Biosolids

Biosolids are nutrient-rich solid materials that are produced from the organic residuals that are a byproduct of the treatment of domestic wastewater 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. 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 Biosolids are an example of beneficial reuse and up to 50% of processed biosolids are land applied.

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. 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.

Processes

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 (there has been considerable research - and there is ongoing research - on the potential impacts of these in the soil environment and significant impacts have not been found when biosolids are applied in accordance with modern regulations). 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.

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). 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. The Part 503 regulations became effective in 1993. Most states in the U.S. have adopted more extensive and stricter regulations that build on Part 503.

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 sewage sludge recycling is occasionally 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.) and trace chemicals (e.g. widely used plasticizers, PDBEs, etc.). In addition, if biosolids are not properly treated or managed, pathogens could be an issue.

Over the years there have been reported - but not scientifically documented - incidents of harm caused by biosolids use on land - but relatively few compared to the thousands of ongoing biosolids recycling projects around the U. S. and the world, some of which have been operating for three decades or more. (Indeed, local and state public officials who reviewed the most widely-cited reported incidents have not found evidence of harm caused by biosolids). Some scientists express concern about potential impacts to the environment and public health from biosolids recycling, but the large majority of the scientific literature and those scientists studying this topic find that biosolids recycling to soils presents "negligible risk" (National Research Council, 1996: [Use of Reclaimed Water and Sludge in Food Crop Production]http://www.epa.gov/owm/mtb/biosolids/useofmid/index.htm). In addition, there are tens of thousands of wastewater and biosolids treatment workers who are highly exposed to biosolids in comparison to the average person - and these workers experience few or minimal impacts (e.g. colds, minor gastrointestinal upsets) from their work environment, which involves wastewater and untreated sewage sludge. Nevertheless, there is ongoing public debate about the sustainability and safety of biosolids recycling.

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.

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, 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.

See also

• Digestate
• Shit
• Toxic Sludge is Good for You

External links

• BioCycle magazine, 2000 article
• National Biosolids Partnership page
• North East Biosolids and Residuals Association
• Northwest Biosolids Management Association
• Mid-Atlantic Biosolids Association
• Great Lakes By-products Management Association
• Disinfopedia article critical of biosolids
• Environmental Health Perspective, 1997 article
• Biosolids Applied to Land: Advancing Standards and Practices, National Research Council, July 2002
• USEPA biosolids page
• The 1978-79 Sludge War, Oct. 1999 essay by William Sanjour

• More on the history and widespread usage of the term "biosolids:" http://www.nebiosolids.org/shownews.html?id=263