(62a) Carbon Intensities and Criteria Air Pollutant Emissions of Waste- and Coproduct- Derived Bioenergy Resources Resulting from on-Road Transportation Applications

Biofuels are anticipated to represent an important portion of the alternative fuels for heavy-duty vehicles (HDVs) required for achieving the decarbonation goals in the United States. Increasing interest in waste- and coproduct-derived biodiesel, renewable diesel, and renewable natural gas (RNG) as alternative transportation fuels necessitates an understanding of carbon intensities and criteria air pollutants from the perspective of full supply chains. This study evaluates carbon intensities and criteria air pollutant emissions of biomass-based diesel (BBD) and RNG produced by different feedstocks as part of a project commissioned by the New York League of Conservation Voters. The feedstocks for BBD pathways contain cooking oil (UCO), distillers corn oil (DCO), tallow, and forest residue. Landfill gas or biogas from anaerobic digestion of animal waste and wastewater sludge are studied to quantify the emissions of RNG. The final biofuel products of BBD and RNG are used to evaluate their potential waste- or coproduct-to-wheel emissions of greenhouse gases (GHG) and criteria air pollutants related to feedstock recovery and transportation, fuel production, transportation and distribution, and use in HDVs. The system boundary is in accordance with the main life cycle stages covered by the fuel cycle module of the Greenhouse Gases, Regulated Emissions, and Energy Use in Technologies (GREET) Model by Argonne National Laboratory. The functional unit for comparison of different transportation fuels is 1 million British thermal unit (mmBtu) of heat delivered that allows for comparison across biofuels. Furthermore, after reviewing different studies and models including the GREET model and CA-GREET3.0, comparisons of the fuel cycle emission levels with different input and output assumptions are conducted to understand the wide range of the emission levels across different studies, allowing for understanding the hotspots of the biofuel pathways. Finally, the emissions of biofuels are compared against petrodiesel and fossil natural gas, allowing an understanding of potential reduction of the carbon intensities and criteria air pollutants as well as to make recommendations to further improve the emission levels of the studied biofuel pathways. While this study focuses on GHG emissions of BBD and RNG, the current findings also show that criteria air pollutant emissions of the biofuels are distinctively lower than their fossil-based counterparts (e.g., low sulfur diesel and liquefied natural gas). BBD has slightly higher emissions of nitrogen oxides (NOx) than petrodiesel; however, NOx can be controlled by a combination of selective catalytic reduction (SCR) with other exhaust after-treatments. The results will be presented at the conference.