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Global biofuel production has increased significantly over the last decade, but firstgeneration biofuels have been identified as a major concern, especially their sustainability as they are produced from food crops (such as cereals, sugar cane and vegetable oils). Depending on the feedstocks and cultivation technique, the production of second and third generation biofuels has the potential to provide benefits, such as the recovery of residues and unusable land. Therefore, second and third generation biofuels are indicated to meet the increasing demand for energy and contribute considerably to the development of rural areas and the increasing of bioeconomy. This short review shows that there may be different types of feedstocks (agricultural residues, forest residues, energy crops and algae) which can be used for the production of 2nd and 3rd generation bioethanol without affecting food security. [ABSTRACT FROM AUTHOR]

In recent years, many countries have adopted a strategy to replace conventional fuels which are obtained from petroleum refining with biofuels. This has happened due to rising oil prices, unpredictable depletion of oil reserves, increased greenhouse gas emissions and the negative impact on the environment. Bioethanol production 1stG has caused competition between fuels and food, because the main raw materials used for are sugar and starch raw materials. The United States is the world's largest producer of bioethanol from corn, followed by Brazil which uses sugarcane. In the Europe Union, the main raw materials for bioethanol production are wheat and sugar beet. Therefore, the second generation energy (including bioethanol production 2ndG) obtained from lignocellulosic materials (LCM) is gradually attracting global attention. Lignocellulosic biomass (LCB) is the most abundant natural organic source, in huge quantities, at low costs and not part of the human food chain. [ABSTRACT FROM AUTHOR]

In the last decade, environmental protection is one of the major challenges. It is necessary to ensure the protection of the environment and the conservation of natural resources, in accordance with the requirements of a sustainable economic and social development. The most important impact of modern human activities is the release of large amounts of different compounds after burning of fossil fuels, which are responsible for increasing of greenhouse gases (GHG) concentrations in the atmosphere. The depletion of fossil fuels and necessity to increase energy reserves, especially for the propulsion of transport, contributed to search and use of alternative fuels. Partially or completely substitution of gasoline with bioethanol is an alternative method to reduce GHG emissions. Currently, biofuels (first generation) are produced from sources which are used to feed the population. The competition between food vs. biofuel could be solved if biofuels were obtained from renewable resources, such as lignocellulosic biomass (LCB). Second-generation biofuels are obtained from raw materials such as agricultural (straws, sugarcane bagasse, corn stalks and cobs) and forestry residues (sawdust, bark, branches, etc.) which do not interfere with global food production. In 2019, the main producers of bioethanol were USA, Brazil and EU which produced about 54%, 30% and 5% respectively of the worldwide bioethanol. This paper reviews the most important steps in bioethanol production are pretreatment, hydrolysis and fermentation of the mash. There are a lot of pretreatments, such as physical, chemical, physicochemical, biological and combined pretreatments. The combined pretreatments have been shown to be more effective compared to single pretreatments, and there is a wide range of combinations which can be applied in the future. Hydrolysis step contributes to the release of fermentable sugars, which are further converted by microorganisms into bioethanol. There are a lot of hidrolysis methods, such as Separated Hydrolysis and Fermentation (SHF), Simultaneous Saccharification and Fermentation (SSF), Simultaneous Saccharification and co-Fermentation (SSCF) and Consolidated Bioprocessing (CBP). The liquid fraction obtained after pretreatment and hydrolysis contain various predominant carbohydrates such as glucose and xylose. Therefore, special microorganisms are needed to perform co-fermentation. [ABSTRACT FROM AUTHOR]