Carbon footprint and environmental impact of poultry manure valorization as organic composts

Valorization of poultry manure (PM) has become increasingly important due to the rapid expansion of poultry production, with composting being the most widely used approach to convert PM into organic fertilizer (OF). Conventional composting (CC) typically requires approximately 40 days for manure maturation, whereas high-temperature microorganism decomposition (HMD) can reduce the process to about 7 days. This study quantifies the life-cycle carbon footprint and environmental impacts of OF produced via CC and HMD (i.e., CCOF and HMDOF) using field-measured data. The results show that carbon footprint of CCOF is ∼684 kg-CO₂e per metric tonne (Mt), while that of HMDOF is ∼801 kg-CO₂e per Mt, approximately 17% higher. The dominant emission source in both systems is direct methane emission, which primarily produced under anaerobic conditions; therefore, enough aeration and frequent turning during composting are essential strategies to reduce GHG emissions. The higher carbon footprint of HMDOF is primarily attributed to the substantial electricity consumption, highlighting the need for energy optimization or a transition to green energy systems. Beyond GHG emissions, this study also examines several environmental impacts, including acidification, freshwater ecotoxicity, fossil resource use, terrestrial eutrophication, and water use. The freshwater ecotoxicity impact in HMDOF reaches ∼886 CTUe/Mt, compared to ∼269 CTUe/Mt in CCOF, approximately four times higher. Acidification impact is also eight times greater. Resource use in HMDOF is also significantly elevated, at ∼3,310 MJ/Mt, compared to only ∼249 MJ/Mt for CCOF. In addition, this study incorporates a sensitivity analysis on two critical parameters: electricity consumption and composting emission. In CCOF, the sensitivity analysis shows that composting emissions are the primary driver of impact variability, leading to 12-19% changes in carbon footprint, acidification, and terrestrial eutrophication when composting emissions shift by ±20%. Conversely, HMDOF responds more strongly to changes in electricity consumption, with the evaluated impact categories showing 8-17% variation under a ±20% change in electricity use. These findings underscore the importance of evaluating environmental performance from multiple perspectives when pursuing faster and more advanced composting technologies. A comprehensive assessment ensures that innovations align with the principles of circular economy and environmental sustainability.