Biosolids Frequently Asked Questions
- How are biosolids produced?
- How are biosolids used?
- Do biosolids smell?
- Are there pathogens in biosolids?
- Are there metals in biosolids?
- Are biosolids safe to use?
- How do biosolids affect groundwater and surface water?
Solids produced from the wastewater treatment process are heated to a high temperature for an extended period of time in “digesters,” to reduce the disease-causing organisms and break down the organic matter. The material from the digesters is called biosolids. After removing the excess water in the biosolids, they look and feel very much like soil. For more information on the wastewater treatment process, see our online tour.
The biosolids produced by EBMUD are used as a soil amendment on farms growing non-edible crops. Biosolids promote plant growth through improving soil properties, supplying nutrients, and replenishing soil organic matter.
EBMUD biosolids are also used as alternative daily cover at landfills to substitute the need of soil for covering the newly disposed waste material at the end of the day, to control fires, odors, and to reduce pathogen transmission by insects, rodents, and birds, etc.
Biosolids do have odors, which tend to be strongest when biosolids are spread onto a field. But odors associated with biosolids are more of a nuisance than a threat to human health or the environment. The odors dissipate after the biosolids are mixed into the soil. In addition to steps taken at the treatment plant to minimize odors, biosolids that leave the treatment plant are covered with tarps. Biosolids are also mixed into the soil within 24 hours of being spread over the field. Buffer zones between the biosolids staging areas and the nearest property and public roads help minimize contact with those who might find the odors offensive.
Yes. Class B biosolids may have low levels of pathogens that rapidly die-off when applied to soils. Class A biosolids have no detectable pathogens. EBMUD currently produces Class B biosolids using an anaerobic digestion process, during which the sludge is subjected to high temperatures (95°F to 120°F) for at least 15 days. This extensive treatment kills the majority of pathogens present and makes the biosolids meet the Class B standard. EBMUD is currently investigating ways to produce Class A biosolids.
Yes. Some metals, such as nickel, zinc and copper can be found in biosolids. Many of the trace metals in biosolids serve as micronutrients that are essential for healthy plant growth.
EBMUD regularly monitors and tests our biosolids to ensure they meet all regulatory and/or quality standards for their intended use. We also have strict pre-treatment and monitoring requirements for industrial and commercial facilities so that metals and other pollutants are reduced or removed before the wastewater is discharged to EBMUD’s treatment plant.
Yes. Class A biosolids can be touched and used safely by people with no restrictions. They can even be sold in stores for use in home-gardens. Class B biosolids are restricted for general public access, but can be safely used by people who trained to do so. In the rare event that EBMUD’s biosolids cannot meet the Class B standard because of a temporary change in treatment plant operations, they will be sent to a landfill for disposal.
Research shows that land application of biosolids poses little or no risk to groundwater. The organic forms of nutrients in biosolids are less water soluble than chemical fertilizers and less likely to leach into groundwater or run off into surface water. Furthermore, potential impacts to water sources are minimized by proper management practices, including not over applying biosolids, maintaining buffer zones between application areas and surface water bodies, and following soil conservation practices.