ABSTRACT
47The effect of various types of salt on the activity of ammonia and nitrite oxidisers was investigated. Enriched cultures of nitrifiers obtained from two lab-scale sequencing batch reactors operated at sludge age (SRT) of 30 and 100 days were used in this study. The fluorescent in situ hybridisation technique was used to identify the presence of ammonia and nitrite oxidisers in both reactors. Respiration activity tests were used to determine the shock load effects of salt on ammonia and nitrite oxidisers under controlled conditions (pH 7.5, T: 30°C).
At the same molar concentration the divalent cations (CaCl2, MgCl2) have a stronger inhibitory effect than monovalent cations both on ammonia and nitrite oxidisers. The effect of different salt ions was evaluated and quantified. Based on this a basic equation for the impact of salts on nitrification processes was proposed.
SRT has no effect on the tolerance of ammonia oxidisers for shock loads of salt, nor on the type of ammonia oxidisers present. Moreover, the different ammonia oxidising species seem to have a similar response to salt stress at similar environmental conditions. In contrast, SRT has a significant impact on salt tolerance of nitrite oxidisers: the longer the sludge age the stronger the inhibition. The results demonstrate that Nitrobacter agilis is more resistant to shock loads of salt than Nitrospira under the same environmental conditions.
