This Diploma thesis was focused on the degradation of dyes Saturn Red L4B (Direct Red 79) and Saturn Blue LB (Direct Blue 106) by DC diaphragm discharge (DC-DD). Supplied power was between 160 and 180 W. Conductivity and pH were changing at each electrode area during the DC diaphragm discharge, therefore the effect of pH and conductivity changes on the dye solution itself were examined. All samples were measured by UV-VIS spectrometer in the wavelength range of 300–800 nm. No significant dependence of dye absorption spectra on conductivity was observed, while pH significantly affected the absorption curves of dyes. Ageing of dye spectra showed significant changes of Saturn Red L4B. Next task was the comparison of dyes destruction efficiency by DC-DD, audiofrequency diaphragm discharge (AF-DD) and electrolysis. Dye decomposition by AF-DD was not observed at set conditions (voltage of 80–120 V, current of 2.2 A and frequency of 2 kHz). In the case of DC diaphragm discharge the electrolysis played an important role. Decomposition efficiency of the dyes by electrolysis was up to 15 %. The pumping effect in the DC diaphragm discharge was also investigated. Although the individual electrode areas were linked only by a small pinhole in a nonconductive barrier (the pinhole diameter of 0.3 mm), solutions of the anode and cathode compartment interacted with each other up to 10 %. Finally, the degradation products of Saturn Red L4B treated by DC-DD in two electrodes parts are also described. Decomposition products were determined by high performance liquid chromatography (HPLC) combined with the mass spectrometer.