Microbial Community Analysis Revealed the Selective Retention of Functionally Important Microorganism by Hydrocyclone in Biological Nutrient Removal (BNR) Processes

As granular sludge may improve biological nutrient removal (BNR) performance, external selectors like hydrocyclones have been installed to retain the fast settling particles, including granules that may form in plug flow activated sludge systems. It has been hypothesized that the high-density granule fraction contains functionally important microorganisms that help in process intensification, but no microbial analysis has been done to date to confirm the hypothesis. In this study, we have investigated three full-scale plants that have installed hydrocyclones. To understand microbial community composition, 16S rRNA gene sequencing was performed on samples collected from overflow, underflow and activated sludge. The results indicate a distinct community composition between the overflow and underflow of the hydrocyclone. The underflow had a lower richness and diversity, indicating selective enrichment of dominant species, while diverse groups of rare bacteria were washed out with the overflow. The underflow had higher abundance of Candidatus Accumulibacter (Phosphate-accumulating organisms; PAOs) and Candidatus Brocadia (anaerobic ammonia oxidizers; AnAOB), indicating the enrichment of functionally important microorganisms. These results indicate that the installation of hydrocyclones can have a positive impact on plant operation and help in process intensification of nutrient removal.