| Summary: | 碩士 === 國立交通大學 === 環境工程所 === 87 === Di-(2-ethylhexyl) phthalate (DEHP), a xenobiotic organic compound is found in the municipal sewage sludge. It has been identified that it is hepatocarcinigenic, nephrotoxic to rats and mice and toxic to mammalians. Since DEHP is a mainly used material to manufacture the polyvinyl chloride (PVC) derivatives, it becomes a ubiquitous pollutant and largely accumulates in the sewage sludge. DEHP in the municipal sewage sludge causes risks to the ecosystems when the sludge is disposed on the environment and utilized for the agriculture purposes. Thus, it is necessary to extract and determine the presence of DEHP in the municipal sewage sludge in order to enhance the feasibility and safety of sludge before agricultural application.
Since supercritical fluid is low viscosity, low surface tensions, high diffusibility, high solubility and non-toxic, it is developed and established as high efficiency sample preparation technique to replace the conventional solvent extraction methods. In the present study, supercritical fluid extraction (SFE) method used to determine DEHP from the sewage sludge, and the extraction parameters were optimized for efficiently determine the concentration of DEHP presented in the sewage sludge. The matrix used in this study were non DEHP contained quartz sand, Stock Raising sludge and real municipal sewage sludge separately in order to discuss the differences of extraction parameters which should be adjusted during extraction process. High purity carbon dioxide is used as extraction fluid, and the analyte collection apparatus is solid-phase trap column. After extraction step completed, n-hexane is used as rinse solvent. The optimal extraction condition for the present study was the extraction pressure of 202 bar, temperature of 80oC, fluid flow rate of 2.0 mL/min and the static and dynamic extraction times were 1 and 20 min respectively with 0.5 mL methanol as the modifier. The amount of DEHP presented in the Min-Shen municipal sludge was 142.86 mg/kg and the RSD value was 0.52%. Comparison of the results with Soxhlet extraction method shows the extraction efficiency and the reproducibility of SFE are both better than Soxhlet method.
In addition to establish the optimal operation parameters of SFE, the aims of this study also focused on the concentration variation of DEHP during the sampling periods. The results showed the amount of DEHP could be quantified largely in the final sludge cake, and the concentration range was 71.69 - 142.86 mg/kg. It showed that neither the wastewater nor the sludge treatment units could possible remove DEHP efficiently. It is noteworthy that the concentrations of DEHP decreased very slowly during 189 days of decaying experiment, and remained 70% in the testing sludge after 189 days and still over the restricted values applied by Danish Environment Protection Agency. The results revealed that DEHP presented in the sewage sludge was stable and difficult to degrade by microorganisms.
Besides cadmium, the concentrations of heavy metals were all below the restricted values. Therefore, comparisons of the impact and the effect between the DEHP and heavy metals, it is clear that DEHP presented in the sewage sludge might caused higher risks than heavy metals. If this sludge will be reused directly for agricultural purpose, a detailed study of risk assessment is necessary to minimize the impact and to reduce the loading to the ecosystem, further achieved the goals of waste sludge minimization and recycling.
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