For an activated sludge nitrification process, how much alkalinity is required to oxidize 0.45 kg (1 lb) of ammonia?

In an activated sludge nitrification process, ammonia is converted into nitrate through the activity of nitrifying bacteria, specifically ammonium-oxidizing bacteria and nitrite-oxidizing bacteria. This process requires not only the presence of ammonia but also sufficient alkalinity to support the reaction, particularly due to the generation of hydrogen ions that occur as ammonia is oxidized.

When 0.45 kg (1 lb) of ammonia is oxidized, approximately 7.14 kg (3.2 lb) of alkalinity is needed. This alkalinity primarily comes from bicarbonate (HCO₃⁻) ions in the water, which help to neutralize the acid produced during nitrification, ensuring that the pH remains stable.

The stoichiometry of the reaction dictates that for every 1 kg of ammonia oxidized, about 7.1 kg of alkalinity is required. This is necessary to maintain conditions conducive for bacterial activity and overall process efficiency. Hence, when calculating the alkalinity needed for 0.45 kg of ammonia, the resulting 3.2 kg aligns with the needed stoichiometric requirements for the nitrification process, making this choice correct.