Analytical Methods for Optimizing Feedstock Performance for Bio- Digester: A

Lagos 13,000 Organic, Plastics ∼70 Overcrowded dumpsites, informal settlements Gani et al. (2013); Ezeah and Roberts (2014) Port Harcourt ∼6000 Organic, Plastics, Paper ∼50 Flood-prone areas, inadequate bin supply Emeka et al. (2021); Ogbonna et al. (2007) Kano ∼5500 Organic, Agricultural ∼60 Open dumping, weak enforcement Maiha and Yusuf (2025); Ogwueleka (2009) Ilorin (peri- urban) ∼1200 Mixed (Organic, Plastic) ∼30 Informal dumping, open burning Shittu et al. (2024); Adebayo et al. (2024) Maiduguri ∼2000 Organic, Recyclables ∼40 Insecurity, reliance on informal sector Kodiya et al. (2023); UNEP (2018) Rural Areas (avg.) <500 Organic, Agricultural <20 No infrastructure, river/bush dumping Aderinoye- Abdulwahab et al. (2022); Orhorhoro and Oghoghorie (2019) Source: Omokaro et al., (2026). Biogas Production Biogas plays a crucial role in the global energy transition, particularly as the demand increases to shift electricity generation from fossil fuel–based systems to low-carbon and renewable energy sources. As countries strive to reduce greenhouse gas emissions and enhance energy sustainability, biogas offers a reliable and environmentally friendly alternative. It supports decentralized energy production while utilizing organic waste resources efficiently. Consequently, biogas contributes significantly to cleaner energy systems, improved waste management, and the advancement of sustainable power generation worldwide (Chidi et al., 2024). Biogas production technology is based on the biological process known as Anaerobic Digestion, where microorganisms break down organic matter in the absence of oxygen. Anaerobic Digestion (AD) is a complex biochemical process involving the breakdown of organic matter by microorganisms under oxygen-free conditions. According to Agbede et al., (2020) Anaerobic IJEMT Digestion is the biodegradation of organic materials by microorganisms in the absence of oxygen, involving four sequential main reactions throughout the process. The technology promotes the production of renewable green energy and supports a circular economy, fosters sustainable socioeconomic development, and simultaneously helps mitigate climate change (Kasinath et al., 2021). During this process, complex organic compounds such as carbohydrates, proteins, and lipids are decomposed into simpler compounds, ultimately forming biogas. The main components of biogas are: i. Methane (CH4) as the primary energy component of biogas, constituting about 50 – 75% of its composition. Methane is the component responsible for the fuel value of biogas (Plugge, 2017). ii. Carbon dioxide (CO2) typically constitutes about 25 – 50% of the composition of biogas (Plugge, 2017). iii. Biogas also contains small amounts of hydrogen sulfide, ammonia, and water vapour. The production of biogas or biomethane through anaerobic digestion is referred to as biomethanation or biomethanisation. The process consists of four major reaction stages: i. Hydrolysis ii. Acidogenesis iii. Acetogenesis iv. Methanogenesis Each stage involves specific microbial communities responsible for converting complex organic compounds into methane and carbon dioxide. These four reaction stages occur concurrently and are mutually interdependent (Kader et al., 2015). i. Hydrolysis Hydrolysis is the first stage of anaerobic digestion, where extracellular enzymes produced by microorganisms break down complex organic materials such as carbohydrates, proteins, and lipids into simpler, soluble monomers. For instance, polysaccharides are converted into sugars, while proteins are degraded into peptides and amino acids. These reactions are carried out by hydrolytic enzymes (hydrolases), which may be secreted into the medium or remain attached to microbial cells. This step is essential because most microorganisms involved in later stages of anaerobic digestion cannot directly utilize complex organic matter. By converting these materials into soluble forms, hydrolysis makes them accessible for further breakdown in subsequent stages. Hydrolysis is often the rate-limiting step in anaerobic digestion, especially when dealing with tough materials such as lignocellulosic biomass, as it determines how quickly the entire process can proceed. The hydrolysis of the waste fraction can be expressed by Equation (1). (C6H10O5)n + nH2O hydrolysis nC6H12O6 (1) The equation represents the hydrolysis of complex carbohydrates such as cellulose during anaerobic digestion, during the process, water is added to break the chemical bonds holding the polymer together. This step is crucial in biogas production because microorganisms cannot directly utilize complex polymers like cellulose. Hydrolysis transforms them into soluble sugars, which can then be further converted into volatile fatty acids, and eventually into methane during later stages of anaerobic digestion. ii. Acidogenesis Acidogenesis is the second phase of anaerobic digestion, occurring after hydrolysis. At this stage, simple soluble compounds generated during hydrolysis such as sugars, amino acids, and fatty acids IJEMT are further degraded by acidogenic (fermentative) microorganisms such as Streptococcus, Lactobacillus, and Clostridium species. During this process, these compounds are converted into various products, including