Sequential combination of pre-chlorination and powdered activated carbon adsorption on iodine removal and I-THMs control in drinking water

Abstract

Combining pre-oxidation with activated carbon adsorption was explored as an ideal approach for removing iodine from water source to eliminate the formation of Iodinated trihalomethanes (I-THMs). Compared with permanganate and monochloramine, chlorine is more suitable as pre-oxidant to obtain higher active iodine species (HOI/I₂). Active iodine species adsorption using both powdered activated carbon (PAC) and granular activated carbon (GAC) can be well fitted the pseudo-second-order kinetic model indicating that chemical adsorption was the dominant mechanism for HOI/I₂ adsorption. The average pore size of activated carbons was the most strongly correlated with the adsorption capacity (R² > 0.98), followed by methylene blue (R² > 0.76), pore volume (R² > 0.70) and iodine number (R² > 0.67). Moreover, three models, including intraparticle diffusion, Byod kinetic, and diffusion-chemisorption were used to illustrate the mechanisms of HOI/I₂ adsorption. Chemical adsorption was the dominant mechanism for HOI/I₂ adsorption. In summary, at the molar ratio of [NaClO] and [I^-] as 1.2, pre-chloriantion time of 5 min, subsequently dosage of 15 mg/L of PAC E with 20 min adsorption can remove 79.8% iodine. In addition, the combined process can eliminate 61%-87.2% of I-THMs in the subsequent chlor(am)ination. The results indicate that pre-chlorination combined with PAC can effectively removed HOI/I₂ and attenuate I-THMs formation in the subsequent disinfection process.

Keywords: Active iodine species (HOI/I(2)); Adsorption kinetics; Iodinated trihalomethanes (I-THMs); Powdered activated carbons (PACs); Pre-chlorination.