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Abstract: This study discusses the results of the continuous monitoring of nitrous oxide emissions from the oxidation tank of a pilot conventional wastewater treatment plant. Nitrous oxide emissions from biological processes for nitrogen removal in wastewater treatment plants have drawn great attention over the last years, due to the high greenhouse effect. However, even if several studies have been carried out to quantify nitrous oxide emission rates from different types of treatment, quite wide ranges have been reported. Only grab samples or continuous measurements over limited periods were considered in previous studies, which can account for the wide variability of the obtained results. Through continuous monitoring over several months, our work tries to fill this gap of knowledge and get a deeper insight into nitrous oxide daily and weekly emission dynamics. Moreover, the influence of some operating conditions (sludge age, dissolved oxygen concentration in the oxidation tank, nitrogen load) was studied to determine good practices for wastewater treatment plant operation aiming at the reduction of nitrous oxide emissions. The dissolved oxygen set-point is shown to play a major role in nitrous oxide emissions. Low sludge ages and high nitrogen loads are responsible for higher emissions as well. An interesting pattern has been observed, with quite negligible emissions during most of the day and a peak with a bell-like shape in the morning in the hours of maximum nitrogen load in the plant, correlated to the ammonia and nitrite peaks in the tank. [Copyright &y& Elsevier]

The objective of this research was to develop a mechanistic model for quantifying N2O emissions from activated sludge plants and demonstrate how this may be used to evaluate the effects of process configuration and diurnal loading patterns. The model describes the mechanistic link between the factors recognized to correlate positively with N2O emissions. The primary factors are the presence of ammonia and nitrite accumulation. Low dissolved oxygen concentrations also may be implicated through differential impacts on ammonia-oxidizing bacteria (AOB) versus nitrite-oxidizing bacteria (NOB) activity. Factors promoting N2O emissions at treatment plants are discussed below. The model was applied to data from laboratory and pilot-scale systems. From a practical standpoint, plant configuration (e.g., plug-flow versus complete-mix), influent loading patterns (and peak load), and certain operating strategies (e.g., handling of return streams) are all important in determining N2O emissions. [ABSTRACT FROM AUTHOR]