Common chemical oxidation methods for hydrogen sulfide (H2S), an odor causing chemical formed by the action of anaerobic bacteria in water and wastewater systems include chlorine, hydrogen peroxide and ozone. Case studies and laboratory studies performed to date show that Mixed Oxidant Solution (MOS) tends to speed reaction rates or drive oxidation reactions to completion compared to sodium hypochlorite.
The oxidation of H2S is a two part reaction in which elemental sulfur (S0 ) is an intermediate before reaching the fully oxidized state as sulfuric acid (H2SO4). S0 is a solid that must be filtered in municipal applications, so if the reaction cannot be driven to completion with hypochlorite, additional capital equipment must be purchased. With sufficient dosing, MOS does not require a detention tank, filter system, and head can be maintained from the wells to distribution.
- Cl2 + H2S = 2HCl + S0 (reaction may stop here if the hypochlorite dose is not high enough)
- S0 + 3Cl2 + 4H2O = 6HCl + H2SO4
The combined reaction is: H2S + 4Cl2 + 4H2O = 8HCl + H2SO4
MIOX and odor control in wastewater systems: In 2013, a MIOX MOS Zuni system replaced a bleach caustic chemical program in the trickling filter and scrubber system of a wastewater treatment plant in the state of Washington. Since its installation, there have been no complaints from nearby neighbors concerning odors from the plant. The MOS is also used to prevent ponding, or excessive growth of biological material in the media of the filter. Since the introduction of the Zuni system, which uses only salt and power to generate the Mixed Oxidant Solution (MOS), the operators have ceased using the caustic, providing a both safety and cost advantage. MIOX MOS was used also used to successfully replace hydrogen peroxide (H2O2) in a sewer collection system, decreasing the H2S concentrations from 15 mg/L to non-detectable. Because of the distributed nature of the wastewater collection system, using a small OSG system that can be remotely monitored often provides operational flexibility.
MIOX and Advanced Oxidation Processes: More recently, MOX’s on-site generators were used in combination with UV to produce hydroxyl radicals. This process is called an Advanced Oxidation Process (AOP) and was used to remove MIB (2-methylisoborneol), an odor causing algal byproduct from the intake water at a large municipal facility in the United States.