Consequences of Different Kinetic Approaches for Simulation of Microbial Degradation on Contaminant Plume Development

Abstract

This study investigates the consequences of assuming different kinetic approaches for calculation of microbial degradation on plume development in a simple case of natural attenuation on field scale. If the required parameters are properly chosen, all approaches can simulate similar plumes for a particular given time step. The differences of contaminant concentrations in the plumes are small and would not attract attention in a natural aquifer. On long term prognoses the kinetics result in very different plumes: A complex Monod approach considering microbial growth prognoses a further spreading of the plume, compared to a first order rate law, which results in a short and early stationary plume. Other approaches show plumes between these two extremes. On the other hand, the forecasts for plumes assuming Monod kinetics are similar, even if different values for parameterization are chosen. The reason for this insensibility is, that degradation is not limited by microbial kinetics in the simulation, but by dispersive mixing. Simplifying approaches may have few and well determinable parameters, but they are not suited for proper prognoses if they neglect the prerequisite, that contaminant and electron acceptor have to be present for a reaction.