Biosolids are the solid, semisolid, or liquid residues generated during treatment of domestic sanitary sewage that has undergone additional treatment to reduce disease-causing organisms and attractiveness to vectors (flies, mosquitos, rodents). Biosolids are frequently called sludge or sewage sludge, but only that portion of sewage sludge that has undergone adequate treatment to meet regulatory standards are biosolids.
Biosolids are nutrient-rich and can be used as a soil amendment or fertilizer and a sustainable alternative to commonly used chemical fertilizers. Nutrients such as nitrogen, phosphorus, sulfur, zinc, calcium, magnesium, and iron are present in most biosolids. Organic matter also is a major component of biosolids. Properly applied they improve soil structure and water-holding capacity, which improves growing conditions for crops, forests, landscaping, lawns, and vegetation on reclaimed lands.
Wastewater facilities that cannot treat their solids sufficiently to meet the requirements of biosolids must either dispose of their solids at a permitted landfill or haul their solids to another permitted facility that will accept their solids for additional treatment.
All facilities that generate biosolids must operate under both federal and state law. The rules specific to biosolids can be found in Oregon Administrative Rules (OAR) Chapter 340, Division 50 and section 40 of the Code of Federal Regulations (CFR) Part 503.
- OAR Chapter 340, Division 50 - Land Application of Domestic Wastewater Treatment Facility Biosolids, Biosolids Derived Products, And Domestic Septage. These are regulations that identify state-specific requirements and best management practices to protect the environment and public health in Oregon. These regulations prescribe the methods, procedures, and restrictions for the management and use of domestic wastewater treatment facility solids, products derived from biosolids and domestic septage. These rules specify Oregon’s program for biosolids and domestic septage management which satisfies or exceeds minimum federal regulations pertaining to land application.
- 40 CFR Part 503 - Standards for the Use or Disposal of Sewage Sludge. These are federal regulations that set national standards for pathogens, vector attraction reduction, and certain contaminants in biosolids. They also define management practices and operational standards for the safe handling and use of biosolids. The provisions of these regulations are applicable regardless of whether a state or federal permit is required.
In Oregon, biosolids are regulated under DEQ's water quality program, specifically through a water quality permit (National Pollutant Discharge Elimination System or Water Pollution Control Facility permit), a biosolids management plan, and site authorization letters. The permit, management plan, and site authorization letters are specific to a facility and include conditions that are relevant to both state and federal regulations. The conditions in the management plan and site authorization letters are considered an integral part of the permit and thus are enforceable. Oregon’s biosolids regulations are more restrictive than federal regulations.
Each permit is open for public comment when the facility’s permit is renewed. The facility’s biosolids management plan is also open for public comment when the facility’s permit is renewed and anytime there are significant changes to the management plan. The public comment period is at least 30 or 35 days depending on the type of permit.
DEQ requires permittees to take the following measures to apply biosolids to land:
Processing of biosolids
Treatment facilities may use several different processes (such as aerobic digestion, anaerobic digestion, alkaline stabilization, pasteurization, etc.) in transforming wastewater solids into biosolids. Regardless of the method used the final product must meet strict quality standards established in federal and state rule. Treatment facilities are required to control pathogens (disease-causing organisms, such as certain bacteria, viruses and parasites); reduce the solids’ attractiveness to vectors (such as rodents or insects); and ensure their material does not have pollutants above the screening levels. Once the material meets these criteria it can be identified as biosolids and can be beneficially applied to land. State and federal regulations identify two classes of biosolids, either Class A or B.
Class A biosolids must meet strict pathogen, vector attraction reduction, and low pollutant content requirements. Some Class A biosolids may be classified as Exceptional Quality (EQ). Class A biosolids can be safely used by the general public like any other commercial fertilizer/soil conditioner product. Class A biosolids are generally produced by composting or heat-drying.
Class B biosolids must meet somewhat less stringent requirements, but have been proven to be as protective of public health and the environment as Class A biosolids when proper site management and access restrictions are observed. The majority of biosolids produced and applied in Oregon are Class B.
To ensure the biosolids are processed correctly, treatment facilities must routinely test for pathogens, nutrients, and pollutants. All biosolids applied to land in Oregon are routinely sampled and tested for plant nutrients (nitrogen, phosphorus, and potassium) and regulated pollutants (arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc) to demonstrate ongoing compliance. This regular laboratory testing is important because it ensures the biosolids are processed correctly and is used to identify the proper amount that can be applied. Treatment facilities must collect representative samples on an on-going basis and the biosolids must be tested by qualified laboratories using approved testing methods. At a minimum, all treatment facilities must test annually and larger treatment facilities must test more frequently. The results of this routine testing are submitted to DEQ for review on an annual basis.
The Oregon State University extension service produces fertilization guides that identify the amount of nutrients needed to grow a healthy crop. DEQ uses this research to identify the agronomic rate that dictates the appropriate application rates for biosolids on each field for different crops. Developing the agronomic rate for land application is one of the key elements for ensuring that land application provides the correct amount of nutrients to the soil. Too much nitrogen in the soil can leach and degrade groundwater. If a permittee applies Class B biosolids on the same area for two out of three years at the agronomic rate for nitrogen, DEQ requires the permittee to test soil conditions to ensure they are not overloading the land with nutrients. If they are applying at lower than the agronomic rate, soil sampling may not be required by DEQ depending on the field location and site conditions. If carryover nitrogen levels in the soil are observed above the level OSU established for a crop, applications must be reduced or stopped until the soil nitrogen levels are reduced by plant growth.
