Large-scale Biogas Research Articles

A matheuristic applied to clustering rural properties and allocating plants for biogas generation

Establishing partnerships among agro-industrial properties and selecting ideal locations for biogas plants are crucial challenges in large-scale biogas production and can influence both operational efficiency and waste management. In this context, this research proposes a new matheuristic that addresses the problems of defining a group of properties and an optimal number of groups and identifies the best allocation to the biogas plant. The group properties were defined by hierarchical and K-means cluster algorithms. The best location for the biogas plant was determined by the proposed multiobjective mathematical model. The best cluster number was decided by two strategies: (1) one that selected the closest non-dominated solutions to the ideal solution (M1) and (2) one that favored the most environmentally friendly solution (M2). The matheuristic was tested using three real databases, which yielded strategic clusters with an average daily biogas production of 544.93 m³/day (M1 and M2) for DataBase 1, 1635,156.00 m³/day (M1) and 403,497.50 m³/day (M2) for DataBase 2, and 318,662.50 m³/day (M1) and 20,479.58 m³/day (M2) for DataBase 3. This research provides an opportunity to add value to agro-industrial properties by achieving energy security and developing new business networks.

Investigating the Energy Potential and Degradation Kinetics of Nine Organic Substrates: Promulgating Sustainability in Developing Economies

To standardize, systematize, and improve the efficiency of the evaluation of biodegradable materials for large-scale biogas projects to support clean and sustainable energy development in emerging economies from a sub-Saharan African perspective, this paper analyzes and fits the potential for methane production (biochemical methane potential, BMP) and degradation kinetics of materials based on the gas production and degradation dynamics obtained from methane potential experiments. The first-order, modified first-order, and Gompertz models are used for analysis and fitting. The Gompertz model shows higher accuracy in fitting the methane production potential curve of screened materials, and the fitted methane potential values are close to the experimental values. When using BMP1% (cumulative gas production reaching 1% of cumulative gas production per day) as a quantitative indicator for the methane production potential of materials, the cumulative methane production reaches over 85% of the cumulative methane production at the end of the experiment. The BMP test time is shortened by 26.98% to 72.06%. Among the screened materials, the methane production potential (calculated using BMP1%) of dry rice straw, maize leaves, fresh rice, soybean straw, maize stalks, chicken manure hydrolysate, chicken feathers, kitchen/food waste, and chicken offal are 234.14, 241.01, 253.34, 331.40, 305.80, 508.41, 510.10, 630.7, and 621.32 mL/g, respectively. The kinetic parameters show that among the nine materials, cellulose materials (except for maize stalks and soybean straw), chicken manure, and kitchen waste are easily degradable materials. In contrast, chicken feathers and offal are slowly degradable materials. The study posits that comparing standardized methane production potential and methane production kinetic parameters among materials improves the efficiency of screening materials and is critical for biogas projects.

From failure to fairness: A call for accountability within household biogas development

The purpose of this perspective piece is to advocate for a paradigm shift in biogas research, and argues for the need to centre accountability and justice in household biogas development research and discussion Drawing from biogas literature and the authors' own experiences in South Asia and Southern Africa, the perspective illustrates how a lack of accountability in biogas programmes has led to negative outcomes and harm to beneficiaries of top-down biogas programmes. The article emphasises the critical need for a research agenda that prioritises accountability and justice, particularly in the context of the increasing number of biogas installations driven by carbon credits and international aid. It proposes a dual approach: firstly, an in-depth analysis of the impacts of accountability deficits in biogas projects; and secondly, strategies for effectively embedding accountability into programme design. The perspective also advocates for incorporating restorative justice principles in domestic biogas research, starting from project initiation, to ensure there are plans for amending the harm caused should projects fail to achieve their intended outcomes. This approach is essential for holding governments and institutions accountable in large-scale biogas installation. The perspective concludes with a call for an overhaul of the aid and biogas sectors, highlighting the necessity for systemic solutions and a more profound engagement with the practical challenges of biogas implementation.

