Scientists Find Mixing is Key to Turning Manure into Biogas

Researchers have taken another step toward turning animal waste into biogas on a large scale.

Farmers have long called the odor of farm waste "the smell of money" in hopes of converting it into a practical energy supply. Animal waste can produce methane, which can be used directly for energy or converted to either methanol or a mix of hydrogen and carbon monoxide. This synthetic mix can then be converted to clean fuels.

In the new study, led by Muthanna Al-Dahhan of Washington University, researchers have found that the manure must be thoroughly mixed when being treated in large reactors called anaerobic digesters. In anaerobic digesters, bacteria is used to break down organic matter without oxygen. Lack of adequate mixing may be one of the main reasons why more than 75% of the 100 anaerobic digester facilities in the US have failed.

As Al-Dahhan explained, turning waste into energy could have a double benefit of minimizing the amount of toxic methane that enters the atmosphere. Methane is a greenhouse gas considered 22 times worse than carbon dioxide.

"Each year livestock operations produce 1.8 billion tons of cattle manure," Al-Dahhan said. "If it sits in fields, the methane from the manure is released into the atmosphere, or it can cause ground water contamination, dust or ammonia leaching, not to mention bad odors. Treating manure by anaerobic digestion gets rid of the environmental threats and produces bioenergy at the same time. That has been our vision."

The final goal, Al-Dahhan says, is to both scale up and simplify the conversion process in order to develop a system that farmers can use on-site for bioenergy production and farm waste management.