Anaerobic Digestion Technology Research Articles

Production of Biofuels from Agricultural Waste

Agricultural waste represents a largely untapped resource that could be utilized for the production of biofuels through various conversion pathways. As the global demand for renewable and sustainable energy grows, biofuels offer solutions to mitigate climate change impacts while improving waste management. This review analyzes using agricultural residues and by-products as feedstocks for biofuel production through biological, thermochemical and chemical conversion processes. The different types of lignocellulosic biomass available from agricultural activities are discussed, along with their compositions. While agricultural waste has advantages like wide availability and low cost, challenges relating to heterogeneous composition, pre-existing contamination and seasonal availability must be addressed. Fermentation, anaerobic digestion, pyrolysis and gasification are examined as established routes for converting agricultural waste into liquid biofuels and biogas. Pretreatment methods, enzyme production pathways and synthesis of fuels like ethanol, butanol and diesel substitutes are outlined. Environmental benefits of biofuels from waste, including greenhouse gas mitigation and recycling of soil nutrients, are evaluated against fossil fuel alternatives. Case studies on operational plants and feasibility studies provide insights into technical and economic viability at scale. Challenges regarding feedstock logistics, conversion efficiency, commercial scale-up and sustainability assessment are identified for future research focus. In conclusion, the review finds that agricultural waste is a promising renewable resource for biofuel production when integrated with appropriate thermochemical, biochemical or anaerobic digestion technologies. While the field is advancing, further improvements in areas such as feedstock supply, pretreatment technologies, and demonstration of sustainability will be critical to realize the full potential of this emerging bioeconomy sector. The review recommends steps to accelerate commercialization and policy frameworks to incentivize waste-to-energy solutions.

Research Progress of Antibiotic Resistance Genes Removal in Food Waste During Anaerobic Digestion

Food waste is one of the important reservoirs of antibiotic resistance genes （ARGs）, and its resource utilization has potential environmental risks. Anaerobic digestion （AD） technology can concurrently achieve resource recovery and ARGs removal, which is one of the popular resource technologies for food waste management. However, the removal efficiency of ARGs during the AD process is limited, and thus the safety of digestate for agricultural use is still questioned. Therefore, how to improve the performance of ARGs removal during the AD process is critical for efficient and environmentally friendly bioconversion of food waste. This study summarized the transmission pathways and mechanisms of ARGs in food waste； discussed the effects of different operation parameters on the transmission of ARGs in food waste during the AD process； described the research progress of exogenous addition of conductive materials, feedstock pretreatment, etc., strategies to enhance the removal of ARGs； and analyzed the migration regularity and removal mechanism of ARGs in food waste during the AD process, which mainly included microbial community structure evolution, mobile genetic element changes, and environmental factor changes. Finally, this study prospected the future improvement of methane yield and ARGs removal in the AD process of food waste based on the existing research.

National Greenhouse Gas Emission Reduction Potential from Adopting Anaerobic Digestion on Large-Scale Dairy Farms in the United States.

Waste-to-energy systems can provide a functional demonstration of the economic and environmental benefits of circularity, innovation, and reimagining existing systems. This study offers a robust quantification of the greenhouse gas (GHG) emission reduction potential of the adoption of anaerobic digestion (AD) technology on applicable large-scale dairy farms in the contiguous United States. GHG reduction estimates were developed through a robust life cycle modeling framework paired with sensitivity and uncertainty analyses. Twenty dairy configurations were modeled to capture important differences in housing and manure management practices, applicable AD technologies, regional climates, storage cleanout schedules, and methods of land application. Monte Carlo results for the 90% confidence interval illustrate the potential for AD adoption to reduce GHG emissions from the large-scale dairy industry by 2.45-3.52 MMT of CO2-eq per year considering biogas use only in renewable natural gas programs and as much as 4.53-6.46 MMT of CO2-eq per year with combined heat and power as an additional biogas use case. At the farm level, AD technology may reduce GHG emissions from manure management systems by 58.1-79.8% depending on the region. Discussion focuses on regional differences in GHG emissions from manure management strategies and the challenges and opportunities surrounding AD adoption.

