Journal of Energy Bioscience 2025, Vol.16, No.3, 117-127 http://bioscipublisher.com/index.php/jeb 118 2 Overview of Sorghum as a Biomass Crop 2.1 Types of sorghum: grain sorghum vs. sweet sorghum vs. forage sorghum Sorghum (Sorghum bicolor) is a crop that can be used as biomass energy. It can be roughly divided into three types: grain sorghum, sweet sorghum and fodder sorghum. Grain sorghum is mainly used to produce food. The stems of sweet sorghum contain a lot of sugar, which is easily fermented into ethanol, so it is a good material for making bioethanol. Fodder sorghum has a high yield and is palatable. It is often used as feed. It can also be used to generate electricity or make other biomass energy (Prasad et al., 2007; Ekefre et al., 2017; Batog et al., 2020). Among these three types, sweet sorghum is widely used in the production of ethanol fuel because of its high sugar content and high yield (Prasad et al., 2007; Ekefre et al., 2017). 2.2 Agronomic advantages 2.2.1 Drought tolerance One of the most prominent advantages of sorghum is that it is very drought-resistant. It can grow well even in places where there is not much water. Especially in marginal or arid and semi-arid areas, it can survive better than many other crops (Prasad et al., 2007; Batog et al., 2020). Compared with corn and sugarcane, which require a lot of water, sorghum is a good alternative that saves a lot of water. 2.2.2 Low input requirements Growing sorghum does not require a lot of fertilizer or pesticides. It is efficient in using water and can adapt to relatively harsh growing environments (Prasad et al., 2007; Ekefre et al., 2017). This means that the cost of growing sorghum is relatively low and the pressure on the environment is also small (Prasad et al., 2007). 2.2.3 Versatile cultivation regions. Sorghum is highly adaptable. It can be grown in temperate, subtropical and even tropical areas. It can grow well and have good yields even in less fertile or saline soils (Prasad et al., 2007; Ekefre et al., 2017; Batog et al., 2020). Some studies have found that in temperate regions such as Central and Eastern Europe, sorghum can produce a lot of biomass and ethanol, whether as a main crop or a rotation crop (Batog et al., 2020). 2.3 Biomass yield potentials Sorghum has a considerable yield, especially some varieties, whose ethanol yield can be similar to or even higher than that of traditional energy crops such as sugarcane (Ekefre et al., 2017; Boboescu et al., 2019; Rivera-Burgos et al., 2019). The theoretical ethanol yield of the sweet sorghum variety Theis can reach 7 619 liters per hectare. Moreover, different sorghum varieties and different planting conditions will result in very different biomass and sugar content. This difference also provides room for breeding, which can be further improved to increase yield (Ekefre et al., 2017; Rivera-Burgos et al., 2019). The straw and field waste left after sorghum harvest can also be used to make cellulosic ethanol. These "leftovers" do not affect food production, but can be turned into treasures, which are very useful resources (Sathesh-Prabu and Murugesan, 2011; Boboescu et al., 2019; Rivera-Burgos et al., 2019). 3 Composition and Bioconversion Properties of Sorghum Biomass 3.1 Chemical composition: cellulose, hemicellulose, lignin content Sorghum biomass, including sweet sorghum stalks, residues and bran, contains three main components: cellulose, hemicellulose and lignin. For example, sweet sorghum residue contains about 29.34% lignin, 17.75% cellulose, and 16.28% hemicellulose (Mafa et al., 2020) (Figure 1). The cellulose content of sorghum bran is 11%, hemicellulose is 18%, and lignin is relatively less (Corredor et al., 2007). The composition of sorghum from different varieties and different parts will be slightly different. But in general, sorghum contains less cellulose and hemicellulose than corn stalks and sugarcane bagasse, while lignin is higher (Corredor et al., 2007; Mafa et al., 2020; Xu et al., 2020).
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