Phosphorus Recovery from Wastewater by Struvite Crystallization: A Review

The present review provides an understanding of principles of struvite crystallization and examines the techniques and processes experimented to date by researchers at laboratory, pilot, and full-scale to maximize phosphorus removal and reuse as struvite from wastewater effluents. Struvite is mainly known as a scale deposit causing concerns to wastewater companies. Indeed, struvite naturally occurs under the specific condition of pH and mixing energy in specific areas of wastewater treatment plants (e.g., pipes, heat exchangers) when concentrations of magnesium, phosphate, and ammonium approach an equimolar ratio 1:1:1. However, thanks to struvite composition and its fertilizing properties, the control of its precipitation could contribute to the reduction of phosphorus levels in effluents while simultaneously generate a valuable by-product. A number of processes such as stirred tank reactors and air-agitated and -fluidized bed reactors have been investigated as possible configurations for struvite recovery. Fluidized bed reactors emerged as one of the promising solutions for removing and recovering phosphorus as struvite. Phosphorus removal can easily reach 70% or more, although the technique still needs improvement with regard to controlling struvite production quality and quantity to become broadly established as a standard treatment for wastewater companies.