Predicting struvite formation in digestion

The solubility constant for struvite (MgNH4PO4. 6H(2)O) was measured in for mation and;dissolution equilibrium experiments. The proposed solubility con stant (pK(SO) = 13.26) accurately predicted struvite precipitation in sludg e handling facilities at the Sacramento Regional Wastewater Treatment Plant , whereas the solubility constant in common use did not. An improved method was developed for predicting struvite precipitation potential in anaerobic digestion and post-digestion processes. Method improvements include consid eration of ionic strength effects on ion activities, magnesium phosphate co mplexation effects on ion speciation, and an experimentally derived struvit e solubility constant. The improved method accurately predicted struvite to be less soluble than predicted by earlier methods. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.