Hydrogen sulfide forms when a collection system has soluble organics, anaerobic conditions, and the presence of sulfate. All of this happens to occur to a limited extent in gravity lines but can become critical in the confines of force mains. We often think of H2S gas a a nuisance due to it causing odor complaints at 1 - 10 ppm, monitoring areas where H2S forms in collection systems can also save lives by limiting potential worker exposure. Even at low levels long term H2S exposure can be a problem. OSHA has limits set at 10 ppm for workers.
- Avoid creating anaerobic zones by adding peroxides, nitrate, oxygen, etc
- Keep reduce sulfides in water phase by increasing the pH (avoid acid conditions that create the H2S (gaseous) form of sulfide (S=)
- Adding Fe or other chemicals that bind to reduced sulfur (S=)
- Adjusting pumping frequencies to prevent long residence time in force mains