Phosphorus recovery through biologically induced precipitation by partial nitritation-anammox granular biomass

- Partial nitritation-anammox granules induce precipitation of calcium phosphate.
- Granules had an inorganic core of 16 wt% phosphorus.
- Ca/P ratio similar to hydroxyapatite, the presence of which was confirmed by XRD.
- Heavy metals content complied with proposed EU fertilizer limits.
- Potential for a new phosphorus recovery product from urban wastewater.

Recovery of phosphorus from waste streams reduces dependence on imported phosphate rock, which is increasingly contaminated with heavy metals and radioactive by-products. This study proves it is possible to recover phosphorus through biologically induced precipitation in granular partial nitritation-anammox sludge. Granules with high inorganic content were harvested from a lab-scale partial nitritation-anammox reactor fed with centrate. Inductively Coupled Plasma (ICP) Optical Emission Spectroscopy showed that the granules had a phosphate content of 36 wt% P2O5 and a Ca/P ratio close to that of hydroxyapatite. Crystalline hydroxyapatite was confirmed accordingly by X-ray diffraction. ICP further showed that the metals content complied with fertilizer regulations as well as with requirements from the phosphorus industry. The results are promising as they raise the possibility of recovering phosphorus from urban wastewater without the addition of chemicals.

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