|M.Sc Student||Sadigov Izhak|
|Subject||Effect of Salt Concentration on the Kinetic Parameters|
of Ammonia Oxidation at Different pH
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Michal Green|
|Dr. Sheldon Tarre|
|Full Thesis text - in Hebrew|
The main objective of this research is to determine if free ammonia is the exclusive substrate for AOB or that AOB can also uptake the anion NH4+. The research was based on two strains of Nitrosomonas: N. oligotropha which seems to be capable to nitrify ammonia at low pH values and N. europaea which is the AOB of choice among microbiologists. Previous results indicated that salinity concentration can also influence ammonia uptake and maximum nitrification rate. In this research, the influence of salinity concentration on bio-kinetics values at each pH is studied.
The kinetic experiments were carried out at different pH values between 6.5-8.
Ammonia oxidation rates were determined by the degradation of ammonia as a function of time. Ks values and qmax were calculated using Lineweaver-Burke plots.
Results showed that both strains have highest nitrification rates in the narrow range of pH 7.5-8 at low salinity. At high salinity, the highest qmax was achieved at pH 7.5 for N. oligotropha, and in the case of N. europaea at pH 8. Values for qmax are lower at higher salinity concentrations. The salt affects qmax in the case of N. oligotropha much more than N. europaea. It seems that for N. oligotropha the Ks for free ammonia changes significantly under ‘high salinity’ and ‘low salinity’ conditions. On the other hand, for N. europaea the change in Ks for free ammonia under low salinity conditions is as much as 8 fold, while under high salinity conditions values drop as much as 5 fold.
These results suggest that under conditions of lower salinity free ammonia isn't the only substrate for nitrification at both strains of N. oligotropha and N. europaea. The difference in kinetic parameters results between high and low salinity suggests that energy demanding functions such as osmoregulation under high salinity can disable or prevent ammonium ion uptake.
In conclusion, the results of this research together with the observation of high rate nitrification at values of pH<4 suggest that AOB are able to use the ammonium ion, NH4+, as a substrate for the biological nitrification process.