Lignocellulose costs

If organisms could be found or metabolically engineered that efficiently ferment both the pentoses and hexoses under practical conditions at high yields and short residence times, fermentation ethanol technology would then have reached another plateau with low-cost lignocellulosic feedstocks. Simultaneous saccharification and fermentation or separate saccharification and fermentation of essentially all the sugars that make up the polysaccharides would each be able to approach the theoretical limit of fermentation ethanol production from the polysaccharides in low-cost lignocellulosic biomass. 

Above aU, feedstock prices influence production cost. In the context of using low-cost lignocellulosic biomass as substrate source, direct cost for raw feedstock is lower, but more energy is needed for the pretreatment, and additional costs arise through consumption of cellulases that are expensive for the production of bulk commodities like fuel. On the other hand, such costs do not arise in starch-based feedstock since clostridia are amylolytic and do not require additional enzymes (Xue et al. 2013a). Research is made on understanding the mechanisms of sugar... 

Fig. 2.13 Feed and processing cost of transportation fuels derived from lignocellulose and fossil resources.

Fig. 2.14 Manufacturing cost of bio-crude, bio-fuels and bio-power from lignocellulose (400 MW or 680 kt a-1, 2005).

Figure 2.13 did not include all the biomass conversion processes discussed above. It only considered those that produce transportation fuels. The processes that convert bio-feedstock into biocrude or electricity could not be included because their products have a different value than the transportation fuels. Such a comparison can be attempted by displaying the total manufacturing cost of biobased products in a graph that shows typical relationships between the price of crude and that its derivatives, i.e., of fuel oil, transportation fuel and electricity. This has been done in Fig. 2.14 for the lignocellulose conversion processes. 

Bioconversion platforms for lignocellulosics-to-ethanol are beginning to become commercially viable, but the effectiveness of the pretreatment stage should still be improved, the cost of the enzymatic hydrolysis stage decreased, and overall process efficiencies improved by better synergies between various process stages. There is also a need to improve process economics by creating co-products that can add revenue to the process. 

Lignocellulosic perennial crops (e.g., short-rotation coppices and grasses) are a promising feedstock becanse of high yields, low costs, good snitability for low-quality land (which is more easily available for energy crops), and the low environmental impacts. 

Lignocelluloses are freely available in the environment as residues from crop plants and trees and there has been a great effort in recent years to develop effective and economic processes for their utilization. However, outside the mushroom industry, few cost-effective options have been identified. This led Wood (1) and Lynch (2) to echo the comments of Thaysen and Bunker... 

Lignocellulosic biomass is a valuable and plentiful feedstock commodity and its high cellulose and hemicellulose content (about 80% of total) provides considerable potential for inexpensive sugars production. However, enzymatic deconstruction of these polysaccharides remains a costly prospect. Strides in cellulase cost reduction have been made, yet further improvements are needed to reach the goal of 0.10/gal of EtOH expected to enable this new industry. Strategies to reach this goal will combine reduction in the cost to produce the needed enzymes as well as efforts to increase enzyme efficiency (specific activity). As this work proceeds, the more easily attained achievements will be made first, and thus the overall difficulty increases with time. 

Industrialbiobased products have enormous potential in the chemical and material industries. The diversity of biomass feedstocks (sugars, oils, protein, lignocellulosics), combined with the numerous biochemical and thermochemical conversion technologies, can provide a wealth of products that can be used in many applications. Targeted markets include the polymer, lubricant, solvent, adhesive, herbicide, and pharmaceutical markets. Industrial bioproducts have already penetrated some of these markets, but improved technologies promise new products that can compete with fossil-based products in both cost and performance. 

Lignocellulosic, often termed cellulosic, biomass is the most abundant renewable resource on Earth, and large-scale production of organic fuels and chemicals from this low-cost sustainable resource would provide unparalleled environmental, economical, and strategic benefits (2-5). 

The first step will be to separate the seed from the straw (collection will obviously occur simultaneously, to minimise energy use and labour cost). The seeds may then be processed to produce starch and a wide variety of products, including ethanol and bioplastics (e.g. polylactic acid). The straw can be processed to products via various conversion processes, as described above for a lignocellulosic feedstock biorefinery. 

Thorsell, S., F.M. Epplin, R.L. Huhnke and C.M. Taliaferro, Economics of a Coordinated Biorefinery Feedstock Harvest System lignocellulosic Biomass Harvest Cost, Biomass and Bioenergy, 27, 327-337 (2004). 

---