Using Aeration to Enhance Phosphorus Adsorption and Immobilization by the Sediment and LMB

Abstract

Dissolved oxygen (DO) in the overlying water is important in influencing internal phosphorus (P) release. However, the potentially associative effect of DO on the P adsorption and immobilization by La-modified bentonite (LMB) has not been quantified. This 80-day incubation experiment showed the synergistic effect of DO and LMB in the overlying water, which caused the reduction of dissolved inorganic phosphorus (DIP) by 51% (DO = 5 mg L−1) and 77% (DO = 7 mg L−1) on average, respectively, compared with the DO of 3 mg L−1. In addition, the DIP in the pore water decreased from 1.12 mg P L−1 (control) to 0.014 mg P L−1 (5 mg L−1) and 0.004 mg P L−1 (7 mg L−1). Besides, the Fe2+ and NH4+ concentrations were also reduced significantly in the pore water, suggesting the rise in the redox potential in the sediment, which helped P immobilization. Chemical P-fractionation experiments indicate that the Fe-P reduction in sediment was the most significant, reduced by 14%, followed by NH4Cl-P (12%), causing a reduction by 13% (3 mg L−1), 23% (5 mg L−1) and 27% (7 mg L−1) of mobile P in the surface 7-cm sediment, respectively. However, the released P ions were rapidly adsorbed by the Al ions and Ca ions, as well as their compounds, thereby leading to the obvious rise in inert P in the sediment. Accordingly, it was suggested that DO and LMB had a synergistic effect on external P adsorption and immobilization.