Estimation of some AM2 model parameters from a derived empirical logistic function of methane production

Because of its capability to convert organic wastes into renewable energy and into some components useful for agriculture, the anaerobic digestion technology can reduce greenhouse gas emissions in the atmosphere and the pollution. Thus, anaerobic digestion can contribute to achieving some of sustainable development goals. Consequently, many theoretical and empirical approaches are proposed for estimating, predicting and optimizing the methane produced by anaerobic digestion. In this context, the logistic function is a mathematical model that can be used to approximate empirical data of the temporal methane production in anaerobic digestion. In a previous paper, under some appropriate approximations, we have derived from AM2 model a single analytical expression in a form of a logistic function for describing the evolution of methane production in batch bioreactors. In the present paper, by comparing the three standard parameters associated with the classical empirical logistic function with that of the derived one from AM2 model; some relationships between them have been established. These relations are exploited for estimating some coefficients and parameters of AM2 model with respect to empiric logistic function parameters and vice-versa. Moreover, this possibility enables more qualitative insight about the evolution of the methane production and the influence of AM2 parameters and coefficients as well as their interaction over its processes.

Enhanced anaerobic digestion of waste-activated sludge by thermal-alkali pretreatment: a pilot-scale study.

The composition of waste-activated sludge (WAS) is complex, containing a large amount of harmful substances, which pose a threat to the environment and human health. The reduction and resource utilization of sludge has become a development demand in sludge treatment and disposal. Based on the technical bottlenecks in the practical application of direct anaerobic digestion technology, this study adopted two different thermal and thermal-alkali hydrolysis technologies to pretreat sludge. A pilot-scale experiment was conducted to investigate the experimental conditions, parameters, and effects of two hydrolysis technologies. This study showed that the optimal hydrolysis temperature was 70 °C, the hydrolysis effect and pH can reach equilibrium with the hydrolysis retention time was 4-8 h, and the optimal alkali concentration range was 0.0125-0.015 kg NaOH/kg dry-sludge. Thermal-alkali combination treatment greatly improved the performance of methane production, the addition of NaOH increased methane yield by 31.2% than that of 70 °C thermal hydrolysis. The average energy consumption is 75 kWh/m3 80% water-content sludge during the experiment. This study provides a better pretreatment strategy for exploring efficient anaerobic digestion treatment technologies suitable for southern characteristic sewage sludge.

TURNING FOOD WASTE INTO GREEN ENERGY A BIO-GAS REVOLUTION

The Bio Gas Revolution stands as a beacon of sustainable innovation, revolutionizing waste management by converting discarded food into valuable green energy through biogas production. This abstract encapsulates the multifaceted approach of this revolution, encompassing waste food diversion strategies, cutting-edge anaerobic digestion technologies, renewable energy generation processes, circular economy principles, and the ensuing environmental-economic sustainability benefits. It underscores the transformative potential of harnessing waste food as a fundamental resource for renewable energy, heralding a new era of environmental preservation, resource optimization, and economic viability in the global energy land scape. It highlights the transformative potential of utilizing waste food as a critical resource for renewable energy, leading to significant environmental benefits, resource efficiency gains, and economic opportunities.. It emphasizes the transformative potential of harnessing waste food as a valuable resource for renewable energy production, contributing significantly to environmental preservation, resource efficiency, and economic viability” Key Words: Food Waste Management, Green Energy, Biogas Production, Sustainable Waste Disposal Submit Research Paper

Comprehensive insights into the effects of acidogenic off-gas utilization on successive biogas production, microbial community structure and metabolite distribution during two-stage anaerobic digestion

Although two-stage anaerobic digestion (TSAD) technology has been investigated, the mechanisms regarding the impact of acidogenic off-gas (AOG) on successive methane production have not been well addressed. In this study, a novel TSAD system was designed. Food waste, as the main substrate, was co-digested with chicken manure and corn straw. The acidogenic gas beyond atmospheric pressure was introduced into the bottom of the methanogenesis reactor through a stainless steel diffuser. Results showed the addition of AOG increased the methane yield from 435.2 to 597.1 mL/g VSin in successive methanogenesis stage, improved by 37.2 %, and increased the energy yield from 9.0 to 11.3 kJ/g VSsubstrate. However, the theoretical contribution of hydrogenotrophic methanogenesis using H2 contained in AOG was only 15.2 % of the increased methane yield. After the addition of AOG, the decreased levels of ammonia nitrogen and butyrate indicate that the stability of the AD system was improved. The electron transfer system and co-enzyme F420 activity were enhanced; however, the decrease in acetate kinase activity indicates aceticlastic methanogenesis may have been weakened. The microbial diversity and species richness were improved by the added AOG. Methanosarcina was more competitive than Methanothermobacter, enhancing the syntrophic effect. The relative abundance of protein degradation bacteria norank_f_Anaerolineaceae and lipid degradation bacteria Syntrophomonas was increased. Metabolite analysis confirmed that the addition of AOG promoted amino acid metabolism, the biosynthesis of other secondary metabolism and lipid metabolism. The improved degradation of recalcitrant organic components (lipids and proteins) in food waste was responsible for the increased methane yield. This study provides an in-depth understanding of the impact of AOG utilization on successive methane production and has practical implications for the treatment of food waste.

