Sludge - Background and History

Background and History

Biosolids, the product generated from tertiary treatment of waste activated sludge, have been in use in UK,European and China agriculture for more than 80 years, though there is increasing pressure to stop the practice of land application due to farm land contamination and public outrage. In the 1990s there was pressure in some European countries to ban the use of sewage sludge as a fertilizer. Switzerland, Sweden, Austria, and others introduced a ban. Since the 1960s there has been cooperative activity with industry to reduce the inputs of persistent substances from factories. This has been very successful and, for example, the content of cadmium in sewage sludge in major European cities is now only 1% of what it was in 1970.

European legislation on dangerous substances has eliminated the production and marketing of some substances that have been of historic concern such as persistent organic micropollutants. The European Commission has said repeatedly that the "Directive on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture" (86/278/EEC) has been very successful in that there have been no cases of adverse effect where it has been applied. The EC encourages the use of sewage sludge in agriculture because it conserves organic matter and completes nutrient cycles. Recycling of phosphate is regarded as especially important because the phosphate industry predicts that at the current rate of extraction the economic reserves will be exhausted in 100 or at most 250 years.Template:Sims and Sharpley 2005

Of general interest on this topic is the Swanson et al. (2004) brief history of sewage management in New York City . Since 1884 when sewage was first treated the amount of sludge has increased along with population and treatment technology. At first the sludge was discharged directly along the banks of rivers surrounding the city, a bit later piped further into the rivers, and then further still out into the harbor. In 1924, to relieve a dismal condition in New York Harbor which actually putrefied in places as a result of decay of sewage, New York City began dumping sludge at sea at a location in the New York Bight called the 12-Mile Site. This was deemed a successful public health measure and not until the late 1960s was there any examination of its consequences to marine life or to humans. There was accumulation of sludge particles on the seafloor and consequent changes in the numbers and types of benthic organisms. In 1970 a large area around the site was closed to shellfishing From then until to 1986, the practice of dumping at the 12-Mile Site came under increasing pressure stemming from a series of untoward environmental crises in the New York Bight that were attributed partly to sludge dumping. In 1986, sludge dumping was moved still further seaward to a site over the deep ocean called the 106-Mile Site. Then, again in response to political pressure arising from events unrelated to ocean dumping, the practice ended entirely in 1992. Since 1992, New York City sludge has been applied to land (outside of New York state). That practice, now employed by two/thirds of the sewage treatment plants in the US, has been under continued scrutiny. The wider question is whether or not changes on the sea floor caused by the portion of sludge that settles are severe enough to justify the added operational cost and human health concerns of applying sludge to land. The cost versus benefit question is moot in the U.S. because ocean dumping of sludge is banned, but international treaty (London Dumping Convention) allows the practice so, on a global basis, as more and more sewage is treated, every sludge management option deserves practical consideration. Recent oceanic studies indicate that bacteria from human gut is destroying coral in the Caribbean.

The term biosolids was formally created in 1991 by the Name Change Task Force of the Water Environment Federation (WEF), formerly known as the "Federation of Sewage Works Associations" to differentiate raw, untreated sewage sludge from treated and tested sewage sludge that can legally be utilized as soil amendment and fertilizer. 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." In June 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 legal term for biosolids by law is sludge. Treatment processes only remove some cancer causing agents; others remain. As detailed in the 1995 Plain English Guide to the Part 503 Risk Assessment, EPA's most comprehensive risk assessment was completed for biosolids.