Water containing sulfides in excess of a 0.5 ppm concentration has an offensive (rotten eggs) odor and is also very corrosive. The sulfide is present at acidic pH levels as hydrogen sulfide gas and at alkaline pH values as sulfide salt. Occasionally, when the water also contains iron, the sulfide may be present as a finely divided black (FeS) precipitate. Hydrogen sulfide is usually removed by aeration at an acidic pH, followed by a final oxidation treatment with chlorine, ozone, or hydrogen peroxide.
Aeration at a low pH removes hydrogen sulfide by purging rather than by oxidation. The aerators are usually constructed of wood rather than metal to avoid corrosion. Bacterial growth aids in sulfide removal. Chemical oxidation of 1-2 ppm of hydrogen sulfide in water can be carried out most economically with ozone. Hydrogen peroxide and chlorine are also effective. The oxidant dosages necessary to remove 1 ppm hydrogen sulfide are ozone 1 ppm, hydrogen peroxide (50%) 2 ppm and chlorine 8 ppm. Table 8.3.8 lists treatment for a 1 MGD wastewater flow containing 5 ppm of hydrogen sulfide.
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