A design of experiments to assess phosphorous removal and crystal properties in struvite precipitation of source separated urine using different Mg sources

• Only the variable Mg:P molar ratio had a significant influence on P recovery.
• 99% of P was recovered with MgO as Mg2+ source, 2:1 molar ratio and 30 rpm.
• Struvite crystals with 50–100 μm size were obtained.
• XRD patterns were coherent with the standard model for struvite crystals.
• Only the variable stirring speed had a significant effect on crystal size.

Phosphorus recycling and recovery has received special attention due to its non-replaceable and non-renewability. Phosphorus recovery from human urine in the form of struvite crystals is a potential alternative source. In this work, the efficiency of struvite precipitation from source separated human urine and struvite crystals size were analyzed using three different Mg2+ sources (MgCl2, Mg(OH)2 and MgO), individually evaluated using a statistical design of experiments to assess the combined effect of Mg2+:P molar ratio (1:1, 1.5:1 and 2:1) and stirring speed (30, 45 and 60 rpm). Formation of struvite crystals was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS). Using the optimal conditions determined, MgO as Mg2+ source at 2:1 molar ratio and a stirring speed of 30 rpm, 99% of P was recovered as struvite crystals with a size of 50–100 μm.

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