Anaerobic digestion of fourth range fruit and vegetable products: comparison of three different scenarios for its valorisation by life cycle assessment and life cycle costing.

Changes in consumer demand due to preferences for a healthier lifestyle have led to a new market offering fruit and salad products ready to eat. This affects the agro-industrial sector and the characteristic of waste streams generated having the organic fraction higher quality and representing a new opportunity of valorisation. This study experimentally evaluated the digestion of wastes derived from the fourth range product sector. It was also proposed the use of this digestate as a fermentation medium for producing plant growth-promoting cultures. Three digestion scenarios were studied: Scenario 1 considered biogas valorisation using a combined heat and power (CHP) unit. Scenario 2 featured biogas upgrading to be used as vehicle fuel. Finally, scenario 3 evaluated the transport of waste materials to the digestion plant by a network of pipes and pumps directly from the production chain. All three scenarios included the land application of a biostimulator based on the production of a plant growth-promoting culture derived from digestate. Life cycle analysis and life cycle costing were used to determine potential environmental impacts and costs over a lifetime of 25 years. The study showed that scenario 1 was the most favourable option for valorising this type of waste, although the economic assessment resulted in negative values for all three alternatives.