volatile fatty acids like acetic, propionic, and butyric acids, along with alcohols, hydrogen (H2), carbon dioxide (CO2), and small quantities of ammonia (NH3) and other by-products (Sarker et al., 2019). This stage is essential as it converts hydrolysis products into intermediate compounds required for the subsequent stage. However, the accumulation of acids can lower the pH, making proper regulation necessary to ensure stable and efficient biogas production. A common equation used to represent the acidogenesis (fermentation) of glucose is: C6H12O6 → 2CH3CH2OH + 2CO2 (2) This equation shows that glucose (C6H12O6), produced during hydrolysis, is converted by acidogenic bacteria into ethanol (CH3CH2OH) and carbon dioxide (CO2). In acidogenesis, this reaction demonstrates the breakdown of simple sugars into intermediate products such as alcohols and gases. While ethanol is depicted in this example, acidogenesis generally generates a variety of compounds, including volatile fatty acids (e.g., acetic, propionic, and butyric acids), hydrogen, and carbon dioxide. These intermediates provide crucial substrates for the subsequent stages, acetogenesis and methanogenesis, ultimately leading to methane production. The accumulation of acids and other by-products also lowers the pH, which must be carefully managed to ensure an efficient and stable anaerobic digestion process. iii. Acetogenesis Acetogenesis is the third stage of anaerobic digestion, occurring after acidogenesis. In this stage, acetogenic bacteria convert the intermediate products from acidogenesis mainly volatile fatty acids such as propionic and butyric acids, alcohols, and some amino acids into simpler compounds, primarily acetic acid (CH3COOH), hydrogen (H2), and carbon dioxide (CO2). This stage is crucial because methanogenic archaea, responsible for methane production in the final stage, can only utilize acetic acid, hydrogen, and carbon dioxide as substrates. Acetogenesis therefore transforms the complex mixture of fermentation products into forms suitable for methane generation. Proper balance during this stage is essential, as excessive accumulation of volatile fatty acids can inhibit both acetogenic and methanogenic microbes, reducing the efficiency of biogas production. A general chemical equation for acetogenesis can be expressed as: C6H12O6 acidogenic intermediate 3CH3COOH+ 3H2 + 3CO2 (3) Propionate (CH3CH2COO−) is the substrate, an intermediate formed during acidogenesis. Water (H2O) is required to facilitate hydrolysis and oxidation reactions. Acetate (CH3COO−) is the main product, which serves as a substrate for methanogenesis. Bicarbonate (HCO3−) and H are produced to help maintain pH balance in the system. Hydrogen (H2) is released and later consumed by hydrogenotrophic methanogens for methane production. iv. Methanogenesis Methanogenesis is the final biological stage in the anaerobic digestion process, where methane (CH4) is produced by a group of specialized microorganisms called methanogenic archaea. It is a crucial step in converting organic waste into biogas, which can be used as renewable energy. Methanogenesis is a biological process that occurs under strictly anaerobic conditions, where methanogenic archaea convert intermediate products from acidogenesis and acetogenesis primarily acetate (CH3COO−), hydrogen (H2), and carbon dioxide (CO2) into methane (CH4) Kader et al., (2015). Methanogens use hydrogen to reduce carbon dioxide, producing methane: CO2 + 4H2→CH4 + 2H2OCO2 + 4H2 → CH4 + 2H2O + CO2 + 4H2 → CH4 + 2H2O (4) IJEMT Methane is generated through two primary pathways: i. Acetoclastic Methanogenesis: Acetoclastic methanogenesis is a type of methanogenesis in which specialized microbes, called acetoclastic methanogens, convert acetate (CH3COO−) into methane (CH4) and carbon dioxide (CO2). The chemical reaction is expressed as: CH3COOH → CH4 + CO2CH3COOH → CH4 + CO2CH3COOH → CH4 + CO2 (5) This pathway produces most methane by converting acetate into biogas, making it the dominant and most significant mechanism in anaerobic digestion systems. ii. Hydrogenotrophic Methanogenesis: Hydrogenotrophic methanogenesis is a pathway of methane production in which methanogenic archaea use hydrogen (H2) to reduce carbon dioxide (CO2) into methane (CH4). The chemical reaction is: CO2 + 4H2 → CH4 + 2H2O + CO2 + 4H2 → CH4 + 2H2O + CO2 + 4H2 → CH4 + 2H2O (6) Hydrogenotrophic methanogens use hydrogen as an electron donor and carbon dioxide as an electron acceptor. This pathway is important when acetate levels are low, as it allows microbes to still produce methane from other intermediates of anaerobic digestion. It often works in conjunction with acetoclastic methanogenesis, ensuring efficient methane production in biogas systems. Methodology The study employed a systematic literature review approach, examining published research articles, books, and technical reports focused on feedstock characterization and optimization in anaerobic digestion. Relevant literature for this study was sourced from major academic databases, including Scopus, Elsevier, ScienceDirect, and Google Scholar, to ensure comprehensive coverage of research on feedstock characterization and optimization in anaerobic digestion. The literature included in this review was selected based on specific criteria such as studies published within the