Carbon reduction trade-off between pretreatment and anaerobic digestion: A field study of an industrial-scale biogas plant

With the implementation of municipal solid waste source segregation, the enormous sorted biogenic waste has become an issue that needs to be seriously considered. Anaerobic digestion, which can produce biogas and extract floating oil for biodiesel production, is the most prevalent treatment in China for waste management and greenhouse gas (GHG) emissions reduction, in accordance with Sustainable Development Goal 13 of the United Nations. Herein, a large-scale biogas plant with a capacity of 1000 tonnes of biogenic waste (400 tonnes of restaurant biogenic waste and 600 tonnes of kitchen biogenic waste) per day was investigated onsite using material flow analysis, and the parts of the biogas plant were thoroughly analyzed, especially the pretreatment system for biogenic waste impurity removal and homogenization. The results indicated that the loss of the total biodegradable organic matter was 41.8% (w/w) of daily feedstock and the loss of biogas potential was 18.8% (v/v) of daily feedstock. Life cycle assessment revealed that the 100-year GHG emissions were −61.2 kgCO2-eq per tonne biogenic waste. According to the sensitivity analysis, pretreatment efficiency, including biodegradable organic matter recovery and floating oil extraction, considerably affected carbon reduction potential. However, when the pretreatment efficiency deteriorated, GHG benefits of waste source segregation and the subsequent biogenic waste anaerobic digestion would be reduced.

THE ROLE OF BACTERIAL AND ARCHAEA IN DETERMINING THE METABOLIC PATHWAY OF BIOGAS FERMENTATION AT LOW TEMPERATURES

The challenge in achieving large-scale biogas production still lies in the biogas fermentation process at low temperatures. Our goal was to delve into the metabolic pathway behind the formation of biogas at these lower temperatures, focusing on the dominant bacterial and archaeal communities. Employing a batch system with activated sludge inoculum at 10°C, we fermented cow manure at 12°C for 150 days. Through genetic sequencing and taxonomic analysis using OTUs from the 16S rDNA gene, we investigated bacterial and archaeal species. Correlation analysis between their abundance was conducted using Pearson correlation and t-tests via IBM SPSS Statistics. Our findings revealed a biogas production of around 0.74 L/day, with CH4 levels surpassing 0.45 L/g VS. Peak efficiency occurred between day 60 and 110, reaching its apex on day 90. Clostridium cellulovorans dominated, ranging from 13.9% to 27%, followed by Terrisporobacter petrolarius, around 16.2% to 23%. Specifically, the formation of biogas (CH4) predominantly occurred through the H2 pathway, led by significant hydrogenotrophic Archaea OTUs like Methanocorpusculum sinense (ranging from 4.95% to 37.10%) and Methanobrevibacter millerae (with relative abundances between 2.00% and 11.20%)

Results from the operation of an efficient and flexible large-scale biogas methanation system

This study reports a comprehensive analysis of the operation of a biogas methanation system with a total 240 kW SNG output.

Comparison of life cycle assessment of large-scale biogas projects with different raw materials in China

Comparison of life cycle assessment of large-scale biogas projects with different raw materials in China

A Case Study on Small- and Centralized Biogas Plants and Energy Production Capacities in South Gyeongsang Province

