From waste to resource: A life cycle assessment of biochar from agricultural residue

Abstract

In recent years, biochar has emerged as a versatile product. Producing biochar from agricultural residue is an environmentally friendly alternative to in-situ burning, reducing the requirement for chemical fertilizers. This study presents a comprehensive assessment of the environmental impact of biochar production. Four feedstocks are compared – rice straw, palm shell, corn stover, and mixed crop residue. The cradle-to-gate system boundary comprises all stages of biochar production – feedstock acquisition, transport and pre-treatment, and biochar production. Results show that the main hotspots are emissions and electricity consumption during production. The palm shell had the highest impact on human health (4.889 kg PM_2.5 eq) and ecosystem quality due to high terrestrial and aquatic acidification potential (159.600 kg SO₂ eq). Mixed crop residue had the greatest global warming potential (281.884 kg CO₂ eq) and resource consumption. Corn stover and rice straw had moderate impacts, with corn stover contributing significantly to ecotoxicity (2.2E+04 kg TEG water) and rice straw impacting respiratory inorganics (3.545 kg PM_2.5 eq), and causes severe depletion of resources, consuming 4339.672 MJ of non-renewable energy. These findings emphasize the importance of selecting low-impact feedstocks for biochar production. While corn stover has high impacts in midpoint categories like carcinogens, non-carcinogens, ionizing radiation, aquatic and terrestrial toxicity, and eutrophication, it has the lowest GWP. Rice straw has the lowest impact on human health and resources. Finally, uncertainty analysis using Monte Carlo Simulation shows that the coefficient of variation for impact categories is within ±10%, indicating that the results are reliable.