Ecotoxicity and Antimicrobial Inhibition Assessment of Effluent from an Anaerobic Bioreactor Applied to the Removal of Sulfamethoxazole and Ciprofloxacin Antibiotics from Domestic Sewage

This study evaluated the ecotoxicity effects of effluent from an anaerobic fixed bed biofilm reactor (AFBBR) removing the sulfamethoxazole (SMX - 403 ± 104 ng L −1 ) and ciprofloxacin (CIP - 294 ± 123 ng L −1 ) antibiotics from domestic sewage in some microorganisms ( Brevundimonas sp., Escherichia coli , Ochrobactrum sp., Sphingomonas sp . ) and benthic organisms ( Allonais inaequalis and Chironomus sancticaroli ). The AFBBR showed high removal efficiency of SMX (85 ± 10%) and CIP (81 ± 16%) and completely eliminated the acute ecotoxicological effect on the C. sancticaroli insect larvae. The bioreactor effluent did not cause any inhibition on the cell growth of the microorganisms. Nonetheless, the A. inaequalis was extremely sensitive to the reactor effluent (100% mortality), probably due to the death of bacteria and algae essential to the nutrition of the Oligochaeta. Regarding the adult insect emergency of C. sancticaroli , a reduction of 50% was observed after 17 days of exposure to the effluent with 40 μgSMX L −1 , inhibiting the larval development, which did not occur for CIP. The antimicrobial inhibition by CIP present in the domestic sewage resulted in EC 50 (median effective concentration) values of 2.5, 0.9, 3.1 and 0.1 mgCIP L −1 for Ochrobactrum sp . , Brevundimonas sp . , Sphingomonas sp. and E. coli , respectively. Assessing the effect of antibiotics in the effluent on the microorganisms’ growth by a disk diffusion test, only E. coli culture showed inhibition at the concentration of 5.0 mgCIP L −1 . The study emphasized the potential of AFBBR to reduce ecotoxicity in the sewage on aquatic biota.