Nanoscaled zero valent iron natural zeolites for removal of antibiotics from wastewater

Abstract

Nowadays, antibiotics have emerged as new kinds of organic micropollutants found in conventional sewage wastewater treatment plants, indicating the failure of coagulation-flocculation in treating antibiotics-containing wastewater. It might lead to the disperse of antibiotic resistance, which has a massive impact on human health and economic consequences globally. In recent years, nanoscale zero-valent iron (NI) has shown promising results for wastewater remediation to remove various contaminants. Thus, natural zeolite-supported nanoscale zero-valent iron (NI-NZ) has been proposed as a novel alternative to remove tetracycline (TC) and oxytetracycline (OTC). Synthesised NI-NZ was characterised using nitrogen adsorption-desorption, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The performance of the TC and OTC removal using NI-NZ in batch adsorption was assessed. The preliminary removal performance of natural zeolite (NZ), NI, and NI-NZ was compared, and it was observed that NI-NZ had a better performance in removing TC (333.33 μmol g−1) compared to OTC (285.71 μmol g−1). Thus, NI-NZ was chosen as the adsorbent and TC as the target antibiotic for further tests involving other parameters. The effect of vital parameters comprising initial pH, adsorbents dosage, temperature, initial antibiotic concentration, and contact time was studied. The optimum condition was at pH 3, 30 ◦C, and 1 g L−1 NI-NZ with approximately 97% of TC removed. Besides, the adsorption of TC has been proven to follow Langmuir and Temkin isotherm models. Kinetically, the process was best suited in the pseudo-second-order (PSO) and Elovich kinetic model. Furthermore, the thermodynamic study indicated that the reaction at room temperature was exothermic and spontaneous. The usability of NI-NZ in the continuous flow process has also been evaluated by using a fixed-bed column. The column experiments demonstrated that the breakthrough time increased with decreased initial TC concentration and flow rate and increased bed height. The cumulative kinetic data were in good agreement with the PSO and Elovich kinetic models. The Thomas and Yoon-Nelson models exhibited the closest predicted dynamic profile with the experimental results for all test conditions regarding the breakthrough curve. The applicability of NI-NZ in the adsorption coagulation-flocculation (ACF) process was evaluated using a jar test to remove TC from simulated wastewater. The outcome was encouraging because NI-NZ in ACF enhanced TC elimination from 10% to 75% at pH 3 with 0.4 g L−1 NI-NZ. The Langmuir isotherm model and PSO kinetic model were the most suitable model to represent the adsorption of TC via ACF. In conclusion, NI-NZ was successfully synthesised in this study. It has a high prospect of becoming one of the most effective solutions to remediate antibiotics-polluted wastewater because of its high applicability in batch adsorption, continuous adsorption, and ACF processes.