Design and optimization of a novel intestinal reactor to efficiently improve organic waste uniformity and solid content in high solid organic waste anaerobic digestion

High solid anaerobic digestion (HSAD) technology, a major treatment method for solid organic waste. Existing HSAD reactors comprise primarily vertical and horizontal reactors. Vertical reactors use high-pressure pneumatic stirring, which has high energy consumption and poor stirring performance. Horizontal reactors use long-uniaxial mechanical stirring, which occupies large land areas and has high strength requirements for stirring shaft material. In addition, during the operation of the two reactor types, the continuous liquefaction of the solid waste produces solid-liquid stratification, thus affecting mixing effects and decreasing the reactor volume rate. To solve the above problems, we designed a new simulated intestinal anaerobic digestion reactor with a natural solid-liquid separation system, short-axis mechanical stirring, and a stirring blade optimized through CFD. Use of the solid-liquid separation system increased the solid content in the reactor by 44%–55%. The operation results indicated that the homogenization of the solid waste with the optimal stirring blade was more than 50% greater than that of a conventional vertical reactor. The intestinal reactor solves the problems of poor uniformity and solid content decrease during anaerobic digestion in traditional HSAD, decreases the strength requirements for stirring shaft material, and has potential to increase urban waste treatment capacity.

Unveiling the impact of temperature shift on microbial community dynamics and metabolic pathways in anaerobic digestion

Anaerobic digestion (AD) technology is a viable solution to the challenges attributed to sewage sludge, but its specific impact on biogas production and the dynamics of methanogenic bacteria has not been widely understood. This research investigated the effects of shifts in AD operational temperatures on microbial communities and biogas production. This was achieved by incrementally raising the temperature from 37 °C to 45 °C in 2 °C increments. Within the temperature range of 37 – 41 °C, there was a notable disturbance in the abundance of acetogenic bacteria and methanogens, leading to a considerable reduction in methane production. However, with further elevation of temperature, the increasing activity of acetogens and methanogens was discerned following the increase in methane production. Methanothrix was identified as the predominant methanogen in the present study, marking the domination of the acetoclastic pathway. In functional analysis, the acetate decarboxylation enzymes demonstrated resilience at 43 °C and 45 °C, in contrast to hydrogenotrophic pathway enzymes. The acetoclastic pathway played a primary role in methane production under temperature shift conditions while the hydrogenotrophic pathway was more susceptible to temperature fluctuations. The findings highlight the potential adaptation of microbial communities when subjected to changing temperatures which led to robustness of digestion in AD processes.

A Life Cycle Assessment of Methane Slip in Biogas Upgrading Based on Permeable Membrane Technology with Variable Methane Concentration in Raw Biogas

While energy-related sectors remain significant contributors to greenhouse gas (GHG) emissions, biogas production from waste through anaerobic digestion (AD) helps to increase renewable energy production. The biogas production players focus efforts on optimising the AD process to maximise the methane content in biogas, improving known technologies for biogas production and applying newly invented ones: H2 addition technology, high-pressure anaerobic digestion technology, bioelectrochemical technology, the addition of additives, and others. Though increased methane concentration in biogas gives benefits, biogas upgrading still needs to reach a much higher methane concentration to replace natural gas. There are many biogas upgrading technologies, but almost any has methane slip. This research conducted a life cycle assessment (LCA) on membrane-based biogas upgrading technology, evaluating biomethane production from biogas with variable methane concentrations. The results showed that the increase in methane concentration in the biogas slightly increases the specific electricity consumption for biogas treatment, but heightens methane slip with off-gas in the biogas upgrading unit. However, the LCA analysis showed a positive environmental impact for treating biogas with increasing methane concentrations. This way, the LCA analysis gave a broader comprehension of the environmental impact of biogas upgrading technology on GHG emissions and offered valuable insights into the environmental implications of biomethane production.

