Abstract Looking for a cost-effective and ecofriendly method for wastewater treatment is a global challenge. Therefore, this study investigated the removal of wastewater pollutants using copper oxide nanoparticles (CuONPs). CuONPs synthesized by a green solution combustion synthesis (SCS) and characterized by ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared (FT-IR), powder X-ray diffraction analysis (PXRD), and scanning electron microscopy (SEM) techniques. PXRD showed nanoparticle sizes ranging from 10 to 20 polycrystalline patterns indexed with two peaks corresponding to (111) and (113) reflections of the face-centered cubic CuO crystal. The energy-dispersive spectroscopy analysis obtained in conjunction with SEM analysis proved the presence of Cu and O atoms at 86.3 and 13.6%, respectively, confirming the reduction and capping of Cu with Hibiscus sabdariffa extract's phytochemicals. The CuONPs proved to be a promising decontaminant for wastewater found to reduce biochemical oxygen demand (BOD) and chemical oxygen demand (COD) by 56%, and very efficient in reducing both the total dissolved matter (TDS) and conductivity (σ) by 99%. The CuONPs removed simultaneously chromium, copper, and chloride with respective percentages of 26, 78.8, and 78.2%. Green synthesis of nanoparticles is a simple, rapid, cost-effective, and ecofriendly method that successfully removed contaminants from wastewater.