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

- Chlorine decay increased as the concentration of preoxidant Fe(VI) increased.
- Chlorine decay followed two first-order decay reactions.
- Kinetics show the chlorine decay rates are dependent on chlorine and Fe(VI) doses.
- Application of preoxidant Fe(VI) reduced levels of THMs during chlorination.

This paper presents the effect of preoxidation with ferrate(VI) (FeVIO42−, 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.