Journal of Energy Bioscience 2025, Vol.16, No.3, 117-127 http://bioscipublisher.com/index.php/jeb 122 6.3 Co-products and value-added streams In the process of making ethanol, many by-products are produced. For example, distiller's grains, distiller's grains liquid fertilizer, sorghum powder, sorghum bran, pellet fuel, etc. (Cai et al., 2013; Wirawan et al., 2024). These things are not waste and can continue to be used. They can be used as animal feed, organic fertilizer, or used to generate electricity. Some can also enter the food or biomaterial market. Using these by-products can not only share part of the production costs, but also help reduce greenhouse gas emissions and improve resource utilization efficiency (Cai et al., 2013; van Rijn et al., 2018; Wirawan et al., 2024). Returning distiller's grains to the fields can reduce the use of chemical fertilizers and make the soil healthier, which is a practice that is conducive to recycling (Cai et al., 2013). 7 Policy, Market, and Adoption Barriers 7.1 Current policy landscape: renewable fuel standards, subsidies Some current policies, such as the Renewable Fuel Standard (RFS), set high targets for cellulosic ethanol. However, the actual situation is far from expectations. For example, in the United States, cellulosic fuel production in 2017 only achieved 5% of the original target (Cui et al., 2018). There are many reasons. One is that farmers are unsure about growing high-yield crops that require many years of cultivation (such as sorghum), and they are worried that the investment is too high and it is not cost-effective. Another problem is that policies and markets change frequently, and people dare not invest money to build those large new ethanol plants. Policy requirements for greenhouse gas emission reduction have also affected the opportunity for sorghum ethanol to enter the market. A simulation study found that the emission reduction effect of sorghum ethanol is similar to that of corn. If sorghum yields are not high enough, it will be difficult to meet the emission reduction standards set by RFS for cellulosic fuels (Kent et al., 2020). 7.2 Market dynamics: price volatility, feedstock competition Whether sorghum ethanol can make money depends largely on its price competitiveness with gasoline. Some technical and economic analyses point out that if the price of enzymes can be reduced or byproducts such as lignin can be effectively utilized, then the minimum selling price of sorghum ethanol may be close to the energy equivalent price of gasoline (van Rijn et al., 2018). Otherwise, it will need to rely on policy subsidies or wait for oil prices to rise. Another big problem is the supply chain of raw materials. Raw materials such as sorghum are seasonal, not easy to store, and the transportation cost is not low. All these limit the expansion of the sorghum ethanol market (Jiang et al., 2024). Taking China as an example, if the output of raw materials decreases or the demand for ethanol suddenly increases, the cost and carbon emissions of the entire supply chain will increase. However, some pressure can be alleviated through more reasonable factory layout and the use of railway transportation. 7.3 Adoption challenges for farmers and industry Farmers still have many concerns when growing new energy crops such as sorghum. Many people are reluctant to try new crops because they are worried about unstable yields, unfamiliarity with technology, and high risks. Moreover, they are used to the original planting methods and are not sure whether the sorghum market is stable or not, and whether the price is reliable (Cui et al., 2018). On the other hand, it takes a lot of money to build or transform a biorefinery. In addition, the market and policies change frequently, so companies are reluctant to invest rashly (Cui et al., 2018; van Rijn et al., 2018). From the perspective of the supply chain, how to collect, deliver and process the raw materials at the right time while controlling costs is also a big problem (Jiang et al., 2024) (Figure 2). Although sorghum can be grown on marginal land and will not compete with grain for land, if this industry is to really take off, it still needs policy encouragement, the improvement of market mechanisms, and the continuous advancement of technology (Batog et al., 2020; Jiang et al., 2024).
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