Ammonium (NH 4 + ) – or its uncharged form, ammonia (NH 3 ) – is a form of nitrogen that aquatic plants can take up and bind to proteins, amino acids and other molecules. High concentrations of ammonium can promote the growth of algae and aquatic plants. Bacteria can also convert high ammonium salts to nitrate (NO 3 -) during nitrification, which reduces dissolved oxygen.
Ammonia in water is either non-ionic ammonia or ammonium ions. Usually, the value reported is the sum of the two forms and is reported as total ammonia or simply – ammonia. The relative proportions of the two forms present in water are strongly influenced by the pH value.
Non-ionic ammonia is the toxic form and dominates at high pH values. NH 4+ ions are relatively non-toxic and dominate at low pH values. Typically, less than 10% of ammonia is in the toxic form at pH values less than 8.0 pH units. This percentage increases significantly with increasing pH. The balance between NH 3 and NH 4 + is also affected by temperature. At any pH, more toxic ammonia is present in colder water.
Nitrogen is present in a wide range of compounds and forms and is considered the ultimate “fast change artist”. In municipal wastewater, it is encountered mainly as a waste product in the form of urea, which has been partially converted to ammonium nitrogen by ammonification. In an aeration tank, the initial step of nitrification consists in the oxidation of the nitrogen present in the wastewater to nitrate by nitrite, which requires oxygen.
For fish, ammonium is already toxic at very small concentrations. Therefore, water bodies with an ammonium concentration of 1 mg/l are not suitable for fishing. Therefore, the discharge values that must be met are very low.
Why monitor ammonia?
Ammonia is used both as a reagent and as a measurement parameter in several areas of water and wastewater treatment.
- To monitor natural ammonia in source water.
- During chloramine disinfection, ammonia is combined with chlorine to treat drinking water and maintain a more permanent residue in the distribution system.
- Sometimes ammonia is used to control pH values, for example in the pharmaceutical industry.
- Ammonia is widely monitored in wastewater nitrification and denitrification processes.
Although generally harmless at low concentrations, ammonia at high concentrations can cause damage and pose a health risk. Therefore, ammonia levels must be properly monitored and maintained.