Enhanced performance and mechanism of nano-iron-nickel modified substrate in the treatment of compound antibiotic wastewater in constructed wetland.

Nano zero-valent iron nickel (nZVI/Ni) was loaded on the walnut shell activated carbon (AC) and its spheres (ACS) to prepare nZVI/Ni-ACS and nZVI/Ni/AC-SAS composites. These were applied in constructed wetlands (CWs) to construct a "substrate-microorganism" synergistic system for treating tetracycline (TC) and sulfamethoxazole (SMX) in livestock and poultry wastewater. Adsorption experiments determined the optimal mass ratios were ACS:Fe:Ni = 2:1:0.05; AC:Fe:Ni = 1:1:0.05; nZVI/Ni/AC:SA = 6:1. At 500 μg/L influent concentrations, TC and SMX removal efficiencies in CWs with modified substrates (CW-LA: 86.96%/87.79%; CW-LB: 89.88%/86.94%) significantly exceeded gravel (CW-G: 26.07%/55.28%) and ACS (CW-Z: 39.90%/67.56%) systems. Mechanistically, the modified substrates strongly adsorbed TC and SMX, while Fe and Ni acted as electron donors and catalysts to drive their chemical reduction and stimulate biological co-metabolism. Metagenomic analysis revealed that the TC/SMX removal mechanisms were associated with an increased abundance of antibiotic-resistant microorganisms (Methanothrix, Desulfobacter, Thauera, Geobacter, Pseudomonas), which benefited efficient antibiotic degradation, while their immobilization within the tightly bound EPS (TB-EPS) matrix effectively minimized ecological risks. This study provided critical data for the enhanced CW treatment of TC and SMX in livestock and poultry wastewater by modified substrates.