Biosolids Fundamentals
The 40 CFR 503 regulatory framework — pathogen reduction, vector attraction reduction, and pollutant limits.
Class A vs Class B Pathogen Reduction
Class A biosolids have detectable pathogen levels below regulatory thresholds and have broader use flexibility; Class B biosolids have restrictions on land application.
Pathogen Reduction Alternatives
EPA provides multiple specific alternatives within each class for demonstrating pathogen reduction — operators should know which their plant uses.
Vector Attraction Reduction
Vector attraction reduction (VAR) prevents insects and rodents from being attracted to the biosolids, a separate regulatory requirement from pathogen reduction.
Pollutant Limits (40 CFR 503 Table)
Pollutant limits for metals (cadmium, copper, lead, mercury, molybdenum, nickel, selenium, zinc) are the third pillar of biosolids regulation.
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