Dynamic simulation of a struvite MSMPR crystalliser with crystal nucleation, growth and aggregation

Magnesium ammonium phosphate (commonly known as struvite) crystallisation is an innovative means of recovering phosphorus from wastewater streams as depletion of non-renewable phosphorus becomes more prevalent. Process understanding is an integral requirement for reduced risk in process design, process control and process optimisation. This paper outlines the development of a struvite crystallisation model for a continuous mixed suspension mixed product removal crystalliser, incorporating solution thermodynamics, mass and population balances and kinetics for crystal nucleation, growth and aggregation processes. Dynamic simulations are performed to show the transient response of the system at varying initial conditions and operating conditions. The importance of modelling nonideal solution thermodynamic behaviour is demonstrated and a sensitivity analysis of key kinetic parameters investigated