Phosphorus Recovery from Wastewater by Struvite Crystallisation: a Review

The present review provides an understanding of principles of struvite crystallisation and examines the techniques and processes experimented to date by researchers at laboratory, pilot and full scale to maximise 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 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 fertilising properties, the control of its precipitation could contribute to the reduction of phosphorus levels in effluents while simultaneously generate a valuable end by-product. A number of processes such as stirred tank reactors, air agitated and fluidised bed reactors have been investigated as possible configurations for struvite recovery. Fluidised 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 regards to controlling struvite production quality and quantity to become broadly established as a standard treatment for wastewater companies.