Total Kjeldahl Nitrogen (TKN) is the U.S. EPA-approved parameter used to measure organic nitrogen and ammonia. The TKN content of influent municipal wastewater is typically between 35 and 60 mg/L. Organic nitrogen compounds in wastewater undergo microbial conversion to NH3 and ammonium ion NH+ 4. Ammonium ion is the first inorganic nitrogen species produced during biological wastewater treatment. Nitrification is a two-step biological process used to remove ammonium in wastewater. The bacterium Nitrosomonas converts ammonium to nitrite (NO2). The bacterium Nitrobacter converts nitrite to nitrate (NO-3).
A denitrification process is used to reduce the nitrate generated in the preceding steps to nitrogen gas. The NPDES effluent limit for ammonium-nitrogen (NH+4 – N) can range from 0.1 to 1.0 mg/L and the limit for nitratenitrogen (NO- 3 – N) from 3-10 mg/L.
On April 17th, 2012, the U.S. EPA Administrator signed a Methods Update Rule (MUR) approving new analytical methods for testing of pollutants in wastewater under the Clean Water Act. The U.S. EPA published the final rule in the Federal Register of May 18, 2012.