title: Iron and phosphorus speciation in Fe-conditioned membrane bioreactor activated sludge.
abstract: Iron dosing of membrane bioreactors (MBRs) is widely used as a means of meeting effluent phosphorus targets but there is limited understanding of the nature of iron and phosphorus-containing solids that are formed within the bioreactor (an important issue in view of the increasing interest in recovering phosphorus from wastewaters). Of particular challenge is the complexity of the MBR system and the variety of reactions that can occur on addition of iron salts to a membrane bioreactor. In this study, the performances of bench scale MBRs with dosing of either ferrous or ferric salts were monitored for a period of four months. The distributions of Fe and P-species in the Fe-conditioned sludges were determined using X-ray absorption spectroscopy (XAS) at the Fe K-edge and the P K-edge. Regardless of whether iron was dosed to the anoxic or aerobic chambers and regardless of whether ferrous (Fe(II)) or ferric (Fe(III)) iron was dosed, iron present in the minerals in the conditioned sludges was consistently in the +III oxidation state. Fitting of the Fe K-edge EXAFS spectra revealed that an Fe(III)-phosphate species was the main Fe species present in all cases with the remaining fraction dominated by lepidocrocite (γ-FeOOH) in the Fe(II)-dosed case and ferrihydrite (am-FeOOH) in the Fe(III)-dosed case. Approximately half the phosphorus in the activated sludge samples was present as a distinct Fe-PO4 mineral (such as strengite or an amorphous ferric hydroxyl phosphate analogue of strengite) and half as phosphorus adsorbed to an iron oxyhydroxide mineral phase indicating that both co-precipitation and adsorption of phosphorus by iron contribute to removal of phosphorus from the MBR supernatant.
authors.affiliation: Water Research Centre, School of Civil & Environmental Engineering, The University of New South Wales, Sydney 2052, Australia.
authors.forename: Hao
authors.initials: H
authors.lastname: Wu
authors.affiliation: Water Research Centre, School of Civil & Environmental Engineering, The University of New South Wales, Sydney 2052, Australia; Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia; Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ikeda-Ohno
authors.affiliation: Water Research Centre, School of Civil & Environmental Engineering, The University of New South Wales, Sydney 2052, Australia; UNESCO Centre for Membrane Science & Technology, School of Chemical Engineering, The University of New South Wales, Sydney 2052, Australia.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Water Research Centre, School of Civil & Environmental Engineering, The University of New South Wales, Sydney 2052, Australia. Electronic address: d.waite@unsw.edu.au.
authors.forename: T David
authors.initials: TD
authors.lastname: Waite
mesh_terms: D019149:Bioreactors; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D010758:Phosphorus / Q000737:chemistry*; D012722:Sewage / Q000032:analysis* / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D012722:Sewage; D010758:Phosphorus; D007501:Iron
keywords: Iron; Membrane bioreactor; Phosphorus; X-ray absorption spectroscopy