Nanometer zero-valent iron (nZVI), Fe 2+ and H 2 were potential electron donors for CT removal by nZVI. However, the action of these electron donors in CT reduction was often ambiguous. In this study, the actual catalytic activity of Ni 4 /Fe@Fe 3 O 4 under common ions and humic acid (HA) was investigated. The results showed that Na + and K + had no effect on CT removal, Cl ‐ , SO 4 2 ‐ and low concentration of Mg 2+ was beneficial to CT removal, while NO 3 ‐ , HCO 3 ‐ , Ca 2+ and HA exhibited the negative effects. According to the analysis results of gas chromatography (GC) and ion chromatography (IC), a possible dechlorination pathway of CT was proposed. Furthermore, the action mechanism of nZVI, Ni 0 and magnetite (Fe 3 O 4 ) on CT removal were explored. Among the three possible nZVI reducing mechanism, the use of H 2 by Ni 0 for the hydrodechlorination was dominant, while the direct reduction of nZVI was secondary. Fe 2+ , the product of nZVI corrosion, contributed little to CT degradation and required longer reaction time. Ni 0 could not only utilize H 2 but also form galvanic cells with nZVI to accelerate CT dechlorination. In addition, the support Fe 3 O 4 significantly improved the dispersion of Ni/Fe nanoparticles and its corrosion product Fe 2+ also promoted the CT removal. These findings were significant for comprehending the mechanisms of bimetallic nanocomposites in reducing CT, and might guide to the development of nZVI based technology for repairing polluted water or soil with organochlorine pollutants.
3, 5, 6-Trichloro-2-pyridinol (TCP) is a metabolite of the insecticide chlorpyrifos and the herbicide triclopyr, and it is higher toxic than the parent compounds. Microbially-mediated mineralization appears to be the primary degradative pathway and the important biological process of detoxification. However, little information is available on TCP complete metabolic pathways and mechanisms. In this study, the degradation of TCP was studied with a novel strain Micrococcus luteus ML isolated from a stable TCP degrading microbiota. Strain ML was capable of degrading 61.6% of TCP (50 mg/L) and 35.4% of chlorpyrifos (50 mg/L) at 24 h and 48 h under the optimal conditions (temperature: 35 °C; pH: 7.0), respectively. It could also degrade 3, 5-dichloro-2-pyridone, 6-chloropyridin-2-ol, 2-hydroxypyridine and phoxim when provided as sole carbon and energy sources. Seven TCP intermediate metabolites were detected in strain ML and two possible degradation pathways of TCP were proposed on the basis of LC–MS analysis. Both the hydrolytic-oxidative dechlorination pathway and the denitrification pathway might be involved in TCP biodegradation by strain ML. To the best of our knowledge, this is the first report on two different pathways responsible for TCP degradation in one strain, and this finding also provides novel information for studying the metabolic mechanism of TCP in pure culture.
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