MODEL SIMULATIONS IN SUPPORT OF FIELD-SCALE DESIGN AND OPERATION OF BIOREMEDIATION BASED ON COMETABOLIC DEGRADATION

This paper addresses questions fundamental to the design and operation of aquifer bioremediation based on cometabolic degradation. A model o f a full-scale, in situ system for bioremediation of chlorinated ethen es relying on cometabolic degradation was developed and applied to a h ypothetical aquifer being considered for a large-scale field demonstra tion of in situ bioremediation with recirculation. The model was used to identify feasible substrate (electron donor and electron acceptor) delivery schedules. Trichloroethylene (TCE) was the target contaminant . Methane and phenol were considered as electron donors. The delivery of the electron donors and the electron acceptor, oxygen, was varied t o evaluate the rate and extent of bioremediation under different subst rate delivery schedules. Maximum removal of TCE was predicted when sub strates are delivered at ratios near the stoichiometric requirement of electron donor and acceptor for net microbial growth. Additionally, t he decrease in TCE removal that results from using substrate delivery schedules other than those achieving the maximum removal of TCE was qu antified. This decrease was greater for the methane-oxygen system beca use the two gaseous substrates compete for transfer into the recircula ted ground water. If one substrate is introduced in excess of the amou nt required for net microbial growth, it accumulates, thus limiting th e ability to introduce the second substrate. This imbalance both limit s the introduction of the second substrate and accelerates the accumul ation of the substrate added in excess. The phenol-oxygen system is le ss sensitive to deviation away from the best observed substrate delive ry schedule because phenol is a relatively soluble liquid and its intr oduction does not compete with the mass transfer of oxygen.