The article is devoted to the modeling of widespread process of blowing gas through a liquid with several interacting substances in closed or top-opened unmovable reservoir. The model can be applied to wastewater treatment of the Kamianske city, as example of medium-size city, particularly to aeration tanks, where maintaining optimal conditions for the biological degradation of pollutants is important. The article presents a fuzzy control system and mathematical model, which accounts for key variables including ammonia concentration, oxygen level, and the concentration of activated sludge, all of which are essential for effective wastewater purification. The results show overall trend of gradual reduction in outlet ammonia concentration. In addition, the observed trends show that increasing of active sludge concentration can lead to worse or the same treatment efficiency when dissolved oxygen is low. In contrast, the level of dissolved oxygen much better affects of the resulting ammonia concentration. The effectiveness of the fuzzy control approach is demonstrated during simulations that show improved regulation of ammonia and oxygen levels, as well as enhanced maintenance of activated sludge concentration. This approach offers a solution with practical significance for optimizing the performance of aeration tanks, contributing to more efficient and sustainable wastewater treatment process.