Nitric and nitrous oxides from denitrifying activated sludge at low oxygen concentration

Abstract

To determine the net-production of the denitrification intermediates nitric oxide (NO) and nitrous oxide (N2O), two batch experiments with different nitrite concentrations have been performed (A: 3.5 g NO2−-Nm−3, B: 12 g NO2−-Nm−3). In these experiments the concentration of oxygen in the reactor has been varied from 4 g O2m−3 to 0 g O2m−3. As NO and N2O might be produced by nitrifiers as well, the sludge used was unable to nitrify due to a low sludge age. High nitrite as well as aerobic conditions favor the production of N2O but not the production of NO. Furthermore, NO was accumulated at very low concentration and the highest emission was under completely anoxic conditions. A mathematical model has been formulated describing the reduction of nitrate, nitrite, and nitrous oxide. Noncompetitive inhibition of these processes by oxygen and nitrite has been included in the kinetics. The estimated parameters indicate that nitrite serves mainly as a denitrification intermediate rather than as an inhibitor. The net-production of N2O at low oxygen concentrations can be explained by different oxygen inhibition of the three reduction steps. The fast reduction of N2O is most inhibited by oxygen. As a consequence, the reduction of N2O is a slower process under low oxygen pressure than the reduction of nitrate and nitrite.

Ecological Aspects of Biological Phosphorus Removal in Activated Sludge Systems

“…At an initial concentration of about 0.3 mM NO in the liquid phase, phosphate release by the sludge was almost completely inhibited; about 0.15 mM NO was required for complete inhibition of adenylate kinase in the crude cell-free extr~cts of the sludge. These levels are significantly higher than the NO levels found in treatment plants (von Schulthess et at., 1994).…”

A consilience model to describe N2O production during biological N removal

“…57 Both approaches describe the electron donor and acceptor limitations with a specific Monod dependency for each denitrification step. 57,58 The known oxygen inhibition of the HD pathway has been described by either a single inhibition constant or a specific oxygen inhibition constant for each denitrification step. 53,57 Even though the indirect approach has been heralded as superior as it can potentially describe more data sets, information about newly proposed reaction kinetics is not available in the literature.…”

Formation of nitrous oxide in a gradient of oxygenation and nitrogen loading rate during denitrification of nitrite and nitrate

“…N 2 O emission during the biological nitrogen removal process in wastewater treatment plants (WWTPs) has been considered as a greenhouse gas source [1][2][3][4]. Both nitrification and denitrification were found to contribute to N 2 O emission [1,[5][6][7][8][9][10][11][12][13]. A low dissolved oxygen (DO) or a high nitrite concentration is the most likely cause of elevated NO and N 2 O emission by ammonia-oxidizing bacteria (AOB) during nitrification [4,14].…”

“…Under anoxic conditions, N 2 O produced can be further reduced to N 2 by nitrous oxide reductase (N 2 OR) in the presence of electron donor [15,16]. To understand the mechanism of N 2 O emission, factors and operational parameters related to N 2 O emission have been investigated, including the level of nitrite, DO concentration, sludge retention time (SRT), pH, and carbon/nitrogen (C/N) ratio [4,5,7,[17][18][19][20].…”