| dc.description.abstract | High energy cost and potential formation of dioxins during incineration/combustion of pentachlorophenol (PCP) have limited their application on simultaneous removal of highly contaminated soil of PCP, polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) at AnShun in Taiwan. In this dissertation, investigation of PCP pyrolysis in soil at a relatively low temperature range (150-400oC) and the behavior of PCDD/Fs formation, dechlorination and destruction during pyrolysis of PCP-contaminated soil have been examined in detail. Most PCP (>90%) and PCP byproducts can be removed from soil at 350oC for 40 min. The PCP decay rates from soil increased exponentially from 0.20 to 1.96 min-1 as temperature was increased from 150oC to 400oC. Very low levels of PCDD/Fs were found in soil (0.38-2.48 ng TEQ/kg) and gaseous phase (0.0015-0.0044 ng TEQ/Nm3) during pyrolysis of PCP-contaminated soil. 70% of PCP removal from the soil was achieved, resulting in 1436?230 ng/kg, the highest PCDD/F formation at 250oC; however, the highest toxic concentration was measured around 4.20 ? 0.62 ng TEQ/kg at 300oC with 80% PCP removal from the soil. Further analysis has revealed that OCDD is the most dominant congener supposed to form from the pyrolysis of PCP, while OCDF is the second prevailing congener, possibly due to 2,3,4,5-TeCP reaction which is a main byproduct of PCP pyrolysis. Detection of less chlorinated dioxins and furans over 300oC indicates the dechlorination of highly chlorinated dioxins and furans, especially OCDD at 350oC and 400oC. Desorption from soil was supposed as a main mechanism for the distribution of PCDD/Fs in the gas phase, and not much difference in dioxins and furan levels was observed at 350oC and 400oC in the gas phase. In order to test the nZVI reactivity with PCP, a thermally enhanced pump-and-treatment method coupled with nZVI was proposed to remove PCP from soil and to detoxify aqueous phase and soil. The results indicated that total PCP removal in soil and aqueous phases increased with increasing nZVI dose. The PCP distribution in aqueous phase was enhanced when PCP-contaminated soil was remediated with nZVI. In addition, decrease in pH resulted in decreasing PCP distribution in aqueous phase but increasing PCP dechlorination. Dechlorination rate was enhanced from 2.26 to 6.84 h-1 as the temperature was increased from 25oC to 85oC. Dechlorination and PCP residual in soil were increased to 42% and decreased to 6%, respectively, at 85oC and pH1. The dechlorination of PCP preferred to occur at ortho> meta> para positions in the respect of OH group. Based on the results of nZVI reactivity with thermal enhancement, the combination of pyrolysis and nZVI was proposed to investigate the PCP removal from soil. Consequently, the decay rate constant (k) of pyrolysis combined with nZVI increased exponentially from 0.59 to 3.67 min-1 which were 4 times higher than that without nZVI in the temperature range of 150°C -300°C. The activation energies of PCP removal from soil with and without nZVI are 23.80 and 36.98 kJ/mol, respectively. PCP degradation increases linearly with increasing nZVI dose. The rate decay constant increased from 0.21 min-1 to 1.56 min-1 as nZVI dose was increased from 0% to 10% at 200oC. The order of PCP dechlorination during pyrolysis coupled with nZVI is the same as that in the absence of nZVI but dechlorination process during pyrolysis with nZVI occurred more completely into the final product as phenol. Increasing temperature to 300oC resulted in the predominant TeCP ((0.4 ? 0.1) %) in soil and none byproducts was detected in soil as either temperature or time was increased above 300oC and 30 min, respectively. Especially, both PCP and byproducts were not detected in gaseous phase. This study provides relevant information for risk assessment for PCP contaminated soils when low thermal pyrolysis is applied for remediation of PCP contaminated soil.
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