Which type of bacteria primarily performs nitrification in wastewater treatment?

• A. Nitrifying bacteria
• B. Denitrifying bacteria
• C. Methanogenic bacteria
• D. Heterotrophic bacteria

Answer: (A)

Nitrification is the aerobic biological process that oxidizes ammonia to nitrite and then to nitrate. This task is carried out mainly by nitrifying bacteria, which are autotrophs using ammonia as an energy source and carbon dioxide as their carbon source. In wastewater treatment, two groups handle the steps: ammonia-oxidizing bacteria convert ammonia to nitrite, and nitrite-oxidizing bacteria convert nitrite to nitrate. Oxygen must be present for this process to occur, which is why nitrification happens in aerated zones of the treatment system.

Denitrifying bacteria perform the reverse under low or no oxygen, turning nitrate into nitrogen gas. Methanogenic bacteria produce methane in anaerobic environments, not in the nitrification pathway. Heterotrophic bacteria primarily consume organic carbon compounds and are not defined by nitrification as their main role, though they contribute to breaking down organics in the system. Therefore, the organisms primarily responsible for nitrification are the nitrifying bacteria.