| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 104 === Once soil and groundwater are contaminated with fuel oils, it may pose health risk to human. In situ chemical oxidation (ISCO) remediation is a rapid and promising soil and groundwater remediation method. Sodium persulfate (SPS) is a common ISCO oxidant, which can be activated by alkaline to produce a powerful oxidant known as the sulfate radical (SO4−．). Hydrogen peroxide (HP) is also an ISCO oxidant, and under a basic condition (i.e., pH > 11.8), HP would dissociate to HO2−, which could promote SPS to produce free radicals via electron transfer. Therefore, this study investigated HP/SPS oxidation of diesel contaminated soils. Initial experiments were designed to examine the removal efficiency of diesel by individual reagent (i.e., HP, NaOH, SPS). The results showed that the removals of diesel were similar possibly due to desorption of diesel from soils. However, the HP/NaOH/SPS seemed not to significantly enhance diesel removal efficiency. The reason was possibly due to the interaction between HP and SPS to decompose each other to produce HSO4− and O2, thereby inhibiting effective contacts between free radicals and contaminants. Nevertheless, the oxidation of diesel-contaminated soils by either HP or SPS showed similar removal efficiencies under basic pH condition and HP is cheaper than SPS; therefore, HP/NaOH system was selected for further evaluation.
Furthermore, experiments were designed to explore the effect of various HP/NaOH molar ratios. The results showed significant diesel removal efficiencies were observed within short time (e.g., < 1 day), and temperature in soils increased to possibly desorbed from soils. However, no further degradation was observed after initial rapid diesel removal. Additionally, various HP/NaOH molar ratios exhibited minor effect on the removal efficiencies. Moreover, the NaOH/HP treated soils was mixed with SPS and the results showed no further diesel degradation occurred. Overall, the oxidation systems evaluated in this study using various concentrations of HP, NaOH, and SPS exhibited approximately 70% diesel removal of 10000 mg/kg of total petroleum hydrocarbons in soils.
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