Coagulation as a Post-Treatment Method for the Defluoridation of Photovoltaic Cell Manufacturing Wastewater

Wastewater containing fluoride requires polishing after lime precipitation treatment in order to meet stringent environmental legislation. In the present study, coagulation is used as a post-treatment method. The experimental results indicated that aluminium salts were more efficient than iron ones. Increasing aluminium concentration results in a significant reduction in fluoride. The removal efficiency strongly depends on solution initial pH. The optimum operating initial pH was found to be in the range of 6 to 7. Concentrations lower than standard limits were obtained. In addition, increasing initial fluoride concentration leads to high residual fluoride concentration. It was also found that fluoride removal was not significantly affected by chloride, sulphate and nitrate co-existing anions, while carbonate anions had a negative effect on fluoride removal. Defluoridation mechanism using aluminum sulfate was investigated, thanks to sludge characterization by SEM/EDAX, XRD and FTIR techniques.