Coagulation behavior of polyferric chloride for removing NOM from surface water with low concentration of organic matter and its effect on chlorine decay model

Abstract

Polyferric chloride (PFC) was used to remove natural organic matter (NOM) from the surface water with low concentration of organic matter to evaluate coagulation behavior and floc parameters. The relationship between PFC dosages and chlorine decay was also investigated and the chlorine demand for reacting with organic compounds was estimated by a chlorine model. Under the raw water conditions, the NOM removal efficiency increased within the dosage investigated. The lower specific UV absorbance (SUVA) values were achieved in the dosage range 10–16 mg/L of PFC. Adsorption, entrapment, and complexation played important roles for PFC in removing NOM besides charge neutralization in the coagulation process. Large flocs formed with a PFC dosage of 22 mg/L were better resistant to increasing shear but showed poor recoverability. Small flocs at a PFC dosage of 3 mg/L were little influenced by the increasing shear and showed full reversibility. Coagulation treatment with 22 mg/L of PFC resulted in higher chlorine decay rate, more free chlorine residuals and less total chlorine demand in the effluent when compared to coagulation with dosages of 14 and 3 mg/L. Furthermore, minimal amount of disinfection by-products (DBPs) would be possibly produced after treatment with 22 mg/L of PFC.