Water pollution is one of the most current problems related to human life and survival. The high degree of pollution of the human environment is contributed, among other things, by the discharge of industrial wastewater into rivers, among which wastewater from the graphic industry is of great importance. With conventional wastewater treatments, such as secondary biodegradation, many pollutants cannot be completely removed. Synthetic dyes can be a potential hazard for living organisms. Also, heavy metals are present in some types of printing inks. On the other hand, with advanced technologies, it is possible to obtain high quality water. Photocatalytic degradation is a promising and widely used method when it comes to the treatment of wastewater and air contaminated with both organic and inorganic pollutants. Photocatalytic processes have many advantages when it comes to removing pollutants from water in low concentrations. The aim of this paper is to investigate the possibility of applying the process of photocatalytic degradation, using titanium (IV) oxide modified with magnetite nanoparticles, in the treatment of magenta effluent originating from the graphic industry. In order to optimize the entire process, a new statistical method of definitive screening design (DSD) was used, where the influence of individual process parameters.