Phosphorus recovery from wastewater through struvite formation in fluidized bed reactors: a sustainable approach

Abstract

Recovery of phosphate as struvite (MgNH4PO4·6H2O), before it forms and accumulates on wastewater treatment equipment, solves wastewater treatment problems and also provides environmentally sustainable, renewable nutrient source for the agriculture sector. A pilot-scale fluidized bed reactor was used to recover phosphate through crystallization of struvite, from anaerobic digester centrate at the Lulu Island Wastewater Treatment Plant, Richmond, British Columbia, Canada. The desired degree of phosphate removal was achieved by maintaining operating pH (8.0–8.2), and recycle ratio 5–9, to control the supersaturation conditions inside the reactor. The performance of the system was found to be optimal when in-reactor supersaturation ratio was 2–6. Among several other operating parameters, apparent upflow velocity and magnesium to phosphate molar ratio were also found important to maintain system performance, both in terms of efficiency of phosphate removal and recovery as struvite pellets. A narrow window of upflow velocity (400–410 cm/min) was found to be effective in removing 75–85% phosphate. TOC level inside the rector was found to affect the performance to some extent. The precipitation potential of struvite could be successfully predicted using a thermodynamic solubility product value of 10−13.36 and its temperature dependence in PHREEQC.