Center for Environmental Research and Technology and Chemical and Environmental Engineering Department, University of California, Riverside, CA 92507, USA.
Bioresour Technol. 2010 Jul;101(13):4862-74. doi: 10.1016/j.biortech.2009.11.009. Epub 2009 Dec 14.
Ethanol made biologically from a variety of cellulosic biomass sources such as agricultural and forestry residues, grasses, and fast growing wood is widely recognized as a unique sustainable liquid transportation fuel with powerful economic, environmental, and strategic attributes, but production costs must be competitive for these benefits to be realized. Continuous hydrolysis and fermentation processes offer important potential advantages in reducing costs, but little has been done on continuous processing of cellulosic biomass to ethanol. As shown in this review, some continuous fermentations are now employed for commercial ethanol production from cane sugar and corn to take advantage of higher volumetric productivity, reduced labor costs, and reduced vessel down time for cleaning and filling. On the other hand, these systems are more susceptible to microbial contamination and require more sophisticated operations. Despite the latter challenges, continuous processes could be even more important to reducing the costs of overcoming the recalcitrance of cellulosic biomass, the primary obstacle to low cost fuels, through improving the effectiveness of utilizing expensive enzymes. In addition, continuous processing could be very beneficial in adapting fermentative organisms to the wide range of inhibitors generated during biomass pretreatment or its acid catalyzed hydrolysis. If sugar generation rates can be increased, the high cell densities in a continuous system could enable higher productivities and yields than in batch fermentations.
由各种纤维素生物质来源（如农业和林业残余物、草类和速生木材）生物合成的乙醇，被广泛认为是一种独特的可持续液体运输燃料，具有强大的经济、环境和战略属性，但为了实现这些好处，生产成本必须具有竞争力。连续水解和发酵工艺在降低成本方面具有重要的潜在优势，但在将纤维素生物质连续加工成乙醇方面做得很少。正如本综述所示，一些连续发酵现在已被用于从甘蔗和玉米中商业生产乙醇，以利用更高的容积生产率、降低劳动力成本以及减少用于清洁和填充的容器停机时间。另一方面，这些系统更容易受到微生物污染，需要更复杂的操作。尽管存在这些挑战，但连续工艺对于降低克服纤维素生物质的顽固性的成本可能更为重要，纤维素生物质的顽固性是低成本燃料的主要障碍，通过提高昂贵酶的利用效率来克服这一障碍。此外，连续处理对于使发酵生物适应生物质预处理或其酸催化水解过程中产生的广泛抑制剂可能非常有益。如果可以提高糖的生成速率，那么连续系统中的高细胞密度可以实现比批式发酵更高的生产率和产率。
