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

Remediation of contaminated groundwater aquifers can be extremely diff icult when desorption of the contaminant from the solid phase to the a queous phase is slow. The effects of desorption rates on the feasibili ty of in situ bioremediation are investigated using an analytical solu tion to the solute transport equation with rate-limited desorption and first-order decay. Sensitivity analyses are used to identify when des orption 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 sho w that when the desorption coefficient is large relative to the degrad ation coefficient (degradation is rate limiting), the performance of i n situ bioremediation compared to groundwater extraction is improved a s the degradation rate increases. Degradation in the aqueous phase inc reases the concentration gradient between solid and aqueous phases, in creasing the rate of desorption and thus the rate of remediation. Howe ver, when the desorption coefficient is small relative to the degradat ion coefficient (desorption is rate limiting), increasing the degradat ion rate any further will not improve the performance of in situ biore mediation. For sites that conform to the assumptions of the model and for which model parameters can be measured or estimated, the results c an be used to perform a preliminary assessment of the feasibility of i n situ bioremediation.