Pumpkin seedlings planted out on windrows of composted biosolids

Biosolids is a term coined in the United States that is typically used to describe several forms of treated sewage sludge that is intended for agricultural use as a soil conditioner. Although sewage sludge has long been used in agriculture,[1] concerns about offensive odors and disease risks from pathogens and toxic chemicals may reduce public acceptance of the practice. Modern use of the term biosolids may be subject to government regulations, although informal use describes a broader range of semi-solid organic products separated from sewage.

Description of biosolids in conformance with local regulations may reduce confusion; but some use an expanded definition including any solids, slime solids or liquid slurry residue generated during the treatment of domestic sewage including scum and solids removed during primary, secondary or advanced treatment processes. Use of alternative terms like solids or wastewater solids may be preferable for non-conforming biosolids.[2]


Biosolids may be defined as organic wastewater solids that can be reused after suitable sewage sludge treatment processes leading to sludge stabilization such as anaerobic digestion and composting.[3]

Alternatively, the biosolids definition may be restricted by local regulations to wastewater solids only after those solids have completed a specified treatment sequence and/or have concentrations of pathogens and toxic chemicals below specified levels.[4]

The United States Environmental Protection Agency (USEPA) defines the two terms - sewage sludge and biosolids - in the Code of Federal Regulations (CFR), Title 40, Part 503 as follows: sewage sludge refers to the solids separated during the treatment of municipal wastewater (including domestic septage), while biosolids refers to treated sewage sludge that meets the USEPA pollutant and pathogen requirements for land application and surface disposal.[4] A similar definition has been used internationally.[5]



Testing for human pathogens in cereal crops after the application of biosolids. Biosolids are applied as fertilizer in the Central Wheatbelt of Australia as a recycling program by the Water Corporation.

Approximately 7,100,000 dry tons of biosolids were generated in 2004 at approximately 16,500 municipal wastewater treatment facilities in the United States.[6]

In the United States, as of 2013 about 55% of sewage solids are turned into fertilizer, despite demand from farmers who wish to buy more.[7] Challenges to increased levels of recycling include capital needed to build digesters, the complexity of complying with health regulations, and avoiding neighbors who object to unpleasant smells. There are also new forms of contaminants in urban sewage systems which make the process of producing high quality biosolids more complex. These have led some municipalities to ban biosolids on farms and even in forests.


Encouraging agricultural use of biosolids is intended to prevent filling landfills with nutrient-rich organic materials from the treatment of domestic sewage that might be recycled and applied as fertilizer to improve and maintain productive soils and stimulate plant growth.[6] Biosolids may contain macronutrients nitrogen, phosphorus, potassium and sulphur with micronutrients copper, zinc, calcium, magnesium, iron, boron, molybdenum and manganese.[5]

Industrial and man-made contaminants

The United States Environmental Protection Agency (USEPA) and others have shown that biosolids can contain measurable levels of synthetic organic compounds, radionuclides and heavy metals.[5][8][9] USEPA has set numeric limits for arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc but has not regulated dioxin levels.[6][10]

So-called "contaminants of emerging concern" may also be present in biosolids.[11] Substantial levels of persistent, bioaccumulative and toxic (PBT) polybrominated diphenyl ethers were detected in biosolids in 2001.[12] This finding came despite the EPA's previous assertion that all PBT organic pollutants of concern had been banned from production in the 1970s and hence these could be ignored in risk assessment. In 2007 toxic PCBs were detected in the biosolid product Milorganite, donated to the City of Milwaukee and subsequently applied on city parkland.[13] The cost to the Milwaukee Metropolitan Sewerage District and tax payers was estimated as $4.7 million.[14] The source of the PCBs was later determined to be a shuttered die-casting facility. The PCBs made their way to the treatment plant via sewer lines years after the facility stopped operation. PCBs were banned from commerce in the US in the mid-1970s. The United States Geological Survey analyzed in 2014 nine different consumer products containing biosolids as a main ingredient for 87 organic chemicals found in cleaners, personal care products, pharmaceuticals, and other products. These analysis detected 55 of the 87 organic chemicals measured in at least one of the nine biosolid samples, with as many as 45 chemicals found in a single sample.[15]


In the United States the USEPA mandates certain treatment processes designed to significantly decrease levels of certain so-called indicator organisms, in biosolids.[6] These include, "...operational standards for fecal coliforms, Salmonella sp. bacteria, enteric viruses, and viable helminth ova."[16]

However, the US-based Water Environment Research Foundation has shown that some pathogens do survive sewage sludge treatment.[17]

USEPA has also classified other pathogens that can appear in biosolids such as various protozoa, bacteria, viruses, and prions as "pathogens of emerging concern".[18] EPA regulations allow only biosolids with no detectable pathogens to be widely applied; those with remaining pathogens are restricted in use.[19]

