Evaluation of Methanotrophic Bacteria during Injection of Gaseous Nutrients for In Situ Trichloroethylene Bioremediation in a Sanitary Landfill

Methanotrophic bacterial populations were quantified in an aquifer that was amended with air (oxygen), methane, triethyl-phosphate, and nitrous oxide to evaluate their effectiveness to stimulate aerobic bioremediation of vinyl chloride (VC), dichloroethylene, and trichloroethylene (TCE). Contaminants in groundwater resulted from leachate originating from a nearby landfill. Groundwater samples were taken during gas injection and analyzed for changes in bacterial populations. The methanotrophic populations were monitored in groundwater using direct fluorescent antibodies (DFA) and the most probable number (MPN) technique. Acridine orange direct counts (AODC) were used to determine the total bacterial population. Methanotrophic populations increased significantly in groundwater during the course of gaseous nutrient injections. As methanotrophic bacteria reached a maximum population in 3-4 days, contaminant levels (TCE) decreased. Cis-dichloroethylene (c-DCE) demonstrated a transient increase in concentration during the experiment but decreased rapidly over the course of the experiment. The total number of groundwater microorganisms did not change, indicating a selective stimulation of the methanotrophic bacterial population. These bacterial data were compared to physical parameters (pH, dissolved oxygen, redox) and contaminant (TCE , c-DCE, VC) concentrations within the saturated and unsaturated zone to reveal the efficiency of the system. The loss of contaminants appears to be due to cometabolic biodegradation through biostimulation since loss by volatilization was accounted for and was minimal. This work clearly demonstrates that one can effectively change the subsurface bacterial population in a relatively short period of time.