Oxidation of Sulfides

In wastewater, sulfides are the primary culprit among malodorous compounds that are most complained about by the general public.  And as a result, there are numerous products in the marketplace utilizing various mechanisms to address the odors stemming from sulfides.

THIOGUARD uses a variety of mechanisms to control sulfide:   Adsorption, neutralization, pH elevation and stabilization, species complexation, biological interference, and oxidative catalysis.

The oxidation of sulfides occurs both organically and inorganically, through biological and/or chemical mechanisms.  Biological mechanisms depend on microbial activity, which is subject to environmental factors such as temperature, pH, food availability and an oxygen source.  Although research has indicated that sulfides will rapidly oxidize in the presence of dissolved oxygen, chemical mechanisms rely on pH, redox potential, oxygen source and metal ions for catalysis and rate of oxidation.

Oxidative catalysis with THIOGUARD occurs from the addition of a light metal cation and pH elevation, which affects both chemical and biological pathways.

Studies by several researchers indicate the addition of metal cations increase the rate of sulfide oxidation from 5 to 100 times, in decreasing order of activity as follows:

Ni²⁺>Co²⁺>Mn²⁺>Cu²⁺>Fe²⁺>Ca²⁺~Mg²⁺

In addition, THIOGUARD increases pH, which in turn shifts the SO₄/HS equilibrium to favor the SO₄ species as shown in the Pourbaix Diagram below.

pE-pH Diagram Sulfide-Sulfate Oxidation

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• The rate of sulfide oxidation is driven by several factors: wastewater redox potential, pH, metal ion concentration, biological activity
• Metal cations catalyze the rate of sulfide oxidation from 5 to 100 times
• THIOGUARD shifts pH to favor SO₄ species in the SO4/HS equilibrium
• THIOGUARD holds sulfides in solution or in complexes until the wastewater reaches a more oxidative environment

Thioguard TST is a nonhazardous application with no required reportable quantities (RQ = None)

Dave North - Webmaster