Microbially Driven Fenton Reaction for Transformation of Pentachlorophenol

A microbially driven transformation system was developed for the oxidative degradation of pentachlorophenol (PCP). The system was based on a free radical-generating Fenton reaction between bacterially produced Fe(II) and H2O2. The Fe(III)-reducing, facultative anaerobe Shewanella putrefaciens strain 200 was used as a catalyst for both Fe(III) reduction and H2O2 production by alternating between anaerobic and aerobic conditions in liquid batch cultures supplemented with Fe(III). The highest observed PCP degradation rate was approximately 0.31 μM h-1. Tetrachlorohydroquinone (TCHQ) and tetrachlorocatechol (TCC) were formed as the principal PCP transformation products, indicating that PCP oxidation proceeded via hydroxyl radical (•OH) attack on the ortho and para positions of the aromatic ring. PCP was degraded, and TCHQ and TCC were produced in a chemically driven (biomimetic) system where H2O2 and Fe(II) were supplied at concentrations comparable to those detected in the microbially driven system. PCP was not degraded (and PCP transformation products were not produced) in a set of control experiments that included (i) the presence of Fe(II)-chelating agents or radical scavenging compounds, (ii) strict aerobic or anaerobic conditions, (iii) the substitution of NO3- for Fe(III) as anaerobic electron acceptor, and (iv) the omission of S. putrefaciens. The microbially driven Fenton reaction system operated at neutral pH and required neither addition of exogenous H2O2 nor UV irradiation to regenerate Fe(II). The newly developed system may provide the basis for novel Fenton-type bioremediation strategies.