Incentivizing methane production
Study shows manure digesters not key to solving CAFO pollution
MADISON – New research conducted by environmental groups argues that manure digesters, seen as a solution to pollution from large-scale livestock farms, do more harm than good because of other ways they impact the environment.
The Friends of the Earth United States and the Socially Responsible Agriculture Program, using state data and information from permits of Kewaunee County concentrated animal feeding operations, or CAFOs, found that manure digesters may be a good way to collect methane from animal waste but aren’t the solution to reducing pollution altogether.
Methane is considered a greenhouse gas because it traps infrared radiation in the atmosphere and raises air temperatures. Livestock farming represents about 30% of the methane emissions produced from human activities in the U.S., with beef and dairy cattle as the major contributors, according to the University of Wisconsin-Madison Extension.
Anaerobic digesters are becoming more popular with large dairy operations in Wisconsin because of their ability to break down animal waste and leave behind biogases and a solid byproduct that is similar to fertilizer.
The biogases can then be burned for heat or electricity, according to the study, or processed and injected into natural gas pipelines or even used as vehicle fuel.
But while the digesters are being heralded as a breakthrough solution, the technology is also encouraging large farms to grow even larger in order to create more gas, said Molly Armus, the animal agriculture program manager for Friends of the Earth.
“We see in this report on Kewaunee County that farms with digesters increase their herd size,” she said. “And part of that is if you’re being rewarded for producing biogas, you want to produce as much biogas as possible, and the only way to do that is to produce as much manure as possible.
“By incentivizing this, it undermines any methane reduction potential that these systems could have.”
According to the study, the number of dairy cows has increased by 88% in the county, while the number of dairy farms has decreased by 82% due to consolidation or closures.
In addition to the growing number of cows, the study raises concerns over the impact of the fertilizer-like byproduct of digesters being over-applied to land in a county plagued with water contamination in private wells.
“Kewaunee County’s systemic pollution will not be resolved through manure biogas production,” the study said.
Kewaunee County, in northeastern Wisconsin, is home to 16 large-scale farms and has been struggling with agricultural pollution for years after testing showed contamination in residents’ private drinking wells.
The fields on which many large-scale farmers typically spread manure are susceptible to pollution due to the short distance between the topsoil and the water table below, and the prevalence of karst geology – fractures in the bedrock that allow liquid manure to seep into the water table.