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The Use of Iron Salts to Control Dissolved Sulfide in Districts' Trunk Sewers

by Navnit A. Padival, County Sanitation District of Los, Angeles County, Whittier, United States,
William A. Kimbell, County Sanitation District of Los, Angeles County, Whittier, United States,
John A. Redner, County Sanitation District of Los, Angeles County, Whittier, United States,



Document Type: Proceeding Paper

Part of: Critical Issues in Water and Wastewater Treatment

Abstract:

Headspace H₂S removal via the precipitation of dissolved sulfide was investigated using iron chlorides. Full-scale experiments were conducted in a 25-mile sewer with an average flow of 200 MGD. Results were sensitive to Fe dosages and Fe³⁺/Fe²⁺ blend ratios injected. A concentration of 16 mg/L Fe and a blend ratio of 1.9:1 (Fe³⁺:Fe²⁺) reduced dissolved sulfide levels by 97%. Total sulfide and headspace H₂S were also reduced by 63 and 79%, respectively. Liquid and gas phase sulfide reductions were largely owed to the effective precipitation of sulfide and the limited volatilization of H₂S gas, respectively. The catalytic oxidation of sulfide in the presence of Fe²⁺ and minute amounts of O₂ may have occurred. When compared to previous work, a combination of Fe³⁺ and Fe²⁺ proved more effective than either salt alone. No specific relation between the concentration of Fe or Fe³⁺/Fe²⁺ blend ratio and crown pH was inferred. Iron salts may retard crown corrosion rates by precipitating free sulfide, thus reducing its release to the sewer headspace as H₂S and/or by inhibiting responsible bacteria.

Subject Headings: Sulfides | Sewers | Water treatment | Oxidation | Corrosion | Salt water | Precipitation

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