| Summary: | 碩士 === 淡江大學 === 水資源及環境工程學系碩士班 === 96 === The objectives of this study are to investigate the removal of lead and antimony from water by chemical coagulation process and to evaluate the treatment alternatives for water treatment plant to meet the new standards. Raw water of Nei-Wan Water Plant was selected in study to assess the removal efficiency. Lead and antimony were spiked into the water samples and standard jar tests were conducted to determine the effects of solution pH, turbidity, the types and dosage of coagulant, and pre-chlorination on the removal of lead and antimony from spiked water.
The results showed that the removal efficiency of Pb (Pb removal per mg/L of coagulant) was in order of PACl, FC, and Alum. With aluminum- or ferric-based coagulants, an 80% removal of Pb was achieved at pH 7.0 to 8.5. Most of the water treatment plants in Taiwan use settled water turbidity as a reference to choose the coagulant dosage, it is recommended that the treatment plants can adopt enhanced coagulation to remove Pb when the concentration of Pb in raw water can’t meet the water quality standard. As a comparison, a poor removal of Sb (<25%) by aluminum-based coagulant was obtained. However, the Sb removal efficiency can reach 70% when iron-based coagulant was used. Since the domestic water treatment plants in Taiwan seldom use iron-based coagulant, it is recommended that the iron-based coagulant is used when the Sb concentration in raw water is high. In this way, both Pb and Sb can be removed simultaneously. In general, a 70% Sb removal can be reached at pH 5.0 to 9.0 by iron-based coagulant, and the optimum pH is between pH 5.5 and 6.5. The dosage of iron-based coagulant required for Sb(V) removal was about 1.43 to 2.76 times higher than that for removal of Sb(III). Oxidation of Sb(III) to Sb(V) due to pre-chlorination increased the coagulant dosages for about 3 to 5 times. When iron-based coagulant was used, it was observed that simultaneous removal of both Pb and Sb(III) can be obtained at the ~pH 7.0, however, better removal for Sb(V) can only be obtained at the pH 5.0. Both active carbon adsorption and lime softening are very effective for lead removal. It is concluded that enhanced coagulation with aluminum-based coagulants is useful for Pb removal. When simultaneous removal of Pb and Sb is necessary, it is recommended that iron-based coagulant should be used.
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