The potential of the ASH DEC technology in phosphorus recovery from ash in Finland
With the ASH DEC technology it is possible to clean phosphorus-bearing ash from heavy metals. The remaining ash can be utilized as phosphorus-rich fertilizer, but is this technology feasible in Finland?
Thermal treatment of sewage sludge has been fairly cautious in Finland throughout the 21st century because of the concerns related to the high content of moisture in sewage sludge. This needs to change because more effective utilization of nutrients will reduce the environmental impact on the lakes and the Baltic Sea. National Waste Treatment Plan has set an objective of recovering 100 % of sludge as material or energy. In Finland, sludge is mostly exploited in landscaping and agriculture. However, fertilizer usage in agriculture is still very moderate, being only three percent of the entire sludge usage during 2005–2007.
Typically, manure has been used to fertilize agricultural soils. Dried manure from poultry and horses is suitable for fertilizing as well. When only manure is incinerated, the remaining ash can be used for fields or for improving the phosphorus balance in soil.
ASH DEC technology is viable when heavy metals need to be removed from ash. Additives (NaCl, MgO, and NaHCO3) are mixed with ash, and the mixture is treated in a furnace at 900–1050 °C for 20 minutes. Heavy metals evaporate during the treatment, and only the phosphorus-rich ash will remain. Subsequently, heavy metals precipitate in air emission cleaning processes as different metal hydroxides.
The object of survey
The object of the survey was to assess whether it is feasible to treat phosphorus-rich ash with ASH DEC technology in Finland. The scope of the survey covered sewage sludge, dried manure from poultry and horses, and sludge from piggeries as sources of phosphorus-rich ash.
So far, in Finland, sewage sludge has mainly been composted or digested in anaerobic processes. However, a part of the generated sewage sludge could be incinerated and the remaining ash treated with the ASH DEC process. Nevertheless, it is difficult to convert the incineration of manure into a feasible process in Finland because of the regulation which classifies the incineration of manure as waste incineration. Obtaining permission for waste incineration for a small-sized plant is not only difficult, but also very expensive. Manure could be used in addition to sludge in the regions with much livestock production but not enough land for spreading the manure.
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Ministry of the Environment. 2012. Valtakunnallisen jätesuunnitelman seuranta 1. Väliraportti. http://www.ymparisto.fi/download.asp?contentid=135152&lan=fi
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Read the entire story: https://www.doria.fi/handle/10024/90919