Nitrogen exists in several ...

 Nitrogen exists in several forms. The principal nitrogen types of concern to wastewater treatment are: total Nitrogen (t-N), Total Kejeldahl Nitrogen (TKN), Ammonia (NH4 ), Organic Nitrogen (org-N), Nitrate (NO3 ), and Nitrite (NO2 ). Concentrations are reported in mg/L, as Nitrogen (N).

treatment facilities with total- nitrogen  effluent limits can oftentimes reduce the  organic nitrogen  to less than one mg/L by subjecting  wastewater  to strongly anaerobic and  organically -rich conditions. Nitrification. Ammonia removal is a strictly aerobic biological process.

Total Kejeldahl Nitrogen (TKN). TKN is made up of Ammonia (NH4 ) and organic-Nitrogen. A municipal wastewater treatment plant with an effluent containing more than 5 mg/L TKN is not fully nitrifying.

TKN = NH4 + org-N

organic-Nitrogen (org-N). A small fraction, typically one or two milligrams per liter, of the organicNitrogen is not amenable to biological treatment and passes through the treatment facility unchanged. A municipal wastewater treatment plant that is effectively nitrifying generally contains less than 3 mg/L organic-Nitrogen.Proteins represent a large portion of organic nitrogen and carbon in wastewater treatment effluents, but their detailed characteristics and their role and fate in receiving waters are virtually unknown.

Treatment plants convert the majority of the incoming nitrogen to nitrogen gas in a three step biological process.

 Step 1. Organic-nitrogen is converted to ammonia-nitrogen (NH4 ) by a mostly anaerobic process called Ammonification.

Step 2. Ammonia-nitrogen (NH4 ) is converted to nitrate-nitrogen (NO3 ) by an aerobic biological process called nitrification.

 Step 3. Nitrate-nitrogen (NO3 ) is converted to nitrogen gas biologically in a low-oxygen (anoxic) environment. During denitrification, nitrogen gas bubbles harmlessly out of wastewater into the atmosphere.

Ammonification.

 The majority of the nitrogen contained in raw sewage (urea and fecal material) is converted from organic-nitrogen to ammonia (NH4 ) as it travels through sewer pipes. As a result, the majority of the influent nitrogen is ammonia (NH4 ), although some organic-nitrogen remains. In most plants, less than 2 mg/L of organicnitrogen passes through the treatment plant untreated. The rest is converted to ammonia (NH4 ).

Ammonification is mostly an anaerobic process. It is sometimes called hydrolysis. Most treatment plants do nothing to enhance organic-nitrogen removal; it is not managed. However, treatment facilities with total-nitrogen effluent limits can oftentimes reduce the organic nitrogen to less than one mg/L by subjecting wastewater to strongly anaerobic and organically-rich conditions.

  Nitrification.

 Ammonia removal is a strictly aerobic biological process. Technically, bacteria convert ammonia (NH4 ) to nitrate (NO3 ); it isn’t really “removed.” Nitrification only works on ammonia (NH4 ). Organic-nitrogen is not converted directly to nitrate (NO3 ); it must first be converted to ammonia (NH4 ), and the ammonia (NH4 ) converted to nitrite (NO2 ) and then nitrate (NO3 ). Nitrifying bacteria are slower growing and more sensitive to environmental upset than BOD removing bacteria. Generally, nitrification occurs only under aerobic conditions at dissolved oxygen levels of more than 1.0 mg/L. In activated sludge facilities, nitrification requires a long retention time, a low food to microorganism ratio (F:M), a high mean cell residence time (measured as MCRT or Sludge Age), and adequate pH buffering (alkalinity).