| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 103 === Adsorption with activated carbon is the most commonly applied technology for removing polychlorinated dibenzop-dioxins/ polychlorinated dibenzofurans (PCDD/Fs) from wastewater, but it just transfers PCDD/Fs from liquid phase to solid phase and may lead to secondary pollutions. On the other hand, it is proved that palladium speeds up hydrogenation and dehydrogenation reactions. In this study, hydrodechlorination of PCDD/Fs was investigated over palladium catalyst with select solvents, alkali agents, catalyst weights and catalyst supports. Experimental results indicate that with the initial OCDD/F concentration of 20 μg/L, stirred speed of 250 rpm and operating temperature of 25 oC, the removal efficiency of PCDD/Fs achieved with 5% (wt.) Pd/Al2O3 varies in different solvents. 5% (wt.) Pd/Al2O3 catalyst exhibited higher activity in methanol than in iso-propanol, n-hexane or toluene. With the treatment time of 60 minutes and methanol as solvent, the mass removal efficiency of PCDD/Fs reaches 96%. Different alkali concentrations were added in the reaction system to evaluate the effect and the results indicate that the mass removal efficiency of PCDD/Fs with 1 mM NaOH is better than that without NaOH at a treatment time 30 minutes. However, after 60 minutes treatment the mass removal efficiency of PCDD/Fs in 0 mM NaOH is better than that of 1 mM NaOH as a result of catalyst surface fouling with sodium. In addition, mass removal efficiency of PCDD/Fs decrease as the concentration of NaOH is increased. Moreover, catalyst support is also an important parameter affecting dehydrogenation reactions. Comparison of the destruction efficiency over 5% (wt.) Pd/Al2O3 and 5% (wt.) Pd/C shows that 5% (wt.) Pd/Al2O3 is more active than 5% (wt.) Pd/C for PCDD/Fs removol. Furthermore, this study investigates the effectiveness of AC adsorption and hydrodechlorination in removing PCDD/Fs from wastewater. First, the effectiveness of activated carbon in adsorbing PCDD/Fs from wastewater is evaluated. The result shows that the toxicity concentration of PCDD/Fs is lower than the standard as the ratio of liquid and activated carbon weight is controled at 3:1, however, it is not cost-effective. Hence, hydrodechlorination process is applied to degrade PCDD/Fs. The PCDD/Fs mass removal efficiency without adding reducing agent is 53.21% after operating 180 minutes; with adding 5% reducing agent (methanol), the removal efficiency increases to 71.86%. In addition, to better understand the differences between hydrogen donor and hydrogen molecules, this test had preaerated hydrogen gas into waste condensed water and then palladium catalyst was added for catalytic hydrodechlorination test. The test results show the PCDD/Fs mass removal efficiency increases to 97.34% with the treatment time of 180 minutes.
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