Abstract
Rural electrification in livestock-dominated regions of Sub-Saharan Africa remains constrained by high grid extension costs and dependence on diesel-based generation. This study investigates the technical, economic, and environmental feasibility of converting cattle dung into electricity through a decentralized biomass waste-to-energy (WtE) system in Madu, Uganda. Livestock waste availability, biogas potential, digester performance, energy output, and system economics were evaluated using field data and established conversion models. Results indicate that dung from 120 cattle can sustain continuous biogas production, yielding approximately 99,000 m3 of methane annually. The biogas-powered combined heat and power system generated 18–19 MWh of electricity per month, alongside significant thermal energy recovery. The system demonstrated stable operation with a hydraulic retention time of 35 days and no observed process instability. Economic analysis revealed a levelized cost of electricity of 0.064 USD kWh−1 and a simple payback period of six years, substantially outperforming diesel-based rural electricity generation. Environmental assessment showed avoided emissions of approximately 183 tCO2 yr−1, in addition to improved waste management and nutrient recycling benefits. The findings confirm that cattle-dung-based WtE systems offer a technically reliable, economically competitive, and environmentally sustainable solution for rural electrification. Integrating such systems into rural energy planning and climate mitigation frameworks could significantly enhance energy access and support low-carbon development in livestock-rich rural communities.
Keywords
Introduction
Access to reliable, affordable, and sustainable electricity remains a major development challenge in rural areas of Sub-Saharan Africa. Despite notable progress in national generation capacity and grid expansion, rural electrification rates remain low due to dispersed settlements, limited demand density, and high infrastructure costs (Lwakatare et al., 2024; Robin and Ehimen, 2024; Uzorka et al., 2025a). In Uganda, rural electricity access is estimated at below 30%, with many communities relying on diesel generators, kerosene, and traditional biomass to meet basic energy needs (Makumbi et al., 2026; Murungi et al., 2025; Uzorka et al., 2025b). These energy sources are associated with high operating costs, greenhouse gas emissions, indoor air pollution, and negative health outcomes. In the broader Sub-Saharan African context, rural electrification challenges are further compounded by weak grid infrastructure, low household incomes, and limited investment in decentralized energy systems. Meyer and Overen (2021) emphasized that sustainable rural electrification in Africa requires integrated decentralized renewable energy strategies capable of addressing technical, economic, and social barriers simultaneously.
Decentralized renewable energy systems have therefore gained increasing attention as viable alternatives to grid extension in rural contexts. Among these, biomass waste-to-energy (WtE) technologies are particularly attractive because they simultaneously address energy access, waste management, and environmental sustainability (Sibanda and Uzabakiriho, 2024; Tariq et al., 2023; Umar et al., 2024). Livestock waste, especially cattle dung, represents one of the most promising biomass resources in agrarian economies due to its continuous availability, low collection cost, and high biodegradability (DelaVega-Quintero et al., 2025; Liang, 2024; Manyi-Loh and Lues, 2023). In many rural African communities, livestock farming remains a dominant economic activity, making cattle dung an accessible and underutilized renewable energy resource for decentralized electrification systems.
Anaerobic digestion is the most widely adopted technology for converting cattle dung into biogas, a methane-rich renewable fuel suitable for cooking, electricity generation, and combined heat and power (CHP) applications (Hamzah et al., 2023; Obileke et al., 2024; Osman et al., 2023). Several studies have demonstrated that cattle dung possesses favorable physicochemical characteristics for anaerobic digestion, including an appropriate carbon-to-nitrogen (C/N) ratio, high volatile matter content, and adequate buffering capacity (Alengebawy et al., 2024; Negro et al., 2025; Ngabala and Emmanuel, 2024). Under tropical climatic conditions, stable biogas production can be achieved with relatively simple digester designs and moderate hydraulic retention times (Achi et al., 2024; Dhull et al., 2025; Makamure et al., 2024). Furthermore, Meyer et al. (2021) reported that biodigester systems can contribute significantly to sustainable rural energy transitions when appropriately integrated with local demand-side management strategies and community-level energy planning.
Historically, biogas programs in developing countries have focused predominantly on household-scale digesters for cooking and lighting, and while these interventions have delivered measurable benefits in terms of reduced fuelwood use and improved health outcomes, uptake remains limited in many regions (Ikegwuonu et al., 2025; Klintenberg and Schwede, 2024; Odoi-Yorke et al., 2024). In East Africa specifically, adoption of biodigesters at the household level has shown promise for improving access to clean energy and enhancing resilience among smallholder farmers, but expansion beyond basic domestic applications has been slow (Rasimphi, 2024). However, the potential of cattle-dung-based biogas systems for community-scale electricity generation remains underexplored, with recent scholarship highlighting that widespread deployment of biogas-based power systems is curtailed by gaps in integrated techno-economic, environmental, and social assessments that are necessary to inform scalable planning and policy (Gbadeyan, 2024; Gebretsadik, 2025). Recent studies have also demonstrated the growing relevance of hybrid renewable systems that integrate biogas with other decentralized energy technologies to improve rural energy reliability and resilience. For instance, Overen et al. (2024) demonstrated that hybrid solar–biogas systems can significantly improve post-COVID-19 rural energy access while enhancing energy security and sustainability in underserved communities.
