Ciprofloxacin biotransformation during anaerobic digestion: Major transformation products elucidation and...

Anaerobic membrane bioreactors (AnMBR) ar a promising alternative for treating high-load sewage, like black water (BW), due to the energy saving (biogas production and lack of aeration). Antibiotics like ciprofloxacin (CIP) are expected to be more concentrated than in a typical urban sewage matrix. Its fate under these conditions remains poorly understood. To broaden this understanding, we combined analysis of transformation products (TPs) and proteomics on 26 batch experiments inoculated with an AnMBR sludge, fed with volatile fatty acids (VFAs) and spiked with CIP. Methanogenic activity was not affected by CIP and the removal was higher than 88 % in all cases. Abiotic controls indicated the removal was mainly driven by sorption processes. However, at the lower concentrations tested (0.1 and 0.5 mg L^-1) biotransformation also occurred. A total of six TPs were identified, some only present in low concentrations while one of them only appeared at the highest concentrations, pointing to hydroxylation and loss of the cyclopropyl ring as the main biological transformations. Methanothrix and Methanosaeta were the main methanogens and not negatively affected by CIP, except at 2 mg CIP. L^-1 suggesting an inhibitory threshold. Environmental proteomics pointed to the key role of dehydrogenases under methanogenic anaerobic conditions.