A novel calcium peroxide/attapulgite-Fe(II) process for high concentration phosphate removal and recovery: Efficiency and mechanism

Phosphorus (P) has been overused in livestock farming, which inevitably results in high-concentration P-containing wastewater. Managing total phosphorus discharge is important to prevent eutrophication in aquatic environments, thus it is critical to develop new technologies for the removal and recovery of high-concentration phosphate. In this study, a novel calcium peroxide/attapulgite (CP/ATP) composite was developed and coupled with Fe(II) for high-concentration phosphate removal and recovery. The results demonstrated that the optimal dosage of the CP/ATP-Fe(II) process was CP/ATP = 0.25 g/L and Fe(II) = 2 mM. The pH effect on phosphate removal was minimal, while phosphate removal efficiency rose by 16.7% with the temperature increased from 10 °C to 25 °C. The co-existing ions exhibited little effect on phosphate removal, and the CP/ATP-Fe(II) process showed effective phosphate removal from the real piggery wastewater. The P content of the precipitates after phosphate removal by this process was as high as 25.82%, indicating its good potential for P recycling. A significant synergistic effect existed in CP/ATP and Fe(II) for phosphate removal, and the SEM-EDS, XRD, Raman and XPS characterization exhibited that the phosphate removal mainly relied on the in-situ-formed Fe(III) and the participation of calcium (Ca) species. Co-precipitation was the predominant mechanism for phosphate removal, and the proportions of Fe(III)–P, Ca–P and Ca–Fe(III)–P in the precipitates were 51.5%, 31.2% and 17.3%, respectively. This study provides a highly efficient process for phosphate removal and recovery from wastewater, and insights into interactions among phosphorus, iron and calcium.