Thermal treatment of sewage sludge for phosphorus fertilizer production: a model experiment. (9th May 2022)

• Record Type: Journal Article
• Authors: Steckenmesser, Daniel; Vogel, Christian; Herzel, Hannes; Félix, Roberto; Adam, Christian; Steffens, Diedrich
• Is Part Of: Journal of plant nutrition. Volume 45:Number 8(2022)
• Page Start: 1123
• Page End: 1133
• Publication Date: 2022-05-09
• Subjects: chemical extraction -- phosphorus plant availability -- phosphorus recovery -- X-ray absorption near-edge structure (XANES) spectroscopy -- X-ray diffraction (XRD); Plants -- Nutrition -- Periodicals; Plants -- Effect of minerals on -- Periodicals; Deficiency diseases in plants -- Periodicals; 575.76
• DOI: 10.1080/01904167.2021.1994595
• Languages: English
• ISSNs: 0190-4167

Abstract

Abstract: Phosphorus (P) resource availability and quality is declining and recycling P-fertilizers from waste materials are becoming increasingly important. One important secondary P resource is sewage sludge (SSL) where P is often bound as aluminum phosphate (Al-P), iron phosphate (Fe-P) and polyphosphate (poly-P), respectively. Thermal treatment in different ways is a promising way in P recycling to produce highly plant-available P-fertilizers. To investigate mechanisms behind transformation of hardly available P-species toward plant-available P forms we treated a model SSL containing different kinds of defined P sources by low-temperature conversion (LTC) at 500 °C and subsequent thermochemical treatment of the LTC product with Na additives (TCT) at 950 °C, respectively. Pot experiments with ryegrass were carried out to determine the plant availability of P of the different treatments. The poly-P (here pyrophosphates) based fertilizers had a very high plant availability after both thermal treatments. During LTC treatment the plant availability of the Fe-P and Al-P variants increased because of the formation of Fe(II)-phosphates and/or pyro-/polyphosphates. Especially the formation of Al-polyphosphate shows a high plant availability. The subsequent TCT further increased strongly the plant availability of the Fe-P variants because of the formation of highly plant-available CaNaPO4 . Thus, a direct TCT without prior LTC probably also produce CaNaPO4 and is recommended for Fe-P based SSL. However, a molar Ca/P ratio of ∼1 in the fertilizer is favorable for CaNaPO4 formation. Thus, the knowledge on the source of primary P in SSL is essential for choosing the accurate thermal treatment method to produce highly plant-available P-fertilizers from SSL.