No abstract

Denitrifying enhanced biological phosphorus removal (EBPR) systems can be an efficient means of removing phosphate (P) and nitrate (NO) with low carbon source and oxygen requirements. Tetrasphaera is one of the most abundant polyphosphate accumulating organisms present in EBPR systems, but their capacity to achieve denitrifying EBPR has not previously been determined. An enriched Tetrasphaera culture, comprising over 80% of the bacterial biovolume was obtained in this work. Despite the denitrification capacity of Tetrasphaera, this culture achieved only low levels of anoxic P-uptake. Batch tests with different combinations of NO, nitrite (NO) and nitrous oxide (NO) revealed lower NO accumulation by Tetrasphaera as compared to Accumulibacter and Competibacter when multiple electron acceptors were added. Electron competition was observed during the addition of multiple nitrogen electron acceptors species, where P uptake appeared to be slightly favoured over glycogen production in these situations. This study increases our understanding of the role of Tetrasphaera-related organisms in denitrifying EBPR systems.

This study aims at investigating the relationship between the nitric oxide (NO) and nitrous oxide (N 2 O) production rates with the ammonia oxidation rate (AORsp) in an enriched AOB culture. Different concentrations of ammonia were applied in a sequential batch reactor (SBR) performing partial nitritation in order to determine the effect of AORsp on N 2 O and NO production rates. Results showed that NO linearly correlates with the AORsp whereas N 2 O presents an exponential relationship. The effect of changes on the dissolved oxygen (DO) concentration on the overall NO and N 2 O emissions was assessed by increasing and decreasing the DO maintaining a constant pH at 7. When DO decreased the AORsp was maintained at the level achieved with the starting DO and led to lower NO and N 2 O emissions than when DO was increased. Finally, the effect of pH on N 2 O and NO was also tested by maintaining the DO at 1.5-2 mg O 2 /L while pH was gradually decreased from 8 to 6.5. Results show that NO was chemically produced due to the addition of HCl when decreasing the pH whereas N 2 O was only produced biologically and was not affected by the addition of HCl.