Abstract
Food production is one of the most polluting anthropogenic activities and thus one of the main contributors to climate change. However, current environmental issues related to food production could be partially mitigated applying a biorefinery approach to food waste.
This thesis wants to experimentally assess a cascade processing for the conversion and valorization of food processing waste in a biorefinery perspective. The idea is to integrate an extraction step of valuable compounds with the subsequent treatment of the residues produced. In this way, residues can be energetically valorized and potentially sustain the energy required for the extraction step. Besides, this integrated approach would definitively contribute to fully take advantage of food waste reducing the environmental pressure related to its disposal and generating wealth through marketable products.
In Chapter 1, state-of-the-art of novel extraction technologies and subsequent valorization strategies of residues was reviewed. Each extraction technology was analyzed from several perspectives (i.e., technological maturity, environmental impact, potential integrations). Moreover, apple, tomato, olive, and grape pomace were selected as side streams with the highest potential for valorization.
Chapter 2 demonstrates the chance to develop an integrated biorefinery for feedstocks characterized by a low moisture content and a high proportion of oils using apple seeds as substrates. The lipid fraction can be isolated by Supercritical CO2 extraction delivering a more thermolabile material in comparison with the untreated substrate, which can be further exploited through dry thermochemical routes (e.g., pyrolysis or combustion).
Chapter 3 considers an integrated biorefinery for the valorization of feedstocks with a high moisture content and a large proportion of fermentable sugars using apple pomace as substrate. Sugars were hydrolyzed by subcritical water, while the solid fraction was further treated through Hydrothermal Carbonization (HTC), a wet thermochemical process, to produce hydrochar. To evaluate this integrated solution, a robust design of experiment was set, and solubilized sugars concentration taken as response. A mass balance of the integrated process was also performed.
Chapter 4 is dedicated to the investigation of the possible applications of hydrochars. In particular, it was demonstrated that, by adjusting extraction operating conditions, it is possible to fine tune hydrochar properties in relation to its application.
To conclude, the combination of an extraction step with processes for the valorization of its residues cannot only deliver already marketable compounds, but also final products with remarkable characteristics. The solutions here proposed can be considered as an opportunity to reduce the environmental impact of the whole food system, a fundamental sector that, at the moment, carries inefficiencies and unsustainable practices. Further research should assess the proposed solutions from a techno-economic and environmental perspective. Moreover, innovative applications of the resulting solid outputs will be evaluated to further close the resource loop and, hence, increase system sustainability.