elements nodes that may be heterogeneous in their physical and hydraulic properties; BRTSim allows full control of initial and boundary conditions, and allows defining a biogeochemical system with an arbitrary number of primary aqueous species, secondary aqueous species, gaseous and mineral species (in chemical equilibrium with primary species), and biological microbial functional groups with any specific metabolic requirement. Chemical and biochemical reactions can be defined for any kinetics framework and order. BRTSim version 1 bases on solvers that have been largely tested, but because of its potentiality, it is under continuing development and improvement in numerical accuracy, robustness, reliability, and computational performance. It is to be noted that, although all methods used to solve physical and chemical processes follow recommendations and methods largely accepted in the scientific literature, the integration of diverse processes, each one requiring time scales that may largely vary from any other, may have potential defects. BRTSim, as a consequence, is also a platform where newly developed algorithms are implemented and tested to improve older and less performing algorithms. Iteration number and tolerances can be set for the various processes but it is practically impossible to exhaustively cross‐check mutual compatibility. The BRTSim framework is therefore designed to allow the user to correct potential instabilities, which depend on the specific problem to be solved, and set the numerical solvers to converge by criteria with an arbitrary level of accuracy.