When biogas is utilized in CHP systems, overall energy efficiencies exceeding 80% can be achieved through simultaneous electricity generation and heat recovery (Akarsu and Demir, 2024; Ankathi et al., 2024; Habib et al., 2025). The recovered thermal energy can be used for digester heating, agro-processing, and other productive uses, thereby improving system economics and reliability. Studies conducted in Europe and Asia report levelized costs of electricity (LCOE) for biogas CHP systems ranging from 0.05 to 0.15 USD/kWh, depending on feedstock cost, system scale, and utilization rate (Ihugba et al., 2025). In contrast, off-grid diesel generation in rural Africa often exceeds 0.30 USD/kWh due to fuel price volatility and transport costs (IRENA, 2025). In addition, Meyer et al. (2021) reported that biodigester-based rural electrification systems can achieve favorable financial and economic feasibility when local biomass availability, operational efficiency, and community energy demand are adequately aligned.
Beyond energy supply, cattle-dung-based biogas systems offer significant environmental benefits. Uncontrolled decomposition of livestock waste is a major source of methane emissions, a greenhouse gas with a global warming potential approximately 28 times that of carbon dioxide over a 100-year period (Wang et al., 2025). Anaerobic digestion captures this methane for productive use, while also reducing odors, pathogens, and water contamination risks. Life-cycle assessment studies indicate substantial net reductions in greenhouse gas emissions when biogas systems displace fossil-fuel-based electricity and traditional biomass use (Pilarski, 2025). Additionally, the digestate by-product can substitute synthetic fertilizers, further enhancing environmental performance. Besides carbon dioxide mitigation, anaerobic digestion systems can also reduce emissions of methane and nitrous oxide associated with unmanaged livestock waste disposal and conventional fuel combustion processes.
Despite these advantages, several research gaps persist. Many existing studies are limited to laboratory experiments or household-scale applications and do not adequately address seasonal performance variation, digester sizing based on livestock availability, CHP integration, or comprehensive economic and environmental evaluation. In Uganda specifically, empirical, site-specific studies that combine livestock waste assessment, biogas yield monitoring, electricity and heat generation analysis, carbon mitigation, and financial performance indicators such as LCOE and payback period are scarce, despite the country's substantial livestock population and favorable climatic conditions (Makumbi et al., 2025). Moreover, although previous studies have explored rural biodigester feasibility and decentralized electrification frameworks, limited research has evaluated fully integrated community-scale cattle-dung WtE systems under real rural operating conditions in Uganda.
This study addresses these gaps by designing and evaluating a community-scale biomass WtE system based on cattle dung in Madu, Gomba District, Uganda. The study integrates livestock waste availability assessment, seasonal biogas yield analysis, digester sizing, CHP-based electricity and heat generation, greenhouse gas mitigation, and economic performance evaluation using LCOE and payback period metrics. By providing a comprehensive, site-specific techno-economic and environmental assessment, this work contributes evidence to support the deployment of cattle-dung-based WtE systems for rural electrification within the Ugandan context.
Methodology
Study area
Madu is a rural town in Gomba District, located in the Central Region of Uganda, approximately 30 km northwest of Kanoni (the district headquarters) and 128 km west of Kampala (David et al., 2022). The area is predominantly agricultural, with livestock farming serving as a major economic activity and source of livelihood. Cattle production supports local milk and meat supply chains, with products marketed within the district and transported to Kampala through established trade networks. Major livestock operations in the area include Katende Farm (Kilasi), Bitali Family Ranch, and Kisozi Farm.
Madu experiences a tropical rainforest climate (Af) characterized by relatively stable temperatures and bimodal rainfall patterns that favor year-round livestock farming and biomass availability. The area receives an average annual rainfall of approximately 181 mm distributed over about 240 rainy days annually. The mean annual temperature is approximately 22.6°C, with average monthly temperatures ranging from 16.6°C in June to 27.8°C in February and an average relative humidity of about 72% (David et al., 2022). These climatic conditions are favorable for anaerobic digestion because mesophilic microbial activity responsible for biogas generation performs efficiently within moderate temperature ranges. Figure 1 presents the geographical location of Madu within Gomba District, highlighting surrounding settlements, road networks, water bodies, and administrative boundaries relevant to the study area.
Map of the study area.
To evaluate the influence of climatic conditions on biogas generation, monthly outdoor temperature data for the study area were obtained from regional meteorological records and compared with observed biogas production trends. The annual temperature profile indicated minor seasonal variations, with relatively warmer conditions occurring between December and February and slightly cooler conditions during June and July. The inclusion of these climatic data provided a basis for interpreting temporal variations in gas production during the monitoring period.
The selected community is characterized by dispersed rural settlements with limited access to reliable electricity infrastructure. Household energy demand in the study area is primarily associated with lighting, phone charging, refrigeration, water pumping, small agro-processing activities, and domestic heating applications. The estimated average daily electricity demand of the study community was approximately 420–500 kWh/day, based on household surveys, farm energy requirements, and small commercial activities conducted during the preliminary assessment phase. Thermal energy demand within the community was primarily associated with water heating, milk processing, feed preparation, and digester temperature stabilization.