last one decade, a focus on anaerobic digestion feedstock analysis, and the provision of experimental or analytical insights into feedstock optimization. Information from selected studies was analyzed to identify trends, analytical techniques, and optimization strategies used for improving feedstock performance. Feedstock used in Bio-Digesters The feedstock that can be utilized for anaerobic digestion includes agricultural wastes or residues, municipal solid wastes, industrial wastes and wastewater, and aquatic biomass. Various feedstock from these different sources have been widely investigated (Usman et al., 2021). The production of biogas from this feedstock largely depends on the physical and chemical composition of the substrate, which influences its biodegradability (Zamri et al., 2021). The recovery of biogas from waste is of critical interest, as it simultaneously supports alternative energy production and mitigates environmental impact by capturing methane and carbon dioxide, two major greenhouse gases (Biodun et al., 2021). Various organic materials can serve as feedstock in anaerobic digestion systems. Common feedstock includes: i. Animal Manure Animal manure, including cow, pig, goat or poultry waste, serves as a widely used source of biodegradable organic biomass, providing an effective feedstock for anaerobic digestion processes. Manure is categorized as either solid or liquid based on its dry solids content, IJEMT with this classification influencing its handling, storage, and suitability as a feedstock for various applications. Biogas is increasingly recognized as a vital fuel for electricity and heat generation. Ofon et al., (2024) evaluated biogas production from cow dung, goat excreta, and chicken droppings under raw, chemically pre-treated, and co-digested conditions. The biogas or biomethane potential of animal manure differs considerably due to various influencing factors, including animal species, bedding type and quantity, feeding regimes, breed, and growth stage. Differences in digestive activity and the composition of intestinal microbial communities also significantly affect biogas yield. In addition, the source of the manure, storage methods prior to anaerobic digestion, and overall farm management practices play important roles in determining the efficiency and productivity of biogas generation from animal manure (Nwokolo et al., 2020). ii. Agricultural Residues Agricultural residues are a widely available and economical feedstock for anaerobic digestion. They consist of organic materials remaining after farming and agro-processing activities, including crop residues such as straw, husks, stalks, and leaves, as well as animal manure and processing by- products like rice bran and cassava peels. These materials contain high levels of biodegradable organic matter, making them suitable for decomposition in oxygen-free environments. Through anaerobic digestion, microorganisms break down these complex compounds in stages hydrolysis, acidogenesis, acetogenesis, and methanogenesis ultimately producing biogas, primarily composed of methane (CH4) and carbon dioxide (CO2). A major benefit of agricultural residues is their abundance, particularly in agricultural regions. Their utilization helps reduce environmental issues such as open burning and improper waste disposal. In addition, the residual digestate serves as a valuable biofertilizer, improving soil quality and crop productivity. However, the effectiveness of these residues as feedstock depends on factors such as moisture content, carbon-to-nitrogen ratio, and lignocellulosic structure. Materials with high lignin content, like straw, may require pre-treatment to enhance their biodegradability and increase biogas yield. Agricultural residues present a sustainable and efficient option for renewable energy generation while supporting integrated waste management systems, as their valorization through anaerobic digestion provides an environmentally responsible alternative to fossil fuels and enhances waste utilization (Mkhize et al., 2023; Adeleke, 2023). iii. Food and Kitchen Waste Food and kitchen waste serve as excellent feedstock for anaerobic digestion because of their high organic content and ease of decomposition (Ayantokun et al., 2025; Salim et al., 2023). These wastes include leftovers, fruit and vegetable peels, cooked food remnants, expired items, and other biodegradable materials generated from households, eateries, and food processing operations. They are rich in carbohydrates, proteins, and fats, which are readily broken down by microorganisms under oxygen-free conditions. Through the stages of hydrolysis, acidogenesis, acetogenesis, and methanogenesis, these materials are efficiently converted into biogas, primarily methane (CH4) and carbon dioxide (CO2). Food and kitchen waste offer a reliable and sustainable resource for biogas production, owing to their low lignin content compared to many agricultural residues, food wastes decompose more quickly and typically produce higher biogas yields, while supporting effective waste management and environmental sustainability. A key advantage of food and kitchen waste is their steady availability, particularly in urban environments. Their use in anaerobic digestion helps reduce the amount of waste disposed of in landfills, thereby lowering greenhouse