**3. Bioenergy potentials**

These residues generally makeup at least 50% by mass of the biomass in US grown crops. Over time, these resources have been sourced for animal bedding, combusted, or allowed to decay on farmlands. The recent development for use of the biomass residues for ethanl production or electricity generation sequel to scientific discovery has raised hope for the resource for both economical and environmental benefits. Significantly, the US agriculture can probably support up to 155 million tons of residues for producing bioenergy in 2030 [8]. Without the need of additional land requirement since these residues is by-product of major crops [16]. Residues are known to offer a lot of advantages ranging from erosion prevention and mitigation against soil carbon depletion, their use for soil bioenergy production may adversely impact on these benefits, therefore, their utilization should be subject to certain circumstances, and even then, only at a predetermined magnitude. The amount of residues that can be collected is subjective and depends on several conditions relative to the farmland, this should be considered sustainably as removal of too much resdiues may cause exposure of the land to excessive erosion while too less or no removal of the residues can inadvertently prevent soils

Removal of residues for bioenergy potential and application can impact negatively on other agricultural practices. The environment could be worsen as a result of excessive exposure of the farmland. In order to minimize the effect of this, farmers can employ various strategies to curb the effect. For instance they can use no-till farming and indulge in cover cropping to decrease soil erosion and water pollution. This will enhance agricultural production sufficiency while also provide abundantly the amount of residues for bioenergy biofuel pro-

In corn-growing regions, large quantities of corn stover—leaves and stalks left over after corn is harvested—are available to produce ethanol. Corn residues are abundant near existing facilities fitted to produce and distribute ethanol made from corn grain. Indeed, companies are building the first three commercial-scale efforts to produce ethanol from agricultural residues near such existing facilities in Iowa and Kansas. Producing ethanol from corn grain and corn stover at the same location can reduce the use of natural gas and electricity by the

Livestock raised in very large confined animal feeding operations generate an enormous amount of manure, which can be used for bioenergy, but also frequently pollute water supplies in many locations. Fortunately, on the smaller end of the livestock production scale, farmers convert manure into biogas with the aid of anaerobic digesters resulting in both economic and environmental paybacks. The biogas can be employed to provide heat and power on the farm, or it can be further purified and sold as renewable natural gas for use elsewhere. Prospect of anaerobic digesters for biogas production from manure can enhance water quality, reduce obnoxious greenhouse gas from manure, and assist farmers to fixate nutrients to the soil. In the United States, reports show that almost 60 million tons of manure can be

combined facility, curbing the environmental footprint of the fuel [18].

from drying in spring, thereby affect the planting season.

duction [17].

74 Agricultural Waste and Residues

**2.2. Waste from livestock**

adopted to produce bioenergy in 2030 [8].

In accordance to the report of World Health Organization (WHO), United Nations Development Program (UNDP), 1.5 billion people, implying an estimated one-quarter of the world's population, do not have access to electricity [23]. In order to meet the UNDP millenium development goals, modern energy service need be supply to about two billion people. Lack of accessible and uninterrupted electricity supply and liquid transportation fuels undermines undeveloped and developing countries deleteriously, where population density is high and access to resources is low. About 2 billion people require on solid fuels (**Figure 1**), which are employed primarily for cooking and heating purposes. This development of combusting biomass environmental pollution and health issues. In the long run, the effect incurs health costs, where the main victims are the woman and children, due to the burning of solid fuels in poorly ventilated housing [23–25].

Contrarily, developed nations sourced for bioenergy to combact the menace of environmental pollution due to CO2 emission and possibly reduce it and provide domestic energy [26]. Energy crops with potential to generate high-yielding lignocellulosic biomass have been studied by [27]. Exploration of the special energy crops in developing countries may possibly displace food crops resulting in food-energy fued [28–30]. Food security, as well as energy provision from these crops, can be ensured when the degraded farmlands are used to grow crops after the deforestation, which can result in CO2 emissions as a result of excessive land use [31]. Hence, opportunities abound from dual cropping process, which can enhance agricultural productivity by generating bioenergy from agricultural waste while food production is ensured.