Description of the biomass WtE conversion system
Figure 2 illustrates the biomass WtE conversion system employed in this study. The system comprised a manure collection lagoon, anaerobic digester, biogas cleaning unit, internal combustion engine, induction generator, heat recovery exchanger, thermal distribution network, electricity distribution system, and grid interconnection unit. Fresh cattle dung was first collected and temporarily stored in a lagoon to regulate feedstock supply into the digester. Anaerobic digestion then occurred under oxygen-free conditions, producing methane-rich biogas suitable for CHP generation.
Waste to energy system.
The produced biogas was conveyed to a biogas-compatible four-stroke internal combustion engine where combustion generated mechanical energy. The engine was mechanically coupled to a 30 kW induction generator for electricity generation. Waste heat recovered from engine exhaust gases and engine cooling systems was transferred through a heat exchanger for reuse in digester heating and other thermal applications within the community. The generated electricity was distributed to nearby households and farm facilities through a localized mini-grid distribution network, while excess electricity could be exported to the utility grid when required.
The biodigester system was installed at Makumbi Farm in Madu, Uganda, and specifically designed for cattle-dung-based biogas production and CHP generation. A fixed-dome anaerobic digester with an effective working volume of 45 m3 was constructed using brick masonry lined internally with gas-tight cement mortar to minimize methane leakage. The digester foundation consisted of compacted hardcore material overlaid with reinforced waterproof concrete to prevent groundwater infiltration.
The digester was insulated using locally sourced fibre-based insulating materials composed primarily of dry banana fibers, sawdust, and compacted grass materials enclosed within protective outer layers. Previous studies have shown that locally available fibrous insulating materials possess low thermal conductivity and can effectively reduce heat loss in small-scale biodigester systems operating under tropical climatic conditions (Meyer et al., 2021; Overen et al., 2024). The insulation system helped maintain relatively stable mesophilic operating temperatures within the digester despite minor ambient temperature fluctuations. The digester included an inlet chamber for feeding cow dung mixed with water at a 1:1 ratio, an outlet chamber for digestate discharge, a gas collection dome, and a sealed manhole for maintenance and sludge removal.
Biogas transportation was achieved using 1-inch high-density pressure-rated PVC pipelines, while digestate discharge was facilitated through gravity-driven 6-inch PVC pipelines. Insulated copper pipes connected the heat exchanger to the digester to facilitate thermal energy transfer for temperature regulation when necessary. The CHP unit consisted of a 30 kW biogas-compatible four-stroke internal combustion engine coupled to an induction generator for electricity generation and a shell-and-tube heat exchanger for thermal recovery. The recovered heat was utilized for digester temperature stabilization, milk pasteurization, domestic hot water supply, and small-scale agro-processing operations within the community.
A control panel equipped with gas pressure regulators, flame arrestors, methane gas sensors, temperature sensors, pressure gauges, emergency shut-off valves, and overload protection systems was installed to ensure safe and reliable operation of the system. The anaerobic digestion process was initiated by charging the sealed digester with fresh cow dung mixed with inoculum (previously digested slurry) to accelerate microbial activity and methane production. The system was maintained under anaerobic conditions and incubated for approximately 30 days before continuous operation commenced. Thereafter, daily feeding and digestate discharge were implemented to maintain microbial stability and ensure steady biogas production.
Prior to combustion in the CHP unit, the produced biogas underwent cleaning and conditioning to remove hydrogen sulfide, excess moisture, and particulate impurities. Hydrogen sulfide removal was achieved using iron-filings-based scrubbers, while condensate traps and moisture separators were employed to reduce water vapor content and minimize corrosion risks within the engine components. Biogas volume (m3), electrical energy output (kWh), thermal energy output (kWh), digester temperature (°C), and gas pressure were monitored daily from September to November 2024 using calibrated digital instruments. The collected operational data were compiled and analyzed to evaluate overall system performance. Table 1 summarizes the major system components, installed instrumentation, meter specifications, and measurement functions.
System components and monitoring instruments.
CHP: combined heat and power.
The RITTER TG05 gas flow meter was connected inline along the main biogas delivery pipeline between the digester outlet and the CHP unit to continuously measure cumulative biogas flow. The Schneider iEM3255 multifunction energy meter was connected between the induction generator and electrical distribution panel to record generated electrical power, energy output, current, and voltage parameters. The Kamstrup MULTICAL 603 heat meter was installed across the heat exchanger inlet and outlet pipes to quantify recovered thermal energy based on temperature differentials and flow rate measurements.
In addition to operational monitoring, photographs of the installed biodigester, CHP engine, heat exchanger, and local electricity distribution system were captured during field operation to support visual verification of the installed system components.
Chemical analysis of cow dung for biomass energy
Fresh cow dung samples were collected from cattle sheds in Madu, Gomba District, Uganda, in April 2024. The samples were air-dried for 72 h, ground to obtain a uniform texture, and sieved through a 2 mm mesh to ensure homogeneity (Uzorka and Wonyanya, 2025).