gas emissions, unpleasant odors, and leachate generation. IJEMT Furthermore, the resulting digestate can be utilized as a nutrient-rich organic fertilizer. However, certain challenges exist, including high moisture levels, rapid acid build-up, and possible imbalances in the carbon-to-nitrogen ratio. These issues can be managed through proper system control, co-digestion with other materials, and suitable pre-treatment techniques iv. Municipal Organic Waste Municipal organic waste consists of the biodegradable portion of waste generated in urban areas, including food scraps, garden trimmings, and paper from households, markets, and restaurants. It serves as an excellent feedstock for anaerobic digestion because it is rich in organic matter, moisture, and nutrients, which promote microbial activity. Within an anaerobic digester, microorganisms decompose MOW in the absence of oxygen, producing biogas primarily methane and carbon dioxide and a nutrient-rich digestate that can be used as fertilizer. Its high biodegradability and relatively consistent composition make MOW an efficient and cost-effective substrate, supporting both renewable energy production and waste management (Meegoda et al., 2025). The main benefits of using municipal organic waste for anaerobic digestion include high biogas production due to its abundant organic content and the generation of nutrient-rich digestate that can enhance soil fertility and promote nutrient recycling (Ibrahim et al., 2025). The efficiency of biogas production largely depends on the physical and chemical characteristics of the feedstock, including moisture content, the carbon-to-nitrogen ratio, and its biodegradability. Also, the biodegradability and nutrient composition of these materials influence their suitability for biogas production. Table 2 indicates the composition of biogas from different types of feedstock in an anaerobic digester. Table 2: Composition of Biogas from Different Types of Feedstock Components (% vol) Household Waste Wastewater Sludge Agricultural Waste Food Industry Waste CH4 50 – 60 60 – 75 60 – 75 68 CO2 34 – 38 19 – 33 19 – 33 26 N2 0 – 5 0 – 1 0 – 1 Nil O2 0 – 1 0 – 0.5 0 – 0.5 Nil H2O 6 (400C) 6 (400C) 6 (400C) 6 (400C) Total 100 100 100 100 Source: Arowanti et al., (2023) Factors Affecting Feedstock Performance The performance of feedstock in an anaerobic digester, and consequently the efficiency of biogas production, depends on several interrelated factors. Optimizing these factors maximizes methane yield and ensures stable operation, they are: • Physical Characteristics The physical characteristics that affects feedstock performance in anaerobic digester are: i. Particle Size: Reducing feedstock particle size increases surface area, facilitating better microbial contact and faster hydrolysis. Pre-treatments such as chopping, grinding, or milling can improve substrate accessibility, accelerate digestion, and enhance overall biogas production efficiency IJEMT ii. Moisture Content: Proper moisture levels are essential for active microbial metabolism in anaerobic digestion. Insufficient moisture slows microbial activity and digestion, whereas excessive water dilutes nutrients, reducing efficiency. Maintaining balanced moisture ensures optimal microbial function and maximizes biogas production • Chemical Composition of the Feedstock The chemical composition that affects feedstock performance in anaerobic digester are: i. Organic Matter Content: Feedstock high in carbohydrates, proteins, and lipids generally generate more biogas. While lipids produce the most methane per unit mass, excessive amounts can inhibit digestion, reducing efficiency. Balancing the composition ensures optimal microbial activity and maximizes biogas yield. ii. Carbon-to-Nitrogen (C/N) Ratio: The ideal C/N ratio for anaerobic digestion is 20:1 to 30:1. Ratios below this range (excess nitrogen) can lead to ammonia inhibition, whereas higher ratios (insufficient nitrogen) may slow microbial activity (Osei-Owusu et al., 2023). Maintaining a balanced C/N ratio supports efficient digestion and stable biogas production • Biodegradability Biodegradability is the ease with which feedstock is broken down by microbes directly influences biogas yield efficiency, they are: i. Lignocellulosic Content: Feedstock with high lignin levels, such as straw or wood, are resistant to microbial degradation, limiting biogas production. Pre-treatments like mechanical, chemical, or thermal processing can break down lignin structures, improving digestibility, accelerating hydrolysis, and enhancing overall methane yield in anaerobic digestion systems. ii. Soluble and Insoluble Components: Readily degradable compounds, such as sugars and starches, promote faster biogas production, whereas complex, insoluble materials decompose more slowly and often need extended retention times. Balancing these components in the feedstock ensures steady digestion, optimizes microbial activity, and maximizes overall methane yield. • Presence of Inhibitors Sometimes feedstock may contain substances harmful to anaerobic microbes, including heavy metals, antibiotics, pesticides, high salt levels, or tannins. These compounds can inhibit microbial activity, slow digestion, or even halt biogas production entirely. Identifying and managing such inhibitory components is essential to maintain