Filling in the gaps in biowaste biorefineries : The use of the solid residue after enzymatic hydrolysis for the production of biopesticides through solid-state fermentation

Alternative production processes using waste are necessary to preserve non-renewable resources and prevent scarcity of materials for future generations. Biowaste, the organic fraction of municipal solid waste, is abundant and easily available. It can be fractionated into building blocks for which fermentative processes can be designed. By using solid-state fermentation, this paper proposes a method of valorizing biowaste's residual solid fraction after enzymatic hydrolysis. In a 22 L bioreactor, two digestates from anaerobic digestion processes were evaluated as cosubstrates to modify the acidic pH of the solid residue after enzymatic hydrolysis and promote the growth of the bacterial biopesticide producer Bacillus thuringiensis. Regardless of the cosubstrate used, the final microbial populations were similar indicating microbial specialization. The final product contained 4 × 10 spores per gram of dry matter and also crystal proteins of Bacillus thuringiensis var israelensis, which have insecticidal activity against pests. This method allows for the sustainable use of all materials liberated during the enzymatic hydrolysis of biowaste, including residual solids.