Due to increasing demand caused by the population growth, society has consumed more goods and products. Environmental contamination under such situations has been an important issue for human being. Contaminants in water resources threaten human's life and increase the cost of treating water for liv...
Due to increasing demand caused by the population growth, society has consumed more goods and products. Environmental contamination under such situations has been an important issue for human being. Contaminants in water resources threaten human's life and increase the cost of treating water for living, agriculture, and industry. In Korea, main contaminants of groundwater are colon bacillus, nitrate nitrogen, and chlorine. Nitrate come from many kinds of sources such as pesticides and fertilizes in agriculture, excretions in livestock industry, domestic sewage, and industrial sewage. In Korea, agriculture and livestock industry are the major source of nitrate.
Nitrate itself is not harmful to human, but when nitrate is reduced to nitrite in human bodies, it combines with hemoglobins in blood. It causes methemoglobin anemia in infants and children. High concentrations of nitrate in surface water can lead to eutrophication. Nitrate concentration is regulated below 20 mg-N/L for agricultural use and 10 mg-N/L for drinking water. Also, ammonium concentration is regulated below 0.5 mg-N/L. Treatment of nitrate-contaminated water can be done using methods including ion exchange, reverse osmosis, biological treatment, and chemical reduction. In chemical reduction, zero valent iron (ZVI) has often been applied to remove contaminants like nitrate (NO3-), nitrite (NO2-) and Cr(VI) in the form of permeable reactive barriers.
Previous research results have showed that almost end-product of nitrate reduction by ZVI was ammonium ion (NH4+), but some results with nano-sized ZVI showed that nitrogen gas was the end-product. These studies were performed under low pH conditions with HCl, H2SO4, CH3COOH, and HEPES buffer (⋍pH 3). Nitrate removal by ZVI is enhanced at lower pH. The surface of ZVI is corroded as nitrate reduction proceeds; iron oxides or iron hydroxides settle on the ZVI surface such that the reactivity of ZVI decreases with the reaction. A previous study suggests that nitrite, a strong oxidizer than nitrate, can cause the formation of passive layers on surface of ZVI. Such passive layers can be readily dissolved at lower pH. The pH of groundwater in Korea is found to be approximately 7.8. For this reason, nitrate removal should be investigated under field pH conditions. To maintain the ZVI surface free of passive layers, some metals have been coated on the ZVI surface. Several studies proposed that Ag, Cu, Ni, Pd, and Pt can be applied as coating materials.
In this study, nitrate solution was reacted with both uncoated and coated ZVI under anaerobic conditions. To investigate the role of dissolved Fe2+ in the nitrate reduction, goethite, magnetite, hydrous ferric oxide (HFO), zeolite 13X were amended to ZVI suspensions. In addtion, the nitrate reduction by ZVI was investigated to assess O2 contamination.
Pure ZVI could not reducted all nitrate(100 mg NO3--N/L) in solution within 3.6 h. Co-, Cu- and Cr-coated ZVI showed improved nitrate removal speed but they did not suppress generation of passive layer on ZVI. Co and Cu coated on ZVI reduce nitrate as a electron-transfer mediators. ZVI amended with (hydr)oxide iron suppressed generation of passive layer on ZVI. Under O2 contamination, ZVI oxidized to (hydr)oxide iron by O2 so
pouring air or O2 can have same effect as a amending (hydr)oxide. Therefore, ZVI coating and amending with (hydr)oxide can maximate nitrate removal by ZVI.
Due to increasing demand caused by the population growth, society has consumed more goods and products. Environmental contamination under such situations has been an important issue for human being. Contaminants in water resources threaten human's life and increase the cost of treating water for living, agriculture, and industry. In Korea, main contaminants of groundwater are colon bacillus, nitrate nitrogen, and chlorine. Nitrate come from many kinds of sources such as pesticides and fertilizes in agriculture, excretions in livestock industry, domestic sewage, and industrial sewage. In Korea, agriculture and livestock industry are the major source of nitrate.
Nitrate itself is not harmful to human, but when nitrate is reduced to nitrite in human bodies, it combines with hemoglobins in blood. It causes methemoglobin anemia in infants and children. High concentrations of nitrate in surface water can lead to eutrophication. Nitrate concentration is regulated below 20 mg-N/L for agricultural use and 10 mg-N/L for drinking water. Also, ammonium concentration is regulated below 0.5 mg-N/L. Treatment of nitrate-contaminated water can be done using methods including ion exchange, reverse osmosis, biological treatment, and chemical reduction. In chemical reduction, zero valent iron (ZVI) has often been applied to remove contaminants like nitrate (NO3-), nitrite (NO2-) and Cr(VI) in the form of permeable reactive barriers.
Previous research results have showed that almost end-product of nitrate reduction by ZVI was ammonium ion (NH4+), but some results with nano-sized ZVI showed that nitrogen gas was the end-product. These studies were performed under low pH conditions with HCl, H2SO4, CH3COOH, and HEPES buffer (⋍pH 3). Nitrate removal by ZVI is enhanced at lower pH. The surface of ZVI is corroded as nitrate reduction proceeds; iron oxides or iron hydroxides settle on the ZVI surface such that the reactivity of ZVI decreases with the reaction. A previous study suggests that nitrite, a strong oxidizer than nitrate, can cause the formation of passive layers on surface of ZVI. Such passive layers can be readily dissolved at lower pH. The pH of groundwater in Korea is found to be approximately 7.8. For this reason, nitrate removal should be investigated under field pH conditions. To maintain the ZVI surface free of passive layers, some metals have been coated on the ZVI surface. Several studies proposed that Ag, Cu, Ni, Pd, and Pt can be applied as coating materials.
In this study, nitrate solution was reacted with both uncoated and coated ZVI under anaerobic conditions. To investigate the role of dissolved Fe2+ in the nitrate reduction, goethite, magnetite, hydrous ferric oxide (HFO), zeolite 13X were amended to ZVI suspensions. In addtion, the nitrate reduction by ZVI was investigated to assess O2 contamination.
Pure ZVI could not reducted all nitrate(100 mg NO3--N/L) in solution within 3.6 h. Co-, Cu- and Cr-coated ZVI showed improved nitrate removal speed but they did not suppress generation of passive layer on ZVI. Co and Cu coated on ZVI reduce nitrate as a electron-transfer mediators. ZVI amended with (hydr)oxide iron suppressed generation of passive layer on ZVI. Under O2 contamination, ZVI oxidized to (hydr)oxide iron by O2 so
pouring air or O2 can have same effect as a amending (hydr)oxide. Therefore, ZVI coating and amending with (hydr)oxide can maximate nitrate removal by ZVI.
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