efficient methane generation and stable digester performance. • Temperature and pH Sensitivity Feedstock behaviour varies under mesophilic (30 – 40°C) and thermophilic (50 – 60°C) conditions. Extreme pH values below 6.5 or above 8.0 can inhibit methanogenic microbes, slowing digestion and lowering biogas production. Maintaining optimal temperature and pH ensures efficient microbial activity and maximizes methane yield. In a study conducted in Nigeria, researchers found that maintaining mesophilic temperature around 33–36 °C and pH between 6.5 and 7.2 significantly improved methane production during anaerobic digestion of substrates like cow dung and pig waste, demonstrating the importance of optimal temperature and pH for stable biogas output (Humphrey et al., 2025). IJEMT • Feeding Rate and Composition Sudden changes in feedstock type or quantity can disrupt the microbial community, reducing biogas production. Gradual adaptation allows microbes to adjust, maintaining stable digestion. Co- digestion, involving the mixing of complementary feedstock, helps balance nutrients, enhances substrate digestibility, and promotes consistent, efficient methane generation in anaerobic digesters (Mkhize et al., 2023). • Storage and Age Storing feedstock before digestion can cause partial decomposition, nutrient depletion, or acid buildup, which may inhibit microbial activity. These changes reduce substrate quality and biogas potential. Proper storage practices, such as minimizing storage time and controlling temperature, are essential to preserve feedstock integrity and ensure efficient anaerobic digestion. Studies on anaerobic digestion have shown that prolonged storage or improper handling of organic feedstock can change their chemical composition, promote acidification, and affect subsequent biogas production, because biochemical changes occur before digestion begins, altering substrate quality and microbial access (Franco et al., 2016). Analytical Techniques for Feedstock Characterization Analytical techniques used to characterize feedstock in anaerobic digestion are important for evaluating substrate suitability, degradability, and potential for biogas production. These approaches examine the physical, chemical, and biological characteristics of the feedstock to ensure efficient digestion performance. i. Physical Analysis: This involves evaluating key physical properties that affect both feedstock handling and the efficiency of anaerobic digestion, including total solids (TS), which indicate the amount of dry matter present, and volatile solids (VS), which represent the biodegradable organic fraction. It also considers moisture content, which influences microbial activity and overall reactor performance, as well as particle size, where smaller particles improve microbial access and accelerate the digestion process. ii. Chemical Analysis: These tests determine the composition and nutrient balance of the feedstock such as the pH, Carbon-to-Nitrogen Ratio (C/N ratio), Carbon (C), Hydrogen (H), Nitrogen (N), Sulfur (S), Oxygen (O), and the Lignocellulosic content. iii. Biological Analysis: These methods assess the biodegradability of feedstock and its potential for methane production, including: Biochemical Methane Potential test, which estimates the maximum methane yield of a substrate. Specific Methanogenic Activity , which evaluates the performance and activity of methanogenic microorganisms. Respirometric tests, which measure overall microbial activity based on gas production or oxygen uptake. Spectroscopic and Advanced Techniques These techniques are employed for detailed compositional analysis of feedstock and digestion products, including Fourier Transform Infrared Spectroscopy , which identifies functional groups present in organic matter, Gas Chromatography (GC), which determines the composition of biogas such as methane and carbon dioxide, and High-Performance Liquid Chromatography , which is used to detect and quantify volatile fatty acids produced during the digestion process. IJEMT Proximate and Ultimate Analysis Proximate and ultimate analyses are essential techniques for evaluating feedstock quality and energy potential in anaerobic digestion. Proximate analysis determines components such as moisture content, ash, volatile matter, and fixed carbon, providing insight into the material’s composition and combustibility. In contrast, ultimate analysis identifies the elemental composition primarily carbon, hydrogen, oxygen, nitrogen, and sulfur which is critical for estimating the theoretical biogas and methane yield of the feedstock. Co-Digestion Strategies Co-digestion refers to the process of combining two or more types of feedstock in an anaerobic digester to achieve a more balanced nutrient profile and stimulate microbial activity. This approach helps optimize parameters such as the carbon-to-nitrogen ratio, reduces the risk of inhibition, and improves overall digestion efficiency. For instance, mixing animal manure, which is typically rich in nitrogen, with food waste, which is high in readily degradable organic matter, can significantly enhance methane production due to their complementary characteristics. Mathematical Modelling and Optimization Various modelling techniques are employed to optimize feedstock mixtures and anaerobic digestion conditions, including Response