Greenhouse gases from wastewater treatment — A review of modelling tools Giorgio Mannina a, ⁎, George Ekama b , Donatella Caniani c , Alida Cosenza a , Giovanni Esposito d , Riccardo Gori e , Manel Garrido-Baserba f , Diego Rosso f,g , Gustaf Olsson h a Dipartimento di Ingegneria Civile, Ambientale, Aerospaziale, dei Materiali, Università di Palermo, Viale delle Scienze, 90100 Palermo, Italy b Water Research Group, Department of Civil Engineering, University of Cape Town, Rondebosch, 7700 Cape, South Africa c Department of Engineering and Physics of the Environment, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy d Department of Civil and Mechanical Engineering, University of Cassino and the Southern Lazio, Via Di Biasio, 43, 03043 Cassino, FR, Italy e Department of Civil and Environmental Engineering, University of Florence, Via Santa Marta 3, 50139 Florence, Italy f Department of Civil & Environmental Engineering, University of California, Irvine, CA 92697-2175, USA g Water-Energy Nexus Center, University of California, Irvine, CA 92697-2175, USA h Department of Industrial Electrical Engineering and Automation (IEA), Lund University, Box 118, SE-22100 Lund, Sweden HIGHLIGHTS • The state of the art in GHG production/ emission/modelling from WWTPs was outlined. • Detailed mechanisms of N 2 O produc- tion by AOB are still not completely known. • N 2 O modelling could be improved considering both AOB pathways contribution. • To improve protocols the regulatory framework among countries has to be equalized. • Plant-wide modelling can help model- ler/engineer/operator to reduce GHG emissions. GRAPHICAL ABSTRACT abstract article info Article history: Received 28 October 2015 Received in revised form 22 January 2016 Accepted 24 January 2016 Available online 12 February 2016 Editor: Simon Pollard Nitrous oxide, carbon dioxide and methane are greenhouse gases (GHG) emitted from wastewater treatment that contribute to its carbon footprint. As a result of the increasing awareness of GHG emissions from wastewater treatment plants (WWTPs), new modelling, design, and operational tools have been developed to address and reduce GHG emissions at the plant-wide scale and beyond. This paper reviews the state-of-the-art and the re- cently developed tools used to understand and manage GHG emissions from WWTPs, and discusses open prob- lems and research gaps. The literature review reveals that knowledge on the processes related to N 2 O formation, especially due to auto- trophic biomass, is still incomplete. The literature review shows also that a plant-wide modelling approach that includes GHG is the best option for the understanding how to reduce the carbon footprint of WWTPs. Indeed, sev- eral studies have confirmed that a wide vision of the WWPTs has to be considered in order to make them more sustainable as possible. Mechanistic dynamic models were demonstrated as the most comprehensive and reliable tools for GHG assessment. Very few plant-wide GHG modelling studies have been applied to real WWTPs due to Keywords: Greenhouse gas Emission Carbon footprint Nitrous oxide Science of the Total Environment 551–552 (2016) 254–270 ⁎ Corresponding author. E-mail address: giorgio.mannina@unipa.it (G. Mannina). http://dx.doi.org/10.1016/j.scitotenv.2016.01.163 0048-9697/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv