Basic Information about Sewage Sludge and Biosolids
On this page:
- Basics of Sewage Sludge and Biosolids
- Sewage Sludge Management Practices
- Use and Disposal Statistics
Basics of Sewage Sludge and Biosolids
When domestic sewage is transported and conveyed to a wastewater treatment plant (WWTP), it is treated to separate liquids from the solids, which produces a semi-solid, nutrient-rich product known as sewage sludge. The terms “biosolids” and “sewage sludge” are often used interchangeably by the public; however, the U.S. Environmental Protection Agency typically uses the term “biosolids” to mean sewage sludge that has been treated to meet the requirements in the EPA’s regulation entitled, “Standards for the Use or Disposal of Sewage Sludge,” promulgated at 40 C.F.R. Part 503, and intended to be applied to land as a soil conditioner or fertilizer.
In the U.S., there are generally three options for use or disposal of sewage sludge: land application, landfilling, and incineration. Land application is the spraying, spreading, incorporation, or injection of sewage sludge into or onto the land to either condition the soil or fertilize crops or vegetation grown in the soil. Landfilling can occur in a sewage sludge-only monofill (i.e., surface disposal) or a municipal solid waste (MSW) landfill. Sewage sludge can also be incinerated in a sewage sludge incinerator (SSI).
Sewage Sludge Management Practices
Land Application
Biosolids can be used on agricultural land, forests, rangelands, disturbed land in need of reclamation, or nonagricultural lands like parks, golf courses, and home lawns and gardens. Biosolids that are to be beneficially used must meet federal, state, Tribal and local requirements.
Landfilling
Biosolids landfilling options include surface disposal (e.g., disposal in a sewage sludge-only landfill called a surface disposal site or monofill) or in a co-disposal landfill (e.g., MSW landfill).
Incineration
Incineration is the combustion of organic matter and inorganic matter in sewage sludge by high temperatures in an enclosed device.
Use and Disposal Statistics
Each year some publicly owned treatment works (POTWs) are required to summarize their sewage sludge management practices and provide pollutant monitoring data in Biosolids Annual Reports (BARs). BARS are required from POTWs that land apply, incinerate, or dispose of their sewage sludge via surface disposal and:
- Serve 10,000 people or more;
- Are Major POTWs (POTWs with a design flow rate greater than or equal to one million gallons per day);
- Are Class 1 management facilities (POTWs with an approved pretreatment program or facilities that have been classified as such by the EPA or state); or
- Are otherwise required to report by the EPA or permitting authority.
The EPA collects annual biosolids reports from roughly 2,250 larger facilities in the U.S in the 41 states where the EPA is the permitting authority. Based on the reports from the facilities that meet the applicability requirements in states where the EPA is the permitting authority, the EPA estimates for 2023:
- Managed: ~4 million dry metric tons (dmt) of sewage sludge
- Land applied: ~2.39 million dmt
- Applied to agricultural land: ~1.24 million dmt
- Applied to reclamation areas: ~32,000 dmt
- Other (e.g., home garden, landscaping, golf course etc.): ~1.12 million tons
- Incinerated: ~560,000 dmt
- Landfilled: ~955,000 dmt
- Disposed of in a municipal solid waste landfill (MSW): ~880,500 dmt
- Surfaced disposed of in a monofill: ~74,500 dmt
- Other management practices (examples include deep well injection and storage): ~92,500 dmt
There are nine states (Arizona, Idaho, Michigan, Ohio, Oklahoma, South Dakota, Texas, Utah, and Wisconsin) that are authorized through the National Pollutant Discharge Elimination System (NPDES) Program to be the permitting authority for biosolids. The EPA will transition to electronic reporting for the remaining authorized states as part of Phase 2 implementation of the NPDES eRule by December 2025.
The EPA does not receive data from smaller facilities or those that use or dispose of their sewage sludge using alternate management practices (like landfilling in an MSW) except for voluntarily submitted information. Because the EPA does not currently receive data from some states that are authorized to implement the biosolids program or from smaller facilities, there is no definitive source that reports the amount of biosolids produced annually in the United States. The EPA tries to ensure the information presented here is as accurate as possible; however, the data in biosolids annual reports may contain errors as submitted by the POTWs.