A two-step process was developed for the complete mineralization of hazardous chlorinated aromatic compounds. The system consisted of an anaerobic reactor, in which reductive dehalogenation took place, coupled with an aerobic reactor in which the complete mineralization of the products of the anaerobic dehalogenation occurred.
A mixed anaerobic culture from a municipal sewage treatment plant was enriched and then immobilized on silica-based porous beads to treat 2,4,6-trichlorophenol (TCP), which is the model target compound in this work. In the anaerobic reactor, TCP was degraded to 2,4-dichlorophenol which was, in turn, reduced to 4-chlorophenol (4-CP). Stoichiometric amounts of 4-CP were recovered at the end of the anaerobic step. No other unknown compound was produced to any significant extent during the anaerobic process. As the anaerobic culture got acclimated to the TCP, the dehalogenation rate of TCP increased from 21.7 to 43.2 μM/day.
The effluent from the anaerobic reactor was subsequently treated in a suspended growth aerobic reactor to remove the 4-CP. The anaerobic effluent had to be buffered with a phosphate solution to adjust its μH to about 7 and maintain aerobic activity.
When the system was run in batch mode, 106.4 μM of TCP could be dechlorinated to 4-CP in three days by an acclimated anaerobic culture. 98 μM of the 4-CP produced were then mineralized in the aerobic reactor in less than three days.
When the system was run in continuous mode, 120 μM of TCP were entirely and continuously dechlorinated to 4-CP in the anaerobic reactor, and then completely mineralized in the aerobic reactor. The average residence times (which were not optimized) in the anaerobic and aerobic reactors were respectively 105 and 98 hours, although there are indications that these were longer than necessary
