Extraction of spores of Metarhizium anisopliae in a rotary drum

Abstract

The fungus Metarhizium anisopliae is widely used as a biological control agent of several agricultural pests. The microbe is produced using rice as substrate and the operation of extraction of spores needs improvement. This study explores an effective method for spore extraction using a rotary drum, with controlled variables including extraction time (4 and 8 hours), fill level (0.25 and 0.50), and drum rotation speed (30 and 60 rpm). The extraction efficiency achieved in this bench-scale setup ranged from 32.93 % to 84.24 %. Among the key parameters investigated, only the operation time showed a significant influence, with an 8-hour duration yielding the best performance. This improvement was attributed to the reduction in substrate moisture content throughout the process, indicating it as a critical factor affecting extraction performance. Lower moisture content reduced the shear force and impact required for spore detachment, leading to a more efficient extraction. Additionally, the results suggest that spores are detached through particle collisions rather than by the dragging force promoted by the flowing air, which is essential for predicting optimal process configurations. This research, therefore, lays the foundation for the development of more efficient extraction systems, contributing to the cost-effective large-scale production of bioinsecticides.