Objectives : The primary goals of this research were to assess the viability and practicality of small-scale village facilities as well as central commercial biogas plants. Additionally, the study aimed to create predictive models by exploring various codigestion scenarios.Methods : The study conducted a comprehensive analysis of available biomass and its maximum energy potential through anaerobic digestion in every city, county, and village within South Gyeongsang province. Five distinct codigestion scenarios were explored, encompassing assessments of processing capacity, energy production potential, and the necessary digester capacity for anaerobic digestion. At the village level, the scenarios comprised: C1, which involved sole digestion of manure; C2, codigestion of manure and food waste in a 7:3 ratio; C3, codigestion of pig slurry and slaughterhouse waste in a 9:1 ratio; C4, multiple codigestion with PS:FW:SW=6.5:2.8:0.8; and finally, C5, involving the addition of sewage and sewage sludge to the codigestion process of C4's biomass.Results and Discussion : The biomass generated in South Gyeongsang province was 9430 tons/day, with a methane production potential of 167 million cubic meters/year. This biomass had an energy production potential of 156,000 TOE/year and a potential electricity generation of 732.7 GW/year, based on the annual petroleum conversion ton. Codigestion (C5) enabled up to 720% more electricity generation compared to sole digestion of manure (C1). Mixing pig slurry and food waste in a 7:3 ratio resulted in approximately 18% more electricity production compared to the case where manure was mixed with slaughterhouse by-products in a 9:1 ratio.Conclusion : Biomass imbalance was significant in most regions, particularly due to high variations in food waste generation between regions. Obtaining alternative resources and integrating various biomass for anaerobic digestion, especially in rural areas, is crucial for achieving stable anaerobic digestion and high methane production. Regions with high biomass density are predicted to support large-scale biogas facilities following European standards, while 25 villages showed the potential for small-scale biogas facilities.

Sustainability of large-scale commercial biogas plants in Nepal

Interest in large-scale compressed biogas (CBG) and biogas for electricity generation is increasing due to these technologies’ potential for addressing dual energy and waste management challenges. However, sustainable operation of large-scale commercial biogas plants requires attention to numerous factors, including technical aspects (feedstock types, plant size, operational parameters, and biogas and fertilizer utilization strategies), costs (capital investment and operational), and affordability, as affected also by subsidies. This study conducts a case study of the sustainability of an existing operational large-scale biogas plant in Nepal, considering its operational condition, financial status, and environmental benefits under designed capacity and actual operating conditions. Design parameters related to biogas and digestate production, financial viability, and greenhouse gas (GHG) emission reduction potential were compared with the realized outcomes of the plant. Operational and financial data for the plant were obtained through visits to the plant supplemented by interviews of the plant manager. The analysis reveals that both the feedstock and digester efficiencies are much lower than the design expectations, by 55% and 62%, respectively. This has led to reductions in the production of biogas and biofertilizers by 72% and 90%, respectively. Moreover, while the internal rate of return (IRR) of the plant at design capacity was 23%, it is indeterminate for the actual operating condition, as the net present value is negative for all discount rates. The biogas plant does generate environmental benefits; the GHG emissions avoided are estimated to be around 274 tons of CO2 equivalent per year under the actual operating conditions. Given these results, it is clear that improving the operational performance of large-scale biogas plants in contexts such as this one should be a priority. Moreover, the findings can help policymakers, investors, and other stakeholders make better plans for future development of biogas facilities, insisting on more realistic and careful assessments of technical and financial viability.

The integrated production of hydrochar and methane from lignocellulosic fermentative residue coupling hydrothermal carbonization with anaerobic digestion

The popularization of large-scale biogas project makes the disposal of fermentative residue an urgent issue to be solved. Hydrothermal carbonization (HTC) technology is suitable for treating wet biomass to produce carbonaceous materials. In this study, the solid residue from the two-phase anaerobic digestion (AD) was hydrothermally converted in the range of 180–240 °C, and the hydrochar and aqueous components were characterized for subsequent utilization. The heating values of hydrochar were indicated to be increased by 14.2% and 16.6% at 210 °C and 240 °C as compared with feedstock, and also the specific surface areas were 34.8 m2/g and 27.1 m2/g with 17.4- and 13.3-fold enhancement, respectively. The migration of elements such as S, Cl, K to aqueous phase was beneficial for fuel application. The mesoporous pores were dominant in hydrochars with ample oxygenated functional groups. In addition, the wastewater involved organic acids, phenols, and nitrogen-containing compounds, etc. Evaluating the biodegradability by AD, it was found that when the initial concentration was ≤8 g COD/L, the maximum methane yields up to 275.9 mL CH4/g CODremoval and 277.6 mL CH4/g CODremoval were obtained. The enhanced toxicity/inhibition of representative pollutants on microorganisms was significant at higher organic loading, which could be indicated in the microbial structure and diversity. As a conclusion, the integrated production of hydrochar and methane will provide an extended route for further processing of lignocellulosic fermentative residue.

