Insoluble Fe-Humic Acid Complex as a Solid-Phase Electron Mediator for Microbial Reductive Dechlorination

• Published in: Environmental science & technology Vol. 48; no. 11; pp. 6318 - 6325
• Main Authors: Zhang, Chunfang, Zhang, Dongdong, Li, Zhiling, Akatsuka, Tetsuji, Yang, Suyin, Suzuki, Daisuke, Katayama, Arata
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 03.06.2014
• Subjects: Applied sciences; Biological and physicochemical phenomena; Bioreactors; Chlorine; Decontamination. Miscellaneous; Earth sciences; Earth, ocean, space; Electrons; Engineering and environment geology. Geothermics; Environmental Pollutants - analysis; Environmental Pollutants - chemistry; Environmental Pollutants - metabolism; Environmental Restoration and Remediation - methods; Environmental science; Exact sciences and technology; Ferric Compounds - chemistry; Halogenation; Humic Substances - analysis; Iron; Natural water pollution; Pentachlorophenol - analysis; Pentachlorophenol - chemistry; Pentachlorophenol - metabolism; Pollution; Pollution, environment geology; Soil and sediments pollution; Water treatment; Water treatment and pollution; Microbial activity; Iron Complexes; Dehalogenation; In situ; Organic ligand; Soil pollution; Sediments; Organic chlorine compounds; Dechlorination; Decontamination; Phenols; Pentachlorophenol; Water pollution; Bioremediation; Humic acid; Organic compounds
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es501056n

We report that the insoluble Fe-HA complex, which was synthesized with both commercial Aldrich humic acid (HA) and natural HA, functions as a solid-phase electron mediator (EM) for the anaerobic microbial dechlorination of pentachlorophenol. Spectroscopic characterizations and sequential Fe extraction demonstrated that the Fe-HA complex was predominated with Na4P2O7-labile Fe (represented as the organically bound Fe fraction) and poorly ordered Fe fraction (the fraction left in the residue after the sequential extraction), which were associated with different possible binding processes with carboxylate and phenolic groups. The change in the electron-mediating activity caused by Fe extraction indicated that the electron-mediating function of the Fe-HA complex is attributable to the Na4P2O7-labile Fe fraction. The Fe-HA complex also accelerated the microbial reduction of Fe­(III) oxide, which suggested the presence of multiple electron-mediating functions in the complex. The electron shuttle assay showed that the Fe-HA complex had an electron-accepting capacity of 0.82 mequiv g–1 dry Fe-HA complex. The presence of redox-active moieties in the Fe-HA complex was verified by cyclic voltammetry analysis of the sample after electrical reduction, with a redox potential estimated at 0.02 V (vs a standard hydrogen electrode).