Anaerobic bioremediation of groundwater containing a mixture of 1,1,2,2-tetrachloroethane and chloroethenes.
This study investigated the biotransformation pathways of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) in the presence of chloroethenes (i.e. tetrachloroethene, PCE; trichloroethene, TCE) in anaerobic microcosms constructed with subsurface soil and groundwater from a contaminated site. When amended with yeast extract, lactate, butyrate, or H2 and acetate, 1,1,2,2-TeCA was initially dechlorinated via both hydrogenolysis to 1,1,2-trichloroethane (1,1,2-TCA) (major pathway) and dichloroelimination to dichloroethenes (DCEs) (minor pathway), with both reactions occurring under sulfidogenic conditions. In the presence of only H2, the hydrogenolysis of 1,1,2,2-TeCA to 1,1,2-TCA apparently required the presence of acetate to occur. Once formed, 1,1,2-TCA was degraded predominantly via dichloroelimination to vinyl chloride (VC). Ultimately, chloroethanes were converted to chloroethenes (mainly VC and DCEs) which persisted in the microcosms for very long periods along with PCE and TCE originally present in the groundwater. Hydrogenolysis of chloroethenes occurred only after highly reducing methanogenic conditions were established. However, substantial conversion to ethene (ETH) was observed only in microcosms amended with yeast extract (200 mg/l), suggesting that groundwater lacked some nutritional factors which were likely provided to dechlorinating microorganisms by this complex organic substrate. Bioaugmentation with an H2-utilizing PCE-dechlorinating Dehalococcoides spp. -containing culture resulted in the conversion of 1,1,2,2-TeCA, PCE and TCE to ETH and VC. No chloroethanes accumulated during degradation suggesting that 1,1,2,2-TeCA was degraded through initial dichloroelimination into DCEs and then typical hydrogenolysis into ETH and VC.
Aulenta
Federico
F
Department of Chemistry, University of Rome La Sapienza, P.le Aldo Moro 5, 00185, Rome, Italy. federico.aulenta@uniroma1.it
Potalivo
Monica
M
Majone
Mauro
M
Papini
Marco Petrangeli
MP
Tandoi
Valter
V
D000693:Anaerobiosis; D041862:Chloroflexi / Q000378:metabolism; D004980:Ethane / Q000031:analogs & derivatives* / Q000378:metabolism; D005618:Fresh Water / Q000737:chemistry*; D006843:Hydrocarbons, Chlorinated / Q000378:metabolism*; D007218:Industrial Microbiology / Q000379:methods; D007220:Industrial Waste; D012988:Soil Microbiology; D013750:Tetrachloroethylene / Q000378:metabolism*; D014241:Trichloroethylene / Q000378:metabolism*; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000378:metabolism*; D018508:Water Purification / Q000379:methods*
D006843:Hydrocarbons, Chlorinated; D007220:Industrial Waste; D014874:Water Pollutants, Chemical; C031336:1,1,1,2-tetrachloroethane; D014241:Trichloroethylene; D004980:Ethane; D013750:Tetrachloroethylene