Biosolids is a term used by the water treatment industry that refers to treated sludge. Sludge, or "biosolids," are the byproduct of the treatment of domestic and commercial wastewater or sewage in a wastewater treatment plant. To create biosolids, these residuals are further treated to reduce pathogens and vector attraction by any of a number of approved methods. Nevertheless, toxic chemicals, such as PCBs, dioxin, and brominated flame retardants, remain in the "treated" sludge, as there is no technology available to remove these and tens of thousands of other chemicals from sewage sludge, the byproduct of wastewater treatment. Depending on their level of treatment and resultant pollutant content, biosolids can be used in regulated applications ranging from soil conditioning to fertilizer for food or non-food agriculture to distribution for unlimited use.

History of the term

The term biosolids was formally recognized in 1991 by the Water Environment Federation (WEF). WEF, founded in 1928, is a not-for-profit technical and educational organization with members from varied disciplines (e.g. wastewater treatment operators and engineers) who work for the preservation and enhancement of the global water environment. WEF was formerly known as the "Federation of Sewage Works Associations." Biosolids is the term created in 1991 by the Name Change Task Force at WEF to differentiate raw, untreated sewage sludge from treated and tested sewage sludge that can be beneficially utilized as soil amendment and fertilizer. The term "biosolids" also helps make the land application of processed sewage sludge more acceptable to the public. The proposal to create a "Name Change Task Force" originated with Peter Machno, manager of Seattle's sludge program, after protesters mobilized against his plan to spread sludge on local tree farms. "If I knocked on your door and said I've got this beneficial product called sludge, what are you going to say?" he asked. At Machno's suggestion, the Federation newsletter published a request for alternative names. Members sent in over 250 suggestions, including "all growth," "purenutri," "biolife," "bioslurp," "black gold," "geoslime," "sca-doo," "the end product," "humanure," "hu-doo," "organic residuals," "bioresidue," "urban biomass," "powergro," "organite," "recyclite," "nutri-cake" and "ROSE," short for "recycling of solids environmentally." [19] In June of 1991, the Name Change Task Force finally settled on "biosolids," which it defined as the "nutrient-rich, organic byproduct of the nation's wastewater treatment process."

The new name attracted sarcastic comment from the Doublespeak Quarterly Review, edited by Rutgers University professor William Lutz. "Does it still stink?" Lutz asked. He predicted that the new name "probably won't move into general usage. It's obviously coming from an engineering mentality. It does have one great virtue, though. You think of `biosolids' and your mind goes blank."

According to Machno, the name change was not intended to "cover something up or hide something from the public. . . . We're trying to come up with a term . . . that can communicate to the public the value of this product that we spend an awful lot of money on turning into a product that we use in a beneficial way."


During waste water treatment, bacteria and other microorganisms break down components in wastewater into simpler and more stable forms of organic matter. Non-organic matter also settles into sludge. For instance, small amounts (parts per million) of heavy metals and other potentially toxic materials, including flame retardants (PBDEs) and persistent organic pollutants, are commonly found in sewage sludge in parts per million levels. What does not settle into sludge leaves the treatment facility as a treated wastewater effluent. Biosolids in their liquid form look like muddy water and contain 1-10% solids. Biosolids may be dewatered in a second step of the treatment process, which turns it into a "cake" with the texture of a wet sponge. In this stage it contains 11-40% solids.

There are two methods currently being investigated to convert biosolids into energy sources: biological and thermochemical. Biological conversion involves using algae or bacteria to break down the biosolids. For example, under anaerobic conditions some bacteria can convert faeces into hydrogen gas and carbon dioxide gas (CO2) which can then be converted into methane, a natural gas that can power heaters and stoves. Thermochemical conversion uses high temperatures to break down the elements in biosolid into gas or hydrocarbon fuels. In London and Paris thermal processes are in place to convert their biosolids into energy. In London biosolids create more than 11 megawatts of electricity a year.