Surface Methodology , Artificial Neural Networks , kinetic modelling, and other machine learning algorithms. These approaches enable the prediction of digestion performance, analysis of process interactions, and identification of optimal feedstock combinations and operating parameters for improved biogas production efficiency. Anaerobic Digester Designs and Configurations Anaerobic digester designs and configurations refer to the structural and operational setups used to perform anaerobic digestion efficiently. These designs are adapted to the type of feedstock, scale of operation, and targeted biogas production. Variations in digester designs arise from factors such as climate, feedstock type and quantity, substrate fluid dynamics, structural strength requirements, availability and cost of construction materials, design complexity, and the intended retention time. Common configurations include Batch Digesters, where feedstock is processed in a single cycle; Continuous Stirred-Tank Reactors , which allow continuous feeding and mixing for steady biogas production. Plug-flow digesters, where substrate moves linearly through the reactor; and Covered Lagoon or pond digesters, suitable for dilute agricultural wastes. Each design affects mixing, temperature control, retention time, and overall biogas yield, making proper selection critical for optimal digestion performance (Ahmad, 2022). The three primary types of anaerobic digesters include covered lagoon digesters, plug-flow digesters, and completely mixed digesters. Covered Lagoon Digesters Anaerobic lagoons are covered ponds designed for liquid or dilute wastes with less than 2% solids, where feedstock enters at one end and residue is removed at the other. They have low reaction rates due to low temperatures, lack mixing which leads to solids settling and reduced bacterial contact, and require additional energy to remove coagulated solids. Figure 1 shows a typical example. IJEMT Plug-Flow Digesters The plug-flow digester is a long tubular tank installed vertically or horizontally. Feedstock enters through an inlet at one end, moves through the digester, and exits through an outlet pipes connected to a digestate extraction system. It is well-suited for high-solids feedstock such as cattle manure and often has few or no moving parts, reducing maintenance needs. Advantages include ease of use, adaptability to extreme conditions, simple installation, low cleaning costs, and overall low operational maintenance. An example is shown in Figure 2. Completely-Mixed Digesters In a completely mixed digester, all organic wastes are combined in a single tank and continuously mixed using agitators such as mechanical mixers or recirculation pumps, with mechanical mixers being the most energy-efficient. This system is suitable for manures with 3 – 10% solids and is a proven technology that efficiently converts solids into biogas. It is widely applied in industrial settings for effective waste-to-energy conversion, as shown in Figure 3. Figure 1: Covered Lagoon Digesters Figure 2: Plug-Flow Digester Source: Aworanti et al., (2023). Figure 3: Completely-Mixed Digester Source: Aworanti et al., (2023). Findings and Discussion Anaerobic Digester offers a dual advantage of providing a reliable source of clean energy in the form of biogas while simultaneously addressing pressing waste management challenges. By IJEMT converting biodegradable waste into useful energy and nutrient-rich digestate, Anaerobic Digester supports environmental protection, reduces greenhouse gas emissions, and contributes to sustainable development. The State of Biogas Development in Nigeria Nigeria’s experience with biogas development reflects a striking disconnect between early ambition and present reality. During the 1970s and 1980s, thousands of biogas plants were installed across the country, largely driven by experimental energy programs and rural development initiatives. However, the majority of these systems eventually failed or became inactive due to poor maintenance practices, lack of technical expertise, and absence of institutional support (Akinbomi, 2014; Okoro et al., 2020). This historical decline has left Nigeria with only about 120 – 200 functional biogas plants today, indicating a significant loss of earlier investments and momentum (Okeke, 2024). As a result, biogas contributes less than 1% to the national energy mix in Nigeria, making its impact on overall energy supply almost negligible (Ibrahim et al., 2025). Where it is still used, application remains highly localized and small-scale, primarily limited to cooking in rural households and small farms. There is minimal integration into electricity generation, industrial processes, or national grid systems, further constraining its relevance in the broader energy sector. Despite this limited utilization, Nigeria possesses one of the highest biogas potentials in Africa due to its abundant organic waste resources, including agricultural residues, animal manure, and municipal solid waste (Ajaero & Anorue, 2023). This creates a paradox in which vast renewable energy potential coexists with extremely low adoption. The situation underscores the need for a more coordinated and sustainable approach to biogas development. Strengthening policy frameworks, improving technical capacity, and promoting awareness could