Nowadays recycling wastewater is a task in progress. New ways of contamination have appeared together with the technology development. Our article deals with the case of wastewater contaminated with dispersed colorants that are used during the decoration of paper boxes for packaging various products. The wastewater treatment is based on the electro-flotation process. The system is fully automatic, with a possibility to set the time interval for the length of electro-flotation in the tank. The set of experimental laboratory work with equipment development is aimed at optimizing the time interval to manage the proper conditions according to the color used for decoration. LEDs are used to monitor the process. The results are analyzed using statistical methods. The optimum time interval of electro-flotation in a tank for the blue color was set at 25 min.