Chemical nitrite oxidation in acid solutions as a consequence of microbial ammonium oxidation.
In long-term experiments with membrane aerated biofilm reactors we observed complete nitrite oxidation in highly concentrated ammonium nitrite solutions with a contaminant pH decrease to values below 3. The maximum initial concentration for ammonium was 42 mM and for nitrite was 41 mM. We hypothesized that (1) acid-tolerant ammonium oxidizing bacteria were responsible for the pH decrease, and (2) chemical processes caused complete nitrite oxidation at low pH values. To test this hypothesis we set up a mechanistic computer model based on kinetic data from literature and we validated the model with additional experiments. The simulations fitted the measurements very well. Additionally, an experiment with the inhibitor allylthiourea showed that ammonium-oxidizing bacteria were active at pH values far below 5.5. Experiments in a sterile reactor confirmed the chemical nitrite oxidation to nitrate. Nitrogen balances revealed that 8 +/- 4% of the initial nitrogen (ammonium, nitrite, and nitrate) were lost during the cycles. On the basis of measurements and simulations we concluded that volatilization was responsible for the significant nitrogen loss. We estimated that about half of the lost nitrogen volatilized as nitrous acid HNO2. The rest mainly volatilized as dinitrogen N2 and nitrous oxide N2O.
Swiss Federal Institute of Environmental Science and Technology (EAWAG), 8600 Dübendorf Switzerland. udert@mit.edu
Kai M
KM
Udert
Tove A
TA
Larsen
Willi
W
Gujer
D001419:Bacteria / Q000378:metabolism*; D019149:Bioreactors; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry* / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009608:Nitrous Acid / Q000737:chemistry / Q000378:metabolism; D009609:Nitrous Oxide / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D013997:Time Factors; D014835:Volatilization; D014865:Waste Disposal, Fluid
D009566:Nitrates; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D009609:Nitrous Oxide; D009584:Nitrogen; D009608:Nitrous Acid