Environmental and economic impacts of improper materials in the recycling of separated collected food waste through anaerobic digestion and composting.

Separately collected food waste (SC-FW) is effectively recycled through industrial anaerobic digestion (AD) and composting. However, the presence of improper materials in SC-FW not only generates technical problems to AD and composting, but also lowers the quality of the outputs of the processes. As a consequence, improper materials found in SC-FW cause not negligible environmental and economic burdens. In this study, the environmental and economic impacts due to the presence of unsuitable materials in the SC-FW, determined through compositional analysis, were estimated through life cycle assessment and environmental life cycle costing approaches. Three different scenarios were analysed for both AD and composting processes: (i) the current situation (CS); (ii) the improved scenario (AS) with an amount of improper materials in SC-FW reduced to 3 % (w/w); (iii) the ideal scenario (IS) with the total absence of foreign materials. Environmental benefits were determined for the AS and IS scenarios in 17 of the 19 analysed impact categories. Considering the GHG emissions, higher savings were measured for AD in AS and IS scenarios (47 % and 79 %, respectively) than in CS scenario. Similarly, savings of -10.4 kg fossil oil eq/ton (AS) and - 17.1 kg fossil oil eq/ton (IS) for AD could be obtained with respect to the CS scenario. Greater economic benefits were calculated for AD (-76.4 €/ton) and composting (-52.2 €/ton) in the IS scenario. Savings up to € 2,249,780 and € 3,888,760 could have been obtained in 2022 by reducing to 3 % (w/w) and eliminating, respectively, the amount of improper materials in the SC-FW. The results of the compositional analyses of SC-FW allowed to identify the incorrect behaviours in FW source-sorting activity and to plan interventions to improve the current FW management system. The quantified environmental and economic benefits could further motivate citizens to correctly differentiate FW.