Nitrogen

In waters and wastewaters the forms of nitrogen of greatest interest are, in order of decreasing oxidation state, nitrate, nitrite, ammonia, and organic nitrogen. All these forms of nitrogen, as well as nitrogen are biochemically inter-convertible and are components of the nitrogen cycle. They are of interest for many reasons

Organic nitrogen is defined functionally as organically bound nitrogen in the trinegative oxidation state. It does not include all organic nitrogen compounds. Organic nitrogen includes such natural materials as proteins and peptides, nucleic acids and urea, and numerous synthetic organic materials. Typical organic nitrogen concentrations vary from a few hundred micrograms per liter in some lakes to more than 20 milligrams per liter in raw sewage.

Total oxidized nitrogen is the sum of nitrate and nitrite nitrogen. Nitrate generally occurs in trace quantities in surface water, but may attain high levels in some groundwater. In excessive amounts, it contributes to the illness known as methemoglobinemia, (blue baby syndrome) in infants. A limit of 10 milligrams of nitrate as nitrogen per liter has been imposed on drinking water to prevent this disorder. Nitrate is found only in small amounts in fresh domestic wastewater, but in the effluent of nitrifying biological treatment plants, nitrate may be found in concentrations of up to 30 milligrams of nitrate as nitrogen per liter.

Nitrite is an intermediate oxidation state of nitrogen, both in the oxidation of ammonia to nitrate and in the reduction of nitrate. Such oxidation and reduction may occur in wastewater treatment plants, water distribution systems, and natural waters. Nitrite can enter a water supply system through its use as a corrosion inhibitor in industrial process water. Nitrite is the actual etiologic agent of methemoglobinemia.

Ammonia is present naturally in surface and wastewaters. Its concentration generally is low in ground-waters because it adsorbs to soil particles and clays and is not leached readily from soils. It is produced largely by deamination of organic nitrogen containing compounds and by hydrolysis of urea. At some water treatment plants ammonia is added to react with chlorine to form a combined chlorine residual. Ammonia concentrations encountered in water vary from less than 10 micrograms ammonia nitrogen per liter in some natural surface and ground-waters to more than 30 milligrams per liter in some waste waters.