Food waste makes up approximately 15% of municipal solid waste generated in the United States, and 95% of food waste is ultimately landfilled. Its bioavailable carbon and nutrient content makes it a major contributor to landfill methane emissions, but also presents an important opportunity for energy recovery. This paper presents the first detailed analysis of monthly food waste generation in California at a county level, and its potential contribution to the state's energy production. Scenarios that rely on excess capacity at existing anaerobic digester (AD) and solid biomass combustion facilities, and alternatives that allow for new facility construction, are developed and modeled. Potential monthly electricity generation from the conversion of gross food waste using a combination of AD and combustion varies from 420 to 700 MW, averaging 530 MW. At least 66% of gross high moisture solids and 23% of gross low moisture solids can be treated using existing county infrastructure, and this fraction increases to 99% of high moisture solids and 55% of low moisture solids if waste can be shipped anywhere within the state. Biogas flaring practices at AD facilities can reduce potential energy production by 10 to 40%.

Digestate and biochar can be land applied to sequester carbon and improve net primary productivity, but the achievable scale is tied to expected growth in bioenergy production and land available for application. We use an attributional life-cycle assessment approach to estimate the greenhouse gas (GHG) emissions and carbon storage potential of biochar, digested solids, and composted digested solids generated from organic waste in California as a test case. Our scenarios characterize changes in organic waste production, bioenergy facility build-out, bioenergy byproduct quality, and soil response. Moderate to upper bound growth in the bioenergy sector with annual byproduct disposal over 100 years could provide a cumulative GHG offset of 50-400 MMTCO2 equiv, with an additional 80-300 MMTC sequestered in soils. This corresponds to net GHG mitigation over 100 years equivalent to 340-1500 MMTCO2 equiv (80-350% of California's annual emissions). In most scenarios, there is sufficient working land to apply all available biochar and digestate, although land becomes a constraint if the soil's rest time between applications increases from 5 to 15 years.

Gaseous streams in biorefineries have been undervalued and underutilized. In cellulosic biorefineries, coproduced biogas is assumed to be combusted alongside lignin to generate process heat and electricity. Biogas can instead be upgraded to compressed biomethane and used as a transportation fuel. Capturing CO₂-rich streams generated in biorefineries can also contribute to greenhouse gas (GHG) mitigation goals. We explore the economic and life-cycle GHG impacts of biogas upgrading and CO₂ capture and storage (CCS) at ionic liquid-based cellulosic ethanol biorefineries using biomass sorghum. Without policy incentives, biorefineries with biogas upgrading systems can achieve a comparable minimum ethanol selling price (MESP) and reduced GHG footprint ($1.38/liter gasoline equivalent (LGE) and 12.9 gCO_2e/MJ) relative to facilities that combust biogas onsite ($1.34/LGE and 24.3 gCO_2e/MJ). Incorporating renewable identification number (RIN) values advantages facilities that upgrade biogas relative to other options (MESP of $0.72/LGE). Incorporating CCS increases the MESP but dramatically decreases the GHG footprint (-21.3 gCO_2e/MJ for partial, -110.7 gCO_2e/MJ for full CCS). The addition of CCS also decreases the cost of carbon mitigation to as low as $52-$78/t CO₂, depending on the assumed fuel selling price, and is the lowest-cost option if both RIN and California's Low Carbon Fuel Standard credits are incorporated.

Numerous adsorption-based technologies are emerging as candidates for hydrogen transportation, and yet little is known about their practical viability. As such, new approaches are needed to conduct early validation of emerging hydrogen transportation concepts despite a lack of clear criteria for viable future hydrogen supply chains. In this work, we conduct technoeconomic modeling to quantify cost, performance, and relations between system components for early-stage adsorbent-based hydrogen supply chains. We compare results with the cost and performance of high pressure compressed gas and liquid hydrogen trucks in the same applications. Using available experimental adsorption data, we simulate the gravimetric performance of tube trailer trucks packed with metal-organic frameworks (MOFs) operated at 100 bar and 77 or 200 K. We also extrapolated available experimental data to study a third scenario where tube trailer trucks are operated at ambient temperature and 250 bar. Models developed for these conditions represent feasible operation scenarios where pressurization or cooling costs can be reduced relative to compressed or liquid hydrogen truck systems. Results suggest that the levelized cost of long-distance transmission, including a gas terminal and MOF-based truck fleet, ranges from $7.3 to $29.0 per kg H2. The levelized cost of transmission using compressed hydrogen gas trucks at 350 and 500 bar and liquid hydrogen trucks is substantially lower, at $1.8, $1.7 and $3.1 per kg H2, respectively. In a short-distance urban distribution application, the MOF-based truck fleet, gas terminal, and refueling stations have a levelized cost between $11.8 and $40.0 per kg H2, which is also more expensive than distribution in the case of the 350 bar, 500 bar and liquid hydrogen trucks, which have levelized costs of $4.7, $4.1 and $3.9 per kg H2, respectively. Key opportunities identified for lowering costs are: increasing the hydrogen capacity of the tube system by developing new MOFs with higher volumetric deliverable capacities, flexible allowable daily deliveries per refueling station, increasing the cycling stability of the MOF, and driverless trucks.

