DEGRADATION OF CHLORINATED HYDROCARBONS IN FLOW-THROUGH MESOCOSMS SIMULATING CONSTRUCTED WETLANDS

Constructed wetlands are commonly used for the removal of inorganic and certain organic contaminants in the wastewater streams and surface water. Our results show that wetlands can be used to degrade volatile organic compounds (VOCs) in the groundwater, e.g., perchloroethene (PCE). Twelve mesocosms were developed in a greenhouse environment to simulate the conditions in a treatment wetlands located at Wright Patterson Air Force Base in Dayton, Ohio. These mesocosms (reactors) were designed with the wetland soil, three species of wetland vegetation, and PCE solution in a 50/50 mix of tap water and distilled water. The microbial and vegetative processes are currently under investigation to assess their impact on PCE biodegradation in the mesocosms. These assessments are based on the analysis for volatiles such as methane, PCE, and its daughter products using gas chromatograph (GC). Other analyses include colorimetric methods for dissolved oxygen, ferrous iron, ammonia, and major ions using ion chromatography (IC). Preliminary results indicate that there is indeed a significant degradation of PCE and evidence of daughter products like trichloroethene (TCE), dichloroethene (DCE), and vinyl chloride (VC) in the mesocosms. The profiles of dissolved oxygen showed a decrease in the lower portions of the mesocosms and an increase in the upper portions, while dissolved iron and ammonia increased in the lower portions and decreased in the upper portions. These results are indicative of the microbial and vegetation-driven processes occurring in the mesocosms that appear to play a role in the biogeochemical processes affecting the degradation of chlorinated compounds.