Biosolids

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Biosolids are the nutrient rich solid material that is produced during the treatment of domestic wastewater at a treatment facility. Solid materials are removed from sewage during the wastewater treatment process. One such example of a biosolid is digestate produced from anaerobic digestion.

1 History of the term
2 Processes
3 Biosolids in the USA
4 Biosolids in the European Union
5 See also
6 External links

[edit] History of the term

The term biosolids was formally recognized in 1991 by the Water Environment Federation (WEF). The WEF is the water and wastewater industry's main trade and lobby organization in the USA. Biosolids is the term created in 1991 by the Name Change Task Force at WEF to make the land application of processed sewage sludge more acceptable to the public.

[edit] Processes

During waste water treatment, bacteria and other microorganisms break components in the wastewater down into simpler and more stable forms of organic matter. Non-organic matter also settles into sludge. For instance, heavy metals and other toxic materials, including flame retardants (PBDEs) and persistent organic pollutants, are commonly found in sewage sludge. 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.

[edit] 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." EPA policy on sewage sludge recycling is highly controversial. Often thought to consist of only "human waste," sewage sludge, or its public relations term, "biosolids," in fact contains all materials from cities which the treatment can remove from wastewater. After the 1991 Congressional ban on ocean dumping, the US EPA instituted a policy of disposing of sludge on agricultural land. EPA promoted this policy by presenting it as recycling. But with more and more incidents of illness reported, there has been increasing concern among scientists about the disposal of sewage sludge on land.

In the United States, as of 2002, about 60% of all biosolids are "beneficially applied" to land as fertilizer for growing crops. Biosolids that meet the Class B treatment and pollutant criteria, in accordance with USA "Standards for the use or disposal of sewage sludge," Title 40 Code of Federal Regulations Part 503 (40 CFR 503) can be land applied with formal site permit restrictions and strict record keeping. Biosolids with lower pollutant content have less 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 other pollutants in sewage sludge.

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. The USEPA claims to have had insufficient funding to implement NRC recommendations as of 2004, though has funneled millions of dollars to the Water Environment Federation to promote the land application of sewage sludge.

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.