Evaluation of the Applicability of Ferric Chloride Coagulant for Drinking Water Treatment of Raw Water in the Lower Nakdong River Water

This study evaluated the applicability of ferric chloride (FeCl₃) as a coagulant for drinking water treatment using raw water from the lower Nakdong River and compared its performance with aluminum sulfate (alum). Jar-tests and pilot-scale experiments were conducted using raw water from the Maeri intake station. Water quality parameters including turbidity, total organic carbon (TOC), chlorophyll-a (Chl-a), color, alkalinity, and pH were monitored. Dissolved organic matter (DOM) fractions were characterized using LC-OCD, while disinfection by-product formation potentials (THMFP and HAAFP) were measured to assess the removal efficiency of organic precursors. The performance of a hybrid coagulant (alum mixed with FeCl₃) was also investigated. Results showed that FeCl₃ outperformed alum in removing turbidity, TOC, and Chl-a in both batch and continuous experiments. Notably, FeCl₃ exhibited superior removal of humic substances (HS) and building blocks (BB) fractions, resulting in a more significant reduction in THMFP and HAAFP. Although the supernatant color increased initially with FeCl₃ application, the filtered water color remained lower than that of alum, suggesting that residual color-causing agents were primarily particulate microflocs. Furthermore, FeCl₃ effectively reduced the DOC load delivered to the subsequent granular activated carbon (GAC) process, enhancing overall treatment efficiency. FeCl₃ is a promising alternative or supplement to alum for treating raw water with high organic and algal content, provided that alkalinity and pH are appropriately controlled during practical application.