Case study of hydrogen sulfide release in the sulfate-rich sewage drop structure

Hydrogen sulfide (H2S) is one of the principal odorous gases released from sewer networks and understanding the rate of hydrogen sulfide release into sewer air space and ventilation to the atmosphere is crucial for preventing or minimizing odor and corrosion issues in sewer systems. The TOXCHEM model was used to simulate the drop structure of the Al-Hur region in Karbala, south of the capital of Iraq, Baghdad. Samples for this drop structure were collected over the course of a year, with two samples taken every month and all of the drop's relevant parameters were included in the model. The model was calibrated for the spring and summer seasons and validated for the remainder of the seasons. The predicted behavior showed a good correlation to measurements in real samples following statistical analysis, with R-2, R, and RMSE results between (0.93-0.97), (0.8-0.82), and (0.000438-0.000838), respectively. A sensitivity study was performed to assess the effect of various pH values, drop heights, tailwater depths, stream widths, and sewer ventilation rate levels. The results showed that all emissions in this drop structure can be considered hazardous, and this was particularly evident during the summer, when the emissions concentrations for the winter.