Why is it necessary to remove nitrogen and phosphorus from sewage and wastewater? Describe the principles of nitrogen and phosphorus removal from sewage and wastewater.

Nitrogen, phosphorus is a nutrient element, industrial wastewater and domestic sewage in the nitrogen, phosphorus into the water body in large quantities, aquatic organisms

particularly algae will be a large number of reproduction, a large number of dead aquatic organisms are microbial decomposition, the decomposition process consumes a large

quantity of dissolved oxygen, dissolved oxygen concentration in the water declined sharply, thereby affecting the survival of aquatic organisms such as fish.

The principle of denitrification and phosphorus removal by activated sludge method in municipal wastewater plants is: the use of microorganisms to decompose organic nitrogen, and then converted to

nitrate, and then denitrify into nitrogen to be removed; phosphorus removal is the use of polyphosphorus bacteria to release phosphorus after a larger amount of phosphorus absorption

receiving phosphorus, so that phosphorus is enriched in the sludge, and phosphorus is removed by discharging the remaining sludge.