Impact of various physico-chemical parameters on spontaneous nucleation of struvite (MgNH_4PO_4·6H_2O) formation in a wastewater treatment plant: kinetic and nucleation mechanism

摘要

In this study, the effect of various physico-chemical parameters such as supersaturation, temperature and pH, and the presence of foreign ion on the nucleation of struvite formation in a wastewater treatment plant were studied experimentally. Mechanism of nucleation kinetics of struvite (MgNH_4PO_4·6H_2O) formation has been identified by thermodynamic parameters study. The time taken for nucleation to occur (often indicated by the induction time) is a measure of struvite nucleation. It was found that induction time decreased with an increase in supersaturation, temperature and pH but increased with the presence of excess chloride (Cl~-) ion. Interfacial energy of two nucleation mechanisms (γ_(s,hom) and γ_(s,het), homogeneous and heterogeneous, increased with an increase in solution pH for all temperatures whereas interfacial energy of crystals increased with decrease in temperature. Thermodynamic parameters such as activation energy and interfacial energy were calculated based on rate of nucleation for both homogeneous and heterogeneous crystallisation. Finally, inhabitation of struvite nucleation by presence of foreign ion has been reported here.