Organic Waste-to-Hydrogen via Anaerobic Digestion and Steam Reforming

Organic Waste-to-Hydrogen via Anaerobic Digestion and Steam Reforming Abstract The global imperative for decarbonized energy systems has positioned hydrogen (H₂) as a pivotal clean fuel, yet its predominant production from fossil sources emits ~830 million tonnes of carbon dioxide (CO₂) annually. The integrated anaerobic digestion and steam reforming (AD-SR) pathway offers a sustainable alternative, converting organic waste—such as food scraps, agricultural residues, municipal solid waste (MSW), and livestock manure—into H₂ via methane-rich biogas. This review critically evaluates AD-SR, synthesizing over 50 studies from 2022-2025 to assess process efficiencies (50-70% H₂ yield), technological advancements, and challenges. Anaerobic digestion (AD) degrades organic matter into biogas (50-70% methane, CH₄), while steam reforming (SR) catalytically transforms biogas into H₂-rich syngas, achieving yields of 0.1-0.3 kg H₂/kg dry waste. Key optimizations include nickel (Ni)-based catalysts for cost-effective SR, steam-to-carbon ratios >2 to mitigate coking, and hybrid reforming for CO₂ utilization, enhancing yields by 10-20%. Challenges encompass biogas impurities (e.g., hydrogen sulfide, H₂S, poisoning catalysts), high energy demands for SR (~800°C), and economic hurdles, with levelized cost of hydrogen (LCOH) at 1.5-5 USD/kg. Environmental benefits are significant, reducing greenhouse gas (GHG) emissions by 70-90% compared to fossil H₂, with potential negative emissions via carbon capture and storage (CCS). Case studies, such as food waste processing in China (0.15 kg H₂/kg) and manure in Canada (8.11 kg H₂/h), demonstrate feasibility. Future directions emphasize AI-driven process control, low-temperature electrocatalytic reforming, and policy incentives like carbon pricing to bridge economic gaps. This review underscores AD-SR’s potential as a scalable, green H₂ production route, advocating for interdisciplinary research and regulatory support to achieve net-zero goals and circular waste management. Keywords: Hydrogen Production, Anaerobic Digestion (AD), Steam Reforming (SR), Organic Waste, Biogas, Sustainability, Carbon Capture and Storage (CCS), Levelized Cost of Hydrogen (LCOH), Greenhouse Gas (GHG) Emissions, Circular Economy. 1. Introduction Hydrogen (H₂) has assumed a pivotal role in the global pursuit of sustainable energy systems, functioning as an adaptable zero-emission energy carrier capable of decarbonizing hard-to-abate sectors such as heavy industry, long-haul transportation, and power generation (Elazab et al., 2025). According to the International Energy Agency (2024), world hydrogen consumption exceeded 97 million tonnes (Mt) in 2023 and is expected to draw to 100Mt in 2024, although mainly due to conventional uses in refining and the chemicals business to date. However, more than 99 percent of this demand is met using fossil fuel-derived hydrogen that emits roughly 830 Mt of carbon dioxide emissions per year in an amount comparable to the total emissions by the United Kingdom and Indonesia combined. In the IEA Net Zero Emissions by 2050 Scenario (NZE Scenario), the need to produce hydrogen with low emission intensity in a cost-effective way that is climate-consistent leads the demand to soar in 2030 (130 Mt) and 2050 (more than 500 Mt) necessitating a paradigm shift to low-emission production routes. Though policy frameworks have spurred investment, especially through the European Union and the U.S. delegated acts and the U.S. Inflation Reduction Act, the pace of implementation has been slow and regulatory uncertainties still prevail; thus, project development has been delayed. These delays risk undoing the efforts to meet high goals with which these frameworks are aimed at tackling (Stokes, 2024; Kasyanenko et al., 2025). The need to have sustainable production of hydrogen is also compounded by the fact that the organic waste management sector is in a crisis which is increasing by the day. Globally, food waste alone generates 9.3 billion tonnes of CO₂-equivalent (GtCO₂e) emissions annually, accounting for 8-10% of anthropogenic greenhouse gas emissions comparable to the total emissions from the U.S. and EU combined in 2017 (Dwyer, 2023; Rai et al., 2025). According to the Food Waste Index Report 2024 by the United Nations Environment Programme (UNEP), 1.05 billion tonnes of food is estimated to be discarded each year, with households contributing 60 % (631 Mt), food services 28 % (290 Mt) and retail 12 % (131 Mt). Such waste increases the amount of methane produced by landfills that produce between 8 and 10 % of greenhouse gas emissions globally. In addition to the environmental damage, it wastes resources that measure 45 trillion gallons of water and territory that is larger than the surface area of China (UNEP, 2024). In the United States the main source of methane is organic waste, with 66.2 Mt of food wastes generated in the year 2019, 40 % generated at household