Industrial Wastewater Treatment - Methods for Removing Ammonia
What is Ammonia?
Ammonia (NH3) is a compound that is made of two gases: nitrogen (N) and hydrogen (H). It is colorless and has a distinct odor. Ammonia is used in many industries. In agriculture, for example, it is used for fertilizer. It is also used in food processing, metal finishing, chemical synthesis, ceramic production, oil refining, and many other industries. All of these industries produce wastewater that will contain concentrations of the Ammonia they use in their manufacturing process. Some forms of Ammonia are toxic to the environment.
What does Ammonia do in water?
WhenAmmonia reacts with water, it forms a weak base (pH >7). Two species of this compound exist in water: ionized NH4 (Ammonium) and non-ionized NH3 (Ammonia). It is the non-ionized form that is toxic. Generally, the equilibrium shifts toward a greater amount of non-ionized toxic NH3 with increasing pH.
NH3 + H2O ↔ NH4 + OH
One molecule of Ammonia reacts with one molecule of water to form an Ammonium ion and Hydroxyl ion. As the pH increases, the reaction moves more to the left, and the amount of toxic Ammonia increase. Concentrations of Ammonia (NH3) ranging between 0.5 ppm and 23 ppm are toxic to freshwater aquatic life.
Ammonium is broken down by aerobic organisms to form nitrate (NO3) in a two step process:
2 NH4+ + 3 O2 → 2 NO2− + 2 H2O + 4 H+
2 NO2− + O2 → 2 NO3−
Ammonia can also complicate wastewater Dissolved air flotation treatment by complexing the metals that are concentrated in the wastewater, making the metals more difficult to remove.
How is wastewater treated for Ammonia?
There are many methods for removing Ammonia/Ammonium from industrial wastewater. Some of the more common methods are listed here:
· Conventional activated sludge: A biological treatment method. This method requires expensive capital equipment and large tanks or concrete basins.
· Aeration: A time consuming and expensive method. This method requires a capital equipment investment and is used with conventional activated sludge to break down organic matter.
· SBR (Sequencing Batch Reactor): This process usually has several treatment steps that may include conventional activated sludge and aeration, in addition to a third and fourth step. This method requires an expensive capital investment and most often uses concrete basins.
· Ion exchange: The most economical method. This method requires lower capital investment in equipment and has a smaller footprint even for a large application. The same resins that are used to remove the Ammonia/Ammonium will also remove nitrates simultaneously.
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