Environmental impact hotspots of an integrated wet anaerobic digestion through life cycle assessment for food waste management

Abstract

Wet anaerobic digestion (AD) is one of the most widely implemented systems that valorize food waste (FW) for biogas production. Despite the undeniable AD benefits, the environmental impact of AD could differ depending on the biogas systems used. This article examines the hotspots on environmental impact of FW management such as global warming and ozone depletion based on integrated wet AD by utilizing a life cycle assessment approach. The integrated wet AD scenario in this study is a technology that combines wet AD, aerobic windrow composting and a landfill. The scenario modelling was accomplished by applying GaBi v6.0 software with 1 ton of pre-treated FW as a functional unit, and the analysis was based on the ReCiPe (H) v1.07 characterization technique. At the midpoint level, it was observed that the integrated wet AD presented the most significant environmental impact in terms of ionizing radiation (1.4×100 kg U235-eq), followed by water depletion (1.11×103 m3-eq), global warming (6.27×102 kg CO2-eq), fossil depletion (2.18×102 kg oil-eq) and human toxicity (2.89×101 kg 1,4-DB-eq). The disadvantages of the integrated wet AD in global warming were associated with CO2, CH4, and N2O emissions from the energy used for process treatment and fossil fuels during transportation, primarily in landfill activities, followed by wet AD and aerobic windrow composting stages. Regarding single-score indicators, integrated wet AD presented the most resource damaging impact (3.50×103 Pt), mainly due to fossil depletion. This study emphasizes the necessity of reducing the life cycle consequences related to CH4, N2O and NH3 emissions throughout the decomposition process in integrated wet AD, particularly landfill activities.