Mathematical modeling of precipitation and dissolution reactions in microbiological systems

We expand the biogeochemical model CCBATCH to include a precipitation/dissolution sub-model that contains kinetic and equilibrium options. This advancement extends CCBATCH's usefulness to situations in which microbial reactions cause or are affected by formation or dissolution of a solid phase. The kinetic option employs a rate expression that explicitly includes the intrinsic kinetics for reaction ormass-transport control, the differencefrom thermodynamic equilibrium, and the aqueous concentration of the rate-limiting metal or ligand. The equilibrium feature can be used alone, and it also serves as check that the kinetic rate never is too fast and ``overshoots' equilibrium. The features of the expanded CCBATCH are illustrated by an example in which the precipitation of Fe(OH)_3(s) allows the biodegradation of citric acid, even though complexes are strong and not bioavailable. Precipitation releases citrate ligand, and biodegradation of the citrate increases the pH.