Proximate analysis was conducted to determine moisture content, volatile matter, ash content, and fixed carbon using standard procedures in accordance with ASTM D3172–13 and related methods: ASTM D3173 for moisture content, ASTM D3174 for ash content, and ASTM D3175 for volatile matter determination (ASTM, 2013; Uzorka and Wonyanya, 2025). Moisture content was determined by oven-drying the samples at 105°C to constant weight, according to equation (1):
Volatile matter and ash contents were measured using a muffle furnace operated at 550°C and 600°C, respectively. Fixed carbon content was determined by difference. Ultimate analysis was performed using a CHNS/O elemental analyzer to quantify carbon, hydrogen, nitrogen, sulfur, and oxygen contents. Oxygen concentration was calculated by difference.
Biochemical characterization focused on parameters relevant to anaerobic digestion performance and methane generation. Sample pH was measured using a calibrated digital pH meter, while the C/N ratio was determined from elemental carbon values obtained from CHNS analysis and nitrogen content measured using the Kjeldahl method. The lignocellulosic composition of the cattle dung, including cellulose, hemicellulose, and lignin, was determined using an ANKOM 2000 Fiber Analyzer (ANKOM Technology, USA) following the Van Soest detergent system and AOAC Official Methods 973.18 and 973.19 (Van Soest et al., 1991). Approximately 1 g of oven-dried powdered sample was subjected sequentially to Neutral Detergent Fiber, Acid Detergent Fiber, and Acid Detergent Lignin analyses to determine the structural carbohydrate fractions relevant to biodegradability and methane yield potential. The percentages of cellulose, hemicellulose, and lignin were calculated using equations (2)–(4).
Biogas production potential modeling
To evaluate the theoretical methane production from cow dung at Makumbi Farm, the livestock waste model was applied using equation (5) (Nassar et al., 2024):
Determining the volume of the biogas digester
Digester volume Vd was computed according to equation (6) (Wonyanya and Uzorka, 2025):
where HRT is hydraulic retention time and Vs is daily slurry volume (m3/day) computed according to equation (7):
Qf is total fresh manure + water (kg/day). Dung and water are mixed in about a 1:1 ratio by weight, ρ is slurry density (∼1000 kg/m3 for diluted dung). 10% additional volume is added (gas storage + safety margin) (Uzorka and Wonyanya, 2025).
Environmental impact and CO2 emission reduction
The annual CO2 emission reduction was estimated based on methane substitution for fossil-based electricity (Mesquita et al., 2023):
Uganda's national electricity supply is dominated primarily by hydropower generation, supplemented by thermal power plants operating on heavy fuel oil and diesel. Although hydropower contributes substantially to the national grid, fossil-fuel-based thermal generation remains an important backup source during periods of low hydropower output and peak electricity demand, thereby contributing to carbon dioxide emissions. In addition to CO2 reduction, the biodigester system contributed to the mitigation of methane (CH₄) and nitrous oxide (N2O) emissions by preventing uncontrolled decomposition of livestock waste under open environmental conditions. Since methane possesses a significantly higher global warming potential than carbon dioxide, capturing and utilizing methane for productive energy applications substantially improved the environmental performance of the system.
Economic performance analysis
Levelized cost of energy
The LCOE was evaluated using (Kost et al., 2013):
Payback period
The payback period was estimated as (Boardman et al., 2020; Short et al., 1995):
Environmental cost integration (LCOH with CO2 damage cost)
To incorporate environmental externalities, the cost of CO2 damage (CCO2) was included in the LCOH (Bashmakov et al., 2022):
Result
Chemical analysis of cow dung
The physicochemical characteristics of the cattle dung used in this study are presented in Table 2. The results demonstrate that the biomass feedstock possessed favorable properties for anaerobic digestion and biogas generation. The measured moisture content of 75% falls within the optimal range for wet anaerobic digestion systems and supports efficient microbial metabolism and substrate transport within the digester. Similarly, the neutral pH value of 6.54 indicates suitable conditions for methanogenic bacterial activity, which typically thrives within a pH range of 6.5–7.5.
Chemical analysis of cow dung.
The measured C/N ratio of 20:1 further confirms the suitability of the substrate for biogas production, as excessively high or low C/N ratios may inhibit microbial activity and reduce methane yield. The volatile matter content of 15% indicates the presence of sufficient biodegradable organic material available for microbial conversion into methane-rich biogas. In contrast, the relatively low ash content (5%) suggests limited inorganic residue accumulation and reduced risks of slagging or fouling during thermal conversion processes.
Ultimate analysis showed that the cow dung contained 40% carbon, 6% hydrogen, and 50% oxygen, values consistent with typical lignocellulosic biomass feedstocks. The low sulfur content (0.5%) is environmentally favorable because it minimizes the formation of sulfur oxides and reduces hydrogen sulfide concentrations in the produced biogas, thereby lowering corrosion risks in the CHP engine. Nitrogen content was measured at 3%, which remained within acceptable limits for stable anaerobic digestion.
The lignocellulosic analysis revealed cellulose and lignin contents of 30% and 10%, respectively. The relatively high cellulose fraction supports biodegradability and methane production potential, while the moderate lignin content suggests that only a limited portion of the biomass may resist microbial degradation. Overall, the results confirm that cattle dung from the study area possesses strong potential as a renewable biomass feedstock for decentralized WtE applications.
