Ammonia – What is it? and why is it measured?

Ammonia - What is it?

ammonia ammonia molecule
  • Ammonia is a biological waste product.
  • It is toxic.
  • It often has to be reduced to a low level in waste water treatment.
  • Consent limits are often in place for ammonia.
  • The chemical formula is NH3.
  • In most natural waters it is present as ammonium NH4+


How is it measured?

  • Ammonia can be measured in four ways
  • by ion selective electrode
  • by gas sensing electrode
  • using a colour reaction and measuring the resulting colour
  • by absorption of infra red wavelengths in the gas phase.

measuring ammonia

Ammonia can be measured on-line or using ammonia test kits

What do NH3, NH4 and NH3-N mean?

NH3 is the ammonia molecule. Molecular weight is 17g/mol

NH4+ is the ammonium ion. It has a positive charge and a molecular weight of 18g/mol.

NH3-N represents the Nitrogen content of the ammonia, NH4-N is the nitrogen content of the ammonium ion. This is used when people wish to track nitrogen  through the treatment process. The nitrogen is converted to nitrate NO3- (a negatively charged ion) by the normal treatment processes. In some cases nitrate removal is required as a stage in the treatment. However the process runs it can be that people wish to track the conversion of NH4+ to NO3- and a good way to do this is to follow the nitrogen. (i.e. How much nitrogen comes in (as NH4+) and how much is converted to NO3-.)

Measurement results are expressed in different ways. Most instruments allow the analytical result to be expressed in different ways - usually setting this is part of the commissioning procedure.It is important to know how the results are expressed, from both the on site measurements and off site laboratory analysis.

17 mg/lt NH3 - ammonia is equivalent to 13 mg/lt NH3-N

18 mg/lt NH4 ammonium is equivalent to 13 mg/lt NH4-N

These are a few practical notes which relate to ammonia measurement, more in depth information is available in our download section.

For more information please contact Envitech or log in to our download page for access to technical documentation.