ABSTRACT
Phosphorus is present in nature only in its compound forms. They occur in the animal, plant, and mineral kingdoms, almost always as one or another variation of the phosphates, which contain the PO43- ion. In natural waters and wastewaters, phosphorus occurs as phosphates. These are classified as ortho-, condensed, organically bound, and total phosphates. The digestion process converts the condensed or polyphosphates and the organic phosphates to orthophosphate for quantitation. The digestion process must oxidize the organic matter effectively to release total phosphorus as orthophosphate. Phosphates belong to the group called nutrients. Nutrients flow in cycles, as carbon cycle, nitrogen cycle, and phosphorus cycle. Phosphates are slowly dissolved from rocks by rain and carried to waterways. Phosphate is the major component of fertilizers. By applying excess fertilizer, farmers may alter the phosphate cycle.
