The abundance of hygienically relevant microorganisms in wastewater requires adequate treatment of wastewater prior to discharge into sensitive natural waters and, in particular, prior to intended reuse. Inactivation of pathogenic microorganisms through wastewater disinfection plays a fundamental role in the protection of public health against waterborne diseases. At the outset of this research project, the principles and methods of wastewater disinfection were introduced through a literature review. Subsequently, pilot plant experiments were performed in a municipal wastewater treatment plant. Hygienic, ecological, and operational aspects of different wastewater disinfection systems were examined, also with regard to feasible reuse applications. In addition to chlorine gas that was produced electrolytically, chlorine dioxide, ozone, and UVradiation were also selected as disinfectants, because they are commonly used for disinfection of treated wastewater. These disinfection techniques were tested in parallel and under identical experimental conditions, subsequent to different wastewater treatment schemes. It could be shown that the investigated disinfection processes, together with preceding biological wastewater treatment, produced an effluent that complies with commonly regulated hygienic discharge parameters (generally E. coli) for sensitive receiving waters and for various reuse purposes. Wastewater treatment prior to disinfection had a decisive influence not only on the disinfection efficiency but also on the microbiological stability of the treated water. On the basis of the current results, at least mechanical-biological wastewater treatment before disinfection is recommended, in particular if water re-use is intended. Advanced wastewater treatment led to a reduction of negative toxicological effects of the effluents. In all effluents that contained no or very low levels of residual disinfectants, an increase in the concentration of heterotrophic culturable miroorganisms was already observed after 24 hours of stagnation. In the course of further stagnation, concentrations were more than 100-fold higher in chemically disinfected samples with no or very low levels of residual disinfectants than in the non-disinfected sample. A substantial increase in E. coli concentration was not detected after application of any of the disinfection techniques. However, in the absence of E. coli, the concentration of facultative pathogenic bacteria increased in the samples disinfected with UV-radiation (low dose) and ozone, which may pose a potential health risk to water users. The formation of a variety of disinfection by-products could be detected in all effluents of the disinfection systems, except after UV-irradiation. At the same time, these effluents showed an increase in toxicity with increasing doses of disinfectants. This increased toxicity was most pronounced after chlorine electrolysis, followed by the effluents following ozonation. After dosage of chlorine dioxide, toxicity increased in only a small percentage of samples. Results of the current study indicate that sand filtration can contribute to a decrease regrowth potential as well as to a decreased toxicity of the disinfected effluents. Simultaneous extensive elimination of micropollutants during wastewater disinfection could be achieved only with ozone. The addition of a further wastewater treatment process enhances capital and operating costs as well as the energy demand of the wastewater treatment plant. The most cost-effective process was UV-irradiation. The highest cost wascaused by wastewater disinfection with chlorine dioxide. Dosing of chlorine dioxide was responsible for the lowest and ozonation for the highest electrical energy demand within the system boundaries (wastewater treatment plant). A strategy to control the dosage of disinfectants was established, on the basis of the results achieved. A plant control system that sets the momentarily required disinfectant dose as a function of the UV absorption (at 254 nm), measured online, can contribute to a decrease in the doses of applied disinfectants and to a minimization of negative environmental impacts of the disinfection process.