Balancing of nitrogen conversion in deammonifying biofilms through batch tests and GC/MS

Growth carriers from a technical deammonifying moving-bed WWTP were used in batch tests to determine possible N-conversion reactions under varying oxygen and substrate conditions. Deammonification, denitrification, and nitrification reactions could be proved using conventional analysis, combined with gas chromatography/mass spectrometry analysis to get additional information about ¹⁵N-isotope labelled gaseous end products of the different reactions. In this orientating study N₂O could be observed in some cases up to 12% of the total gas production. N₂O production came from incomplete denitrification processes under anoxic or oxygen-limiting conditions and in the absence of organic substrate. It seems as if structural components of deammonifying biofilms play a crucial role for the portion of side-reactions, leading to undesirable gaseous end products.