A two-phase model for simulation of water transfer during lipase production by solid-state cultivation in a tray bioreactor using babassu residues as substrate

Abstract

This research aimed to model and to simulate water transfer during lipases production by solid-state cultivation of the fungus Metarhizium anisopliae using babassu coconut bagasse as substrate in a pilot-scale tray bioreactor. A material balance was applied for water and individual equations for drying processes were adapted for both solid and gas phases. Physical and thermal properties of the bed, fermentation process conditions and microbial were determined experimentally or extracted from literature. Simulations were run in Matlab R2019a. Results showed that inlet air with 50% relative humidity is predicted to cause severe reduction in the moisture content of the solid matrix up to half of the trays' total length. Afterwards, air and solid reach the equilibrium and the drying process stops. Substrate dries when the air is introduced with 50% relative humidity independently of its velocity. By keeping the temperature of the solid-phase constant, fungal growth is limited by its water activity. For high relative humidity (95%) of the inlet air, the water activities are predicted to remain above 0.97 throughout the cultivation and on the entire length of the tray, ensuring the optimal fungal growth. The model proposed is a powerful tool for guiding the bioreactors scale-up.