[Trace Amounts of Phosphorus Removal Based on the in-suit Oxidation Products of Iron or Manganese in a Biofilter].

In order to remove trace amounts of phosphorus from water bodies, a lab-scale biofilter was constructed to investigate the capacity of in situ oxidation products of iron or manganese for phosphorus adsorption. SEM, EDS, BET, and zeta technologies were employed to reveal the adsorption mechanisms. The results indicated that phosphorus could be removed by the oxide products generated from the iron or manganese removal process, at 106.28 μg·mg and 77.98 μg·mg, respectively, as shown by the linear relationships between phosphorus removal and the two oxides. SEM, EDS, and BET analysis demonstrated that the BET specific surface areas for the iron- and manganese-rich oxides were 96 m·g and 67 m·g, respectively, with the former accumulated between the pore spaces of the filtering sand and easily washed out of the layer by backwashing, whereas the latter coated the surface of the filtering sand. Thus, backwashing was favorable for phosphorus adsorption in the iron oxidation process to avoid overaccumulation. Moreover, the zero point of charge of the two oxides indicated electrostatic attraction may have occurred between iron-rich oxide and phosphorus; however, inner-sphere complex reactions obviously occurred for the two oxides because the zero point of charge after phosphorus adsorption decreased to a lower level. In addition, other anions were negatively complexed with the phosphorus on the surface of the oxides, it demonstrated that phosphorus adsorption on the surface of the two oxides seemed to be a specific adsorption.