Conditions influencing the precipitation of magnesium ammonium phosphate

Struvite precipitation in wastewater treatment works has caused substantial operational problems since the early 1960s. Struvite, magnesium ammonium p hosphate hexahydrate (MgNH4PO4. 6H(2)O). is a white inorganic crystalline m ineral that precipitates in places with increased turbulence such as pumps, aerators and pipe bends. Batch experiments were conducted to examine the i nfluence of a number of physical and chemical parameters on struvite crysta llisation. This was undertaken by dosing a medium of de-ionised water with varying concentrations of Mg2+, NH4+ and PO43- ions. Preliminary experiment s found that struvite could be precipitated out of solution at PH 10 and in creasing the ion concentration stoichiometrically could increase crystal yi eld. Increasing the NH4+ concentration increased purity of the precipitate. As reaction time was increased from I to 180 min, crystal size was found t o increase from 0.1 to 3 mm. (C) 2001 Elsevier Science Ltd. All rights rese rved.