Particles and enzymes: Combining nanoscale zero valent iron and organochlorine respiring bacteria for the detoxification of chloroethane mixtures

Nanoscale zero valent iron (nZVI) and organochlorine respiring bacteria (ORB) are two technologies used to detoxify chlorinated aliphatic hydrocarbons (CAHs). nZVI can rapidly detoxify high CAH concentrations, but is quickly oxidised and unable to degrade certain CAHs (e.g., 1,2-dichlorothane). In contrast, ORB can dechlorinate CAHs resistant to nZVI (e.g., 1,2-dichlorothane) but are inhibited by other CAHs of concern degradable by nZVI (e.g., chloroform and carbon tetrachloride). Combining the two was proposed as a unique treatment train to overcome each technology's shortcomings. In this study, this combined remedy was investigated using a mixture of 1,2-dichloroethane, degradable by ORB but not nZVI, and 1,1,2-trichloroethane, susceptible to both. Results indicated that nZVI rapidly dechlorinated 1,1,2-trichloroethane when supplied above 0.5 g/L, however ORB were inhibited and unable to dechlorinate 1,2-dichloroethane. pH increase and ionic species associated with nZVI did not significantly impact ORB, pinpointing Fe0 particles as responsible for ORB inhibition. Below 0.05 g/L nZVI, ORB activity was stimulated. Results suggest that combining ORB and nZVI at appropriate doses can potentially treat a wider range of CAHs than each individual remedy. At field sites where nZVI was applied, it is likely that in situ nZVI concentrations were below the threshold of negative consequences.