Assessment of hydrogen sulfide emissions in combined sewer odor: A quantitative source contribution analysis.

Odor emissions from urban sewer systems pose persistent environmental and social challenges, yet the relative contributions of individual sources remain poorly understood. This study presents a comprehensive quantitative assessment of odor generation in combined sewer systems, focusing on septic tanks, sediments, and slime layers. Extensive field monitoring and analyses identified hydrogen sulfide as the primary representative odorant, owing to its high concentrations, frequent occurrence, and strong correlation with odor intensity. The results indicate that septic tanks are the dominant source, contributing more than 90 % of total sulfide emissions, primarily due to anaerobic conditions and turbulence-induced volatilization during effluent discharge. A strong correlation (R2 = 0.8448) between sulfide concentrations in septic tank effluent and gaseous H2S in catch basins confirms the dominant role of septic tank emissions in governing odor perception. Although emissions from sediments and slime layers were less significant, they remained non-negligible and require periodic management. Overall, the findings suggest that controlling septic tank emissions could reduce odor complaints by up to 80-90 %, underscoring the importance of source-specific strategies for sustainable odor mitigation. This study provides critical insights into the quantitative contributions of sewer odor sources and informs future management practices and policy frameworks.