Phosphorus release enhancement by EDTA combined with thermal hydrolysis and high-efficient recovery of vivianite from digested sewage sludge

In this study, EDTA combined with thermal hydrolysis was employed as a pretreating process of digested sludge to investigate the effect of EDTA on the phosphorus release anaerobically and effectiveness of vivianite generation to achieve efficient recovery of phosphorus from the residual sludge of a municipal wastewater treatment plant. The results showed that EDTA combined with thermal hydrolysis could effectively complex metal ions and improve the phosphorus release performance, reducing the influence of metal ions on the recovery of vivianite. The complexation of EDTA and metal ions was found in the order of Al3+ > Fe3+ > Ca2+ > Mg2+. Moreover, the concentration of phosphate in the supernatant increased with the amount of EDTA added during the anaerobic process and reached the peak value as the dosage of EDTA was 15 mmol/L. Furthermore, the concentrations of PO43- and Fe2+ in the supernatant of the anaerobic system decreased after 3-4 h days in iron-rich the environment, indicating the formation of vivianite considerably. The characterization of XRD and SEM-EDS proved that the ideal phosphorus recovery product could be obtained through EDTA + thermal hydrolysis pretreatment. The results of this study could provide theoretical basis and technical support for high quality phosphorus recovery in municipal wastewater treatment plants.