H2S treatment

 

 Hydrogen sulfide is a flammable, colorless, and highly toxic gas, and it contains a rotten-egg odor that is detectable even at very low concentration: 0.5 ppb. Even at low levels of exposure, it can cause painful dermatitis, burning eyes, and respiratory system damage. Furthermore, the exposure to high level (100 ppm) causes life-threatening damages: shock, convulsion, rapid unconsciousness, coma, and death. As a solution, several methods have been studied, and they can be categorized into one or combinations of three basic methods: biological, chemical, and physical. Among them, our research group applied chemical/physical absorption method, utilizing impeller-based wet scrubber system.

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 As an absorbent, alkaline solution like sodium hydroxide and hydrogen peroxide can be used in the waste water treatment plants, according to the following equations.

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H2S + NaOH → NaHS + H2O
NaHS + NaOH → Na2S + H2O

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 Moreover, with the use of iron chelated with EDTA as an oxidant, hydrogen sulfide can be efficiently removed. There is a mass transfer of hydrogen sulfide from gaseous to aqueous phase, a physical absorption, and at pH above 7, hydrogen sulfide reacts with Fe3+(EDTA) and breaks down into insoluble elemental sulfur form and precipitates, expressed in the following equations

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H2S(g) → H2S(aq)
H2S(aq) + Fe3+(EDTA) → S(s) + 2H+ + Fe2+(EDTA)

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 The reduced form of iron EDTA must be regenerated to the oxidized form for continuous operation in the industry by way of oxygen purging.

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O2 + 4Fe2+(EDTA) + H2O → 4Fe3+(EDTA) + 4OH-

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 This oxidation regeneration can be done electrochemically as well.

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Cl2 treatment

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 Chlorine gas is one of odor-causing pollutants with the extremely small odor threshold: 0.02-0.31 ppm. It causes the corrosion of construction, destruction of ecosystem, and serious damage to respiratory system. In fact, this toxic pollutant can be easily removed via wet-scrubber using alkaline or sulfite solution as an absorbent. In the case of existing scrubber, there occurs back flow with high gas flow rate, so it results in emission of chemical mist, which requires secondary wastewater treatment. When using our impeller-based scrubber, however, this issue can be prevented by the flows generated by the impeller. Moreover, chlorine gas becomes hypochlorous acid when reacting with alkaline solution, so it has additional benefit of recovery of chlorine oxidant.