15This work presents a numerical model able to simulate the effect of biomass growth on the hydrau-16 lic properties of saturated porous media, i.e., bioclogging. A new module for an existing coupled 17 flow and reactive-transport code-PHWAT-was implemented. Laboratory experiments were used to 18 validate the model.. Good agreement with the experimental data was found. Model behavior was 19 satisfactory in terms of numerical discretization errors and parameter calibration, although-grid-20 independent results were difficult to achieve. The new code was applied to investigate the effect of 21 the initial conditions on clogging development. A set of simulations was conducted considering 1D 22 and 2D flow conditions, for both uniform and heterogeneous initial biomass concentrations. The 23 simulation results demonstrated that the rate and patterns of bioclogging development are sensitive 24 to the initial biomass distribution. Thus, the common assumption of an initially uniform biomass 25 distribution may not be appropriate and may introduce a significant error in the modeling results. 26

A fully kinetic biogeochemical model of sequential reductive dechlorination (SERD) occurring in conjunction with lactate and propionate fermentation, iron reduction, sulfate reduction, and methanogenesis was developed. Production and consumption of molecular hydrogen (H(2)) by microorganisms have been modeled using modified Michaelis-Menten kinetics and has been implemented in the geochemical code PHREEQC. The model have been calibrated using a Shuffled Complex Evolution Metropolis algorithm to observations of chlorinated solvents, organic acids, and H(2) concentrations in laboratory batch experiments of complete trichloroethene (TCE) degradation in natural sediments. Global sensitivity analysis was performed using the Morris method and Sobol sensitivity indices to identify the most influential model parameters. Results show that the sulfate concentration and fermentation kinetics are the most important factors influencing SERD. The sensitivity analysis also suggests that it is not possible to simplify the model description if all system behaviors are to be well described.

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