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

In the present study, cometabolic TCE degradation was evaluated using NH 4–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 ( T y ) of TCE, the amount of TCE degraded per unit mass of NH 4–N, strongly depended on the initial NH 4–N and TCE concentrations. In order to allow a rough estimation of TCE removal and nitrification at different influent TCE and NH 4–N concentrations, a linear relationship was developed between 1/ T y and the initial NH 4–N/TCE ratio. The estimated T y values lead to the conclusion that nitrifying systems are promising candidates for biological removal of TCE through cometabolism.