Copper oxide nanoparticles removal by coagulation and optimization by matter–element analysis model

Nanoparticles have been inspected in water environment and sewage treatment plants, but how to achieve efficient removal of them through existing treatment processes is a potential issue. In this study, the organic–inorganic composite coagulant (PAC-CA) was applied to remove copper oxide nanoparticles (CuO-NPs) and study their coagulation behavior and the characteristics of flocs produced by coagulation. Under the optimal coagulation conditions with a dosage of 25 mg/L, pH of 7, stirring intensity of 200 s⁻¹, and settling time of 15 min, the removal rates of CuO-NPs and turbidity were 89.83% and 93.51%, respectively. Zeta potential studies show that the main action mechanism of PAC-CA under low dosage or alkaline conditions is charge neutralization, and under high dosage or acidic conditions, the main action mechanism is adsorption bridging. A matter–element analysis model was established based on the evaluation index of stirring intensity, kaolin concentration, humic acid concentration, initial CuO-NPs concentration, pH, PAC-CA dosage, turbidity removal rate, and CuO-NPs removal rate. Kaolin can promote the removal of CuO-NPs and turbidity by PAC-CA. The main action mechanisms of PAC-CA are charge neutralization and adsorption bridging. PAC-CA has good coagulation performance for CuO-NPs wastewater, and provides a theoretical basis for the practical engineering application of coagulation for removing nanoparticles in wastewater.