Total Kjeldahl Nitrogen (TKN) is the U.S. EPA-approved parameter used to measure organic nitrogen and ammonia.

The nitrogen cycle is the means by which atmospheric nitrogen is made available in various forms to living organisms. From the basic molecules of ammonia, nitrate, and nitrite to the more complex amino acids and proteins, nitrogen is essential for living organisms to function. It is also an important part in the smooth operation of many wastewater treatment plants. In order for the cycle to operate smoothly it is vital to know the amount of nitrogen contained in.