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Development of an efficient and environmentally friendly phosphate fertiliser from sewage sludge ashes

This project will evaluate the effects of phosphate rich granules obtained from the ashes of sewage sludge from which heavy metals have been extracted on plant nutrition and soil fertility, as well as their economic impact.

On one side, SWITZERLAND imports annually about 6,000 tons of P (phosphorus) in the form of mineral fertilizers for its agriculture (Spiess, 2005). On the other side, because of the presence of inorganic and organic pollutants, it is now forbidden to recycle sewage sludge in agriculture, whereas this sludge contains an amount of P equivalent to a third of the amount annually imported in SWITZERLAND (Herter et al., 2001). Sewage sludge is now incinerated and put in landfills. The actual production of ashes derived from the incineration of sewage sludge amounts to 20,000 ton/year (t/y). With the ban on recycling sewage sludge in agriculture, this production will increase to 35,000 t/y. The disposal of sludge ashes costs CHF 120/t. Therefore disposing all the sludge ashes in landfill would cost CHF 4.2 million per year to Swiss incinerators. Furthermore, putting sludge ashes in landfills would represent a net loss of the non-renewable phosphate resource. The world reserve of P resources that can be mined at a reasonably low price will be exhausted within the next 200 years (Steward et al., 2005). SWITZERLAND does not yet have the technology that would allow for safe and cheap recycling of sewage sludge ashes in agriculture. The hypothesis of this project is that if such technology could become available in SWITZERLAND, it would be adopted by groups running incinerators as it would decrease their disposal costs, it would create jobs to produce fertilizer derived from ashes, decrease the expenses of the country for importing phosphate fertilizers, and decrease the pressure on the non-renewable phosphate resources. ASH DEC, an Austrian group represented in SWITZERLAND by ARTHO BIOVIS, developed technology to extract heavy metals from the ashes of sewage sludge producing an alkaline residue with a high P and Ca content, which is free from organic contaminants and which contains very low concentrations in heavy metals (well below the limits set by the Swiss government; see the description of the new technology in chapter 3.b) and which has good potential for use as a P fertilizer in agriculture. It can also provide significant amounts of Ca, which has a very important role in the soil and which is too often neglected. However, before the production of this ash-based fertilizer can start, its advantages and the risks it could pose must be carefully evaluated. Since ASH DEC is an Austrian group, a decision was made to set up a EUREKA/EUROAGRI+/CTI research project in cooperation with the VERBAND DER BETRIEBSLEITER UND BETREIBER SCHWEIZERISCHER ABFALLBEHANDLUNGSANLAGEN (VBSA), which brings together among other groups the Swiss groups running sludge incinerators, and with the ETH as scientific partner. The objective of the project is the agronomic and economic evaluation of a fertilizer made from phosphate rich granules obtained from sewage sludge ashes from which heavy metals have been extracted under Swiss conditions. Keywords: phosphorus recovery, P-fertilizer.
Acronym: 
PHOSKRAFT
Project ID: 
3 634
Start date: 
01-06-2006
Project Duration: 
48months
Project costs: 
550 000.00€
Technological Area: 
Recycling, Recovery
Market Area: 
Cultivation of cereals / crops / vegetables

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