Formulation of the CBC-model for modelling the contaminants and footprints in natural attenuation of BTEX

This paper provides the details of the Coupled Biological and Chemical (CBC) model for representing {\it in situ} bioremediation of BTEX. The CBC model contains novel features that allow it to comprehensively track the footprints of BTEX bioremediation, even when the fate of those footprints is confounded by abiotic reactions and complex interactions among different kinds of microorganisms. To achieve this comprehensive tracking of all the footprints, the CBC model contains important new biological features and key abiotic reactions. The biological module of the CBC-model includes these important new aspects: (1) it separates BTEX fermentation from methanogenesis, (2) it explicitly includes biomass as a sink for electrons and carbon, (3) it has different growth rates for each biomass type, and (4) it includes inhibition of the different reactions by other electron acceptors and by sulfide toxicants. The chemical module of the CBC-model includes abiotic reactions that affect the footprints of the biological reactions. In particular, the chemical module describes the precipitation/dissolution of CaCO ₃, Fe ₂O ₃, FeS, FeS ₂, and S°. The kinetics for the precipitation/dissolution reactions follow the critical review in Maurer and Rittmann (2003a).