Precipitation of phosphate minerals from liquid swine manure is an established means of
reducing the orthophosphate (OP) concentration. This project investigated the usefulness
of a chemical equilibrium model, Visual Minteq, for prescribing the amendments needed to
maximize struvite precipitation from liquid swine manure and thus reduce the OP
phosphorus concentration. The actual concentrations of Mg2+, Ca2+, K+, OP, NH4
+, alkalinity
and pH from a liquid swine manure system were used as inputs to the model. The model
was modified to remove species with extremely low formation rates, because they would
not significantly precipitate in the reaction occurring in a short retention-time process such
as those envisioned for swine manure struvite-formation reactors. Using the model’s
output, a series of 19-L reactors were used to verify the results. Verification results
demonstrated that Visual Minteq can be used to pre-determine the concentration of
amendments required to maximize struvite recovery.