The purification and densification of wastewater play an important role in water recycling, especially if the materials used in water recycling are other types of recycled waste. Therefore, considering this view in this study, the biosynthesis of silver-decorated chromium oxide nanoparticles utilizing a wasted (garlic) peel extract is investigated. The aqueous extract of garlic peel (GPE) was treated with silver nitrate, chromium nitrate, and a mixture of silver nitrate and chromium nitrate to synthesize silver nanoparticles (Ag-garlic), chromium oxide nanoparticles (CrO-garlic), and silver-decorated chromium oxide nanoparticles (Ag@CrO-garlic), respectively. The synthesized nanoparticles were elucidated via thermal gravimetric analysis (TGA), infrared spectra (FT-IR), absorption spectra (UV-Vis), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Antimicrobial activity studies were conducted against waterborne germs, bacterial strains (, , , and ), and fungal strains (, , , , and ) and showed significant levels of antimicrobial activity. The results revealed that Ag@CrO significantly improved antimicrobial activity due to their synergistic effect. The photocatalytic activity of nanoparticles was assessed using Rhodamine B dye (5 ppm) under solar irradiation. CrO-garlic exhibited the best activity as a photocatalyst among the studied nanoparticles, with 97.5% degradation efficiency under optimal conditions.