Investigation of the impact of hydrodynamic parameters for phosphorus recovery from synthetic anaerobic digester supernatant in a fluidized bed reactor

Recovering phosphorus (P) from wastewater as struvite has been investigated widely as this approach represents a solution to several wastewater-related problems. Some of the typical process units applied in the industry for struvite recovery from wastewater streams include fluidized bed reactors where individual struvite crystals are being agglomerated into spherical granules, or pellets. Various hydrodynamic parameters affect the extent of inter-particle collisions, the intensity of mixing, localized concentrations of ionic species, nature of eddies, etc. which determine the efficiency of the crystal agglomeration. This study evaluated the impact of three key hy-drodynamic parameters (up-flow velocity, feed injection nozzle velocity, and nozzle configuration) on P-removal and recovery efficiencies in a newly designed novel fluidized bed reactor (FBR). Lowering up-flow velocities from 60 cm/min to 20 cm/min resulted in higher P-removal and recovery efficiency, whereas high up-flow velocities were favorable for the production of larger pellets and fines. Nevertheless, higher nozzle velocity (18.04 m/s) was responsible for improving P-recovery efficiencies. The nozzle velocity had a strong influence on the morphology of pellets and fines. High nozzle velocity contributed to the formation of the smooth-surfaced pellets and plate-shaped fines. Three different nozzle-configurations generating different flow patterns within the agglomeration zone were studied.