BIOGEOCHEMICAL MEASUREMENTS TO CHARACTERIZE DUAL ANAEROBIC AND AEROBIC BIODEGRADATION PROCESSES FOR REMEDIATION OF CHLORINATED BENZENES IN A WETLAND

Anaerobic and aerobic processes advantageous for contaminant bioremediation can co-occur in areas of groundwater-surface water interactions, and new molecular biological tools assist in evaluation of these processes. The feasibility of dual aerobic and anaerobic bioremediation was investigated to address high concentrations (greater than 80 milligrams/liter) of tri-, di-, and mono-chlorobenzenes and benzene in discharging groundwater and wetland sediments at a Delaware Superfund site. In situ microcosms, incubated 25-55 cm below the wetland surface, were analyzed using QuantArray for numerous functional and taxonomic genes that indicate potential for anaerobic and aerobic biodegradation of benzene and chlorinated solvents. Microcosms that were bioaugmented with an anaerobic dechlorinating consortium (WBC-2), as well as biostimulated with lactate to induce reducing conditions, had one to five orders of magnitude higher quantities of both anaerobic and aerobic targeted microbial populations and functional genes than microcosms that were either untreated or biostimulated with lactate. Targets that were quantified in moderate to high numbers in the bioaugmented microcosm included Dehalococcoides and Dehalobacter species associated with anaerobic degradation of chlorinated benzenes; benzoyl coenzyme A reductase and benzylsuccinate synthase functional genes associated with anaerobic degradation of aromatic hydrocarbons; and trichlorobenzene dioxygenase, phenol hydroxylase, and toluene monooxygenases associated with aerobic degradation of chlorinated benzenes and benzene. ¹³C-labelled testing in some microcosms verified that anaerobic and aerobic degradation of chorobenzene is possible in the wetland. In flow-through laboratory bioreactors seeded with the native wetland community, removal rates for tri- and dichlorobenzenes were similar under anaerobic and aerobic conditions, but the increase in degradation rates for monochlorobenzene and benzene under aerobic conditions indicated that efficiency could be improved with simultaneous anaerobic and aerobic biodegradation. Column experiments bioaugmented with both WBC-2 and a native aerobic culture currently are underway to further evaluate a dual anaerobic-aerobic biodegradation approach for effective remediation.