From agricultural use of sewage sludge to nutrient extraction: A soil science outlook

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From: Ambio(Vol. 46, Issue 2)
Publisher: Springer
Document Type: Author abstract
Length: 482 words

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To access, purchase, authenticate, or subscribe to the full-text of this article, please visit this link: Byline: Holger Kirchmann (1), Gunnar Borjesson (1), Thomas Katterer (1), Yariv Cohen (1) Keywords: Ash; Long-term field experiments; Metals; Mono-ammonium phosphate; Soil biology; Urban--rural nutrient recycling Abstract: The composition of municipal wastewater and sewage sludge reflects the use and proliferation of elements and contaminants within society. In Sweden, official statistics show that concentrations of toxic metals in municipal sewage sludge have steadily decreased, by up to 90 %, since the 1970s, due to environmental programmes and statutory limits on metals in sludge and soil. Results from long-term field experiments show that reduced metal pollution during repeated sewage sludge application has reversed negative trends in soil biology. Despite this Swedish success story, organic waste recycling from Swedish towns and cities to arable land is still limited to only about 20 % of the total amount produced. Resistance among industries and consumers to products grown on land treated with sewage sludge may not always be scientifically grounded however, there are rational obstacles to application of sewage sludge to land based on its inherent properties rather than its content of pollutants. We argue that application of urban organic wastes to soil is an efficient form of recycling for small municipalities, but that organic waste treatment from large cities requires other solutions. The large volumes of sewage sludge collected in towns and cities are not equitably distributed back to arable land because of the following: (i) The high water and low nutrient content in sewage sludge make long-distance transportation too expensive and (ii) the low plant availability of nutrients in sewage sludge results in small yield increases even after many years of repeated sludge addition. Therefore, nutrient extraction from urban wastes instead of direct organic waste recycling is a possible way forward. The trend for increased combustion of urban wastes will make ash a key waste type in future. Combustion not only concentrates the nutrients in the ash but also leads to metal enrichment hence, direct application of the ash to land is most often not possible. However, inorganic fertiliser (e.g. mono-ammonium phosphate fertiliser, MAP) can be produced from metal-contaminated sewage sludge ash in a process whereby the metals are removed. We argue that the view on organic waste recycling needs to be diversified in order to improve the urban--rural nutrient cycle, since only recycling urban organic wastes directly is not a viable option to close the urban--rural nutrient cycle. Recovery and recycling of nutrients from organic wastes are a possible solution. When organic waste recycling is complemented by nutrient extraction, some nutrient loops within society can be closed, enabling more sustainable agricultural production in future. Author Affiliation: (1) Department of Soil and Environment, Swedish University of Agricultural Sciences, P.O. Box 7014, 75007, Uppsala, Sweden Article History: Registration Date: 23/08/2016 Received Date: 27/01/2016 Accepted Date: 23/08/2016 Online Date: 20/09/2016

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Gale Document Number: GALE|A479192917