help revive the sector and transform biogas into a viable component of Nigeria’s energy future. Distribution of Feedstock in Biogas Production Figures 4 illustrates the distribution of biogas feedstock, showing a strong dominance of animal manure, which accounts for 47.9% of the total share. This indicates that livestock waste is the primary resource for biogas production, likely due to its high availability and favorable methane yield. Crop residues contribute 15.5%, making them the second-largest source, reflecting the role of agricultural by-products such as straw and husks. Abattoir waste represents 11.1%, highlighting the importance of slaughterhouse waste as a rich organic substrate. Goat manure contributes 10.5%, demonstrating its relevance in regions with significant goat farming activities. Sheep and poultry manure account for 6.5% and 6.3%, respectively, indicating moderate utilization levels. In contrast, pig manure contributes only 2.3%, making it the least utilized feedstock. The chart emphasizes a heavy reliance on animal-based wastes, with plant residues and industrial organic wastes playing supportive but important roles in biogas production systems (Ofon et al., 2024; Seglah et al., 2022). Also, the chart below shows the contribution of various feedstock to biogas potential in Nigeria (Figure 5). Animal manure leads significantly with nearly 48%, highlighting its central role in biogas production. Followed by crop residues having 15.5% and abattoir waste 11%. Goat manure 10.5%, sheep (6.3%), and poultry manure 6.3%, provide moderate input, while pig manure has 2.3% contributing the least (Ngumah et al. (2013). Animal-based wastes dominate biogas feedstock utilization, with plant and industrial residues playing secondary roles. IJEMT Figure 4: Biogas Feedstock Distribution Figure 5: Feedstock Utilization in Nigeria. Biogas Yield Variations Biogas yield varies significantly depending on the type and composition of feedstock used in anaerobic digestion. Substrates such as food waste and municipal organic waste typically produce higher volumes of biogas because they are rich in easily degradable compounds like carbohydrates, proteins, and lipids, which are rapidly broken down by microorganisms (Sayara and Sanchez 2019). In contrast, lignocellulosic agricultural residues like crop stalks and straw tend to generate lower biogas yields due to their complex structure, particularly the presence of lignin, which resists microbial degradation. As a result, such materials often require pre-treatment methods such as mechanical, thermal, or chemical to enhance their digestibility. Feedstock with a higher proportion of readily biodegradable organic matter not only increases total biogas production but also accelerates the rate of gas generation, leading to more efficient anaerobic digestion processes (Obileke et al., 2025). Methane Yield Potential of Food Waste in Anaerobic Digestion Systems Food waste and related organic substrates are widely recognized for their high methane generation potential in anaerobic digestion systems due to their rich composition of readily biodegradable organic matter, particularly carbohydrates, proteins, and lipids. These components are easily hydrolyzed and metabolized by anaerobic microorganisms, resulting in enhanced biogas production efficiency. Empirical evidence supports this assertion; for instance, Sayara and Sanchez (2019) reported that co-digestion processes involving food waste significantly improve methane yield compared to mono-digestion, thereby demonstrating the strong biogas potential of such substrates. This high biodegradability not only accelerates microbial activity but also contributes to process stability and increased energy recovery. Feedstock Selection The findings highlight the pivotal role of feedstock quality and selection in determining the efficiency and overall success of anaerobic digestion systems. Nigeria possesses abundant organic waste resources, the absence of structured waste management practices and inadequate scientific evaluation of feedstock properties significantly constrain the performance of biogas production IJEMT systems. One of the facts from this study is that feedstock does not contribute uniformly to biogas generation. Readily biodegradable materials, such as food waste, yield higher and faster methane production due to their rich content of simple organic compounds that are easily metabolized by microorganisms (Ayantokun et al., 2025; Olatunji et al., 2025). In contrast, lignocellulosic materials, including crop residues, exhibit lower biodegradability because of their complex structural composition, thereby requiring pre-treatment to enhance their digestibility. This limitation explains why hydrolysis often serves as the rate-limiting stage in anaerobic digestion processes. Moreover, the study emphasizes that imbalances in feedstock composition can adversely affect digester stability. For instance, excessive nitrogen can result in ammonia inhibition, while a high carbon content may limit microbial growth and activity. These challenges underscore the importance of maintaining an optimal carbon-to-nitrogen (C/N) ratio, which can be effectively achieved through careful feedstock selection and the application of co-digestion strategies. Research findings revealed that food waste is widely regarded