| Summary: | 碩士 === 淡江大學 === 水資源及環境工程學系 === 90 === The polyvinyl alcohol (PVA) and a reactive dye of R94H were used to simulate the refractory organics (expressed by chemical oxygen demand (COD) or dissolved organic carbon (DOC)) and color, respectively, in the synthetic textile wastewater samples. The synthetic textile wastewater samples contained color of 1000 ADMI unit, COD of 250 mg/L and DOC of 60 mg/L. Using the synthetic textile wastewater samples, this study was conducted to (1) compare the treatment performances between the Fenton oxidation and ferric coagulation, and (2) to investigate the effects of the Fenton pre-oxidation on subsequent GAC adsorption of organics. The Fenton oxidation and ferric coagulation experiments were conducted by the jar test. The activated carbon adsorption of organics was evaluated by the isothermal adsorption. The treatment performance was evaluated by the terms of DOC, COD and molecular weight (MW) distribution.
The results showed that the treatment performance for the removal of COD or DOC by the Fenton oxidation was almost the same as that by ferric coagulation. However, the MW distribution of residual DOC in the Fenton oxidation differed from that in ferric coagulation. Ferric coagulation is poor in removing low MW DOC (below 1K Daltons). The Fenton oxidation can effectively decompose high MW DOC into low MW DOC, and then mineralize the low MW DOC into CO2. The ratio of low MW DOC in the wastewater after the Fenton oxidation was 91%, whereas, it was only 34% after ferric coagulation. The higher the low MW DOC, the organics can be more easily adsorbed by activated carbon. The organics adsorption by activated carbon in the isotherm adsorption experiments followed the Freundlich isotherm model. The n value in the model expresses the adsorption affinity. After the Fenton oxidation and ferric coagulation processes, the n values (0.74-1.60) after the Fenton oxidation were greater than that (0.46) after ferric coagulation. The n value increased with the increase of H2O2 dosage after the Fenton oxidation. Furthermore, after the Fenton oxidation the ki values, the coefficients of intraparticle diffusion rate, all were greater than that after ferric coagulation, and increased with increasing H2O2 dosage but decreased with decreasing Fe2+ dosage. Based on the above results, the Fenton oxidation was more feasible for the pre-treatment before activated carbon adsorption than ferric coagulation. The main reason for this is because the ratio of low MW DOC increased after the Fenton oxidation.
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