Degradation of selected pharmaceuticals detected in wastewater systems using an enzyme-mediator system and identification of resulting transformation products

Pharmaceuticals are often found in municipal wastewater due to human excretion and disposal of drugs into sewerage systems. Conventional wastewater treatment plants were not designed for pharmaceutical removal and, hence, pharmaceutical concentrations ranging from ng L-1 to mu g L-1 are often detected in treated wastewater, with additional treatment required for full removal. This study has investigated the potential of Trametes versicolour laccase enzyme and 2,2'-azino-bis-(3-ethyl-benzthiazoline-6-sulphonic acid) diammonium salt (ABTS) mediator system to degrade sulfamethoxazole, trimethoprim, metronidazole and phenytoin. The best degradation was observed at pH 5 for both sulfamethoxazole (97% in 12 hours) and trimethoprim (44% in 168 hours), using an initial micropollutant concentration of 100 mu M, an enzymatic activity between 110-115 U L-1, and an ABTS concentration of 200 mu M. Phenytoin and metronidazole were not degraded. Deamination followed by hydroxylation led to the formation of the two major sulfamethoxazole transformation products (TPs), whilst hydroxylation and hydroxylation/demethylation mechanisms formed the majority of the trimethoprim TPs. The sulfamethoxazole and trimethoprim TPs observed from the laccase-ABTS system were similar to the TPs obtained from degradation processes such as advanced oxidation or photodegradation. The laccase-ABTS system shows promise for control of emerging contaminants containing electron donating groups (such as amines and methoxy groups) on aromatic rings in wastewater systems.