Chlorine decay and trihalomethane formation following ferrate(VI) preoxidation and chlorination of drinking water

Abstract

This paper presents the effect of preoxidation with ferrate(VI) (Fe^VIO₄^2-, Fe(VI)) prior to chlorination on chlorine decay and formation of disinfection by-products in filtered raw water from a full-scale drinking water treatment plant. The rate of chlorine decay became significantly faster as the concentration of ferrate(VI) increased. Chlorine degradation followed two first-order decay reactions with rate constants k₁ and k₂ for fast and slow decay, respectively. Kinetic modeling established the relationships between k₁ and k₂ and varying dosages of chlorine and ferrate(VI). When ferrate(VI) was used as a pre-oxidant, the levels of trihalomethanes (trichloromethane (TCM), dichlorobromomethane (DCBM), dibromochloromethane (DBCM), and tribromomethane (TBM)) in water samples decreased as the ferrate(VI) concentration increased. The concentrations of these trihalomethanes followed the order TCM > DCBM ≈ DBCM > TBM.

Keywords: Chlorination; Disinfection byproducts; Ferrate; First-order; Kinetics; Preoxidation.