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- Title
The Molecular Environment of Phosphorus in Sewage Sludge Ash: Implications for Bioavailability.
- Authors
Nanzer, Simone; Oberson, Astrid; Huthwelker, Thomas; Eggenberger, Urs; Frossard, Emmanuel
- Abstract
Producing a P fertilizer from sewage sludge ash (SSA) is a strategy to efficiently recycle P from a secondary raw material. The P speciation in four SSAs was characterized before and after the removal of heavy metals by a thermo-chemical treatment that involved CaCl2 addition. We chose complementary techniques to determine the direct P speciation, including X-ray powder diffraction, solid-state 31P direct-polarization magic-angle spinning nuclear magnetic resonance, and X-ray absorption near edge structure. Results from these techniques were compared with operational and functional speciation information obtained from a sequential P extraction and a plant biotest with Italian ryegrass grown on a soil-sand mixture with little available P. The speciation of P in untreated and thermo-chemically treated SSAs depended on their elemental composition. At a molar ratio of Ca:P ≤ 2, SSAs contained combinations of polymorphs of AlPO4, b-tricalcium phosphate, and apatite-like P species. In SSAs with a molar ratio of Ca:P > 2, an apatite-like molecular environment was predominant. The thermo-chemical process induced an increase in crystalline phases and enhanced the crystallinity of the P species. The structural order of the bulk sample was the most decisive parameter in controlling the P availability of the studied SSAs to plants. We conclude that, to produce a high-quality fertilizer and despite of the successful heavy metal removal, the thermo-chemical process requires further development toward enhanced P bioavailability.
- Subjects
PHOSPHORUS; PHOSPHATE fertilizers; SEWAGE sludge ash; THERMOCHEMISTRY; BIOAVAILABILITY; X-ray powder diffraction
- Publication
Journal of Environmental Quality, 2014, Vol 43, Issue 3, p1050
- ISSN
0047-2425
- Publication type
Article
- DOI
10.2134/jeq2013.05.0202