Why is it so hard to maintain ammonia removal in wastewater treatment systems?

When compared to BOD/COD removing microbes, we spend an inordinate amount of time monitoring or worrying about ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) populations. What makes these bacteria so difficult to maintain in a wastewater treatment unit? Here are a few reasons:

• Both AOB & NOB are slow growing when compared to many heterotrophic organisms. They are among the slowest growing organisms in the biological waste treatment unit.
• Require a relatively narrow pH range - AOB/NOB work between roughly 6.8 - 8.2 pH. Outside the range you have problems with substrate toxicity or substrate not being available to the microbes.
• Must have D.O. - oxidizing ammonia requires oxygen. Even newer Anaerobic Ammonia Oxidation (ANAMMOX) systems must have an aerobic section to produce nitrite before the anaerobic step.
• Alkalinity - in addition to maintaining pH stability, carbonates also provide carbon for AOB/NOB cell growth.
• Easily harmed by many common influent compounds - this list includes phenol, cyanide, sulfides, and many surfactants or household chemicals.
• Require most COD/BOD to be removed for a population to develop - this is a low F/M where competition for dissolved oxygen and micronutrients drops.
• Temperature - AOB/NOB do not grow well at low or high temperatures. The general good growth range is 15 - 35 Deg C.