## 1 Introduction  
According to the Food and Agriculture Organization (FAO), an estimated one third of all food produced worldwide is lost or wasted every year [1]. Food loss and food waste represent an amount of approximately 1.3 billion tons of food resources wasted per year [2, 3] throughout the food chain. Despite the need for more sustainable food management systems [4, 5, 6], food waste is always expected to be produced, at least at both the distribution and consumption levels. Food wastes are a major fraction of municipal solid wastes (MSWs). Since they are composed of different organic wastes, they are referred to as the organic fraction of municipal solid wastes (OFMSW) [7]. Currently, the OFMSW is mainly landfilled, thermally treated with heat recovery, composted, or anaerobically digested in high- to medium-income countries. In low-income countries, this fraction is dumped with no significant environmental control [8]. In Europe, the most effective and sustainable valorization routes for OFMSW are being pursued as the European Directive 2018/851 [9] will impose the segregated collection of biowastes from 31 December 2023 onwards with the aim of valorizing them. Biohydrogen (bioH\({}_{2}\)) (H\({}_{2}\) produced from biological processes) is a renewable, fossil carbon-free fuel and has received considerable attention as an alternative energy carrier to fossil fuels in recent years. Effectively, H\({}_{2}\) is the fuel with the highest energy content per mass unit of all known fuels (142 MJ.kg\({}^{-1}\)). The only final by-product of its combustion is water, which can be collected and further used, and consequently, no greenhouse gases (GHGs) are released. H\({}_{2}\) can be directly burnt in internal combustion engines or in fuel cells to produce different types of energy [10]. The major challenges related to the use of H\({}_{2}\) lie in its sustainable production and safety storage [11; 12]. Currently, in industrial applications, H\({}_{2}\) is mainly being produced from fossil fuels and through highly energy-intensive processes, rendering it less attractive from an environmental point of view [13]. However, H\({}_{2}\) can be also obtained from sustainable technologies such as water electrolysis, the deployment of which is taking leverage around the world, and biological processes which need further study for sustainable up-grading. These technologies will generate a cleaner and more sustainable fuel (H\({}_{2}\)) and avoid or minimize GHG emissions [14; 15]. To date, the production rate, stability, and efficiency of H\({}_{2}\) from biological sources must be improved to make it commercially viable [16]. Dark fermentation (DF) has been proposed as a promising process to produce bioH\({}_{2}\) owing to its low chemical energy demand and more environmentally friendly performance when compared to thermochemical processes. During DF, carbohydrate-rich substrates are anaerobically fermented, in the absence of light by a consortium of microorganisms or pure cultures [17]. Their metabolic activity causes the oxidation of the organic substrate, generating an excess of electrons. In the presence of the hydrogenase enzyme, the protons (H\({}^{+}\)) present in the anaerobic environment work as electron acceptors and produce molecular hydrogen [18; 19]. The OFMSW, generally constituted of food wastes with a high biodegradable fraction and approximately 85-95% \(w/w\) volatile solids (VS) and 75-85% \(w/w\) moisture content, is one of the organic feedstocks that can be used in DF [20]. The OFMSW is rich in proteins, lipids, complex polysaccharides, nitrogen, phosphorus, and metal ions that work as micronutrients. This organic waste is abundant and can be used as a superior feedstock for the fermentative processes of hydrogen-producing microorganisms [21].