Municipal wastewater is characterized by diverse microbial content, largely dependent on their sources as well as many other factors like condition and health of their producer, but also environmental factors. The number and share of individual bacterial population in wastewater is changing during the process of their treatment in wastewater treatment plants. The microbial content of treated wastewater is significantly affected by the type of technology used for wastewater treatment. The paper presents the results of the species composition of bacteria present in the wastewater at various stages of treatment for the two different technologies. Samples of wastewater from hydroponic wastewater treatment plant and from the plant which technology is based on biofilters were analysed. A key mechanism for wastewater treatment in both cases is biological treatment, using microbial activity that decomposes pollutants in the wastewater, which significantly contributes to changes in the species composition of bacteria comparing to microbiological composition of sewage flowing into the treatment plant. Analyses of microbial composition showed that in the objects consisting of preliminary tank and biofilter, composition of bacteria species is changing, but many species isolated from raw sewage is also found in treated wastewater. In the plant with hydroponic lagoon after wastewater treatment throughout the process system, bacteria present in raw sewage or in wastewater after biological treatment were not identified in the outlet.