Pentachlorophenol dechlorination by an acidogenic sludge

This study reports the feasibility of removing pentachlorophenol (PCP) by an acidogenic process in batch reactors. When the acidogenic sludge was first acclimated with 2,4,6-trichlorophenol (2,4,6-TCP) and developed 2,4,6-TCP dechlorinating activity, PCP could be ortho-dechlorinated to 3,4,5,-trichlorophenol (3,4,5-TCP) via 2,3,4,5-tetrachlorophenol as the intermediary. However, due to PCP's higher hydrophobicity and its higher expected Gibbs free energy yield, it was adsorbed to the sludge and dechlorinated preferentially to 2,4,6-TCP. This resulted in the inhibition of 2,4,6-TCP dechlorination. PCP removal under acidogenic condition was attributed to both reductive dechlorination and adsorption. At low PCP loads of 0.48 μmoles/g MLVSS.d, dechlorination was the dominant removal mechanism (69% of total removal), while at the higher PCP load of 9.3 μmoles/g MLVSS.d, adsorption was the main mechanism (82% of total removal). Attempts to induce meta or para position dechlorination of PCP failed when using meta position chlorophenols such as 2,3,6-TCP, 3,4,5-TCP and 3,5-DCP as the initial substrates. Overall, acidogenic biotreatment was an effective process in reducing PCP loads prior to downstream biological treatment.