Effects of ozonation sludge reduction on nutrient removal and microbial community diversity of conventional A ² /O and reversed A ² /O processes

To optimise ozonation sludge reduction in the activated sludge process, it is crucial to monitor nutrient removal and pay particular attention to the influential biological species. This study employed high-throughput sequencing to examine the microbial composition and diversity in the anaerobic-anoxic-oxic (A²/O) process, the A²/O process with ozonation, and the reversed A²/O process with ozonation. The diversity analysis aimed to identify discrepancies and similarities in microbial communities among these groups, thereby elucidating the varying biological efficiencies. Furthermore, the results from Illumina MiSeq sequencing revealed significant diversification in microbial community structures in different processes. Ozonation sludge notably inhibited certain species, including the order <i>Bacteroidales</i> within the class <i>Bacteroidia</i>, as well as the orders <i>Rhizobiales</i> and <i>Rhodospirillales</i> within the class <i>Alphaproteobacteria</i>. Additionally, ozonation sludge exerted a notable impact on specific orders within the class <i>Gammaproteobacteria</i>, including <i>Aeromonadales</i>, <i>Chromatiales</i>, and <i>HOC36</i>. In contrast, it stimulated the proliferation of other microbial groups, such as <i>Lactobacillales</i>, <i>Clostridiales</i>, as well as <i>Burkholderiales</i> and <i>Rhodocyclales</i>. The inhibition and promotion of ozonation sludge in conventional and reversed A²/O processes resulted in various microbial richness and diversity, which rendered the distinctive biochemical activities and wastewater treatment performances. <i>Betaproteobacteria</i> increased significantly, especially in the reversed A²/O process, and <i>Betaproteobacteria</i> played an important role in the nitrogen removal and phosphorus removal process. These findings are useful for guiding the ozonised sludge system to reduce carbon, denitrification, and phosphorus removal to meet the emission standards, and the identification and enhancement of the construction of potential key biological flora for better wastewater treatment and sludge reduction.