碩士 / 國立聯合大學 / 環境與安全衛生工程學系碩士班 / 94 / Chlorophenols constitute an important category of organic pollutants that are highly toxic and are not readily biodegradable. Consequently, conventional biological treatment process is not very effective for removing chlorophenols from chemical effluents. In this study, one of advanced oxidation processes (AOPs) - solar photo-Fenton process was used as a pretreatment step to increase biodegradability (BOD5/COD) and reduce microtoxicity (TU) of chlorophenol wastewaters including 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP). The effects of chlorophenol concentration, dosage of H2O2, dosage of Fe2+, and initial ratio of H2O2/Fe2+/chlorophenol were examined. In addition, to understand the enhancing motivation of solar photo-Fenton process for biodegradability of chlorophenol wastewater, the decomposition intermediates and average oxidation state (AOS) variation of wastewater would be intensely investigated.
In this study, all experiments were carried out in batch mode. Artificial chlorophenol wastewaters with a concentration of 1 or 3 mM were prepared for experiments. It was found that the solar photo-Fenton process improved significantly the biodegradability of chlorophenol wastewater. Basically, increasing initial H2O2 dosage was much more beneficial for increasing biodegradability of wastewater than increasing initial Fe2+ dosage. This could be due to incessant photo-reduction reaction of Fe3+ (Fe(OH)2+) ion under solar irradiation, leading to a lower dosage of Fe2+ being sufficient to catalyze H2O2 for generating more biodegradable intermediates in solution. Among the conditions studied, the optimum pretreatment condition of enhancing biodegradability of chlorophenol wastewaters was with a [H2O2]0/[Fe2+]0/[chlorophenol]0 ratio of 30.0/0.6/3.0, 30.0/0.9/3.0, and 30.0/0.6/3.0 for 2-CP, 4-CP, and 2,4-DCP, respectively. As a result, BOD5/COD was increased from 0 for untreated solution up to 0.231, 0.248, and 0.193 for 2-CP, 4-CP, and 2,4-DCP, respectively at 15-min pretreatment point. Moreover, based on the oxidation behaviors and identified intermediates of chlorophenol wastewater, three oxidation state could be illustrated. The first one with an AOS (average oxidation state) value below 0 showed the system with insufficient oxidative power to effectively decompose chlorophenols, leading to some benzene-ring containing compounds such as quinone, catechol, and hydroquinone were accumulated in solution. In the second stage (AOS value was between 1 and 2), some organic acids such as muconic acid, maleic acid, and oxalic acid were found in solution, indicating that the benzene-ring structure of chlorophenol was decomposed and then produced more biodegradable aliphatic organic compounds. Finally, mineralization of wastewater was almost complete in the third state which was with an AOS value of 3~4. Under the operation of optimum conditions, the oxidative state of chlorophenol wastewater could be easily controlled into the second stage which implied a higher biodegradability state. At the same time, more than 95 % of microtoxicity of chlorophenol solution could be decreased. Furthermore, the COD and TOC removal efficiency could be in excess of 90 % on the whole as the preoxidized chlorophenol solution treated by following batch-type biological unit. Under the same degradation efficiency of chlorophenols, the required overall operation time was less 50 % with a pretreatment of solar photo-Fenton process than that of Fenton process.
Based on the results obtained in this study, it was suggested that the solar photo-Fenton process could be operated effectively as a pretreatment step to convert biorecalcitrant compounds into more readily biodegradable and less toxic intermediates. A conspicuous COD and TOC removal efficiency could be achieved as the preoxidized solution treated by a following biological process. Consequently, the integrated solar photo-Fenton and biological treatment process showed a potential and feasible application for the treatment of a high concentration of biorecalcitrant compounds such as chlorophenols in wastewater.
| Identifer | oai:union.ndltd.org:TW/094NUUM5515013 |
| Date | January 2006 |
| Creators | Yi-Dian Lin, 林怡典 |
| Contributors | W. S. Kuo, 郭文旭 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 132 |
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