Constructed wetlands (CWs) have attracted increasing attention for the reduction of heavy metals and antibiotics in tailwaters of livestock and poultry breeding because of stable and considerable purification efficiency, low costs, and minimal land consumption. However, the coadsorption behaviors and mechanisms regarding coexisting heavy metals and antibiotics in CWs remain unclear.

Researchers from Wuhan Botanical Garden and Institute of Hydrobiology investigated heavy metal and antibiotic removal efficiency, and their migration characteristics and underlying interactions in CWs using small-scale CWs and laboratory dynamic adsorption experiments.

Results revealed that the removal efficiency for sulfamethoxazole (SMZ) and copper (Cu) in CWs exceeded 99%. Over 50% of Cu and SMZ reductions occurred by one hour, and approximately 90% of the pollutants were intercepted by 10 h. Ceramsite adsorption was mainly responsible for Cu removal, and its contribution declined by 39%-41% when Cu concentration increased to 20 mg L^-1. SMZ promoted the absorption and transfer of Cu in C.indica. SMZ removal in the CWs was mainly dependent on microbial degradation, accounting for over 92% of the total removal. The addition of 2 mg L^-1 of Cu enhanced bacterial diversity in CWs, and a high level of Cu (20 mg L^-1) under SMZ stress conditions significantly increased the relative abundance of anaerobic denitrifying bacteria and SMZ-degrading bacteria.

Cu and SMZ exhibited complex competitive and synergistic adsorption effects on the ceramsite particle surfaces. Cu and SMZ adsorption capacities remained stable at pH values ranging from four to six and five to eleven, respectively. Additional cations had a positive effect on SMZ adsorption via hydrophobic interactions but had no effect on Cu adsorption. In the combined system, absorbed Cu (II) on surface-NH (neutral amine) sites facilitated additional SMZ-coordination binding, because in SMZ, heterocyclic nitrogen (N) and sulfonamide N groups could both complex with Cu (II). Anionic SMZ bonded with protonated primary amines via electrostatic interactions, facilitating increased Cu-N coordination bonding.

This study provides a scientific basis for the application and optimization of CWs to treat the combined pollution in the tailwater of livestock and poultry breeding.

This work was supported by the National Natural Science Foundation of China. Associate professor MA Lin is the first author and Professor HE Feng is the corresponding author. The relevant research results have been published in Chemical Engineering Journal entitled “The occurrence characteristics and underlying removal mechanism of combined copper and sulfamethoxazole pollution in constructed wetlands”. (Available online 15 April 2023)

 The underlying removal mechanism of combined copper and sulfamethoxazole pollution in constructed wetlands (Image by MA Lin)