Product Description


The PHOSPAQ™ process is applied to recover phosphate from effluents as struvite. Phosphate is becoming scarce, thus making recovery more and more interesting. PHOSPAQ™ is a cost-effective technology compared to e.g. dosing of iron salts. Moreover, the produced struvite is an excellent slow release fertilizer for N, P and Mg.

The PHOSPAQ™ process removes biological degradable COD, phosphate (PO43-) and ammonium (NH4+) from wastewater. With oxygen, the COD is biologically converted into new biomass and CO2. By adding magnesium oxide (MgO), phosphate and ammonium precipitate as struvite (MgNH4PO4.6H20 or MAP). The struvite granules are being removed from the water phase, and are ready for agricultural use (fertilizer). The struvite complies with EU standards for fertilizer.


PHOSPAQ™ is feasible from approximately:

  • Load: > 100 kg P/d
  • 50 mg/l PO4-P
  • 200 mg/l NH4-N

The removal efficiency is about 70-95%.


Advantages of PHOSPAQ™

  • Combined phosphate- and COD-removal in one reactor
  • Aeration provides the oxygen for the biological conversion of COD
  • Aeration provides optimal conditions for struvite formation
  • Stripping of carbon dioxide raises the pH and stimulates struvite precipitation
  • Good struvite quality


Working principle

The PHOSPAQ™ process takes place in an aerated reactor. Magnesium oxide is added to remove phosphate that is recovered by precipitation as struvite at a pH of 8.2 to 8.3. The PHOSPAQ™ reactor is equipped with separators that retain the struvite.

The struvite is harvested from the bottom of the reactor by means of a hydrocyclone, followed by a screw press and transferred into a container. The dry weight of the harvested struvite is around 50% and the crystals have an average size of around 0,7 mm.



The PHOSPAQ™ process is the preferred technology in combination with ANAMMOX® for ammonia removal, as it:

• adds alkalinity (MgO)
• removes BOD and inhibiting compounds
• prevents uncontrolled struvite scaling

The combination PHOSPAQ™ – ANAMMOX® offers a compact and cost-effective solution to nutrient-rich effluents. The PHOSPAQ™ process has proven its robust performance since its commercial introduction in 2006.

• incoming phosphate > 50 mg P/L
• references for 60 – 1100 kg P/d
• removal efficiencies > 80-90%




For more information about PHOSPAQ, visit PAQUES’ website.

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