# Rationale for the Combined Use of Biological Processes and AOPs in Wastewater Treatment Tasks
## 3 Results and Discussion
### Modeling the Effects of Antibiotics and Surfactants on the Activity of Bioprocesses  
Based on the obtained quantitative data, the diagram in Figure 7 shows the diameter of the antibiotic growth suppression zone. In in vitro experiments in all Petri dishes, we observed the same pattern. The value diameter of the growth retardation of the standard disk with amoxiclav by the accumulative culture of activated sludge was 17.3 \(\pm\) 2 mm at a concentration of 4 mg/dm\({}^{3}\) (I), and 31.3 \(\pm\) 3 mm at a concentration of 6 mg/dm\({}^{3}\) (S). The mean growth retardation when cultured with an antibiotic concentration of 2 mg/dm\({}^{3}\) and without antibiotic was 4.7 \(\pm\) 2 mm and 3.2 \(\pm\) 2 mm (R), respectively, which shows the insensitivity of the accumulative activated sludge culture to low concentrations of this antibiotic. The zone of stunting around the disc with amoxiclav at a maximum dose of 8 mg/dm\({}^{3}\) was the largest in all dishes, and was 40.8 \(\pm\) 5 mm (S). To distinguish between the three categories of sensitivity (or resistance), the so-called breakpoint concentrations of the antibiotic (or borderline values of the diameter of the zone of microbial growth suppression) are used. During the first 24 h, colonies began to grow; by the fourth day, colonies filled almost the entire surface of the growth medium, except for circles of different diameters around several standard disks with different antibiotic doses. It is worth noting that the maximum bactericidal concentrations (MBCs) are not fixed values. They can be revised, depending on changes in the sensitivity of the microbial population in the activated sludge's biocenosis, which is consistent with previous studies [14; 16]. The high duration of inhibition of the active biomass in the presence of non-ionogenic surfactant should be noted. At almost all concentrations studied--even at the minimum concentration of 10 mg/dm\({}^{3}\)--the activated sludge was not completely recovered, which was expressed in a decrease in its quantity and in the inability to aggregate flakes of activated sludge at the end of the indication process (16 h) compared to the initial content (Figure 8). Figure 7: Interpretation of the results of determining the sensitivity of the storage culture of activated sewage sludge. Increasing the concentration of surfactants significantly worsened the condition of the mixed population of microorganisms, as evidenced by the process of deflocculation of activated sludge observed by visual inspection using light microscopy (Figure 7). The recovery potential of activated sludge at the end of the biological wastewater treatment process was significantly influenced by its initial condition, indicating the need for the long-term regeneration of impaired activated sludge, as confirmed in several previous studies [5,19]. Thus, the results of this experiment cannot be accepted as positive, even at a surfactant concentration of 10 mg/dm\({}^{3}\). This has a negative effect, which may be associated with structural changes in the qualitative composition of the microbiocenosis, leading to a decrease in species diversity, which confirms the results of previous studies [5,6,20]. A well-functioning activated sludge system always depends on a wide range of species within it, which has also been noted in [19]. When exposed to various unfavorable factors, there is a high probability that overly sensitive and less adapted species will leave the given community, and that their ecological niches will be occupied by the most adapted species and, as a whole, the community can continue its existence. However, from a practical point of view, considering the activated sludge's biocenosis as a biological system of wastewater treatment for various kinds of pollutants, such shifts in species composition will negatively affect the processes of removing a wide range of substances and water treatment in general, as confirmed in previous studies [5,13,19,35].