Kinetics effects on preferential struvite accumulation in wastewater

The kinetics of struvite (MgNH4PO4. 6H(2)O) formation was studied to determ ine the cause of preferential accumulation at certain locations within the anaerobic digestion and postdigestion processes in wastewater treatment. Me chanisms controlling nucleation were also studied in laboratory induction t ime experiments. A field study of struvite accumulation on postdigestion pr ocess appurtenances was conducted to evaluate mechanisms affecting crystal growth rates. Struvite nucleation was found to be reaction-controlled, with nucleation strongly dependent on the struvite supersaturation level. incre ased mixing intensity at constant supersaturation had a minor effect on ind uction times. The crystal growth rate was found to be transport-limited, wi th the growth rate a function of mixing energy input. Evaluation of the eff ect of pH change resulting from CO2 evolution in high turbulence areas show ed that it has a minor influence on the crystal growth rate. Preferential s truvite accumulation was found to be primarily controlled by growth kinetic s, which was strongly dependent on mixing energy. Preferential accumulation of struvite on selected construction materials was also studied, and exper imental evidence suggested that surface roughness exerted the greatest cont rol over preferential struvite accumulation on various materials under simi lar mixing and supersaturation conditions.