The reliance on fossil fuels for energy is projected to continue until 2050, driven by a lack of reliable renewable energy systems. This contributes to increased carbon emissions. Biogas, with its 55-65% methane content, offers a potential negative emission path for methane control and fossil fuel replacement. It also presents a comparable energy-return-on-investment ratio to fossil gas when ecological costs are considered. To simultaneously improve clean energy access and address climate change, efficient biogas production and utilization systems require widespread application. This is crucial for substantially increasing biogas usage while reducing methane emissions from organic matter management sources such as anaerobic lagoons for manure treatment. Despite biogas's history in cooking, heating, and power generation, its impact in rural developing areas remains limited due to intermittent supply and incomplete utilization. In China, approximately 800 million people, mostly in rural areas, lack access to natural gas or biogas. Extensive natural gas infrastructure development is impractical due to potential peak-period shortages and energy security risks. Therefore, biogas is considered a feasible technology to address this energy gap, given China's significant methane production potential from manure and crop straw (73.6 billion m³ yr⁻¹). High-quality biogas systems are recognized as the most efficient strategy to reduce methane emissions from organic waste treatment, potentially achieving a 6.4 × 10⁷ tons CO₂-eq yr⁻¹ reduction in China through manure treatment alone. The most efficient biogas system and its deployment in developing areas are key research questions. European biogas utilization primarily involves Combined Heat and Power (CHP) units or biomethane upgrading, with real-time energy transmission to grids. However, these models pose challenges in developing areas due to economic feasibility and operational requirements, including inadequate subsidies and technical support. On-site generation and direct supply to consumers offer significant advantages in terms of supply chain efficiency and co-benefits of sustainable energy and greenhouse gas emission mitigation, particularly with on-demand supply and minimal methane leakage. A community biogas production and distribution system (CBPD) is considered the most feasible choice for providing an adjustable and flexible biogas supply in rural areas. To maximize co-benefits, the CBPD aims for a consumption-to-production ratio (CPR) near 1, maximizing methane utilization and minimizing atmospheric release.

Existing literature highlights the need for reliable renewable energy systems to replace fossil fuels and mitigate climate change. Studies have shown the potential of biogas as a negative emission technology and its comparable energy return on investment to fossil gas. Research also emphasizes the importance of efficient biogas production and utilization systems in reducing methane emissions from organic waste, particularly manure. However, there's a gap in addressing the challenges of intermittent renewable energy supply and incomplete biogas utilization in rural developing areas. The literature demonstrates the success of biogas in developed countries using CHP units and biomethane upgrading, but these models are not easily transferable to developing countries due to economic and operational constraints. This study addresses these gaps by proposing an optimized CBPD system tailored to rural communities.

The study proposes an upgraded CBPD system with a focus on optimizing biogas flow to achieve a CPR of approximately 1. This optimization involves four analytical steps: (1) Data-driven identification of the biogas demand rate, considering both routine and intermittent community activities. The authors included various potential biogas customers, including households, restaurants, and local agricultural factors. (2) Quantification of biogas production capacity based on fermentation temperature and organic load rate using mathematical models or improved equations derived from operational data fitting. Sensitivity analyses refined the biogas production curve to account for factors like feeding intervals. (3) Determination of biogas storage capacity to manage supply-demand mismatches. This involves estimates of biogas consumption, precise feeding process controls, and margin designs to achieve a CPR of 1, accounting for variations in fermentation temperatures and biogas usage. (4) Definition of a management scheme to coordinate biogas flows on both the plant and user sides, employing an active adjusting mechanism based on data-driven analysis. On the user side, incentives or regulatory measures may influence biogas usage. Five actual CBPDs in Chinese rural areas were examined to investigate current operations, supplying biogas directly to rural households. The biogas production capacities were designed based on the number of customers (1 m³ biogas per customer per day). The study analyzed the biogas generation regularity, consumption characteristics, and carbon mitigation potential under different operational scenarios. The analysis included hourly biogas production (showing a 1.5-day lag after feeding) and consumption (following a daily repeating cycle) data to quantify the current methane loss (assumed to be 32.5%). Sensitivity analyses investigated storage capacity requirements to achieve CPR = 1 through various strategies (increased consumption or reduced production). The impact of climate conditions on CBPD performance was assessed using data from 10 cities representing varying temperatures and solar radiation intensities, considering the effect of ambient temperature on biogas production and heating requirements. Calculations of GHG emissions considered both methane emission reduction from waste management and fossil fuel replacement. National deployment feasibility in China was evaluated based on manure availability, biogas demand, and the potential contribution to meeting China's 1.5 °C target. This involved calculating the rate of methane production potential from manure and domestic biogas demand (RPD) at the provincial level. Detailed methods for biogas flow, biogas storage capacity, data analysis of CBPD, GHG emission calculations, RPD calculations and methane mitigation calculations were provided. Specific equations for mass balance, biogas consumption rate, biogas storage capacity, GHG emissions, and RPD were presented. The data cleaning process for the CBPD data analysis involved removing outliers and inconsistencies based on established criteria. The GHG emission calculations accounted for utilizable biogas and methane leakage. The methane mitigation calculations for manure management optimization considered the methane conversion factor of the biogas system. The study also provides detailed information on the data sources and instruments used in the measurements.

