# Production of Cellulosic Ethanol from Enzymatically Hydrolysed Wheat Straws
## 1 Introduction
All these parameters contribute significantly to the conversion of saccharides during hydrolysis. [PERSON] et al. (2010) reported in their study that mechanical pretreatment (chopping and grinding) contributes significantly to the improvement of enzymatic hydrolysis of WS. It was established that, after 24 h of hydrolysis, the content of glucose and xylose was increased by 39% and 20% respectively when the particle size was reduced from 2-4 cm to 53-149 \(\upmu\)m [8]. However, the very small particles is a disadvantage because it leads to a high energy consumption in the milling phase. On the other hand, the additional elimination of lignin contributes significantly to the decrease of energy consumption [20]. The acid pretreatment leads to the formation of inhibitory compounds at a low value of pH, high temperature and pressure. The degradation of lignin and hemicellulose produces free organic acids (acetic, formic and levulinic acid) or phenolic derivatives (4-hydroxybenzoic acid or vanillin), and 2-furaldehyde (furfural-FF) with 5-hydroxymethyl-2-furaldehyde (hydroxymethylfurfural-HMF) which affect negatively the chemical composition, enzymatic hydrolysis and fermentation. The FF and HMF are obtained from the transformation of pentoses (xylose and arabinose) and hexoses (glucose, mannose and galactose) [21]. Acid pretreatment is a significant phase for obtaining bioethanol which destroys the crystalline structures of cellulose and increases the accessibility of the enzyme during enzymatic hydrolysis [22; 23]. [PERSON] et al. (2017) studied the impact of acid pretreatment on WS, using 2% and 4% of H\({}_{2}\)SO\({}_{4}\). This pretreatment led to the elimination of high amount of hemicellulose [24]. The acid pretreatment is most suitable for WS, but also has some disadvantages, such as acid pollution of the environment and feed, and production of secondary compounds [25; 26; 27]. [PERSON] et al. (2018) established that pretreatment with 2% diluted H\({}_{2}\)SO\({}_{4}\) improved the rate of lignin removal from WS [27]. [PERSON] et al. (2018) reported that pretreatment with 0.5% H\({}_{2}\)SO\({}_{4}\) was more effective in obtaining a higher amount of glucose (4.84 g/L) for 10 min at 200 \({}^{\circ}\)C compared to 4.09 g/L glucose obtained by using 2% H\({}_{3}\)PO\({}_{4}\)[28]. During pretreatment, HMF can be converted to formic and levulinic acid, while FF to formic acid [19]. The structure of hemicellulose is composed of acetylated sugars which can turn into acetic acid during pretreatment. Also, during lignin pretreatment, significant amount of phenolic and aromatic compounds was achieved [29]. These compounds limit the transformation of sugars into bioethanol which reduce the final yield of this alcohol. Enzymatic hydrolysis is the most efficient method of releasing carbohydrates from lignocellulosic materials. Thus, the hydrolysis of cellulose is catalysed by a class of enzymes, called cellulases. This type of hydrolysis is influenced by the lignocellulosic substrate, enzyme activity and process conditions [8]. By hydrolysis, high concentrations of acetic and formic acids were detected, with values between 4.9-9.4 g/L and 1.6-10.3 g/L, respectively, and levulinic acid of 0.3-0.6 g/L. Acetic acid, furfural and HMF are the products that result from hydrolysis and has inhibitory effects on the fermentation process [30]. The aim of this paper is to obtain bioethanol as a result of the superior recovery of wheat straw. A number of objectives have also been set for monitoring the whole process, such as the pretreatment, enzymatic hydrolysis and fermentation steps. To find out which is the most indicated option for pretreatment of wheat straws and its effect on the hydrolysis step, a diluted concentration of 1, 2 and 3% (_v/v_) H\({}_{2}\)SO\({}_{4}\) was used.