Unlocking the Potential of Solid-State Fermentation with Insights into Organic Waste Selection and Thermal Dynamics for Sustainable Sophorolipids Production

Solid State Fermentation (SSF) is proposed as an emergent technology in the transformation of organic solid waste into diverse valuable products, playing a key role in creating new value chains for the development of the circular bioeconomy. Sophorolipids are a glycolipid type of biosurfactants, and their production has been proven feasible through SSF. However, the commercialization and scale-up of SSF presents some challenges, among others, the adaptation to a variable feedstock (different types of waste, heterogeneity, seasonality, etc.); or the heat transfer limitations leading to temperature rise over optimal values for the microorganisms’ growth. Understanding the potential of various types of waste and their complementarity is crucial for designing an optimal solid matrix and defining an efficient SSF process with high productivities and potential scalability. In this work, we assessed the potential of different types of organic solid waste including food and cosmetic industry waste such as oil cakes, agricultural byproducts, or cosmetic-derived sludge. Optimization of C/N ratio resulted in a 30% increase in sophorolipids production. Besides, substrates composition and availability strongly influenced fermentation yields. Fat content strongly affected crude extracts purity. A model of the fermenting solid matrix has been developed to predict heat generation and temperature dynamics. The influence of organic solid waste chemical composition and their inherent physical parameters (such as thermal conductivity or heat capacity) have been assessed in terms of temperature profiles at lab and pilot scale. Higher heat capacity limits T rise, specially at pilot scale. Specific growth rate highly influences temperature dynamics at both scales. The design of solid matrices should target the balance in these properties beyond nutrients optimization to ensure process scalability.