Optimization of FeSO4-Al2(SO4)3 Composite Flocculant for Enhanced Phosphorus Removal in Wastewater Treatment: A Response Surface Methodology Study

The persistent challenge of achieving cost-effective total phosphorus (TP) removal in wastewater treatment necessitates innovative coagulant development. While polyaluminum chloride (PAC) demonstrates efficacy in eliminating total nitrogen (TN), ammonia nitrogen (NH4+-N), suspended solids (SSs), and pH stabilization, its limitations in attaining economical TP removal remain unresolved. This study introduces a novel FeSO4-Al2(SO4)3 composite coagulant to address PAC’s shortcomings through systematic formulation optimization. Utilizing single-variable experiments and response surface methodology (RSM), we determined the optimal reagent combinations under simulated high-efficiency sedimentation tank conditions. The results revealed that the FeSO4-Al2(SO4)3 composite achieved a TP removal efficiency approximately 40% greater than the PAC at equivalent dosages. A cost–benefit analysis indicated an approximate 50% reduction in the chemical expenditure relative to conventional PAC-based systems. The optimized formulation demonstrated synergistic effects between the Fe2+ and Al3+ ions, enhancing the charge neutralization and sweep flocculation mechanisms. These findings establish FeSO4-Al2(SO4)3 as a technically and economically viable alternative for TP-centric wastewater treatment, with implications for process sustainability. Further investigations should validate the long-term operational stability across diverse water matrices and assess the environmental impacts of residual metal ions.