Side-Stream Enhanced Biological Phosphorus Removal (S2EBPR) enables effective phosphorus removal in a pilot-scale A-B stage shortcut nitrogen removal system for mainstream municipal wastewater treatment

While the adsorption/bio-oxidation (A/B) process has been widely studied for carbon capture and shortcut nitrogen (N) removal, its integration with enhanced biological phosphorus (P) removal (EBPR) has been considered challenging and thus unexplored. Here, full-scale pilot testing with an integrated system combining A -stage highrate activated sludge with B -stage partial (de)nitrification/anammox and side -stream EBPR (HRAS-P(D)N/AS2EBPR) was conducted treating real municipal wastewater. The results demonstrated that, despite the relatively low influent carbon load, the B -stage P(D)N-S2EBPR system could achieve effective P removal performance, with the carbon supplement and redirection of the A -stage sludge fermentate to the S2EBPR. The novel process configuration design enabled a system shift in carbon flux and distribution for efficient EBPR, and provided unique selective factors for ecological niche partitioning among different key functionally relevant microorganisms including polyphosphate accumulating organisms (PAOs) and glycogen -accumulating organisms (GAOs). The combined nitrite from B -stage to S2EBPR and aerobic -anoxic conditions in our HRAS-P(D)N/AS2EBPR system promoted DPAOs for simultaneous internal carbon -driven denitrification via nitrite and P removal. 16S rRNA gene -based oligotyping analysis revealed high phylogenetic microdiversity within the Accumulibacter population and discovered coexistence of certain oligotypes of Accumulibacter and Competibacter correlated with efficient P removal. Single -cell Raman micro -spectroscopy -based phenotypic profiling showed high phenotypic microdiversity in the active PAO community and the involvement of unidentified PAOs and internal carbon -accumulating organisms that potentially played an important role in system performance. This is the first pilot study to demonstrate that the P(D)N-S2EBPR system could achieve shortcut N removal and influent carbon -independent EBPR simultaneously, and the results provided insights into the effects of incorporating S2EBPR into A/B process on metabolic activities, microbial ecology, and resulted system performance.