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Cometabolism of Trihalomethanes by Nitrosomonas europaea

Wahman, David G., Katz, Lynn E., Speitel, Gerald E.
Applied and environmental microbiology 2005 v.71 no.12 pp. 7980-7986
Nitrosomonas europaea, ammonia, ammonium nitrogen, bromine, chloroform, drinking water, models, temperature, toxicity, water treatment
The ammonia-oxidizing bacterium Nitrosomonas europaea (ATCC 19718) was shown to degrade low concentrations (50 to 800 [micro]g/liter) of the four trihalomethanes (trichloromethane [TCM], or chloroform; bromodichloromethane [BDCM]; dibromochloromethane [DBCM]; and tribromomethane [TBM], or bromoform) commonly found in treated drinking water. Individual trihalomethane (THM) rate constants ([Formula: see text]) increased with increasing THM bromine substitution, with TBM > DBCM > BDCM > TCM (0.23, 0.20, 0.15, and 0.10 liters/mg/day, respectively). Degradation kinetics were best described by a reductant model that accounted for two limiting reactants, THMs and ammonia-nitrogen (NH₃-N). A decrease in the temperature resulted in a decrease in both ammonia and THM degradation rates with ammonia rates affected to a greater extent than THM degradation rates. Similarly to the THM degradation rates, product toxicity, measured by transformation capacity (T[subscript c]), increased with increasing THM bromine substitution. Because both the rate constants and product toxicities increase with increasing THM bromine substitution, a water's THM speciation will be an important consideration for process implementation during drinking water treatment. Even though a given water sample may be kinetically favored based on THM speciation, the resulting THM product toxicity may not allow stable treatment process performance.