Assessment of hydrogen sulfide emission from a sewage treatment plant using AERMOD

Air quality modeling plays an important role in prediction of air pollutants in urban areas. Moreover, it is also an essential component to make crucial decisions in environmental management. In this study, environmental protection agency (EPA) regulatory model (AERMOD) was implemented in order to assess the urban air quality in the city of Muscat, Sultanate of Oman. Dispersion modeling was employed for the prediction of hydrogen sulfide (H₂S) emissions, a neighborhood claimed issue, from Al-Ansab sewage treatment plant (STP). Meteorological, elevation data, and H₂S survey results were implemented into the model. From the site survey study, four different H₂S emission sources were identified as sewage tanker connection points, biofilter, old odor control unit (OCU), and open channels of raw sewage. It was observed that based on maximum 24-h analysis, the ground level concentration outside the STP exceeded the concentration limit, 40 μg/m³, recommended by the local regulating agency in Oman. By applying a sensitivity analysis study, the locations with the highest predicted H₂S levels were identified. The most affected area in the worst-case scenario was the nearby expressway with 450.9 μg/m³ of H₂S. The highest ground level concentration of H₂S was detected in March, while the lowest was measured in December. The model also predicted that the impact of odor nuisance is greater at the summer season than that of other seasons due to the elevated temperatures. The study revealed an adverse environmental impact from the STPs on urban air quality, which may pose a threat to the public health.