Valorisation of digestate from biowaste through solid-state fermentation to obtain value added bioproducts: A first approach

Digestate from biowaste was assessed as a potential source of bioproducts of commercial and industrial interest through solid-state fermentation. The targeted bioproducts were hydrolytic enzymes (cellulases and proteases from autochthonous microbiome), biosurfactants (sophorolipids produced from Starmella bombicola) and biopesticides (produced from Bacillus thuringiensis). Low cellulase production was observed within the range of 0.5-1.5 FPU g−1 DM while protease production showed two discrete peaks of 66 ± 8 and 65 ± 3 U g−1 DM at 3.5 and 48 h, respectively. Low sophorolipids production was also obtained, with a maximum yield of 0.02 g g−1 DM using hygienised digestate supplemented with external sugar and fat sources. Biopesticides produced by B. thuringiensis were successfully at 72 h of operation, reaching a maximum spore production of 8.15 ± 0.04 (107) CFU g−1 DM and 2.85 ± 0.22 (107) CFU g−1 DM using sterile and hygienised digestate, respectively. These biopesticides could contribute to the substitution of chemically produced pesticides, moving towards a sustainable digestate management in a circular economy scheme.