Abstract
This study explored the application of iron turning waste for the degradation of heptachlor and endosulfan. In batch experiments, 2.5 g of iron turning waste efficiently removed 96% of heptachlor and 85% of endosulfan in 200 mL of water (20 μg/L for each pesticide) in ten minutes. By increasing the iron turning dose from 1 g to 2.5 g, pseudo second order removal rates of heptachlor and endosulfan increased 1.5-fold and 1.37-fold, respectively. Among the minerals in groundwater, calcium and potassium lowered heptachlor removal (8–10%), whereas their effect on endosulfan removal was minimal. Endosulfan removal increased 16%, when water pH was raised from 4 to 10. The effect of water pH on heptachlor removal was minimal. The removal of heptachlor and endosulfan dropped to 55% and 46%, respectively, when the initial concentration was 1 μg/L. In a continuous flow system, iron turning worked better in combination with sand media. Water flow rate (5–15 mL/min) had a limited effect on the removal of both pesticides (initial concentration of 2 μg/L) which increased with increasing iron turning dose (100–150 g) for endosulfan. Heptachlor removal remained stable (100%) regardless of the iron turning amount (100–150 g) used in a filtration column. Iron turning based filter completely removed heptachlor throughout the filtration period (600 h), whereas endosulfan removal dropped from 100% to 88–90% after 300 h. Endosulfan and heptachlor were degraded into nonanal and heptanal, respectively. Iron turning waste was characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) before and after its reactions with both pesticides. XRD and XPS analyses revealed that virgin iron turning waste consisted of zerovalent iron (Fe0) and iron oxides, and Fe0 was transformed to magnetite (Fe3O4) after reacting with both pesticides. Based on detected degradation by-products, the removal mechanism and degradation pathways for both pesticides were elucidated.
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