Challenges in Quantifying Greenhouse Gas Impacts of Waste-Based Biofuels in EU and US Biofuel Policies: Case Study of Butanol and Ethanol Production from Municipal Solid Waste.

Fanran Meng,Jon Mckechnie

doi:10.1021/acs.est.9b04286

Abstract

Conversion of wastes to biofuels is a promising route to provide renewable low-carbon fuels, based on a low- or negative-cost feedstock, whose use can avoid negative environmental impacts of conventional waste treatment. However, current policies that employ LCA as a quantitative measure are not adequate for assessing this type of fuel, given their cross-sector interactions and multiple potential product/service streams (energy, fuels, materials, waste treatment service). We employ a case study of butanol and ethanol production from mixed municipal solid waste to demonstrate the challenges in using life cycle assessment to appropriately inform decision-makers. Greenhouse gas emissions results vary from -566 gCO2 eq/MJbiofuel (under US policies that employ system expansion approach) to +86 gCO2 eq/MJbiofuel and +23 gCO2 eq/MJbiofuel (under initial and current EU policies that employ energy-based allocation), relative to gasoline emissions of +94 gCO2 eq. LCA methods used in existing policies thus provide contradictory information to decision-makers regarding the potential for waste-based biofuels. A key factor differentiating life cycle assessment methodologies is the inclusion of avoided impacts of conventional waste treatment in US policies and their exclusion in EU policies. Present EU rules risk discouraging the valorisation of wastes to biofuels thus forcing waste toward lower-value treatment processes and products.

Highlights

Liquid biofuels can play a key role in the decarbonisation of the transport sector, and have been studied extensively with life cycle assessment (LCA) tools to quantify their net contribution to addressing greenhouse gas (GHG) emissions associated with conventional, fossil fuels
Excluding avoided waste treatment would still result in very low GHG emissions under system expansion approach (11 gCO2eq./MJbiofuel) as a result of significant co-product credits for electricity export and metals recovery (-166 and -202 gCO2eq./MJbiofuel, respectively)
Emissions and primary energy demand (PED) relative to gasoline, the magnitude of these reductions are dependent on the allocation method employed

Summary

Introduction

Liquid biofuels can play a key role in the decarbonisation of the transport sector, and have been studied extensively with life cycle assessment (LCA) tools to quantify their net contribution to addressing greenhouse gas (GHG) emissions associated with conventional, fossil fuels. The development of waste-based fuels has received significant attention as they can avoid land use implications of crop-based biofuels (e.g., carbon stock reductions in biomass and soil pools; biodiversity impacts) while contributing to waste treatment objectives in the perspective of a more circular economy. LCA frameworks employed in existing policies which were developed to principally consider crop- and agriculture/forestry residue-based biofuels. These approaches face challenges in evaluating biofuels produced from more complex, mixed waste feedstock streams and in accounting for interactions between the waste treatment and energy sectors

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Results

Conclusion