Performance and bacterial community structure of a granular autotrophic nitrogen removal bioreactor amended with high antibiotic concentrations

•A CANON bioreactor was subjected to a mix of antibiotics at high concentrations.•Nitrogen removal performance was irreversibly affected by the antibiotics.•Granular biomass changed its structure when exposed to antibiotics.•The fungus Scedosporium boydii proliferated under the antibiotics pressure.•The bacterial community structure shifted to antibiotics-resistant phylotypes.

An autotrophic nitrogen removal bioreactor with granular biomass was exposed to high antibiotics concentration in order to evaluate its impact over the performance and the biomass of this bioprocess. A mixture of azithromycin, norfloxacin, trimethoprim and sulfamethoxazole caused loss of autotrophic nitrogen removal performance, coupled to a deep change in the bacterial community diversity and structure of the granular biomass. Azithromycin, norfloxacin and trimethoprim were efficiently removed in the CANON bioreactor, reducing its concentration 77.9 ± 11.2%, 51.7 ± 10.7% and 57.8 ± 8.1%, respectively. The granular biomass changed significantly with the addition of the antibiotics, decreasing in settling velocity but increasing in compactness, losing its inner porous structure but developing a protective outer layer build of cell material. Prolonged operation under the antibiotics loading promoted the adaptation of multi-drug resistant fungus Scedosporium boydii fungal species and of Acidovorax ebreus TPSY, Alcaligenes aquatilis, Paracoccus versutus or Ochrobactrum antropii, which have been identified as human, animal and/or plant pathogens.