Alternative strategies to perform solid-state cultivation in a multilayer packed-bed bioreactor: Continuous and cyclic operations

Abstract

The packed-bed bioreactor (PBB) is one of the equipment most used in solid-state cultivation (SSC) processes. However, PBBs present problems in the removal of metabolic heat generated by microorganisms, making difficult to scale up these equipment, that are usually operated in batches. Aiming to minimize the overheating problems and to provide more versatility for biorefineries, this work aimed to evaluate alternative modes of operation of a multilayer PBB applied in the production of endoglucanase by SSC, namely cyclic and continuous operations. For this purpose, the fungus Myceliophthora thermophila I-1D3b was used as inoculum and sugarcane bagasse and wheat bran were used as substrates. In the cyclic operation, the layers had their positions changed every 24 h. In the continuous process, newly inoculated layers were added and spent layers fermented were removed every 24 h, leading to a regular flow of layers. Maximum temperatures reached 48.1, 48.2 and 48.3 °C and endoglucanase productivities were 2.85, 3.18 and 3.35 U/g of dry solid/h for classical, cyclic and continuous operations, respectively. These results showed no significant difference according to the Tukey test (α = 0.05). Despite that, in the continuous operation, the maximum CO2 concentration recorded was 60% lower than in batch operations. In addition, it was possible to estimate the biomass production rate in continuous operation, which was 5.32 g/h. Therefore, the continuous operation proved to be applicable and advantageous, being able to contribute to the scale up and operational versatility of PBBs and, consequently, to the industrial advancement of SSC.