Nanomaterials have revolutionized the battery industry by enhancing energy storage capacities and charging speeds, and their application in hydrogen (H2) storage likewise holds strong potential, though with distinct challenges and mechanisms. H2 is a crucial future zero-carbon energy vector given its high gravimetric energy density, which far exceeds that of liquid hydrocarbons. However, its low volumetric energy density in gaseous form currently requires storage under high pressure or at low temperature. This review critically examines the current and prospective landscapes of solid-state H2 storage technologies, with a focus on pragmatic integration of advanced materials such as metal-organic frameworks (MOFs), magnesium-based hybrids, and novel sorbents into future energy networks. These materials, enhanced by nanotechnology, could significantly improve the efficiency and capacity of H2 storage systems by optimizing H2 adsorption at the nanoscale and improving the kinetics of H2 uptake and release. We discuss various H2 storage mechanisms—physisorption, chemisorption, and the Kubas interaction—analyzing their impact on the energy efficiency and scalability of storage solutions. The review also addresses the potential of “smart MOFs”, single-atom catalyst-doped metal hydrides, MXenes and entropy-driven alloys to enhance the performance and broaden the application range of H2 storage systems, stressing the need for innovative materials and system integration to satisfy future energy demands. High-throughput screening, combined with machine learning algorithms, is noted as a promising approach to identify patterns and predict the behavior of novel materials under various conditions, significantly reducing the time and cost associated with experimental trials. In closing, we discuss the increasing involvement of various companies in solid-state H2 storage, particularly in prototype vehicles, from a techno-economic perspective. This forward-looking perspective underscores the necessity for ongoing material innovation and system optimization to meet the stringent energy demands and ambitious sustainability targets increasingly in demand.

Liquid organic hydrogen carriers will likely be a key element of a future hydrogen economy by enabling the storage and transport of large quantities of hydrogen. Ethanol is a liquid organic hydrogen carrier that is readily available from biological resources, which undergoes a reversible reaction to yield hydrogen and ethyl acetate. The objective of the present study is to obtain a better understanding of the thermodynamic and environmental suitability of the ethanol–ethyl acetate cycle for hydrogen storage applications. The analysis covers three aspects: thermodynamics of the chemical reaction, energy balance of the process, and a first-order assessment of greenhouse gas emissions. Thermodynamics of the reaction are characterized by a standard Gibbs energy of reaction close to zero which allows the reaction to be shifted between hydrogenation and dehydrogenation within a moderate window of temperature and pressure conditions. The energy demand for dehydrogenation is comparatively small, resulting in an overall system efficiency of 88%. A life cycle greenhouse gas analysis over a 20-year storage system lifetime gives a carbon intensity of 7.0 kg-CO2eq/kg-H2 delivered. These results indicate that the ethanol–ethyl acetate system has considerable promise as a hydrogen carrier and should be the subject of further research.

Waste-to-energy systems can play an important role in diverting organic waste from landfills. However, real-world waste management can differ from idealized practices, and emissions driven by microbial communities and complex chemical processes are poorly understood. This study presents a comprehensive life-cycle assessment, using reported and measured data, of competing management alternatives for organic municipal solid waste including landfilling, composting, dry anaerobic digestion (AD) for the production of renewable natural gas (RNG), and dry AD with electricity generation. Landfilling is the most greenhouse gas (GHG)-intensive option, emitting nearly 400 kg CO_2e per tonne of organic waste. Composting raw organics resulted in the lowest GHG emissions, at -41 kg CO_2e per tonne of waste, while upgrading biogas to RNG after dry AD resulted in -36 to -2 kg CO_2e per tonne. Monetizing the results based on social costs of carbon and other air pollutant emissions highlights the importance of ground-level NH₃ emissions from composting nitrogen-rich organic waste or post-AD solids. However, better characterization of material-specific NH₃ emissions from landfills and land-application of digestate is essential to fully understand the trade-offs between alternatives.