Life Cycle Assessment of the Production of Biofertilizers from Agricultural Waste

This study reviewed 98 references on the Life Cycle Assessment (LCA) of the conversion of agricultural waste into biofertilizers. Feedstocks were manure (39%), organic/ food/wood waste (30%), and crop waste (26%). Biofertilizers were digestate, compost, biochar, and pellets, and full-scale application was prevalent. Approximately 64% of references cited anaerobic digestion (AD) and composting, often combined. Thermochemical and mechanical processes were less (24%) involved, mostly incineration and gasification (10% each) and pyrolysis (4%), with few cases of pelletization. Approximately 30% of references coupled LCA with an economic analysis tool. All references considered the Life Cycle Impact Assessment (LCIA) categories Global Warming Potential (GWP), Ozone Depletion Potential, Eutrophication, and Acidification. In overall AD, compared to other technologies, displayed the largest average impacts, particularly when the chosen functional unit (FU) involved manure. Composting provided lower average impacts compared to AD, and FU referring to organic/food waste largely topped manure. Thermochemical processes exhibited the smallest average impacts, compared to AD and composting, particularly when the FU was related to food/organic waste. In conclusion, further research is needed to explore technologies (particularly thermochemical and mechanical) applied at full-scale in different contexts and to the assessment of economic and social sustainability, identified as main knowledge gaps.