The response of nitrous oxide emissions to different operating conditions in activated sludge wastewater treatment plants in Southeastern Brazil.

The continuous measurements of NO emissions from the aeration tanks of three activated sludge wastewater treatment plants (WWTPs) operated with biological nitrogen removal (BNR) and non-BNR were performed during the different operating conditions of several parameters, such as aeration, dissolved oxygen (DO) profiling and organic shock loading (with landfill leachate). The nitrification process is the main driving force behind NO emission peaks. There are indications that the variation of the air flow rate influenced NO emissions; high NO emissions denote over-aeration conditions or incomplete nitrification, with accumulation of NO concentrations. Thus, continuous measurements of NO emissions can provide information on aeration adequacy and the efficiency of complete nitrification, with major focus on DO control, in order to reduce NO emissions. An additional concern is the observed propensity of WWTPs in developing countries to receive landfill leachates in their wastewater systems. This practice could have adverse effects on climate change, since wastewater treatment during periods of organic shock loading emitted significantly higher amounts of NO than without organic shock loading. In short, non-BNR WWTPs are subject to high NO emissions, in contrast to BNR WWTP with controlled nitrification and denitrification processes.