A GENERAL REACTION NETWORK APPROACH FOR MODELING BIOGEOCHEMICAL REACTIVE TRANSPORT

Most biogeochemical reactive transport simulators require reactions and rate laws to be specified in a limited number of canonical forms. In some cases, (e.g., to describe the adsorption process with langmuir isotherm, or to describe the reaction mechanism for pyrite oxidation using shrinking core model, etc.), this requirement is overly restrictive and the simulator must be recoded, not only to accept the new forms, but also to address the construction of corresponding jacobians for the Newton-Raphson solution scheme. A methodology to overcome these difficulties and limitations was recently developed and tested in the BIOGEOCHEM simulator. The simulator interprets symbolic, user-specified equilibrium and kinetic reactions, and rate laws of virtually any type for input to the MAPLE symbolic mathematical software package. MAPLE generates Fortran-90 code for the analytical jacobian expressions which are compiled and linked into the BIOGEOCHEM executable. A reaction network with user-defined expressions for equilibrium reactions and rate laws for kinetic reactions is used to demonstrate the methodology and test the efficiency against numerically approximated jacobians.