Techno-economic analysis of a mini biogas electricity plant (MBEP) for a typical farm in the Zimbabwean off-grid areas

AbstractIn response to declining electricity production in Zimbabwe, the energy regulator engaged various stakeholders to work together to solve the energy shortage problem. Biomass waste, abundant in the country, can contribute to electricity generation for consumption and export to the grid. Compared to other renewable energy resources such as wind and solar, biomass has lower investment and per unit operational costs, making it more affordable. Although farmers in the remote off-grid areas produce large amounts of waste, which can be used for biogas production via anaerobic digestion (AD), the farmers are still ‘energy-poor’. There is insufficient information to enable farmers to make informed decisions on AD technology uptake. This study conducted a techno-economic assessment for a mini biogas electric plant (MBEP) for a typical farm in Zimbabwe’s off-grid areas. The sustainably available biomass for biogas production was determined, followed by quantifying the biogas produced, sizing and selecting the digester type, and sizing the generator. The MBEP produces 435,350.7 kWh of heat and electrical energy from 452 t of biowaste. The first biodigester-type option, the garage-shaped, has a negative net present value ($$NPV$$ NPV ) of − US$416.4. The Carmatec biodigester, the most popular AD technology in the country, has a positive $$NPV$$ NPV (US$216,447.7), but its economics needs improvement. Adopting AD technology allows farmers to mitigate environmental pollution and improve soil fertility by converting organic waste into biogas and biofertilisers and promoting sustainable agricultural practices. Research was recommended to investigate supportive policies, incentives, and regulatory frameworks to promote the widespread adoption of AD technology in agricultural settings.

Biosolids management and utilizations: A review

Biosolids, derived from wastewater treatment processes, have garnered increasing attention as a valuable resource due to their rich organic and inorganic constituents, which can be beneficially utilized in multiple sectors, including agriculture, civil engineering, and energy recovery. The present review article begins by providing an overview of biosolids, including their production methods and classification based on treatment processes. Subsequently, the chemical composition of biosolids is explored, highlighting the diverse array of organic and inorganic components present. The characterization techniques employed for analyzing biosolids, such as spectroscopy, chromatography, and microscopy, are thoroughly discussed, emphasizing their role in determining the quality and suitability of biosolids for different applications. Furthermore, the environmental impacts associated with biosolids disposal are extensively examined. This includes the potential risks posed by heavy metals, pathogens, and emerging contaminants, as well as strategies for mitigating these risks through proper treatment and management practices. In addition to environmental considerations, the article explores the various products that can be derived from biosolids. These include organic matter-rich soil amendments for agricultural applications, inorganic nutrient supplements for enhancing plant growth, and the potential for energy recovery through anaerobic digestion and thermal conversion technologies. The utilization of biosolids in civil engineering projects, such as landfill capping and construction materials, is promising. Land application of biosolids also can have economic and waste management benefits (e.g., conservation of landfill space; reduced demand on non-renewable resources like phosphorus; and a reduced demand for synthetic fertilizers).

Techno-economic analysis of electron beam irradiation pretreatment of corn straw for anaerobic digestion

The complexity of anaerobic digestion process and the risks of investing in new technologies are the main obstacles to improving anaerobic digestion technology. There is still a gap between research results and commercial applications. This study investigated the techno-economic feasibility and bottlenecks of introducing electron beam irradiation pretreatment technology into the commercial-scale anaerobic digestion plant. Model construction, parameter initialization and economic analysis were performed in SuperPro Designer software. The parameters used in the model were derived from experimental results, software built-in model and recent literature. The results show that the gross margin, return on investment, payback time, internal rate of return, and net present value of the system with electron beam irradiation pretreatment are 4.4 %, 9.8 %, 10.1 years, 8.0 % and $0.6 million, respectively. The corresponding values of the system without electron beam irradiation pretreatment are 9.9 %, 11.1 %, 8.9 years, 9.7 % and $1.5 million, respectively. The main factor affecting gross profit is tipping fee of liquid anaerobic digestion effluent, followed by plant size of anaerobic digestion, degradation efficiency of corn straw, and compost price. This study has guiding significance for the application of electron beam irradiation pretreatment technology in the production of renewable energy from lignocellulosic biomass.

