| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系 === 93 === Goethite at neutral pH can effectively catalyze H2O2 to produce the hydroxyl radical (HO•), which is very powerful in oxidizing recalcitrant contaminants to easily biodegradable products or CO2. Such a reaction is called the Fenton-like oxidation. Therefore in recent years, many researches discussed the Fenton-like oxidation catalyzed by synthesized or natural goethite to decompose contaminations in the wastewater, soil and groundwater.
However, past studies were aimed at the evaluation and comparison of oxidation in the singular contaminant system. Many kinds of contaminations usually coexist in the environment; therefore, this research evaluated the influence of hydroxyl radical competition and Fenton-like oxidation efficient when two contaminants coexisted.
Experimental results revealed that when contaminants coexisted, the oxidation efficiency of each compound was less than that in singular-contaminant system. Increasing H2O2 dose 50 times and the goethite contents 10 folds only resulted in a slight oxidation improvement (about 10%). The most significant factors in the oxidation of dural contaminant system were the KHO•,P value and initial concentration of contaminants. For example, in the toluene/benzene group (KHO •,P value difference is small), the oxidation of toluene (KHO •,P = 3.39× 109) was not easily affected by benzene (KHO •,P = 3.2×109). The oxidation difference of toluene with and without the presence of benzene was about -10%. Expect at lower toluene/benzene molar ratios, the oxidation difference of benzene the presence of toluene increase more than -10%. On the other hand, when the concentration of benzene was much higher than toluene (e.g., [toluene] / [benzene] = 0.11), competing the HO• by toluene was weakened, causing its oxidation difference enhanced to -20%. However the oxidation of benzene was easily affected by toluene
KHO •,P value difference of two compounds is larger, the one with higher KHO‧,P and at high molar ratios can further depress the oxidation of lower KHO‧,P pollutant. For example, in the benzene / cis 1,2-DCE and benzene / MTBE groups, because the KHO •,P ratio of benzene / cis 1,2-DCE and benzene/MTBE was 3.2 and 17.8, respectively, benzene out-competed for the HO•and caused no degradation of cis 1,2-DCE and MTBE at [ benzene ] / [cis 1,2-DCE ] and [ benzene ] / [ MTBE ] > 1.
Multiple doses of H2O2 gradually relaxed the HO• competition phenomena, due to the concentration reduction of the more competitive compounds after each H2O2 dose and shift of molar ratio favored the less competitive contaminants. The oxidation of two contaminations can reach very close ranges after adding 5 times of 5% of H2O2.
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