Enhanced removal of estrogens from simulated wastewater by biochar supported nanoscale zero-valent iron: performance and mechanism

Highlights

•	Porous and functional nZVI-biochar was prepared and applied for estrogens removal.
•	nZVI-biochar exhibited high adsorption capacities to estrogens pollutants due to π–π interaction, hydrophobic interaction and hydrogen bonding.
•	The estrogens adsorption process of nZVI-biochar conformed to quasi-second-order kinetics and the Freundlich model.
•	The production of free radicals contributed to the degradation of estrogens.

Abstract

The intensification of estrogen non-point source pollution has drawn global attention due to their contribution to ecological environment problems worldwide, and it is critical to develop effective, economic and eco-friendly methods for reducing estrogens pollution. To address the agglomeration and oxidation of nano zero-valent iron (nZVI), biochar-nanoscale zero-valent iron composite (nZVI-biochar) could be a feasible choice for estrogens removal. This study summarized biochar and nZVI-biochar preparation, characterization, and unusual applications for estrone (E1), 17β-estradiol (E2), and estriol (E3) removal. The properties of biochar and nZVI-biochar in characterization, effects of influencing factors on the removal efficiency, adsorption kinetics, isotherm and thermodynamics were investigated. The experiment results showed that nZVI-biochar exhibited the superior removal performance for estrogens pollutants compared to biochar. Based on the quasi-second-order model, estrogens adsorption kinetics were observed, which supported the mechanism that chemical and physical adsorption existed simultaneously on estrogens removal. The adsorption isotherm of estrogens could be well presented by the Freundlich model and thermodynamics studies explained that nZVI-biochar could spontaneously remove estrogens pollutants and the main mechanisms involved π-π interaction, hydrophobic interaction, hydrogen bonding and degradation through ring rupture. The products analyzed by GC–MS showed that estrogens degradation was primarily attributed to the benzene ring broken, and Fe³⁺ promoted the production of free radicals, which further proved that nZVI-biochar had the excellent adsorption performances. Generally, nZVI-biochar could be employed as a potential material for removing estrogens from wastewater.

Funding

Study on Colloidal Coagulation and Heavy Metal Adsorption Mechanism of Sediment River(42007158); Study on the distribution characteristics of birds and the reduction technology of typical pollutants in their habitats in the Yellow River basin (Henan section)(23B180008)