Azolla microphylla extract ZnO nanoparticles and antibacterial activity: eco-friendly wastewater treatment

Antibiotic resistance in bacteria is a concern for wastewater treatment worldwide. Having bactericidal properties, the use of nanomaterials for disinfecting wastewater has become the interest to overcome the limitations of the existing technologies. ZnO nanoparticles have shown their characteristic antibacterial properties; however, synthesizing the same in conventional chemical-based methods is not environmentally sustainable. Therefore, green synthesis of ZnO NPs might be the option for utilizing the nanomaterial. In this study, extract of Azolla microphylla, an invasive aquatic weed was tested for its potential for ZnO NPs synthesis. The synthesized nanoparticles were characterized using spectroscopic techniques and scanning and transmission electron microscopy. Disk diffusion assay of these nanoparticles demonstrated significant antibacterial zones against Pseudomonas aeruginosa and Staphylococcus aureus. Growth kinetics broth dilution study established bactericidal activity with minimum inhibitory concentration (MIC) in the range of 80–100 mg/L which is much less than values previously reported in the literature. These findings demonstrate that the synthesized ZnO nanoparticles display excellent antibacterial activity against both Gram-positive and Gram-negative bacteria. Based on the above findings, a continuous flow quartz column study was performed using ZnO NPs and activated carbon in layers, which disinfect and decolorize water contaminated with P. aeruginosa, suggesting the use of ZnO nanoparticles as a potential component for wastewater treatment. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.