Optimization design of aerated struvite-crystallizer for recovering phosphorus from swine manure using computational fluid dynamics

The aerated struvite-crystallizer (ASC) is widely used to recover phosphorus from swine manure. However, there is a lack of knowledge on the optimization of ASC design in view of hydrodynamics. In this study, computational fluid dynamics (CFD) is used to describe the behavior of water and air bubble in terms of velocity magnitude and stagnant volume in a column-shape ASC with cone bottom under different conditions i.e., ratio of height to diameter in the reaction zone (Hi:Di ratio) and aeration intensity. Results show that decreasing Hi:Di ratio does harm to the settlement in the bottom of ASC for the vortex fluid, whereas increasing Hi:Di ratio will shorten the retention time for air. Additionally, the aeration intensity has influence not only on the mixture effectiveness within the inner cylinder reaction zone of ASC, but also on the fluid field in the bottom of ASC. The optimized Hi:Di ratio is determined as 2:1 and the suitable aeration intensity is 14.6m3/h for the ASC system mentioned in this study.