The prospect of biomass feedstock for synthesis of biofuel and as starting materials for industrial processes cannot be overemphasized, following this development; experts forecast the potential of agricultural residues in augmenting the energy need globally in the near future thereby accounting for a significant part of international agricultural transactions in the nest few decades. However, the cost of petroleum product is usually the yardstick for evaluating the economic viability of bioenergy, although social ane environmental concerns are possible

Typically, biomass composition is usually considered from three major components namely, cellulose, hemicellulose, and lignin (**Table 1**). The process of biochemical transformation processes of biomass is aimed at the disruption of the hemicellulose part in order to enable easy reachability to the cellulose, however, there is no alteration done to the lignin component [21]. Nevertheless, the lignin fraction can be converted to important fuel using a thermochemical conversion mean. Anaerobic digestion and fermentation are the two biochemical methods

Anaerobic digestion is an important conversion method appropriate for bioenergy synthesis from agricultural residues and some other organic products [40]. It has been researched

**Crop Residues Residue Composition (Dry weight basis)**

0.26

Rice Straw, husk, stalk 0.36 0.24 0.16 Maize Cob, husk, stalk, stover 0.35 0.23 0.19 Soybean Husk, stalk 0.40 0.16 0.16 Groundnut Husk 0.30 0.30 0.40

Tobacco Stalk, leaf 0.36 0.34 0.12 Sunflower Stalk, head 0.48 0.35 0.17 Almond Shell 0.51 0.29 0.20 Wheat Pods, stalk 0.38 0.27 0.18 Sugar cane Baggasse, top and leaves 0.44 0.32 0.24 Cotton lint and cotton seed Boll, shell, husk, stalks 0.80 0.20 — Grasses Straw 0.40 0.50 0.10 Barley Straw 0.46 0.23 0.16

Cellulose Hemicellulose Lignin

Significance of Agricultural Residues in Sustainable Biofuel Development

http://dx.doi.org/10.5772/intechopen.78374

77

0.53 0.43

0.16 0.30

factors that can possibly fast track the schedule [39].

where biomass is converted into a valuable substance (**Table 2**).

Hazelnut Husk shell 0.30

**Table 1.** Some crop residue and their lignocellulosic composition [71, 72].

**3.1. Biomass conversion processes**

*3.1.1. Biochemical conversion process*

**Figure 1.** Primary energy supply of biomass resources globally in 2013 (WBA Global Bioenergy Statistics 2016). Source: Based on data from World Bioenergy Association (2016).

Albeit the enormous advantages of using agricultural residues as a waste stream [32], Kim and Dale opined that clearing the farm of some types of agricultural residues may result in some serious environmental concerns [26]. For instance, recurrent continual harvesting of total above ground biomass from annual cereal crops can ultimately reduce soil organic matter, causing long-term degradation of soil fertility, and rapidly promoting CO2 emissions [33]. However, an example of removing partial residues has been demonstrated for rice (*Oryza sativa*) grain husks in India, which are gasified in small-scale ecofriendly units to produce electricity for users spending approximately \$2 a month for energy [34]. Such a model for renewable energy could serve globally as an inexpensive decentralized energy mechanism.

In exploring parallel circumstances, environmental factors such as temperature, rainfall, and altitude affect the production of crop from different locations. Thus, identification of source feedstocks suitable for dual-use cropping and that are available in regions with energy scarcity is imperative. In this regard, an existing dual-use feedstock that is underused is endocarp tissues from horticultural fruit crops. For instance, the endocarp of a drupe fruit is the inedible shaft of the fruit that encloses the seed, and which is mostly thrown out after processing. The hardened drupe endocarp is made up of predominantly lignin content of any woody feedstock which can be as high as 50% wt/wt [35, 36].

In biofuel synthesis, lignin offers much higher energy content compared to cellulosic biomass [37, 38]. In practice these crops are majorly horticultural crops. The geographical distribution of selected crops and their individual potential for bioenergy synthesis was studied by Mendua et al. [35] The considered crops include coconut (*Cocos nucifera*), mango (*Mangifera indica*), olive (*Olea europaea*), walnut (*Juglans* spp.), pistachio (*Pistacia vera*), cherry (*Prunus cerasus*, *P. avium*), peach (*P. persica*), plum (*P. domestica*, *P. salicina*), apricot (*P. armeniaca*), and almond (*P. dulcis*). The focus of the study was to determine the relationship between diversity of endocarp and the proliferation of energy insufficiency by investigating the potential of endocarp biomass for energy [39].

