ABSTRACT
The effect of salinity on the activity, the composition of nitrifiers and floc characteristics of nitrifying sludge was studied. Non-adapted and adapted (to 10 NaCl- Cl−/L for one year) enriched cultures of nitrifiers were tested in three sequencing batch reactors. Salt was increased gradually with 5 g Cl−/L up to 40 g C1−/L.
No difference in activity was observed between the adapted and non-adapted sludge. The activities of ammonia and nitrite oxidisers dropped 36% and 11%, respectively, at salt concentrations of 10 g Cl−/L. At 40 g Cl−/L inhibition reached 95% of salt free activity for ammonia and nitrite oxidisers in both adapted and non-adapted reactors. Nitrosomonas europaea and Nitrobacter sp. were the only nitrifiers present at high salt levels (using Fluorescent In Situ Hybridisation). Increased salt concentrations resulted in better settling characteristics of the nitrifying sludge. After 118 days the sludge was brought back to the initial conditions (0 g Cl−/L for non-adapted and 10 g Cl−/L for adapted). Despite the change in population composition similar kinetics as before the salt stress were observed.
