The results reported in this paper indicate that B. subtilis SPB1 could be cultivated under solid-state fermentation for the production
of a lipopeptide biosurfactant using agro-industrial residues. To the best of our knowledge, the use of olive cake and olive leaf
residue flours is unique. Under mixed solid-state fermentation conditions, B. subtilis SPB1 produces 30.67 mg/g of dry solid material
in 48 h. The microorganism's performance could be improved by further investigation in larger scale operations. The technique of
solid-state fermentation would help in producing B. subtilis SPB1 biosurfactant of any desired concentration in a shorter time and
may consequently help in reducing the cost of SPB1 lipopeptide production. Although considerable further research remains to be
conducted before this biosurfactant can be applied in the field, the results presented in this paper demonstrate that the bioconversion
of solid waste to secondary active metabolites could be of special economic interest for countries with an abundance of biomass and
agroindustrial residues, as this technique could lower their production costs.