FRANKFORT, Ky. – A new collaborative study by Kentucky State University (KSU) is exploring how dairy manure can produce more renewable methane.

Liang Yu, assistant professor of biological and agricultural engineering, conducted the study with Washington State University (WSU) collaborators Meghana Mendon, a WSU doctoral student, and Shulin Chen, WSU professor of biological systems.

According to the researchers, dairy manure is a waste-management challenge for producers, but it also holds renewable energy potential.  

At the center of the study is anaerobic digestion, where microorganisms break down organic material, such as manure, in a sealed environment where oxygen is not present. Researchers said that process produces biogas, an energy-rich gas that contains methane. When captured and used properly, methane from biogas can become a renewable energy source instead of being released as waste.

The research examined a three-stage process: dairy manure first moves through conventional anaerobic digestion. The remaining fibrous material is then treated with heat and water through hydrothermal treatment, and finally, the material goes through a second digestion phase.

Across all tested conditions, he said the integrated approach increased methane production. The strongest result came when digestate solids were heated to 180 degrees Celsius for one hour, producing a 52 percent higher methane yield. The process also improved the breakdown of tough plant-based fibers and reduced solids, he added.

Digestate solids are the nutrient-rich, fibrous solid material separated from the liquid portion of anaerobic digestate, which is the residue left after breaking down organic waste for biogas production, according to the EPA.

Yu told Farm World the idea for this study emerged from his long term work with a student on developing more efficient and effective anaerobic digestion technologies over the past decade.

“About four years ago, when this student began her Ph.D. program, we identified an opportunity to integrate improved anaerobic digestion approaches into existing mesophilic anaerobic digesters used on dairy farms,” he said. 

“Our goal was to enhance the degradation of dairy manure fibers and increase biogas production, which ultimately shaped the direction of the research,” Yu said.

He said livestock manure presents a major opportunity for renewable energy production when treated efficiently. “This study demonstrates that targeted hydrothermal treatment can unlock more usable energy from agricultural waste, while remaining practical for real-world farm operations.”

One of the study’s key findings is not simply that more methane can be produced, he added, but that the process can be designed to avoid a major drawback of many pretreatment technologies: the need for substantial outside energy.

The researchers modeled a closed-loop system that recovers and reuses heat generated during processing. That configuration allowed the enhanced system to remain thermally self-sustaining, while producing more renewable methane.

According to KSU, a closed-loop system in anaerobic digestion refers to an integrated waste-to-energy model that treats agricultural waste, specifically livestock manure, while recovering and reusing heat to remain thermally self-sustaining. This approach maximizes methane production for renewable energy, while minimizing reliance on outside energy sources, turning waste management into a sustainable resource-recovery process.

For producers, Yu said, the findings point toward a practical possibility: manure management systems that reduce waste concerns, strengthen environmental stewardship, and create additional value through renewable natural gas production.

“This work supports the development of more sustainable agricultural systems,” he said. “By improving how manure is converted into energy, we can help producers strengthen both environmental stewardship and economic resilience.”

Unlike other university studies that use external energy to pretreat all raw materials to boost biogas production, he said, “Our approach targets only a small portion of the digestate after anaerobic digestion.”

The EPA said digestate is the nutrient-rich, solid-liquid residue produced from anaerobic digestion of organic materials (e.g., manure, food waste). It acts as an organic fertilizer, rich in nitrogen, phosphorus, and potassium, improving soil health, and enhancing plant growth: “This fraction no longer contains easily degradable organic matter, as those components have already been consumed by microorganisms in the digester,” Yu said.

By treating only this remaining material, he said, system performance can be improved with significantly lower energy input: “The heat required for this treatment can be fully offset by the thermal energy already needed to operate the mesophilic anaerobic digester, so no additional external energy is required. This makes our method more energy efficient and more practical for farm scale operations.”