Phosphorus removal and recovery from water and wastewater by the struvite crystallization

The precipitation of phosphorus naturally present in water, in the form of struvite, constitutes an interesting alternative for the phosphate water treatment. In this context, the main objective of the present study is to follow the crystallization of struvite, in a stirred tank, from real phosphated water (wastewater and natural water) at 25 °C and at optimum pH 8.5 and to study the effect of environmental conditions on the crystallization stages (nucleation and crystal growth) and the morphology of struvite crystals. Various analytical methods (spectrophotometry, FTIR, SEM and XRD) were used to characterize the solid and liquid phases. In the light of the results obtained in this investigation, it appears that the precipitates formed in all the samples of treated waters were identified as ammonium magnesium phosphate (i.e. struvite). The precipitation of struvite in water allowed a significant elimination of phosphorus (up to 70 %). On the other hand, the SEM analysis was able to highlight the presence of large clusters of large struvite crystals up to 146.8 µm, as in the case of the precipitation of struvite with wastewater, where the conversion rate was the highest. The supersaturation ratio is the most important factor influencing the crystallization process. • Removal of phosphorus in water and wastewater by struvite precipitation is presented. • Struvite crystallization in water and wastewater was controlled by crystal growth, at pH 8.5. • The kinetics of struvite crystallization was controlled by the conductimetric method. • The morphology of recovered struvite crystals has been characterized using SEM, XRD and FTIR. • Up to 70 % of soluble P was removed from water in the form of struvite.