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Sequential Anaerobic Dechlorination of Pentachlorophenol:  Competitive Inhibition Effects and a Kinetic Model

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journal contribution
posted on 31.03.1999, 00:00 by Victor S. Magar, H. David Stensel, Jaakko A. Puhakka, John F. Ferguson
The fate and dechlorination kinetics of PCP and its intermediates were studied in two fluidized-bed reactors (FBRs) with methanogenic enrichments. The two FBRs were operated at a 1-day hydraulic retention time and fed lactate at 400 mg/L and pentachlorophenol (PCP) at 5 mg/L (18.8 μmol/L). PCP was meta-dechlorinated to 2,3,4,6-tetrachlorophenol (2346-TeCP). Approximately 75% of the 2346-TeCP was meta-dechlorinated to 2,4,6-trichlorophenol (246-TCP), followed by sequential o-chlorine removals to 4-monochlorophenol (4-MCP); the remaining 2346-TeCP was ortho-dechlorinated via 245-TCP to 3,4-dichlorophenol (34-DCP). Neither 34-DCP nor 4-MCP were dechlorinated throughout the 18-month testing period. In mixed-CP batch tests, CPs competed with each other, resulting in reduced dechlorination rates; competition was position-specific with respect to ortho- and meta-dechlorination reactions. Michaelis−Menten dechlorination kinetic coefficients and linear solid−liquid partition coefficients were determined for PCP, 2346-TeCP, 246-TCP, 245-TCP, 24-DCP, 34-DCP, and 4-MCP. These coefficients were used in a Michaelis−Menten, sequential dechlorination, competitive inhibition kinetic model that used the experimentally determined CP half-saturation coefficients (Ks) for respective inhibition coefficients. The model reasonably predicted CP concentra tions over time in batch tests fed 246-TCP or PCP. Without competitive inhibition, the model increasingly overestimated CP dechlorination rates with each successive dechlorination step and underestimated the time for dechlorination.

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