Wetland systems provide both anaerobic (reducing) and aerobic (oxidizing) zones for the treatment of groundwater contaminated with halogenated aliphatic hydrocarbons (HAHs). Roots of wetland plants may provide micro-oxidizing environments for methanotrophic and ammonia oxidizing bacteria. In the shallow subsurface, methanotrophic and ammonia oxidizing bacteria are supported by methane and ammonia produced in the surrounding anaerobic soil and oxygen, which is brought to the root zone through aerenchyma tissues of wetland plants. The present study demonstrated the potential for aerobic degradation of HAHs in plant rhizosphere by natural attenuation processes. The microorganisms naturally associated with rhizosphere of the common wetland plant (e.g., Carex comosa) can biodegrade HAHs by aerobic cometabolism. The drinking water contaminants included in this investigation include brominated and chlorinated trihalomethanes; the fumigants 1,3-dichloropropane and 1,2-dibromoethane; and solvents trichloroethene, cis1,2-dichloroethene, 1,1-dichloroethene, 1,2-dichloroethane, and dichloromethane. Because of their recent discovery in drinking water systems, fumigants and certain trihalomethanes are considered to be emerging contaminants.  In this investigation, laboratory experiments were carried out for a period of 2 years. Batch reactors were prepared with aliquots of soil-free Carex comosa roots that were freshly harvested from a local natural fen. Roots, along with an oxygenated growth medium, were sealed in 160 mL glass serum bottles, and amended with ammonia or methane and HAHs. The concentrations of HAHs ranged from 50-2000 mg/L and control reactors were poisoned with inhibitors. The cometabolic breakdown of HAHs in the presence of methane and ammonia were investigated through systematic chemical analysis in numerous, successive cycles, each lasting a week. Transformation yield and pseudo first-order degradation rate constants were calculated for each cycle. Results of this study provide better understanding of the potential for aerobic degradation of pollutants in a strongly anaerobic wetland environment. Results also support the application of wetlands in naturally attenuating contaminants in groundwater.

Biodegradation of emerging contaminants in plant rhizosphere: Role of aerobic-anaerobic interface in shallow wetland environments

246th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.