## 1 Introduction  
Sustained demographic growth and increased economic activities in cities have contributed to the escalating rise in municipal solid waste (MSW). In Bogota, by the year 2020, the disposal at the Dona Juana landfill reached 6237.655 tons/day, leading to pressure on facilities and adverse effects on the area's inhabitants [1, 2]. In this regard, the national policy for integrated solid waste management introduces the concept of a circular economy, emphasizing the importance of utilization and valorization for reintegrating waste into the local production network [3]. In a megacity, organic waste accounts for 45 to 50% of the total MSW and represents the fraction with the highest potential for recovery [4]. Hence, all actions related to the utilization and valorization of the organic fraction of municipal solid waste (OFMSW) are pertinent. The failure to do so would lead to the decomposition of these waste materials, contributing to greenhouse gas (GHG) emissions, leachate production, landfill cell saturation, soil degradation, and other environmental impacts [5]. Among the primary strategies for valorizing the organic fraction of urban solid waste (OFUSW) in a megacity, composting (non-energy valorization), single-stage anaerobic digestion (aiming to produce biogas), and dark fermentation followed by anaerobic digestion (a developing scheme to produce biohydrogen and biogas) stand out. Evaluating these pathways through the lens of life cycle assessment will help to define their environmental, technical, and energy viability within the circular economy framework. This article assesses the dark fermentation process for a megacity, with Bogota serving as a case study. Anaerobic digestion (AD) is considered the most effective method for valorizing OFMSW and converting waste into energy, provided that the biodegradability exceeds 40% [6]. The benefits of AD include the ability to apply high loading rates due to reduced space requirements and the potential for recovering by-products, such as ammonia, through post-treatment methods [7]. Additionally, biogas valorization technology is currently being applied at the Dora Juana landfill, where an average flow of 7938 Nm\({}^{3}\)/h of biogas was captured in 2019, resulting in an estimated 1,192,729.40 kWh of electricity generation and an average reduction of approximately 541 t CO\({}_{2}\) eq in GHG emissions [5]. While AD and biogas capture are relatively low-complexity alternatives for OFMSW utilization, analyzing each stage reveals that when the biochemical process is complete, the composition of the resulting biogas consists mainly of methane. However, a closer examination of each stage of AD shows that hydrogen can be biologically recovered from the hydrolysis stage (prior to methanogenesis), a product with higher energy value than methane. This hydrolysis stage is also known as dark fermentation, which produces volatile fatty acids (VFAs), carbon dioxide (CO\({}_{2}\)), and biohydrogen. The latter is a biofuel with energy yields ranging from 120 MJ/kg to 140 MJ/kg, in comparison to other sources such as natural gas with 50-55 MJ/kg, crude oil 42-47 MJ/kg, or coal 10-23 MJ/kg [8]. In contrast to conventional hydrogen, which requires high-energy-demanding methods for recovery, such as the non-catalytic partial oxidation of fuels, steam methane reforming, membrane processes, selective methane oxidation, oxidative dehydrogenation, and electrochemical processes [9], biohydrogen recovered through dark fermentation is one of the metabolic by-products of microorganisms degrading sugars and carbohydrates found within organic matter; therefore, its energy demand is not significantly high. In the dark fermentation process, anaerobic bacteria degrade carbohydrates under anaerobic conditions and absence of light to produce biohydrogen [10]. Starting from glucose, the maximum theoretical moles of H\({}_{2}\) can be obtained, corresponding to a value of 4 moles of H\({}_{2}\) when acetic acid and CO\({}_{2}\) are among the products, as shown in Equation (1).