Multi-objective optimization of straw-based bio-natural gas supply chains considering cost, CO2 emission, and safety

Bio-natural gas (BNG) has received recent interest as a renewable alternative to natural gas (NG). BNG supply chains (BSC), including production, transportation, and utilization, are compatible and can overlap with existing NG infrastructure. The goal is to develop a set of models that achieve the various trade-offs between economic, environmental and safety risks by combining life cycle assessment (LCA), mixed-integer linear programming (MILP) and fuzzy optimization, expanding the utilization of BSC while quantifying the risk of the whole process, so as to improve the safety awareness of the project operation. BNG technologies were considered: anaerobic digestion (AD), gasification, and syngas methanation. This model can analyze the changes in the different objectives of each module and the distribution of biomass mass flow by comparing different straw-based harvesting rates. Results indicate that AD technology possesses the lowest economic cost, and BNG as transportation fuel will generate the most benefits. The unit cost of BNG for different technologies ranges from 0.36 to 0.67 $/m³，the emission reduction is from 5.18 kg/m³ to 10.28 kg/m³，and the maximum safety risk value is 1.96. The proposed model was applied to a case study in China to illustrate the optimization of a regional straw-based BSC. The results illustrate how BNG supply chains can be systematically planned as part of an integrated decarbonization policy while mitigating safety risks that may occur from handling this fuel.

Optimization of alkaline hydrothermal treatment for humic acids production from corn straw digestate using the response surface methodology

Anaerobic digestion (AD) technology was widely used for treating waste biomass, during which a large amount of lignin-rich digestate would be produced, needing further treatment. In this study, corn straw digestate (CSD) was used as raw material for hydrothermal humic acids (HHA) producing through alkaline hydrothermal treatment (AHT). According to the response surface analysis, the optimal reaction conditions were determined to be 156°C, 2 hours, and 5% KOH (% of the dry digestate), resulting in a HHA yield of 40.3 wt%. Structural characterization analysis showed the produced HHA had abundant oxygen-containing functional groups (e.g., C-O and CO) in HHA and aromatic structures, which also showed good thermal stability. By AHT with hemicellulose and lignin, the HHA yields reached 79.2%. Hemicellulose and lignin proved to be important components for HHA formation. In addition, the protein content in the EPS extraction solution of HC was significantly reduced compared to CSD, indicating that the dewaterability of the digestate were improved after AHT. This technique provides a feasible approach for the further utilization of residual lignocellulosic materials after anaerobic digestion.

Effect of model methanogens on the electrochemical activity, stability, and microbial community structure of Geobacter spp. dominated biofilm anodes

Combining anaerobic digestion (AD) and microbial electrochemical technologies (MET) in AD-MET holds great potential. Methanogens have been identified as one cause of decreased electrochemical activity and deterioration of Geobacter spp. biofilm anodes. A better understanding of the different interactions between methanogenic genera/species and Geobacter spp. biofilms is needed to shed light on the observed reduction in electrochemical activity and stability of Geobacter spp. dominated biofilms as well as observed changes in microbial communities of AD-MET. Here, we have analyzed electrochemical parameters and changes in the microbial community of Geobacter spp. biofilm anodes when exposed to three representative methanogens with different metabolic pathways, i.e., Methanosarcina barkeri, Methanobacterium formicicum, and Methanothrix soehngenii. M. barkeri negatively affected the performance and stability of Geobacter spp. biofilm anodes only in the initial batches. In contrast, M. formicicum did not affect the stability of Geobacter spp. biofilm anodes but caused a decrease in maximum current density of ~37%. M. soehngenii induced a coloration change of Geobacter spp. biofilm anodes and a decrease in the total transferred charge by ~40%. Characterization of biofilm samples after each experiment by 16S rRNA metabarcoding, whole metagenome nanopore sequencing, and shotgun sequencing showed a higher relative abundance of Geobacter spp. after exposure to M. barkeri as opposed to M. formicicum or M. soehngenii, despite the massive biofilm dispersal observed during initial exposure to M. barkeri.

An Overview of Anaerobic Digestion of Cow Dung

In the past decade, governments and development agencies have contributed significantly to society through anaerobic digestion technology (ADT). Anaerobic digestion technology (ADT) has become an important tool in the fight against global poverty and environmental issues, leading to positive change in communities around the world. The technology works as a wet or dry process, depending on its classification. The process is complex and yields multiple benefits, such as creating a natural fertilizer that can be used to help crops grow, as well as generating renewable energy sources. It is common knowledge that many household-sized digesters installed in different areas are one-stage digesters. One-stage digesters do not require a separate pre-treatment stage before the digestion process. This makes them simpler and more cost-effective to install and operate than traditional two-stage digesters. Thus, some drawbacks are associated with these systems since they feed on just one type of feedstock. Many researchers fail to adequately address interactions critical to ADT’s operation, including interactions among growth factors and operating parameters. In a single-stage and one-substrate digester, researchers commonly neglect to study the digester feeding and operational conditions. Anaerobic digestion was the subject of this review, covering research conducted between 2001 and 2022. The study identified a significant drawback associated with mono-digestion and single-stage digestion. The findings illustrate that mono-substrate and single-stage digestion are worthwhile approaches, even though they have their challenges. However, adding a further digestion stage can significantly improve biogas production.

