Hydrogen sulfide (H2S) results from septic conditions during the collection and treatment of wastewater. It has long been recognized as a major problem for municipal wastewater systems. This colorless gas, known for its rotten egg smell, is produced by the biological reduction of sulfates and the decomposition of organic material. It forms at virtually every point in a system from interceptors, force mains, and lift stations, to holding tanks, mechanical dewatering equipment, and drying beds.
Beyond its nuisance odor, hydrogen sulfide also poses a serious problem for the structural integrity of the collection system. Millions of dollars are lost to corrosion caused by the sulfuric acid formed from the interaction of H2S with moisture. Of greatest concern are the safety hazards associated with H2S. Hydrogen sulfide gas is acutely toxic and a leading cause of death among workers in sanitary sewer systems. Although disagreeably pungent at first, it quickly deadens the sense of smell and a worker may not be aware that it is there. Even at low concentrations in air, exposure to hydrogen sulfide has been linked to fatigue, headaches, eye irritation, sore throats and other health problems.
Permanganate oxidation treatment rapidly destroys hydrogen sulfide in wastewater and biosolids. Sulfide oxidation chemistry is very complex and the reaction can follow different pathways depending on the conditions encountered. In anaerobic systems, permanganate directly oxidizes hydrogen sulfide. The endpoints can vary based on the time, temperature, and pH of the treatment system. In the presence of air, the oxidation of sulfide by permanganate occurs by two paths. The first is, again, the direct oxidation of sulfide by permanganate and different, non-odorous sulfur compounds result. Importantly, this reaction also generates manganese dioxide (MnO2) and freshly produced MnO2 acts as an oxygen-transfer catalyst resulting in further sulfide oxidation. Through these multiple pathways, the amount of permanganate needed for sulfide oxidation is minimized.
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