TiCl4混凝劑去除有機物與無機物及實場應用可行性之研究

Abstract

This study aimed to use titanium tetrachloride (TiCl4) as coagulant to remove humic acid (HA) and kaolinite which represent organic matters and inorganic matters, respectively. The efficiency of coagulation for five target parameters (turbidity, colority, UV254, COD, and TOC) were employed and considered in this study. Moreover, the leachate withdrawn from Sanjuku Landfill located in Taipei, Taiwan was tested with TiCl4. After coagulation process, the sludge was dehydrated in an oven overnight at 105℃, and then calcined at a final temperature of 550℃ to produce HA-TiO2 (HA: humic acid) and LC-TiO2 (LC: leachate). These photocatalysts were characterized in terms of SEM, EDS, XRD, UV/Vis.-DRS and XPS. The assessment of the catalytic activity was performed by photocatalysis of acid green 25 (AG 25) dye. The optimum conditions were found to be 61 mg/L TiCl4 and pH ≤ 11 for 100 ppm HA. On the other hands, kaolinite (100-1000 mg/L) cannot be removed after coagulation-flocculation process due to the low pH value resulted from TiCl4 hydrolysis. However, when HA and kaolinite coexisted, kaolinite can be well removed from the flocs during the adsorption/sweep coagulation process. In addition, the zeta potential showed that the sludge after coagulation process is close to zero. When adding 1.12 g/L coagulant into leachate, and the colority, UV254, COD, and TOC removals at 1.12 g/L TiCl4 were 60%, 50%, 55%, and 20%, respectively. The UV254/DOC value of leachate withdrawn from Sanjuku Landfill is 1.18 L/mg-m. It clearly showed that the organic matters in the leachate were difficult to be removed by coagulation-flocculation process and resulted to the low TOC removals. In photocatalyst characteristic analysis, in terms of the particle size, shape, and crystal structures of HA-TiO2 was similar to P25, and the redshift phenomenon of the former was found by UV/Vis.- DRS. Nevertheless, only the particle size and shape were found similar to P25 from LC-TiO2. The crystal structures were quite different from P25 and even brookites phase were showed. Eventually, the results showed that AG 25 can be removed from photocatalytic reaction with HA-TiO2 and the degradation and mineralization rate were 25% and 20%, respectively.