| dc.description.abstract | The study mainly involues the chemical coagulation and precipitation method to treat the wastewater containing low concentration of fluoride generated by a crystalline silicon solar cell plant. The experiment is conducted based on the operating factors such as different pH values, dose of chemicals added to the processing parts, different calcium salts, different volume of refluxing sludge and iron material, as well as the acid mixed in the wastewater. Moreover, it analyzes the effect of various operating factors on F- removal, and the valid CaF2 concentration of the sludge.
As shown in the results, the original wastewater has pH<2.28, with the F- value of 300ppm, which also contains HNO3, H2SO4, HCl and anion. It is the wastewater containing low concentration of fluoride. As shown in the treatment results of calcium salt precipitation method, the optimal parameters for adding chemicals into various processing units to remove F- concentration are pH=7, 0.15ml PAC, and 1.5ml Polymer. When CaCl2(Ca/F=1.4), Ca(OH)2(Ca/F=3) and CaCO3 (Ca/F=2.4) are added to various processing units, it will reach the F- removal efficiency as high as 95%(about 13.3ppm) under the optimal parameters. In addition, in terms of reusing resources in the sludge (the valid CaF2 concentration of the sludge>70%), only when the CaCl2(84.61%) is added, can it reach the reuse conditions. During the chemical coagulation process with respecl to CaCl2 as the main calcium salt, addition of refluxing sludge (2ml) and iron material (0.8g) can increase the F- removal efficiency by 21.4%(10.3ppm) and 15%(11.3ppm) respectively. Moreover, when the refluxing sludge (2ml) is added in the chemical coagulation process, change in the volume of added CaCl2 (Ca/F=1.2) can increase the F- removal efficiency(quality of treated water) by 12.5%(13.9ppm). Moreover, it confirms the Discharged Water Control Standards and reduces the chemical cost. The operation cost per kiloton wastewater in the treatment plant can be saved by about NTD1,920.
Moreover, the original water contains some other anions, and so H2SO4 is added to change the property of original water. As shown in the results, high H2SO4 content in the wastewater favours the F- removal efficiency and valid CaF2 concentration of the sludge. | en_US |