Walnut shell biochar based sorptive remediation of estrogens polluted simulated wastewater: Characterization, adsorption mechanism and degradation by persistent free radicals

The presence of steroid hormones in aquatic ecosystems is of prevailing concern attributable to their potential for endocrine disruption. Biochar (BC) is capable of liquid organic pollutants removal because of distinctive characteristics. The purpose of this study was to investigate the results of steroid hormone removal by walnut shell biochar produced at pyrolysis temperatures ranging from 400 to 700 °C. Surface assimilation mechanism and degradation behavior of the most important estrogens: estrone (E1), 17β-estradiol (E2), together with estriol (E3) were unequivocally supported by biochar characterization. The results indicated that the chemosorptive removal of estrogens was directly associated with the pyrolysis temperature of biochar due to completely different surface structure and chemical composition. The following conditions were investigated for maximum surface assimilation of estrogens: biochar at pyrolysis temperature 700 °C, pH 4, biochar dosage of 0.1 mg mL −1, and estrogen concentration of 2500μg L−1 at 25 °C. The experimental data fit well with the Pseudo-second-order and Freundlich isotherm models. Through electron paramagnetic resonance spectrometry (EPR) and gas chromatograph–mass spectrometer (GC–MS) analysis, it was discovered that persistent free radicals contributed to estrogen degradation, and the estrogen degradation pathway was tentatively projected to support the intermediate merchandise. Based on the findings of this study, biochar will doubtless be used for the fast and economical removal of toxicant organic pollutants in water and sewer water.