Pathways for the thermally optimal design and practice of anaerobic digestion in large-scale biogas plants: Heat transfer modeling and energy analysis

A flexible and configuration-dependent heat model framework is developed, validated, and used to perform in-depth energy analyses and to identify the optimal design and operating conditions in wet anaerobic digesters in stirred reactors with multi-membrane gasholders in modern biogas plants. This framework enables a detailed geometrical representation of the gasholder and digester at different scales, such that different gasholder designs from single- to multi-membrane systems with varying configurations can be studied and compared to increase thermal efficiency. The model operates in the dynamic regime and includes longwave infrared surface-to-surface heat exchanges. This includes the impact of dynamic environmental conditions (e.g., ambient air temperature, wind, rain, and solar radiation) on the thermal behavior of the unit. Throughout the parametric analyses, the influences of key operating and design parameters, as well as synergistic features such as the feasibility and efficiency of various waste heat recovery strategies, are investigated on the basis of the thermal performance of the digester. The analysis shows that, based on a 3,000-m3 double-membrane biogas plant with a raw biogas self-consumption of 7.4%, thermal autarky can be achieved using (i) a three-membrane gasholder (−2.1%), (ii) outgoing digestate heat recovery (−3.7%), and (iii) recovery of heat from biogas purification (−1.6%).

An ecological and economic approach to enhancing the agronomic quality of anaerobic digestate: Effects of adding agricultural Jiaosu on metabolism and the microbial community

Anaerobic digestate disposal is challenging, hampering the development of large-scale biogas projects. Currently, digestate is primarily stabilized naturally and subsequently applied to farmland. However, during this process, the number of beneficial microorganisms decreases, free ammonia nitrogen increases, and pH rises, decreasing the benefits of digestate to soil and plants. In this study, digestate was treated by adding agricultural Jiaosu (AJ). The agronomic quality of the digestate was explored by conducting a pot experiment. Subsequently, the mechanisms of the changes in digestate properties were investigated based on chemical and microbial parameters. The results showed that the digestate with a 10% AJ supplement significantly improved the plant characteristics such as plant height, fresh weight, and leaf area. Regarding chemical properties, the addition of 10% AJ decreased the total ammonia nitrogen and free ammonia nitrogen in the digestate to below the toxicity threshold. With respect to microorganisms, the addition of AJ improved the microbial diversity of the digestate and increased the relative abundances of Advenella, Trichococcus, and Comamonas spp., which are beneficial to both soil and plants. Moreover, AJ decreased the abundance of potentially threatening microorganisms such as Thiopseudomonas and Papillibacter spp. Collaborative analysis showed that the improvement in digestate agronomic quality was closely related to its effects on microorganisms. Based on these results, the present study suggests an approach to the post-treatment of anaerobic digestate that can improve its fertilizer value while reducing its phytotoxicity. Furthermore, this study provides a model for a more comprehensive evaluation of the agronomic quality of digestate.

Comprehensive Analysis and Greenhouse Gas Reduction Assessment of the First Large-Scale Biogas Generation Plant in West Africa

