Comprehensive Study on the Removal of Orthophosphate in Domestic Wastewater by Polyferric Sulfate: Mechanism, Practical Engineering, and Biological Impact

In this study, the optimization strategy and underlying mechanisms of chemical deep phosphorus removal using polyferric sulfate (PFS) were systematically investigated through a combination of engineering validation and mechanistic analysis, revealing the FePO4 precipitation-dominated phosphorus removal mechanism and the influence of coexisting impurities and clarifying the key liganding role of Fe3+ by FTIR/XPS. The engineering applicability of secondary PFS dosing and PFS–polyacrylamide (PAM) codosing was validated in a full-scale wastewater treatment plant with a treatment capacity of 4 × 104 t·d–1, where a substantial enhancement in orthophosphate (Ortho-P) removal efficiency was achieved (increased by 30.6% and 28.1%, respectively). In addition, the threshold effects of PFS on the microbial activity in the AAO system were clarified under practical operating conditions. Collectively, this study offers both theoretical insights and engineering-level evidence to support the fine regulation of chemical phosphorus removal in wastewater treatment plants (WWTPs), and it exhibits substantial practical value for enhancing phosphorus removal efficiency and operational stability.