# Microbes and Parameters Influencing Dark Fermentation for Hydrogen Production
## 1 Introduction
The production of H\({}_{2}\) is not continuous in this method, as the activity of water splitting is susceptible to oxygen (O\({}_{2}\)) evolution  
Figure 1: Biological methods of hydrogen production. during photosynthesis, resulting in a brief period of H\({}_{2}\) production [12]. Both microalgae and cyanobacteria are capable of performing indirect photolysis, a process in which light is used to produce carbohydrates that are then converted into H\({}_{2}\). This method mitigates the issue of O\({}_{2}\) sensitivity by partially separating CO\({}_{2}\) fixation-based O\({}_{2}\) and H\({}_{2}\) generation by the nitrogenase enzyme [11]. Microbial electrohydrogenesis cells produce H\({}_{2}\) simultaneously with wastewater treatment. They promote the degradation of volatile fatty acids produced and are therefore considered a promising approach to optimize biomass conversion to H\({}_{2}\)[13]. In this method, a microbial anode is coupled to a hydrogen-evolving cathode, and the oxidation of water at the anode is replaced by the oxidation of low-cost compounds. Despite considerable efforts to scale up the system, this approach has faced major difficulties [14]. Among the different biological methods for H\({}_{2}\) production, dark fermentation is the main focus of this article. Dark fermentation, which is part of the acidogenic step of anaerobic digestion [15], offers several advantages as it does not require light and can use various raw materials as substrates for H\({}_{2}\) production by microbes [16]. In this process, microbes use organic compounds as an energy source and convert them into organic acids, alcohols, and gases, such as H\({}_{2}\), through fermentative pathways under anaerobic conditions [15]. The H2 Boost project, led by the Biorenewables Development Centre at the University of York, has become the first initiative to successfully produce hydrogen on a large scale through dark fermentation. The project aims to develop a commercially viable and sustainable process for producing hydrogen from organic waste. It is believed that these new technologies have the potential to decarbonize the UK's transport sector and provide up to 35% of the country's energy needs by 2050 [17]. This biological method is used not only for H\({}_{2}\) production but also to convert solid residues into high-quality biofertilizers and to minimize the generation of residues when food waste is used as the substrate [18]. Studies in recent years have suggested that the introduction of synthetic materials or nanoparticles can enhance H\({}_{2}\) production during dark fermentation [19]. Doped composites of metal ions are characterized by a high surface area and exceptional electrical conductivity, which allows the enhancement of colony enrichment and the inter-species efficiency of electron transfer [20]. Dark fermentation is a promising technique for bioenergy production, offering a sustainable approach to generating H\({}_{2}\) through the anaerobic degradation of organic compounds. Parameters such as pH, temperature, microbes used, hydraulic retention time (HRT), substrate type and its concentration, and bioreactor design and its material play a key role in the efficiency of H\({}_{2}\) production using dark fermentation. This article aims to provide data on biological H\({}_{2}\) production via dark fermentation using different microbial strains under varying environmental conditions to compare and devise optimal conditions and microbes that can be used for efficient production.