One of the biggest problems nowadays is the severe pollution of the environment by unwanted emissions of persistent organic compounds into different parts of the ecosystem. Persistent organic pollutants include a large number of compounds that can be classified into several characteristic groups, such as pesticides, industrial chemicals, and unintentionally generated/produced by-products from incomplete combustion of fuels, thermal waste treatment, and other anthropogenic activities. In order to prevent or mitigate the harmful effects of such compounds on the environment and preserve the quality of life, scientists and experts are paying more and more attention to the research and development of heterogeneous photocatalytic processes. In this work, the photocatalytic degradation of the neonicotinoid acetamiprid, which belongs to the group of pesticides, was studied. The reactions took place in a rotating photoreactor under conditions of recirculation of the reaction mixture with an immobilized layer of TiO2 photocatalyst and with a UV-A radiation source under different operating parameters. The influence of various parameters was studied: recirculation flow rate of aqueous acetamiprid solution (30 - 400 mL/min), the rotation speed of the central tube of the photoreactor coated with photocatalytic layer (0 - 400 rpm), and surface area of photocatalytic layer (80 and 160 cm^2). The obtained results show that the optimization of working conditions significantly affects the efficiency of photodegradation. It was found that the optimal conversion of the organic component is achieved at a speed of 100 rpm of the central tube of the photoreactor, at a recirculation flow rate of the reaction mixture of 200 mL/min, and at the largest surface area of the immobilized photocatalyst layer (160 cm^2). The presence of a photocatalyst in the reaction system is not a sufficient prerequisite for successful degradation of the model component unless suitable photoinduced activation of the photocatalyst occurs. It was also found that photolytic degradation is negligible compared to photocatalytic degradation.