Biological removal of the xenobiotic trichloroethylene (TCE) through cometabolism in nitrifying systems

In the present study, cometabolic TCE degradation was evaluated using NH4–N as the growth-substrate. At initial TCE concentrations up to 845 μg/L, TCE degradation followed first-order kinetics. The increase in ammonium utilization rate favored the degradation of TCE. This ensured that biological transformation of TCE in nitrifying systems is accomplished through a cometabolic pathway by the catalysis of non-specific ammonia oxygenase enzyme of nitrifiers. The transformation yield (Ty) of TCE, the amount of TCE degraded per unit mass of NH4–N, strongly depended on the initial NH4–N and TCE concentrations. In order to allow a rough estimation of TCE removal and nitrification at different influent TCE and NH4–N concentrations, a linear relationship was developed between 1/Ty and the initial NH4–N/TCE ratio. The estimated Ty values lead to the conclusion that nitrifying systems are promising candidates for biological removal of TCE through cometabolism.