More than 500 million people will be added to Africa’s cities by 2040, marking the largest urbanization in history. However, nonrenewable fossil energy sources are inadequate to meet Africa’s energy needs, and their overexploitation leads to intensified global warming. Fortunately, Africa has a huge potential for biomass energy, which will be an important option for combating climate change and energy shortage. In this study, we present a typical large-scale biogas plant in Burkina Faso, West Africa (Ouagadougou Biogas Plant, OUA), which is the first large-scale biogas generation plant in West Africa. The primary objective of OUA is to treat human feces, and it serves as a demonstration plant for generating electricity for feed-in tariffs. The objectives of this study are to assess the greenhouse gas reduction capacity and economic, environmental, and social benefits of OUA and to analyze the opportunities and challenges of developing biogas projects in Africa. As a result, the net economic profit of the OUA biogas plant is approximately USD 305,000 per year, with an anticipated static payback period of 14.5 years. The OUA plant has the capacity to treat 140,000 tons of human feces and 3000 tons of seasonal mixed organic waste annually, effectively reducing greenhouse gas emissions by 5232.61 tCO2eq, improving the habitat, and providing over 30 local jobs. Finally, the development of biogas projects in Africa includes advantages such as suitable natural conditions, the need for social development, and domestic and international support, as well as challenges in terms of national policies, insufficient funding, technical maintenance, and social culture.

Anaerobic Digestion (AD) Based Waste Management in Nepal: Technologies and Implementation Modalities

Developing countries are still facing severe challenges for providing access to clean energy, managing waste and struggling to meet Sustainable Development Goals (SDG) targets. Anaerobic Digestion (AD) based waste management technologies have great potential for addressing these challenges. Public Private Partnerships (PPP) are the key government's policy and strategic directions for promoting biogas as a multi-beneficiary's product and services in Nepal. Nepal's biogas promotion PPP model and technologies in domestic biogas sector have been replicated in many African and Asian countries. AD based Gobar Gas Company (GGC 2047 model) and Continuously Stirred Tank Reactor (CSTR) based technologies have been promoted for domestic and large applications respectively in wider scale. Comprehensive review and analysis using technological and implementation progress results through government interventions revealed that with the potential of 1.1 million of domestic biogas 433,173 systems have been installed. Quantification of outcomes of AD based technologies revealed that in addition to the energy access to more than 1.8 million people, these significantly contributed for production of gas amounting 456,282 m3 and substituted equivalent 15,578 nos. of LPG cylinders and 2229.91 tons of fertilizer daily. Under Carbon Development Mechanism (CDM), Total 21.20 million USD have been earned as carbon revenue from this sector, which has played significant role for earning revenue from carbon financing. Similarly, Developing Carbon Program for Large Scale Biogas through ITMO (Internationally Transferred Mitigation Outcomes: a new carbon mechanism) is under way. Overall, biogas sector is contributing for country' s energy security and circular economy through replacement of fossil fuels and chemical fertilizers along with the waste management.

Economic and Technological Feasibility Analysis of Biogas Production from Biomass Wastes by Adding Hydro char and Hydrothermal Pre-treatment

Anaerobic digestion is an effective method of treating animal wastes and biomass wastes, reducing pollution by them and producing regenerative energy in the form of methane (methane gas). As renewable bioenergy resources, fish processing wastes, tofu residue and lignocellulose biomass (bamboo residue and rice straw) are identified as cheap and have a wide range of sources, so they can be used as an effective substrate for biogas production. When fish processing waste with additive Hydro char (200°C and 220°C), hydrothermal pretreated tofu residue (140°C) and lignocellulose biomass (rice straw: 160°C) are subjected to anaerobic co-digestion, biogas production can be increased. In addition, when liquid fraction from hydrothermal carbonization (200°C-280°C) and fish processing wastes are mixed in a certain ratio and used as raw materials for anaerobic digestion to carry out anaerobic co-digestion, optimal output of biogas can be produced. This paper aims at the technology of producing biogas and maximizing the production by anaerobic digestion of fish processing wastes and tofu residue with Hydro char obtained from bamboo residue at a certain temperature (200°C) according to hydrothermal carbonization, and making an economic and technological analysis of production process. Through a Break-even point analysis, producing biogas using hydrothermal Pre-treatment and adding Hydro char has more advantages than the without Pre-treatment method in both production volume and investment recovery duration. It was demonstrated that the comparison and evaluation of without Pre-treatment and adding Hydro char, hydrothermal Pre-treatment approach, the investment recovery duration could be reduced from 419 days to 256 days with the large-scale biogas plants of 1 000 m3 as a criterion.

