From laboratory to field: performance and mechanisms of enhanced ventilation for hydrogen sulfide control in gravity sewers.

Hydrogen sulfide (H2S) accumulation in sewers threatens occupational safety, infrastructure integrity, and the urban environment. Although ventilation is operationally attractive, its multi-level mechanisms and the translation of laboratory-derived parameters to engineering conditions remain unclear. This study combined laboratory optimization with long-term field validation to evaluate the performance, mechanisms, sulfur-load characteristics, and end-of-pipe implications of enhanced ventilation in gravity sewers. Laboratory experiments using a simulated gravity-flow sewer reactor showed simultaneous decreases in gas-phase H2S and dissolved sulfide, accompanied by increases in dissolved oxygen, oxidation-reduction potential, and sulfate, together with decreased sulfate-reducing bacteria and increased sulfur-oxidizing bacteria, indicating that the control mechanism extended beyond gas-phase dilution. An S-equivalent assessment showed that 10 min air renewal time combined a lower gas-phase H2S-S exhaust rate with greater dissolved sulfide depletion, sulfate-S accumulation, and suppression of sulfide production. Field application in a 300 m sewer reach, with an equivalent air renewal time of 8-9 min, reduced mean H2S concentrations by 92.74% and 85.05% at two fixed monitoring points, while P90 reductions exceeded 84%. Over nearly 8 months of monitoring, time-above-threshold ratios for high-risk concentrations were markedly compressed, H2S levels declined progressively along the sewer, and concentrations within the ventilation zone remained systematically lower than outside the zone. The near-exhaust H2S-S load fell from 9.47 to a low of 0.28 g S/h, remaining below the initial operating-stage level during most of the monitoring period. These findings provide a mechanistic basis and practical parameter reference for engineering applications of enhanced ventilation in sewer H2S management.