Phosphorus removal from wastewater through struvite crystallization in a continuous fluidized-bed reactor: An improved comprehensive model

Promoting a wider application of struvite precipitation for nutrient recovery from wastewaters requires more efficient reactor designs, supported by models that integrate thermodynamic, kinetic and hydrodynamic behavior. The present work addresses the modeling of phosphorus recovery by struvite crystallization in fluidized-bed reactors, revealing discrepancies and errors in the literature and proposing corrections and improvements. A reduced thermodynamic model is presented. The potential of the struvite solubility constant was estimated to be 13.12 < pK < 13.30. Furthermore, a new strategy for a simple and quick estimation of the surface-area specific rate constant ka (1.70 dm/h < ka < 2.19 dm/h) was implemented. The technique involves operating the reactor with liquid in the transient regime as a completely stirred tank and solid-mixed bed in the pseudosteady state. Size distribution simulation results were obtained for different operational conditions using a one-dimensional perfect size classification model for the solid phase and a plug-flow model for the liquid phase.

Automated summary

The study focuses on modeling phosphorus recovery by struvite crystallization, proposing improvements and corrections including a simplified thermodynamic model and a new strategy for estimating the surface-area specific rate constant. Results were obtained by operating the reactor with liquid in the transient regime and utilizing size distribution simulation.