Water Guide - Understanding Ammonium and Ammonia in Water Systems

Ammonium and Ammonia

Article contents:

1. What Are Ammonium and Ammonia?

2. How Is Ammonia Made?

3. Ammonia and Ammonium in Nature

4. Why Ammonia Is Dangerous to Aquatic Life

5. Membrane Technology Challenges with Ammonia

6. C0nclusion

7. FAQ

What Are Ammonium and Ammonia?

Ammonia (NH₃) is a pungent, toxic, water-soluble gas with a molecular weight of 17 g/mol. In water, it undergoes a chemical reaction forming ammonium ions (NH₄⁺) with a molecular weight of 18 g/mol. This balance between ammonia and ammonium is heavily pH-dependent:

• High pH (alkaline): favors ammonia (NH₃)

• Low pH (acidic): favors ammonium (NH₄⁺)

  
  

Understanding this equilibrium is key for both environmental monitoring and water treatment technologies.

How Is Ammonia Made?

Industrially, ammonia is synthesized using the Haber-Bosch process, combining nitrogen and hydrogen under specific conditions:

• N₂:H₂ ratio = 1:3

• Pressure = 250–350 bar

• Temperature = 450–550°C

• Catalyst = α–iron

  
  

Reaction equation: N₂ + 3 H₂ → 2 NH₃

This process is vital for producing ammonia used in fertilizers, chemicals, and water treatment agents.

Ammonia and Ammonium in Nature

In natural environments, ammonia and ammonium arise from biological processes:

• Nitrogen fixation: Microorganisms like cyanobacteria and rhizobium fix atmospheric nitrogen into ammonia.

  
  

• Decomposition: Organic proteins decompose into ammonium through microbial activity.

  
  

• Nitrification: In oxygen-rich water, bacteria oxidize ammonium → nitrite, → nitrate.

While helpful in nutrient cycling, excessive ammonium leads to oxygen depletion and toxic nitrate buildup, which damages aquatic ecosystems.

Why Ammonia Is Dangerous to Aquatic Life

Ammonia is highly toxic to fish. As pH increases, more ammonia (NH₃) is present, raising toxicity levels. The danger threshold is:

• 0.5 to 1 mg/L ammonium concentration

Fish kills can occur due to direct toxicity or due to oxygen consumption from nitrification.

Membrane Technology Challenges with Ammonia

In processes like reverse osmosis (RO), this balance causes complications:

• Ammonium ions (NH₄⁺) are retained by the membrane

• Ammonia gas (NH₃) passes through, contaminating the permeate

  
  

This raises conductivity in the treated water, affecting quality.

Best Practices to Mitigate This Issue

1. Pre-treatment pH adjustment: Lower pH to favor NH₄⁺ formation

   
   

2. Ion removal: Use ion exchange or chemical precipitation to remove ammonium

   
   

3. Post-treatment pH restoration: Raise pH to meet final water specs

This approach ensures both effective filtration and compliance with water quality standards.

Conclusion

• Ammonia/ammonium equilibrium is pH-sensitive

  
  

• Toxicity and oxygen demand increase with ammonium overload

  
  

• Water treatment systems must adapt pH levels to retain ammonium and block ammonia gas

  
  

By mastering this balance, engineers and environmental professionals can improve water safety and filtration efficiency.

FAQs

1. Is ammonia in water always harmful?

Not always, but it becomes dangerous when pH is high and ammonia (NH₃) becomes more dominant, which is toxic to aquatic life.

2. Can ammonium be removed through reverse osmosis?

Partially. Ammonium ions are retained, but ammonia gas can pass through the membrane if the pH is too high.

3. What is the ideal pH to minimize ammonia presence in RO systems?

Lowering the pH to below 7 helps shift the balance toward ammonium, which membranes can better retain.

4. Does nitrification remove ammonium naturally in lakes or rivers?

Yes, but it consumes oxygen and produces nitrate, which can also be problematic in excess.

5. Why is ammonia dangerous in aquaculture?

It interferes with fish respiration and can be fatal even at low concentrations.