## 3 Results and Discussion
The total number of 118,579 _165 rRNA_ sequence reads assigned to different operational taxonomic units was obtained by Illumina MiSeq platform (Appendix A Table A2). To assess the within-sample complexity of microbial population, the Shannon-Wiener diversity index (H\({}^{\prime}\)) was evaluated. The Shannon-Wiener species diversity index in inoculum was 3.67. At the final stage of the experiment the index was by about 8% higher in R\({}_{2}\) (3.67) compared to R\({}_{1}\) (3.39). At a species level (Table 1), the most abundant in inoculum was _Dokdonella ginsengoli_ (19.6%), _Tetrasphaera_ sp. (3.8%), _Lysobacter daejonenensis_ (3.7%), _Terrinonas arctica_ (3.3%) and _Candidatus Competibacter_(3.2%). In R\({}_{1}\) at the end of the experiment, biomass was dominated by _Dokdonella ginsengoli_ (20.0%), _Amaricoccus tamworthensis_ (10.9%), _Thuera_ sp. (10.7%), _Candidatus Competibacter_ sp. (5.1%) and _Arenimonas_ sp. (4.1%). _Dokdonella ginsengoli_ (16.0%), _Candidatus Competibacter_ (7.7%), _Arenimonas_ sp. (2.5%) and _Thuera_ sp. (2.4%) dominated also at the end of the experiment in R\({}_{2}\). During the experiment disappearance or reduction of the percentage was observed for _Acidobacterium_ sp., _Tetrasphaera_ sp., _Terrimonas arctica_, _Roseiflexus_ sp., _Ignavibacterium_ sp., _Ottowia_ sp., _Rhodoferax_ sp., _Nannocystis_ sp., _Tolumonas_ sp., _Aquimonas_ sp. and _Lysobacter daejonenensis_. In the present research, large changes in the structure of microorganisms colonizing the inoculum and granular sludge were noted throughout the experiment. [PERSON] et al. [30], observed that during the granulation of activated sludge the percentage of _Competibacter_ sp. increased and bacteria of the _Xanthomonadaceae_, _Rhodospirillaceae_, and _Aminobacter_ family appeared. According to the authors, occurrence of such bacteria as _Zoogloea_ sp., _Xanthomonadadeae_, _Splingomonadales_, and _Rhizobiales_ promotes the formation of EPS that are responsible for biomass granulation. In the present study, _Xanthomonadaceae_ (_Dokdonella ginsengoli_, _Lysobacter daejonenensis_) were found to be responsible for the formation of EPS and denitrification in biomass. The presence of microorganisms from the above-mentioned families promotes granulation and affects the strength of the resulting granules. Bacterial taxa unique for the biomass from R\({}_{1}\) were identified including e.g., _Pseudonocardiabensis_, _Amaricoccus tamworthensis_, _Paracoccus_ sp., _Paracoccus_ yeei_, _Arenimonas_ sp. Many environmental bacteria isolated, among others, from water and soil possess the ability to break down fats, oils and greases [55]. The presence of complex compounds such as proteins, lipids or polysaccharides in wastewater stimulates growth of microorganisms in the biomass that carry out the hydrolysis of complex organic compounds, e.g., _Splingobacteriales_, _Chitinophagaceae_, or _Flavobacterium_ sp., which were also observed in the presented studies. In the granules, _Burkholderia_ sp., and _Pseudomonas_ sp. have been also identified that can break down lipids to fatty acids [56; 57]. In the structure of aerobic granules, lipids occur peripherally in EPS, thus, the fats in the influent may attach to the surface of the granules and impede the transfer of oxygen deep into its structure increasing the demand of oxygen for microorganisms [58]. The ordination diagram (Figure 8) shows that at the level of the species variable aeration conditions in the reactor cycle did not affect the composition of microbiota (\(p=0.18\), F = 1.66), while the number of reactor working cycles significantly affected it (\(p<0.01\), F = 3.61). There was a strong positive correlation between the percentage share in the biomass of _Gemmbacter_ sp. (R = 0.98), _Flexibacter_ sp. (R = 0.96), _Paracoccus yeei_ (R = 0.85) and _Rhodobacter_ sp. (R = 0.97) and the experimental cycle indicating that these taxa were important for efficient treatment of meat-processing wastewater. A negative correlation was observed, among others, for _Ignavibacterium_ sp.