Environmental impacts of food waste biological processing techniques: composting and methanization - Final report + Synthesis + Short synthesis - Critical review report, December 2019

It is foreseen by the Energy Transition and Green Growth Act of August (published on August 17, 2015) that by 2025 every private individual shall have access to a separate food waste collection. For this, different solutions can be implemented such as individual, public or private composting, agro-industrial or agricultural anaerobic digestion. These solutions allow for the production of agronomic feedstock along with energy in the case of anaerobic digestion. Yet, these treatment options also present environmental impacts that should be evaluated when assessing their interest. In this context, and to meet concerns that have been addressed, the ADEME (Agence de l'Environnement et de la Maitrise de l'Energie) wants to compare through a Life Cycle Analysis (LCA) the various food waste collection and upgrading solutions from an environmental point of view: private composting, public composting, industrial composting, 'on-farm' anaerobic digestion and centralized anaerobic digestion. The Life Cycle Assessment is attributional, and the functional unit is the treatment of 1 kg of food waste (FW). The system boundaries include the waste collection and the upstream storage of food waste if relevant, the composting or anaerobic digestion process, the downstream storage, the transportation and the spreading of the resulting agronomic product (compost or digestate). The environmental impacts are presented in three different ways: generated impact (negative impacts on the environment related to feedstock production and emissions), avoided impacts (positive impacts on the environment related to valuable products and energy production) and aggregated impacts that are the sum of generated and avoided impacts. Value-chain and process equipment design has been based on existing facilities. The impacts have been assessed based on a literature study and existing LCAs studies and databases (Ecoinvent V3). The results show that negative impacts on the environment are mainly related to nitrogen, phosphate and carbon emissions during the process (composting or anaerobic digestion) and during the spreading of the compost and the digestate. However, it has been extremely difficult to evaluate the emissions during the composting/anaerobic digestion (especially biogas leaks) and to differentiate the value chains/scenarios due to the lack of data source and their poor reliability. Moreover, the spreading techniques for compost and digestate also have a strong influence on the impacts generated. Regarding the potentially avoided impacts, the agronomic value of digestate and composts is the main lever to improve the environmental benefits, thanks to substitution of soil enricher (compost) and mineral fertilizer (digestate). The energy produced in the case of anaerobic digestion is also of great interest in terms of avoided impacts when substituted for electricity in the case of Combined Heat and Power (CHP) or natural gas in the case of injection in the public grid. It shall be stressed that this LCA is based on standard facilities and that the environmental comparison with other value chains can be generalized by no means. The collected data may be used on a given territory to compare various combinations of these value chains reminding that they are designed to coexist with a view to territorial optimization. Considering economic, technical and social contexts and regulations is essential when drawing these comparisons. (authors)