A comparative study on sulfide removal by HClO and KMnO4 in drinking water

Abstract

Sulfides, which are highly toxic to aquatic organisms and the human body, can be widely detected in water sources, especially in summer. Measures should be taken to eliminate them. In this paper, methods for the removal of sulfides and the formation of innocuous sulfate ion (SO₄²⁻) products using hypochlorite (HClO) and potassium permanganate (KMnO₄) were compared; moreover, the effects of the oxidation conditions and co-existing components in the water were investigated. In addition, the proportions of different sulphur (S) species obtained using the two oxidants were evaluated. The results demonstrated that both oxidants are effective for sulfide removal, and the removal efficiency increased with increasing oxidant dosage. The removal rate of sulfides using HClO (97.8%) was higher than when using KMnO₄ (87.6%) at the same oxidant dosage (3.2 mg L⁻¹); moreover, more sulfides were transformed to innocuous SO₄²⁻ when using the former (91.2%) than the latter (58.9%). The removal rate (from 97.4 to 30.9%) and proportion of SO₄²⁻ formed (from 51.8 to 46.8%) both decreased upon raising the initial sulfide concentration from 0.2 to 0.8 mg L⁻¹, while for KMnO₄ these values decreased from 54.6 to 16.5%, and from 28.9 to 25.8%, respectively. Dissolved oxygen (DO) facilitated the removal of sulfides and the formation of SO₄²⁻ when using either HClO or KMnO₄. The presence of bicarbonate ions (HCO₃⁻) raised the sulfide removal rate from 58.7 to 78.9% when using HClO, but it had little effect on removal using KMnO₄. Co-existing SO₄²⁻ facilitated the removal of sulfides during HClO oxidation but depressed their removal with KMnO₄. Co-existing components in actual water matrices played minor roles in the sulfide removal process with HClO, but they had an inhibitory role when using KMnO₄. These results can provide evidence for appropriately selecting a chemically effective method for oxidizing sulfides.