Waste-to-energy systems can provide a functional demonstration of the economic and environmental benefits of circularity, innovation, and reimagining existing systems. This study offers a robust quantification of the greenhouse gas (GHG) reduction potential of industry-level adoption of anaerobic digestion (AD) technology on large-scale dairy farms in the contiguous United States. National GHG reduction estimates were developed through a robust life cycle modeling framework considering 20 dairy configurations that capture important differences in housing and manure management practices, applicable AD technologies, regional climates, storage cleanout schedules, and methods of land application. Results illustrate the potential for AD adoption to reduce GHG emissions from the dairy industry by 2.90 MMT of CO2-eq per year considering current economic barriers, and as much as 5.17 MMT of CO2-eq per year with economic barriers removed. At the farm level, AD technology may reduce GHG emissions from manure management systems by 55-77% depending on the region. Discussion focuses on regional differences in GHG emissions from manure management strategies and the challenges and opportunities surrounding AD adoption.

The US government’s Sustainable Aviation Fuel (SAF) Grand Challenge strives to increase annual SAF production to 35 billion gallons by 2050 while decreasing aviation emissions by 50%. The SAF Grand Challenge Roadmap notes that the purpose-grown biomass feedstock potential exists to provide at least 30 billion gallons of SAF, but limited research exists on the large-scale, country wide feasibility of these feedstocks in the US. Additionally, the SAF Grand Challenge Roadmap and others note that power-to-liquid (PtL) fuels could provide limitless fuel production if the required renewable energy is available. Therefore, this research compares the county-level production potential, economics, and environmental impact of purpose grown bioenergy feedstocks and PtL technologies for SAF throughout the Contiguous United States (CONUS) using GIS analysis, multi-objective optimization, and agent-based modeling.

In total, eight bioenergy crops (switchgrass, Miscanthus, poplar, willow, sorghum, algae, corn, and soybeans) and eight land types (barren, deciduous forest, evergreen forest, mixed forest, shrubland, grassland, pastureland, and cropland currently used for bioenergy) were considered for SAF production. Geographic information system mapping techniques were used to partition the CONUS into 200 m by 200 m patches to understand bioenergy production feasibility on various land types while excluding land with prohibitively low yield, unfavorable terrain (e.g. steep slopes), or protected status. Additionally, the Fischer-Tropsch PtL technology was also evaluated using green hydrogen production and renewable electricity to provide the minimum emissions possible. County-level results include SAF production potential, minimum fuel selling price, and greenhouse gas emission impacts including direct land use change (dLUC).

GIS results show that Miscanthus is the most promising bioenergy crop by providing both a competitive fuel selling price ($4.97-$5.81/gal) and low emissions (1.1-38.8 g CO2-eq/MJ vs 84.8 g CO2 eq/MJ for traditional jet fuel) when grown on non-forest land. All bioenergy feedstocks grown on forest land were found to have a larger environmental impact than conventional jet fuel due to dLUC impacts. Algae was found to have the highest fuel selling price ($10.25-$14.77/gal) and emissions (65.4-72.7 g CO2 eq/MJ) of the bioenergy feedstocks, but it also has a SAF productivity (fuel per land area) 10X that of the other feedstocks. Comparatively, the Fischer-Tropsch PtL pathway has low emissions (17 g CO2 eq/MJ) but high fuel selling price ($15.54/gal).

Multi-objective optimization results illustrate the tradeoffs between optimizing CONUS SAF production for minimum fuel selling price, emissions, carbon price, or land use. When minimizing for emissions using bioenergy feedstocks, 14.4% of total CONUS land is required to provide 30 billion gallons of SAF with Miscanthus as the primary feedstock. However, when land area is minimized, only 0.6% of CONUS land is required because high productivity algae is used as the feedstock, but this comes at the cost of higher emissions and fuel prices. Multi-objective optimization results for the Fischer-Tropsch PtL pathway show that 1.4% of CONUS land is required while having lower emissions and higher prices compared to traditional jet fuel.

The transition to low-carbon technologies is reshaping the U.S. economy, catalyzed by the goals set by the Biden administration to reduce economy-wide net greenhouse gas emissions (GHG) to half of their 2005 levels by 2030 and to attain net-zero emissions by 2050. To fulfill these objectives, the Inflation Reduction Act (IRA) and the Bipartisan Infrastructure Law invest in the scale up of clean energy technologies. The IRA also provides incentives to producers of clean fuels and hydrogen to increase their production, alongside the already existing incentives provided by the U.S. Environmental Protection Agency’s Renewable Fuel Standard and the California Air Resources Board’s Low Carbon Fuel Standard (LCFS). These policies are integral in promoting low-carbon technologies, with biofuels emerging as a critical complement to other decarbonization strategies such as electrification with grid decarbonization, especially for some specific sectors which cannot be electrified, e.g., aviation and marine sectors. The surging interest in the biofuel industry has spurred a demand for anticipated biofuel supply in the markets.To address the inherent uncertainty in biofuel markets, this study quantifies the GHG reductions achievable through planned biofuel production and capacity expansions and provides quantitative metrics to track the transition of U.S. fuel use across sectors to alternative fuels and the effect on key environmental performance criteria. We quantified the life cycle GHG emissions and carbon intensity (CI) of U.S. fuel use across all sectors of the economy together with a 10-year projection based on the existing and producers’ planned expansions of alternative fuel production capacity and fuel use projections.

