Prediction of H2S production rate in sewer systems using the Z model: a case study in Dehloran city, Iran

Modeling of H2S buildup in sewers is performed due to the health problems associated with the high concentration of H2S, destruction of non-resistant structures in corrosion processes, and high costs of repairing corroded concrete sewer pipes. This analytical study aimed to predict the risk of H2S production in the sewage collection network of Dehloran city, Iran using the Z model. In total, 11 main sewage lines with various diameters were selected for wastewater sampling. For each pipeline, two samples per month were collected and processed for the analysis of various parameters in order to determine the H2S production based on the Z value. Biochemical oxygen demand, chemical oxygen demand, and SO4-2 values in warm seasons were 117, 291, and 251 mg/l, while they were 101, 247, and 234 mg/l in cold seasons, respectively. In all the samples, the Z value was >13,000. In addition, the Z level was higher in warm seasons (Z value in guaranteed H2S production category) compared to cold seasons (Z value in a large possibility of H2S production category), which could be due to the high temperature and anaerobic decomposition of organic matter in summer. A significant correlation was also observed between the Z value in different seasons and various diameters of the sewers. Considering the high risk of H2S production, it is recommended that proper scheming and planning be performed to eliminate this gas and prevent corrosion.