Enhancing Waste-to-Energy and Hydrogen Production through Urban–Industrial Symbiosis: A Multi-Objective Optimisation Model Incorporating a Bayesian Best-Worst Method

A surging demand for sustainable energy and the urgency to lower greenhouse gas emissions is driving industrial systems towards more eco-friendly and cost-effective models. Biogas from agricultural and municipal organic waste is gaining momentum as a renewable energy source. Concurrently, the European Hydrogen Strategy focuses on green hydrogen for decarbonising the industrial and transportation sectors. This paper presents a multi-objective network design model for urban–industrial symbiosis, incorporating anaerobic digestion, cogeneration, photovoltaic, and hydrogen production technologies. Additionally, a Bayesian best-worst method is used to evaluate the weights of the sustainability aspects by decision-makers, integrating these into the mathematical model. The model optimises industrial plant locations considering economic, environmental, and social parameters, including the net present value, energy consumption, and carbon footprint. The model’s functionalities are demonstrated through a real-world case study based in Emilia Romagna, Italy. It is subject to sensitivity analysis to evaluate how changes in the inputs affect the outcomes and highlights feasible trade-offs through the exploration of the ϵ-constraint. The findings demonstrate that the model substantially boosts energy and hydrogen production. It is not only economically viable but also reduces the carbon footprint associated with fossil fuels and landfilling. Additionally, it contributes to job creation. This research has significant implications, with potential future studies intended to focus on system resilience, plant location optimisation, and sustainability assessment.

Research progress and perspectives of biogas production from municipal organic solid waste

Abstract Anaerobic digestion is a prevailing technology for the treatment and utilization of municipal organic solid waste (MOSW). In this technology, the macromolecular organic matter in waste degrades into small molecular substances through the anaerobic decomposition of microorganisms, producing biogas that can provide enormous energy. This paper focuses on the research progress of anaerobic digestion of various organic wastes for biogas production. The principle and process of anaerobic digestion for biogas production are introduced, along with the key factors affecting anaerobic digestion efficiency, such as temperature, pH, and sealing conditions. At the same time, the current cycle treatment technology and comprehensive treatment system of MOSW are also summarized. Furthermore, the paper explores biogas purification technologies, including desulfurization, deoxidation, drying, and decarbonization. Finally, the state-of-the-art of the utilization of MOSW for biogas production in the world and the problems faced by the utilization of MOSW for biogas production in China are reviewed. By summarizing the anaerobic digestion technology of MOSW, this review hopes to provide some reasonable solutions for the high-value utilization of MOSW.

Multiple-criteria decision analysis techniques for anaerobic digester technology assessment

Effective decision-making requires the evaluation of several criteria rather than a single, preferred criterion. The best decision options (alternatives) are recommended to decision-makers when a multi-criteria decision problem is addressed. This study develops a multi-criteria selection method for the assessment of small-scale anaerobic digester technology by combining two existing methods. The Simple Multi-Attribute Rating Technique (SMART) and the Analytical Hierarchy Process (AHP) approaches of multiple-criteria decision analysis were used as a decision support tool, and the preferred anaerobic digester technology was selected from a list of eleven potential small-scale digester technologies used in low to middle-income countries. These techniques were applied under two scenarios for a case study in the South African smallholder farmers. Scenario 1 involves a subsistence smallholder farming context, while scenario 2 involves a commercially oriented smallholder farming context. The overall results revealed that the DIY Biobag and Puxin digester design models achieved 82.1 and 73.7 % preference in comparison to other digester technologies for scenarios 1 and 2, respectively. The Biobag digester technology achieved the highest ranking, which is consistent with the significant cost advantage and technical characteristics of the technology. However, for those households with sufficient access to funds for the initial expenditure, the method identifies the Puxin digester as the most appropriate alternative, excluding cases where underground construction is not possible. The AGAMA BiogasPro digester was ranked in the second position in both scenarios. A sensitivity analysis was conducted to determine the effect of changes in the assessment criteria weights and found the selected alternatives stable and robust. Finally, it can be concluded that the developed technology selection model contributed a knowledge-based framework to be used in various situations by different decision-makers, thereby providing a method applicable to particular local conditions to identify the most suitable technology choices.