Characterization of Metarhizium anisopliae spore extraction in a rotary drum using DEM method--颗粒学报PARTICUOLOGY

a São Paulo State University, Institute of Biosciences, Letters and Exact Sciences, São José do Rio Preto, SP, Brazil
b Federal University of Goiás, Institute of Chemistry, Goiânia, GO, Brazil
c Otto-von-Guericke-University Magdeburg, Institute of Process Engineering, Magdeburg, Germany

10.1016/j.partic.2025.12.005

Volume 109, February 2026, Pages 59-74

Received 17 July 2025, Revised 22 October 2025, Accepted 5 December 2025, Available online 13 December 2025, Version of Record 19 December 2025.

E-mail: daiane.b.ferreira@unesp.br

Highlights

• Collisions during M. anisopliae spore extraction were studied using rotating drums and DEM simulations.

• Moisture content and drum rotation speed were evaluated as key variables in particle behavior.

• Frictional properties for particle–particle and particle–wall contacts were measured at varied moisture levels.

• Lower moisture altered friction, drum fill dynamics, and the frequency and intensity of particle collisions.

• Higher forces occurred at 60 rpm, yet the effective impact frequency remained comparable to that at 30 rpm.

Abstract

The fungus Metarhizium anisopliae is commonly cultivated on rice, and the extraction of its spores remains a critical step with room for optimization in biofactories. Rotary drums are emerging as a promising technology. This study evaluated the effect of drum rotation speed (30 and 60 rpm) and particle moisture content (0.250; 0.111; and 0.053 kg-w/kg-ds) on the collision forces and frequencies of rice particles during the extraction process. To this end, the Discrete Element Method (DEM) was applied to simulate particle motion and collisions. The simulations were carried out using a rotary drum with a diameter of 20 cm and a length of 33 cm, equipped with two straight lifters. Spherical particles with structural and material properties referring to conidiated rice particles of different moisture contents were used. The DEM input parameters, restitution as well as static and rolling friction coefficients for particle-particle and particle-wall contacts, were experimentally determined. The experiments indicated that the moisture content of the particles predominantly affects the sliding friction coefficient, while the softness resulting from the cooking of the rice mainly influences the coefficient of restitution. The rolling friction coefficient, in turn, was primarily impacted by the sphericity of the particles. Additionally, the reduction in moisture content, by decreasing the drum's filling degree, promoted the expansion of the active layer, the region associated with more intense particle collisions. The results indicated that, despite the higher collision velocities observed at 60 rpm, the frequency of impacts with sufficient energy to overcome adhesive forces did not significantly increase compared to the 30 rpm condition. As a major outcome, DEM simulations clearly revealed that the reduction of particle size, associated with decreasing moisture content, resulted in a considerable drop of the filling degree, yielding an expansion of the active layer and therefore enhanced particle mobility. This is an important finding with great interest for the scale-up of continuous spore extraction in rotary drums.

Graphical abstract

Keywords

DEM; Rice; Spores; Metarhizium anisopliae; Extraction; Moisture content; Experimental validation

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