Anaerobic–aerobic treatment of halogenated phenolic compounds

Abstract

2,4,6-trichlorophenol (2,4,6-TCP) was successfully and completely degraded in a two-stage anaerobic–aerobic biological process in which the initial step was conducted anaerobically, resulting in the reductive dechlorination of the target compound to 2,4-dichlorophenol (2,4-DCP), and then 4-chlorophenol (4-CP). Stoichiometric conversion of 2,4,6-TCP to 4-CP was achieved. The latter compound was then attacked and completely degraded aerobically in a second stage. The effects of parameters such as temperature and pH were determined for individual components of the process. The process was studied in serum bottles and shake flasks, and in anaerobic and aerobic bioreactors operating in both batch and continuous modes. A sequential anaerobic–aerobic bioreactor system was assembled, in which complete 2,4,6-TCP degradation was achieved. A mathematical model was developed to describe both anaerobic and aerobic processes, and the complete system. The model assumed that 2,4,6-TCP and 2,4-TCP could be anaerobically attacked according to a sequential irreversible reductive dechlorination reaction scheme based on Michaelis–Menten kinetics. A similar model was used to quantify aerobic degradation. The kinetic parameters for each step were obtained in independent batch experiments with suspended cultures, and were internally consistent. The model was able to predict the experimental results, which lends validity to the postulated kinetics mechanism.