The inhibitory effect of free
ammonia (NH(3) or FA) and free
nitrous acid (HNO(2) or FNA) on the
ammonia oxidizing bacteria (AOB) and the dependence of the AOB activity on the concentration of total inorganic
carbon (
TIC) are well-established. In contrast, less is know about the effect of high FA and FNA concentrations in combination with
TIC limitation. Respirometric tests performed with an enriched AOB sludge (81% of AOB as measured with fluorescent in situ hybridization) established that AOB inhibition by FA under
TIC limitation was higher than under non-limiting
TIC conditions (Haldane inhibition coefficients of 139 and 376 mg NH(3)L(-1)). AOB affinity for FA decreased under
TIC limitation conditions (half-saturation coefficient of 0.28 mg NH(3)L(-1) without
TIC limitation and 4.3 mg NH(3)L(-1) with
TIC limitation). Higher inhibition by FNA was observed when
TIC was limited since the non-competitive inhibition coefficient decreased from 1.31 mg HNO(2)L(-1) (without
TIC limitation) to 0.21 mg HNO(2)L(-1) (with
TIC limitation). This study demonstrates that AOB inhibitions by FA and FNA are amplified with
TIC limitation and consequently, AOB dynamics are strongly modified under
TIC limitation conditions.