| 英文摘要 |
Sediments are transported by the flowing water then build up on the bottom of water bodies as the materials settle. Contaminated sediments are composed of soils, sand, organic matters, and other minerals that accumulate on the bottom of water bodys and contain toxic or hazardous materials at levels that may adversely affect human health or the environment. The contaminated deposits can be decomposed and released into liquid phase by dramatic changes on environmental conditions. However, the contaminated deposits have a potential of causing changes of nature water system, especially for aquatic livings. Sediments contaminated by light non-aqueous-phase liquids (e.g., fuel oil) and heavy metal are prevalent and of a great concern. The major advantage of Fenton-like and ozone oxidation process is that the reagent components are safe to handle and environmentally benign. However, protective enclosure of contaminants with aged sediment matrices and the hydrophobic nature of contaminants limit their accessibility to treatment agents; these obstacles prevent treatment efforts from widespread successes. The interactions of hydrophobic contaminants with the soil matrix in various ways often limit contaminant availability for remediation. In order to overcome this limitation and increase contact, a novel extraction technique that utilized chelants or oxidation agent and mildly elevated pressure in consecutive cycles of compression and decompression was developed and applied to soil slurry in the presence of chelating or oxidation agent. The objective of this study was to design a pressure-cycling system that integrates the oxidation agent and chelating agent. This system has the following advantages over traditional chemical treatment: (1) increased process speed, (2) lower operating costs, and (3) the transition metal elements can catalyze the oxidized pollutants. In this study, copper and fuel oil were selected as the target compounds to evaluate the effectiveness of pressure-cycling system on the treatment of copper and fuel oil contaminated sediment. The heavy metal extraction reagent included HCl, citric acid, and EDTA. The oxidizing agents used in this study included H2O2 and ozone. The operating parameters included system pressure, pressure cycles, extraction agent/ oxidizing agent concentration, particulate size of sediment, organic matter, pollutant concentration, pH and reaction time. The experimental results show that approximately 34, 72, and 79% of treatment efficiencies were observed when HCl, citric acid, and EDTA were used to treat copper contaminated sediments with the assistance of pressure-cycling system. Results also indicate that system pressure, number of pressure cycles, and pH would affect the treatment efficiency of the copper contaminated sediments. In the pressure assisted oxidation system, concentration of oxidation agent, TPH, concentration, and ferrous iron concentration would affect the treatment efficiency of fuel oil contaminated sediments. Results reveal that approximately half to one third of the contaminants can be removed using pressure-cycling oxidation system. Results of this study show that the quantity of chelating agents is the major factor that affects the extraction efficiency of copper in sediments using the pressure-cycling system. Results also show that the percentage of fine particles (e.g., <0.05 mm) increased after the pressure cycling with pressure at 6 bar. This indicates that the increased pressure would cause the disruption of sediment grains and cause the decrease in particle size. This could also cause the increase in TPH removal.
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