Effect of basicity on coagulation performance of polyferric chloride applied in eutrophicated raw water

Effects of the basicity of polyferric chloride (PFC) on the removal efficiencies of algal cell, turbidity and humic acid (HA) contained in eutrophicated raw water were investigated and the mechanisms were explored. The removal efficiency of both algae cells and clay particles increased gently at three different PFC dosages as the PFC basicity increased from 0 to 2.4. Adsorption of PFC species on algae and clay was the major mechanism contributing to the removal of algae and clay. PFC with a higher basicity underwent a lessened further hydrolysis when contacted with the water and resulted in less residual iron. The basicity of PFC influenced the characteristics of flocs, such as density, stability and color, when PFC was applied to remove algae. The presence of algae species with either small size or special shape made the removal of algae more difficult compared to the removal of single algae species. PFC with basicity no less than 2.0 was necessary for removing algae from micro-algal system to achieve a high removal efficiency. The optimum removal of HA was achieved at PFC basicity of 0.8 and HA removal kept almost stable with further increase in PFC basicity. The distribution of iron species in PFC solution as a function of basicity was determined in this study to better understand the mechanism of pollutants removal by PFC.