Global warming is one of the major challenges for our society and all industry sectors must take responsibility for their emissions and implement new strategies to minimize them. Wastewater systems are recognised to contribute to greenhouse gas (GHG) emissions not just through their energy consumption but also through their direct fugitive GHG. Recent studies have shown that direct emissions of fugitive GHG as nitrous oxide (N2O) and methane (CH4) from wastewater treatment plants (WWTPs) are significantly larger than anticipated and can even overcome the indirect emissions. Research carried out during the past 5 years indicates that nitrifying bacteria are the main responsible of N2O emissions in WWTP performing nutrient removal. There is a need to fully understand N2O production mechanisms in these microorganisms. The NITRI-GHG project aims to minimise N2O production from novel pathways active in ammonia oxidizing bacteria, the hydroxylamine oxidation and the nitrifier denitrification pathway.On the other hand, the project also explores a novel methane oxidation process carried out by nitrifying bacteria. CH4 is being increasingly produced in WWTPs due to the large implementation of anaerobic wastewater treatment technology and anaerobic sludge digestion process. Although methane in the gas phase is captured, significant uncertainty exists regarding the loss of dissolved methane which can be up to 50%. The introduction of an economically feasible methane oxidation unit in the typical polishing step of anaerobic digester effluents could significantly lower the overall direct GHG emissions from WWTP.The approach of this project is to gain fundamental understanding at the micro level to develop advanced operational strategies to reduce N2O and CH4 emissions from our WWTPs. The project combines environmental engineering with microbial ecology tools to generate new knowledge immediately applicable to WWTP management.