Acid-tolerant ammonia oxidizers allow for fast but unstable nitrification at low pH values. Acid-tolerant ammonia oxidizers allow for fast but unstable nitrification at low pH values

Ammonium oxidation and acidotolerant AOB growing under acidic conditions and high TN concentrations was investigated. Starting with activated sludge (AS) from a urine nitrification reactor, acidotolerant AOB were enriched with source-separated urine at a pH value of 5 and TN concentrations above 1000 mg N L-1. The predominant AOB specie was determined, and the effect of various environmental conditions on the acidotolerant AOB were tested. In particular, the long-term effect of pH values between 5 to 7 on the activity of acidotolerant AOB was investigated, which is important in cases where acidotolerant AOB should be avoided in the first place.