# Pretreatments Applied to Wheat Straw to Obtain Bioethanol
## 1 Introduction  
Energy from renewable sources is at the heart of the priorities of the European Green Deal. Directive (UE) 2018/2002, regarding the promotion of the use of energy from renewable sources [1], is a central element of the EU's energy policy and a key factor in achieving the renewable energy targets by 2030, when at least 32% of energy should be from renewable sources [1]. An important target set out in the Climate Action Plan under the European Green Deal [2] is to reduce greenhouse gas (GHG) emissions by 55% by 2030. To achieve this target, the EU has set a balanced path towards climate neutrality by 2050 through decarbonizing all sectors of the economy. In this sense, a transition from the current energy system to an integrated energy system based largely on renewable sources is necessary. As specified in the impact assessment related to the plan for achieving the climate objective, for the 55% reduction in greenhouse gases, the share of energy from renewable sources in 2030 will have to reach 38-40% [2]. According to the estimates of the European Environment Agency (EEA), in 2022 renewable energy represented 23.0% of energy consumed in the EU, up from 21.9% in 2021. In addition, the EU as a whole is above the slightly more ambitious trajectory defined by the Member States themselves in their National Renewable Energy Action Plans (NRAPs) [3]. In recent years there has been a continuous increase in the overall share of renewable energy sources (RES) at the EU level and the sectoral share of energy from renewable sources of electricity (E-SRE), heating and cooling, and (to a lesser extent) from transport (T-SRE). Overall, bioenergy continues to be the main renewable energy source in the EU. Solid biofuels account for 68.4%, the largest share of bioenergy. Of these solid biofuels, forestryaccounts for about 91%. The other forms of bioenergy consist of liquid biofuels (12.6%), biogas (11.6%), the renewable share of municipal waste (7.2%), and coal (2%) [4]. Globally, bioethanol production is mostly involved in elements of cereal manufacturing, such as corn and sugarcane. According to the data in Figure 1, the largest production of bioethanol was in the United States, followed by Brazil. The use of biofuels allows for a reduction in greenhouse gas emissions of up to 95% compared to fossil fuels. This target is in line with the United Nations' targets for reducing greenhouse gas emissions. Globally, the land surface occupied by agriculture is between 10 and 12% [6]. Worldwide, approximately 354 million tons of wheat straw are produced annually, which can represent raw material for energy sources, reducing the use of fossil fuels [6; 7; 8; 9]. Additionally, 40% of CO\({}_{2}\) emissions result from agriculture [10]. In the context of the circular bioeconomy, given the climate changes and the increase in pollution, environmentally friendly energy sources are sought, and so agricultural straws are of interest due to their valorization and transformation into bioethanol [9]. To reduce environmental pollution, renewable energy must be utilized using waste obtained from agricultural production. The ratio of lignin, hemicellulose, and cellulose in the content of wheat straw is 3:3:4 [11]. Wheat straw, due to its hemicellulose and cellulose content, is a raw material for the production of bioethanol, which is a clean fuel that can replace gasoline, reducing CO\({}_{2}\) emissions from car engines [6; 7]. Biofuels are liquid or gaseous fuels, such as biodiesel, bioethanol and biogas, which are made from plants [12; 13; 14; 15; 16; 17; 18]. Part of the wheat straw is used as animal feed, while the rest of the straw is burned in the field, increasing air pollution [19; 20; 21; 22]. Overall, 442 billion liters of bioethanol can be obtained from lignocellulosic biomasses, and 491 billion liters of bioethanol can be obtained annually from total crop residues [23]. The following processes are necessary: pretreatment, enzymatic hydrolysis and fermentation.