Antibiotics inhibit nitrogen removal and promote greenhouse gas emissions in high-density earthworm-enhanced constructed wetlands

Antibiotics in wastewater present significant ecological risks. However, their effects on nitrogen (N) removal and greenhouse gas (GHG) emissions in constructed wetlands (CWs) have been largely neglected in previous studies. This study investigated the effects of antibiotics on N removal and GHG emissions in earthworm-enhanced CWs constructed with three earthworm densities (0 g m -2 , 156 g m -2 , and 312 g m -2 ). The results showed that (1) antibiotics significantly increased effluent total inorganic nitrogen (TIN) concentrations by 49.17 % in systems with the high-density earthworm, whereas no significant effects were observed in the other treatments; (2) in systems without earthworms, antibiotics significantly reduced N₂O emissions by 139 %. In systems with low-density earthworms, CH₄ and CO₂ emissions were significantly reduced by 366 % and 70.3 %, respectively. In contrast, in high-density earthworm systems, N₂O emissions significantly increased by 289 %; (3) antibiotics led to a significant reduction in non-CO₂ global warming potential (GWP non-CO₂ , -143 %) in the systems without earthworms and a reduction in total global warming potential (GWP CH₄+N₂O+CO₂ , -57.3 %) in the systems with low-density earthworms. However, both indices significantly increased by 289 % and 51.2 % in systems with high-density earthworms; (4) antibiotics altered the microbial community composition and significantly increased nitrite reductase activity in the systems with low-density earthworms (+24.5 %) but significantly decreased it in systems with high-density earthworms (-33.0 %). In summary, antibiotic contamination markedly influenced both N removal performance and GHG emissions in earthworm-enhanced CWs, with effects varying depending on earthworm density.