## 3 Results
### Toxicity of BPA in Activated Sludge
#### 3.1.5 BPA Interferes with the Microbial Population Structure of Activated Sludge
mobilis_ increased in stage I in the BPA group reactor, but showed a downward trend in stages II and III, indicating that the strain had strong BPA tolerance and could survive under a low concentration of BPA. However, medium and high concentrations of BPA were not conducive to the survival of this species, and eventually led to the decline of bacterial abundance until this species was eliminated. Different concentrations of BPA led to different dominant bacterial species aggregates. With the gradual increase of BPA concentration, the dominant bacterial species showed resistance to stress, and certain bacterial species \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **OTU** & **ACE** & **Chao1** & **Simpson** & **Shannon** & **Coverage** \\ \hline Control & 78 & 94.1917 & 95.1 & 0.0623 & 3.2316 & 0.9917 \\ stage I & 57 & 70.9609 & 72 & 0.169 & 2.4256 & 0.9932 \\ stage II & 32 & 38.1307 & 42.5 & 0.1667 & 2.1439 & 0.9979 \\ stage III & 24 & 47.6446 & 33 & 0.3546 & 1.3776 & 0.9981 \\ \hline \hline \end{tabular} Note: Sample ID is the sample name; Operational taxonomic unit (OTU) is the number of OTUs; Chao1, Ace, Shannon, and Simpson represent the indices; Coverage is the coverage of the sample library.  
\end{table} 
Table 1: Alpha diversity of each sludge sample. adapted to BPA and increased in abundance. In the future, the EDC degradation ability of these dominant strains and the role of related genes can be explored. A species heat map at the genus level (Figure 5C) was constructed to analyze the abundance of functional bacterial genera and their correlations with water purification. This study analyzed the top 40 most abundant genera, of which 24 genera were relatively abundant in the control sludge. However, under BPA stress, the abundances of these dominant genera decreased significantly, while different concentrations of BPA showed different population niches. Consistent with the research results of [PERSON] et al., the dominant bacterial genera in artificial sewage domesticated sludge were _Labilithrix_ and _Ferribaterium_[54]. _Porthiot_ can grow and attach to the surface of biofilms [55] and can decompose various organic macromolecules [56]. As an indigenous genus in activated sludge, _Ferruginibacter_ is the main strain involved in the degradation of organic matter [57]. _Polaromonas_ has an excellent ability to metabolize a variety of organic compounds and can efficiently degrade  
Figure 5: The effect of bisphenol A (BPA) on the microbial populations of sequencing batch reactor (SBR) activated sludge. (**A**) Phylum-level abundance; (**B**) Species-level abundance; (**C**) Genus-level heat map. (The color gradient from blue to red indicates a relative abundance from low to high). organic pollutants [58]. _Dechloromonas_ has a strong ability to accumulate polyphosphoric acid, as well as the ability to remove phosphorus during wastewater treatment [59]. _Zoogloea_ is involved in the biosynthesis of extracellular polysaccharide and protein, is a genus necessary for floc formation, and plays a central role in the activated sludge process [60]. [PERSON] et al. reported that _Thuuera_ was related to the denitrification process, and that its role in the removal of nitrogen and phosphorus from wastewater under the condition of low-carbon sources was critical [61]. _Nitrospira_, a genus of nitrite-oxidizing bacteria, is mainly responsible for the second step of aerobic nitrification, and plays an important role in the nitrogen cycle in WWTPs. The nitrification reaction is an important denitrification step in biological sewage treatment, and _Nitrospira_ is an important bacterium that can ensure nitrification activity. This genus is only found in abundance in domesticated sludge. Among the activated sludge microorganisms in the BPA group reactor, the dominant bacterial genus _Aeromonas_ has the function of denitrification and phosphorus removal [62]. In a study on autotrophic denitrification sludge, _Curvibacter_ was found to be beneficial to improving the nitrate removal rate of sludge [63].