Class A and Class B Biosolids

Sludge from Waste water treatment can be treated or untreated. Ssludge can be treated to Class A or Class B.

To ensure that biosolids applied to the land do not threaten public health, the U.S. Environmental Protection Agency (EPA) created the 40 CFR Part 503 Rule.  It categorizes biosolids as Class A or B, depending on the level of pathogenic organisms in the material, and describes specific processes to reduce pathogens to these levels. 

The rule also requires “vector attraction reduction” (VAR) – reducing the potential for spreading of infectious disease agents by vectors (i.e., flies, rodents and birds) – and spells out specific management practices, monitoring frequencies, record keeping and reporting requirements.  Incineration of biosolids is also covered in the regulation.

Class A Biosolids

Class A biosolids contain minute levels of pathogens.  To achieve Class A certification, biosolids must undergo heating, composting, digestion or increased pH that reduces pathogens to below detectable levels.  Some treatment processes change the composition of the biosolids to a pellet or granular substance, which can be used as a commercial fertilizer.  Once these goals are achieved, Class A biosolids can be land applied without any pathogen-related restrictions at the site.  Class A biosolids can be bagged and marketed to the public for application to lawns and gardens.

Class B Biosolids

Class B biosolids have less stringent standards for treatment and contain small but compliant amounts of bacteria.  Class B requirements ensure that pathogens in biosolids have been reduced to levels that protect public health and the environment and include certain restrictions for crop harvesting, grazing animals and public contact for all forms of Class B biosolids.  As is true of their Class A counterpart, Class B biosolids are treated in a wastewater treatment facility and undergo heating, composting, digestion or increased pH processes before leaving the plant.  This semi-solid material can receive further treatment when exposed to the natural environment as a fertilizer, where heat, wind and soil microbes naturally stabilize the biosolids.

The biosolids rule spells out specific treatment processes and treatment conditions that must be met for both A or B classifications. Click here to read about Class A Biosolids Technologies. Click here to read about Class A Biosolids Technologies.



Compiled by Rami E. Kremesti M.Sc.