The toxicity of different forms of mineral nitrogen, particularly the reduced ones, is a significant factor driving the attention to water quality in rivers within the Republic of Moldova. Ammonium, in particular, is of great concern due to its similarity to an amino acid, where a hydrogen atom is substituted with an organic radical containing a carboxylic group. Amino acids are the building blocks of proteins, the essential molecules supporting life processes. As a result, ammonium in aquatic environments can play a dual role: it can serve as a building block for the creation of living organisms and also provide energy support for the activities of aquatic organisms. Ammonium serves also as a universal catalyst for the emergence of a new state within the aquatic environment. Laboratory modeling involving by ammonium initiation is highly responsive to the presence of anthropogenic pollutants, such as surfactants, heavy metals, and the existence of antibacterial agents, among others. It can even detect variations in the different states of these pollutants within the aquatic (polluted) environment. Consequently, the discharged water into the natural water bodies often fails to meet these two crucial (trophic and environmental) water quality indicators for a river. Starting from the pollution source (the city of Soroca, Republic of Moldova) along the water course, laboratory simulations easily highlight the degree of selfpurification. For instance, comparing the ammonium (NH4 +) oxidation process in water samples from the Nistru River, Vărăncău section, with those from the Bursuc section, reveals a difference in the time required for ammonium oxidation in samples subjected to the same modeling approach. This difference becomes even more pronounced when fine particles of calcium carbonate are added to the river water samples. The decomposition of the complex compounds of anionic and cationic surfactants (SAS An ∙ SAS Ct), in which the cationic component constitutes a bacteriotoxic pollutant, leads to the stagnation of self-purification process. This phenomenon is commonly observed in technologized biological treatment systems. In wastewater treatment plants (WWTPs), the phenomenon of inhibiting ammonium oxidation occurs, especially when oxidation did not occur at the initial stage of treatment, where both aerobic and anaerobic processes take place, involving the oxidation of ammonium ions, as well as the reduction of nitrates and nitrites returning from the final stage of the treatment process. Typically, in wastewater treatment plants (e.g., WWTP Chisinau), the emergence phenomenon is combined in the final stage with an inhibition of the oxidation and assimilation of both organic carbon and ammonia nitrogen. Therefore, the discharged water into the natural water bodies often fails to meet these two crucial water quality indicators for a river. Laboratory simulations conducted with river water samples exhibit sensitivity to the presence of various substrates, including different fractions of granite and spongy clay. These simulations reveal an acceleration in the oxidation of both ammonium and nitrite ions, underscoring the clear and beneficial effects of self-purification processes.