Manure Digesters: Not the Climate Solution or Farm Fix They're Claimed To Be

Anaerobic manure digesters, which capture biogas from animal waste, have seen a steady increase in adoption across U.S. livestock operations, significantly driven by federal and state incentives. Proponents tout these digesters as a multi-faceted solution, promising climate, energy, and economic benefits for farms. However, this technology faces strong opposition, with critics arguing that it worsens the climate crisis, entrenches fossil fuel reliance, and exacerbates public health and environmental justice issues already associated with industrial animal agriculture. A recent review aimed to critically assess these conflicting claims by examining evidence across various aspects including pollutant emissions, occupational health, environmental injustice, economics, and climate impact.

The review uncovered a complex reality: while manure digesters can indeed mitigate some immediate problems from industrial animal agriculture, such as reducing odors and certain methane emissions, they simultaneously risk increasing or perpetuating other significant issues like ammonia emissions and nutrient pollution. Crucially, despite being framed as a broad climate solution, these digesters only address a fraction of livestock-related greenhouse gas emissions. Furthermore, the technology may exacerbate or introduce new occupational and community hazards, particularly from flared biogas, and potentially worsen environmental injustices for rural populations already burdened by large-scale farming operations.

A significant finding points to the substantial role of current policies in subsidizing manure digesters, which incentivizes the further expansion of industrial animal agriculture – an industry with documented harms to rural populations. The study concludes that many proponent claims regarding the benefits of digesters were overstated, while opponent concerns were largely validated by the evidence or warranted further investigation. Based on this comprehensive assessment of available evidence, as lead author Wainer notes in the paper, "manure digesters should not be promoted as a solution for manure management and energy production."