The instant application describes methods of treating wastewater containing pathogenic microorganisms to reduce the concentration of those pathogenic microorganisms. The methods include measuring parameters or qualities of the wastewater, and using those parameters or qualities to determine the wastewater's ozone demand. The wastewater is dosed with ozone, with the dosage being less than the ozone demand. The ozone and wastewater are mixed with a static mixer, and the wastewater is oxidized by the ozone. Thereafter, the wastewater is disinfected via ultraviolet radiation treatment. The instant application further relates to a wastewater treatment system. The system includes an ozone reactor with a static mixer, an ozone supply device, at least one sensor, and an ultraviolet radiation disinfection unit. The ultraviolet radiation disinfection unit is located downstream from the ozone reactor.