| dc.description.abstract | The process of combining O3 with UV/H2O2 could make serial chemical reactions and produce more active hydroxyl radicals, which have stronger oxidation capacity than conventional oxidants. Consequently, the O3/UV/H2O2 process would be more effective compared to other types of oxidation combination systems. Accordingly, this study evaluates the treatment of alkylphenol aqueous solutions by using the O3/UV/H2O2 process. The effect of various operating parameters including initial pH, H2O2 dosage, initial rate of ozone concentration and initial substrate concentration on the removal of alkylphenols in the O3/UV/H2O2 process was investigated. Moreover, the possible degradation mechanism of alkylphenols in the O3/UV/H2O2 process, bio-toxicity tests (Microtox), and estrogenic activity of reaction aqueous solution were evaluated.
The results of the investigation show that using the O3/UV/H2O2 process can remove 90% of alkylphenols within 15 minutes, and the reaction time is shorter than other processes. Nevertheless, the mineralization efficiency of alkylphenols in the O3/UV/H2O2 process was only 60%, the results indicated that the alkylphenols only destroyed their own structure and formed numerous intermediate products. However, removal of total organic carbon in solution was ineffective. In order to enhance mineralization of alkylphenols, the oxidation time must be increased.
The optimum operating conditions for the O3/UV/H2O2 process to destroy alkylphenols found in this study were summarized as follows：UV light intensity = 1.9×10-6 Einstein L-1s-1, pH = 4, [O3] = 0.06mg/min, [H2O2]0/[AP]0 molar ratio = 20. In which, the treatment effectiveness of OP and NP were 91.94% and 90.41% after 15 minutes, respectively.
The degradation products were analyzed by LC/MS, and revealed that the degradation of alkylphenols begins from shortening the alkyl chain. The following may be substitution of the hydrogen on chain with a hydroxyl radical, as well as an additional hydroxyl radical to the aromatic ring. The degradation intermediates are alkylcatechol, 1,2,4-trihydroxybenzene, hydroquinone, muconaldehyde, muconic acid, and other small fragments, such as alkanes, acetic acid, carboxylic acids and other compounds.
With the oxidation time increasing, the bio-toxicity (Microtox) and estrogenic activity of alkylphenols aqueous solution was reduced. However, the results of the investigation show that the intermediate products still had estrogenic activity. The possible causes with the formation of numerous intermediate products to enhance the synergistic effect on the estrogenic activity after alkylphenol degradation, thus, increasing the estrogenic activity of the compounds themselves.
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