Nitrate Applications for Hydrogen Sulfide Control
Nitrates are a proven technology for medium to long-duration hydrogen sulfide control in collection system gravity and force mains and can be used in applications where hydrogen sulfide odor is already present (curative) or to prevent the formation of hydrogen sulfide odor before it forms (preventative). Typical nitrate formulations contain 3.5lbs of nitrate-oxygen per gallon of calcium nitrate.
Curative Applications – Nitrate reacts in the sewer biofilm and water column providing electrons (and oxygen) for the biological oxidation of existing dissolved sulfide to sulfate. In the curative application mode, a typical retention time of 2-3 hours is required in order to be effective. Practical curative dose rates for calcium nitrate vary anywhere from 1 to 3 gallons per pound H2S depending on the application.
Preventative Applications – In the preventative mode, nitrates condition the biofilm for the reduction of nitrate to nitrogen gas under anoxic conditions. Nitrate is provided as alternative electron and oxygen source to sulfate and prevents sulfate from being reduced to hydrogen sulfide in anaerobic sewer conditions. This treatment strategy is typically effective for systems with retention times up to 3 hours. When applied properly, control to low hydrogen sulfide levels is possible; however, preventative treatment is typically less efficient than curative treatment, and in practice preventative dose rates for calcium nitrate vary anywhere from 2 to 8 gallons per pound H2S depending on the specifics of the application.