Over the past month, I read about two Texas area water treatment workers, while working on a pump, were overcome by hydrogen sulfde exposure. One of the workers died and the other required hospitalization. This reminds us of how deadly hydrogen sulfide can become when working in wastewater.
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.
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.
How can H2S be controlled in the collection system? Keys methods are:
- 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
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