The study found that achieving a CPR of approximately 1 in CBPD systems is crucial for maximizing carbon mitigation and energy benefits. Optimization of biogas flow through strategic adjustments in both biogas production and consumption rates is essential for minimizing methane losses. The analysis of five existing CBPDs in China revealed a significant methane loss of 32.5%, highlighting the need for improved system design and operation. Optimal storage capacity and precisely timed feeding were identified as key factors in reducing this loss and achieving CPR = 1. Sensitivity analyses showed that a 1.79 times increase in biogas storage capacity enhances system robustness. A coordinated scenario, incorporating a fluctuation adjustment threshold, further improves system performance. Analysis of the impact of climate showed that even in cold climates, the upgraded CBPD offers significant carbon mitigation advantages over conventional CHP systems. National deployment of the upgraded CBPD in China could potentially eliminate 62.4% of rural inhabitants' carbon emissions and contribute 3.77% towards the country's 1.5 °C warming target. This contribution arises from both methane emission reduction from optimized manure management and fossil fuel substitution. The study highlighted the significant potential of biogas utilization to meet the growing energy demands in rural areas and reverse the trend of increasing carbon emissions. Current rural biogas usage only accounts for 25.4% of manure's methane production potential, indicating significant room for improvement through increased biogas consumption in various applications.

The findings address the research question by demonstrating the feasibility and effectiveness of an upgraded CBPD system in achieving significant carbon mitigation and improved energy access in rural areas. The study's significance lies in providing a practical and scalable solution for addressing energy poverty and climate change in developing economies. The results highlight the importance of a systems approach, integrating both production and consumption aspects, for maximizing the environmental and social benefits of biogas technology. The findings challenge the conventional approach of centralized biogas utilization, emphasizing the advantages of on-site generation and direct supply for enhancing efficiency and reducing emissions. The study’s relevance to the field extends to policy implications, advocating for targeted subsidies and regulatory measures to support the widespread adoption of the proposed CBPD system.

This study presents an upgraded CBPD system design that effectively addresses the challenges of biogas supply-demand mismatch in rural communities. By achieving a CPR of nearly 1, this system maximizes both energy production and climate change mitigation benefits. National deployment in China offers considerable potential for reducing carbon emissions and contributing to the country's climate goals. Future research should focus on refining regional-specific manure collection strategies, optimizing biogas storage and operational parameters, and investigating the integration of the upgraded CBPD with other renewable energy systems.

The RPD analysis was conducted at the provincial level, potentially overlooking variations at smaller regional scales. The assumed methane conversion factors for manure management may not reflect the full range of real-world scenarios. The study's focus on China may limit the direct applicability of findings to other contexts with different socio-economic and environmental conditions. Future studies should investigate these limitations to further enhance the generalizability and robustness of the findings.