Monod Kinetics for Aerobic Biodegradation of Calcium Magnesium Acetate

Monod kinetics were used to recalibrate published sets of soil microcosm data that document the aerobic biodegradation of calcium magnesium acetate in a highway shoulder. The natural attenuation is important because acetate can exert an appreciable oxygen demand on ground-water if it persists from the ground surface to the water table. Biomass dynamics were modeled, as well as acetate degradation, in the assumed abundance of oxygen and nutrients. The maximum specific growth rate (μM) and half saturation constant (KS) quantify the ability of an individual aerobe to degrade acetate and accordingly calibrate microcosm data from all locations in the shoulder. Thirty-two microcosm sets from SR-25 in southeastern Massachusetts yielded a calibrated μM of 0.00133 h[minus]1 and a KS of 0.087 kg acetate/m3 soil moisture. Calibrated (not measured) initial biomass concentrations varied from 10 to 1,000 μg biomass/g dry soil, with the largest values near the surface of the loamy sand cover layer and the smallest values above the capillary fringe consisting of uniform sand. The initial biomass concentrations and Monod kinetics yielded reaction rates consistent with field scale estimates of acetate degradation.