Life cycle assessment of agro-industrial byproduct reuse: a comparison between anaerobic digestion and conventional disposal treatments

Different treatments of six selected Mediterranean agro-industrial by-products, i.e., citrus pulp, olive pomace cattle and poultry manure, whey and silage, were investigated through LCA application with the aim of analysing their environmental sustainability, in terms of “level of greenness”. In detail, an AD-based treatment system composed of four biogas plants fed by a mix of the selected agro-industrial by-products (scenario 1) was compared with the conventional treatment of those feedstocks (scenario 2), i.e., land application, biowaste composting, olive pomace treatment, and feeding treatment. The results clearly demonstrated that the AD-based treatment system is the most environmentally sustainable solution, since the environmental damages associated with the investigated scenarios are equal to 11.08 μpt and 598.44 μpt, for scenario 1 and scenario 2, respectively. These results confirmed that, as reported in the literature, anaerobic digestion of agro-industrial feedstocks is considered to be a “green” solution with high saving potential with respect to greenhouse gas (GHG) emissions, and plays a relevant role in renewable energy production by valorising agro-industrial by-products, by contributing to closing of organic matter cycles within a circular economy perspective. The results achieved in this study could represent a guideline to improve sustainability of energy generation by AD-based systems. In fact, since the results were obtained by means of real-world modelled scenarios, they could be extended to other AD-based systems analogous to that analysed in this study for developing and supporting sustainable economy concepts and energy-food-waste nexus approaches.