Class A biosolids are commonly characterized similar to other commercial fertilizers and soil sampling is not required on fields where class A biosolids are applied.
Other protective measures
Before Class B biosolids can be applied on a field, DEQ must conduct a site evaluation. This ensures the field meets specific criteria as outlined in state and federal rule. This evaluation reviews the site location, slope, vegetation, and distance to surface and groundwater. If the field passes the site evaluation, a site authorization letter is issued that also establishes site-specific setbacks or buffer zones between where biosolids can be placed and surrounding features such as surface water, wells, residences, public roadways and property lines. To further ensure that the activity is protective of public health and the environment, DEQ requires other site management practices at Class B biosolids application sites such as limiting public access for a minimum of 12 months following application and not allowing the grazing of livestock or the harvesting of crops for 30 days following application of biosolids.
Because class A biosolids are treated to a higher standard, these extra protective measures are not required, but safe fertilizer management activities are advised.
Record Keeping and Reporting
All treatment facilities must keep detailed records of their operations, the quality of biosolids they produce and their management activities. These requirements are specified in the facility’s water quality permit and biosolids management plan. Each treatment facility that produces biosolids must submit an annual report to DEQ for review. The larger treatment facilities must also submit an annual report to the U.S. Environmental Protection Agency .
DEQ inspections and data review
DEQ's regional staff is responsible for assuring that wastewater treatment facilities and biosolids operations comply with pertinent state and federal regulations, which are stated as conditions in their water quality permit, management plan, and site authorization letters. Monitoring and reporting requirements provide process and operational data which is reviewed and evaluated for compliance purposes. Regional staff also conduct inspections of wastewater treatment facilities, biosolids, septage operations, and application sites.
To assure effective compliance, DEQ responds to public concerns about potential biosolids management issues. These problems may be associated with land application activities at a particular site, including odors, site management, or timing of application. These concerns are discussed with the responsible facility, including what corrective action may be needed. Any concerns regarding potential problems should be directed to DEQ’s complaints page.
Biosolids are applied at agronomic rates that benefit soil quality and the growth of crops. Biosolids can also be used for enhancing vegetative growth on reclamation sites and the US Department of Agriculture Conservation Reserve Program lands at greater than agronomic rates. These sites are reviewed on a case-by-case basis and appropriate agronomic rates are determined. Biosolids have been used to help reforest former logging roads as well as establish vegetative cover at landfills and former mines.
Land application sites
All Class B biosolids land application sites must be authorized in writing by DEQ before use. DEQ regional water quality staff will visit a site to ensure site characteristics allow for appropriate land application. Sensitive areas, setbacks, drinking water wells, and unique site features all need to be identified. Many sites are used seasonally depending on climatic conditions, where the site is geographically located, and the site use. The crop management system is also important. Field accessibility, frequency of biosolids application, irrigation practices, nutrients available from the biosolids, and application methods need to be considered. Crop management factors such as type of crop, timing of crop harvest, waiting periods for crop use (e.g., 30 days for grazing), nutrient management, irrigation, and conservation practices will also affect the use of biosolids.
The quantity and quality of biosolids dictate how they are used. Agronomic rate refers to an application rate that provides the nutrient needs for a given crop or vegetation while minimizing the amount of nutrients that pass below the root zone of the crop or vegetation. The nutrient content of biosolids will vary depending on the primary source of the biosolids, the age of the biosolids, the method of processing before land application, and the method of application. DEQ requires facilities to use a worksheet developed by researchers at OSU and Washington State University to calculate the appropriate application rate. For fields that regularly receive biosolids, DEQ may require soil sampling for residual nutrients using protocols published by OSU and the American Society of Agronomy. This testing is used to ensure the appropriate application rate is utilized.
Please see the Pacific Northwest Extension Publication Fertilizing with Biosolids and Worksheet for Calculating Biosolids Application Rates in Agriculture for more information concerning agronomic rates and nutrient management with biosolids.
There are many different wastewater and treatment processes that result in a biosolids product each with different characteristics. No matter what process is used, the product must meet certain pollutant concentration limits as well as operational standards to control pathogens and reduce the attraction of vectors, such as flies, mosquitoes, and other potential disease-carrying organisms.
Under federal and state regulations, biosolids are designated as "Class A" or "Class B" depending on the process used to reduce pathogens. More extensive treatment is required for Class A than for Class B, and for each of these classes, land application requirements vary. If requirements are met for Class A pathogen reduction, vector control, and the more stringent pollutant concentration limits for metals (Table 3, 40 CFR 503.13), the biosolids are defined as "Exceptional Quality" or “EQ” and are not subject to land application general requirements and management activities. Class A biosolids may be used by the public like any other fertilizer or soil amendment product.
Class B biosolids have more stringent reporting and management requirements. This includes neighbor notification, DEQ land application approval, land use restrictions, setbacks, and crop restrictions.