Simultaneous Removal of Nitrate and Typical Antibiotics Using Fe/MS/C Composite: Performance, Mechanism, Ecological...

Nitrate (NO₃⁻-N) and antibiotics frequently co-occur in water, and their combined effects complicate treatment. While iron-carbon (Fe/C) micro-electrolysis and manganese-based materials offer distinct advantages in electron supply and oxidative regulation, their integration of material for simultaneous contaminant transformation remains largely underexplored. To address this, a novel Fe/MS/C composite was developed by incorporating metallurgical manganese slag (MS), an industrial byproduct rich in multi-valent manganese used in place of conventional manganese materials. The optimized formulation (Fe:MS = 3:1, 30 % cement, 5 % activated carbon) achieved simultaneously removal NO₃⁻-N and four antibiotics (sulfamethoxazole (SMX), enrofloxacin (ENR), ofloxacin (OFX), and florfenicol (FLO)) efficiently under both acidic and neutral conditions, and there was no inhibitory effect between NO₃⁻-N and antibiotic degradation. The system exhibited strong resistance to interference from coexisting anions and humic acid. Fe and carbon constructed an in situ micro-electrolysis structure through mechanistic processes. In conjunction with MS, they facilitated the release and regeneration of Fe²⁺, electrons, and reducing hydrogen species (H•/H₂), thereby enabling the selective reduction of NO₃⁻-N to nitrogen gas (N₂) and the cleavage of reduction-sensitive bonds in antibiotics. Simultaneously, the Mn³⁺/Mn²⁺ and Fe²⁺/Fe³⁺ redox couples established a stable cycle, producing reactive oxygen species (•OH, ¹O₂) through Fenton-like reactions, which facilitated oxidative degradation and reduced ecological risks. Batch microreactors and pilot-scale columns were constructed. The microbial system achieved higher NO₃⁻-N and antibiotic removal than the sterile control, with Fe/MS/C outperforming M-Fe/C and M-MS. In Fe/MS/C pilot-scale column, over 90 % removal of NO₃⁻-N and approximately 100 % degradation of antibiotics across different loads was achieved, along with the selective enrichment of key denitrifying and antibiotic-degrading bacteria, such as Trichococcus and Acidiferrimicrobium. Metal release was consistently below detection limits. In continuous-flow aquaculture tailwater experiments, the Fe/MS/C system maintained >95 % NO₃⁻-N and >70 % antibiotic removal over 60 days. Additionally, the operational cost was 30-40 % lower than that of conventional Fe/C materials. Overall, the Fe/MS/C composite exhibited high catalytic efficiency, ecological adaptability, and engineering feasibility, providing a promising strategy for the synergistic treatment of complex waterborne pollutants.