Using anaerobic digesters to treat cow manure is rightfully considered an eco-friendly farming technique. The technology uses bacteria to break down organic matter in the manure before farmers apply it to their fields as fertilizer. The process helps reduce the amount of eutrophication-causing nutrients that end up in waterways. It also generates biogas, a renewable energy source that can be used to power the farm, reducing its carbon footprint.

But a study published recently in the journal Science of the Total Environment, revealed a troubling and little-known effect of this technology. Researchers from the University at Buffalo found that digesters make the processed manure even more estrogenic than the raw manure. That’s bad news, says co-author Diana Aga, if the processed manure is spread near water bodies. These estrogens act as endocrine disruptors, chemicals which, even at very low levels, have been shown to affect the reproductive organs of fish.

In the study, researchers collected raw manure samples from a 2,200-cow dairy farm in western New York and at two points in the system used to treat it. They used mass spectrometry and a Yeast Estrogen Assay to conduct the chemical and biological analyses, respectively. The chemical analysis found the same amount of total estrogens in the processed manure. But the biological analysis found the increased estrogen potential. That’s because during the processing of the manure, a less-harmful form of estrogen was converted into a more estrogenic form, increasing the overall potential to act as a hormone disruptor in fish, Aga says.

The highest estrogen concentration researchers found was 7,000 nanograms/liter, which even when diluted a thousandfold in water, is high enough to affect fish, Aga says. As she points out, digesters are about to become a lot more common, with the USDA promoting the construction of 500 plants over the next decade as part of its climate-smart agriculture initiative.

The good news, however, is that unless manure is spread on a sloping area close to a body of water, the estrogen won’t get into the water, as it remains on the surface. It is also good news, says Aga, that we now know that digesters need an upgrade.

“Estrogen was an issue that was never addressed when thinking about improving the digestion process, there was more interest in the issue of biogas production,” says Aga. “The study has served as motivation to think about how to improve the digestion process to treat this chemical.”

Indeed, that is precisely what Aga will be researching next as part of a new, USDA-funded project. — Catherine Elton | 18 February 2016

Source: Katia Noguera-Oviedo and Diana S. Aga. (2016).Chemical and biological assessment of endocrine disrupting chemicals in a full scale dairy manure anaerobic digester with thermal pretreatment. Science of the Total Environment (550) doi:10.1016/j.scitotenv.2016.01.084

Header image: ©Tim Snell