| 英文摘要 |
Since there is a significant demand on the circulating water for the use of cooling tower, the circulation operation with high frequency is often facilitated by many industries to moderately cut the running cost. Therefore, the accumulated concentration of chemicals and organic matters in the cooling water is relatively high, which would potentially result in the difficulties on wastewater treatment or reclamation, and even locally polluted air by organics striping as well. This project was proposed using a combined process of heterogeneously catalytic ozonation and ion exchange unit to treat the wastewater discharged from cooling water tower, where the organic compounds can be effectively oxidized by hydroxyl radicals induced via the catalytic ozonation reaction into the final products, such as carbon dioxide and water, and inorganic ions, including chloride, nitrate, sulfate, calcium, magnesium, ferric iron, are removed by ion exchange resins. Based on the operation mentioned above, the cooling water could be substantially recycled for fresh water supplement to achieve a sustainable development objective of preserving water resource.
Two phases, including laboratory operation and pilot-scale system assembling and testing, were carried out in this project. It is noted that the optimal conditions, such as 50 mg/L of inlet ozone applied dosage, 400 mL/min of ozone flowrate, 627 grams of goethite catalysts, 600 mL/min of inner circulation flowrate, and 50 mL/min of inlet test sample flowrate, etc., was experimentally determined to meet the suggestion standards at chemical oxygen demand (COD) less than 10 mg/L of cooling water tower quality with the operation of two consecutive circulations. If the cooling water was subsequently treated by ion exchange processes, including anion and cation resins, the removal rates for hardness, chloride, and calcium were 95%, 99.7%, and 93%. Other than that, the removals for silicate, nitrate, sulfate, magnesium, and ferric iron were almost complete. Pilot plant was fabricated and transported to Taiwan Formosa Incorporation in Mai-liaw for in-situ practices. The operational conditions were controlled as 3 L/min of ozone flowrate and 9.5 L/min and 3 L/min of inflow cooling water through heterogeneous ozone-based AOPs and ion exchange resins, respectively. The results reveal that all concentrations in the cooling water as treated were able to meet the standards of industrial water use. The degradation rate of COD was found to be higher than 85% and the removal rate of all ion species were more than 90%. Because only 3 to 5 percent of water was necessitated for the purpose of resin regeneration, the recovery of spent cooling water would reach 90 percent at least. As for the evaluation of economic cost using AOPs and ion exchange technology, it is found that the operational cost is estimated as merely NT$ 9.8 and total cost including facility depreciation is NT$ 12.9 for per ton of cooling water treatment.
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