Bi-level Energy Trading Model Incorporating Large-scale Biogas Plant and Demand Response Aggregator

Increasing intermittent renewable energy sources (RESs) intensifies the imbalance between demand and generation, entailing the diversification of the deployment of electrical energy storage systems (ESSs). A large-scale biogas plant (LBP) installed with heating devices and biogas energy storage (BES) usually exhibits a storage-like characteristic of accommodating an increasing penetration level of RES in rural areas, which is addressed in this paper. By utilizing the temperature-sensitive characteristic of anaerobic digestion that enables the LBP to exhibit a storage-like characteristic, this paper proposes a bi-level energy trading model incorporating LBP and demand response aggregator (DRA) simultaneously. In this model, social welfare is maximized at the upper level while the profit of DRA is maximized at the lower level. Compared with cases only with DRA, the results show that the proposed model with the LBP improves the on-site accommodation capacity of photovoltaic (PV) generation up to 6.3%, 18.1%, and 18.9% at 30%, 40%, and 50% PV penetration levels, respectively, with a better economic performance. This nonlinear bi-level problem is finally recast by a single-level mathematical program with equilibrium constraints (MPEC) using Karush-Kuhn-Tucker (KKT) conditions and solved by the Cplex solver. The effectiveness of the proposed model is validated using a 33-bus test system and a sensitivity analysis is provided for analyzing what parameter influences the accommodation capacity most.

Toward thermal autarky for large-scale biogas plants: Dynamic energy modeling for energy efficiency in anaerobic digesters with enhanced multimembrane gasholders

Biogas production via anaerobic digestion could approach thermal autarky (less biogas self-consumption and better energy efficiency) using enhanced solutions for thermal insulation based on new multimembrane gasholder configurations, loss avoidance, and heat recovery strategies. In this study, a predictive and configuration-dependent dynamics energy model is developed to daily and seasonally assess the thermal efficiency and heating requirements of industrial biogas plants involving wet digesters with upper multimembrane gasholders. The model is validated using experimental data from a full-scale biogas plant in operation over a one-year period.The energy model involves a set of dynamic energy balances defined for each compartment of the digester and gasholder. All possible heat sources and sinks (ambient air temperature, wind, rain, and solar radiation) and heat exchanges or losses via advection, convection, and conduction, as well as a complete representation of the infrared radiative networks between the surfaces of the digester, are included for each compartment depending on the operating and design parameters. These heat exchanges are subject to fluctuating environmental conditions (e.g., ambient air temperature, wind, rain, and solar radiation).The results indicate that triple-membrane gasholders with a third insulation membrane made of a suitable material and thickness, together with the involvement of heat recovery from the digestate advective heat, are capable of reducing the overall thermal losses by more than 95 % (e.g., −51 % of the gasholder cover loss and − 81 % of the advective digestate loss) and when the waste heat from biogas purification is also valorized, the biogas plant can become thermally self-sufficient.

Mineral residue accelerant-enhanced anaerobic digestion of cow manure: An evaluation system of comprehensive performance

Anaerobic digestion (AD) is an efficient technology for treating biowaste and generating biogas. A reasonable evaluation of AD performance is crucial to its development. Herein, a comprehensive evaluation system covering five dimensions (energy output, process stability, degradation efficiency, digestate fertility, and digestate safety) was established to assess AD performance. Each dimension in the evaluation system was assigned a specific indicator defined by a threshold or range. Additionally, the proposed evaluation system was applied to assess a case study of batch-mode mesophilic AD that employed three industrial waste residues as mineral accelerants (nickel‑iron slag, steel slag, and fly ash). The mineral accelerants enhanced the energy output (methane yield by 66.55 %–87.54 %) and the feedstock degradation (chemical oxygen demand removal ratio by 11.23 %–32.42 %). The digestates also retained promising safety (heavy metal contents of 190–1260 mg/kg) and fertility (total nutrient contents of 3.71 %–4.69 %). The evaluation system reasonably appraised the comprehensive performance of accelerant-enhanced AD systems with cow manure. This work provides a reliable methodology for evaluating and comparing the performance of different novel accelerants and can be applied to evaluate the comprehensive performance of large-scale biogas projects with cow manure.

