Anaerobic digesters are facilities that decompose organic waste, separating biogas from a sludge called “digestate.” Biogas can be used on-site, paired with a facility like a livestock confinement, or processed into purified pipeline-grade biomethane for electricity or transportation. While biogas can be part of a sustainable farm operation, it has many potential shortfalls that must be evaluated carefully to protect the public interest.

On concentrated animal feeding operations (CAFOs), a digester may be a cover on a cesspit. After the methane is captured, CAFO operators spread untreated digestate — which may contain biological hazards like thermotolerant, antibiotic-resistant E. coli bacteria — onto farm fields as “fertilizer.” Digesters fed by sources like municipal food waste may produce digestate that is contaminated by high levels of heavy metals and toxic compounds like PFAS and PFOS, which may then be sold or given away to spread on fields.

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