title: Phosphorus removal mechanisms in active slag filters treating waste stabilization pond effluent.
abstract: Phosphorus (P) removal mechanisms from waste stabilization pond effluent by a melter slag filter were investigated. The studied filter had treated pond effluent for a decade, but lost its P removal efficiency after 5 years. The P distribution in the slag was examined by scanning electron microscopy (SEM), electron dispersive spectrometry (EDS), X-ray fluorescence (XRF), X-ray diffraction (XRD), and chemical fractionation. The results showed the slag to be covered by a film comprising metal oxides/oxyhydroxides, organic resin, and Fe-phosphate precipitates. The slag porous matrix beneath this film hosted lower P concentrations and consisted of metal oxides/oxyhydroxides and calcmagnesium silicates. The study revealed the following mechanisms for P removal from effluent by the melter slag: (1) P adsorption onto metal oxides/oxyhydroxides which are ubiquitous throughout the porous slag matrix and its surface film; (2) P precipitation, mainly as Fe-phosphates (determined by SEM/EDS) on the surface film, derived from the release of metal ions into the solution phase; and (3) P sequestration by an amorphous organic resin that comprises a substantial proportion of the surface film, which was deduced by SEM/EDS and XRF. Results of chemical extractions performed on the slag demonstrated that 1 M HCl, which has been used to determine Ca-associated P in previous studies, is an unreliable Ca-P marker. By contrast, the citrate-dithionite reagent was shown to be a good indicator of Fe/Al-associated P and revealed that adsorption onto metal oxides/oxyhydroxides, in the porous matrix as well as its surface film, is the most significant P removal mechanism achieved by the slag filter.
authors.affiliation: Centre for Environmental Technology and Engineering, Massey University, Palmerston North, Turitea Campus, New Zealand. C.C.Pratt@massey.ac.nz
authors.forename: Chris
authors.initials: C
authors.lastname: Pratt
authors.forename: Andy
authors.initials: A
authors.lastname: Shilton
authors.forename: Steven
authors.initials: S
authors.lastname: Pratt
authors.forename: Richard G
authors.initials: RG
authors.lastname: Haverkamp
authors.forename: Nanthi S
authors.initials: NS
authors.lastname: Bolan
mesh_terms: D006878:Hydroxides / Q000737:chemistry; D007220:Industrial Waste; D008670:Metals / Q000032:analysis; D010087:Oxides / Q000737:chemistry; D010758:Phosphorus / Q000302:isolation & purification*; D013232:Steel; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*
chemical_list: D006878:Hydroxides; D007220:Industrial Waste; D008670:Metals; D010087:Oxides; D014874:Water Pollutants, Chemical; D013232:Steel; D010758:Phosphorus