| 英文摘要 |
The project titled “Removal of Nonylphenol Precursor by Two-Stage Reduction/Oxidation Processes” is a research proposed to combine zero valent iron (reduction)/Fenton (oxidation) process for nonylphenol ethoxylate removal. Nonylphenol ethoxylate is a major ingredient in nonionic detergent and is a precursor of nonylphenol which is an endocrine-disrupting chemical affecting human endocrine system, including variety of glands and hormones. Since nonylphenol ethoxylate has micelle property at high concentration, typical biological treatment is not effective. Besides, the degradation of the phenolic structure by Fenton process along is also difficult due to that its micelle property where the non-polar/hydrophobic property of phenol is wrapped by the long-chained polar/hydrophilic ethylene oxide. The advantage of the designed reduction/oxidation process is that in the first stage, the zero valent iron, an electron donor, is capable of destructing the micelle structure under acidic condition. Therefore, in the second stage, the dissolution of ferrous ion in the first stage together with the added hydrogen dioxide could easily attack the phenolic structure to destruct the non-polar phenolic structure and enhance their biodegradability.
Biodegradability was assessed by the ratio of BOD5/TOC, and the degradation of nonylphenol ethoxylate was determined by UV spectrum at wavelengths of 277 nm. The batch study results showed lower pH achieved better biodegradability enhancement and the optimum condition (59 % TOC removal) was obtained at pH 1.5 for first stage reduction time of 60 min, ZVI dosage of 10 g/L and H2O2 of 1360 mg/L. In the continuous flow pilot study results, the optimum conditions were occurred at pH 2, HRT 1.5 min for the first stage and pH 3 for the second stage. Under this circumstance, 52 % of TOC was removed but BOD was increased to 2.71 times compared to the BOD of the raw water. Biodegradability (BOD5/COD) was also increased from 0.045 to 0.24, which is better than the biodegradability of using Fenton process alone. Waste iron was also tested to replace ZVI and the efficiency was acceptable but was not as good as ZVI itself, but using air of 50 % oxygen can effectively replace H2O2. Consequently, the proposed two-stage reduction/oxidation process is able to enhance the biodegradability and removal for nonylphenol ethoxylate. The obtained results are applicable for further use in the relative surfactant industry.
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