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

• Published in: Chemosphere (Oxford) 2023-02, Vol.313, p.137529, Article 137529
• Main Authors: Pan, Renjie, Lin, Yi-Li, Zhang, Tian-Yang, Wei, Xiu-Li, Dong, Zheng-Yu, Hu, Chen-Yan, Tang, Yu-Lin, Xu, Bin
• Format: Article
• Language: English
• Subjects: Active iodine species (HOI/I2); Adsorption; Adsorption kinetics; Charcoal; Drinking Water; Halogenation; Iodinated trihalomethanes (I-THMs); Iodine; Powdered activated carbons (PACs); Pre-chlorination; Trihalomethanes; Water Purification - methods
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.137529

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. [Display omitted] •Optimizing prechlorination can enhance HOI/I2 formation, facilitating subsequent adsorption.•Active iodine species (HOI/I2) were chemically adsorpted by PACs and GACs.•HOI/I2 adsorption followed pseudo-second-order kinetics.•Film diffusion was the rate-limiting process for HOI/I2 adsorption on activated carbon.•Pre-chlorination with PAC adsorption can effectively remove HOI/I2 and attenuate I-THM formation.