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Effect of pyrolysis temperature on the properties of the coffee grounds biochar and composition of its leachates

Kamilla das Graças Souza, Magno A. de Oliveira, Giovanni U. Alcantara, Gleicia M. Paulino, Robson P. de Lima, Osania E. Ferreira, Augusto C. da Silva Bezerra, Lúcia P. S. Pimenta, and Alan R. T. Machado

Department of Exact Sciences, State University of Minas Gerais, João Monlevade Unity, Minas Gerais, João Monlevade, Brazil

 

E-mail: alan.machado@uemg.br

Received: 12 November 2022  Accepted: 23 February 2023

Abstract:

The potential of biochar obtained from spent coffee grounds (SCG) for soil conditioning and removal of contaminants from aqueous media has already been proven. However, the influence of temperature on the composition of the biochar leachate is still unclear. Therefore, this research aimed to evaluate the effects of pyrolysis temperatures (300, 400, 600, 800, and 1000 °C) on the physicochemical properties, on the composition of leachates, and maize seed germination index of the SCG biochars. The increased pyrolysis temperature promoted an increase in the pH, specific surface area, thermal stability, and nutrients (K, P, Ca, Mg), while the yield and oxygenated functional groups decreased. The temperature also displayed a strong influence on leachate ecotoxicological substances, emphasizing the caffeine obtained from the biochar prepared at 300 °C and aromatic compounds at temperatures above 400 °C. On the other hand, biochars prepared at temperatures up to 600 °C showed stimulating effects on germination and initial growth of maize, while biochars prepared at 800 and 1000 °C inhibited or did not influence the germination index. Thus, these results unravel the ecotoxicological potential of biochar obtained from SCG leading to the search for strategies that allow its effective use.

Graphical abstract

Keywords: NMR; Ecotoxicological; Carbon; Pyrolysis; Coffee; Conditioner

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-023-02755-x

 

Chemical Papers 77 (7) 3947–3956 (2023)

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