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What are Biosolids?

Biosolids are nutrient-rich natural by-products of wastewater treatment. They are highly processed and tested to ensure their safety and have several beneficial uses.

There are two classes of biosolids suitable for agricultural applications: Class A which contain less than detectable levels of pathogens, and Class, B which contain low levels of pathogens and are also safe to use in land application. Strict regulatory safeguards and rigorous treatment and management practices are used with both type A and B biosolids. Sunlight, drying and other natural processes cause pathogens to die-off rapidly when applied to soil. Federal and state standards for nine classes of pollutants must be met for land applied biosolids. Almost all biosolids in California meet the risk-based “high quality” limits for all pollutants. Strict pretreatment requirements were installed in the 1980’s which regulate what industries can discharge to wastewater treatment plants.

California data for 2013 shows that a total of 723,000 dry metric tons of biosolids were used as follows:

  • Alternative use (alternative fuel, deep well injection, incineration, etc) - 3%,
  • Surface disposal - 3%
  • Other - 4%
  • Landfill disposal - 13%
  • Landfill alternative daily or final cover - 19%
  • Class B soil amendment/fertilizer - 20%
  • Class A soil amendment/fertilizer - 36%
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