Valorization of soy waste through SSF for the production of compost enriched with Bacillus thuringiensis with biopesticide properties

• A soil amendment with biopesticide effect can be obtained from soy waste by SSF.
• Bacillus thuringiensis (Bt) is able to grow on solid soy residue.
• Sterile and non-sterile culture conditions have been investigated at lab scale.
• Bt is able to survive under non-sterile and thermophile conditions.
• This bench-scale research is the first for Bt culture under non-sterile conditions.

There is a growing generation of biodegradable wastes from different human activities from industrial to agricultural including home and recreational activities. On the other hand, agricultural and horticultural activities require significant amounts of organic amendments and pesticides. In this framework, the present study evaluates the viability of soy fiber residue valorization as organic soil amendment with biopesticide properties through aerobic solid-state fermentation (SSF) in the presence of Bacillus thuringiensis (Bt). The experiments were performed first under sterile and non-sterile conditions at lab scale using 115 g of sample and controlled temperature (30 °C). Bt growth was successful in sterile conditions, obtaining 6.2 × 1011 CFU g−1 DM and 8.6 × 1010 spores g−1 DM after 6 days. Bt survived on solid culture under non-sterile conditions (3.8 × 109 CFU g−1 DM and 1.3 × 108 spores g−1 DM). Further, the valorization process was scaled-up to 10 L reactors (2300 g) under non-sterile conditions obtaining a final stabilized material with viable Bt cells and spores (9.5 × 107 CFU g−1 DM and 1.1 × 108 spores g−1 DM in average) after 9 days of SSF. These results confirm the possibility of managing biodegradable wastes by their transformation to a waste derived soil amendment with enhanced biopesticide effect, in comparison to traditional compost using a valuable and low-cost technique (SSF).

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