Abstract Description

In this study, an extracellular silver nanoparticle synthesis approach was employed using Bacillus safensis cell culture under varying pH conditions. These were further characterized via the Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses. The bioremediation capabilities of the biosynthesized B. safensis nanoparticles (Bs-AgNPs) were tested in the removal of nutrients (total nitrogen and total phosphorus) and heavy metals (Cu, Ni, Cd) from the sludge. Furthermore, the antibacterial activities of Bs-AgNPs were also tested against enteric bacterial pathogens, namely, Staphylococcus aureus, Enterococcus faecalis, and Shigella flexneri. The XRD analysis of Bs-AgNPs (Bs4-AgNPs, Bs7-AgNPs, and Bs10-AgNPs) revealed peaks at 2θ angles of 32.6˚, 48.4˚, 55.5˚, 67.5˚, and 77.4˚, confirming the face-centered cubic crystalline structure of the nanoparticles. The FT-IR spectra displayed prominent peaks at the regions of 3200-3500 cm⁻¹, 2800-3000 cm⁻¹, 1600-1700 cm⁻¹, and 1000-1500 cm⁻¹, corresponding to hydroxyl, alkanes, and amine groups, respectively. According to the TEM analysis, it was observed that Bs10-AgNPs exhibit the smallest nanoparticles, with a median size of approximately 30 nm and a narrow size distribution. In comparison, Bs7-AgNPs produce slightly larger nanoparticles, measuring around 35 nm, but with a narrower distribution than Bs4-AgNPs. The results indicate that Bs4-AgNPs and Bs7-AgNPs demonstrated remarkable efficiency in removing Cu, Ni, and Cd within the initial 24-hour treatment period, surpassing Bs10-AgNPs. Bs4-AgNPs demonstrated the highest removal efficacy, achieving 70 % for TN and 90 % for TP, while also exhibiting antibacterial efficacy against all tested bacterial pathogens. Taken together, the study highlights that extracellular synthesis of silver nanoparticles using B. safensis under varying pH conditions yields nanoparticles with diverse sizes and distributions. Bs4-AgNPs showed the highest efficiency in removing nutrients and heavy metals and exhibited notable antibacterial activity, outperforming Bs7-AgNPs and Bs10-AgNPs in both bioremediation and antimicrobial tests.