Energy and environmental sustainability assessment of thermochemical conversion pathways for poultry litter from the attributional and consequential perspectives

Thermochemical conversion can recover energy and nutrients from poultry litter, but recovered products perturb electricity, heat, fuel, and fertilizer markets. This study compares six technologies with direct land application under attributional and consequential life cycle assessment. The attributional analysis favors gasification for carbon footprint and resource use because of high heat and electricity recovery. In the consequential analysis, this climate advantage weakens because electricity displacement is evaluated through marginal market responses. The consequential results depend on recovered product quantities and the markets in which those products displace existing supply. Slow pyrolysis provides the most robust climate outcome, retaining the lowest carbon footprint across 243 parameter combinations, because biochar carbon sequestration dominates over market-mediated fertilizer displacement. Resource outcomes show greater variation. Gasification achieves the lowest primary energy use in most combinations when its large net electricity output displaces grid electricity, whereas supercritical water gasification achieves the lowest natural resource depletion in most combinations because aqueous phase nutrients carry large benefits under scarcity based characterization. Market-mediated effects can change the preferred reaction condition when product distributions shift. For hydrothermal liquefaction, attributional analysis favors 300 °C for carbon footprint, whereas consequential analysis favors 350 °C across all tested market parameter combinations. Lowering reaction temperature from 350 to 250 °C increases the consequential carbon footprint by 28% because reduced bio-oil yield weakens fuel displacement. Attributional credits alone provide an incomplete basis for comparison when technology performance depends on market responses. Consequential assessment helps evaluate robustness under variable market conditions alongside controllable reaction conditions.