CO2 EMISSIONS FROM BIOLOGICAL WASTEWATER TREATMENT FACILITIES OPERATING UNDER THE AO SCHEME

The biological treatment of municipal wastewater is an essential component of modern environmental protection strategies, significantly reducing the anthropogenic load on natural water ecosystems. However, this process is associated with substantial emissions of greenhouse gases, particularly CO2, N2O, and CH4, which contribute to global climate change. Despite the recognized high warming potential of nitrous oxide and methane, carbon dioxide remains the most voluminous greenhouse gas released during biological wastewater treatment. Yet, due to its biogenic origin, these emissions are often underestimated or excluded from national and global inventories, potentially distorting the actual impact of urban wastewater treatment plants on the climate system. This study focuses on the quantitative assessment of carbon dioxide emissions generated during the aerobic treatment of municipal wastewater at a full-scale treatment facility operating under the anoxic-oxic scheme. The research aims to determine the locations and stages within the technological process that are characterized by the highest intensity of carbon dioxide emissions, thereby contributing to the identification of emission hotspots and the development of climate-conscious technological improvements. Experimental measurements were carried out at a treatment plant in Germany with varying daily inflow capacities during two separate observation periods. Using high-precision analytical equipment, the concentration of carbon dioxide and oxygen in the air above the wastewater surface was measured across multiple treatment stages. Complementary physicochemical and hydrochemical analyses of the wastewater were performed to determine the oxygen content and degradation intensity of organic pollutants throughout the system. The results revealed a distinct correlation between the oxygen concentration in treated wastewater and the level of carbon dioxide emissions at various stages. The highest levels of carbon dioxide were recorded in zones where biological oxidation was most intense, particularly in the aeration tanks. In contrast, areas with limited aeration or anaerobic conditions exhibited lower emission levels.