| Title |
Influences of pH and Coagulant Basicity in Precipitating Orthophosphate by Al / Fe Salts |
| Authors |
( Jong Woon Kwak ; Lars Gillberg ) |
| Abstract |
The removal of ortho-phosphates(ortho-P) was conducted by several aluminum and iron salts at different pH on a laboratory scale. All experimental tests was conducted by jar tests. Three phosphorous compounds as the sources of ortho-P were used for the standard waters: Na₂HPO₄: 2H₂O, NaH₂PO₄, H₂O, and H₃PO₄. The molar ratio of Al/P (aluminum/phosphorus) in all doses was 1. The influence of pH on the removal of ortho-P was described when aluminum salts of different basicities, ferric and ferrous salts were added to solutions of ortho-P and in turn, when solutions of ortho-P to fresh hydroxides. More ortho-P was precipitated by the fresh hydrolysis products of the metal salts than by the metal hydroxides. Ferrous sulfate precipitated ortho-P in a narrow pH range, but aluminum and ferric salts precipitated ortho-P in a broad pH range. It was concluded that flashing mixing is critical to both high pH and low basicity of the coagulant in removing ortho-P. The removal of ortho-P by the ferrous salt was found to be more sensitive to the way of mixing than the other salts. In practice, removals of both non-ortho-P and suspended solid was enhanced with increasing coagulant basicity, but rather that of ortho-P was decreased. |