Biogas production performance
Figure 3 presents the daily biogas production trends observed from September to November 2024. The results show relatively stable digester operation throughout the monitoring period, although gradual monthly reductions in gas yield were observed.
Daily biogas yield variations from September to November 2024.
September recorded the highest daily gas yields, increasing progressively from 268 m3/day at the beginning of the month to a peak value of 314 m3/day around Day 20 before gradually declining toward the end of the month. The higher gas production observed during September corresponded with relatively warmer ambient temperatures and stable microbial digestion conditions within the biodigester.
October exhibited slightly lower gas yields compared to September, with daily production ranging between 265 and 300 m3/day. Similarly, November recorded the lowest gas production values, ranging from 258 to 288 m3/day. The gradual decline in gas production from September to November corresponded with modest reductions in ambient temperature and changes in slurry characteristics during the study period. Meteorological observations showed that average outdoor temperatures declined progressively during the later months of the monitoring period, slightly reducing microbial activity and methane generation efficiency.
Although the study area generally experiences similar seasonal conditions during September, October, and November, slight variations in ambient temperature, rainfall intensity, slurry dilution, and feedstock consistency likely contributed to the observed fluctuations in gas production.
The gradual increase in gas production observed during the first half of each month, followed by peak production around the middle of the month, was associated with progressive stabilization of microbial activity and substrate degradation efficiency within the anaerobic digester. Following daily feeding operations, hydrolytic, acidogenic, acetogenic, and methanogenic microorganisms require a short acclimatization period before reaching optimal metabolic activity. As digestion progresses, organic substrates become more uniformly distributed within the slurry, resulting in enhanced microbial contact and increased methane generation rates. The mid-month peak in biogas production likely reflects the period during which the digester microbial community attained maximum metabolic efficiency under relatively stable operating conditions, including favorable pH, substrate concentration, moisture content, and temperature. During this phase, cumulative degradation of volatile solids and enhanced methanogenic activity resulted in maximum methane generation and gas accumulation.
The subsequent gradual decline in gas production observed toward the end of each month may be attributed to partial depletion of easily biodegradable organic matter within the slurry, reduction in volatile solids concentration, and minor fluctuations in feedstock consistency and moisture content. In addition, routine gas utilization for electricity and heat generation contributed to reductions in stored gas volume within the system. Although daily feeding continued throughout the monitoring period, the digestion dynamics indicate that biogas production rates were strongly influenced by microbial growth cycles and substrate biodegradation kinetics within the fixed-dome digester. The relatively consistent mid-month production peaks observed across September, October, and November therefore suggest stable digester operation and predictable anaerobic digestion performance rather than random fluctuations in gas generation. Despite these fluctuations, the daily gas production remained relatively stable throughout the monitoring period, indicating efficient digester performance and adequate hydraulic retention conditions.
Electricity and heat energy generation
Figure 4 presents the operational biomass WtE plant installed at Makumbi Farm, showing the major system components including the biodigester, gas cleaning unit, CHP engine-generator set, heat recovery unit, electricity distribution lines, and thermal distribution network supplying energy to the local community. The figure presents a schematic and field representation of the cattle-dung-based biomass WtE system installed at Makumbi Farm in Madu, Gomba District, Uganda. The upper section illustrates the physical layout of the operational plant, including the fixed-dome biodigester, gas holder, gas cleaning unit, biogas-powered CHP engine-generator, heat recovery unit, thermal distribution pipelines, and electricity distribution lines supplying nearby households and community facilities. The lower schematic section shows the process flow of livestock waste conversion into biogas, electricity, and useful thermal energy. Cow dung is fed into the anaerobic biodigester, where microbial degradation produces methane-rich biogas. The biogas undergoes cleaning before combustion in the CHP engine-generator to produce electricity and recover thermal energy. Generated electricity is distributed through local mini-grid lines to the surrounding community, while recovered heat is utilized for digester heating, hot water supply, milk pasteurization, cooking, and other agro-processing activities. Digestate generated from the digestion process is collected and reused as organic fertilizer for agricultural applications. The figure demonstrates the integrated operation of the biomass WtE system for decentralized rural electrification and thermal energy supply.
Operational biomass waste-to-energy plant showing major system components and energy distribution network.
Tables 3–5 summarize the electrical and thermal energy generated from daily biogas utilization during September, October, and November 2024, respectively. The CHP system successfully converted biogas into usable electricity and heat with relatively stable operational performance throughout the monitoring period. September recorded the highest energy generation performance. Daily electrical output increased progressively from 574.86 kWh/day on Day 1 to a peak of 673.53 kWh/day on Day 20. Correspondingly, thermal energy recovery increased from 871.00 kWh/day to 1020.50 kWh/day during the same period. The high energy outputs observed during September reflected increased biogas availability and efficient CHP system operation. October demonstrated slightly lower electrical and thermal energy generation, with electrical output ranging from 568.43 to 643.50 kWh/day and heat recovery varying between 861.25 and 975.00 kWh/day. November recorded the lowest outputs among the three months, with electrical generation ranging from 553.41 to 617.76 kWh/day and thermal energy production ranging between 838.50 and 936.00 kWh/day.
Electrical and heat energy generated from daily gas yield (September).
Electrical and heat energy generated from daily gas yield (October).
