Keywords: secondary phosphate, struvite, sewage sludge ash, meat and bone meal ash, acidulation, granulation
Phosphate recycling is an important issue, since it is a finite resource which is essential to food security. The phosphate used in the fertiliser industry, which now solely comes from mining, has to be replaced with so-called secondary phosphates. Different sources present opportunities to recover phosphates, the most important being manure, litter, wood ashes, sewage sludge ashes, meat and bone meal ashes and struvite.
At ICL Fertilizers, trials have been conducted to investigate the potential implementation of these sources of secondary phosphates into the fertiliser production. Extensive pilot-scale testing and several plant-scale tests have yielded promising results for the use of sewage sludge ash, meat and bone meal ash and struvite. These sources are readily available for implementation and require only little modifications to the current fertiliser production facilities of ICL. Also, the environmental impact of producing fertiliser using these secondary phosphate sources suggests the emissions of phosphate and fluorine is lower than with regular phosphate rock.
The main issue remaining is the legislation for the use of these sources, as they are currently regarded as waste. Struvite is also suspected to be able to contain contaminants such as pathogens and pharmaceuticals, encapsulated in its crystals. Therefore, further research on this topic is necessary. In the WG3 meetings of the European Commission, maximum values for heavy metal content in fertiliser were specified in greater detail. The first results show that products produced from sewage sludge ash meets these demands. Since heavy metal content in struvite and meat and bone meal ash is low, no problems are expected.
The use of secondary phosphate in fertiliser production yields great opportunities.
C P Langeveld and K W ten Wolde, ICL Fertilizers Europe C.V., Fosfaatweg 48, 1013 BM Amsterdam, The Netherlands.
24 pages, 12 figures, 7 tables, 32 references.