Pyrolyzing pharmaceutical sludge to biochar as an efficient adsorbent for deep removal of fluoroquinolone antibiotics from pharmaceutical wastewater: Performance and mechanism

This study explored the impact of pyrolysis parameters and modification methods on the characteristics of pharmaceutical sludge biochar, and investigated its capacity and mechanisms for levofloxacin (LEV), a typical fluoroquinolone antibiotics, adsorption. The results showed that SBET of the biochar was improved with temperature increase, but decreased when temperature reached 900 °C. Under the optimal pyrolysis condition of 800 °C and 90 min, the biochar possessed the highest SBET of 264.05 m2 g-1, excellent iodine value of 401.41 ± 3.84 mg∙g-1 and phenol adsorption of 57.36 ± 3.39 mg∙g-1. Among KOH, ZnCl2, and CO2 modifications, ZnCl2 modification achieved the highest phenol adsorption of 123.40 ± 4.65 mg g-1, with a significantly improved SBET of 534.91 m2 g-1. The maximum LEV adsorption capacity of ZnCl2 modified biochar, PZBC800, reached 159.26 mg g-1, which overwhelmed the reported sludge biochars. BET, zeta potential, FT-IR, XPS, and Raman analysis, along with quantum chemistry calculation, revealed that pore filling, hydrogen bonding, π-π interaction, surface complexation, and electrostatic interaction were the main mechanisms for the excellent LEV adsorption performance of PZBC800. Deep removal (99.9%) of Fluoroquinolones (FQs) from pharmaceutical wastewater was also achieved by PZBC800 adsorption. The study promoted the development of pharmaceutical sludge biochar preparation and its application in advanced treatment of FQs pharmaceutical wastewater.