Dechlorination of 2,4,6-trichlorophenol by a nitrifying biofilm

Abstract

To study the possibility of removing nitrogen and organic halogens from bleached kraft pulp mill effluent, we investigated nitrification and dechlorination in a laboratory scale fluidized-bed reactor. The nitrifying reactor was fed with ammonia and exposed to 2,4,6-trichlorophenol as a model substrate. The reactor responded with a decrease in the production of nitrate and acid. Nitrification recovered after six days of continuous 2,4,6-trichlorophenol feed and inorganic chloride began to accumulate into the effluent. When the application of 2,4,6-trichlorophenol was repeated, no inhibition of nitrification was observed and dechlorination began with no lag phase. Inorganic chloride release and total organic carbon removal pointed out that 2,4,6-trichlorophenol was dechlorinated and mineralized in the reactor. Batch experiments showed that enzyme synthesis was necessary for the adaptation of the nitrifying biofilm to 2,4,6-trichlorophenol dechlorination. 2,6-dichlorohydroquinone formed as an intermediate product from 2,4,6-trichlorophenol. The electron micrographs of the biomass revealed bacteria morphologically similar to known ammonia oxidizing species; mainly Nitrosomonas and Nitrosospira.