as the most efficient feedstock for anaerobic digestion due to its high content of readily biodegradable organic compounds, including carbohydrates, lipids, and proteins (Kleynhans et al., 2026). This composition enables rapid microbial degradation, resulting in very high methane yields, typically in the range of 400 – 600 m3 CH4 per ton of volatile solids. In addition to its high biogas potential, food waste supports faster digestion rates, making it particularly suitable for efficient energy recovery. However, when used as a sole substrate, it may lead to process instability through rapid acidification, which can inhibit methanogenic activity. Despite this limitation, food waste remains the most efficient single feedstock in terms of both biogas yield and digestion kinetics. Additionally, co-digestion is identified as a practical and cost-effective strategy for optimizing anaerobic digestion, especially in urban environments where diverse waste streams are readily available (Ayantokun et al., 2025). By integrating substrates with complementary characteristics, this approach promotes a more balanced nutrient profile, enhances microbial activity, minimizes the risk of inhibition, and ultimately improves the stability and efficiency of the digestion process. Decadal Trends in Biogas Adoption in Nigeria Between 2016 – 2026 Biogas usage in Nigeria over the past decade shows a gradual but uneven upward trend. Despite recorded 6.8 million m3/day accrued from animal waste, and 15 billion m3/year from crop residues the actual usage is far below potential (Godfrey, 2024). Between 2016 and 2019; adoption remained minimal, largely confined to pilot projects and academic research, with limited practical impact. From 2020 to 2022, awareness of renewable energy increased, leading to the introduction of small-scale digesters in rural households and farms, though progress was slowed by funding and technical challenges. From 2023 to 2026, rising fuel costs and environmental concerns significantly boosted interest and investment in biogas systems. Despite these improvements, overall utilization remains low compared to Nigeria’s vast resource potential, with persistent issues such as weak policy support, limited infrastructure, and insufficient technical expertise hindering large-scale adoption and sustainability nationwide. Table 3 shows indicator of biogas trends and adoption for the last decade in Nigeria. In the last decade, biogas utilization in Nigeria has evolved from small-scale experimental projects into a gradually developing renewable energy source. Although recent years, particularly after 2023 have recorded notable progress, the sector still lags behind its significant potential. Figures 6 and 7 shows adoption trends in Nigeria within the period under review. With improved policies, increased investment, and greater public awareness, biogas has the capacity to become a major contributor to Nigeria’s energy mix. IJEMT Table 3: Indicator of Biogas Trends and Adoption Between 2016 – 2026 in Nigeria Indicator 2016–2019 2020–2022 2023–2026 Adoption level Very low (pilot plants only) Low–moderate (small- scale systems) Moderate but growing Technology use Mostly experimental digesters Household & farm digesters increasing Expansion into commercial and industrial uses Government support Weak and inconsistent Slight policy interest Increased investment and awareness campaigns Public awareness Very low Improving gradually Significantly higher Private sector involvement Minimal Emerging Increasing investments Energy contribution Negligible Still minimal Growing but still small Fig 6: Adoption Trends in Nigeria Fig 7: Comparison in African Countries Between 2016 – 2026 Comparison of Biogas Adoption Between Nigeria and Selected African Countries Over the past decade, biogas adoption in Africa has shown significant variation between countries (Table 4). In Nigeria, despite enormous potential from agricultural and organic waste, utilization remains low, with only a few small-scale digesters in operation and weak policy support limiting growth. Kenya, by contrast, has emerged as a continental leader, with over 20,000 household digesters installed (Rasimphi et al., 2024). This development is driven by strong government programs, subsidies, and technical training that promote widespread rural adoption. South Africa focuses more on commercial and industrial-scale systems, with around 700 plants supporting electricity generation and agro-processing industries, aided by private sector investment. This comparison highlights the impact of structured policies, financial support, and targeted programs on the success of biogas initiatives. IJEMT The Figure 8 illustrated the disparity in biogas adoption among three African countries. Kenya leads with 85% of installations, reflecting extensive household-level deployment supported by strong government programs, subsidies, and technical training, particularly in rural areas. South Africa, with 10%, focuses on industrial and commercial-scale biogas plants, contributing to electricity generation and agro-processing, driven mainly by private sector investment. Nigeria, at only 5%, remains underdeveloped, with limited small-scale digesters and pilot projects. Despite enormous potential from agricultural and organic waste, weak policy implementation, insufficient