Synergistic integration of in situ generated Fe-S species and organohalide-respiring bacteria for complete dechlorination of carbon tetrachloride in groundwater.

Carbon tetrachloride (CCl₄) is a persistent DNAPL contaminant in groundwater, which cannot be completely dechlorinated to non-toxic compound(s) solely by known organohalide-respiring bacteria (OHRB) or abiotic dechlorinating materials. In this study, a strategy synergistically integrating iron-sulfur species (FemSn) and OHRB was developed for consequent abiotic-biotic dechlorination and complete removal of CCl₄. The FemSn in subsurface soil was synthesized abiotically with oil-protected NaBH4 or biotically with a co-culture of dissimilatory iron-reducing bacteria (DIRB) and sulfate-reducing bacteria (SRB) to dechlorinate CCl₄, of which dechlorination products can be completely degraded by a Desulfitobacterium- and Dehalobacterium-containing microcosm within 30 days. The abiotically-generated FemSₙ exhibited Fe-S network with short-range order and continuous FeS/FeS₂ heterointerfaces that improved CCl₄ interfacial adsorption and electron affinity, creating an electron-transfer dominated channel for selective C-Cl bond cleavage. The generation of FemSn for CCl₄ removal was devised based on the fact of massive iron/sulfur species in groundwater, which largely simplified the remediation process and reduced the remediation cost. Our results provided an economic strategy and insight into underlying mechanisms for efficient remediation of CCl₄-contaminated groundwater.