Wastewater contaminated with organic substances (dye production and food industry) causes great harm to the environment. Among food enterprises, the dairy industry leads in wastewater production. The purpose of this article is to study the use of a heterogeneous Fenton system based on a pre-synthesized nanostructured magnetically separable catalyst CoFe2O4/SiO2/CuO for fine post-treatment of dairy wastewater. The structure of the obtained composite was confirmed by Fourier transform infrared spectroscopy (FTIR). The surface morphology of the particles and the elemental composition were determined using a scanning electron microscope (SEM). The studied catalyst was tested on simulated dairy wastewater. The content of organic compounds was analyzed by chemical oxygen demand (COD), O2 content, redox potential (ORP) and medium pH. The effect on the oxidation process of organic compounds in the Fenton system of replacing the oxidant hydrogen peroxide with air oxygen was studied. The dependence of the efficiency of the oxidation process on the amount of supplied oxygen was shown. It was established that when using O2 as an oxidant, the catalyst forms organoperoxide compounds that are responsible for the complete oxidation of organic pollutants. It was determined that for fine treatment of dairy wastewater the optimal system is «dairy wastewater : O2 : CoFe2O4/SiO2/CuO», in which the degree of oxidation of organic pollutants reaches 96%, and the value of chemical oxygen demand (COD) decreases from 115 mgO2/dm3 to 10 mgO2/dm3. The efficiency and easy extraction of the magnetically separable catalyst allows for the implementation of a cyclic water use scheme and makes the proposed system economically viable and environmentally friendly.