Deconstructing the Livestock Manure Digester and Biogas Controversy

Abstract

Purpose of Review
Anaerobic manure digesters are a hotly debated and rapidly expanding technology that extracts biogas from animal manure. We assessed claims by proponents and opponents of the technology by reviewing evidence regarding digesters and pollutant emissions, occupational health, environmental injustice, economics, and climate.

Recent Findings
Manure digesters can mitigate some impacts from industrial animal agriculture, such as odors and methane emissions, while potentially increasing or perpetuating others, such as ammonia emissions and nutrient pollution.

Summary
While promoted as a climate solution, manure digesters only address a fraction of livestock-related greenhouse gas emissions and may exacerbate or introduce new occupational and community hazards, such as from flared biogas. Policies play a large role in subsidizing manure digesters, incentivizing further expansion of industrial animal agriculture—an industry with documented harms to rural populations. In summary, proponent claims in many cases overstated the evidence of actual benefits, while opponent concerns were either validated by the evidence or merit further investigation. Based on the current state of available evidence, manure digesters should not be promoted as a solution for manure management and energy production.

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