EFFECTS OF RATE-LIMITED DESORPTION ON THE FEASIBILITY OF IN-SITU BIOREMEDIATION

Remediation of contaminated groundwater aquifers can be extremely difficult when desorption of the contaminant from the solid phase to the aqueous phase is slow. The effects of desorption rates on the feasibility of in situ bioremediation are investigated using an analytical solution to the solute transport equation with rate-limited desorption and first-order decay. Sensitivity analyses are used to identify when desorption or degradation is the rate-limiting process for bioremediation for the range of desorption rates, degradation rates, and equilibrium distribution coefficients reported in the literature. The results show that when the desorption coefficient is large relative to the degradation coefficient (degradation is rate limiting), the performance of in situ bioremediation compared to groundwater extraction is improved as the degradation rate increases. Degradation in the aqueous phase increases the concentration gradient between solid and aqueous phases, increasing the rate of desorption and thus the rate of remediation. However, when the desorption coefficient is small relative to the degradation coefficient (desorption is rate limiting), increasing the degradation rate any further will not improve the performance of in situ bioremediation. For sites that conform to the assumptions of the model and for which model parameters can be measured or estimated, the results can be used to perform a preliminary assessment of the feasibility of in situ bioremediation.