Novel side-stream-enhanced biological phosphorus removal system for highly efficient nitrogen and phosphorus removal: performance, microorganisms, and mechanisms.

A novel side-stream-enhanced biological phosphorus removal system was successfully operated for 203 days, with controlled influent carbon-to-phosphorus ratio (25.8), side-stream influent (20 %), and oxidation-reduction potential (-150 to - 300 mV). This system facilitated synergistic collaboration of Candidatus Accumulibacter, Dechloromonas, and side-stream fermentative microorganisms, without relying on Tetrasphaera. During two-stage operation, COD and PO₄^3--P removal efficiencies increased from 73.7 % and 75.3 % to 83.2 % and 91.8 %, respectively. The system exhibited high biological activity, with peak phosphorus release of 49.3 mg·L^-1, a 66 % increase from Phase I. Microbial analysis revealed the enrichment of Candidatus Accumulibacter (12.9 %) and Dechloromonas (6.2 %) in the mainstream reactor. Key genes and enzymes related to phosphorus removal were also enriched. Overall, the experiment achieved stable system operation, with Candidatus Accumulibacter and Dechloromonas effectively collaborating with fermentative microbes. Future research will focus on optimizing parameters and evaluating their potential for large-scale wastewater treatment applications to enhance stability and reduce costs.