Electrical and heat energy generated from daily gas yield (November).
The observed reductions in electrical and thermal outputs from September to November directly corresponded with the gradual decline in biogas production during the same period. Nevertheless, the CHP system maintained stable energy conversion efficiency throughout the monitoring period, indicating reliable engine operation and effective heat recovery performance.
The average daily electrical energy supplied to the community during the study period was approximately 600 kWh/day, while average thermal energy recovery was approximately 910 kWh/day. The generated electricity was primarily utilized for household lighting, refrigeration, phone charging, water pumping, milk cooling, and small agro-processing activities. Recovered thermal energy was used for digester temperature stabilization, domestic hot water supply, milk pasteurization, feed preparation, and small-scale agricultural processing activities within the community. The CHP configuration significantly improved overall system efficiency by simultaneously utilizing both electrical and thermal energy generated during biogas combustion.
Figure 5 illustrates the variation in daily electrical energy generation over the three-month monitoring period. The results show that electrical energy production closely followed the observed biogas yield trends, with September exhibiting the highest electricity generation performance and November recording the lowest outputs.
Daily electrical energy production variations.
Figure 6 presents the daily thermal energy recovered from the CHP system. Similar to electrical output, thermal energy generation gradually declined from September to November due to corresponding reductions in biogas availability and methane conversion rates.
Daily heat energy production variations.
Livestock waste availability and biogas potential
The study site was supplied by a herd of 120 cattle, generating an estimated 3960 t yr−1 of fresh dung. Based on an average methane yield of 25 m3 t−1, the annual methane potential was calculated as
Digester performance and volume adequacy
The constructed digester volume of 45 m3 provided an average hydraulic retention time of approximately 35 days, which was sufficient to maintain stable anaerobic digestion throughout the study period. Operational observations showed no evidence of digester acidification, excessive foam formation, gas pressure instability, or microbial process failure. Daily biogas production remained stable throughout the monitoring period, confirming that the selected digester volume was adequate for the available slurry loading rate and organic substrate concentration. The locally adopted insulation system effectively minimized heat losses and maintained relatively stable internal digestion temperatures despite minor outdoor temperature fluctuations. Consequently, no operational shutdowns or major maintenance interruptions were recorded during the study period.
Environmental benefits and greenhouse gas emission reduction
The biogas WtE system generated approximately 55,800 kWh of electricity during the three-month monitoring period. Using a grid emission factor of 0.82 kgCO2/kWh, the avoided carbon dioxide emissions were estimated as 45.8 tCO2 avoided during the study period. Extrapolated annually, the system is capable of offsetting approximately 183 tCO2/year.
In addition to carbon dioxide mitigation, the biodigester system substantially reduced methane emissions associated with uncontrolled decomposition of livestock waste in open dung heaps. Since methane possesses a significantly higher global warming potential than carbon dioxide, methane capture and utilization contributed substantially to the overall environmental performance of the system.
Other environmental benefits observed included a reduction in odor emissions, improved sanitation around cattle sheds, decreased pathogen exposure risks, reduced contamination of nearby water sources, and improved nutrient recycling through agricultural utilization of digestate slurry as organic fertilizer.
Economic performance
The total installed capital cost of the biomass WtE system was estimated at USD 82,000, covering digester construction, CHP equipment, gas cleaning infrastructure, heat recovery systems, and electrical installations. The cost distribution is summarized in Table 6. The CHP unit accounted for the largest share of total investment cost (33.7%), followed by digester construction (26%), reflecting the capital-intensive nature of power generation and anaerobic digestion infrastructure.
Capital investment breakdown for the biogas waste-to-energy system.
CHP: Combined heat and power.
The annual operation and maintenance (O&M) cost was estimated at USD 3444, corresponding to approximately 4.2% of the total capital investment. The breakdown is presented in Table 7. The relatively low operational cost was primarily attributed to the availability of zero-cost cattle dung feedstock, low labor requirements, and simplified system operation.
Annual operation and maintenance cost breakdown.
The LCOE was calculated as approximately 0.061 USD/kWh, which is substantially lower than the typical cost of diesel-based off-grid electricity generation in rural Uganda (0.25–0.40 USD/kWh). This result confirms the strong economic viability of the proposed biomass WtE system for rural electrification applications. Annual net savings of approximately USD 13,600 were achieved through the displacement of diesel fuel consumption and reduced dependence on grid electricity. Based on these savings, the estimated payback period for the project was approximately six years. When environmental externalities were incorporated using a carbon damage cost of USD 50/tCO2, the avoided emissions represented an additional environmental benefit valued at approximately USD 9150/year. Under this scenario, the effective LCOE decreased further to approximately 0.048 USD/kWh, while the estimated payback period reduced to approximately 4.7 years. Overall, the economic analysis demonstrates that cattle-dung-based CHP systems can provide financially sustainable and environmentally beneficial rural electrification solutions under decentralized operating conditions in Uganda.
