Bacillus thuringiensis derived biopesticides from biowaste digestate at 290-L demonstration scale through solid-state fermentation

This study faces the challenge of scaling up and validating the production of Bacillus thuringiensis (Bt) derived biopesticides at both pilot (100-L) and demonstrative scale (290-L), following a novel operation strategy for solid-state fermentation (SSF) based on two consecutive and differentiate aeration stages. Digestate and vegetable biowaste served as the carbon and nutrient source for Bt growth and sporulation. The operation strategy, which combines an anoxic and an aerobic phase, was successfully implemented at the pilot scale, achieving proper temperature control, which is crucial for SSF development at commercial scale. A total final concentration of spores was achieved on the order of 107 spores per gram of dry matter with a production ratio of 2.4 spores per inoculated Bt viable cell. Results at the demonstrative scale were hindered, likely due to the alteration of the anoxic environment during reactor sampling and the longer anoxic time. The fermented solids with biopesticidal properties, could be considered compost-like amendments exhibiting good maturity based on low respirometric indices and phytotoxicity. This study underscores the importance of addressing these challenges to enhance the sustainability of biowaste management practices and promote the transition towards a circular economy model.