April 2009, Vol. 21, No.4


Decoding Nitrogen Terminology

Woodie Mark Muirhead

Discharge permits regulate various forms of nitrogen based on the environmental concern related to the specific form. The nitrogen’s form dictates how it affects water quality, as the points below show:

  • Ammonia and organic nitrogen can result in oxygen depletion in receiving waters, but nitrate does not.
  • Ammonia, specifically un-ionized ammonia, can cause aquatic toxicity.
  • Nitrite can cause methemeglobinemia (blue baby syndrome), but nitrate is often regulated because it is more prevalent in effluent discharges and can be converted to nitrite in the human digestive system.
  • Organic nitrogen can be oxidized progressively by different microorganisms to produce all forms of nitrogen and cause a wide range of environmental impacts.


Multiple environmental impacts might be a concern for some discharges, resulting in permit limits for total nitrogen, total inorganic nitrogen, and other forms.

Knowing the relationships among various forms of nitrogen helps explain the basis for our permit limits, understand the treatment processes used to achieve those limits, and interpret data for process control and compliance. The table (above) lists the symbols, names, and components of the various classifications of nitrogen. The Nitrogen Map (below) shows the same information graphically.


Once the differences among types of nitrogen are known, it’s equally important to know which analytical method will yield the desired result. The Nitrogen Map also shows which methods are appropriate. The referenced methods are from Standard Methods for the Examination of Water and Wastewater (SM) or from the U.S. Environmental Protection Agency.

Woodie Mark Muirhead is an operations specialist and vice president in the Honolulu office of Brown and Caldwell (Walnut Creek, Calif.). Thanks to Keith Chapman, laboratory program manager at the Willow Lake Water Pollution Control Facility (Salem, Ore.).