Scaling up solid-state fermentation for organic waste valorisation: Current challenges and emerging opportunities.

Solid-state fermentation (SSF) is becoming an attractive approach to transform organic waste into valuable bioproducts. By using microorganisms on solid substrates with low water requirements water, SSF supports the shift towards more circular and sustainable systems. Although SSF offers potential environmental and operational advantages, its industrial adoption is still limited. Nevertheless, SSF has strong potential to complement conventional submerged fermentation and other bioprocessing technologies within future sustainable biorefinery strategies Scaling up SSF processes faces challenges mainly related to heterogeneous mass transfer distribution and temperature gradients during fermentation. This work summarises the key limitations observed when moving from laboratory to large scale and explores promising strategies to overcome them. Potential solutions include the use of biotrickling reactors to achieve more uniform moisture distribution and improve mass transfer, the integration of advanced modelling tools such as computational fluid dynamics and AI for process control, and the application of thermotolerant strains capable of maintaining activity across a wide temperature range, among others. These advances could help SSF become a more reliable and scalable technology for waste valorisation.