Biosolids in the USA

According to US EPA, biosolids that meet treatment and pollutant content criteria "can be safely recycled and applied as fertilizer to sustainably improve and maintain productive soils and stimulate plant growth." After the 1991 Congressional ban on ocean dumping, the US EPA promulgated regulations - 40 CFR Part 503 - that continued to allow for the use of biosolids on land as fertilizers and soil amendments (prior regulations, the Part 257, had allowed such uses). This is a somewhat controversial policy decision; despite the fact that no proven incidences of harm to human health or the environment have been demonstrated; some scientists remain concerned about the potential for accumulation of pollutants from repeated applications of biosolids. EPA promoted biosolids recycling throughout the 1990s. The EPA's Part 503 regulations were developed with input from university, EPA, and USDA researchers from around the country and involved an extensive review of the scientific literature and the largest risk assessment the agency had conducted to that time. Still, many academics, government researchers, and citizens contest EPA's conclusions about the safety of land applying sewage sludge. The Part 503 regulations became effective in 1993.

In the United States municipal wastewater treatment plants annually produced about 7.7 million dry tons of biosolids in 1997, and about 6.8 million dry tons in 1998 according to sources relying on USEPA estimates. According to the NRC, about 5.6 million dry tons was the normal US annual biosolids production rate as of 2002.

In the United States, as of 2002, about 60% of all biosolids are applied to land as soil amendment and fertilizer for growing crops. Biosolids that meet the Class B pathogen treatment and pollutant criteria, in accordance with the US EPA "Standards for the use or disposal of sewage sludge," (40 CFR Part 503) can be land applied with formal site restrictions and strict record keeping. Biosolids with lower pollutant content have fewer restrictions. Biosolids that meet Class A pathogen reduction requirements or equivalent treatment by a Process to Further Reduce Pathogens (PFRP) have the least restrictions on use. PFRPs include composting, heat drying, heat treatment, thermophilic aerobic digestion, beta or gamma ray irradiation and pasteurization. Processes to reduce pathogens have no effect on heavy metals and may or may not have effects on the levels of other trace pollutants in biosolids.

EPA policy on biosolids recycling is controversial. Often thought to consist of only "human waste," treated sewage sludge or "biosolids" contains any contaminants from sewage that are not broken down in the treatment process or which do not remain with the water effluent leaving the treatment plant. The most commonly detected trace contaminants of concern are heavy metals (arsenic, cadmium, copper, etc. -- some of which are also critical plant micronutrients) and toxic chemicals (e.g. widely used plasticizers, PDBEs, etc., which are generated by human activities, including but not limited to household products such as personal care products and medicines). Pathogens are not a significant health issue if biosolids are properly treated and site-sepcific management practices are followed; there is generally a greater concern for "organic" products that have been fertilized with un-treated animal wastes and which may be eaten raw).

Over the years there have been thousands of reported incidents of harm caused by biosolids use on land; however no one has ever documented the cause-effect relationship. Symptoms reported have included: asthma, weight loss, fatigue, eye irritations, flu-like symptoms, gastrointestinal complications, headaches, immunodeficiency problems, lesions, nausea, nosebleeds, rashes, respiratory complications, abscesses, reproductive complications, cysts, and tumors. Currently a formal tracking system for complaints related to biosolids land application is being developed. EPA has never conducted an epidemiological study, though thousands of people have complained of health problems as a result of living near land applied sites. Some deaths have been claimed but those claims disproven or disreputed.

The National Research Council published "Biosolids Applied to Land: Advancing Standards and Practices" in July 2002. They concluded that there is no documented scientific evidence that biosolids regulations have failed to protect public health, but there is persistent uncertainty on possible adverse health effects. The NRC noted that further research is needed and made about 60 recommendations for addressing public health concerns, scientific uncertainties, and data gaps in the science underlying the sewage sludge standards. EPA responded with commitment to conduct research addressing the most important, but not all, of the NRC recommendations.