Classification systems

United States

In the United States Code of Federal Regulations (CFR), Title 40, Part 503 governs the management of biosolids. Within that federal regulation biosolids are generally classified differently depending upon the quantity of pollutants they contain and the level of treatment they have been subjected to (the latter of which determines both the level of vector attraction reduction and the level of pathogen reduction). These factors also affect how they may be disseminated (bulk or bagged) and the level of monitoring oversight which, in turn determines where and in what quantity they may be applied.[20]


Further information: Sewage sludge § History

As public concern arose about disposal in the United States of increasing volumes of solids being removed from sewage during sewage treatment mandated by the Clean Water Act, the Water Environment Federation (WEF) sought a new name to distinguish the clean, agriculturally viable product generated by modern wastewater treatment from earlier forms of sewage sludge widely remembered for causing offensive or dangerous conditions. Of three-hundred suggestions, biosolids was attributed to Dr. Bruce Logan of the University of Arizona, and recognized by WEF in 1991.[21]

Microbiolgist and EPA whistleblower, David. L. Lewis, has documented illness, death and livestock destruction traced to the use of biosolids. He also charges that the National Academy of Sciences, EPA, USDA, and other vested interests have expunged documentation and studies from reports in order to protect the EPA policy of using biosolids. Furthermore, Dr. Lewis charges that the emphasis on using biosolids in low-income urban and rural settings especially in the early years of "sludge magic" is an Environmental Injustice and human experimentation without informed consent.[22][23]


See also


  1. Gohil, M.B. (2000). Land Treatment of Waste Water. New Age International. p. 6. ISBN 8122412270.
  2. Turovskiy, Izrail S. "Biosolids or Sludge? The Semantics of Terminology". Water and Wastes Digest. Retrieved 24 April 2015.
  3. Wastewater engineering : treatment and reuse (4th ed.). Metcalf & Eddy, Inc., McGraw Hill, USA. 2003. p. 1449. ISBN 0-07-112250-8.
  4. 1 2 "Sewage Sludge/Biosolids Program". United States Environmental Protection Agency. Retrieved 24 April 2015.
  5. 1 2 3 "What are biosolids?". Australian Water Association. Retrieved 24 April 2015.
  6. 1 2 3 4 "Questions and Answers on Land Application of Biosolids" (PDF). Water Environment Federation. Retrieved 24 April 2015.
  7. Cities Turn Sewage Into 'Black Gold' For Local Farms (2013)
  8. "Biosolids: Targeted National Sewage Sludge Survey Report - Overview | Biosolids | US EPA". Retrieved 2015-05-18.
  9. "ISCORS Assessment of Radioactivity in Sewage Sludge: Recommendations on Management of Radioactive Materials in Sewage Sludge and Ash at Publicly Owned Treatment Works" (PDF). United States Environmental Protection Agency (EPA). Interagency Steering Committee on Radiation Standards. April 2004. Retrieved 18 May 2015.
  10. "Final Action Not to Regulate Dioxins in Land-Applied Sewage Sludge | Biosolids | US EPA". Retrieved 2015-05-18.
  11. "Analytical Methods: Contaminants of Emerging Concern | Pharmaceuticals & Personal Care Products | US EPA". Retrieved 2015-05-18.
  15. "Land Application of Municipal Biosolids". Environmental Health - Toxic Substances. United States Geological Survey. Retrieved 24 April 2015.
  16. Biosolids Applied to Land: Advancing Standards and Practices. National Academy of Sciences. 2002. p. 22. ISBN 0-309-08486-5.
  17. "Assessing the Fate of Emerging Pathogens in Biosolids". Water Environment Research Foundation. Retrieved 2015-05-18.
  18. "" (PDF). p. xxxv. Retrieved 2015-05-18. External link in |title= (help)
  19. "Biosolids FAQ, Questions 17-18". Retrieved 2015-06-21.
  20. "A Plain English Guide to the EPA Part 503 Biosolids Rule, Chapter 2 "Land Application of Biosolids"" (PDF). p. 31. Retrieved 2015-05-20.
  21. "Biosolids: A Short Explanation and Discussion" (PDF). WEF/U.S. EPA Biosolids Fact Sheet Project. Water Environment Federation. Retrieved 24 April 2015.
  22. Lewis DL, Gattie DK, Novak ME, Sanchez S, Pumphrey C. Interactions of pathogens and irritant chemicals in land-applied sewage sludges (biosolids). New Solut. 2002;12(4):409-23.
  23. David L. Lewis, PhD. Science for Sale: How the US Government Uses Powerful Corporations and Leading Universities to Support Government Policies, Silence Top Scientists, Jeopardize Our Health, and Protect Corporate Profits. Sky horse Publishing. 2014.
  24. "About us". Milorganite/Milwaukee Metropolitan Sewerage District. Retrieved 27 April 2015.
  25. "What is Loop?". King County Wastewater Treatment Division. Retrieved 20 June 2015.
  26. "About TAGRO". City of Tacoma. Retrieved 20 June 2015.
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