Wetlands have been known to degrade nutrients and other common contaminants in wastewater and groundwater by natural attenuation processes. This study evaluates the degradation potential of various chlorinated aliphatic hydrocarbons (CAHs) in the root zone of wetland plant species, Scripus atrovirens
in large bench-scale flow-through reactors. The study focuses on the role of methane oxidizing microorganisms that are naturally associated within the root zone of Scripus atrovirens
, which may facilitate aerobic cometabolic oxidation of CAHs. Plants were grown in multiple flow-through reactors with a constant flow of deoxygenated hydroponic solution; various ratios of methane and nitrogen were bubbled into the solution. Aqueous mixtures of CAHs investigated include chloroform (CF), 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2-trichloroethane (1,1,2-TCA), trichloroethene (TCE), perchloroethene (PCE), and 1,2-dichloropropane (1,2-DCP) that were mixed with the influent through a syringe pump entering the planted and unplanted (control) reactors.
The dissolved inorganic carbon (DIC), dissolved oxygen, conductivity, pH, [methane] and [CAHs] were monitored frequently at sampling points water entering and leaving the reactors to estimate their loss/production rate. Loss of CAHs due to volatilization and hydraulic retention time of the conservative tracer through the reactors were also estimated.
The results provide good evidence for removal of CAHs in the root zone of Scripus atrovirens species during its transit through the reactor. In planted reactors in water saturated with 10 and 25% methane, it was completely removed at the effluent port (410 mm), with 92.4% methane oxidized within 200 mm of influent port. The decrease in methane coincided with an increase in DIC. The results showed significant removal with CAH mixture; the percent removal of TCE and 1,1,1-TCA in the effluent was ~66% and ~67%, respectively, with respect to their levels in the influent. The percent loss of CF in the effluent was quite similar, ~58.4%. The loss of PCE and 1,1,2-TCA in the effluent were smaller, ~40.3% and 43.1% respectively, which may be attributed mainly to volatilization. The lowest removal was observed for 1,2-DCP at 28.6%. As much as 21% of total CAHs were lost overall mainly to volatilization.