Biocinosis refers to the totality of all living organisms, in particular microorganisms, that live together and interact in a specific ecosystem or technological system. In biological wastewater treatment or in biofilters, the biocinosis is decisive for the performance of the system, as the microorganisms break down pollutants through their metabolic processes. The composition and balance of the biocinosis significantly influence the efficiency of biological degradation processes in water and wastewater treatment plants.