Effects of thermal drying on phosphorus availability from iron-precipitated sewage sludge

Camilla Lemming, Charlotte Scheutz, Sander Bruun, Lars Stoumann Jensen, Jakob Magid

    Research output: Contribution to journalJournal articleResearchpeer-review


    Thermal drying of sewage sludge implies sanitation and improves practical handling options of the sludge prior to land application. However, it may also affect its value as a fertilizer. The objective of this study was to assess whether thermal drying of sewage sludge, as well as drying temperature, affects plant P availability after application to soil. The experiment included dewatered sewage sludge (20% DM) and thermally dried sewage sludge (95% DM) collected at a Danish wastewater treatment plant, as well as laboratory oven-dried (70, 130, 190, and 250°C; DM > 95%) subsamples of the dewatered sludge, and a triple superphosphate as a reference. Plant P availability was studied in a 197 d soil incubation experiment, with sampling for Diffusive Gradients in Thin films (DGT) and water extractable P (WEP) analyses over time, and in a pot experiment with spring barley (Hordeum vulgare L.). In both experiments, thermal drying reduced P availability, as shown by 37 and 23% lower DGT and WEP values, respectively, and a 16% lower P uptake by barley in the pot experiment. The specific drying temperature did not appear to have much effect. Overall, our results suggest that thermal drying of iron-precipitated sewage sludge is not an optimal treatment option if the aim is to optimize plant P availability.
    Original languageEnglish
    JournalJournal of Plant Nutrition and Soil Science
    Issue number6
    Pages (from-to)720-728
    Publication statusPublished - 2017


    • DGT
    • Hordeum vulgare
    • Incubation
    • Pot experiment
    • Spring barley
    • Water-extractable P


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