טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentSadigov Izhak
SubjectEffect of Salt Concentration on the Kinetic Parameters
of Ammonia Oxidation at Different pH
Values
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Emeritus Michal Green
Dr. Sheldon Tarre
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Biological nitrification, the oxidation of ammonia to nitrite and nitrate, is a key microbial process in the global nitrogen cycle. Free ammonia (NH3) is assumed to be the real substrate for ammonia oxidizing bacteria (AOB) and not the ion NH4+. This assumption is based on experiments where the affinity constant, Ks, for free ammonia did not significantly change at different pH values.

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 NitrosomonasN. 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.