title: Vivianite as an important iron phosphate precipitate in sewage treatment plants.
abstract: Iron is an important element for modern sewage treatment, inter alia to remove phosphorus from sewage. However, phosphorus recovery from iron phosphorus containing sewage sludge, without incineration, is not yet economical. We believe, increasing the knowledge about iron-phosphorus speciation in sewage sludge can help to identify new routes for phosphorus recovery. Surplus and digested sludge of two sewage treatment plants was investigated. The plants relied either solely on iron based phosphorus removal or on biological phosphorus removal supported by iron dosing. Mössbauer spectroscopy showed that vivianite and pyrite were the dominating iron compounds in the surplus and anaerobically digested sludge solids in both plants. Mössbauer spectroscopy and XRD suggested that vivianite bound phosphorus made up between 10 and 30% (in the plant relying mainly on biological removal) and between 40 and 50% of total phosphorus (in the plant that relies on iron based phosphorus removal). Furthermore, Mössbauer spectroscopy indicated that none of the samples contained a significant amount of Fe(III), even though aerated treatment stages existed and although besides Fe(II) also Fe(III) was dosed. We hypothesize that chemical/microbial Fe(III) reduction in the treatment lines is relatively quick and triggers vivianite formation. Once formed, vivianite may endure oxygenated treatment zones due to slow oxidation kinetics and due to oxygen diffusion limitations into sludge flocs. These results indicate that vivianite is the major iron phosphorus compound in sewage treatment plants with moderate iron dosing. We hypothesize that vivianite is dominating in most plants where iron is dosed for phosphorus removal which could offer new routes for phosphorus recovery.
authors: Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 7, 8911 MA, Leeuwarden, The Netherlands; Dept. Biotechnology, Delft Univ Technol, Van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors: P
authors: P
authors: Wilfert
authors: Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 7, 8911 MA, Leeuwarden, The Netherlands.
authors: A
authors: A
authors: Mandalidis
authors: Fundamental Aspects Mat & Energy Grp, Delft Univ Technol, Mekelweg 15, 2629 JB Delft, The Netherlands.
authors: A I
authors: AI
authors: Dugulan
authors: Fundamental Aspects Mat & Energy Grp, Delft Univ Technol, Mekelweg 15, 2629 JB Delft, The Netherlands.
authors: K
authors: K
authors: Goubitz
authors: Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 7, 8911 MA, Leeuwarden, The Netherlands. Electronic address: Leon.Korving@Wetsus.nl.
authors: L
authors: L
authors: Korving
authors: Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 7, 8911 MA, Leeuwarden, The Netherlands; Sub-department of Environmental Technology, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.
authors: H
authors: H
authors: Temmink
authors: Dept. Biotechnology, Delft Univ Technol, Van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors: G J
authors: GJ
authors: Witkamp
authors: Dept. Biotechnology, Delft Univ Technol, Van der Maasweg 9, 2629 HZ Delft, The Netherlands.
authors: M C M
authors: MCM
authors: Van Loosdrecht
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry; D012722:Sewage / Q000737:chemistry*; D014865:Waste Disposal, Fluid
chemical_list: D005290:Ferric Compounds; D010710:Phosphates; D012722:Sewage; D010758:Phosphorus; D007501:Iron
keywords: Iron; Mössbauer spectroscopy; Phosphorus; Sewage; Sewage sludge; Vivianite