Potential of Agricultural Wastes
Agricultural industry waste is the byproduct of industries which use agricultural products as raw materials. The major crops that produce large quantities of wastes on a global scale are rice, corn, barley, oat, wheat, sorghum, and sugarcane. The potential of producing ethanol from the crop residues as well as wasted agricultural products have been estimated. To avoid conflicts between human food use and industrial use of crops, only the wasted crop, which is defined as crop lost in distribution, is considered as feedstock. There are about 74 Terra grams (Tg) of dry wasted crops in the world that could potentially produce 49 GL year-1 of bioethanol. Lignocellulosic biomass forms such as crop residues and sugarcane bagasse are the main components of agricultural waste, and about 1549 Tg year-1 of dry lignocellulosic biomass from these global crops is also available for conversion to bioethanol with a potential of producing up to 442 GL year-1 of cellulosic bioethanol. Thus, the total potential bioethanol production from crop residues and wasted crops is 491 GL year-1 [1].
Chemical composition of lignocellulosic feedstocks is a key factor affecting efficiency of biofuel production during the complex conversion process. The structural and chemical composition of lignocellulosic feedstocks is a highly variable factor, because of genetic and environmental influences and their interactions. Low lignin, globally abundant crop residues like rice and wheat straws are excellent biomass resources for the aqueous-phase cellulose hydrolysis-fermentation route. A comparison of major components: cellulose, hemicellulose, lignin and ash in major crop residues are shown in Table 3.1.
Dale and Kim [1] have studied the global potential in crop residues as well as agricultural wastes for bioethanol production, and the totals (Terra grams [Tg]) of seven major crops: corn, barley, oat, rice, wheat, sorghum, and sugarcane in five continents are shown in Table 3.2.
The U. S. National Renewable Energy Laboratory (NREL) has estimated that 288-447 L of ethanol can be produced from a dry
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Table 3.1 A comparison of cellulose, hemicellulose, lignin and ash in major crop residues that can be used in cellulosic ethanol production (wt% on dry basis).
|
|
Africa |
Asia |
Europe |
America |
Oceania |
Subtotal |
|
|
Wasted crop (Tg) |
||||||
|
Corn |
3.12 |
9.82 |
1.57 |
6.17 |
0.01 |
20.70 |
|
Barley |
0.17 |
1.23 |
2.01 |
2.04 |
0.19 |
3.66 |
|
Oat |
0.004 |
0.06 |
0.43 |
0.06 |
0.001 |
0.55 |
|
Rice |
1.08 |
21.8 |
60.02 |
2.45 |
0.02 |
25.44 |
|
Wheat |
0.83 |
10.28 |
4.09 |
1.17 |
0.82 |
17.20 |
|
Sorghum |
2.27 |
0.54 |
0.004 |
0.31 |
0.001 |
3.12 |
|
Sugarcane |
0.46 |
1.64 |
0.00 |
1.10 |
0.00 |
3.20 |
|
Subtotal |
7.94 |
45.43 |
8.13 |
11.31 |
1.05 |
73.86 |
|
Table 3.2 Total quantities of wasted crops and agricultural wastes in different continents, that are potentially available for bioethanol production [1]. |
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48 Handbook of Cellulosic Ethanol |
tonne of corn stover [14]. The ethanol yields from other forms of agricultural wastes can be calculated by using composition data of these materials and an "ethanol yield calculator" developed by the U. S. Department of Energy [15]. Even though the ethanol production efficiency depends on the form of biomass, in many of these calculations they have assumed that the ethanol production efficiency of other crop residues is also similar to that of corn stover [1]. Potential for bioethanol production from crop waste and crop residues around the globe by different continents is shown in Table 3.3.