Fungal biopesticide production: Process scale-up and sequential batch mode operation with Trichoderma harzianum using agro-industrial solid wastes of different biodegradability

Abstract

This work presents a sequential batch operational strategy (SBR) for fungal conidia production in solid-state fermentation (SSF) to improve the traditional batch operation, while also aiming to present a robust and scalable process. Trichoderma harzianum was fermented using two substrates with different biodegradability (rice husk and beer draff), scaling from 1.5 L to 22 L bioreactors. Before the SBR operation, the optimum time to get inoculum from each SBR batch was determined as 4 days. While single batch process scale-up was successful with both substrates, SBR strategy was only feasible using beer draff as substrate: conidia production was sustained during 3 consecutive batches in 1.5 L bioreactors and for 5 batches at 22 L. At both scales conidia production was around 2.0x109 conidia g-1dm, achieving maximum specific oxygen consumption rate (sOUR) values close to 4 g O2 kg-1dm h-1 in most reactors. Air filled porosity was found as a key parameter regarding process scale-up, with a minimum value of 80% as necessary to proper scaling up to 22 L. Process robustness was statistically demonstrated as no significant differences in conidia production, moisture and pH were found at different reactor heights using both substrates in most 22 L reactors tests. Consequently, SBR operation has been presented as a reproducible method to overcome traditional packed-bed drawbacks while also improving SSF performance in comparison to traditional industrial SSF processes.