Precipitation of iron-hydroxy-phosphate of added ferric iron from domestic wastewater by an alternating aerobic–anoxic process

• Precipitation of phosphate by an alternating aerobic anoxic process was assessed.
• The empirical formulas of iron-hydroxy-phosphate were defined.
• Physicochemical-biological phosphorus removal was investigated.
• Effects of Fe/P molar ratio and pH on phosphorus precipitation were verified.
• The optimum efficiencies to remove SRP and TP were verified.

Removal of phosphorus from a municipal wastewater by simultaneous precipitation of iron-hydroxy-phosphate (IHP) was investigated. The addition of Fe3+ was performed to supplement biological excess phosphorus removal by a completely mixed alternating aerobic–anoxic (AAA) activated sludge process. The cycles of 3-h anoxic time and 3-h aerobic digestion were set to controlling a single-sludge nitrification–denitrification. In this study, attempt has been made to analyse the effects of initial dissolved Fe/P molar ratio and pH on IHP precipitation. The AAA treatment process to remove soluble reactive and total phosphorus from domestic wastewater had a moderate efficiency. The empirical formula of IHP that differs from different pH ranges was verified. Two types of Fe4(OH)9PO4 and Fe5(OH)6(PO4)3 precipitate may occur in different conditions of the AAA process. The efficiency of phosphorus removal from domestic wastewater by an AAA process was verified to contribute to a working methodology for the application of technologies in the field of domestic wastewater treatment.

Formation of iron-hydroxy-phosphate by an alternating aerobic–anoxic process is dependent on the environmental conditions.Figure optionsDownload as PowerPoint slide