## 1 Introduction  
The environmental constraints of fossil fuels are accelerating the change from fossil energy resources to renewable and environmentally-friendly ones. Every year, the earth provides us with a considerable amount of organic waste products, which are even more complex than fossil fuels, presenting very high concentrations of carbohydrates. Most of these carbohydrates are polysaccharides, mainly based on glucose, fructose or xylose units. The advantages of these polysaccharides are their low cost and their large-scale availability. However, despite their large-scale availability and low cost, it must be said that nowadays the energy industry scarcely uses these polysaccharides [1]. As fossil fuel prices and environmental regulations begin to adversely affect traditional fossil fuel energy sources, the transition to an energy industry based on renewable energy sources is practically inevitable.  
One of the best ways to extract the energy contained in organic waste is through the application of acidogenic fermentation processes. In these processes, the substrates contained in the waste are able to be transformed into a gas stream that is rich in hydrogen, a promising energy vector due to characteristics including its energy yield and carbon neutral abilities [2], as well as carbon dioxide. Simultaneously, the liquid phase is rich in short-chain fatty acids (SCFAs), mainly acetate, butyrate and propionate at low pH and butanol, ethanol and isopropanol at high pH, all of which are very interesting substrates [3]. The acidogenic fermentation process can be carried out with mixed or pure cultures [4]. Mixed culture fermentations are characterized by their low operational costs due to the absence of sterilization processes. Additionally, due to the lack of sterilization stages, it is possible to implement continuous fermentative processes. On the other hand, pure culture fermentation processes require sterilization stages [5,6]. Because of this, pure culture fermentative processes consume significant amounts of energy and are not recommended for the treatment of waste because of the microbial contamination of the culture. These drawbacks impede the practical implementation of the acidogenic fermentation of wastes with pure cultures [7].  
In Spain one of the most representative agro-industries is the winery industry. Castilla-La Mancha is the region with the highest grape production, about 3.7 million tons in 2018, which represents about 55% of Spanish production. Like most industrial activities, wine production generates large volumes of wastewater, mainly due to washing and sanitizing operations [7]. In Spain, the overall wastewater production ranges from 0.7 to 3.8 m\({}^{3}\) per ton of grapes processed, a value within the ranges reported in the literature [8]. These effluents contain high concentrations of easily biodegradable pollutants, mainly carbohydrates, that could be converted into hydrogen by means of acidogenic fermentation processes [9,10]. Hydrogen is an environmentally-friendly energy vector presenting a high specific energy yield, 122 kJ g\({}^{-1}\), and significant advantages over fossil energy sources, such as its production using environmental sustainable bio-processes and the possibility of the conversion of renewable raw materials, including biowastes [11, 12, 13, 14].  
In this context, the aim of this work was to study the conversion of winery wastewater into energy. To achieve this, winery wastewater was characterized and its main components were identified. Subsequently, bio-hydrogen production from winery wastewater was studied and the potential bio-hydrogen production from winery wastewater was determined. Finally, the bio-hydrogen produced from winery wastewater was fed into a fuel cell stack of 150 cm\({}^{2}\), operated at 150 \({}^{\circ}\)C and the electric power generated was determined.