Agricultural Waste Utilization: Life Cycle Assessment for Selecting Carbon-Management Best Practices on a Global Scale

Abstract

Crop residues are a widely available form of agricultural waste with several possible reuse applications, including use as biofertilizers, animal feed, biofuels, and for carbon sequestration. However, in many parts of the world, large quantities of these residues are still burned in the field, releasing significant amounts of greenhouse gases (GHGs) and air pollutants to the atmosphere. This study aims to evaluate alternative and carbon-efficient strategies for reusing crop residues – especially focusing on rice straw and wheat straw – by conducting life cycle assessments (LCA) of multiple utilization pathways. Different alternative scenarios for utilizing crop residues are assessed: incorporating residue in field, animal usage for feeding, pyrolysis for electricity generation, pyrolysis for carbon sequestration, and electricity generation through residue combustion. Specifically, for the scenarios of pyrolysis and electricity generation through residue combustion, the maximum feasible transport distances of crop residues from agricultural fields to processing facilities are modeled for different logistics methods, providing information for the locations for establishing centralized facilities while maintaining GHG benefits for the scenarios. The results of this study highlight that electricity generation using crop residues, either through pyrolysis or direct residue combustion, offers the greatest climate benefits among all evaluated options. Carbon sequestration through pyrolysis also yields substantial GHG reductions, although slightly lower than the benefits from electricity generation. While crop residue-based electricity emits 4.35 to 31.25 times more GHGs per unit of electricity generated than renewable sources and 50.00 to 67.57 times more than nuclear sources, it still performs better than fossil fuels and provides added value in terms of agricultural waste management, resulting in 30.56 to 66.67% lower GHG emissions. Moreover, transportation emissions account for only a small share of the total life cycle global warming potential (GWP) in the electricity generation scenarios, ranging from 0.66% (via ships) to 16.40% (via trucks) for every 1000 km traveled. This makes long-distance residue transport viable. The findings of this study underscore the potential for crop residues to play a meaningful role in climate mitigation and sustainable agricultural waste management.