Targeted biofuel types include biodiesel, renewable diesel, ethanol, sustainable aviation fuel, and renewable natural gas. Data on biofuel facilities, production capacity (existing and producers’ capacity expansion plans), operational dates, fuel pathways, and CI are compiled from the U.S. Energy Information Administration (EIA) biofuel production report, LCFS database, biofuel producers’ websites/reports, and other sources. We employed a bottom-up analysis based on scenarios that account for the impact of increased electrification on the US economy-wide future fuel use and existing and planned biofuel facility-level data and linked the biofuel production to the corresponding fuel pathway in greenhouse gases, regulated emissions, and energy use in technologies (GREET) model to estimate the potential economy-wide GHG emissions reduction resulting from the replacement of conventional fuels with biofuels from 2020-2035 .

Our findings indicate that biofuels have the potential to replace up to 3.84 exajoules of conventional fuels, resulting in a saving of approximately 266 million metric tonnes of GHG emissions by 2035. This impact is most profound in the transportation and industrial sectors, due to substitution of diesel with biodiesel/renewable diesel and jet fuel with sustainable aviation fuel. In an economy-wide context, biofuels reduced the total U.S. GHG emissions by 14% in 2035 while the combined impact of electrification and biofuel results in a 39% reduction . This study provides valuable insights for bioenergy stakeholders, enabling them to track the contribution of biofuel technologies to the decarbonization of the U.S. economy over time based on producers’ plan.

Agriculture and animal husbandry is responsible for 11% of the total US national greenhouse gas (GHG) emissions. Manure management alone makes up 9% of the total national methane emissions (EPA, 2023). As such changes to manure management within agricultural settings, including diversion of manure from lagoons to anaerobic digesters, could have substantial impacts on national GHG emissions. However, manure management, particularly in the dairy sector (Meyer et al., 2011), is complex and this contributes to the uncertainty surrounding any estimates of emissions reduction potential. There are a wide range of manure management technologies and designs currently in use. Differences in regional climate, pasture management, economics, and local tradition result in varying farm layouts and emissions. Local climate influences farm layout and pasture availability, as well as the chemistry and microbial community’s activity within manure management technologies, and these factors influence the rate of gaseous emissions (IPCC, 2006; Maldaner et al., 2018).

While factors such as local temperatures and herd sizes can be easily modeled via available government databases, data of real-world farm layouts is generally unavailable. As such it is challenging to model manure availability and farm emissions accurately on a large scale. To capture the breadth of potential baseline conditions across the US, this work utilized county-level temperature data (NOAA) and herd size data (NASS) to estimate housing conditions (barn, feed lots, pastures) as well as emissions rates. To capture the impact of different manure management technologies, this study modeled several potential baseline scenarios including no emissions mitigation, manure solids removal, the inclusion of anaerobic digestion, and covering lagoons.

This presentation will summarize the findings of these models to show volumes and location of: 1) Collectable manure per county; 2) Potential biogas production per county based on manure availability; and 3) Potential CH4, N2O, and eCO2 emissions for an array of manure management scenarios. The data presented will indicate which technologies can be used to target reductions in GHG emissions and improve air quality.

The legalization of industrial hemp farming in the United States has created an abundance of residual biomass, and consequently, an untapped potential for biogas production. Cannabidiol (CBD) has emerged as a highly sought after hemp derived product for its medicinal benefits. Although the hemp plant itself may be considered sustainable for its potential to be a carbon sink, the CBD production process currently follows an unsustainable linear process model. About 80% of the hemp feedstock is wasted during CBD production. In-situ anaerobic digestion is proposed to transform the residual hemp into biomethane which can be used to replace or supplement an existing fuel in a heating element in the CBD production process. Thus, the goal of this research is to investigate the utilization of hemp crop-residue as a biogas and explore the potential for creating a circular CBD industry. A process model is created using SuperPro Designer to simulate theoretical biogas yield and is compared with literature values and preliminary results from our experimental anaerobic digester located in North Carolina. The maximum theoretical biomethane yield produced by the process model is 360 mL CH4/g VS which is in line with our expectations since the average literature value for experimental anaerobic digestion of hemp is about 236 mL CH4/g VS. The percent composition of the biogas is also in line with literature values for biogas composition and preliminary results from our experimental digester. Future work will include measuring the biogas yield from the experimental digester to compare with our process model results. A comparative life cycle assessment (LCA) is conducted to compare the traditional end-of-life options for residual hemp (i.e., composting, incineration, and landfill) to the proposed alternative waste to energy scenario. The alternative scenario accounts for replacing the fossil fuel used in traditional CBD production with biomethane from the anaerobic digestion of hemp. Preliminary results show that the hemp waste-to-energy scenario has the lowest global warming impact compared to baseline scenarios which demonstrates that the proposed system has the potential to be environmentally sustainable. To create circularity within the industry, the system must also be economically sustainable for CBD producers. The global CBD market is projected to reach 44 billion USD with a compound annual growth rate of 27.8% for the forecast period of 2022-2029. This calls for a techno-economic evaluation of the existing and alternative biofuel system. Future work includes calculating biogas production potential for the whole state of North Carolina and working with CBD producers to implement this technology.