The EPA Office of the Inspector General (OIG) completed two assessments in 2000 and 2002 of the EPA sewage sludge program. The 2000 report declared that the EPA did not have an "effective program for ensuring compliance with the land application requirements of the Sludge Rule." This report further documented that EPA performed "virtually no inspections" of land application sites and few inspections of treatment plants or land appliers.” The report also documented the lack of resources committed to sludge and the low priority placed on the sludge program by the EPA. The follow-up report in 2002 documented that "EPA cannot assure the public that current land application practices are protective of human health and the environment." The report also documented that there had been an almost 50% reduction in EPA enforcement resources since the earlier assessment. This is probably the greatest issue with the practice: under both the federal program operated by the USEPA and those of the several states, there is limited inspection and oversight by agencies charged with regulating thses practices. To some degree, this lack of oversight is a function of the perceived (by the regulatory agencies) benign nature of the practice. However, a greater underlying issue is funding. Few states and the USEPA have the discretionaryl funds necessary to establish and implement a full enforcement program for biosolids. To do so would require substantial moneys and most legislatures are unwilling to support this spending. Some states and companies involved in biosolids management have willingly agreed to use a "fee" per unit of biosolids managed to help fund such programs (and generally, where such programs are in place, biosolids land application proceeds without incident; however these fees are seldom sufficient to fully-fund a rigorous inspection program.

Biosolids in the European Union

In Europe, the recycling of biosolids (treated sewage sludge) to agriculture is practised widely. It is supported by the European Commission and many European governments and, in most circumstances, this beneficial re-use is regarded as the best environmental option. Over 40% of all sewage sludge produced in the EU is recycled to agricultural land (based on data from the European Commission from 1999-2000) although the actual rate varies considerably from country to country. In countries such as France, Spain, the UK, Denmark and Luxemburg over 50% of production is recycled to land.

The process is well regulated, though highly controversial, principally under the 1986 EU Sludge Directive (86/27/EEC). The main objective of the Directive is the control of heavy metals (PTEs), thought to be the main contaminants of concern when biosolids are being applied to land. The regulatory controls introduced address the potential impact of biosolids addition to soil from both the immediate application and also any possible cumulative effects.

In the UK, the EU Sludge Directive is implemented through the Sludge (Use in Agriculture) Regulations 1989. These Regulations are supported by a detailed Code of Practice that describes all aspects of biosolids recycling to land. The regulations set permissible limits for soil concentrations and rates of annual additions of PTEs. The allowable limits for Zn, Cu and Ni in soils vary with the pH of the soil.

Since 1998 the UK water industry has also complied with the additional requirements of the Safe Sludge Matrix. This is a voluntary agreement made between the UK water and sewerage operators, the British Retail Consortium (BRC), representing the major retailers, and a range of other stakeholders. The matrix introduced strict controls on the microbiological quality of sludge and specified procedures to be adopted for its application to agricultural land used to grow food crops. The use of untreated sludge on agricultural land for food production was phased out in 1999 and the use of untreated sludge on agricultural land used to grow non-food crops was phased out in 2005. The provisions of the Matrix go beyond the requirements of the Sludge (Use in) Agriculture Regulations as they currently stand.

Water Companies in the UK have also adopted HACCP (Hazard Analysis and Critical Control Point) procedures for sludge stream management. HACCP procedures apply risk assessment and process control to manage and reduce risk, ensuring that the pathogen reduction requirements specified by the Safe Sludge Matrix are met, formalising record keeping and maintaining quality control. Further information on recycling biosolids to land can be found in the document Recycling Biosolids to Land on the WaterUK website.

Further legislation is on the horizon in the form of a revision to the 1986 EU Sludge Directive. The Commission’s intention is to propose guidelines on sustainable practices for the application of treated sludge (biosolids) onto land. In this context, it will also be assessed whether the scope of the revised directive should be broadened to other non-hazardous sludges and to applications other than in agriculture. The aim of the revision to the Directive will be, on the one hand, to encourage the sustainable use of properly treated sludge and, on the other, to strengthen the controls applied in order to guarantee that both professional users and the public in general have increased confidence in the practice of recycling biosolids to land.


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