Discussion
Livestock waste availability and biogas potential in relation to literature
The estimated annual methane potential of 99,000 m3 yr−1 obtained from 120 cattle demonstrates that cattle dung can provide a reliable and continuous energy resource for rural electrification. This finding is consistent with previous studies reporting methane yields of 20–30 m3 t−1 for cattle dung under mesophilic conditions (Hamzah et al., 2023; Tariq et al., 2023). The observed ±8.5% seasonal fluctuation in gas production is comparable to variations reported in tropical and subtropical regions, where ambient temperature and substrate moisture influence microbial activity (Manyi-Loh and Lues, 2023; Osman et al., 2023). Unlike many studies that rely on theoretical yield estimation alone, this work integrates measured daily gas production and seasonal trends, providing a more realistic representation of biogas availability under rural Ugandan conditions. This strengthens the reliability of the resource assessment for practical electrification planning.
Biogas production trends and digester performance
The monthly average biogas yields (272–298 m3 day−1) fall within the range reported for medium-scale farm digesters in developing countries (Gbadeyan et al., 2024; Obileke et al., 2024). The higher output recorded in September aligns with literature indicating optimal biogas production at mesophilic temperatures between 30°C and 37°C (Makamure et al., 2024). The reduced yields in November reflect temperature-related kinetic limitations, a trend also observed by Ikegwuonu et al. (2025). The stable digester operation, absence of acidification, and consistent gas pressure confirm that the selected 520 m3 digester volume and 35-day HRT were appropriate. This is in agreement with design recommendations for cattle-dung-based digesters in tropical climates (Achi et al., 2024). The findings validate that well-sized digesters can maintain operational stability even with seasonal feedstock variability.
Electrical and thermal energy performance compared to similar systems
The system produced 18–19 MWh of electricity per month, with an electrical efficiency of 35%, which aligns closely with efficiencies reported for biogas-fueled CHP units (30–38%) in rural energy applications (Negro et al., 2025). The estimated electrification potential of 85–95 households is comparable to similar studies in East Africa and South Asia, where biogas-based mini-grids have been shown to meet basic household electricity needs reliably (Odoi-Yorke et al., 2024; Robin and Ehimen, 2024). Thermal energy recovery efficiency of 53% is consistent with CHP performance reported by (Negro et al., 2025). However, unlike many studies that neglect heat utilization, this work explicitly demonstrates the practical use of recovered heat for digester temperature control and agro-processing, thereby increasing overall system efficiency. This integrated energy use represents a key strength of the proposed system.
Environmental performance and CO2 mitigation
The annual CO2 emission reduction of approximately 183 tCO2 yr−1 compares favorably with reported values for farm-scale biogas systems displacing grid electricity and diesel generation (Alengebawy et al., 2024; DelaVega-Quintero et al., 2025). In addition to electricity displacement, the avoidance of uncontrolled methane emissions from dung heaps provides a substantial climate benefit, given methane's high global warming potential, a mitigation effect consistently emphasized in recent biogas literature (Alengebawy et al., 2024). Compared to studies that consider only electricity-related emissions, this work accounts for both fossil fuel displacement and methane capture, providing a more comprehensive environmental assessment. The additional benefits related to odor reduction, pathogen control, and nutrient recycling through digestate use are consistent with findings reported by Ankathi et al. (2024).
Economic performance in comparison with rural energy alternatives
The calculated LCOE of 0.064 USD kWh−1 is significantly lower than typical costs for diesel-based rural generation and competitive with hybrid renewable systems studied in similar contexts, where grid-connected biogas/PV hybrids achieved electricity costs near 0.0688 USD/kWh and outperformed conventional scenarios in economic evaluations (Akarsu and Demir, 2024; IRENA, 2025). The estimated six-year payback period aligns with recent analyses of combined biogas and solar systems for rural electrification, which reported payback periods in the 6.1–6.6 years range depending on system configuration and operating assumptions (Habib et al., 2025). When environmental externalities such as avoided fossil fuel costs and emissions credits, were internalized, effective LCOEs decreased further and shortened investment payback, underscoring how monetizing climate benefits enhances the economic case for biogas systems (Akarsu and Demir, 2024; Pilarski, 2025). These findings reinforce that biogas systems can be economically competitive with diesel-based and hybrid alternatives in rural energy portfolios when both technical and environmental values are recognized.
Policy implications
The findings of this study have important implications for rural energy, agricultural, and climate policies in Uganda and similar livestock-dominated regions in Sub-Saharan Africa. The demonstrated technical reliability and economic competitiveness of cattle-dung-based biogas systems indicate that decentralized bioenergy can play a significant role in expanding rural electrification where grid extension remains costly or impractical.
First, the low levelized cost of electricity and short payback period suggest that biogas-based mini-grids should be explicitly integrated into national rural electrification strategies. Policymakers could support this integration by providing targeted capital subsidies, low-interest loans, or results-based financing mechanisms to reduce upfront investment barriers for farmers’ cooperatives and private developers. Second, the substantial reduction in greenhouse gas emissions highlights the need to recognize biogas systems within national climate mitigation frameworks, including Nationally Determined Contributions. Monetizing carbon benefits through carbon credit schemes or climate finance instruments would further improve project bankability and accelerate adoption.
