Abstract Summary
Nitrous oxide (N₂O) is a greenhouse gas that can account for more than 70% of direct emissions from Wastewater Treatment Plants (WWTPs). It is primarily produced in aerated tanks within biological treatment systems, such as conventional activated sludge. Activated sludge processes are widely used in high-population-density areas, such as the Metropolitan Region of São Paulo (MRSP), Brazil, and its five main treatment plants. During the removal of organic and nitrogenous matter, factors such as pH, temperature, dissolved oxygen, and ammonia and nitrite concentrations influence N₂O formation. Thus, operational strategies can be implemented to mitigate emissions. Analyzing four years (2019–2022) of operational data from WWTPs revealed that ammonia loads in aeration tanks range from 1.84 to 47.76 tons of N-NH₄/day, presenting opportunities for nutrient recovery strategies and reintegration into the circular economy. High ammoniacal nitrogen levels, increased nitrite concentrations, dissolved oxygen fluctuations, low pH, and high temperatures are critical factors contributing to greater N₂O formation and emissions. Additionally, studies suggest the possibility of energy recovery from N₂O once collected. Therefore, these factors must be considered in developing measures to reduce emissions, recover resources, and consequently lower the WWTP’s carbon footprint.
