Microbially Driven Fenton Reaction for Transformation of Pentachlorophenol

Abstract

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 H{sub 2}O{sub 2}. The Fe(III)-reducing, facultative anaerobe Shewanella putrefaciens strain 200 was used as a catalyst for both Fe(III) reduction and H{sub 2}O{sub 2} 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 {micro}M h{sup {minus}1}. Tetrachlorohydroquinone (TCHQ) and tetrachlorocatechol (TCC) were formed as the principal PCP transformation products, indicating that PCP oxidation proceeded via hydroxyl radical ({sup {sm_bullet}}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 H{sub 2}O{sub 2} 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 (1) the presence of Fe(II)-chelating agents or radical scavenging compounds, (2) strict aerobic or anaerobic conditions, (3) the substitution of NO{sub 3}{sup {minus}} for Fe(III) as anaerobic electron acceptor, and (4) the omissionmore » of S. putrefaciens. The microbially driven Fenton reaction system operated at neutral pH and required neither addition of exogenous H{sub 2}O{sub 2} nor UV irradiation to regenerate Fe(II). The newly developed system may provide the basis for novel Fenton-type bioremediation strategies.« less