ViviMag will develop and up-scale a magnetic separation process to recover the insoluble iron phosphate mineral vivianite from the Sewage Treatment Plants (STPs) that rely on chemical Phosphate removal. The separation process will be applied on sewage sludge after anaerobic digestion. Anaerobic digestion reduces the sludge volume and recovers energy in the form of biogas. During anaerobic digestion Fe(III) is reduced to Fe(II), which results in vivianite formation.
The separation relies on the paramagnetic character of the vivianite mineral (figure 1). In the first stage of the project, a SLon magnetic separator (figure 2 and 3) will be used to investigate the vivianite separation from digested sewage sludge.
- Phosphate recovery from sewage sludge can cover 20% of the Phosphate demand.
- Vivianite separation from sewage sludge will create a new Phosphate resource.
- Production of fertilizer from vivianite will contribute to a sustainable future.
Phosphorus (P) is a limited resource and our agriculture relies on a steady supply. Phosphate rock is mined and processed to produce phosphorus containing fertilizers, like PK-fertilizers. However, exploitable phosphate rock reserves are found in just a few countries. The EU itself has hardly any phosphate rock reserves and depends nearly entirely on the import of this crucial resource; in 2005 the primary P import of the EU-27 was 1.8 Mton. Phosphorus use has to become more sustainable and should include P-recycling from secondary sources (i.e. wastewater). This will not only prevent eutrophication of surface waters, but will also minimize costs for disposal of phosphorus rich wastes.
Phosphorus rich waste streams such as sewage have a high potential for P recovery. Phosphorus has to be eliminated from these wastewaters to prevent environmental damage, like harmful algae blooms. Annually, Europe’s Sewage Treatment Plants (STPs) remove approximately 370 kton P by immobilization in the sewage sludge. The direct use of the sludge as fertilizer is problematic due to its bulky volume, the fixed nutrient ratios and the low bioavailability of a nutrient like phosphate.
Therefore, there is an increasing interest to separate the phosphorus in concentrated form from the bulk sludge for subsequent reuse in the fertilizer industry. The majority of Europe’s STPs apply chemical precipitation with an iron-based coagulant to achieve sufficient phosphorus removal.