Biosolids

Biosolids are nutrient rich, organic byproducts of wastewater treatment. These byproducts make a valuable amendment to soils. EBMUD’s biosolids are highly processed, monitored, and tested to ensure that they meet or surpass the strict quality and safety standards established by the U.S. Environmental Protection Agency, the State of California, and local governments.

EBMUD is a member of the Bay Area Biosolids Coalition, a group of utilities and industry partners in the San Francisco Bay Area who collaborate to advance the science and beneficial use of biosolids. You can find links to biosolids research and more on the Bay Area Biosolids Coalition website.

EBMUD’s biosolids are sent from the wastewater treatment plant to one of three uses: land application on farms, feedstock for compost, or alternative daily cover at landfills. The distribution of biosolids among these uses varies each year depending on weather and other factors. The chart below shows the distribution for the past three calendar years.

Frequently Asked Questions about EBMUD’s Biosolids

Solids are separated from liquids in the wastewater treatment process, then conveyed to tanks, known as “digesters," where they are heated to a high temperature for at least 15 days to reduce disease-causing organisms and break down organic matter. The remaining solid material is called biosolids. After excess water is removed through centrifugal separation, the biosolids look and feel very much like soil.

The biosolids produced by EBMUD are used primarily as a soil amendment on farms. Biosolids promote plant growth through improving soil properties, supplying nutrients, and replenishing soil organic matter. Federal regulations specify how the biosolids are land applied and how soon crops can be harvested from the fields after application.

EBMUD biosolids that are sent to compost are processed at the Central Valley Compost Facility in Dos Palos, CA. There they are blended with wood waste and cured in windrows. The resulting compost is sold in bulk to local farmers.

EBMUD biosolids that are sent to landfill are used as alternative daily cover to substitute the need for soil for covering the newly disposed waste material at the end of the day. This cover helps to control fires, reduce odors, and deter rodents and birds.

Biosolids do have odors, which tend to be strongest when biosolids are first spread onto a field. 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, trucks transporting biosolids from the treatment plant are fully enclosed and covered with tarps. Biosolids are also mixed into the soil within 24 hours of being spread over the field. Buffer zones between the biosolids application 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. EBMUD currently produces Class B biosolids using an anaerobic digestion process, during which the sludge is subjected to high temperatures (95°F to 131°F) for at least 15 days. This extensive treatment kills most pathogens and enables the biosolids to meet the Class B standard.

Yes. Some metals, such as nickel, zinc, and copper can be found in biosolids. Many of the trace metals in biosolids are micronutrients that are essential for healthy plant growth.

EBMUD regularly monitors and tests our biosolids to ensure they meet all regulatory 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. As a result, pollutant concentrations in the biosolids are well below the regulatory limits.

Yes. Class B biosolids are restricted for general public access, but they 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.

When used as a soil amendment, biosolids supply much-needed organic matter to the ground. Biosolids contain high amounts of carbon and organic forms of nutrients, which are released more slowly than chemical fertilizers. Biosolids are produced with fewer greenhouse gas emissions than chemical fertilizers. Furthermore, a portion of the carbon in biosolids becomes sequestered in the soil matrix after land application. In fact, the State of California’s Climate Action Reserve recently adopted the Soil Enrichment Protocol to quantify agricultural practices that sequester carbon and decrease greenhouse gas emissions. The Protocol includes biosolids as a valuable amendment for such credits.

The regulations for Class B biosolids extend from the wastewater treatment process to the fields where biosolids are land applied. Regulations limit the quantity of biosolids that can be applied, how soon can crops be harvested after application, and more. EBMUD biosolids are therefore not available for home gardening with our current practices, but they could be one day in the future. If you are interested in garden-ready biosolids products, please let us know at the contact information below.

For more information on EBMUD’s biosolids management program, contact Rebecca Overacre at Rebecca.overacre@ebmud.com, or 510-287-1251.