Low-carbon integrated biorefinery for the valorization of agro-food waste at a local scale

In addressing the ecological transition toward a future beyond petroleum, the industry sector should rely on new process design, to ensure the sustainable production of commodities while limiting the pressure on natural resources. This Thesis provides a cascade-integrated biorefinery approach to encourage the efficient and feasible valorization of agro-food wastes on a local scale. It comprises enzyme production from food waste, biochemical conversions of the waste biomass into high-value products, and energy recovery from the leftover residue, to be integrated into the upstream processes' energy demand. The strategy is displayed through three cases of study covering different stages of the biorefinery model: the processing of hemp oil seed cake, rice grain, and pomegranate pomace. The produced enzymes are used as biocatalysts to hydrolyze the specific substrates, through the plant cell wall disassimilation into an aqueous solution. This leads to the recovery of specific chemical building blocks with the function of emulsifier, lipid substances, and antioxidant molecules, then recombined in the form of cosmetic emulsion prototypes, as examples of locally marketable products. The residue obtained from these processes finally acts as feedstock in a newly designed energy plant, currently pending patent, able to convert in a non-specific way waste biomass directly into renewable electrical energy. It is based on a 3D-printed alkaline glucose biofuel cell, preceded by an alkalinization unit generating the biofuel, and followed by a neutralizer capable to convert the spent organic residue into bio-fertilizer, enabling the closure of the food cycle. The biofuel cell design is realized with low-cost material and components, uses organic-based electrodes, and works under environmental conditions. It was conceived ex novo and implemented via experimental trials to allow the continuous electrolyte feeding with variable volumetric processing capacity, to easily reach the scaling up of the system by stacking multiple units.