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What are Biosolids?

Biosolids are nutrient rich natural by-products of wastewater treatment. They are highly processed and analyzed to ensure their safety. Biosolids are generally used in one of four different forms: a rich moist solid, dried pellet, liquid, or compost. Biosolids are typically recycled as a soil amendment, but may also be used as a daily or final cover at landfills. They may also be used as an alternative energy source.

There are two classes of biosolids: 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 regulated pollutants must be met for land applied biosolids. All biosolids in California virtually fall below 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. In 2009, over 665,000 dry tons of biosolids were generated by Californians most of which became Class A biosolids.