Assessment of airborne pollutants in wastewater treatment plants

Wastewater generation rates have increased considerably in recent years due to population growth, urbanisation, and industrialisation. Although wastewater treatment plants (WWTPs) play a crucial role in purifying wastewater and mitigating industrial and domestic pollution in global freshwater reserves, their impact on air quality in nearby areas is frequently neglected. Therefore, this study assessed air quality in two WWTPs in Toledo, Spain. One is located in an industrial area and processes both industrial and domestic sewage (WWTP1), and the other is situated in a rural area and treats domestic wastewater (WWTP2), handling approximately double the treatment flow. Moreover, the aeration systems in the bioreactors differ. Measurements were made over a period of 6 months and included levels of gaseous emissions, such as SO₂, CO, NOx, O₃, volatile organic compounds (VOCs), particulate matter (PM_2.5 and PM₁₀), and trace elements (TEs). Environmental and health risk indicators were calculated to estimate the impact of exposure to air pollution on nearby ecosystems and the population's health, respectively. The study revealed a low contribution of the WWTPs to the SO₂, CO, and PM levels. However, WWTP1 showed an NOx annual average concentration close to the legislated threshold, and the target O₃ value for the protection of human health was also exceeded. Regarding VOCs, the main contribution was the group of oxygenated aromatics. Concerning TEs, a high enrichment factor value was obtained for sodium, arsenic, selenium, potassium, nickel, copper, zinc, and lead at WWTP1 and for zinc, cadmium, copper, and selenium at WWTP2.