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

Abstract

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 60rpm). 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 30rpm, 99% of P was recovered as struvite crystals with a size of 50–100μm.