Protecting Public Health and the Environment.

Sludge & Biosolids

Sludge is the solid, semisolid, or liquid untreated residue created during the wastewater treatment process. When treated and processed, sludge becomes biosolids, which are the stabilized residuals that settle from the water during the treatment process. Biosolids may be disposed of or beneficially used.

Biosolids Beneficial Reuse/Disposal Options

Beneficial Reuse

Because biosolids contain nutrients and organic matter, they are considered a beneficial resource by EPA and DEQ; therefore, the reuse of biosolids through land application is encouraged. When land applied, biosolids can be used as fertilizer to help improve and maintain productive soils and stimulate plant growth.

Before biosolids may be land applied, they must be treated to meet standards for pathogens, vectors, and metals. Biosolids treatment is designed to kill pathogens, stabilize organic matter, reduce odors, and minimize vector attraction.


Biosolids may be disposed of by various means such as landfilling, incineration, or surface disposal.

Regulation of Biosolids

Regardless of whether biosolids are disposed of or beneficially reused, they are subject to certain federal, state, and local regulations. Any or all of the following regulations may apply to those who generate biosolids, derive a material from biosolids, land-apply biosolids, or own or operate a site where biosolids may be applied:

  • Standards for the Use or Disposal of Sewage Sludge (40 CFR 503): Federal regulation that sets national standards for pathogens and certain heavy metals in sewage sludge; also defines standards for the safe handling and use of sewage sludge. The provisions of this regulation are applicable regardless of whether a permit is required.
  • Environmental Protection and Health Act of 1972 (Idaho Code §39-1): State law that assigns responsibility for protecting human health and the environment to DEQ.
  • Wastewater Rules (IDAPA 58.01.16) and Water Quality Standards (IDAPA 58.01.02): State rules that include provisions for protection of human health and the environment from contamination by land application of municipal biosolids. In particular, IDAPA regulates the use of sludge for soil augmentation and requires a DEQ-approved sludge disposal plan (a biosolids management plan).
  • Recycled Water Rules (IDAPA 58.01.17): State rules that authorize DEQ to issue permits for biosolids land application sites. In most situations, a permit is not necessary as long as IDAPA is followed. A permit may be required on a case-by-case basis.

Biosolids Management Plan

An approved biosolids management plan is required before land application of biosolids.* (A biosolids management plan is equivalent to a sludge disposal plan, as referenced in IDAPA As prescribed in a memorandum of understanding between DEQ and Idaho's public health districts, responsibility for approving the plan may rest with either DEQ or a public health district.

* Exception: Under a rule interpretation issued by DEQ, the plan submission requirement has been waived for land application of biosolids that meet Class A Exceptional Quality requirements. (See categories section below for a description of the three categories of biosolids.)

Categories of Biosolids

Biosolids must meet either Class A or B pathogen requirements for land application.

  • Class A biosolids must meet strict pathogen, vector attraction reduction, and low metals content requirements. Some Class A biosolids may be classified as Exceptional Quality.
  • Class B biosolids must meet somewhat less stringent pathogen, vector attraction reduction, and low metals content requirements, but are considered as safe as Class A biosolids when proper site management and access restrictions are observed. 

Note that representative sampling is needed for meeting biosolids class requirements. Recommendations for the unique requirements for representative pile sampling were published in Pile Sampling White Paper, by Jeff Myers, a nationally and internationally recognized expert in characterization, sampling, statistics, uncertainty management, and data quality. This paper provides technical background for systematic planning, executing, and assessing pile sampling programs. The techniques presented here are intended to assist both regulators and regulated parties in characterizing and disposing pile materials.

Sources of Biosolids that May Be Land-Applied

Municipal Waste Treatment Facilities

As required by 40 CFR 503, biosolids from municipal waste treatment facilities must meet either Class A or Class B pathogen reduction requirements for land application.

Nonmunicipal Waste Treatment Facilities

Generators of nonmunicipal biosolids are advised to consult with DEQ to develop an appropriate biosolids management plan.

Pumpers and Haulers: Domestic Septage

Domestic septage is either liquid or solid material removed from septic tanks, cesspools, portable toilets, marine sanitation devices, or similar treatment works that receive only domestic sewage. It does not include liquid or solid material removed from septic tanks, holding tanks, or similar treatment works that receive either commercial or industrial waste (i.e., grease trap waste, commercial wastewater, or industrial liquid).

Land application of domestic septage is regulated by the following state rules:

The Rules Governing the Cleaning of Septic Tanks (IDAPA 58.01.15) restrict the manner in which septage may be disposed. DEQ recognizes the value of recycling septage; therefore, septage may be used for soil augmentation if requirements of the Wastewater Rules (IDAPA are met.

Septage pumpers and haulers are responsible for ultimate disposal of the septage and must obtain a permit before the septage may be land-applied. The public health district issues this permit, inspects pumper trucks, and evaluates sites and operations for one-time application of domestic septage. The permit application must identify the method and place of disposal.

DEQ, through the public health district, reviews operating procedures for sites approved to receive septage from multiple pumpers or from a single pumper multiple times. DEQ also reviews and approves sites for septage application other than single application sites.

Operators of septage disposal sites are advised to submit septage disposal plans for land application annually to DEQ for yearly evaluation and approval. The plan should be kept current and remain on file with the permit or license. Plan modification requires written approval from DEQ. For large-scale application systems on lands specifically dedicated to septage application, an engineering report (septage management report) may be required. For smaller-scale applications on individual, private parcels, approval may be granted on a case-by-case basis.

Operators of septage disposal sites are responsible for ensuring all septage disposed at a septage land-application site comes from residential sources. Only domestic septage may be land-applied or placed on a septage land application site unless specified in the septage disposal plan. Operators of septage disposal sites are responsible for the actions of any septage management firm that the operator allows to use the land-application site.

Staff Contacts

Wastewater Analyst
Tressa Nicholas
DEQ State Office
Water Quality Division
1410 N. Hilton
Boise, ID 83706
(208) 373-0116

DEQ Resources

More Information on EPA's Website

Related Pages

Wastewater Disposal Options

Basics of Biosolids Management Workshop

Protect Your Right to Land Apply Biosolids — Understanding EPA’s 503 Regulation Workshop