Adsorption and release of phosphorus in the surface sediment of a wastewater stabilization pond

In wastewater stabilization ponds, sedimentary phosphorus usually presents significant release and adsorption differences from that in lakes. However, their mobile potentials in stabilization pond have seldom been studied. In this study, the transformation characteristics of sedimentary phosphate in a wastewater stabilization pond are studied. The adsorption and release potential under different pH and Eh conditions is investigated and possible mechanisms involved are also proposed. Additionally, the forming process of iron-bound-phosphorus with Eh steadily increasing is also discussed. Results of this study show that the binding capability of each phosphorus fraction differed greatly under different pH conditions as follows: iron–phosphorus (Fe–P) and aluminium–phosphorus (Al–P) possessed the greatest binding capability at pH 7–8; and organic phosphorus extracted at alkaline conditions (OPalk) and calcium–phosphorus (Ca–P) showed the greatest binding capability at pH 5 and pH 9, respectively. Mainly through changing the proportion of Fe(III) in Total-Fe and the subsequent binding of its possible forms with phosphate, Eh can effectively affect the adsorptive and releasing behaviors of sedimentary phosphorus. With Eh increasing from −650 mV to −50 mV, Fe(II) was gradually oxidized to Fe(III), and Fe(III)–P significantly formed at the same time. Furthermore, the results show that there was no Eh threshold for phosphorus adsorption with increasing Eh.