The production of biogas from anaerobic digestion (AD) of residual agro-food biomasses represents an opportunity for alternative production of energy from renewable sources, according to the European Union legislation on renewable energy. This review provides an overview of the various aspects involved in this process with a focus on the best process conditions to be used for AD-based biogas production from residual agro-food biomasses. After a schematic description of the AD phases, the biogas plants with advanced technologies were described, pointing out the strengths and the weaknesses of the different digester technologies and indicating the main parameters and operating conditions to be monitored. Subsequently, a brief analysis of the factors affecting methane yield from manure AD was conducted and the AD of fruit and vegetables waste was examined. Particular attention was given to studies on co-digestion and pre-treatments as strategies to improve biogas yield. Finally, the selection of specific microorganisms and the genetic manipulation of anaerobic bacteria to speed up the AD process was illustrated. The open challenges concern the achievement of the highest renewable energy yields reusing agro-food waste with the lowest environmental impact and an increment of competitiveness of the agricultural sector in the perspective of a circular economy.

This study aimed to verify whether consumers confirm their willingness to pay extra costs for higher animal welfare standards in a situation where a potential purchase performed by consumers, such as the Vickrey auction, is used. A 104-member consumer panel was asked to rate its willingness to pay (WTP) for plain and low-fat yogurts in 3 information conditions: tasting without information (blind WTP), information about animal welfare without tasting (expected WTP), tasting with information about animal welfare (actual WTP). Information was provided to the consumers under the form of labels indicating the level of animal cleanliness and freedom of movement (5-point scale, from poor to very good). Consumers were influenced by information about low standards of animal welfare (low cleanliness and low freedom of movement) and moved their willingness to pay in the direction of their expectations. However, the discrepancy between expectancy and actual WTP was not totally assimilated, indicating that WTP was also expressed in relation to other aspects (e.g., the sensory properties of the products). Conversely, the information concerning high standards of animal welfare (high cleanliness and high freedom of movement) was able to affect expectancy but had an effect on actual WTP only when the most acceptable yogurt was offered to the consumers. In the case of discordant information on animal welfare, partly indicating high levels of welfare (freedom of movements) and low levels of welfare (cleanliness), expected WTP was always lower than blind WTP. However, when the least acceptable product was presented, they completely assimilated their actual WTP to the expectations. Conversely, with the most acceptable yogurt, no assimilation occurred and sensory properties prevailed in orienting consumer WTP. Within each product, consumers expressed a higher WTP for products with labels indicating high welfare standards as compared with yogurts with labels reporting intermediate and low welfare standard. These results show that information about animal welfare, if given to the consumers, can be a major determinant of consumer WTP for animal-based food products. However, information about high standards of animal welfare should be paired with products presenting a good eating quality.