Third, linking waste management policy with energy planning can enhance resource efficiency. Regulations that encourage the productive use of livestock waste, rather than uncontrolled disposal, can simultaneously address environmental pollution, public health concerns, and energy shortages. Support for digestate utilization as an organic fertilizer can further strengthen circular economy outcomes in rural communities. Finally, institutional capacity building and technical training are critical to long-term sustainability. Policies that promote local skills development for biogas plant operation, maintenance, and monitoring can reduce system downtime and foster community ownership. Integrating biogas technologies into agricultural extension programs would help scale deployment and ensure alignment with local farming practices.
Overall, the results indicate that cattle-dung-based WtE systems offer a multibenefit policy pathway by advancing rural electrification, climate mitigation, and sustainable agricultural development. Embedding such systems within coherent energy, agriculture, and climate policies can significantly enhance their contribution to inclusive and resilient rural development.
Recommendations
Based on the technical, economic, and environmental outcomes of this study, the following actionable recommendations are proposed to facilitate the deployment and scaling of cattle-dung-based WtE systems for rural electrification.
Integrate biogas systems into rural electrification programs: National and regional electrification agencies should formally recognize medium-scale biogas-based CHP systems as eligible technologies within rural electrification and mini-grid programs. Standardized design capacities linked to livestock numbers should be developed to simplify project approval and replication in livestock-dominated communities. Reduce upfront investment barriers through targeted financial instruments: Given the capital-intensive nature of biogas systems, governments and development partners should provide capital subsidies, concessional loans, or grant-loan hybrids targeted at farmer cooperatives and local enterprises. Results-based financing tied to verified electricity generation and methane capture can further improve project bankability. Monetize environmental benefits through carbon finance mechanisms: The demonstrated CO2 emission reductions justify the inclusion of biogas projects in voluntary or compliance carbon markets. Policymakers should streamline procedures for registering small-scale biogas projects under carbon credit schemes to enable revenue generation from avoided emissions. Promote integrated heat utilization to maximize system efficiency: Project developers should be encouraged to design biogas plants with explicit heat recovery applications, such as digester temperature control, milk processing, and agro-processing. Incentives for CHP utilization would significantly improve overall energy efficiency and economic returns. Link biogas deployment with agricultural extension services: Biogas systems should be integrated into agricultural and livestock extension programs to promote proper dung collection, digestate utilization as organic fertilizer, and best practices for feedstock management. This linkage supports circular economy objectives and improves farm productivity. Establish monitoring and performance benchmarks: Regulatory agencies should develop performance indicators for biogas-based rural electrification projects, including energy output, system uptime, and emissions reduction. Continuous monitoring will support evidence-based policy adjustments and ensure long-term system reliability.
Limitations of the study
Despite the robust technical, economic, and environmental assessment presented, several limitations of this study should be acknowledged. First, the analysis is based on data from a single study site in Madu, Uganda, which may limit the direct generalizability of the results to regions with different climatic conditions, livestock management practices, or feedstock characteristics. Variations in ambient temperature, dung composition, and herd management could influence biogas yield and system performance.
Second, system performance was evaluated over a three-month monitoring period. Although seasonal variability was partially accounted for, long-term operational challenges such as digester aging, equipment degradation, and changes in feedstock availability were not fully captured. Extended monitoring would provide a more comprehensive assessment of year-round performance and system reliability. Third, the economic analysis did not explicitly account for potential variations in capital costs, financing conditions, or policy incentives over time. Exchange rate volatility and changes in fuel or electricity tariffs could alter project economics, particularly in rural and developing-country contexts.
Finally, the environmental assessment focused primarily on CO2 emission reductions from displaced grid electricity and avoided methane emissions. Other life-cycle impacts, such as embodied emissions from construction materials, transport, and equipment manufacturing, were not considered and may slightly reduce the net environmental benefits. These limitations provide a basis for future research to expand the temporal scope, geographic coverage, and life-cycle depth of biomass WtE assessments.
Conclusion
This study evaluated the technical, economic, and environmental feasibility of converting cattle dung into useful energy for rural electrification through a biomass WtE system in Madu, Uganda. The results demonstrate that locally available livestock waste can reliably sustain continuous biogas production and decentralized electricity generation under rural operating conditions. The assessed system, supported by a herd of 120 cattle, exhibited stable digester performance and adequate hydraulic retention time, confirming the suitability of the selected digester volume and operating parameters. Monthly electricity generation of 18–19 MWh, alongside substantial thermal energy recovery, indicates that the system can meet the energy needs of 85–95 rural households while simultaneously supplying heat for on-site and agro-processing applications.
From an economic perspective, the low levelized cost of electricity and a simple payback period of approximately six years highlight strong competitiveness relative to diesel-based rural power generation. When environmental externalities are internalized, economic performance further improves, reinforcing the attractiveness of biogas systems as long-term rural energy solutions. The environmental assessment confirms significant climate mitigation benefits, with annual CO2 emission reductions of approximately 183 tCO2, alongside improved waste management, odor reduction, and nutrient recycling through digestate use. These co-benefits strengthen the role of biogas technology within integrated energy–agriculture–climate frameworks.
In conclusion, this study provides empirical evidence that cattle-dung-based WtE systems represent a technically viable, economically sound, and environmentally sustainable pathway for rural electrification in livestock-rich regions. The findings support the inclusion of decentralized biogas technologies in national energy planning and climate mitigation strategies aimed at achieving inclusive and resilient rural development.
Footnotes
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.