Journal of Energy Bioscience 2024, Vol.15, No.4, 221-232 http://bioscipublisher.com/index.php/jeb 222 2 Types and Sources of Agricultural Waste 2.1 Classification of agricultural waste Agricultural waste can be broadly classified into three main categories: crop residues, animal manure, and agro-industrial byproducts. Crop residues include materials such as straw, unmarketable or culled fruits and vegetables, post-harvest or post-processing wastes, clippings, and residuals from forestry or pruning operations (Medina et al., 2015). Animal manure, another significant category, is produced in large quantities from livestock farming and can be utilized for biogas production and as a soil amendment (Schievano et al., 2009; Ardebili, 2020). Agro-industrial byproducts encompass a variety of materials such as sugar beet pulp, starch and confectionary industry by-products, oil cereal industry by-products, and grain and legume by-products (Seidavi et al., 2021). 2.2 Quantitative data on agricultural waste generation The generation of agricultural waste is substantial. For instance, in Iran, the total amount of agricultural waste is assessed to be 24.3 million tonnes, which can be used to produce significant quantities of biogas, bio-butanol, and bio-hydrogen (Ardebili, 2020). In the United States, the utilization of all available agricultural and forestry residues, animal manure, and municipal solid waste can generate between 3.1 to 3.8 exajoules (EJ) of renewable energy annually (Liu and Rajagopal, 2019). This highlights the vast potential of agricultural waste as a resource for energy production. 2.3 Regional variations in agricultural waste types and quantities The types and quantities of agricultural waste vary significantly by region. For example, in Italy, swine manure is a common substrate used in biogas plants due to the prevalence of pig farming (Schievano et al., 2009). In contrast, in Iran, the primary agricultural wastes include residues from crops such as wheat, rice, barley, maize, and industrial crops like sugar cane and sugar beet (Ardebili, 2020). These regional differences are influenced by the types of crops grown, the scale of livestock farming, and the specific agro-industrial activities prevalent in each area. Understanding these variations is crucial for developing region-specific strategies for the effective utilization of agricultural waste. 3 Biomass Energy Production from Agricultural Waste 3.1 Technologies for biomass energy production 3.1.1 Anaerobic digestion Anaerobic digestion (AD) is a well-established technology for converting organic waste into biogas, which primarily consists of methane and carbon dioxide. This process not only reduces greenhouse gas emissions but also produces a valuable digestate that can be used as a fertilizer. Recent advancements in AD technology have focused on optimizing parameters, pretreatments, and co-digestion strategies to enhance biogas yield and process efficiency (Zhang et al., 2019; Atelge et al., 2020). For instance, the integration of AD with gasification has shown promise in improving the economic viability and energy recovery from agricultural waste (Antoniou et al., 2019). 3.1.2 Combustion Direct combustion is one of the simplest methods for converting biomass into energy. This process involves burning biomass in the presence of oxygen to produce heat, which can be used for power generation or industrial processes. In Colombia, the potential for using agricultural and livestock waste for direct combustion has been explored, showing significant potential to replace traditional fossil fuels and reduce environmental impacts (Gutiérrez et al., 2020). However, the efficiency of combustion systems can be improved by optimizing the design of combustors to enhance oxidative characteristics and increase the yield of high-quality steam (Sarkar and Praveen, 2017). 3.1.3 Gasification Gasification involves the partial oxidation of biomass to produce syngas, a mixture of carbon monoxide, hydrogen, and methane. This syngas can be used for electricity generation, as a fuel for internal combustion engines, or as a feedstock for chemical synthesis. Studies have shown that gasification of agricultural waste can achieve high
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