## 3 Results and Discussion
### Anaerobic Digestion of the BWW and PE Mixture
#### 3.2.2 Molecular Characterization of Microbial Communities in the Hybrid Anaerobic Reactor
The composition of the phyla with relative abundances of bacterial communities greater than 1% in at least one sample is illustrated in Figure 5. There were detected nine major phyla including Actinobacteria, Bacteroidetes, Cloacimonetes, Firmicutes, Fusobacteria, Proteobacteria, Spirochaetae, Synergistetes, and Tenericutes, accounting for 97.1% (PE)-99.9% (BWW) of the entire bacterial community. Members of phyla Bacteroidetes, \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Relative Abundance (\%)**} \\  & **Bacteria** & **Archaea** & **Unassigned** \\ \hline BWW & 100.0 & 0.00 & 0.00 \\ PE & 99.73 & 0.27 & 0.00 \\ HRT 6.7 d (IN) & 99.26 & 0.71 & 0.03 \\ HRT 3.0 d (OUT) & 99.81 & 0.19 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Relative abundance of the Bacteria and Archaea domains. Figure 4: Alpha rarefaction curves for the occurrence with which OTUs were detected at each sample from effluents and from hybrid anaerobic reactor. PE—piggery effluent; BWW—brewery wastewater; HRT—hydraulic retention time; OUT—operational taxonomic unit. Cloacimonetes, Firmicutes, Proteobacteria, Spirochaetae, and Synergistetes are known to be part of a structural community that efficiently converts the biomass, chemically complex feedstocks, into high-yield methane containing biogas [62]. Proteobacteria, Firmicutes, and Bacteroidetes are likely abundant in all anaerobic digestion systems and have been referred to by several authors (e.g., [59; 60; 61; 63]). Moreover, these phyla contain several species whose metabolism can contribute to one or more of the phases of the general anaerobic digestion process. A diverse bacterial population was found in both effluents (Figure 5), being dominated mainly by Bacteroidetes (53%) on BWW and by Firmicutes (65%) on PE. These bacterial populations remain predominant throughout the experiment, and Firmicutes increases from 41% to 49% on the last phase (HRT 3 d OUT) becoming the predominant phylum in this sample. The observed decrease in Bacteroidetes during anaerobic digestion further implies that it may have competed with Firmicutes over the same resources on the reactor, the latter prevailing. [PERSON] et al. [64] already mentioned that Bacteroidetes and Firmicutes have been identified as the main bacterial phyla present within anaerobic digesters. Most of members of the phyla Bacteroid are known for their ability either to convert easily degradable amino acids, sugars, and alcohols into VFA, which emphasizes their potential crucial role in acido- and acetogenesis. On the other hand, the Bacteroidetes activity can be self-inhibited by the accumulation of acids [65]. Some Firmicutes are known to be syntrophic bacteria capable of degrading VFAs, such as butyrate and its analogues [63]. In addition, most of strains in the phylum Firmicutes might hydrolyze cellulose, glucose, starch, and proteins into small molecular organic acids such as acetate, highly contributing to improvement of the methane production yield [66; 67]. Microbial community profiles are demonstrated with more detail at genus level in Figure 6. In the anaerobic digestion process, most of the members of Bacteroidetes were assigned to _Bacteroidates or Flavobacteriales_, respectively, at 33% and 18% for HRT 6.7 d IN and HRT  
Figure 5: Relative abundance and dynamics of bacterial communities, taxonomic classification of bacterial reads at phylum level in samples collected at different operating conditions and effluents. BWW—Brewery wastewater, PE—Piggery effluent, HRT—Hydraulic retention time, OUT—Operational taxonomical unit.