Improved biostimulant production through solid-state fermentation of green waste using low-temperature strategy in tray bioreactors

This study investigates solid-state fermentation (SSF) of Trichoderma harzianum on green waste (GW) to produce the biostimulant indole-3-acetic acid (IAA) and conidial spores. Initial experiments without temperature control achieved high yields (201.3 µg g⁻¹ dry matter (DM) of IAA and 1.1 × 10⁹ spores g⁻¹ DM) exceeding reported literature values. However, variability was observed in the production of IAA. A principal component analysis revealed that temperature, especially in the later stages of fermentation, was intricately linked to the final IAA levels. Based on these findings, a new process strategy was developed, applying a low-temperature pattern to prevent IAA decrease and enhance its production. Experimental validation confirmed improved reproducibility and efficiency, yielding 199.9 µg g⁻¹ DM of IAA and 1.56 × 10⁸ spores g⁻¹ DM. This work suggests a novel and easily scalable SSF approach that simultaneously produces biostimulants and biopesticides while valorizing green waste, contributing to sustainable practices within a circular bioeconomy.