Elucidation of biotransformation of diclofenac and 4′hydroxydiclofenac during biological wastewater treatment

This study aimed at gaining knowledge on the degradation pathway during biological treatment of wastewater of diclofenac and 4′-hydroxydiclofenac, its main human metabolite. For that purpose, an aerobic MBR was acclimatised to diclofenac, and the MBR biomass subsequently incubated with 14C-diclofenac or 14C-4′hydroxydiclofenac over 25 days. It was demonstrated that diclofenac degradation was much slower and limited than that of 4′-hydroxydiclofenac. Indeed, after 18 days of batch incubation, diclofenac was removed up to 40%, this rate remained stable till the end of the experiment, while 4′-hydroxydiclofenac was completely degraded within nine days. The analyses of supernatant samples have shown that diclofenac degradation led to four transformation products, more polar than the parent compound, one of them being 4′-hydroxydiclofenac. The degradation of 4′-hydroxydiclofenac led to the formation of the same metabolites than those detected during diclofenac degradation. With these results, the hydroxylation of diclofenac to 4′-hydroxydiclofenac was identified as one major bottleneck in diclofenac degradation during biological treatment of wastewater.