SIMULATION OF AEROBIC AND ANAEROBIC BIODEGRADATION PROCESSES AT A CRUDE-OIL SPILL SITE

A two-dimensional, multispecies reactive solute transport model with s equential aerobic and anaerobic degradation processes was developed an d tested. The model was used to study the field-scale solute transport and degradation processes at the Bemidji, Minnesota, crude oil spill site. The simulations included the biodegradation of volatile and nonv olatile fractions of dissolved organic carbon by aerobic processes, ma nganese and iron reduction, and methanogenesis. Model parameter estima tes were constrained by published Monod kinetic parameters, theoretica l yield estimates, and field biomass measurements. Despite the conside rable uncertainty in the model parameter estimates, results of simulat ions reproduced the general features of the observed groundwater plume and the measured bacterial concentrations. In the simulation, 46% of the total dissolved organic carbon (TDOC) introduced into the aquifer was degraded. Aerobic degradation accounted for 40% of the TDOC degrad ed. Anaerobic processes accounted for the remaining 60% of degradation of TDOC: 5% by Mn reduction, 19% by Fe reduction, and 36% by methanog enesis. Thus anaerobic processes account for more than half of the rem oval of DOC at this site.