and 60 % in services and retail. At the same time, food waste has both social justice and economic implications as there are around 800 million people struggling with hunger and one-third of the generated food, which would cost 400- to 500-billion dollars, is going to waste. Transforming some type of organic waste, including food scraps, agricultural residues, sewage sludge, and livestock manure to hydrogen through integrative approaches, e.g., anaerobic digestion (AD) followed by steam reforming (SR), has a twofold value: wasted materials are valorised and low-emission energy is obtained. The AD-SR pathway utilizes microbial degradation in AD to produce methane-rich biogas (typically 50–70 % CH₄, 30–50 % CO₂) that is subsequently hydrogenated in SR, yielding H₂-rich syngas via the endothermic reaction. Such an approach corresponds to the concepts of a circular economy and Sustainable Development Goal (SDG) 12.3 to reduce food wasted by 50 % by 2030 (Mazzanti et al., 2025). CH₄ + H₂O ⇌ CO + 3H₂ (ΔH = +206 kJ/mol), often coupled with water-gas shift (WGS: CO + H₂O ⇌ CO₂ + H₂) for enhanced yields (Zhu et al., 2021). The integrated synthesis of biogas via anaerobic digestion (AD) and hydrogen via steam-reforming (SR) has achieved an operational efficiency of 50-70 % for H₂ production, with H₂ yields ranging from 0.1 to 0.3 kg H₂ per kg of dry waste, as demonstrated by studies undertaken with food waste in China and manure in Canada (Seglah et al., 2023). There is still, however, significant impediments. Biogas impurities, especially hydrogen sulphide (up to 5000 ppm) may poison catalysts; and higher temperature ranges (700-900) require large energy inputs; and economic viability depends on levelized costs of hydrogen (LCOH) which range between 2 and 5 USD/kg with the scale and subsidy levels determining viability. Recent progress, such as the hybrid steam–dry reforming of biogas-derived CO₂, has improved carbon utilisation by 10-15 % while diminishing coking risks (Werkneh, 2022). A critical appraisal, however, indicates that although AD-SR reduces GHG emissions by up to 80 % relative to fossil-based hydrogen, lifecycle assessments (LCAs) frequently overlook emissions from feedstock collection and carbon management downstream, potentially overstating environmental benefits (Bird et al., 2011). Nishimura et al. (2024) and Chattanathan et al. (2014) examined the combination of AD and biogas reforming, achieving hydrogen yields of 2.5-3.5 mol H₂ per mol CH₄ using Ni-based catalysts; nonetheless, catalytic deactivation by biogas impurities was problematic. In South Korea, AD–SR systems configured from food waste demonstrated conversion efficiencies of 60-70 %, yet scalability was constrained by seasonal feedstock variability (Rawoof et al., 2021). That paper also emphasised the energy intensive character of SR and the necessity to pretreat feedstocks to increase digestibility. To maximize conversion and energy recovery, AD has been studied as a biohythane production method, but no studies have comprehensively explored its capability to integrate with injection in order to enable potentially overlooked synergistic negative emissions opportunities via carbon capture. Usoro and Umoh (2025) assessed animal waste steam reforming, reporting efficiencies comparable to natural-gas reforming (85-95% CH₄ conversion), but highlighting heightened impurity challenges in biogas feeds. This review undertakes a critical synthesis of recent developments in AD-SR for H₂ production. The analysis will analyse the following: the fundamental aspects of a process with a specific focus on kinetics and thermodynamics; examining the issues related to integration, especially mitigation of impurities and energy balances, an analysis of the effect of the feedstock, the comparative yield analysis, economic and environmental metrics through LCAs and TEAs, and proposed optimisations, including control through AI and hybrid reforms. The review further highlights that, although AD-SR possesses large-scale potential capable of supplying approximately 16 Mt H₂ equivalent by 2030, as reported by several announced projects the disparity between the announced capacities (520 GW electrolysis equivalent) and the few projects that have achieved FIDs (only 20 GW) underscores the imperative for accelerated policy intervention to address current demand–supply mismatches. Anaerobic digestion (AD) refers to a biological process that involves converting of complex organized substances into biogas in an oxygen-free environment. Such a metabolic cascade is comprised of four mutually dependent stages hydrolysis, acidogenesis, acetogenesis, and methanogenesis (Achinas et al., 2020). Polymers which are carbohydrates, proteins, and lipids are dissolved by extracellular enzymes to monomeric form during hydrolysis. In the acidogenic stage, these released constituents are metabolised into volatile fatty acids (VFAs), alcohols, hydrogen (H₂), and carbon dioxide (CO₂

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