The science behind the experiment is a well-orchestrated sequence of microbial chemistry. Anaerobic digestion relies on communities of bacteria and archaea that break down organic matter without oxygen, passing carbon through four successive stages: hydrolysis, acidogenesis, acetogenesis and finally methanogenesis. In this study, dried poultry manure was collected from two prominent farms in Lafia and from the depths of their manure disposal sources, then thoroughly stirred to create a homogeneous mixture. Because the raw manure contained about 20 percent solids, the researchers diluted it with water at a 1:2 ratio, producing an input slurry with 12 percent total volatile solids by weight. The digester was maintained at mesophilic conditions, the temperature window between roughly 20 and 45 degrees Celsius that laboratory studies have shown to be most favorable for the methane-producing microbes at the heart of the process.

The startup phase proved to be a study in microbial patience. For the first 29 days, no gas was produced at all. During this period, volatile fatty acid concentrations rose as hydrolysis, acidogenesis and acetogenesis dominated the reactor, driving the pH below 7 for the first 11 days of operation. Methanogenic archaea are famously sensitive to acidity, and the low pH initially suppressed them. Only after the pH began to recover and alkalinity stabilized, between August 2 and August 14, did conditions become hospitable for methanogenesis. Chemical analyses confirmed the process remained stable throughout: the ratio of volatile fatty acids to alkalinity stayed between 0.05 and 0.11, well below the threshold values of 0.1 to 0.7 reported in the literature, indicating no risk of acidification and a healthy balance between buffering capacity and acid production.

The feedstock itself carried encouraging chemistry. The poultry waste contained a high concentration of total volatile solids at 84.11 percent, reflecting its rich organic content, and the carbon-to-nitrogen ratio of the solid chicken manure measured 29.38, within the ideal range for biological treatment. The slurry’s C:N ratio of 27.11 and the sludge’s ratio of 11.74 further indicated that sufficient nutrients were available to sustain a steady digestion process and produce high-quality digestate fertilizer. Chemical oxygen demand values ranged from 2 to 70 grams per liter, and total Kjeldahl nitrogen from 0.1 to 0.5 grams per liter, figures consistent with those reported in comparable studies worldwide.

When biogas finally flowed, it came in modest but meaningful quantities. The digester produced an average of 0.3 liters per day, accumulating a total yield of 4.5 liters over the operating period. The highest daily output, 0.65 liters per gram of chemical oxygen demand, coincided with digester temperatures of 43 to 45 degrees Celsius. Conversely, when temperatures fell to 26 or 27 degrees Celsius, production dropped to just 0.1 liters. The relationship between heat and gas output was strikingly direct: even minor variations in temperature visibly shifted the rate of methane production, confirming that temperature is among the most powerful levers controlling anaerobic digestion performance.

It was here that the study delivered its most novel contribution. As August rainfall drove ambient temperatures down, the researchers connected a solar water heating system to the digester, circulating warm water through a U-shaped pipe inside the reactor to stabilize the temperature. The effect was dramatic. On sunny days, the solar-thermal system raised the average digester temperature by 35 percent and increased biogas production by 85 percent compared with rainy days. The mechanism is straightforward: stable, optimal temperatures boost enzymatic activity and metabolic rates across the microbial consortium, particularly the methanogens, accelerating the conversion of organic acids into methane and carbon dioxide. In a region with abundant sunshine but unreliable energy infrastructure, pairing digesters with solar heating could be a game-changing design principle.

The quality of the gas offered its own confirmation of success. On August 19, the researchers tested the biogas by attempting to burn it; it failed at first, but the following day it ignited with a clean blue flame, a classic indicator of high methane purity and efficient combustion. A blue flame in anaerobic digestion signals that the process has stabilized, with methane typically comprising between 55 and 65 percent of the gas and carbon dioxide between 30 and 45 percent, along with trace amounts of hydrogen sulfide and water vapor. Had carbon dioxide levels risen beyond about 50 percent, the flame would have shifted toward yellow, signaling a lower energy content.

Yet the study is equally candid about its limitations. The biogas productivity rate, ranging from zero to 0.002 liters per liter per day, was low, reflecting the small scale of the reactor, the short retention time of 54 days, the absence of co-substrates, and the lack of gas purification beyond a simple steel wool scrubber designed to strip hydrogen sulfide. The researchers recommend co-digesting poultry droppings with crop residues such as wheat straw, corn stalks and grain husks, and maintaining digester temperature throughout the run with solar thermal water heaters or boilers. These optimizations could substantially raise yields and move the technology closer to the economic thresholds at which farm-scale adoption becomes compelling.

The broader implications reach well beyond a single digester in Lafia. Globally, more than 2.24 billion tonnes of municipal solid waste were generated in 2020, and organic waste decomposing in landfills accounts for roughly 30 to 40 percent of methane emissions, a greenhouse gas with 25 times the warming potential of carbon dioxide over a century. Meanwhile, fossil fuels drive about 75.7 percent of global greenhouse gas emissions, and energy price volatility, with Brent crude averaging around 81 dollars per barrel in 2024, exposes developing economies to punishing swings. Biogas programs have already scaled in India since the 1940s, China, and much of Europe, and researchers estimate that reactor-based biogas production could meet up to 30 percent of energy demand in industrialized and emerging cities. For Nigeria, which has committed to net-zero emissions by 2060 under its long-term climate vision, the study demonstrates that small-scale anaerobic digestion of poultry manure, especially when supported by solar-thermal temperature stabilization, is a viable strategy for waste management and bioenergy recovery. The authors argue that scaling such agricultural waste-to-energy models, supported by co-digestion strategies, improved collection systems, biogas incentives and public-private partnerships, could deliver the reliable and affordable green energy services needed to meet Sustainable Development Goal 7 by 2030, while simultaneously curbing pollution, improving soil health through nutrient-rich digestate, and opening new markets in sustainable agriculture and organic fertilizer manufacturing.

Subject of Research: Pilot-scale anaerobic digestion of poultry droppings for biogas production using continuous stirred tank reactor technology with solar-thermal temperature optimization in Nigerian agriculture

Article Title: Anaerobic digestion of poultry droppings for biogas production: a pilot study of renewable energy technology in the agricultural sector

Article References: Ayua, T. J., Ambrose, I. S., & Omaku, D. S. (2026). Anaerobic digestion of poultry droppings for biogas production: a pilot study of renewable energy technology in the agricultural sector. BMC Environmental Science, 3(1), Article 7. https://doi.org/10.1186/s44329-026-00048-8

Image Credits: AI Generated

DOI: 10.1186/s44329-026-00048-8

Keywords: biogas, anaerobic digestion, poultry manure, renewable energy, continuous stirred tank reactor, solar heating, waste management, methane, Nigeria, circular economy, sustainable development, agricultural waste