Organic halogen removal from chlorinated humic ground water and lake water by nitrifying fluidized-bed biomass characterised by electron microscopy and molecular methods.

Abstract

The dechlorinating and genotoxicity-removing activities of nitrifying fluidized-bed reactor biomass towards chlorinated organic compounds in water were shown at level below 1 ppm. The removal rates of adsorbable organic halogens were 200 micrograms Cl (g VS day)-1 for chlorinated humic ground water and 50 micrograms Cl (g VS day)-1 for chlorinated lake water when studied in batch mode. In a sequenced batch mode the removal rates [micrograms Cl (g VS day)-1] were 2000 from chlorohumus, 1400-1800 from chlorophenols in chlorinated ground water, and 430-720 from chlorohumus in chlorinated lake water. Genotoxicity was removed to a large extent (60%-80%) from the chlorinated waters upon incubation with nitrifying reactor biomass. 2,6-Di-, 2,4,6-tri and 2,3,4,6-tetrachlorophenols competed with chlorinated water organohalogens for dechlorination. The dechlorination of chlorophenols and chlorohumus required no ammonia and was not prevented by inhibitors of ammonia oxidation, nitrapyrin, parathion, sodium diethyldithiocarbamate, or allylthiourea. Electron microscopical inspection of the biomass showed the dominance of clusters of bacteria resembling known nitrifying species, Nitrosomonas, Nitrobacter, and Nitrosospira. This was supported by polymerase chain reaction amplification of the biomass DNA with four different primers, revealing the presence of 16S rDNA sequences assignable to the same species. The most intensive band obtained with the Nitroso4E primer was shown to be closely related to Nitrosomonas europaea by restriction analysis.