Single stage biological nitrogen removal by nitritation and anaerobic ammonium oxidation in biofilm systems

in full scale wastewater treatment plants with at times considerable defici ts in the nitrogen balances, it could hitherto not be sufficiently explaine d which reactions are the cause of the nitrogen losses and which micro-orga nisms participate in the process. The single stage conversion of ammonium i nto gaseous end-products - which is henceforth referred to as deammonificat ion - occurs particularly frequently in biofilm systems. In the meantime, o ne has succeeded to establish the deammonification processes in a continuou s flow moving-bed pilot plant. In batch tests with the biofilm covered carr iers, it was possible for the first time to examine the nitrogen conversion at the intact biofilm. Depending on the dissolved oxygen (DO) concentratio n, two autotrophic nitrogen converting reactions in the biofilm could be pr oven: one nitritation process under aerobic conditions and one anaerobic am monium oxidation. With the anaerobic ammonium oxidation, ammonium as electr on donor was converted with nitrite as electron acceptor. The end-product o f this reaction was N-2. Ammonium and nitrite did react in a stoichiometric al ratio of 1 :1.37, a ratio which has in the very same dimension been desc ribed for the ANAMMOX-process (1 : 1.31+/-0.06). Via the oxygen concentrati on in the surrounding medium, it was possible to control the ratio of nitri tation and anaerobic ammonium oxidation in the nitrogen conversion of the b iofilm. Both processes were even ly balanced at a DO concentration of 0.7 m g/l, so that it was possible to achieve a direct, almost complete eliminati on of ammonium without addition of nitrite. One part of the provided ammoni um did participate in the nitritation, the other in the anaerobic ammonium oxidation. Through the aerobic ammonium oxidation into nitrite within the o uter oxygen supplied layers of the biofilm, the reaction partner was produc ed for the anaerobic ammonium oxidation within the inner layers of the biof ilm.