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 mu gSMX L-1, inhibiting the larval development, which did not occur for CIP. The antimicrobial inhibition by CIP present in the domestic sewage resulted in EC50 (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.

Automated summary

This study evaluated the ecotoxicity effects of effluent from an AFBBR removing antibiotics from domestic sewage on various microorganisms and benthic organisms. The results showed that the effluent did not inhibit the cell growth of microorganisms, but was extremely sensitive to A. inaequalis, causing 100% mortality, while eliminating acute effects on C. sancticaroli larvae. The study highlighted the potential of AFBBR in reducing the ecotoxicity of sewage on aquatic biota.