The U.S. dairy industry is a major contributor to agricultural greenhouse gas emissions, with manure storage and handling representing a significant source of methane. Anaerobic digestion - a biological process in which microorganisms break down biodegradable organic matter - of cow manure has been widely studied as a strategy to mitigate manure-related emissions while producing renewable energy. That energy comes in the form of biogas that can be used to generate electricity or make renewable natural gas. But adoption of the strategy has been constrained by costs. Now, a team led by researchers at Penn State may have found a way to make the process profitable.
The researchers, who recently published their findings in Biomass Conversion and Biorefinery, reported that mixing manure with plant biomass can increase methane production - which is necessary for biogas - and improve the economic feasibility of farm-scale anaerobic digestion. They found that winter rye, a tough, cold-hardy cereal grain planted in the fall to protect and enrich the soil over the winter months, is particularly useful for this application.
But anaerobic digester projects remain highly dependent on financial incentives, so they carry substantial investment risk for farmers, noted study senior author Juliana Vasco-Correa, assistant professor of agricultural and biological engineering in Penn State's College of Agricultural Sciences. The problem, she explained, is that building and operating a digester is expensive, while the revenue from selling electricity or gas may not be high enough.
"Anaerobic digestion can help dairy farms manage manure while producing renewable energy, but many projects struggle economically," she said. "A key question is whether adding crop residues or dedicated biomass to manure can make these systems more financially viable. The results of our study demonstrate that co-digestion with plant material can enhance the economic performance of manure-based anaerobic digestion."
