Adsorption of levofloxacin on natural zeolite: effects of ammonia nitrogen and humic acid

Abstract

The persistence of antibiotics in sewage treatment plants in recent years has become a serious problem. Meanwhile, humic acid and ammonia nitrogen are widely distributed in natural reservoirs and might influence the sorption, migration and transformation of antibiotics. In this study, natural zeolite (NZ) was evaluated as an adsorbent for the removal of levofloxacin (LEV). The physical and chemical properties of NZ before and after adsorption were characterized by various analytical techniques to develop the mechanism. The effects of ammonia nitrogen and humic acid (HA) on the interfacial behavior of LEV on NZ were explored. Comparative experiments revealed that LEV adsorption on NZ involved electrostatic interactions and ion exchange, and the adsorption processes were well fitted by the Langmuir isotherm model and pseudosecond-order kinetic model. The maximum experimental adsorption capacity of LEV was 22.17 mg·g−1 at pH 6.5. The presence of ammonia nitrogen and HA significantly suppressed the adsorption of LEV due to competitive adsorption, and the adsorption capacity decreased 58 and 46%, respectively. It is obvious that low concentrations of ammonia nitrogen and HA are conducive to improving the treatment effect of sewage. This study demonstrates that NZ is a promising and efficient material for LEV adsorption. HIGHLIGHTS The adsorption mechanisms are electrostatic interactions and ion exchange mainly.; Chemical reaction mechanism and intraparticle diffusion mechanism are proposed.; Ammonia nitrogen leads to cation competition and electrostatic competition.; Humic acid performs a negative effect on adsorption.;

Keywords

• competitive adsorption
• electrostatic interaction
• ion exchange
• levofloxacin
• natural zeolite