Impact of Ammonium Availability on Atenolol Biotransformation during Nitrification

The impact of ammonium availability on atenolol biotransformation at an environmentally relevant level of 15 μgL^-1 by enriched nitrifying cultures was investigated in terms of atenolol degradation kinetics and biotransformation product formation dynamics. Different concentrations of growth substrate ammonium (0, 25, and 50 mg-NL^-1) were applied constantly during batch experiments. The results suggested the higher ammonium concentrations led to lower atenolol removal rates probably due to the substrate competition between ammonium and atenolol. The formation of the biotransformation product atenolol acid was positively related to the ammonium oxidation activity, resulting in a higher amount at the end of experiments at higher ammonium concentrations. Linear correlations between ammonia oxidation rate and atenolol degradation rate at ammonium levels of 25 and 50 mg-NL^-1 suggested the cometabolism of atenolol by ammonia oxidizing bacteria (AOB) in the presence of ammonium. The biotransformation reaction, i.e., hydroxylation on amide group to carboxylic group, could be catalyzed by the nonspecific ammonia monooxygenase (AMO) of AOB. Comparison between atenolol degradation at ammonium levels of 0 and 50 mg-NL^-1 demonstrated the formation of atenolol acid was independent of the ammonium availability. This work might give further indication of how to prevent pharmaceuticals from entering into the environment.