Changes in availability of Ca, K, Mg, P and S in sewage sludge as affected by pyrolysis temperature
Mercl, Filip | Kosnar, Zdenek | Pierdona, Lorenzo et al.
Pyrolysis is a promising technology for sewage sludge (SS) treatment providing several improvements of SS properties for soil application. However, information on the influence of pyrolytic temperature on the availability of nutrients in resulting biochar (BC) is limited. In this study, anaerobically stabilised SS was pyrolysed in a laboratory fixed-bed reactor at 220, 320, 420, 520, and 620 °C for 30 min in the N2 atmosphere. Pyrolysis resulted in a higher total content of all studied nutrients in BCs. Aromaticity and hydrophobicity of BCs increased with increasing temperatures while solubility decreased. Relative availability (% from total content) of nutrients in BCs was in order: Ca > Mg ~ K > S > P. Pyrolysis at 220 °C produced acidic BC with a higher content of acetic acid-extractable nutrients compared to non-pyrolysed control. An increment in pH and a significant drop in the content of available Ca, Mg, K and S were found at temperature 320 °C. Pyrolysis at 320 °C increased the content of available P by 28 % compared to non-pyrolysed SS. At the temperature of 420 °C and higher, available contents of all studied nutrients were lower than in non-pyrolysed SS.
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