Deciphering the effects of antibiotics on nitrogen removal and bacterial communities of autotrophic denitrification systems in a three-dimensional biofilm electrode reactor

In this study, three-dimensional biofilm electrode reactors (3D-BERs) were constructed, and the effects of metronidazole (MNZ) on the nitrogen removal performance and bacterial communities of autotrophic denitri-fication systems were evaluated. The results showed that nitrogen removal decreased slightly as the MNZ con-centration increased. Specifically, nitrate-nitrogen removal efficiency decreased from 97.98% to 89.39%, 86.93%, 82.64%, and 82.77% within 12 h after the addition of 1, 3, 5, and 10 mg/L MNZ, respectively. The 3D-BERs showed excellent MNZ degradation ability, especially at a concentration of 10 mg/L. The MNZ removal efficiency could be as high as 94.38% within 6 h, and the average removal rate increased as the MNZ concen-tration increased. High-throughput sequencing results showed significant changes in the bacterial community under different MNZ concentrations. As the antibiotic concentration increased, the relative abundances of Hydrogenophaga and Silanimonas increased, from only 0.09% and 0.01% without antibiotics to 3.55% and 2.35%, respectively, at an antibiotic concentration of 10 mg/L. Changes in antibiotic concentration altered the abun-dances of genes involved in nitrogen metabolism. Redundancy analysis showed that MNZ removal efficiency was positively correlated with SBR1031, SC-I-84, Hydrogenophaga, Silanimonas and Denitratesoma, whereas the removal efficiencies of nitrate-nitrogen and total nitrogen were negatively correlated with these genera. The results of this study provide a theoretical basis for studying the toxic effects of antibiotics on the denitrification process and also provide guidance for the control of antibiotics and nitrogen pollution in ecosystems.

Automated summary

This study constructed three-dimensional biofilm electrode reactors (3D-BERs) to assess the effects of metronidazole (MNZ) on autotrophic denitrification systems. The results indicated a slight decrease in nitrogen removal efficiency as the MNZ concentration increased. The 3D-BERs demonstrated excellent ability to degrade MNZ, especially at a concentration of 10 mg/L. High-throughput sequencing analysis revealed significant changes in the bacterial community under different MNZ concentrations, affecting the abundance of genes involved in nitrogen metabolism. The findings provide a theoretical basis for studying the toxic effects of antibiotics on denitrification processes and guidance for controlling antibiotics and nitrogen pollution in ecosystems.