The prospect of biomass feedstock for synthesis of biofuel and as starting materials for industrial processes cannot be overemphasized, following this development; experts forecast the potential of agricultural residues in augmenting the energy need globally in the near future thereby accounting for a significant part of international agricultural transactions in the nest few decades. However, the cost of petroleum product is usually the yardstick for evaluating the economic viability of bioenergy, although social ane environmental concerns are possible factors that can possibly fast track the schedule [39].

#### **3.1. Biomass conversion processes**

### *3.1.1. Biochemical conversion process*

Albeit the enormous advantages of using agricultural residues as a waste stream [32], Kim and Dale opined that clearing the farm of some types of agricultural residues may result in some serious environmental concerns [26]. For instance, recurrent continual harvesting of total above ground biomass from annual cereal crops can ultimately reduce soil organic mat-

**Figure 1.** Primary energy supply of biomass resources globally in 2013 (WBA Global Bioenergy Statistics 2016). Source:

However, an example of removing partial residues has been demonstrated for rice (*Oryza sativa*) grain husks in India, which are gasified in small-scale ecofriendly units to produce electricity for users spending approximately \$2 a month for energy [34]. Such a model for renewable energy could serve globally as an inexpensive decentralized energy mechanism.

In exploring parallel circumstances, environmental factors such as temperature, rainfall, and altitude affect the production of crop from different locations. Thus, identification of source feedstocks suitable for dual-use cropping and that are available in regions with energy scarcity is imperative. In this regard, an existing dual-use feedstock that is underused is endocarp tissues from horticultural fruit crops. For instance, the endocarp of a drupe fruit is the inedible shaft of the fruit that encloses the seed, and which is mostly thrown out after processing. The hardened drupe endocarp is made up of predominantly lignin content of any woody

In biofuel synthesis, lignin offers much higher energy content compared to cellulosic biomass [37, 38]. In practice these crops are majorly horticultural crops. The geographical distribution of selected crops and their individual potential for bioenergy synthesis was studied by Mendua et al. [35] The considered crops include coconut (*Cocos nucifera*), mango (*Mangifera indica*), olive (*Olea europaea*), walnut (*Juglans* spp.), pistachio (*Pistacia vera*), cherry (*Prunus cerasus*, *P. avium*), peach (*P. persica*), plum (*P. domestica*, *P. salicina*), apricot (*P. armeniaca*), and almond (*P. dulcis*). The focus of the study was to determine the relationship between diversity of endocarp and the proliferation of energy insufficiency by investigating the potential of

emissions [33].

ter, causing long-term degradation of soil fertility, and rapidly promoting CO2

feedstock which can be as high as 50% wt/wt [35, 36].

Based on data from World Bioenergy Association (2016).

76 Agricultural Waste and Residues

endocarp biomass for energy [39].

Typically, biomass composition is usually considered from three major components namely, cellulose, hemicellulose, and lignin (**Table 1**). The process of biochemical transformation processes of biomass is aimed at the disruption of the hemicellulose part in order to enable easy reachability to the cellulose, however, there is no alteration done to the lignin component [21]. Nevertheless, the lignin fraction can be converted to important fuel using a thermochemical conversion mean. Anaerobic digestion and fermentation are the two biochemical methods where biomass is converted into a valuable substance (**Table 2**).

Anaerobic digestion is an important conversion method appropriate for bioenergy synthesis from agricultural residues and some other organic products [40]. It has been researched


**Table 1.** Some crop residue and their lignocellulosic composition [71, 72].


Transesterification reaction is used to synthesize biodiesel by employing the ethanol along with large branched triglycerides into smaller straight-chain molecules usually in the presence of a catalyst [40]. The biodiesel produced is used in diesel engines either pure or in blend with fossil diesel. In spite of the success recorded in various part of the world, biodiesel production in commercial scale is still at evolving stage in Africa [40, 45] despite the myriad

Significance of Agricultural Residues in Sustainable Biofuel Development

http://dx.doi.org/10.5772/intechopen.78374

79

Various other methods of thermochemical conversion processes for biomass conversion abounds, which are carried out at supercritical temperature and pressure and are usually at higher reaction condition compared to biochemical processes [46]. This process has been employed to generate a number of important bio-based products. These methods include

An important method for biomass conversion via thermochemical route is direct combustion methods is employed to produce the major bioenergy resource of the world accounting well above 97% of world bioenergy index [43]. It is the most common way of extracting energy from biomass. Direct combustion methods produce energy only in the form of heat and electric power as such it is not employed for biofuel production [47] and it considered several feedstocks such as energy crops, agriculture residues, forest residues, industrial and other

