Phosphorus

Phosphorus is usually present in natural water as phosphates (orthophosphates, polyphosphates, and organically bound phosphates), one of the essential nutrients required for growth of aquatic algae. In many ecosystems, phosphorus appears to be a limiting nutrient. It means that if an increased quantity of phosphorus is discharged, a rapid and intense algal growth can be expected. Such growth (called algal bloom or eutrophication) is objectionable for a number of reasons. First, water becomes green. A more important objection to an excessive algal growth is that when they die, microorganisms, which consume oxygen for their metabolism, decompose them. As a result of this consumption, oxygen is depleted in water and other aquatic species, mainly fish are affected. For these reasons, phosphorus discharge to such sensitive waters is controlled. Since, of the two major sources of phosphorus - agricultural runoff and municipal wastewater - the latter is easier to put under regulatory control, many wastewater treatment plants have phosphorus concentration limit imposed on their effluent.