RESEARCH ARTICLE Factors controlling nitrous oxide emissions from a full-scale activated sludge system in the tropics Ariane C. Brotto 1,3 & Débora C. Kligerman 2 & Samara A. Andrade 1 & Renato P. Ribeiro 1 & Jaime L. M. Oliveira 2 & Kartik Chandran 3 & William Z. de Mello 1 Received: 12 December 2014 /Accepted: 30 March 2015 # Springer-Verlag Berlin Heidelberg 2015 Abstract Despite interest in characterizing nitrous oxide (N 2 O) emissions from wastewater treatment plants (WWTPs) in several parts of the globe, there are few studies in tropical zones. This study focus on the contribution of the scientific knowledge of anthropogenic nitrogen greenhouse gas emissions to climate change in tropical countries, investi- gating factors controlling N 2 O emissions in a non-biological nitrogen removal municipal WWTP. In terms of operational parameters, dissolved oxygen (DO) concentrations displayed a biphasic impact on N 2 O production and emission, with the highest emission at DO of 2.0 mg O 2 L -1 . The low solids retention time of 3 days also played a significant role, leading to nitrite accumulation, which is an important trigger for N 2 O production during nitrification. Furthermore, other factor es- pecially important for tropical countries, namely, temperature, also had a positive correlation with N 2 O production. Emission factors estimated for this study were 0.12 (0.02–0.31)% of the influent total nitrogen load and 8.1 (3 – 17)g N 2 O person -1 year -1 , 2.5 times higher than currently proposed emission factors. Therefore, the highly variability and depen- dence on operational parameters reinforce the use of a single emission factor is inadequate, especially for developing coun- tries with limited or variable extent of biological wastewater treatment and in regions of the world with widely varying climate patterns. Keywords Greenhouse gas . Nitrous oxide emission . Wastewater treatment . Activated sludge . Nitrite . Solids retention time Introduction Emissions of nitrous oxide (N 2 O) from wastewater treatment processes are gaining increased recognition as the collective action on the reduction of anthropogenic greenhouse gas (GHG) emissions has been globally recognized (UNFCCC 2007). Nitrous oxide has a global warming potential of ap- proximately 300 times that of CO 2 at a 100-year lifespan and it is the main ozone-depleting substance in the twenty-first cen- tury (Intergovernmental Panel on Climate Change (IPCC) 2007; Ravishankara et al. 2009). Domestic wastewater treat- ment systems contribute with 1.6 % of the total worldwide N 2 O emissions in 2010, and over 20 years, those emissions increased by 1.6 Tg CO 2 eq. (46 %) (USEPA 2012). The processes of N 2 O production in biological wastewater treatment results especially from biochemical transformations, called nitrification and denitrification, and are essentially those responsible for N 2 O production in soils, sediments, and water bodies as well (Wrage et al. 2001). Nitrification is a two-step biological process, first the oxidation of ammonia (NH 3 ) or ammonium (NH 4 + ) to nitrite (NO 2 - ) carried out by ammonia-oxidizing bacteria (AOB), followed by the oxida- tion of NO 2 - to nitrate (NO 3 - ) by nitrite-oxidizing bacteria Responsible editor: Bingcai Pan Electronic supplementary material The online version of this article (doi:10.1007/s11356-015-4467-x) contains supplementary material, which is available to authorized users. * Débora C. Kligerman deboracyklig@gmail.com 1 Departamento de Geoquímica, Instituto de Química, Universidade Federal Fluminense, Niterói, RJ 24020-141, Brazil 2 Departamento de Saneamento e Saúde Ambiental, Escola Nacional de Saúde Pública, Fundação Oswaldo Cruz, Rio de Janeiro, RJ 21041-210, Brazil 3 Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027, USA Environ Sci Pollut Res DOI 10.1007/s11356-015-4467-x