Oxalic Acid Boosts Phosphorus Release from Sewage Sludge Biochar: A Key Mechanism for Biochar-Based Fertilizers

Marcela Granato Barbosa dos Santos, Camila Rodrigues Costa, Gilberto de Oliveira Mendes, Andressa Blasi Paiva, Ludmila Soares Peixoto, Jéssica da Luz Costa, Giuliano Marchi, Éder de Souza Martins and Cícero Célio de Figueiredo ()
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Marcela Granato Barbosa dos Santos: Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Brasília 70910-970, Brazil
Camila Rodrigues Costa: Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Brasília 70910-970, Brazil
Gilberto de Oliveira Mendes: Instituto de Ciências Agrárias, Universidade Federal de Uberlândia, Rodovia LMG-746, Km 1, Bloco 1A-MC, Monte Carmelo 38500-000, Brazil
Andressa Blasi Paiva: Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Brasília 70910-970, Brazil
Ludmila Soares Peixoto: Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Brasília 70910-970, Brazil
Jéssica da Luz Costa: Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Brasília 70910-970, Brazil
Giuliano Marchi: Embrapa Cerrados, CPAC, Brasília 70275-970, Brazil
Éder de Souza Martins: Embrapa Cerrados, CPAC, Brasília 70275-970, Brazil
Cícero Célio de Figueiredo: Faculdade de Agronomia e Medicina Veterinária, Universidade de Brasília, Brasília 70910-970, Brazil

Agriculture, 2024, vol. 14, issue 9, 1-14

Abstract: Sewage sludge biochar (SSB) exhibits higher phosphorus (P) concentrations than the original sewage sludge (SS) and can be used as a P fertilizer. However, SSB-associated P is strongly retained in chemical compounds, which hinders its release and subsequent plant uptake. The use of organic acids facilitates P solubilization from SSB. Herein, we evaluated the effect of oxalic acid on P release from SSB applied to soil over time. Biochar was produced at 300 °C (SSB300) and 500 °C (SSB500). P release from SSB increased with an increasing concentration of oxalic acid in the SSB incubation solution and in SSB-treated soil. P speciation in SSB showed that P was predominantly inorganic (P i ), which represented 81% and 92% of the total P in SSB300 and SSB500, respectively. P i in SSB consisted mainly of non-apatite P, accounting for 91% and 96% of all P i in SSB300 and SSB500, respectively. Because SSB is predominantly insoluble in water, oxalic acid is crucial for the release of P from SSB. Oxalic acid increased P release from SSB300 and SSB500 by 103- and 600-fold, respectively, compared to the control, from which P was extracted with water. Oxalic acid enhancement of P release from SSB increases the possibility of using SSB as a sustainable source of P for agriculture.

Keywords: pyrolysis; thermal treatment; biosolids; phosphorus (search for similar items in EconPapers)
JEL-codes: Q1 Q10 Q11 Q12 Q13 Q14 Q15 Q16 Q17 Q18 (search for similar items in EconPapers)
Date: 2024
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