When the nitrification process is controlled properly, nitrite-nitrogen seldom exceeds 1.0 mg/L. As soon as ammonia is oxidized to nitrite by ammonia-oxidizing bacteria (AOB), the nitrite is oxidized to nitrate by nitrite-oxidizing bacteria (NOB). Nitrite will increase, however, under certain environmental conditions, such as poorly established or inhibited NOB population. The NOB population may be poorly established during nitrification startup or inhibited because of environmental conditions—some of which operators can control.