Due to the potential microbiological hazard associated with discharging treated sewage into the receiving body, its disinfection is a key issue to protect ecological safety and human health. Water scarcity and drinking water supply, irrigation, rapid industrialization, use of treated water, protection of water sources, overpopulation and environmental protection force us to look for solutions to ensure safe reuse of wastewater, and this depends primarily on the quality of wastewater disinfection. Many wastewater disinfection methods are commonly used. One of the chemical processes of disinfection sludge is ozonation. Ozonation is widely used in wastewater treatment by oxidation, because ozone is a very strong and effective oxidizing agent. Studies have shown that the effectiveness of ozone in disinfecting water and sewage is up to 50% greater than that of chlorine . An additional advantage of this method is that it also eliminates odors that may be unavailable. The article presents the results of research on the effectiveness of ozonation treatment in the disinfection of treated sewage, based on indicator bacteria such as coliforms, including Escherichia coli, mesophiles, psychrophiles, and spores. The study took into account various effects of time (dose) and temperature. For the purpose of this study, both traditional and modern methods of assessing microbiological quality of wastewater were used. The first one is represented by conventional culture measurements and the second one by using a luminometer (ATP) and flow cytometer (FCM).