Sustainable Biochar Fertiliser Production Using Melt Adsorption and Optimisation

Xia Zhang, Yiyang Wang, Panjie Su, Weida Zeng, Jingzhe Zhu and Zongshou Cai ()
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Xia Zhang: Faculty of Mechanical and Electrical Engineering, Yunnan Agricultural University, Kunming 650201, China
Yiyang Wang: Faculty of Mechanical and Electrical Engineering, Yunnan Agricultural University, Kunming 650201, China
Panjie Su: Faculty of Mechanical and Electrical Engineering, Yunnan Agricultural University, Kunming 650201, China
Weida Zeng: Faculty of Mechanical and Electrical Engineering, Yunnan Agricultural University, Kunming 650201, China
Jingzhe Zhu: Faculty of Mechanical and Electrical Engineering, Yunnan Agricultural University, Kunming 650201, China
Zongshou Cai: Faculty of Mechanical and Electrical Engineering, Yunnan Agricultural University, Kunming 650201, China

Sustainability, 2025, vol. 17, issue 5, 1-16

Abstract: The global production of coffee generates substantial waste in the form of coffee husks, presenting an opportunity for sustainable resource utilisation. This study investigates the conversion of coffee husks into biochar-based fertilisers using an optimised pyrolysis process and the melt adsorption method, with the aim of improving slow-release nutrient characteristics. Coffee husks were pyrolysed under controlled conditions, and the resulting biochar was blended with urea in a 1:1 ratio to produce the fertiliser. The nutrient release rates of the fertiliser were evaluated through soil column leaching experiments. For slow-release fertilisers, less release in a period means better performance, and the optimal nutrient release rate is the minimum in the experiment. Single-factor experiments assessed the effects of critical process parameters, including raw material particle size (0.25–2.8 mm), pyrolysis atmosphere (CO 2 to N 2 ratios ranging from 0% to 100%), pyrolysis temperature (400–800 °C), heating rate (10–30 °C min −1 ), and pyrolysis time (20–100 min). Orthogonal experiments were subsequently conducted to analyse the interactions between selected parameters of pyrolysis temperature, CO 2 to N 2 ratio, heating rate, and pyrolysis time using regression analysis. The optimal process conditions determined through MATLAB optimisation were a pyrolysis temperature of 591 °C, a heating rate of 15.4 °C∙min⁻ 1 , and a pyrolysis time of 44.4 min, resulting in the minimum nutrient release rate of 40%. The sequence of process parameters influencing the slow-release characteristics was found to be heating rate > pyrolysis time > pyrolysis temperature > CO 2 to N 2 ratio. This study provides a framework for transforming agricultural residues into high-performance biochar-based fertilisers, aligning with sustainable resource management and pollution control strategies.

Keywords: coffee husks; biochar-based fertiliser; optimisation; pyrolysis; slow-release performance; melt adsorption method (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2025
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