Another production process is pyrolysis, which is an important biomass conversion method that heralds the combustion or gasification of solid fuels. It comprises of thermal degradation of biomass feedstock at temperatures of about 350–550°C, under pressure, in air tight compartment [21]. This approach affords three fractions: liquid fraction (bio-oil), solid (largely ash), and gaseous fractions. Pyrolysis has been useful over time in charcoal production, however, it is only been recently considered due to the mild temperature and short residence time [49]. The product generated from the fast pyrolysis technic is known to be made up of more than two-third of the feedstock in liquid content and is suitable for use in engines, machinery and myriads of other applications [49]. An integrated approach where fast-pyrolysis can be co-processed with fossil fuel in conventional refinery is the current trends in research in which refined hydrogen can be utilized for blend to upgrade the oil into locomotive fuels and, in turn, some gases of pyrolysis are employed in the refinery [42, 50]. The feasibility of this approach is a measure of the comparable cost of natural gas, biomass feedstock, and incremental capital costs. Co-processing of petroleum with renewable agricultural residues

Subject to sustainable practices and advocacy as well as the availability of feedstock, the utilization of biomass feedstock in biofuel and bioenergy production promise to be prominent approach and the generated biofuel products are known to be comparative in characteristic feature with petroleum products. The first large-scale plant facility employing fast pyrolysis and bio-crude refining method in the United States amounting to about \$215 million projects

offers advantages from both technological and economic considerations.

is the KiOR Inc. plant situated in Columbus, Mississippi [50].

direct combustion, pyrolysis, gasification and hydrothermal liquefaction (**Table 2**).

of feedstock available and the potential of this important biofuel.

*3.1.2. Thermochemical conversion processes*

wastes [48].

**Table 2.** Primary biomass conversion process and processed biomolecules [21].

extensively in the production of bioenergy for both domestic and industrial applications [41]. The process involves the utilization of microorganism for conversion of moist organic substance in an anaerobic environment to generate CO2 , biogas and some other impurities such as hydrogen sulfide [21]. Along the product a waste stream digestate is generated which are usually utilized as manure of the farmland. The generated biogas is characterized with highenergy content of one-third of the lower heating magnitude of the feedstock from which it is produced [42]. In the quest for renewable energy production in the form of biogas, this method has been studied succinctly. Moreover, there is inherent advantage of carbon capture for CO2 mitigation [39, 41]. Among the various biomass resources that has been investigated, algae stand prominent as an agricultural residue producing significant amount of biogas in many locations of the world [39].

Besides, another vital approach of biomass conversion is an enzymatic controlled anaerobic process [43], which is employed in the synthesis of bioethanol from lignocellulosic biomass. In this process, the first action is the pretreatment of the raw biomass and subsequent hydrolysis prior to fermentation process. The cellulosic component of the biomass is transformed into glucose via enzymatic hydrolysis converts the cellulose component of the biomass into glucose while the hemicellulose part affords pentose and hexoses. Microorganism then converts the glucose into ethanol. This is affected by the action of biological catalysts to turn fermentable sugars to important chemicals (usually alcohols or organic acids). The most essential product of fermentation has been ethanol; however, there are some other useful substances such as hydrogen, methanol, and succinic acid that are generated. The major fermentation substrates are hexoses, which are mostly glucose, while modified fermentation organisms are used to convert pentose, glycerol, and other hydrocarbons to ethanol [44].

Furthermore, fermentation process is a conventional and extensively considered method in the treatment of waste streams, as well as for ethanol synthesis from agricultural residues, such as corn cobs and sugar beets [43]. Using fermentation sugars in sugarcane as feedstock, Brazil established a successful bioethanol plant. In 2011, about 5.57 billion gallons of ethanol is generated as fuel from this program, an equivalent of about 24.9% of the world's total ethanol utilization in form of fuel [21].

Transesterification reaction is used to synthesize biodiesel by employing the ethanol along with large branched triglycerides into smaller straight-chain molecules usually in the presence of a catalyst [40]. The biodiesel produced is used in diesel engines either pure or in blend with fossil diesel. In spite of the success recorded in various part of the world, biodiesel production in commercial scale is still at evolving stage in Africa [40, 45] despite the myriad of feedstock available and the potential of this important biofuel.
