Wastewater

Anhydrous ammonia (NH3) is a key chemical used in the wastewater treatment industry, serving two main functions: pH and alkalinity control and disinfection.

1. pH and Alkalinity Control

The most common and critical use of ammonia in wastewater is to adjust the pH and alkalinity of the water, which is essential for the biological treatment process.

• Balancing Nitrification: The biological removal of nitrogen (ammonia/ammonium) from wastewater, known as nitrification, is highly pH-sensitive and consumes a significant amount of alkalinity. Nitrifying bacteria thrive in a near-neutral pH range, typically 7.0 to 7.4
  
  

• The reaction of converting ammonia (NH4) to nitrate (NO3) destroys about 7.14 of alkalinity (as CaCO) for every mg of ammonia-nitrogen oxidized.
  
  

• If the alkalinity drops too low (e.g., below 50 mg/L), the pH of the water will fall, inhibiting the nitrifying bacteria and leading to a failure to remove nitrogen from the effluent.
  
  

• The Role of Anhydrous Ammonia:

• Anhydrous ammonia (a strong base) is added to neutralize acidity and raise the pH when influent wastewater is acidic or when the nitrification process has depleted the natural alkalinity.
  
  

• A key advantage of using ammonia for pH control is that it adds no additional salts to the solution, which can help eliminate solid precipitates and sludge that would require further handling.
  
  

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2. Disinfection (Chloramination)

Anhydrous ammonia is used in conjunction with chlorine to form more stable disinfectant compounds, a process called chloramination.23 This is particularly common in the final stage of drinking water treatment, but is also used for secondary disinfection in wastewater.

• Process: Chlorine (Cl) is added to the water, followed by the addition of ammonia (NH3).

• Resulting Chemical: The ammonia reacts with the chlorine to form chloramines (monochloramine, dichloramine, etc.).
  
  

• Function: Chloramines retain the oxidizing power of chlorine but are more stable and less reactive than free chlorine. This means they can maintain a disinfectant residual for a much longer time as the treated water flows through the distribution system, preventing microbial regrowth.
  
  

3. As a Nutrient Source (Less Common)

While wastewater already contains high levels of ammonia (which must be removed), some specialized industrial wastewaters are deficient in the nitrogen required for effective biological treatment.

• Context: Biological wastewater treatment relies on microorganisms to consume organic matter. These organisms require a balance of carbon, nitrogen, and phosphorus (C:N:P).
  
  

• Application: If the wastewater has a very high Carbon-to-Nitrogen (C/N) ratio (i.e., too much carbon and not enough nitrogen), a source of nitrogen, which could be anhydrous ammonia, may be added to maintain a healthy microbial population.

In summary, the use of anhydrous ammonia in the wastewater industry is primarily an operational necessity for pH buffering and alkalinity management to ensure the core biological nutrient removal process works efficiently, and secondarily for disinfection.