ABOUT BIOSOLIDS
Sacramento County, CA
Biosolids are a carbon- and nutrient-rich alternative to synthetic fertilizer; a renewable, safe, reliable resource for farmers with multiple benefits for California soils.
Biosolids are produced during the wastewater treatment process. It all begins when people flush the toilet or discard food down the drain. That wastewater flows to a treatment plant that cleans the water by separating the solids from the liquid. The cleaned water is disinfected and returned to the Bay, ocean, or used for irrigation or building cooling to conserve potable water.
The solids are typically treated in large covered tanks called anaerobic digesters, where microorganisms digest the solids. This kills disease-causing organisms and breaks down pollutants. A natural by-product of anaerobic digestion is methane gas, which is used by treatment plants as a renewable, carbon-neutral alternative to fossil-fuel-derived natural gas. At the end of the solids treatment process, a safe, clean, renewable, soil-like resource called biosolids is produced. In most cases, biosolids are used in this form as an alternative to synthetic fertilizer, but sometimes biosolids are used as an ingredient to make compost or potting mix.
Wastewater travels to the treatment plant from businesses and homes. Solids are captured from the liquids through a process called settling. Solids are treated through an engineered process called digestion. Dewatering removes excess water to create a soil-like product. The finished product, biosolids, are transported to customers who typically use the material instead of synthetic fertilizer.
What happens next — how are biosolids used?
Ideally, biosolids are transported to farms where they are used as an alternative to synthetic fertilizer. Before they go into the ground, biosolids must meet stringent safety and quality standards. They are tested to confirm they meet federal requirements for pathogens, metals, and other constituents. In fact, they are regulated much more intensely than synthetic fertilizers, manure, and compost.
When biosolids are incorporated into the soil, they supply it with essential nutrients and rich organic matter. These nutrients are slowly released, just as the crops need them. Farmers then harvest the crops, people eat those crops, and the process begins again — a great example of the circular economy at work.
The benefits of biosolids
Biosolids are a powerful natural resource beneficial to the planet and people. Biosolids help:
Enhance soil health.
A natural alternative to synthetic fertilizer, biosolids enrich and condition the soil by returning nutrients and organic matter back to the land. Rich in organic matter, biosolids benefit the land by helping the soil retain water and nutrients. They also help improve soil structure, enhancing its resilience to erosion and drought.
Grow better crops and plants.
By adding nutrients and improving soil quality, crops and plants benefit. Biosolids contain all 16 elements essential for plant growth, including nitrogen, phosphorus, and a variety of micronutrients. Plants absorb some of these elements immediately, while others are taken up slowly over time. This provides a consistent nutrient supply that helps plants thrive throughout the growing season.
Fight climate change.
By helping plants grow, biosolids play a supporting role in removing carbon dioxide from the atmosphere and returning it to the soil. Because they are full of organic matter, they add a significant amount of carbon directly to the soil as well, and much of this carbon remains sequestered in the soil for long periods of time. What’s more, using biosolids offsets the carbon emissions associated with synthetic fertilizer. With more carbon confined underground, versus warming the planet in the atmosphere, the environment wins.
Produce renewable fuel.
The production of biosolids does not require the intense amount of fossil fuels that are needed to make synthetic fertilizers. In fact, the most common biosolids treatment process, anaerobic digestion, naturally produces methane gas, which can be captured and used as a 100% renewable fuel source.
Prevent erosion and runoff.
The organic matter in biosolids helps soil resist erosion and runoff primarily by feeding healthy soil microorganisms that glue soil particles together and improve soil structure. The addition of organic matter and improved soil structure help soils infiltrate and store more water, enhancing its resilience during tough California droughts, and preventing erosion and unclean runoff into streams, rivers, and the Bay.
Reclaim depleted land.
From wildfires to mining operations, California soils can be negatively impacted by any number of things. Biosolids are an effective and affordable tool to restore soil at large scales in harsh conditions. Applying biosolids to mined or fire-ravaged land supplies nutrients and replenishes soil organic matter, thereby encouraging plant re-growth and stabilizing slopes.
Provide financial benefits.
Biosolids are a low-cost alternative to synthetic fertilizers, providing a significant financial savings for farmers, ranchers, and land managers. They produce nutrient-rich crops and increased yields, improving profits for farmers and helping to bolster the California economy.
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Oceanside Treatment Plant in San Francisco, CA.
After large debris is screened out, wastewater flows into chambers that remove grit at the San José-Santa Clara Regional Wastewater Facility.
The cycle begins with the food we eat. What our bodies don’t use gets flushed down the toilet and travels to a wastewater treatment plant. At the plant, the solids are transformed into a fertilizer alternative called biosolids. The quality of the biosolids is closely monitored through laboratory testing. The finished product is transported to customers as an alternative to synthetic fertilizer. In California, typical crops grown with biosolids are hay and forage grasses. These crops feed animals, which creates food, and the cycle continues.
Fertilizing with carbon-rich biosolids allows us to 1) reduce the use of synthetic fertilizers, which require a lot of energy to produce; 2) grow larger plants, which removes carbon dioxide (CO2) from the air and returns carbon to the soil; 3) stores carbon in the soil long-term (sequestration).