Importance of Feedstock in a Small-Scale Agricultural Biogas Plant

Although no legal sustainability criteria have been formulated for electricity and heat production from biogas, the sustainability and profitability of large-scale biogas plants which use mainly energy crops is now questioned. Small (farm-size) biogas plants characterized by CHP electrical output in the range between 15 kWel and 99 kWel, operating on agricultural wastes and by-products, seem more suitable; however, the variety of feedstock may be crucial in the proper design and operation of such family biogas plants. This paper aims to present the problems that occurred in small agricultural biogas plants fed with sheep manure (SM), horse manure (HM), and grass-clover silage (GCS). This paper also focuses on analyzing the energy balance and carbon dioxide (CO2) emissions related to four technological solutions (Scenarios 1–4) based on various feedstocks, grinding and feeding systems, and wet/dry fermentation. The biogas plant was originally based on dry fermentation with an organic loading rate ~10.4 kgVS·m−3·d−1, a hydraulic retention time of 16 days, and temperature of 45 °C in the fermentation chamber. The material was shredded and mixed in a mixing device, then the mixture of manures and silage was introduced to the horizontal fermentation chamber through a system of screw feeders. The biogas and the digestate were collected in a reinforced concrete tank. The biogas was sent to the CHP unit of an installed electrical power of 37 kWel, used to produce electricity and recover the heat generated in this process. Scenario 1 is based on the design assumptions used for the biogas plant construction and start-up phase. Scenario 2 includes a new feeding and grinding system, in Scenario 3 the feedstock is limited to SM and HM and wet fermentation is introduced. In Scenario 4, a dry fermentation of SM, HM, and maize silage (MS) is assumed. Avoided CO2 emissions through electricity and heat production from biogas were the highest in the case of Scenarios 1 and 4 (262,764 kg CO2·y−1 and 240,992 kg CO2·y−1) due to high biogas production, and were the lowest in Scenario 3 (7,481,977 kg CO2·y−1) because of the low specific methane yield (SMY) of SM and HM. Nevertheless, in all scenarios, except Scenario 3, CO2 emissions from feedstock preparation and biogas plant operation are much lower than that which can be avoided by replacing the fossil fuel energy for the electricity and heat produced from biogas. Our observations show that a small agricultural biogas plant can be an effective energy source, and can contribute to reducing CO2 emissions only if the appropriate technological assumptions are adopted, and the entire installation is designed correctly.

Feasibility Analysis of Biogas Production by Using GIS and Multicriteria Decision Aid Methods in the Central African Republic

Organic waste-derived biogas production is an effective way to transform biowaste into renewable energy for the electricity supply in developed and developing countries. This study analyzes the feasibility of biogas production as a solution to waste management and electricity supply in Bangui, the capital city of the Central African Republic. The selection of the biogas plant site in an urban area is a complex process due to the area availability and different factors. The GIS, combined with the MCDA, could analyze the environmental, social, and economic factors and criteria such as slope, settlement, rivers, land, urban growth, and local and major roads. Applying the ELECTRE TRI as the MCDA method enhanced the techniques to determine the suitable biogas plant site. The biowaste amount and distance from the suitable site were determined using the ArcGIS distance toolset. The biogas plant’s economic and environmental benefits, such as the electricity production capacity and CO2 reduction, were analyzed based on the population growth and the biogas production per year. The analyzed results obtain an area of 3.5 km2 for a large-scale biogas plant construction, with a potential production of 2,126,799.68 kW per year using combined heat and power and 2,303,100.23 kW by converting the thermal energy to electricity. This large-scale biogas plant could treat 20% of the organic waste per year, cover 60% of the city’s electricity demand, and reduce 946,200 kg of CO2 equivalent per year.