The development of H2S in sanitary sewer systems create major problems, including corrosion that carries its own challenges. When the anaerobic slime layer from submerged pipe walls rise into an airway portion of the sewer pipe and reacts with bacteria and moisture on the pipe walls, it releases hydrogen sulfide gases. Biogenic sulfide corrosion, a bacterially mediated process of hydrogen sulfide gas with the conversion to sulfuric acid, attacks concrete and steel within wastewater environments. Therefore, the goal of designers is to eliminate corrosion and health hazards associated with H2S.
The key is to break the cycle by reducing dissolved sulfide concentration and avoiding the release of H2S gas. This ensures the prevention of not only unpleasant odors and health risks but biogenic sulfide corrosion in wastewater infrastructure.
The Problem with Biogenic Hydrogen Sulfide
To understand how biogenic hydrogen corrosion occurs, it’s important to know how the process begins. H2S generates in sewers and depends on a rather complicated process that includes biological, chemical, and physical pathways. When natural microbiology, which lives below the waterline in a sewer, converts sulfate (naturally and harmlessly occurring in nearly all drinking water supplies) into ionic sulfide, it changes chemically into dissolved H2S. It’s only when the dissolved hydrogen sulfide is released from the water by splashing and turbulence that it exists as H2S gas, resulting in the horrible stench.
Hydrogen Sulfide or H2S has 2 phases, liquid, and vapor. The liquid stage typically isn’t a concern – unless it’s in a flammable environment. That “rotten egg” stench occurs in the 2nd phase, the vapor phase. It is highly corrosive to concrete and metal. Hydrogen sulfide typically forms in “septic “conditions, i.e. when the wastewater stops moving in the collection system. The wastewater then becomes anaerobic and the SRBs (sulfate reducing bacteria) go to work.
The hydrogen gas converts to sulfuric acid by the bacteria Thiobacillus living above the water line. The acid then drops back down into the wastewater where it becomes neutralized back into sulfate, thus repeating the process.
Infrastructure Effects from an Excess of Hydrogen Sulfide
There’s no question that H2S is nasty stuff. Not only is the colorless gas unpleasant with that “rotten egg” smell, but it’s flammable and even explosive in high concentrations. It also leads to metal and concrete corrosion. In the U.S. alone, biogenic sulfide corrosion caused an estimated $14 billion increase in sewer assets per year. As aging infrastructure continues to fail, that cost will increase. If there’s more than 0.5 ppm of hydrogen sulfide in water, it can do major damage to steel, copper, brass, and iron in well casing/plumbing/bathroom fixtures.
Because of the risks to both human and environment, the Occupational Safety and Health Administration or OSHA sets strict requirements for Permissible Exposure Limits (PELs) to H2S gas. The General Industry has a Ceiling Limit of 20 ppm; a General Industry Peak Limit of 50 ppm (up to 10 minutes if no other exposure during shift); Construction, an 8-hour Limit of 10 ppm, and Shipyard, 8-hour Limit of 10 ppm.
ATS Innova MB Treatment Program
At ATS Innova, our mission is to Improve Life One Drop at a Time, and that means ensuring drinking water is safe for everyone and that wastewater treatment plants get the most comprehensive program for the elimination of hydrogen sulfide corrosion. Controlling sulfates, fluid acidity, and oxygen can make a vast difference in the prevention of biogenic sulfide corrosion.
We invite you to contact our team of water experts at 855.215.9953 and request a FREE treatment plant walk-through. We look forward to hearing from you!
